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1

Structural analysis of sonochemically prepared PtRu versus Johnson Matthey PtRu in operating direct methanol fuel cells.  

PubMed

Sonochemically prepared PtRu (3 : 1) and Johnson Matthey PtRu (1 : 1) were analyzed by X-ray absorption spectroscopy in operating liquid feed direct methanol fuel cells. The total metal loadings were 4 mg cm(-2) unsupported catalysts at the anode and cathode of the membrane electrode assembly. Ex situ XRD lattice parameter analysis indicates partial segregation of the Ru from the PtRu fcc alloy in both catalysts. A comparison of the in situ DMFC EXAFS to that of the as-received catalyst shows that catalyst restructuring during DMFC operation increases the total metal coordination numbers. A combined analysis of XRD determined grain sizes and lattice parameters, ex situ and in situ EXAFS analysis, and XRF of the as-received catalysts enables determination of the catalyst shell composition. The multi-spectrum analysis shows that the core size increases during DMFC operation by reduction of Pt oxides and incorporation of Pt into the core. This increases the mole fraction of Ru in the catalyst shell structure. PMID:18972031

Stoupin, Stanislav; Rivera, Harry; Li, Zhengrong; Segre, Carlo U; Korzeniewski, Carol; Casadonte, Dominick J; Inoue, Hisashi; Smotkin, Eugene S

2008-11-14

2

Pt-Ru adatom nanoparticles as anode catalysts for direct methanol fuel cells  

NASA Astrophysics Data System (ADS)

A series of prototype direct methanol fuel cells (DMFCs) were constructed and operated under identical procedures and conditions except for the surface compositions of the anode electrocatalysts. The cathode electrocatalyst was Pt black (loading 2 mg/cm 2, specific surface area: ca. 27 m 2/g), the electrolyte membrane was Nafion™ 117, and the anode electrocatalysts were a series of Pt-Ru adatom (Pt-Ru ad) nanoparticles (loading 2 mg/cm 2, specific surface area: ca. 27 m 2/g) prepared by a direct surface reductive deposition of Ru ad onto Pt black. The optimum surface coverage of Pt by Ru ad was ca. 33% for DMFCs operating at 60 °C. The optimum ranged from ca. 30 to 60% at 90 °C. A DMFC using Pt-Ru ad nanoparticles supported on carbon (Vulcan XC-72™) as anode electrocatalyst was operated for 20 days at 8 h each day without loss of activity. These results, combined with those from an in situ cyclic voltammetry study, indicate that no significant Ru ad dissolution and/or redistribution occurred during fabrication and operation of the prototype DMFCs.

Cao, Dianxue; Bergens, Steven H.

3

Investigation of the performance decay of anodic PtRu catalyst with working time of direct methanol fuel cells  

Microsoft Academic Search

Life tests of direct methanol fuel cells (DMFC) were carried out with three individual single cells at a current density of 100mAcm?2 for three different times under ambient pressure and at a cell temperature of 60°C. X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS) were used to characterize the anodic PtRu catalysts before and after the life tests. XRD results

Zhen-Bo Wang; Xin-Peng Wang; Peng-Jian Zuo; Bo-Qian Yang; Ge-Ping Yin; Xian-Ping Feng

2008-01-01

4

Microwave synthesis of polymer-embedded Pt-Ru catalyst for direct methanol fuel cell.  

PubMed

Platinum-ruthenium nanoparticles stabilized within a conductive polymer matrix are prepared using microwave heating. Polypyrrole di(2-ethylhexyl) sulfosuccinate, or PPyDEHS, has been chosen for its known electrical conductivity, thermal stability, and solubility in polar organic solvents. A scalable and quick two-step process is proposed to fabricate alloyed nanoparticles dispersed in PPyDEHS. First a mixture of PPyDEHS and metallic precursors is heated in a microwave under reflux conditions. Then the nanoparticles are extracted by centrifugation. Physical characterization by TEM shows that crystalline and monodisperse alloyed nanoparticles with an average size of 2.8 nm are obtained. Diffraction data show that crystallite size is around 2.0 nm. Methanol electro-oxidation data allow us to propose these novel materials as potential candidates for direct methanol fuel cells (DMFC) application. The observed decrease in sulfur content in the polymer upon incorporation of PtRu nanoparticles may have adversely affected the measured catalytic activity by decreasing the conductivity of PPyDEHS. Higher concentration of polymer leads to lower catalyst activity. Design and synthesis of novel conductive polymers is needed at this point to enhance the catalytic properties of these hybrid materials. PMID:16852945

Bensebaa, Farid; Farah, Abdiaziz A; Wang, Dashan; Bock, Christina; Du, Xiaomei; Kung, Judy; Le Page, Yvon

2005-08-18

5

The Mechanism of Direct Formic Acid Fuel Cell Using Pd, Pt and Pt-Ru  

NASA Astrophysics Data System (ADS)

The electro-oxidation of formic acid, 2-propanol and methanol on Pd black, Pd/C, Pt-Ru/C and Pt/C has been investigated to clear the reaction mechanism. It was suggested that the formic acid is dehydrogenated on Pd surface and the hydrogen is occluded in the Pd lattice. Thus obtained hydrogen acts like pure hydrogen supplied from the outside and the cell performance of the direct formic acid fuel cell showed as high as that of a hydrogen-oxygen fuel cell. 2-propanol did not show such dehydrogenation reaction on Pd catalyst. Platinum and Pt-Ru accelerated the oxidation of C-OH of 2-propanol and methanol. Slow scan voltammogram (SSV) and chronoamperometry measurements showed that the activity of formic acid oxidation increased in the following order: Pd black > Pd 30wt.%/C > Pt50wt.%/C > 27wt.%Pt-13wt.%Ru/C. A large oxidation current for formic acid was found at a low overpotential on the palladium electrocatalysts. These results indicate that formic acid is mainly oxidized through a dehydrogenation reaction. For the oxidation of 2-propanol and methanol, palladium was not effective, and 27wt.%Pt-13wt.%Ru/C showed the best oxidation activity.

Kamiya, Nobuyuki; Liu, Yan; Mitsushima, Shigenori; Ota, Ken-Ichiro; Tsutsumi, Yasuyuki; Ogawa, Naoya; Kon, Norihiro; Eguchi, Mika

6

Role of hydrous ruthenium oxide in Pt-Ru direct methanol fuel cell anode electrocatalysts: The importance of mixed electron/proton conductivity  

SciTech Connect

Pt-Ru is the favored anode catalyst for the oxidation of methanol in direct methanol fuel cells (DMFCs). The nanoscale Pt-Ru blacks are accepted to be bimetallic alloys as based on their X-ray diffraction patterns. These bulk and surface analyses show that although practical Pt-Ru blacks have diffraction patterns consistent with an alloy assignment, they are primarily a mix of Pt metal and Ru oxides plus some Pt oxides and only small amounts of Ru metal. Thermogravimetric analysis and X-ray photoelectron spectroscopy of as-received Pt-Ru electrocatalysts indicate that DMFC materials contain substantial amounts of hydrous ruthenium oxide (RuO{sub x}H{sub y}). A potential misidentification of nanoscale Pt-Ru blacks arises because RuO{sub x}H{sub y} is amorphous and cannot be discerned by X-ray diffraction. Hydrous ruthenium oxide is a mixed proton and electron conductor and innately expresses Ru-OH speciation. These properties are of key importance in the mechanism of methanol oxidation, in particular, Ru-OH is a critical component of the bifunctional mechanism proposed for direct methanol oxidation in that it is the oxygen-transfer species that oxidatively dissociates {single_bond}C{triple_bond}O fragments from the Pt surface. The catalysts and membrane-electrode assemblies of DMFCs should not be processed at or exposed to temperatures >150 C, as such conditions deleteriously lower the proton conductivity of hydrous ruthenium oxide and thus affect the ability of the Ru component of the electrocatalyst to dissociate water. With this analytical understanding of the true nature of practical nanoscale Pt-Ru electrocatalysts, the authors can now recommend that hydrous ruthenium oxide, rather than Ru metal or anhydrous RuO{sub 2}, is the preferred Ru speciation in these catalysts.

Rolison, D.R.; Hagans, P.L.; Swider, K.E.; Long, J.W. [Naval Research Lab., Washington, DC (United States). Surface Chemistry Branch] [Naval Research Lab., Washington, DC (United States). Surface Chemistry Branch

1999-02-02

7

Pt and Ru X-ray Absorption Spectroscopy of PtRu Anode Catalysts in Operating Direct Methanol Fuel Cells  

SciTech Connect

In situ X-ray absorption spectroscopy, ex situ X-ray fluorescence, and X-ray powder diffraction enabled detailed core analysis of phase segregated nanostructured PtRu anode catalysts in an operating direct methanol fuel cell (DMFC). No change in the core structures of the phase segregated catalyst was observed as the potential traversed the current onset potential of the DMFC. The methodology was exemplified using a Johnson Matthey unsupported PtRu (1:1) anode catalyst incorporated into a DMFC membrane electrode assembly. During DMFC operation the catalyst is essentially metallic with half of the Ru incorporated into a face-centered cubic (FCC) Pt alloy lattice and the remaining half in an amorphous phase. The extended X-ray absorption fine structure (EXAFS) analysis suggests that the FCC lattice is not fully disordered. The EXAFS indicates that the Ru-O bond lengths were significantly shorter than those reported for Ru-O of ruthenium oxides, suggesting that the phases in which the Ru resides in the catalysts are not similar to oxides.

Stoupin, S.; Chung, E-H.; Chattopadhyay, S.; Segre, C.U.; Smotkin, E.S. (IIT); (Puerto Rico)

2008-06-16

8

Pt and Ru X-ray absorption spectroscopy of PtRu anode catalysts in operating direct methanol fuel cells.  

PubMed

In situ X-ray absorption spectroscopy, ex situ X-ray fluorescence, and X-ray powder diffraction enabled detailed core analysis of phase segregated nanostructured PtRu anode catalysts in an operating direct methanol fuel cell (DMFC). No change in the core structures of the phase segregated catalyst was observed as the potential traversed the current onset potential of the DMFC. The methodology was exemplified using a Johnson Matthey unsupported PtRu (1:1) anode catalyst incorporated into a DMFC membrane electrode assembly. During DMFC operation the catalyst is essentially metallic with half of the Ru incorporated into a face-centered cubic (FCC) Pt alloy lattice and the remaining half in an amorphous phase. The extended X-ray absorption fine structure (EXAFS) analysis suggests that the FCC lattice is not fully disordered. The EXAFS indicates that the Ru-O bond lengths were significantly shorter than those reported for Ru-O of ruthenium oxides, suggesting that the phases in which the Ru resides in the catalysts are not similar to oxides. PMID:16706450

Stoupin, Stanislav; Chung, Eun-Hyuk; Chattopadhyay, Soma; Segre, Carlo U; Smotkin, Eugene S

2006-05-25

9

Preparation of Pt–Ru bimetallic anodes by galvanostatic pulse electrodeposition: characterization and application to the direct methanol fuel cell  

Microsoft Academic Search

The electrodeposition of platinum and ruthenium was carried out on carbon electrodes to prepare methanol anodes with different Pt\\/Ru atomic ratios using a galvanostatic pulse technique. Characterizations by XRD, TEM, EDX and atomic absorption spectroscopy indicated that most of the electrocatalytic anodes consisted of 2 mg cm-2 of Pt–Ru alloy particles with the desired composition and with particle sizes ranging

C. Coutanceau; A. F. Rakotondrainibé; A. Lima; E. Garnier; S. Pronier; J. M. Léger; C. Lamy

2004-01-01

10

Novel method for the synthesis of hydrophobic Pt-Ru nanoparticles and its application to preparing a Nafion-free anode for the direct methanol fuel cell.  

PubMed

Pt-Ru alloy is a bimetallic catalyst most commonly used in the direct methanol fuel cell (DMFC). In this paper, a new process to synthesize an unsupported Pt-Ru colloid has been introduced. The characteristics of synthesized nanoparticles were identified by XRD, TEM/EDX, and SEM, and it shows that Ru atoms are incorporated into the Pt fcc structure and the well-dispersed particles (diameter approximately 4 nm) possess a Pt-rich feature. This catalyst shows a hydrophobic characteristic which can adsorb very well on the hydrophobic-treated carbon paper or carbon cloth without the need of Nafion. Accordingly, this method can avoid particle agglomeration, and the synthesized catalyst demonstrates strong adsorption with carbon paper. In addition, this colloid-type Nafion-free catalyst was measured via linear sweep voltammetry (LSV) and exhibited electrochemical activity for methanol oxidation comparable to the commercial one with Nafion binding. PMID:16898755

Tu, Hung-Chi; Wang, Wen-Lin; Wan, Chi-Chao; Wang, Yung-Yun

2006-08-17

11

Pt-Ru supported on double-walled carbon nanotubes as high-performance anode catalysts for direct methanol fuel cells.  

PubMed

Pt-Ru supported on carbon nanotubes (CNTs) (single-walled nanotubes, double-walled nanotubes (DWNTs), and multi-walled nanotubes) catalysts are prepared by an ethylene glycol reduction method. Pt-Ru nanoparticles with a diameter of 2-3 nm and narrow particle size distributions are uniformly deposited onto the CNTs. A simple and fast filtration method followed by a hot-press film transfer is employed to prepare the anode catalyst layer on a Nafion membrane. The Pt-Ru/DWNTs catalyst shows the highest specific activity for methanol oxidation reaction in rotating disk electrode experiments and the highest performance as an anode catalyst in direct methanol fuel cell (DMFC) single cell tests. The DMFC single cell with Pt-Ru/DWNTs (50 wt %, 0.34 mg Pt-Ru/cm(2)) produces a 68% enhancement of power density, and at the same time, an 83% reduction of Pt-Ru electrode loading when compared to Pt-Ru/C (40 wt %, 2.0 mg Pt-Ru/cm(2)). PMID:16884255

Li, Wenzhen; Wang, Xin; Chen, Zhongwei; Waje, Mahesh; Yan, Yushan

2006-08-10

12

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

13

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

PubMed

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. PMID:24763438

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

2014-05-16

14

An investigation on the antibacterial and antibiofilm efficacy of cationic nanoparticulates for root canal disinfection.  

PubMed

This study aimed to investigate the antibacterial and antibiofilm efficacy of cationic nanoparticulates for root canal disinfection. Experiments were performed in two stages. In stage 1, experiments were conducted to examine the physical properties of three types of nanoparticulates. The antibacterial properties of nanoparticulates alone and nanoparticulates mixed with zinc oxide-eugenol-based sealer were studied. In stage 2, the ability of nanoparticulates-treated dentin to prevent bacterial adherence was examined. Zinc oxide nanoparticulates, chitosan nanoparticulates, a mixture of zinc oxide and chitosan nanoparticulates, and zinc oxide nanoparticulates with multilayered coating of chitosan were tested. This study showed that the incorporation of nanoparticulates did not alter the flow characteristics of sealer but improved the direct antibacterial property and the ability to leach out antibacterial components. There was a significant reduction in the adherence of Enterococcus faecalis to nanoparticulates-treated dentin (p < 0.05). These experiments highlighted the potential advantage of nanoparticulates in root canal disinfection. PMID:19026885

Kishen, Anil; Shi, Zhilong; Shrestha, Annie; Neoh, Koon Gee

2008-12-01

15

Kinetic analysis of carbon monoxide and methanol oxidation on high performance carbon-supported Pt–Ru electrocatalyst for direct methanol fuel cells  

Microsoft Academic Search

The kinetic parameters of carbon monoxide and methanol oxidation reactions on a high performance carbon-supported Pt–Ru electrocatalyst (HP 20% 1:1 Pt–Ru alloy on Vulcan XC-72 carbon black) have been studied using cyclic voltammetry and rotating disk electrode (RDE) techniques in 0.50M H2SO4 and H2SO4 (0.06–0.92M)+CH3OH (0.10–1.00M) solutions at 25.0–45.0°C. CO oxidation showed an irreversible behaviour with an adsorption control giving

Amado Velázquez-Palenzuela; Francesc Centellas; José Antonio Garrido; Conchita Arias; Rosa María Rodríguez; Enric Brillas; Pere-Lluís Cabot

2011-01-01

16

Direct electrochemistry of nanoparticulate Fe2O3 in aqueous solution and adsorbed onto tin-doped indium oxide  

Microsoft Academic Search

Nanoparticulate iron oxides occur naturally, for example, in soil, water, and in the cytoplasm of living cells. The redox properties and detection of these nanoparticles are there- fore of considerable importance. Understanding and mimicking nanoparticle-based redox reactions may lead to new types of water-based electrochemical processes. In this study, the electrochemical detection of 4-5 nm diameter Fe2O3 nanoparticles dissolved in

Katy J. McKenzie; Frank Marken

2001-01-01

17

PtRu nanoparticles supported on 1-aminopyrene-functionalized multiwalled carbon nanotubes and their electrocatalytic activity for methanol oxidation.  

PubMed

A new synthesis method for the preparation of high-performance PtRu electrocatalysts on multiwalled carbon nanotubes (MWCNTs) is reported. In this method, bimetallic PtRu electrocatalysts are deposited onto 1-aminopyrene (1-AP)-functionalized MWCNTs by a microwave-assisted polyol process. The noncovalent functionalization of MWCNTs by 1-AP is simple and can be carried out at room temperature without the use of expensive chemicals or corrosive acids, thus preserving the integrity and the electronic structure of MWCNTs. PtRu electrocatalysts on 1-AP-functionalized MWCNTs show much better distribution with no formation of aggregates, higher electrochemically active surface area, and higher electrocatalytic activity for the electrooxidation of methanol in direct methanol fuel cells as compared to that on conventional acid-treated MWCNTs and carbon black supported PtRu electrocatalysts. PtRu electrocatalysts on 1-AP-functionalized MWCNTs also show significantly enhanced stability. PMID:18690733

Wang, Shuangyin; Wang, Xin; Jiang, San Ping

2008-09-16

18

PtRu Nanofilm Formation by Electrochemical Atomic Layer Deposition (E-ALD).  

PubMed

The high CO tolerance of PtRu electrocatalysis, compared with pure Pt and other Pt-based alloys, makes it interesting as an anode material in proton exchange membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC). This report describes the formation of bimetallic PtRu nanofilms using the electrochemical form of atomic layer deposition (E-ALD). Metal nanofilm formation using E-ALD is facilitated by use of surface-limited redox replacement (SLRR), where an atomic layer (AL) of a sacrificial metal is first formed by UPD. The AL is then spontaneously exchanged for a more noble metal at the open-circuit potential (OCP). In the present study, PtRu nanofilms were formed using SLRR for Pt and Ru, and Pb UPD was used to form the sacrificial layers. The PtRu E-ALD cycle consisted of Pb UPD at -0.19 V, followed by replacement using Pt(IV) ions at OCP, rinsing with blank, then Pb UPD at -0.19 V, followed by replacement using Ru(III) ions at OCP. PtRu nanofilm thickness was controlled by the number of times the cycle was repeated. PtRu nanofilms with atomic proportions of 70/30, 82/18, and 50/50 Pt/Ru were formed on Au on glass slides using related E-ALD cycles. The charge for Pb UPD and changes in the OCP during replacement were monitored during the deposition process. The PtRu films were then characterized by CO adsorption and electrooxidation to determine their overpotentials. The 50/50 PtRu nanofilms displayed the lowest CO electrooxidation overpotentials as well as the highest currents, compared with the other alloy compositions, pure Pt, and pure Ru. In addition, CO electrooxidation studies of the terminating AL on the 50/50 PtRu nanostructured alloy were investigated by deposition of one or two SLRR of Pt, Ru, or PtRu on top. PMID:24568151

Jayaraju, Nagarajan; Banga, Dhego; Thambidurai, Chandru; Liang, Xuehai; Kim, Youn-Guen; Stickney, John L

2014-03-25

19

Direct contact cytotoxicity assays for filter-collected, carbonaceous (soot) nanoparticulate material and observations of lung cell response  

NASA Astrophysics Data System (ADS)

A simple, direct contact, cytotoxicity (in vitro) assay has been developed where particulate matter (PM) collected on glass fiber filters was exposed to human epithelial (lung) cells. Carbonaceous (soot) PM included tire, wood, diesel, candle, and variously combusted natural gas PM from a kitchen stove range. Black carbon PM and a commercial multiwall carbon nanotube aggregate PM was also examined in vitro as surrogate materials, and all experimental PM was characterized by field emission scanning electron microscopy and transmission electron microscopy. Assay results for 48 h cultures showed toxicity for all carbonaceous PM with various natural gas PM being the most toxic; this was comparable to the toxicity induced by the surrogate PM. Light microscopy examination of affected epithelial cells confirmed the semi-quantitative results. Comparison of polycyclic aromatic hydrocarbon (PAH) content and concentration for the carbonaceous PM showed no PAH correlation with relative cell viability (cell death) after 48 h.

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

20

Boosting fuel cell performance with a semiconductor photocatalyst: TiO2/Pt-Ru hybrid catalyst for methanol oxidation.  

PubMed

A hybrid carbon fiber electrode (CFE) consisting of TiO2 semiconductor photocatalyst and Pt-Ru catalyst has been developed to boost the performance of direct methanol fuel cells (DMFC). These two catalyst nanoparticles are deposited on opposite sides of the carbon fiber paper such that methanol oxidation is carried out catalytically on Pt-Ru and photocatalytically on TiO2 under UV-light irradiation. Since both catalysts carry out methanol oxidation independently, we observe an additive effect in the current generation. The carbon support fibers provide a large network to collect the electrons from both of these catalytic processes and thus assist in efficient current generation. In addition, TiO2 improves the performance of the Pt-Ru catalyst in dark, indicating possible surface area improvement or diminished poisoning effects. The concept of incorporating a photocatalyst provides new ways to minimize precious metal content and enhance the performance of DMFCs. At low catalyst loadings (0.15 mg/cm2) at 295 K, a 25% enhancement in the peak power density is observed upon illumination with light. PMID:16852456

Drew, Kristine; Girishkumar, G; Vinodgopal, K; Kamat, Prashant V

2005-06-23

21

Synthesis of ordered macroporous Pt/Ru nanocomposites for the electrooxidation of methanol.  

PubMed

Highly catalytic PtRu catalysts with different molar ratios of Pt to Ru have been synthesized by using the inverted colloidal crystals template technique. Three-dimensional ordered Pt/Ru alloys with pore size of 320 nm could be conveniently obtained by electrochemical codeposition of metal precursors inside the voids of the template. The structural and chemical properties of the macroporous catalysts were studied by using SEM, XPS and XRD methods. The decomposition and oxidation of methanol on the macroporous catalyst surfaces with different Pt and Ru molar ratios (Pt100Ru0, Pt90Ru10, Pt80Ru20, Pt70Ru30 and Pt56Ru44) were systemically discussed. Potentiostatic experiments showed that the special structure characteristics (e.g., interconnected pore framework and the flexible curvature) lead to enhanced methanol oxidation efficiency on the macroporous materials as compared to the directly deposited catalyst. These results demonstrate that the three-dimensional ordered porous bimetallic catalysts are promising alternatives for developing high performance DMFC anodic catalysts, especially for the fabrication of microfuel cells. PMID:18464437

Zhang, Dai; Ding, Ya; Gao, Wei; Chen, Hong-Yuan; Xia, Xing-Hua

2008-02-01

22

Methanol oxidation on PtRu electrodes. Influence of surface structure and Pt-Ru atom distribution  

SciTech Connect

The activities of different types of PtRu catalysts for methanol oxidation are compared. Materials used were: UHV-cleaned PtRu alloys, UHV-evaporated Ru onto Pt(111) as well as adsorbed Ru on Pt(111) prepared with and without additional reduction by hydrogen. Differences in the catalytic activity are observed to depend on the preparation procedure of the catalysts. The dependence of the respective catalytic activities upon the surface composition is reported. UHV-STM data for Pt(111)/Ru show the formation of two- and three-dimensional structures depending on surface coverage. A molecular insight on the electrochemical reaction is given via in situ infrared spectroscopy. Analysis of the data indicates that the most probable rate-determining step is the reaction of adsorbed CO with Ru oxide.

Iwasita, T.; Hoster, H.; John-Anacker, A.; Lin, W.F.; Vielstich, W.

2000-01-25

23

Toxicological characteristics of nanoparticulate anatase titanium dioxide in mice  

Microsoft Academic Search

In an effort to examine liver injury, immune response, and other physiological effects in mice caused by intragastric administration of nanoparticulate anatase titanium dioxide (5nm), we assessed T lymphocytes, B lymphocyte and NK lymphocyte counts, hematological indices, biochemical parameters of liver functions, and histopathological changes in nanoparticulate titanium dioxide -treated mice. Indeed, mice treated with higher dose nanoparticulate titanium dioxide

Yanmei Duan; Jie Liu; Linglan Ma; Na Li; Huiting Liu; Jue Wang; Lei Zheng; Chao Liu; Xuefeng Wang; Xiaoyang Zhao; Jingying Yan; Sisi Wang; Han Wang; Xueguang Zhang; Fashui Hong

2010-01-01

24

X-ray absorption and electrochemical studies of direct methanol fuel cell catalysts.  

National Technical Information Service (NTIS)

In order for polymer electrolyte fuel cells to operate directly on methanol instead of hydrogen, methanol oxidation must be catalyzed in the acidic cell environment. Pt-Ru and Pt-Ru oxide are considered to be the most active catalysts for this purpose; Ru...

D. J. Zurawski A. J. Aldykiewicz S. F. Baxter M. Krumpelt

1996-01-01

25

Supported Pt and Pt–Ru catalysts prepared by potentiostatic electrodeposition for methanol electrooxidation  

Microsoft Academic Search

Methanol electrooxidation was investigated on Pt–Ru electrocatalysts supported on glassy carbon. The catalysts were prepared\\u000a by electrodeposition from solutions containing chloroplatinic acid and ruthenium chloride. Bulk composition analysis of the\\u000a Pt–Ru catalyst was performed using an X-ray detector for energy dispersive spectroscopy analysis (EDX). Three different compositions\\u000a were analyzed in the range 0–20 at.% Ru content. Tafel plots for the oxidation

J. M. Sieben; M. M. E. Duarte; C. E. Mayer

2008-01-01

26

Structure and Chemical Composition of a Supported Pt-Ru Electrocatalyst for Methanol Oxidation  

Microsoft Academic Search

High resolution electron microscopy and X-ray microchemical analysis were used to characterize the composition, size, distribution, and morphology of Pt-Ru particles with nominal Pt:Ru ratios of 1:1 and 3:1, supported on carbon black. The particles are predominantly single nanocrystals with diameters in the order of 2.0 to 2.5 nm. Occasionally, twinned particles are also observed. All investigated particles represent solid

V. Radmilovic; H. A. Gasteiger; P. N. Jr. Ross

1995-01-01

27

Electrochemical deposition of PtRu on an uncatalyzed carbon electrode for methanol electrooxidation  

Microsoft Academic Search

This research aims to increase the utilization of platinum–ruthenium alloy (PtRu) catalysts and thus to lower the catalyst loadings in the electrode for methanol electrooxidation. The electrodeposition of PtRu was performed on a rotating disk electrode (RDE) of glassy carbon (GC), on which a layer of Nafion®-bonded carbon (Vulcan XC 72R) was dispersed in advance. First, the behavior of Pt

Z. D. Wei; S. H. Chan

2004-01-01

28

Structure of carbon-supported Pt–Ru nanoparticles and their electrocatalytic behavior for hydrogen oxidation reaction  

Microsoft Academic Search

The electrochemical activity towards hydrogen oxidation reaction (HOR) of a high performance carbon-supported Pt–Ru electrocatalyst (HP 20wt.% 1:1 Pt–Ru alloy on Vulcan XC-72 carbon black) has been studied using the thin-film rotating disk electrode (RDE) technique. The physical properties of the Pt–Ru nanoparticles in the electrocatalyst were previously determined by transmission electron microscopy (TEM), high resolution TEM, fast Fourier transform

Amado Velázquez; Francesc Centellas; José Antonio Garrido; Conchita Arias; Rosa María Rodríguez; Enric Brillas; Pere-Lluís Cabot

2010-01-01

29

An Investigation on the Antibacterial and Antibiofilm Efficacy of Cationic Nanoparticulates for Root Canal Disinfection  

Microsoft Academic Search

This study aimed to investigate the antibacterial and antibiofilm efficacy of cationic nanoparticulates for root canal disinfection. Experiments were performed in two stages. In stage 1, experiments were conducted to examine the physical properties of three types of nanoparticulates. The antibacterial properties of nanoparticulates alone and nanoparticulates mixed with zinc oxide–eugenol–based sealer were studied. In stage 2, the ability of

Anil Kishen; Zhilong Shi; Annie Shrestha; Koon Gee Neoh

2008-01-01

30

PtRu nanofiber alloy counter electrodes for dye-sensitized solar cells  

NASA Astrophysics Data System (ADS)

With an aim of enhancing the light-to-electric power conversion efficiency of dye-sensitized solar cell (DSSC), here we synthesize PtRu nanofiber alloys using a low-temperature hydrothermal technique which are employed as counter electrodes (CEs) for DSSCs. Owing to the good electrical conduction and electrocatalysis, light-to-electric power conversion efficiencies of PtRu-based DSSCs have been elevated in comparison with that of Pt CE based DSSC. The DSSC employing PtRu3 alloy CE gives a power conversion efficiency of 6.80% in comparison with 6.17% from Pt-based DSSC. The reasonable conversion efficiency, simple preparation, and scalability demonstrate the potential use of PtRu alloys in efficient DSSCs.

Cai, Hongyuan; Tang, Qunwei; He, Benlin; Li, Pinjiang

31

Schottky barrier height behavior of Pt-Ru alloy contacts on single-crystal n-ZnO  

SciTech Connect

We investigated the Schottky barrier height (SBH) behavior of binary alloy Schottky contacts on n-type zinc oxide (n-ZnO) single crystals. Pt-Ru alloy electrodes were deposited on the Zn-polar and O-polar faces of ZnO substrates by combinatorial ion-beam deposition under identical conditions. The crystal structures of the Pt-Ru alloy film changed from the Pt phase (cubic structure) to the Ru phase (hexagonal structure) in the Pt-Ru alloy phase diagram with decreasing Pt content. The SBH, determined from current-voltage measurements, decreased with decreasing Pt content, indicating that the SBH behavior also followed the Pt-Ru alloy phase diagram. The alloy electrodes on the Zn-polar face showed better Schottky properties than those on the O-polar face. Hard x-ray photoelectron spectroscopy revealed a difference in the interface oxidization of the Pt-Ru alloy: the interface of the O-polar face and Pt-Ru mixed phase with poor crystallinity had a more oxidized layer than that of the Zn-polar face. As a result of this oxidization, the O-polar face, Pt-Ru mixed, and Ru phases showed poor Schottky properties.

Nagata, T.; Haemori, M.; Hayakawa, R.; Yoshitake, M.; Chikyow, T. [Advanced Electronic Materials Center, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan); Volk, J. [Research Institute for Technical Physics and Materials Science, H-1121 Budapest, Konkoly Thege Miklos ut 29-33 (Hungary); Yamashita, Y. [Advanced Electronic Materials Center, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan); NIMS Beamline Station at SPring-8, National Institute for Materials Science, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan); Yoshikawa, H.; Ueda, S.; Kobayashi, K. [NIMS Beamline Station at SPring-8, National Institute for Materials Science, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148 (Japan)

2010-05-15

32

IrO2 as a promoter of Pt-Ru for methanol electro-oxidation.  

PubMed

A multifunctional catalyst may represent a valid route to enhance methanol electro-oxidation. Ternary catalysts based on Pt modified with both Ru and Ir oxides show better performance for methanol electro-oxidation than bi-metallic Pt-Ru catalysts. PMID:24760311

Baglio, V; Amin, R S; El-Khatib, K M; Siracusano, S; D'Urso, C; Aricò, A S

2014-06-14

33

The effect of composition of Ni-supported Pt-Ru binary anode catalysts on ethanol oxidation for fuel cells  

Microsoft Academic Search

The effect of the composition of a platinum-ruthenium (Pt-Ru) binary catalyst on a Ni-support for the anodic oxidation of ethanol in aqueous alkaline media has been studied. Co-deposition of nano-crystallites of a Pt-Ru electrocatalyst of varying composition, has been made on Ni-supports by galvanostatic deposition from precursor salt solutions of suitable composition, without using any capping agent. Conjugated scanning electron

Joyeeta Bagchi; Swapan Kumar Bhattacharya

2007-01-01

34

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

35

Nanoparticulate Alnico Thin Films with High Coercivity  

NASA Astrophysics Data System (ADS)

Alnico V (Fe--8% Al--14% Ni--24% Co--3% Cu) nanoparticulate thin films have been produced by dc magnetron sputtering. The films were sputtered on Si substrates for magnetic measurements and carbon-coated copper grids for TEM measurements. The as-deposited films have a fine grained microstructure with the bcc crystal structure. The as-made films were subjected to a full heat treatment which consists of heating the sample to 900 ^oC, then cooling it to 600 ^oC and finally annealing it at 600 ^oC for several hours. After the heat treatment, the thin films broke up into large nanoparticles (20-60 nm) surrounded by small nanoparticles (2 nm). Electron diffraction data showed that the annealed samples had an fcc structure. The maximum room temperature coercivity was found to be 2 kOe after 6h of annealing at 600 ^oC. The high coercivity could be due to strain that was induced during precipitation. The evolution of crystal structure and microstructure with annealing will be monitored and related to the observed magnetic properties.

Akdogan, Ozan; Hadjipanayis, George C.

2009-03-01

36

A simple method for the synthesis of PtRu nanoparticles on the multi-walled carbon nanotube for the anode of a DMFC  

Microsoft Academic Search

We report the synthesis of PtRu nanoparticles on the multi-walled carbon nanotubes (MWCNTs) by a simple sodium borohydride reduction method. Transmission electron microscopy (TEM) analysis indicated that well-dispersed small (2–3nm) PtRu particles were formed on the MWCNTs. X-ray diffraction (XRD) analysis confirmed the formation of the PtRu alloy on the MWCNTs. X-ray photoelectron spectroscopy (XPS) measurements revealed that 70.4% Pt

J. Prabhuram; T. S. Zhao; Z. X. Liang; R. Chen

2007-01-01

37

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

38

Formation of carbon supported PtRu alloys: an XRD analysis  

Microsoft Academic Search

Carbon supported PtRu alloys were prepared by impregnation of Pt and Ru precursors on a porous carbon support, followed by reduction of the metals with Na2S2O4. After reduction, the samples were thermal treated in argon up to 700°C. The samples were characterized by atomic absorption (AAS) and X-ray diffraction (XRD) measurements. Before thermal treatment only carbon reflexions were visible in

E. Antolini; F. Cardellini

2001-01-01

39

Temperature-dependent methanol electro-oxidation on well-characterized Pt-Ru alloys  

Microsoft Academic Search

The kinetics of methanol electro-oxidation on well-characterized Pt-Ru alloy surfaces were measured in sulfuric acid solution as a function of temperature. The alloy surfaces were prepared in ultrahigh vacuum with the surface composition determined by low energy ion scattering. It was found that the activity of Ru towards the dissociative adsorption of methanol is a strong function of temperature. This

Hubert A. Gasteiger; N. Markovic; P. N. Jr. Ross; E. J. Cairns

1994-01-01

40

Glycerol Hydrogenolysis on Carbon-Supported PtRu and AuRu Bimetallic Catalysts  

SciTech Connect

Bimetallic PtRu and AuRu catalysts were prepared by a surface redox method in which Pt or Au was deposited onto the surface of carbon-supported Ru nanoparticles with an average diameter of 2-3 nm. Characterization by H2 chemisorption, analytical TEM, and X-ray absorption spectroscopy at the Ru K-edge, Pt LIII-edge, and Au LIII-edge confirmed that Pt and Au were successfully deposited onto Ru without disrupting the Ru particles. Depression of the ethane hydrogenolysis rate over Ru after addition of Au provided further evidence of successful deposition. The bimetallic particles were subsequently evaluated in the aqueous-phase hydrogenolysis of glycerol at 473 K and 40 bar H2 at neutral and elevated pH. Although monometallic Pt and Ru exhibited different activities and selectivities to products, the bimetallic PtRu catalyst functioned more like Ru. A similar result was obtained for the AuRu bimetallic catalyst. The PtRu catalyst appeared to be stable under the aqueous-phase reaction conditions, whereas the AuRu catalyst was altered by the harsh conditions. Gold appeared to migrate off the Ru and agglomerate on the carbon during the reaction in liquid water.

Maris,E.; Ketchie, W.; Murayama, M.; Davis, R.

2007-01-01

41

Supporting PtRu catalysts on various types of carbon nanomaterials for fuel cell applications  

NASA Astrophysics Data System (ADS)

PtRu catalysts were supported on five types of carbon nanomaterials of various shapes, sizes, and graphitic properties and the catalyst supports evaluated. The carbon nanomaterial used included three types of nanoparticles: Arc Black (AcB), Vulcan XC-72 (Vulcan) and graphene oxide (GO), and two types of nanofibers: carbon nanocoil (CNC) and carbon nanotube (CNT). Pt and Ru were supported by the reduction method using sodium borohydride. The metal catalyst loading was confirmed by thermo-gravimetric analysis (TGA), electron microscopy, and X-ray diffraction (XRD). Transmission electron microscopy (TEM) and XRD revealed that the diameter of PtRu catalyst nanoparticles loaded on reduced GO (rGO) and AcB were ~2 nm and was the smallest among all the samples. Shifts in Pt (111) XRD peaks of CNC and CNT were larger than those of AcB, Vulcan, and rGO. These results suggest that the diameters of catalyst nanoparticles became smaller by loading on the carbon nanoparticles with a large surface area including rGO, AcB, and Vulcan. Loading onto the carbon nanofibers enhanced the degree of PtRu alloying.

Suda, Yoshiyuki; Ozaki, Masahiro; Tanoue, Hideto; Takikawa, Hirofumi; Ue, Hitoshi; Shimizu, Kazuki; Muramoto, Hirokazu

2013-04-01

42

Advances in direct oxidation methanol fuel cells  

Microsoft Academic Search

FLICI cells that can operate directly on fuels such as methanol are attractive for low to medium power appl i cations in view of their low weight. and volume relative to other power sources. A liquid feed direct methanol fuel cell has been developed based on a proton exchange membrane electrolyte and Pt\\/Ru and Pt catalyzed fuel and air\\/02 electrodes

G. K. Suryaprakash; G. A. Olah; E. Vamos; H. Frank; G. Halpert; A. LaConti; J. Kosek; G. K. Surya Prakash

1994-01-01

43

In vitro and in vivo equivalence testing of nanoparticulate intravenous formulations.  

PubMed

The topic of bioequivalence evaluation of nanoparticulate intravenous formulations is one that has been intensely debated in recent times since the release of the specific recommendations by many regulatory authorities worldwide. Product specific bioequivalence guidelines for many of the nanoparticulate systems where therapeutic molecules are directly coupled (human albumin bound paclitaxel nanosuspension), functionalized (iron- carbohydrate preparations) or entrapped/coated to a carrier (doxorubicin liposomal formulations), have been approved by the drug regulatory agencies. These current regulatory procedures include complete characterization of the generic formulation in terms of its physicochemical characteristics, pharmacokinetics disposition and/or non clinical testing with respect to the reference formulation. The concept of in vitro equivalency is emerging as a valuable tool in these guidances as generic product differing in in vitro parameters can result in a different biopharmaceutical profile with respect to pharmacokinetics and biodistribution. Furthermore, in case of systems with entrapped drug, classical pharmacokinetic parameters alone may only ensure the equivalent clearance of test and reference product from systemic circulation but may fail to detect the extent to which the nanoparticles are taken up by different target organs and, consequently, the safety and efficacy effects. Hence, additional tissue distribution study in preclinical study models has reflected in recent guidances. Understanding and interpretation of these regulatory requirements thus presents most critical component of a generic product development cycle. This article reviews these current regulatory procedures with special emphasis on in vitro population bioequivalence (POP BE) and preclinical testing of generic formulations. PMID:24203084

Pathak, S M; Ruby, P K; Aggarwal, D

2014-04-01

44

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

45

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.

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

2013-01-01

46

Development of a polymeric nanoparticulate delivery system for indocyanine green  

NASA Astrophysics Data System (ADS)

Purpose. The objective of this project was to develop an intravenously administrable poly(dl-lactic-co-glycolic acid) (PLGA) nanoparticulate delivery system for Indocyanine Green (ICG), to enhance the potential for ICG use in tumor imaging and therapy. Methods. For this purpose PLGA nanoparticles entrapping ICG were engineered by spontaneous emulsification solvent diffusion method. ICG entrapment in nanoparticles was determined and physicochemical characterization of nanoparticles was performed. The stability of ICG in nanoparticles formulation under various conditions was determined. The intracellular uptake of ICG in nanoparticles by B16-F10 and C-33A cancer cell lines was studied in comparison with the free ICG solution. Anti-proliferation studies against cancer cells were performed to prove the photodynamic activity of ICG in nanoparticles. Biodistribution of ICG when delivered through nanoparticles and solution were evaluated in mice after tail vein injection. Results. PLGA nanoparticles with a mean diameter of 350 nm and 74% ICG entrapment were obtained. The nanoparticles were nearly spherical in shape with zeta potential of -16 mV. The nanoparticles formulation provided overall stability to ICG with degradation half-lives of 2.5--3.5 days as compared to 10--20 hr of free ICG solutions. The intracellular uptake of ICG through nanoparticles was directly proportional to time and extracellular nanoparticle concentration. The intracellular uptake of ICG was enhanced about 100-fold by nanoparticles formulation as compared to the free ICG solution. Nanoparticles formulation showed significant photodynamic effect at nano-molar ICG concentrations and very low light dose (fluence: 0.22 W/cm2 and energy density: 1.1 J/cm2). In-vivo, the blood circulation-time and retention-time of ICG in various organs was enhanced 2--5 times by nanoparticles formulation as compared to the free ICG solution. Conclusions. A PLGA nanoparticlute delivery system was developed for ICG, which demonstrated its capability in enhancing the potential of ICG use in tumor diagnosis and anticancer therapy.

Saxena, Vishal

47

Thermal stability and reconstruction of nanoparticulate Au film on model molecular surfaces  

Microsoft Academic Search

Thermally activated morphological reconstruction of nanoparticulate gold films deposited onto model molecular surfaces was investigated at 200?°C as a function of the annealing time. Results show a strong correlation of the spatial reorganization of the metallic particles to the surface chemistry of the underlying substrate. On the nonpolar surface, the thin nanoparticulate Au film dewets by the formation of randomly

K. Mougin; Z. Zheng; N. Piazzon; E. Gnecco; H. Haidara

2009-01-01

48

Catalysts for direct formic acid fuel cells  

NASA Astrophysics Data System (ADS)

Previous work has demonstrated that formic acid fuel cells show interesting properties for micro power generation. In this paper the effects of the anode catalyst composition on fuel cell performance is investigated. In particular, the performance of Pt, Pt/Pd and Pt/Ru catalysts for direct formic acid fuel cells is investigated and their effect on cell power density output at 30 °C are compared. It is found that the open cell potential varies significantly with the catalyst composition. The Pt/Pd catalyst shows an open cell potential of 0.91 V compared to 0.71 V with pure platinum and 0.59 V with Pt/Ru. The current at a cell potential of 0.5 V is 62 mA/cm 2 with Pt/Pd compared to 33 mA/cm 2 with pure platinum and 38 mA/cm 2 with Pt/Ru. Interestingly, the Pt/Ru catalyst gives the most power at low voltage 70 mW/cm 2 at 0.26 V, compared to 43 mW/cm 2 for pure platinum and 41 mW/cm 2 for Pt/Pd. All of the catalysts showed stable operation during several hour tests. Analysis of the data indicates that the addition of palladium enhances the rate of formic acid electrooxidation via a direct reaction mechanism, while ruthenium additions suppress the direct pathway and enhance electrooxidation via a reactive CO intermediate.

Rice, C.; Ha, S.; Masel, R. I.; Wieckowski, A.

49

The use of nanoparticulate delivery systems in metronomic chemotherapy.  

PubMed

Metronomic chemotherapy aiming at inhibiting tumor angiogenesis with conventional chemotherapeutics is a promising strategy for antiangiogenic cancer therapy. However, current metronomic chemotherapy mainly focuses on free small-molecule drugs, without any effort to achieve tumor-specific biodistribution, which may lead to long-term toxicity concerns. Metronomic chemotherapy using nanoparticulate drug delivery system (DDS) offers significant upside to reduce off-target side effects, decrease accumulated dose, and enhance the efficacy of tumor vessel targeting without compromising antitumor efficacy; but there has been a lack of thorough experimental data describing the targeted metronomic chemotherapy. Here, we develop a new nanoparticulate DDS, SP5.2 peptide conjugated, Flt-1 (VEGFR-1) targeted nanoparticles for docetaxel (SP5.2-DTX-NP), as a model for the investigation of targeted metronomic chemotherapy with respect to both antitumor efficacy and toxicity. The results demonstrate that metronomic SP5.2-DTX-NP exerts antitumor activity mainly through the antiangiogenic effect of docetaxel, which is specifically delivered into the tumor vascular endothelial cells through the nanoparticle internalization mediated by the interaction of SP5.2 and over-expressed Flt-1 receptors on tumor vessels. Moreover, the antitumor efficacy of targeted metronomic chemotherapy is better than that of the treatment with the DDS given in the maximum tolerated dose (MTD) regimen, which is shown in significantly prolonged mice survival and minimal drug-associated toxicity (bone marrow suppression, hematological toxicity, and mucosal injury of small intestine). The present research reveals and highlights the significance of targeted metronomic therapy with nanoparticulate DDS in antiangiogenic cancer therapy. PMID:23465835

Yu, De-Hong; Ban, Fu-Qiang; Zhao, Mei; Lu, Qin; Lovell, Jonathan F; Bai, Fan; Wang, Chao; Guan, Ying-Yun; Luan, Xin; Liu, Ya-Rong; Fang, Chao; Chen, Hong-Zhuan

2013-05-01

50

Kinetic Analysis of Nanoparticulate Polyelectrolyte Complex Interactions with Endothelial Cells  

PubMed Central

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.

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

2007-01-01

51

Analysis of the oxidation kinetics and barrier layer properties of ZrN and Pt\\/Ru thin films for DRAM applications  

Microsoft Academic Search

ZrN and Pt\\/Ru thin films have been grown by an automated ion beam sputter-deposition system. Both materials were evaluated for use as barrier layers (ZrN) and bottom electrodes (Pt\\/Ru) in dynamic random access memory (DRAM) applications. The ZrN films had resistivities on the order of 250–300 ?? cm. The ZrN films were (002) oriented and were rather smooth with an

H. N. Al-Shareef; X. Chen; D. J. Lichtenwalner; A. I. Kingon

1996-01-01

52

Iceberg-hosted nanoparticulate Fe in the Southern Ocean: Mineralogy, origin, dissolution kinetics and source of bioavailable Fe  

NASA Astrophysics Data System (ADS)

Sediments from icebergs and glaciers contain nanopartculate Fe(III) oxyhydroxides (including ferrihydrite) which form in aqueous, oxic (micro)environments where Fe(II)-bearing rock minerals oxidise and high degrees of supersaturation are promoted by freezing and thawing. An ascorbic acid extraction dissolves only labile Fe present in fresh (loosely aggregated) ferrihydrite that is directly or indirectly bioavailable. Glacial and iceberg sediments contain ferrihydrite aggregates that provide 0.04 to 0.17% Fe soluble in ascorbic acid, rather larger than the concentrations in a limited suite of atmospheric dusts. The dissolution behaviour of labile Fe from glacial and iceberg sediments by ascorbic acid is controlled by the access of reactant, or removal of solute, through micropores to or from active sites in the interior of ferrihydrite aggregates. A first-order kinetic model is presented to examine the rates at which bioavailable Fe can be supplied by melting icebergs in the Weddell Sea. The model utilizes rate constants from the literature for the processes which solubilise Fe from nanoparticulate ferrihydrite (dissolution, photochemical reduction and grazing) and the processes that remove Fe nanoparticulates (sinking, scavenging and incorporation in faecal material), and render them less reactive (transformation, aging). Model results demonstrate that icebergs can supply bioavailable Fe to the Weddell Sea by the dissolution of nanoparticulate ferrihydrite (despite loss/removal of nanoparticles by sinking, aging, transformation, scavenging and incorporation into faecal pellets) at rates that are comparable to atmospheric dust. Dissolution enhanced by photochemical reduction and grazing provides the most rapid rates of bioavailable Fe production.

Raiswell, Rob

2011-06-01

53

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.

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

2013-01-01

54

Carbon support effects on bimetallic Pt-Ru nanoparticles formed from molecular precursors  

SciTech Connect

The authors describe the preparation, structural characterization, and support interactions experienced by two different compositions of Pt-Ru nanoparticles supported on several carbons (carbon black, fullerene soot, and desulfurized carbon black). The bimetallic nanoparticles, obtained by reduction of the neutral molecular precursors PtRu{sub 5}C(CO){sub 16} and Pt{sub 2}Ru{sub 4}(CO){sub 18} (the latter of which lacks a central stabilizing carbide core) at elevated temperatures in a hydrogen atmosphere, show a structural homology, exhibiting exceptionally narrow size and compositional distributions. A detailed structural picture of the nanoparticles has been deduced on the basis of in-situ extended X-ray absorption fine structure (EXAFS), scanning transmission electron microscopy (STEM), energy-dispersive X-ray analysis (EDX), and X-ray absorption near edge structures (XANES). These techniques reveal that the bimetallic nanoparticles have Pt/Ru compositions of 1:5 and 2:4, respectively, and average diameters lying between 1.0 and 1.5 nm. The local metal coordination environments reveal a nonstatistical distribution of the two metals in the nanoparticles. Specifically, Pt shows a marked preference for segregation to the particle surfaces under an H{sub 2} atmosphere. The data also reveal a difference in the structural environment of the nanoparticles when formed on the fullerene soot support. Interactions between Ru and low-Z atoms are revealed through XANES, which, taken collectively with the other data presented, leads the authors to propose a possible Ru-C compound formation on this latter support phase.

Hills, C.W.; Nashner, M.S.; Frenkel, A.I.; Shapley, J.R.; Nuzzo, R.G. [Univ. of Illinois, Urbana, IL (United States)] [Univ. of Illinois, Urbana, IL (United States)

1999-02-02

55

Nanoparticulate formulations of mithramycin analogs for enhanced cytotoxicity  

PubMed Central

Mithramycin (MTM), a natural product of soil bacteria from the Streptomyces genus, displays potent anticancer activity but has been limited clinically by severe side effects and toxicities. Engineering of the MTM biosynthetic pathway has produced the 3-side-chain-modified analogs MTM SK (SK) and MTM SDK (SDK), which have exhibited increased anticancer activity and improved therapeutic index. However, these analogs still suffer from low bioavailability, short plasma retention time, and low tumor accumulation. In an effort to aid with these shortcomings, two nanoparticulate formulations, poly(ethylene glycol)-poly(aspartate hydrazide) self-assembled and cross-linked micelles, were investigated with regard to the ability to load and pH dependently release the drugs. Micelles were successfully formed with both nanoparticulate formulations of each drug analog, with an average size of 8.36 ± 3.21 and 12.19 ± 2.77 nm for the SK and SDK micelles and 29.56 ± 4.67 nm and 30.48 ± 7.00 nm for the SK and SDK cross-linked micelles respectively. All of the drug-loaded formulations showed a pH-dependent release of the drugs, which was accelerated as pH decreased from 7.4 to 5.0. The micelles retained biological activity of SK and SDK entrapped in the micelles, suppressing human A549 lung cancer cells effectively.

Scott, Daniel; Rohr, Jurgen; Bae, Younsoo

2011-01-01

56

Photothermal analysis of individual nanoparticulate samples using micromechanical resonators.  

PubMed

The ability to detect and analyze single sample entities such as single nanoparticles, viruses, spores, or molecules is of fundamental interest. This can provide insight into the individual specific properties which may differ from the statistical sample average. Here we introduce resonant photothermal spectroscopy, a novel method that enables the analysis of individual nanoparticulate samples. Absorption of light by an individual sample placed on a microstring resonator results in local heating of the string, which is reflected in its resonance frequency. The working principle of the spectrometer is demonstrated by analyzing the optical absorption of different micro- and nanoparticles on a microstring. We present the measurement of a simple absorption spectrum of multiple polystyrene microparticles illuminated with an unfocused LED light source. Using a diode laser, single 170 nm polystyrene nanoparticles are detected. With the current setup, nanoparticulate samples with a mass of ~40 ag are detectable. By using nanostrings, visible and infrared photothermal spectroscopy in the subattogram mass regime is possible and single molecule detection is within reach. PMID:23799869

Larsen, Tom; Schmid, Silvan; Villanueva, Luis G; Boisen, Anja

2013-07-23

57

Electroactivity of high performance unsupported Pt–Ru nanoparticles in the presence of hydrogen and carbon monoxide  

Microsoft Academic Search

The electrochemical activity of high performance unsupported (1:1) Pt–Ru electrocatalyst in the presence of hydrogen and carbon monoxide has been studied using the thin-film rotating disk electrode (RDE) technique. The kinetic parameters of these reactions were determined in H2- and CO-saturated 0.5M H2SO4 solutions by means of cyclic voltammetry, including CO stripping, and RDE voltammetry. Pt–Ru\\/Nafion inks were prepared in

Amado Velázquez-Palenzuela; Pere-Lluís Cabot; Francesc Centellas; José Antonio Garrido; Conchita Arias; Rosa María Rodríguez; Enric Brillas

2010-01-01

58

PtRu catalysts supported on heteropolyacid and chitosan functionalized carbon nanotubes for methanol oxidation reaction of fuel cells.  

PubMed

A simple self-assembly approach has been developed to functionalize carbon nanotubes (CNTs) with chitosan (CS) and heteropolyacids (HPAs) of phosphomolybdic acid (H(3)PMo(12)O(40), HPMo) and phosphotungstic acid (H(3)PW(12)O(40), HPW). The non-covalent functionalization method, which introduces homogenous surface functional groups with no detrimental effect on graphene structures of CNTs, can be carried out at room temperature without the use of corrosive acids. The PtRu nanoparticles supported on HPAs-CS-CNTs have a uniform distribution and much smaller size as compared to those of the PtRu nanoparticles supported on conventional acid treated CNTs (PtRu/AO-CNTs). The onset and peak potentials for CO(ad) oxidation on PtRu/HPAs-CS-CNTs catalysts are more negative than those on PtRu/AO-CNTs, indicating that HPAs facilitate the electro-oxidation of CO. The PtRu/HPMo-CS-CNTs catalyst has a higher electrocatalytic activity for methanol oxidation and higher tolerance toward CO poisoning than PtRu/HPW-CS-CNTs. The better electrocatalytic enhancement of HPMo on the PtRu/HPAs-CS-CNTs catalyst is most likely related to the fact that molybdenum-containing HPAs such as HPMo have more labile terminal oxygen to provide additional active oxygen sites while accelerating the CO and methanol oxidation in a similar way to that of Ru in the PtRu binary alloy system. PMID:21842101

Cui, Zhiming; Li, Chang Ming; Jiang, San Ping

2011-09-28

59

Catalysis of CO electrooxidation at Pt, Ru, and PtRu alloy. An in situ FTIR study  

SciTech Connect

A comparative study of CO electrooxidation on different catalysts using in situ FTIR spectroscopy is presented. As electrode materials, polycrystalline Pt and Ru and a PtRu (50:50) alloy are used. The latter is one of the well-known active alloys for CO oxidation. The potential dependence of the band frequencies for the CO stretch indicates the formation of relatively compact islands at pure Pt and Ru, and a loose adlayer structure at the alloy. This loose structure has a positive effect on the rate of oxidative desorption. CO submonolayer coverages are obtained by integrating the absorption bands for CO{sub 2} produced upon oxidation of adsorbed CO. The band intensities measured at Pt, Ru, and PtRu indicate an influence of the substrate on the absorption coefficient of the CO stretch. It is shown that for a correct description of the catalyst properties toward CO electrooxidation, it must be distinguished between bulk and adsorbed CO. In contrast to the statement of most of the recent papers that a PtRu alloy (50:50) is the material with the highest activity for CO oxidation, it is demonstrated and rationalized in the present paper that for bulk CO oxidation pure Ru is the best catalyst.

Lin, W.F.; Iwasita, T.; Vielstich, W. [Univ. der Bundeswehr Muenchen, Neubiberg (Germany). Inst. fuer Physik] [Univ. der Bundeswehr Muenchen, Neubiberg (Germany). Inst. fuer Physik

1999-04-22

60

Nanoparticules d'or: De l'imagerie par resonance magnetique a la radiosensibilisation  

NASA Astrophysics Data System (ADS)

Cette thèse approfondit l'étude de nanoparticules d'or de 5 nm de diamètre recouvertes de diamideéthanethioldiethylènetriaminepentacétate de gadolinium (DTDTPA:Gd), un agent de contraste pour l'imagerie par résonance magnétique (IRM). En guise de ciblage passif, la taille des nanoparticules a été contrôlée afin d'utiliser le réseau de néovaisseaux poreux et perméable des tumeurs. De plus les tumeurs ont un drainage lymphatique déficient qui permet aux nanoparticules de demeurer plus longtemps dans le milieu interstitiel de la tumeur. Les expériences ont été effectuées sur des souris Balb/c femelles portant des tumeurs MC7-L1. La concentration de nanoparticules a pu être mesurée à l'IRM in vivo. La concentration maximale se retrouvait à la fin de l'infusion de 10 min. La concentration s'élevait à 0.3 mM dans la tumeur et de 0.12 mM dans le muscle environnant. Les nanoparticules étaient éliminées avec une demi-vie de 22 min pour les tumeurs et de 20 min pour le muscle environnant. Les nanoparticules ont été fonctionnalisées avec le peptide Tat afin de leur conférer des propriétés de ciblage actif La rétention de ces nanoparticules a ainsi été augmentée de 1600 %, passant d'une demi-vie d'élimination de 22 min à 350 min. La survie des souris a été mesurée à l'aide de courbes Kaplan-Meier et d'un modèle mathématique évalue l'efficacité de traitements. Le modèle nous permet, à l'aide de la vitesse de croissance des tumeurs et de l'efficacité des traitements, de calculer la courbe de survie des spécimens. Un effet antagoniste a été observé au lieu de l'effet synergétique attendu entre une infusion de Au@DTDTPA:Gd et l'irradiation aux rayons X. L'absence d'effet synergétique a été attribuée à l'épaisseur du recouvrement de DTDTPA:Gd qui fait écran aux électrons produits par l'or. De plus, le moyen d'ancrage du recouvrement utilise des thiols qui peuvent s'avérer être des capteurs de radicaux. De plus, contrairement a ce qui était escompté, un effet chimiothérapeutique de ces nanoparticules a été observé in vitro et in vivo. Par contre, le mécanisme précis de cet effet est encore à être expliquer, mais on sait déjà que les nanoparticules d'or affectent les fonctions des macrophages ainsi que l'angiogenèse. MOTS-CLÉS : Radiosensibilisateur, Nanoparticules d'or, Agent de contraste pour l'IRM, Électrons de basses énergies, Kaplan-Meier, Effet chimiothérapeutique.

Hebert, Etienne M.

61

Development and pharmacological evaluation of a PEG based nanoparticulate camptothecin analog for oral administration.  

PubMed

The aim of this study was to formulate polyethylene glycol (PEG) based nanoparticulate camptothecin analog for oral administration and to evaluate its pharmacological activity. Camptothecin analog (CA) belongs to topoisomerase-I inhibitor class of compounds with proven antitumor activity but exhibits poor solubility. To enhance solubility and oral bioavailability, a PEG based nanoparticulate formulation was developed using a high pressure homogenization technique. The saturation solubility and dissolution characteristics of the nanoparticulate formulation were investigated and compared with as-is drug formulation to ascertain the impact of particle size on drug dissolution in physiologically relevant dissolution media. Systemic exposure of nanoparticulate formulation were evaluated in Wistar rats for increase in the rate and extent of drug absorption. The antitumor activity of nanoparticulate formulation was evaluated on human tumor xenografts (NCI-H460 cell lines) grown in athymic nude mice and compared with a positive control, Irinotecan Hydrochloride administered intravenously. The saturation solubility and dissolution rate of the nanoparticulate formulation were significantly higher as compared to as-is drug formulation. Pharmacokinetic (PK) studies in Wistar rats indicated significant increase in the rate and extent of absorption for the nanoparticulate formulation. Pharmacological activity of nanoparticles in athymic nude mice with implanted tumors revealed that the tumor inhibition activity was equivalent to Irinotecan Hydrochloride intravenous formulation with comparable safety profile at lower doses. These studies demonstrated the feasibility of developing a safe and efficacious oral formulation for a sparingly soluble camptothecin analog that may provide a viable, patient compliant and, cost effective option for the treatment of solid tumors. PMID:22313161

Nekkanti, Vijaykumar; Venkateswarlu, Vabalaboina; Ansari, Khalid Akhter; Pillai, Raviraj

2011-11-01

62

Synthesis of PVP-stabilized Pt\\/Ru colloidal nanoparticles by ethanol reduction and their catalytic properties for selective hydrogenation of ortho-chloronitrobenzene  

Microsoft Academic Search

Stable poly(N-vinyl-2-pyrrolidone)-stabilized Pt\\/Ru colloidal nanoparticles (PVP-Pt\\/Ru) were prepared via ethanol reduction of H2PtCl6?6H2O and RuCl3?nH2O. The average diameters of the nanoparticles with different molar ratio of Pt\\/Ru were in a range of 2.1–2.8nm with narrow size distributions. X-ray photoelectron spectroscopy verified that both Pt and Ru were in the metallic state and Ru was rich on the surface. These nanoparticles

Manhong Liu; Jin Zhang; Jinqiang Liu; William W. Yu

2011-01-01

63

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.

Murr, L. E.

2008-01-01

64

Nanoparticulate carriers for the treatment of coronary restenosis  

PubMed Central

The current treatment for coronary restenosis following balloon angioplasty involves the use of a mechanical or a drug-eluting stent. Despite the high usage of commercially-available drug-eluting stents in the cardiac field, there are a number of limitations. This review will present the background of restenosis, go briefly into the molecular and cellular mechanisms of restenosis, the use of mechanical stents in coronary restenosis, and will provide an overview of the drugs and genes tested to treat restenosis. The primary focus of this article is to present a comprehensive overview on the use of nanoparticulate delivery systems in the treatment of restenosis both in-vitro and in-vivo. Nanocarriers have been tested in a variety of animal models and in human clinical trials with favorable results. Polymer-based nanoparticles, liposomes, and micelles will be discussed, in addition to the findings presented in the field of cardiovascular drug targeting. Nanocarrier-based delivery presents a viable alternative to the current stent based therapies.

Brito, Luis; Amiji, Mansoor

2007-01-01

65

Sol-Gel Process for Making Pt-Ru Fuel-Cell Catalysts  

NASA Technical Reports Server (NTRS)

A sol-gel process has been developed as a superior alternative to a prior process for making platinum-ruthenium alloy catalysts for electro-oxidation of methanol in fuel cells. The starting materials in the prior process are chloride salts of platinum and ruthenium. The process involves multiple steps, is time-consuming, and yields a Pt-Ru product that has relatively low specific surface area and contains some chloride residue. Low specific surface area translates to incomplete utilization of the catalytic activity that might otherwise be available, while chloride residue further reduces catalytic activity ("poisons" the catalyst). In contrast, the sol-gel process involves fewer steps and less time, does not leave chloride residue, and yields a product of greater specific area and, hence, greater catalytic activity. In this sol-gel process (see figure), the starting materials are platinum(II) acetylacetonate [Pt(C5H7O2)2, also denoted Pt-acac] and ruthenium(III) acetylacetonate [Ru(C5H7O2)3, also denoted Ru-acac]. First, Pt-acac and Ru-acac are dissolved in acetone at the desired concentrations (typically, 0.00338 moles of each salt per 100 mL of acetone) at a temperature of 50 C. A solution of 25 percent tetramethylammonium hydroxide [(CH3)4NOH, also denoted TMAH] in methanol is added to the Pt-acac/Ruacac/ acetone solution to act as a high-molecular-weight hydrolyzing agent. The addition of the TMAH counteracts the undesired tendency of Pt-acac and Ru-acac to precipitate as separate phases during the subsequent evaporation of the solvent, thereby helping to yield a desired homogeneous amorphous gel. The solution is stirred for 10 minutes, then the solvent is evaporated until the solution becomes viscous, eventually transforming into a gel. The viscous gel is dried in air at a temperature of 170 C for about 10 hours. The dried gel is crushed to make a powder that is the immediate precursor of the final catalytic product. The precursor powder is converted to the final product in a controlled-atmosphere heat treatment. Desirably, the final product is a phase-pure (Pt phase only) Pt-Ru powder with a high specific surface area. The conditions of the controlled- atmosphere heat are critical for obtaining the aforementioned desired properties. A typical heat treatment that yields best results for a catalytic alloy of equimolar amounts of Pt and Ru consists of at least two cycles of heating to a temperature of 300 C and holding at 300 C for several hours, all carried out in an atmosphere of 1 percent O2 and 99 percent N2. The resulting powder consists of crystallites with typical linear dimensions of <10 nm. Tests have shown that the powder is highly effective in catalyzing the electro-oxidation of methanol.

Narayanan, Sekharipuram; Valdez, Thomas; Kumta, Prashant; Kim, Y.

2005-01-01

66

Chemical components, pharmacological properties, and nanoparticulate delivery systems of Brucea javanica  

PubMed Central

Brucea javanica has demonstrated a variety of antitumoral, antimalarial, and anti- inflammatory properties. As a Chinese herbal medicine, Brucea javanica is mainly used in the treatment of lung and gastrointestinal cancers. Pharmacological research has identified the main antitumor components are tetracyclic triterpene quassinoids. However, most of these active components have poor water solubility and low bioavailability, which greatly limit their clinical application. Nanoparticulate delivery systems are urgently needed to improve the bioavailability of Brucea javanica. This paper mainly focuses on the chemical components in Brucea javanica and its pharmacological properties and nanoparticulate formulations, in an attempt to encourage further research on its active components and nanoparticulate drug delivery systems to expand its clinical applications. It is expected to improve the level of pharmaceutical research and provide a strong scientific foundation for further study on the medicinal properties of this plant.

Chen, Meiwan; Chen, Ruie; Wang, Shengpeng; Tan, Wen; Hu, Yangyang; Peng, Xinsheng; Wang, Yitao

2013-01-01

67

Catalyst inks and method of application for direct methanol fuel cells  

Microsoft Academic Search

Inks are formulated for forming anode and cathode catalyst layers and applied to anode and cathode sides of a membrane for a direct methanol fuel cell. The inks comprise a Pt catalyst for the cathode and a Pt--Ru catalyst for the anode, purified water in an amount 4 to 20 times that of the catalyst by weight, and a perfluorosulfonic

Piotr Zelenay; John Davey; Xiaoming Ren; Shimshon Gottesfeld; Sharon C. Thomas

2004-01-01

68

A comparative in situ 195Pt electrochemical-NMR investigation of PtRu nanoparticles supported on diverse carbon nanomaterials.  

PubMed

This paper reports a detailed in situ 195Pt electrochemical-nuclear magnetic resonance (EC-NMR) study of PtRu nanoparticles (NPs) that had a nominal atomic ratio of Pt : Ru = 1 : 1 and were supported on carbon nanocoils and carbon black (Vulcan XC-72) respectively. The particle sizes of the two samples were determined by X-ray diffraction using the Sherrer equation: 3.6 nm for the former and 3.2 nm for the latter, which were further corroborated by transmission electron microscope measurements. By taking advantage of a unique correlation between the spectral frequency of the 195Pt NMR resonance and the radial atomic position in a particle, qualitatively- and spatially-resolved local Pt atomic fractions in the particles were deduced by using a Ruderman-Kittel-Kasuya-Yosida (RKKY) J-coupling-based method as a function of different electrode potentials. The results indicated that both samples had Pt-enriched cores and Pt-deprived surfaces and, most importantly, the local Pt concentration varied as the electrochemical environment changed. The spatially-resolved Fermi level local densities of states (E(f)-LDOS), which are a measure of the electronic frontier orbitals in metals, were deduced across the NMR spectrum and correlated with the EC activity in methanol electro-oxidation. The results were also compared to those obtained previously from Pt/Ru NPs supported respectively on carbon and graphite nanofibers. PMID:19213315

Tan, Fatang; Du, Bingchen; Danberry, Aaron L; Park, In-Su; Sung, Yung-Eun; Tong, YuYe

2008-01-01

69

The interplay of catechol ligands with nanoparticulate iron oxides.  

PubMed

The unique properties exhibited by nanoscale materials, coupled with the multitude of chemical surface derivatisation possibilities, enable the rational design of multifunctional nanoscopic devices. Such functional devices offer exciting new opportunities in medical research and much effort is currently invested in the area of "nanomedicine", including: multimodal imaging diagnostic tools, platforms for drug delivery and vectorisation, polyvalent, multicomponent vaccines, and composite devices for "theranostics". Here we will review the surface derivatisation of nanoparticulate oxides of iron and iron@iron-oxide core-shells. They are attractive candidates for MRI-active therapeutic platforms, being potentially less toxic than lanthanide-based materials, and amenable to functionalisation with ligands. However successful grafting of groups onto the surface of iron-based nanoparticles, thus adding functionality whilst preserving their inherent properties, is one of the most difficult challenges for creating truly useful nanodevices from them. Functionalised catechol-derived ligands have enjoyed success as agents for the masking of superparamagnetic iron-oxide particles, often so as to render them biocompatible with medium to long-term colloidal stability in the complex chemical environments of biological milieux. In this perspective, the opportunities and limitations of functionalising the surfaces of iron-oxide nanoparticles, using coatings containing a catechol-derived anchor, are analysed and discussed, including recent advances using dopamine-terminated stabilising ligands. If light-driven ligand to metal charge transfer (LMCT) processes, and pH-dependent ligand desorption, leading to nanoparticle degradation under physiologically relevant conditions can be suppressed, colloidal stability of samples can be maintained and toxicity ascribed to degradation products avoided. Modulation of the redox behaviour of iron catecholate systems through the introduction of an electron-withdrawing substituent to the aromatic ?-system of the catechol is a promising approach towards achieving these goals. PMID:22241454

Yuen, Alexander K L; Hutton, Georgina A; Masters, Anthony F; Maschmeyer, Thomas

2012-03-01

70

Systematic Performance Evaluation of Nanoparticulate ZnO Thin Film Based Chemoresistive Sensor for Food Safety  

Microsoft Academic Search

Volatile organic compounds (VOCs) such as organic acids released by bacterial pathogens is being used as an indicator for detecting microbial contamination in food by our research group. One of our current research thrust is to develop novel sensor that will be sensitive to a specific compounds (at room or low operating temperature) associated with food safety. Nanoparticulate zinc oxide

Sindhuja Sankaran; Suranjan Panigrahi

71

Optimal Cytocompatibility of a Bioceramic Nanoparticulate Cement in Primary Human Mesenchymal Cells  

Microsoft Academic Search

IntroductionThe aim of this study was to evaluate and compare the cytotoxic effects of BioAggregate (Innovative BioCaramix Inc, Vancouver, BC, Canada), a novel bioceramic nanoparticulate cement, on human mesenchymal cells. White Pro-Root MTA (Dentsply, Tulsa Dental, Tulsa, OK) was used as a reference for comparison.

Gustavo De-Deus; Antonio Canabarro; Gutemberg Alves; Adriana Linhares; Maria Isabel Senne; Jose Mauro Granjeiro

2009-01-01

72

Comparison between aesthetic and thermal performances of copper oxide and titanium dioxide nano-particulate coatings  

Microsoft Academic Search

Nano-particulate coatings with high reflectance against solar irradiation can control undesirable thermal heating by sunlight absorption. It can reduce the energy consumption for air conditioning of houses and cars. For the objects covered by these coatings and subjected to human sight, e.g. roofing surfaces, high dazzle of reflected visible light can offend the human eyes and spoil the fine view

Mehdi Baneshi; Shigenao Maruyama; Atsuki Komiya

2011-01-01

73

Nanoparticulate Iron Oxide Minerals in Soils and Sediments: Unique Properties and Contaminant Scavenging Mechanisms  

Microsoft Academic Search

Nanoparticulate goethite, akaganeite, hematite, ferrihydrite and schwertmannite are important constituents of soils, sediments and mine drainage outflows. These minerals have high sorption capacities for metal and anionic contaminants such as arsenic, chromium, lead, mercury and selenium. Contaminant sequestration is accomplished mainly by surface complexation, but aggregation of particles may encapsulate sorbed surface species into the multigrain interior interfaces, with significant

Glenn A. Waychunas; Christopher S. Kim; Jillian F. Banfield

2005-01-01

74

Design issues for improved environmental performance of dye-sensitized and organic nanoparticulate solar cells  

Microsoft Academic Search

Though environmental improvement has been claimed for the application of nanotechnology to solar cells, several characteristics of the fullerene-based organic, and the dye-sensitized nanoparticulate, solar cell are not conducive to such improvement. These include relatively high energy and materials inputs in the production of nanoparticles, a relatively low solar radiation to electricity conversion efficiency, a relatively short service life, the

L. Reijnders

2010-01-01

75

Systemic and biophase bioavailability and pharmacokinetics of nanoparticulate drug delivery systems.  

PubMed

The development of the vectorized delivery systems combining advantages of the colloidal carriers, with active targeting to the receptors sites suggests that nanoparticles have a considerable potential for treatment after biophase internalization and pharmacokinetics, as for example gene therapy. Two major mechanisms can be distinguished for addressing the desired sites for drug release: (i) passive and (ii) active targeting. Examples of passive targeting were presented: organ targeting by the Enhanced Permeability and Retention (EPR) effect; targeting the mononuclear phagocitic system; organ targeting by chemoembolization or local (organ) administration;sterical stabilization of nanoparticles (PEGylation). A strategy that could allow active targeting involves the surface functionalization of drug carriers with ligands that are selectively recognized by receptors on the surface of the cells of interest. The source for biophase bioavailability can be the systemic bioavailability following common routes of administration (generally for systemic delivery of medicines), or directly the site specific biophase bioavailability for the formulations capable of cellular or nuclear drug internalization where the drug release only will take place (for nanoparticulate drug delivery systems, DDS). Once the pharmaceutical nanosystem was internalized, begins the release of the active moiety by different mechanisms, as for example the escape from endosome, or biodegradation of the polymer carrier or liberation of the active peptide or gene from a biological construct in the nucleus, etc. The presentation will discusses the pharmacokinetics of drugs after systemic administration but especially the biophase bioavailability and pharmacokinetics after the administration of biotechnology origin of therapeutic proteins like monoclonal antibodies, gene transfer products, plasmid DNAs, nucleotides, antisense oligonucleotides (AODNs) or small interfering RNAs (siRNA). PMID:23116084

Leucuta, Sorin Emilian

2013-04-01

76

Photo-enhanced activity of Pt and Pt-Ru catalysts towards the electro-oxidation of methanol  

NASA Astrophysics Data System (ADS)

Electrocatalyst materials, consisting of Pt or Pt-Ru supported on carbon with and without TiO2, are evaluated for their activity towards the methanol oxidation reaction (MOR) in 1.0 M H2SO4 at 25 °C in the presence and absence of visible light irradiation. Electrochemical studies showed that enhanced MOR activity is achieved upon irradiation with visible light for each catalyst, in both the presence and absence of TiO2. Irradiation leads to no improvement in activity towards the formic acid oxidation reaction (FAOR) indicating that irradiation aids in the removal of adsorbed intermediate species, such as CO, during MOR. While the presence of a TiO2 support does lead to an increase in activity upon irradiation, about 50% of the improvements arise solely from the irradiation of the metal-containing electrocatalysts themselves.

Arulmani, Dheevesh V.; Eastcott, Jennie I.; Mavilla, Stephanie G.; Easton, E. Bradley

77

Application of x-ray nano-particulate markers for the visualization of intermediate layers and interfaces using scanning electron microscopy  

NASA Astrophysics Data System (ADS)

In this study the methodology of biological sample preparation for dental research using SEM/EDX has been elaborated. (1)The original cutting equipment supplied with 3D user-controlled sample fixation and an adjustable cooling system has been designed and evaluated. (2) A new approach to the root dentine drying procedure has been developed to preserve structure peculiarities of root dentine. (3) A novel adhesive system with embedded X-Ray nanoparticulate markers has been designed. (4)The technique allowing for visualization of bonding resins, interfaces and intermediate layers between tooth hard tissues and restorative materials of endodontically treated teeth using the X-ray nano-particulate markers has been developed and approved. These methods and approaches were used to compare the objective depth of penetration of adhesive systems of different generations in root dentine. It has been shown that the depth of penetration in dentine is less for adhesive systems of generation VI in comparison with bonding resins of generation V, which is in agreement with theoretical evidence. The depth of penetration depends on the correlation between the direction of dentinal tubules, bonding resin delivery and gravity.

Bessudnova, Nadezda O.; Bilenko, David I.; Zakharevich, Andrey M.

2011-10-01

78

Experimental Study of the Photocatalytic Degradation of Formaldehyde in Indoor Air using a Nano-particulate Titanium Dioxide Photocatalyst  

Microsoft Academic Search

Formaldehyde in the indoor environment may be degraded using nano-particulate titanium dioxide (TiO2) photocatalysis to improve air quality. In the work described, a polytetrafluoroethylene filter is employed as the substrate for a nano-particulate TiO2 coating. This is mounted in an experimental setup developed for the tests, similar to an actual air purification system, which are conducted at room temperature. The

Huili Yu; Kaili Zhang; Carole Rossi

2007-01-01

79

Insights into the electro-oxidation of ethylene glycol at Pt\\/Ru nanocatalysts supported on MWCNTs: Adsorption-controlled electrode kinetics  

Microsoft Academic Search

Electrocatalytic properties of Pt\\/Ru nanoparticle-electrodecorated MWCNT platform towards the oxidation of ethylene glycol (EG) have been interrogated using cyclic voltammetry and electrochemical impedance spectroscopy. Both forward and reverse oxidative reactions exhibited distinct electrochemical behaviour following changes in EG concentrations, scan rates and during repetitive cyclic voltammetric scanning. Our results suggest that the overall electro-oxidation reaction of EG is governed mainly

Nobanathi W. Maxakato; Christopher J. Arendse; Kenneth I. Ozoemena

2009-01-01

80

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.

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

2013-01-01

81

Nanoparticulates for Antibiofilm Treatment and Effect of Aging on Its Antibacterial Activity  

Microsoft Academic Search

IntroductionIssues pertaining to the effective elimination of bacterial biofilm and disruption of biofilm structure still remains in endodontic disinfection. Nanoparticulates such as chitosan (CS-np) and zinc oxide (ZnO-np) are known to possess significant antibacterial properties. This study aimed to test (1) the efficacy of CS-np and ZnO-np in disinfecting and disrupting biofilm bacteria and (2) the long-term efficacy of these

Annie Shrestha; Shi Zhilong; Neoh Koon Gee; Anil Kishen

2010-01-01

82

Inactivation of Escherichia coli by nanoparticulate zerovalent iron and ferrous ion.  

PubMed

The mechanism of Escherichia coli inactivation by nanoparticulate zerovalent iron (nZVI) and Fe(II) was investigated using reactive oxygen species (ROS) quenchers and probes, an oxidative stress assay, and microscopic observations. Disruption of cell membrane integrity and respiratory activity was observed under deaerated conditions [more disruption by nZVI than Fe(II)], and OH or Fe(IV) appears to play a role. PMID:20870787

Kim, Jee Yeon; Park, Hee-Jin; Lee, Changha; Nelson, Kara L; Sedlak, David L; Yoon, Jeyong

2010-11-01

83

NCL supports the first biocompatible NIST nanoparticulate reference material - Nanotechnology Characterization Laboratory  

Cancer.gov

In late December 2007, the National Institute of Standards and Technology (NIST) released its first reference standards for nanoscale particles targeted for the biomedical research community. The new nanoparticulate reference materials (RMs) consist of colloidal gold nanoparticles with nominal diameters of 10, 30, and 60 nanometers (nm) in suspension. Production of these RMs was supported in part by the National Cancer Institute (NCI) Alliance for Nanotechnology in Cancer and the Nanotechnology Characterization Laboratory (NCL) at NCI-Frederick.

84

Nanoparticulate-induced toxicity and related mechanism in vitro and in vivo  

Microsoft Academic Search

In urban areas, the quantity of exhaust particles from vehicle emissions is tremendous and has been regarded as the main contributor\\u000a to particulate matter (PM) pollution. Recently, the nano-sized PM on public health has begun to raise the attention. The increased\\u000a toxicity of nanoparticulate can be largely explained by their small size, high airborne concentration, extensive surface area\\u000a and high

Hye Won Kim; Eun-Kyung Ahn; Bo Keun Jee; Hyoung-Kyu Yoon; Kweon Haeng Lee; Young Lim

2009-01-01

85

The effect of drying on dispersions of nano-particulate titanium dioxide in ethylene glycol  

Microsoft Academic Search

This paper first demonstrates that the UV attenuation of a well-milled aqueous dispersion of nano-particulate rutile TiO2 is 200 times greater than the attenuation of visible 550 nm light. The corresponding UV attenuation of rutile dispersions in ethylene glycol is however only ?50% of that of the aqueous dispersion. It is shown that the different behaviour of suspensions in water and

Terry A. Egerton; Liwei Wang

2008-01-01

86

Photodegradation of an azo dye by silver-doped nano-particulate titanium dioxide  

Microsoft Academic Search

The synthesis of silver doped nano-particulate titanium dioxide (Ag\\/TiO2) using a microemulsion method and an investigation of its photocatalytic activity for the degradation of Acid Red 27 in distilled water under UV-irradiation is reported. The prepared Ag\\/TiO2 is characterized using transmission electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. The size of the Ag nanoparticles is around 5–15?nm, with almost

Mir Ghasem Hosseini; Mohammad Shokri; Morteza Khosravi; Reza Najjar; Masih Darbandi

2011-01-01

87

Study of an ultrasound-based process analytical tool for homogenization of nanoparticulate pharmaceutical vehicles.  

PubMed

There are currently no adequate process analyzers for nanoparticulate viscosity enhancers. This article aims to evaluate ultrasonic resonator technology as a monitoring tool for homogenization of nanoparticulate gels. Aqueous dispersions of colloidal microcrystalline cellulose (MCC) and a mixture of clay particles with xanthan gum were compared with colloidal silicon dioxide in oil. The processing was conducted using a laboratory-scale homogenizing vessel. The study investigated first the homogenization kinetics of the different systems to focus then on process factors in the case of colloidal MCC. Moreover, rheological properties were analyzed offline to assess the structure of the resulting gels. Results showed the suitability of ultrasound velocimetry to monitor the homogenization process. The obtained data were fitted using a novel heuristic model. It was possible to identify characteristic homogenization times for each formulation. The subsequent study of the process factors demonstrated that ultrasonic process analysis was equally sensitive as offline rheological measurements in detecting subtle manufacturing changes. It can be concluded that the ultrasonic method was able to successfully assess homogenization of nanoparticulate viscosity enhancers. This novel technique can become a vital tool for development and production of pharmaceutical suspensions in the future. PMID:21412782

Cavegn, Martin; Douglas, Ryan; Akkermans, Guy; Kuentz, Martin

2011-08-01

88

Nanoparticle platinum-ruthenium adatom catalysts for direct methanol fuel cells. The study of a direct 2-propanol polymer electrolyte fuel cell  

NASA Astrophysics Data System (ADS)

Pt-Ru systems are the most active, stable anode catalysts tested in direct methanol fuel cells. Investigations into the real activity and optimum surface composition of nanoparticle Pt-Ru catalysts toward methanol electrooxidation are difficult because there is a lack of proven, accurate methods to measure the number of active sites and the surface Pt/Ru ratio. In this study, Pt-Ru ad systems (Ruad is a ruthenium adatom) were employed to address these problems because controlled amounts of Ruad can be deposited onto Pt nanoparticles of known surface area to produce Pt-Ru ad nanoparticles of known surface areas and controlled surface compositions. Two non-electrochemical, self-limiting methods to deposit Ru adatoms onto nanoparticle Pt were devised and investigated. The organometallic precursor, Ru4(mu-H)4(CO)12, reacts with hydrogen over either blacked Pt gauze or Pt nanoparticles to deposit Ru adatoms and CO onto the Pt surface. The deposition is self-poisoned by the adsorbed CO, and it stops after ca. 0.05 surface equivalents (moles Ruad vs. moles surface Pt) of Ruad are deposited onto blacked Pt gauzes, and after ca. 0.10 surface equivalents of Ruad are deposited onto nanoparticle Pt black. Aqueous RuCl3 reacts with hydrogen pre-adsorbed onto nanoparticle Pt black surfaces to deposit 0.18 surface equivalents of Ruad. The deposition was repeated several times, with each reaction depositing ca. 0.18 surface equivalents of more Ruad onto the Pt-Ruad nanoparticles. The resulting nanoparticle Pt-Ruad electrocatalysts with Ruad surface coverages ranging from 0.18 to 0.75 were studied as catalysts for methanol electrooxidation in 1.0 M H2SO 4 (3-electrode experiments), as well as in prototype direct methanol fuel cells. The optimum Ruad surface coverage is ca. 0.33 between 22°C and 60°C. It shifts to higher values as the temperature is increased. A NafionRTM-117 membrane fuel cell consisting of a Pt-Ru anode and a Pt black cathode was operated at 90°C using aqueous 2-propanol as fuel. The performance of the cell operating on 2-propanol was substantially higher than operating on methanol at current densities lower than ˜200 mA/cm2. This result shows that direct 2-propanol fuel cells are promising alternatives to direct methanol fuel cells.

Cao, Dianxue

89

Novel anode catalyst for direct methanol fuel cells.  

PubMed

PtRu catalyst is a promising anodic catalyst for direct methanol fuel cells (DMFCs) but the slow reaction kinetics reduce the performance of DMFCs. Therefore, this study attempts to improve the performance of PtRu catalysts by adding nickel (Ni) and iron (Fe). Multiwalled carbon nanotubes (MWCNTs) are used to increase the active area of the catalyst and to improve the catalyst performance. Electrochemical analysis techniques, such as energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS), are used to characterize the kinetic parameters of the hybrid catalyst. Cyclic voltammetry (CV) is used to investigate the effects of adding Fe and Ni to the catalyst on the reaction kinetics. Additionally, chronoamperometry (CA) tests were conducted to study the long-term performance of the catalyst for catalyzing the methanol oxidation reaction (MOR). The binding energies of the reactants and products are compared to determine the kinetics and potential surface energy for methanol oxidation. The FESEM analysis results indicate that well-dispersed nanoscale (2-5?nm) PtRu particles are formed on the MWCNTs. Finally, PtRuFeNi/MWCNT improves the reaction kinetics of anode catalysts for DMFCs and obtains a mass current of 31?A g(-1) catalyst. PMID:24883406

Basri, S; Kamarudin, S K; Daud, W R W; Yaakob, Z; Kadhum, A A H

2014-01-01

90

Novel Anode Catalyst for Direct Methanol Fuel Cells  

PubMed Central

PtRu catalyst is a promising anodic catalyst for direct methanol fuel cells (DMFCs) but the slow reaction kinetics reduce the performance of DMFCs. Therefore, this study attempts to improve the performance of PtRu catalysts by adding nickel (Ni) and iron (Fe). Multiwalled carbon nanotubes (MWCNTs) are used to increase the active area of the catalyst and to improve the catalyst performance. Electrochemical analysis techniques, such as energy dispersive X-ray spectrometry (EDX), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS), are used to characterize the kinetic parameters of the hybrid catalyst. Cyclic voltammetry (CV) is used to investigate the effects of adding Fe and Ni to the catalyst on the reaction kinetics. Additionally, chronoamperometry (CA) tests were conducted to study the long-term performance of the catalyst for catalyzing the methanol oxidation reaction (MOR). The binding energies of the reactants and products are compared to determine the kinetics and potential surface energy for methanol oxidation. The FESEM analysis results indicate that well-dispersed nanoscale (2–5?nm) PtRu particles are formed on the MWCNTs. Finally, PtRuFeNi/MWCNT improves the reaction kinetics of anode catalysts for DMFCs and obtains a mass current of 31?A g?1 catalyst.

Basri, S.; Kamarudin, S. K.; Daud, W. R. W.; Yaakob, Z.; Kadhum, A. A. H.

2014-01-01

91

C2H2 treatment as a facile method to boost the catalysis of Pd nanoparticulate catalysts.  

PubMed

A facile method to boost the catalysis of Pd nanoparticulate catalysts by simple C2H2 treatment is developed. During the C2H2 treatment, Pd nanoparticles serve as active catalysts to polymerize C2H2 into trans-polyacetylene. The deposition of trans-polyacetylene layer on Pd nanoparticles makes their surface hydrophobic. Such a hydrophobic surface modification helps to accumulate more hydrophobic substrates during catalysis, making the modified Pd nanoparticulate catalysts more active than untreated catalysts in the catalytic reaction involving hydrophobic substrates. Moreover, the coating of polyacetylene on Pd creates encapsulated Pd nanocatalysts, stabilizing Pd nanoparticles against sintering or aggregation. Since the catalytic polymerization of polyacetylene on Pd is not facet dependent, the development is readily applied to enhance the catalysis of commercial Pd nanoparticulate catalysts by simple C2H2 treatment. PMID:24670007

Dai, Yan; Liu, Shengjie; Zheng, Nanfeng

2014-04-16

92

Electrodeposition of mesoscopic Pt-Ru on reticulated vitreous carbon from reverse emulsions and microemulsions: Application to methanol electro-oxidation  

Microsoft Academic Search

High surface area Pt-Ru (between 120 and 400cm2mg?1) meso-sized particles and mesoporous coatings were electrodeposited on reticulated vitreous carbon (RVC) three-dimensional electrodes using reverse emulsions and microemulsions. The organic phase of the colloidal media was composed of cyclohexane, Triton X-100 non-ionic surfactant and tetrabutylammonium perchlorate (for ionic conductivity) while the aqueous phase contained H2PtCl6 and RuCl3 (or (NH4)2RuCl6). For microemulsification

Tommy T. Cheng; El?d L. Gyenge

2006-01-01

93

Determination of proton conductivity in anode catalyst layers of the direct methanol fuel cell (DMFC)  

Microsoft Academic Search

A new method for the determination of the specific proton conductivity in PEMFC and direct methanol fuel cell (DMFC) electrodes is proposed. The proton conductivity of DMFC anode catalyst layers was determined as a function of the Nafion® content (5–16 wt%, 6–12 vol.%). The catalyst layers consisted of Pt\\/Ru black and Nafion® polymer. Following the theory published in [J. Electroanal.

A. Havránek; K. Wippermann

2004-01-01

94

Ethylene glycol electrooxidation on carbon supported Pt, PtRu and Pt 3Sn catalysts—A comparative DEMS study  

NASA Astrophysics Data System (ADS)

We present results of a comparative study on the interaction of ethylene glycol (EG) with carbon supported Pt, PtRu and Pt 3Sn nanoparticle catalysts, employing electrochemical and quantitative differential electrochemical mass spectroscopy (DEMS) measurements under continuous reaction and continuous electrolyte flow conditions. For all three catalysts EG adsorption is inhibited at very cathodic adsorption potentials, dissociative adsorption starts above 0.06 V and increases with increasing potential. Based on the electron yield per formed CO 2 molecule and on the similarity with the CO ad stripping characteristics CO ad is identified as the main stable adsorbate; the relative coverage in terms of adsorbed C1 species, relative to that of a saturated CO adlayer on the respective catalyst, reaches a maximum of ca. 0.6 at around 0.4 V on Pt/Vulcan, ca. 0.2 at around 0.2 V on PtRu/Vulcan and ca. 0.4 at around 0.35 V on Pt 3Sn/Vulcan. Bulk EG electrooxidation under steady-state conditions shows a very small current efficiency for CO 2 formation of below 6% for 0.1 M EG on all three catalysts, the oxidation of EG mainly generates partly oxidized C2 by-products. Catalyst modification by Ru or Sn improves the activity for EG oxidation at low potentials (?0.56 V), but does not lead to better selectivities for complete EG oxidation to CO 2 at potentials with significant oxidation rates. Hence, C-C bond breaking is rate limiting for complete oxidation under present reaction conditions for all three catalysts. The data are consistent with a parallel pathway reaction mechanism, with formation and subsequent oxidation of CO ad in the one pathway and partial oxidation, via a sequence of reaction steps, to increasingly oxidized C2 species in the other pathway.

Wang, H.; Zhao, Y.; Jusys, Z.; Behm, R. J.

95

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

96

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.

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

2010-01-01

97

Mediatorless bioelectrocatalysis of dioxygen reduction at indium-doped tin oxide (ITO) and ITO nanoparticulate film electrodes  

Microsoft Academic Search

Bilirubin oxidase was immobilised on ITO electrodes: bare or covered by ITO nanoparticulate film. The latter material was obtained by immersion and withdrawal of the substrate into ITO nanoparticles suspension. Formation of a protein deposit was confirmed by scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. The electrode surface is covered by a protein film in the form

Ewa Rozniecka; Martin Jonsson-Niedziolka; Janusz W. Sobczak; Marcin Opallo

2011-01-01

98

The Science Behind Nanosun-Screens: Learning about Nanoparticulate Ingredients Used to Block the Sun's Ultraviolet Rays  

ERIC Educational Resources Information Center

In this article, the authors provide a brief overview of the emerging field of nanoscience and why it is an important area of education. They next explain the science behind the new nanoparticulate sunscreens, describe the different elements of the unit, and reflect on some of the opportunities and challenges of teaching nanoscience at the high…

Wise, Alyssa; Schank, Patricia; Stanford, Tina; Horsma, Geri

2009-01-01

99

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

100

Nanoparticulate mackinawite formation; a stopped and continuous flow XANES and EXAFS investigation  

NASA Astrophysics Data System (ADS)

The sequestration of sulfur and iron within sedimentary iron sulfides, and ultimately as pyrite, is a major sink in global biogeochemical cycles of those elements and has impacts on global carbon and oxygen cycles. The formation of the metastable black iron (II) monosulfide mackinawite is a key process because mackinawite forms in aqueous solutions where the Fe(II) and S(-II) IAP exceeds mackinawite’s Ksp. Mackinawite is the first formed iron sulfide phase, a consequence of Ostwald’s step rule and is a reactant phase during the formation of thermodynamically stable sedimentary iron sulfide minerals such as pyrite. The reaction of dissolved Fe(II) and sulfide is extremely fast and reactions in the environmentally significant near-neutral pH range tend to completion in <1 second. We have combined stopped and continuous flow techniques with X-ray absorption spectroscopy to evaluate the products of the fast precipitation kinetics of mackinawite over millisecond timescales. EXAFS spectra and data collected during flow experiments were compared with those from a well characterised freeze-dried nanoparticulate mackinawite standard and with published data. Published work has used Rietveld crystal structure refinement to determine bond distances of 2.2558 and 2.5976Å for Fe-S and Fe-Fe respectively. In our experiments Fe K edge XANES is consistent with tetrahedrally coordinated Fe in the precipitated sulfide phase. EXAFS data show that local Fe-S and Fe-Fe coordination and interatomic distances (Fe-S = 2.24Å; Fe-Fe = 2.57Å) are consistent with those determined for the standard mackinawite and published data. The coordination and spacing are developed in the precipitated phase after <10ms reaction at pH5, and considerably faster in experiments at near neutral to alkaline pH. No evidence for phases structurally intermediate between hexaqua Fe(II) and precipitated mackinawite was observed. Aqueous FeS° cluster complexes previously identified as intermediates during mackinawite formation and iron sulfide mineral transformations did not contribute significantly to the EXAFS spectra collected. For environmental, geological and biogeochemical applications, the precipitation of the mineral mackinawite can be considered to proceed rapidly from aqueous Fe(II) and S(-II) ions to the nanoparticulate crystalline mineral. The materials labelled “disordered mackinawite”, or “amorphous FeS” phase which have been widely quoted in the iron sulfide literature do not form at any stage of the precipitation of mackinawite from aqueous solutions. Physical and chemical properties previously ascribed to an amorphous or disordered structure are a consequence of the nanoparticulate form of the first precipitated solid.

Butler, I. B.; Bell, A. M.; Charnock, J. M.; Rickard, D.; Vaughan, D. J.; Oldroyd, A.

2009-12-01

101

Effects of SiC volume fraction and aluminum particulate size on interfacial reactions in SiC nanoparticulate reinforced aluminum matrix composites  

Microsoft Academic Search

The SiC nanoparticulate reinforced Al–3.0wt.% Mg composites were fabricated by combining pressureless infiltration with ball-milling and cold-pressing technology at 700°C for 2h. The effects of SiC nanoparticulate volume fractions (6%, 10% and 14%) and Al particulate sizes (38?m and 74?m) on interfacial reactions were investigated by SEM, TEM and X-ray diffraction. The results show that the MgO at the interface

Bowen Xiong; Zhifeng Xu; Qingsong Yan; Baiping Lu; Changchun Cai

102

Ligand-Enhanced Reactive Oxidant Generation by Nanoparticulate Zero-Valent Iron and Oxygen  

PubMed Central

The reaction of zero-valent iron or ferrous iron with oxygen produces reactive oxidants capable of oxidizing organic compounds. However, the oxidant yield in the absence of ligands is too low for practical applications. The addition of oxalate, nitrilotriacetic acid (NTA), or ethylenediaminetetraacetic acid (EDTA) to oxygen-containing solutions of nanoparticulate zero-valent iron (nZVI) significantly increases oxidant yield, with yields approaching their theoretical maxima near neutral pH. These ligands improve oxidant production by limiting iron precipitation and by accelerating the rates of key reactions, including ferrous iron oxidation by oxygen and hydrogen peroxide. Product yields indicate that the oxic nZVI system produces hydroxyl radical (OH·) over the entire pH range in the presence of oxalate and NTA. In the presence of EDTA, probe compound oxidation is attributed to OH· under acidic conditions and a mixture of OH· and ferryl ion (Fe[IV]) at circumneutral pH.

Keenan, Christina R.; Sedlak, David L.

2009-01-01

103

Synthesis of nanoparticulate silica composite membranes by the pressurized sol-gel technique  

SciTech Connect

A crack-free silica composite membrane has been synthesized from a nanoparticulate silica sol (particle diameter < 10 nm) by a pressurized sol-gel coating technique developed in this study. The microporous silica layers with an estimated pore radius of 0.78 nm were deposited inside the pores (average pore size of 0.1 [mu]m) of slip cast [alpha]-alumina support tubes. The microstructure of the coated layers was controlled by adjusting sol properties and pressurizing conditions. The room-temperature intrinsic permeability of N[sub 2] through the silica membrane layer after heat treatment at 200 C is about 4.9 [times] 10[sup [minus]12] mol[center dot]m/m[sup 2][center dot]s[center dot]Pa, and the mechanism of gas transport is Knudsen flow. The thermal stability of the silica composite membrane is excellent up to 500 C.

Hyun, S.H.; Kang, B.S. (Yonsei Univ., Seoul (Korea, Republic of). Dept. of Ceramic Engineering)

1994-12-01

104

Antitumor efficacy of doxorubicin released from crosslinked nanoparticulate chondroitin sulfate/chitosan polyelectrolyte complexes.  

PubMed

It is demonstrated that nanoparticulate PEC with a crosslinked shell sustains DOX release and increases DOX activity against cancer cells. CSMA was synthesized to prepare PEC with chitosan. The double bonds among CSMA were used to form a shell crosslink. The released DOX from DOX-loaded PECs against human cancer KB cells and A549 cells were qualitatively traced by confocal laser scanning microscopy and flow cytometry, and quantitatively measured by capillary electrophoresis. All the results implied the DOX-loaded PEC with a crosslinked shell had the best anti-cancer potency of free DOX and the DOX-loaded PEC prepared from pure chondroitin sulfate and chitosan in both the cell lines. PMID:21360679

Tsai, Hun-Yu; Chiu, Chien-Chih; Lin, Ping-Chih; Chen, Su-Hwei; Huang, Shih-Jer; Wang, Li-Fang

2011-05-12

105

Construction of porous anode by sacrificial template for a passive direct methanol fuel cell  

NASA Astrophysics Data System (ADS)

Simple addition of magnesium oxide (MgO) nanoparticles as a sacrificial pore-former into the catalytic layer (CL) and micro-porous layer (MPL) in the anode of a membrane electrode assembly (MEA) leads to the formation of porous anodic structure, thus greatly enhancing the performance of a passive direct methanol fuel cell. At the same PtRu(1:1) loading of 2.0 mg cm-2, the MEAs with porous CL and with both porous MPL and CL exhibit the maximal power densities of 37.0 and 43.7 mW cm-2 at a temperature of 25 °C and with 3 M of methanol solution, respectively. When the PtRu loading decreases to 1.0 mg cm-2, the maximum power density of an MEA with both porous MPL and CL is ca. 32.8 mW cm-2, which is even higher than that of a conventional MEA with a PtRu loading of 2.0 mg cm-2. The improved performance of the novel MEA can be ascribed to an increased electrochemical surface area, a decreased charge-transfer resistance as well as an efficient mass transfer of methanol after the formation of porous structure in the anode. The present work provides a very simple but very effective way to reduce the dosage of the noble metal catalysts for fuel cells.

Huang, Qinghong; Jiang, Jingjing; Chai, Jieshi; Yuan, Ting; Zhang, Haifeng; Zou, Zhiqing; Zhang, Xiaogang; Yang, Hui

2014-09-01

106

Novel low voltage and solution processable organic thin film transistors based on water dispersed polymer semiconductor nanoparticulates.  

PubMed

Two novel organic thin film transistor structures that combine a hygroscopic insulator with the use of water-dispersed polymer nanoparticles as the active layer are presented. In the first device structure, the semiconducting layer was fabricated from a nanoparticulate suspension of poly-(3-hexylthiophene) prepared through a mini-emulsion process using sodium dodecyl sulfate as the surfactant whereas a surfactant-free precipitation method has been used for the second device structure. In both cases, fully solution processable transistors have been fabricated in a top gate configuration with hygroscopic poly(4-vinylphenol) as the dielectric layer. Both device structures operate at low voltages (0 to -4V) but exhibit contrasting output characteristics. A systematic study is presented on the effect of surfactant on the synthesis of semiconducting nanoparticles, the formation of thin nanoparticulate films and, consequently, on device performance. PMID:23623401

Darwis, Darmawati; Elkington, Daniel; Ulum, Syahrul; Bryant, Glenn; Belcher, Warwick; Dastoor, Paul; Zhou, Xiaojing

2013-07-01

107

Magnetic beads-based electrochemiluminescence immunosensor for determination of cancer markers using quantum dot functionalized PtRu alloys as labels.  

PubMed

A novel electrochemiluminescence (ECL) immunosensor for sensitive detection of human chorionic gonadotrophin antigen (HCG-Ag) was constructed using CdTe quantum dot functionalized nanoporous PtRu alloys (QDs@PtRu) as labels for signal amplification. In this paper, nanoporous PtRu alloy was employed as the carrier for immobilization of CdTe QDs and antibodies. Primary monoclonal antibody to alfa-HCG antigen (McAb(1)) was immobilized onto the surface of chitosan coated Fe(3)O(4) magnetic nanoparticles (Fe(3)O(4)/CS MNPs) by glutaraldehyde (GA) as coupling agent. Then McAb(1) could be easily separated and assembled on the surface of indium tin oxide glass (ITO) owing to their excellent magnetic properties with external magnetic forces holding the MNPs. Due to signal amplification from the high loading of CdTe QDs, 4.67-fold enhancements in ECL signal for HCG-Ag detection was achieved compared to the unamplified method (single QDs as labels). Under optimal conditions, a wide detection range (0.005~50 ng mL(-1)) and low detection limit (0.8 pg mL(-1)) were achieved through the sandwich-type immunosensor. The novel immunosensor showed high sensitivity and selectivity, excellent stability, and good reproducibility, and thus has great potential for clinical detection of HCG-Ag. In particular, this approach presents a novel class of combining bifunctional nanomaterials with preferable ECL properties and excellent magnetism, which suggests considerable potential in a wide range of applications for bioassays. PMID:22421801

Zhang, Yan; Ge, Shenguang; Wang, Shaowei; Yan, Mei; Yu, Jinghua; Song, Xianrang; Liu, Weiyan

2012-05-01

108

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

Microsoft Academic Search

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

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

2007-01-01

109

RuO 2-wired high-rate nanoparticulate TiO 2 (anatase): Suppression of particle growth using silica  

Microsoft Academic Search

To enhance the high-rate capability (up to 120C, 20A\\/g) of nanoparticulate TiO2 (anatase) formed by thermal treatment of protonated TiO2 nanotubes, we used two types of additives: RuO2 as an electron-conductive material [Y.-G. Guo, Y.-S. Hu, W. Sigle, J. Maier, Adv. Mater. 19 (2007) 2087] and silica as a suppressant of particle growth during heat treatment. We show systematically that

B. Erjavec; R. Dominko; P. Umek; S. Sturm; S. Pejovnik; M. Gaberscek; J. Jamnik

2008-01-01

110

In situ Fourier transform infrared-diffuse reflection spectroscopy of direct methanol fuel cell anodes and cathodes  

SciTech Connect

In situ Fourier transform infrared-diffuse reflection spectroscopy (FTIR-DRS) was used to study both the adsorbed and desorbed species produced on high surface area anodes and cathodes of direct methanol/oxygen fuel cells. The authors investigated platinum-ruthenium and platinum black as anodes. The cathodes studied were platinum black. The primary product detected on both Pt-black and Pt-Ru anodes at low methanol/water vapor ratios (P{sub methanol}: 15.2 kPa) was CO{sub 2}. Consistent with previous work, CO adsorption is more prevalent on Pt-black than on Pt-RU. In addition to CO and CO{sub 2}, vibrational modes due to formic acid, methylformate, and formaldehyde are detected by FTIR-DRS under potentiostatic control. At higher methanol/water vapor ratios (P{sub methanol}: 38.0 kPa) and low potentials (0.10 to 0.50 V), formaldehyde is the only product at the Pt-Ru anode. Methylformate and formic acid vibrational modes appear at potentials from 0.60 to 0.80 V. CO{sub 2} and methanol are observed at open circuit on the cathode side as a result of methanol permeation from the anode to the cathode region. CO{sub 2} increases in the cathode region with increasing anode potential.

Fan, Q.; Pu, C.; Smotkin, E.S. [Illinois Inst. of Tech., Chicago, IL (United States). Dept. of Chemical and Environmental Engineering

1996-10-01

111

Expanding the atrane route: Generalized surfactant-free synthesis of mesoporous nanoparticulated xerogels  

NASA Astrophysics Data System (ADS)

A diversity of silica-based and non-silica nanoparticulated mesoporous xerogels have been synthesized from aqueous solution using a surfactant-free strategy, and starting from molecular atrane complexes as precursors. This approach constitutes an extension of the "atrane route" previously described for the surfactant-assisted synthesis of mesoporous materials, and allows us to unify the multiplicity of protocols described for the preparation of conventional xerogels. In fact, we have used exactly the same preparative conditions for obtaining all the compositions reported here. The xerogels synthesized in this way include pure silica (UVM-11), aluminosilicates and titanosilicates (M-UVM-11, M = Al, Ti), hybrid organic-inorganic silica-based derivatives, and also non-silica materials such as pure titania and alumina. Moreover, post-hydrothermal treatments allow modulating the mesopore average size in the ca. 3-30 nm range. The key factor making available such a diversity of materials is the inertness of the atrane complexes, which allows orchestrating the hydrolytic reactivity of different oxide-forming elements. In turn, this avoids subsequent phase segregation and results in chemically homogeneous materials.

Ortiz de Zárate, David; Fernández, Lorenzo; Beltrán, Aurelio; Guillem, Carmen; Latorre, Julio; Beltrán, Daniel; Amorós, Pedro

2008-05-01

112

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

PubMed

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

2010-03-01

113

Ice sheets as a significant source of highly reactive nanoparticulate iron to the oceans.  

PubMed

The Greenland and Antarctic Ice Sheets cover ~ 10% of global land surface, but are rarely considered as active components of the global iron cycle. The ocean waters around both ice sheets harbour highly productive coastal ecosystems, many of which are iron limited. Measurements of iron concentrations in subglacial runoff from a large Greenland Ice Sheet catchment reveal the potential for globally significant export of labile iron fractions to the near-coastal euphotic zone. We estimate that the flux of bioavailable iron associated with glacial runoff is 0.40-2.54 Tg per year in Greenland and 0.06-0.17 Tg per year in Antarctica. Iron fluxes are dominated by a highly reactive and potentially bioavailable nanoparticulate suspended sediment fraction, similar to that identified in Antarctic icebergs. Estimates of labile iron fluxes in meltwater are comparable with aeolian dust fluxes to the oceans surrounding Greenland and Antarctica, and are similarly expected to increase in a warming climate with enhanced melting. PMID:24845560

Hawkings, Jon R; Wadham, Jemma L; Tranter, Martyn; Raiswell, Rob; Benning, Liane G; Statham, Peter J; Tedstone, Andrew; Nienow, Peter; Lee, Katherine; Telling, Jon

2014-01-01

114

Characterization and ecological risk assessment of nanoparticulate CeO2 as a diesel fuel catalyst.  

PubMed

Nanoparticulate cerium dioxide (nano-CeO2 ), when combusted as an additive to diesel fuel, was transformed from 6?nm to 14?nm sizes into particles near 43?nm, with no obvious change in the unit cell dimensions or crystalline form. Cerium sulfate, if formed during combustion, was below detection limits. Ceria nanoparticles were agglomerated within the soot matrix, with a mean aerodynamic diameter near 100?nm. The dissolution of cerium from the dried ceria catalyst in synthetic soft water was extremely small (<0.0006% or <0.2?µg Ce/L), with particles being highly agglomerated (<450?nm). Agglomeration was reduced in the presence of humic acid. In the combusted samples, soot was dominant, and the solubility of cerium in soft water showed an almost 100-fold increase in the <1?nm fraction compared to that before combustion. It appeared that the nano-CeO2 remained agglomerated within the soot matrix and would not be present as dispersed nanoparticles in aquatic or soil environments. Despite the increased dissolution, the solubility was not sufficient for the combusted ceria to represent a risk in aquatic ecosystems. The predicted environmental concentrations were still orders of magnitude below the predicted no effects concentration of near 1?mg/L. In the soil environment, any cerium released from soot materials would interact with natural colloids, decreasing cerium concentrations in soil solutions and further minimizing the potential risk to soil organisms. PMID:23595783

Batley, Graeme E; Halliburton, Brendan; Kirby, Jason K; Doolette, Casey L; Navarro, Divina; McLaughlin, Mike J; Veitch, Colin

2013-08-01

115

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

116

Advances in direct oxidation methanol fuel cells  

NASA Technical Reports Server (NTRS)

Fuel cells that can operate directly on fuels such as methanol are attractive for low to medium power applications in view of their low weight and volume relative to other power sources. A liquid feed direct methanol fuel cell has been developed based on a proton exchange membrane electrolyte and Pt/Ru and Pt catalyzed fuel and air/O2 electrodes, respectively. The cell has been shown to deliver significant power outputs at temperatures of 60 to 90 C. The cell voltage is near 0.5 V at 300 mA/cm(exp 2) current density and an operating temperature of 90 C. A deterrent to performance appears to be methanol crossover through the membrane to the oxygen electrode. Further improvements in performance appear possible by minimizing the methanol crossover rate.

Surampudi, S.; Narayanan, S. R.; Vamos, E.; Frank, H.; Halpert, G.; Laconti, Anthony B.; Kosek, J.; Prakash, G. K. Surya; Olah, G. A.

1993-01-01

117

Advances in direct oxidation methanol fuel cells  

NASA Astrophysics Data System (ADS)

Fuel cells that can operate directly on fuels such as methanol are attractive for low to medium power application in view of their low weight and volume relative to other power sources. A liquid feed direct methanol fuel cell has been developed based on a proton-exchange membrane electrolyte and Pt/Ru and Pt-catalyzed fuel and air/O 2 electrodes, respectively. The cell has been shown to deliver significant power outputs at temperatures of 60 to 90 °C. The cell voltage is near 0.5 V at 300 mA/cm 2 current density and an operating temperature of 90 °C. A deterrent to performance appears to be methanol crossover through the membrane to the oxygen electrode. Further improvements in performance appear possible by minimizing the methanol crossover rate.

Surampudi, S.; Narayanan, S. R.; Vamos, E.; Frank, H.; Halpert, G.; LaConti, A.; Kosek, J.; Prakash, G. K. Surya; Olah, G. A.

118

Advances in direct oxidation methanol fuel cells  

NASA Astrophysics Data System (ADS)

Fuel cells that can operate directly on fuels such as methanol are attractive for low to medium power applications in view of their low weight and volume relative to other power sources. A liquid feed direct methanol fuel cell has been developed based on a proton exchange membrane electrolyte and Pt/Ru and Pt catalyzed fuel and air/O2 electrodes, respectively. The cell has been shown to deliver significant power outputs at temperatures of 60 to 90 C. The cell voltage is near 0.5 V at 300 mA/cm(exp 2) current density and an operating temperature of 90 C. A deterrent to performance appears to be methanol crossover through the membrane to the oxygen electrode. Further improvements in performance appear possible by minimizing the methanol crossover rate.

Surampudi, S.; Narayanan, S. R.; Vamos, E.; Frank, H.; Halpert, G.; Laconti, Anthony B.; Kosek, J.; Prakash, G. K. Surya; Olah, G. A.

1993-11-01

119

Low-Pt-Content Anode Catalyst for Direct Methanol Fuel Cells  

NASA Technical Reports Server (NTRS)

Combinatorial experiments have led to the discovery that a nanophase alloy of Pt, Ru, Ni, and Zr is effective as an anode catalyst material for direct methanol fuel cells. This discovery has practical significance in that the electronic current densities achievable by use of this alloy are comparable or larger than those obtained by use of prior Pt/Ru catalyst alloys containing greater amounts of Pt. Heretofore, the high cost of Pt has impeded the commercialization of direct methanol fuel cells. By making it possible to obtain a given level of performance at reduced Pt content (and, hence, lower cost), the discovery may lead to reduction of the economic impediment to commercialization.

Narayanan, Sekharipuram; Whitacre, Jay

2008-01-01

120

Autogenic reactions for preparing carbon-encapsulated, nanoparticulate TiO 2 electrodes for lithium-ion batteries  

Microsoft Academic Search

We report an anhydrous, autogenic technique for synthesizing electronically interconnected, carbon-encapsulated, nanoparticulate anatase anode materials (TiO2–C) for lithium-ion batteries. The TiO2–C nanoparticles provide a reversible capacity of ?200mAhg?1, which exceeds the theoretical capacity of the commercially attractive spinel anode, Li4Ti5O12 (175mAhg?1) and is competitive with the capacity reported for other TiO2 products. The processing method is extremely versatile and has

Vilas G. Pol; Sun-Ho Kang; Jose M. Calderon-Moreno; Christopher S. Johnson; Michael M. Thackeray

2010-01-01

121

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

122

Thiomers: preparation and in vitro evaluation of a mucoadhesive nanoparticulate drug delivery system.  

PubMed

It was the aim of this study to develop a mucoadhesive nanoparticulate delivery system. Nanoparticles were generated by in situ gellation of the thiomer chitosan-4-thiobutylamidine (chitosan-TBA) with tripolyphosphate (TPP) followed by stabilization via the formation of inter- and intrachain disulfide bonds by oxidation with H(2)O(2) in various concentrations. Afterwards TPP was removed by exhaustive dialysis at pH 1-2. Incorporation of the model compound fluorescein diacetate (FDA) was achieved by incubation of this fluorescence marker, dissolved in acetonitrile, with aqueous particle suspensions for 1h at room temperature. Mucoadhesion studies were performed on porcine intestinal mucosa. Results showed that the preparation method described above leads to nanoparticles of a mean diameter of 268+/-15 nm and a FDA load of 2%. Due to the removal of the anionic crosslinker TPP, the zeta potential of the nanoparticles was raised from 4+/-1 up to 19+/-2 mV without loosing stability of the nanoparticles. The more H(2)O(2) was added to the particles, the more inter- and intrachain disulfide bonds were formed. The more thiol groups were oxidized within the particles, however, the lower was the improvement in mucoadhesive properties. Nevertheless, even when 91% of all thiol groups on the nanoparticles were oxidized, their mucoadhesive properties were still twice as high as the mucoadhesive properties of unmodified nanoparticles. Thiolated chitosan nanoparticles show a two-fold higher zeta potential (I), improved stability (II) and more than doubled mucoadhesive properties (III) than corresponding unmodified chitosan nanoparticles. Therefore, they seem to be advantageous over ionically crosslinked chitosan nanoparticles. PMID:16595166

Bernkop-Schnürch, Andreas; Weithaler, Andrea; Albrecht, Karin; Greimel, Alexander

2006-07-01

123

Inkjet-printed gold nanoparticulate patterns for surface finish in electronic package  

NASA Astrophysics Data System (ADS)

Gold (Au) pads for surface finish in electronic package were developed by the inkjet printing method. The Au ink for printing was prepared by Au nanoparticles (NPs) coated with capping molecules of dodecylamine (C12H25NH2). The microstructures of the inkjet-printed Au films were characterized after sintering in various gas flows. The film sintered in air showed that bonding between NPs was not enough for further grain growth due to the incomplete decomposition of the capping layer. The film sintered under nitrogen (N2) had NPs existing on the surface and the bottom which did not participate in sintering. When the film was sintered under N2-bubbled through formic acid (FA/N2), a large portion of the pores were observed to make a holey pancake-like structure of the film. The microstructures of the inkjet-printed Au film became denser with grain growth when Au NPs were sintered under mixed gas flows of FA/N2 and N2. The resistivity of film was 4.79 ?? cm, about twice the bulk value. Organic analysis showed that about 0.43% of residual organics was left in the film. Therefore, this Au film was chosen for solder ball shear test because the microstructure was denser compared to the films sintered under other gasses such as N2 or FA/N2 and less organic residue was found from organic analyses. Even though the film sintered under N2 showed the best electrical property (4.35 ?? cm), it was not adopted in the shear test because NPs remaining on the bottom of the film could lead to the poor adhesion between the film and substrate and show low shear strength. The shear force was 8.04 newton (N) on average and the strength was 64 MPa. This shear strength is good enough to substitute the inkjet-printed Au nanoparticulate film for electroplating in electronic package.

Jang, Seonhee; Cho, Hyejin; Kang, Seongkoo; Oh, Sungil; Kim, Donghoon

2011-11-01

124

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

125

Electronic structures of Pt-Co and Pt-Ru alloys for CO-tolerant anode catalysts in polymer electrolyte fuel cells studied by EC-XPS.  

PubMed

CO tolerance at pure Pt, Pt-Co, and Pt-Ru alloys was investigated by X-ray photoelectron spectroscopy combined with an electrochemical cell (EC-XPS) in order to discover a hint for designing higher performance anode catalysts. After the electrochemical stabilization and/or CO adsorption, these electrodes were immediately transferred to the XPS chamber without exposure to air to avoid contamination of the surfaces. It was revealed that alloying with Co or Ru modified the electronic structures of Pt atoms, resulting in a positive core level (CL) shift of Pt 4f(7/2) which could weaken the Pt-CO interaction. For the Pt-Co alloy electrode, the Pt 4f(7/2) CL shift remained after the electrochemical stabilization despite Co dissolution and formation of a Pt skin layer. Changes in surface core level shifts (DeltaSCLSs) induced by CO adsorption were evaluated and related to the CO adsorption energy. The values of DeltaSCLS at these alloys were smaller than that of pure Pt, indicating that Ru and Co are effective elements to weaken the bond strength of Pt-CO. PMID:17107203

Wakisaka, Mitsuru; Mitsui, Satoshi; Hirose, Yoshikazu; Kawashima, Katsura; Uchida, Hiroyuki; Watanabe, Masahiro

2006-11-23

126

Biological tolerance of different materials in bulk and nanoparticulate form in a rat model: sarcoma development by nanoparticles.  

PubMed

In order to study the pathobiological impact of the nanometre-scale of materials, we evaluated the effects of five different materials as nanoparticulate biomaterials in comparison with bulk samples in contact with living tissues. Five groups out of 10 rats were implanted bilaterally for up to 12 months with materials of the same type, namely TiO2, SiO2, Ni, Co and polyvinyl chloride (PVC), subcutaneously with bulk material on one side of the vertebral column and intramuscularly with nanoparticulate material on the contralateral side. At the end of each implantation time, the site was macroscopically examined, followed by histological processing according to standard techniques. Malignant mesenchymal tumours (pleomorphic sarcomas) were obtained in five out of six cases of implanted Co nanoparticle sites, while a preneoplastic lesion was observed in an animal implanted with Co in bulk form. In the Ni group, all animals rapidly developed visible nodules at the implanted sites between 4 and 6 months, which were diagnosed as rhabdomyosarcomas. Since the ratio of surface area to volume did not show significant differences between the Ni/Co group and the TiO2/SiO2/PVC group, we suggested that the induction of neoplasia was not mediated by physical effects, but was mediated by the well-known carcinogenic impact of Ni and Co. The data from the Co group show that the physical properties (particulate versus bulk form) could have a significant influence on the acceleration of the neoplastic process. PMID:17015296

Hansen, Torsten; Clermont, Gaëlle; Alves, Antonio; Eloy, Rosy; Brochhausen, Christoph; Boutrand, Jean Pierre; Gatti, Antonietta M; Kirkpatrick, C James

2006-12-22

127

Performance of PtPd electrocatalysts in direct methanol fuel cell.  

PubMed

PtPd nanoparticles on carbon black were prepared to investigate the role of Pd in the anode and cathode of a direct methanol fuel cell (DMFC). The PtPd catalysts in the anode showed a significantly lower performance than the PtRu catalyst. However, the cell performances of these catalysts in the cathode were comparable to that of the Pt catalyst. From cyclic voltammetry, it was observed that the Pd with the Pt catalyst lowered the peak potential and increased the coulombic charge for oxide reduction on the surface of the catalyst. Also, the Pd catalyst without Pt showed relatively high activity for oxygen reduction reaction. PMID:20359018

Kim, In-Tae; Choi, Mahnsoo; An, Jung-Chul; Lee, Hong-Ki; Shim, Joongpyo

2010-05-01

128

Particulate Emissions from the Combustion of Diesel Fuel with a Fuel-Borne Nanoparticulate Cerium Catalyst  

NASA Astrophysics Data System (ADS)

To address the adverse impacts on health and climate from the use of diesel-fueled vehicles, a number of technological solutions have been developed for reducing diesel soot emissions and to improve fuel economy. One such solution is the use fuel-borne metal oxide catalysts. Of current interest are commercially-available fuel additives consisting of nanoparticulate cerium oxide (CeO2). In response to the possible use of CeO2-containing fuels in on-road vehicles in the U.S., the Environmental Protection Agency is conducting research to address the potential toxicity and environmental effects of particulate CeO2 emitted with diesel soot. In this study, emissions from a diesel-fueled electric generator were size-segregated on polished silicon wafers in a nanoparticle cascade impactor. The diesel fuel contained 10 ppm Ce by weight in the form of crystalline CeO2 nanoparticles 4 nm to 7.5 nm in size. Primary CeO2 nanoparticles were observed in the diesel emissions as well as CeO2 aggregates encompassing a broad range of sizes up to at least 200 nm. We report the characterization of individual particles from the size-resolved samples with focused ion-beam scanning electron microscopy and energy-dispersive x-ray spectroscopy. Results show a dependency between the impactor size range and CeO2 agglomeration state: in the larger size fractions of the impactor (e.g., 560 nm to 1000 nm) CeO2 nanoparticles were predominantly attached to soot particles. In the smaller size fractions of the impactor (e.g., 100 nm to 320 nm), CeO2 aggregates tended to be larger and unattached to soot. The result is important because the deposition of CeO2 nanoparticles attached to soot particles in the lung or on environmental surfaces such as plant tissue will likely present different consequences than the deposition of unagglomerated CeO2 particles. Disclaimer The U.S. Environmental Protection Agency through its Office of Research and Development funded and collaborated in the research described here under Interagency Agreement DW-13-92339401 to National Institute of Standards and Technology. It has been subjected to Agency review and approved for publication.

Conny, J. M.; Willis, R. D.; Weinstein, J. P.; Krantz, T.; King, C.

2013-12-01

129

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.

2013-01-01

130

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

131

Influence of ionomer content in catalyst layers on direct methanol fuel cell performance  

SciTech Connect

The ionomer content in catalyst layers has a marked influence on direct methanol fuel cell (DMFC) performance. In an anode which contains unsupported PtRu as the catalyst, the recast ionomer may not always be necessary because the protonic conductivity of hydrous RuOx, the presence of which is inferred from the X-ray diffraction pattern, may be sufficient to allow effective utilization of catalyst sites. To examine interpenetration of catalyst and membrane material as a possible explanation for the lack of an apparent need of added ionomer, ultramicrotomed thin sections of the membrane-electrode assembly (MEA) were examined by scanning electron microscopy. Microscopic examination of such MEA cross sections revealed significant porosity in layers made by mixing unsupported catalysts with recast ionomer. Images of such sections did not reveal significant interpenetration, supporting the interpretation that hydrous RuOx may by itself provide sufficient protonic conductivity in PtRu catalyst layers prepared with no added ionomer. In contrast they show that the presence of recast ionomer in DMFC cathodes based on unsupported Pt as the catalyst is essential for optimum DMFC performance, because the recast ionomer is the primary source of protonic conductivity in the latter case. Having shown its potential function as proton conductor, they stress that Ru oxide is apparently not the key for maximizing DMFC anodic activity.

Thomas, S.C.; Ren, X.; Gottesfeld, S.

1999-12-01

132

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

2014-06-01

133

Physicochemical characterization and toxicological evaluation of plant-based anionic polymers and their nanoparticulated system for ocular delivery.  

PubMed

The water-soluble fractions of mucilages and gum from the seeds of fenugreek, isphagula and mango bark exudate were isolated, purified and characterized using X-ray diffraction (XRD) spectrometry, Fourier transform infrared spectroscopy (FT-IR), maldi/GC-MS, elemental analysis, 1D ((1)H and (13)C) and 2D (HMQC, COSY) nuclear magnetic resonance spectroscopy (NMR). The fenugreek mucilage was identified to be a galactomannan chain consisting of 4 units of galactose attached to the backbone of 6 mannose units in 1:1.5 ratio. The isphagula mucilage was identified to be an arabinoxylan polysaccharide chain consisting of 4 units of arabinofuranose attached to the backbone of 9 xylopyrannose units in 1:3 ratio. The mango gum showed the presence of amylose, ?-arabinofuranosyl and ?-galactopyranosyl, respectively. The characterized mucilages and gum were individually formulated into nanoparticulate system using their complementarily charged polymer chitosan. The particles were observed to be spherical in shape in the range of 61.5-90 nm having zetapotential between 31 and 34 mV and PDI of 0.097-0.241. The prepared nanoparticles were observed to be nonirritant and nontoxic in vitro and in vivo upto 2000 ?g/ml. Therefore, these mucilages and gum can be the alternatives of anionic polymers for the ocular drug delivery system. PMID:23952497

Pathak, Deepa; Kumar, Prashant; Kuppusamy, Gowthamarajan; Gupta, Ankur; Kamble, Bhagyashree; Wadhwani, Ashish

2014-12-01

134

Revisiting the Fundamentals in the Design and Control of Nanoparticulate Colloids in the Frame of Soft Chemistry1  

PubMed Central

This review presents thoughts on some of the fundamental features of conceptual models applied in the design of fine particles in the frames of colloid and soft chemistry. A special emphasis is placed on the limitations of these models, an acknowledgment of which is vital in improving their intricacy and effectiveness in predicting the outcomes of the corresponding experimental settings. Thermodynamics of self-assembly phenomena illustrated on the examples of protein assembly and micellization is analyzed in relation to the previously elaborated thesis that each self-assembly in reality presents a co-assembly, since it implies a mutual reorganization of the assembling system and its immediate environment. Parameters used in the design of fine particles by precipitation are discussed while referring to solubility product, various measures of supersaturation levels, induction time, nucleation and crystal growth rates, interfacial energies, and the Ostwald–Lussac law of phases. Again, the main drawbacks and inadequacies of using the aforementioned parameters in tailoring the materials properties in a soft and colloidal chemical setting were particularly emphasized. The basic and practical limitations of zeta-potential analyses, routinely used to stabilize colloidal dispersions and initiate specific interactions between soft chemical entities, were also outlined. The final section of the paper reiterates the unavoidable presence of practical qualitative models in the design and control of nanoparticulate colloids, which is supported by the overwhelming complexity of quantitative relationships that govern the processes of their formation and assembly.

Uskokovic, Vuk

2013-01-01

135

Electronic properties of the interface between p-CuI and anatase-phase n-TiO2 single crystal and nanoparticulate surfaces: a photoemission study.  

PubMed

We present a study of the growth of the p-type inorganic semiconductor CuI on n-type TiO2 anatase single crystal (101) surfaces and on nanoparticulate anatase surfaces using synchrotron radiation photoemission spectroscopy. Core level photoemission data obtained using synchrotron radiation reveal that both the substrate (TiO2) and the overlayer (CuI) core levels shift to a lower binding energy to different degrees following the growth of CuI on TiO2. Valence band photoemission data show that the valence band maximum of the clean substrate differs from that of the dosed surface which may be interpreted qualitatively as due to the introduction of a new density of states within the band gap of TiO2 as a result of the growth of CuI. The valence band offset for the heterojunction n-TiO2p-CuI has been measured using photoemission for both nanoparticulate and single crystal TiO2 surfaces, and the band energy alignment for these heterojunction interfaces is presented. With the information obtained here, it is suggested that the interface between p-CuI and single crystal anatase-phase n-TiO2 is a type-II heterojunction interface, with significant band bending. The measured total band bending matches the work function change at the interface, i.e., there is no interface dipole. In the case of the nanoparticulate interface, an interface dipole is found, but band bending within the anatase nanoparticles remains quite significant. We show that the corresponding depletion layer may be accommodated within the dimension of the nanoparticles. The results are discussed in the context of the functional properties of dye-sensitized solid state solar cells. PMID:17887866

Kumarasinghe, A R; Flavell, W R; Thomas, A G; Mallick, A K; Tsoutsou, D; Chatwin, C; Rayner, S; Kirkham, P; Warren, S; Patel, S; Christian, P; O'Brien, P; Grätzel, M; Hengerer, R

2007-09-21

136

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.

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

2012-01-01

137

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.

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

2011-01-01

138

Nebulization of nanoparticulate amorphous or crystalline tacrolimus – Single-dose pharmacokinetics study in mice  

Microsoft Academic Search

Developing a pulmonary composition of tacrolimus (TAC) provides direct access to the graft in lung transplant offering the possibility of high drug levels. The objective of this study was to investigate the physicochemical and pharmacokinetic characteristics of the nanostructured aggregates containing amorphous or crystalline nanoparticles of TAC produced by ultra-rapid freezing (URF). TAC and lactose (1:1 ratio; URF-TAC:LAC) and TAC

Prapasri Sinswat; Kirk A. Overhoff; Jason T. McConville; Keith P. Johnston; Robert O. Williams

2008-01-01

139

Direct methanol fuel cells: The effect of electrode fabrication procedure on MEAs structural properties and cell performance  

NASA Astrophysics Data System (ADS)

In the present paper, the effect of electrode preparation procedure on the structural properties of membrane electrode assembly (MEA) and consequently on the performance of direct methanol fuel cells (DMFCs) was investigated. Commercial PtRu black anode catalyst and Pt black cathode catalyst were characterized by XRD in their initial form and in their intermediate and final states after each step involved in catalyst-coated membrane electrode preparation procedure by a decal transfer method (DTM). XRD results demonstrated that the DTM process has a significant effect on the catalyst structural properties, especially on the particle size of Pt black cathode catalyst. It is also discussed that among all the steps involved in the electrode fabrication procedure, catalyst ink preparation and high temperature transfer process are key factors affecting the particle size of Pt black catalyst. Furthermore, it was found that the maximum power density of the single DMFC using a MEA fabricated by the DTM, when air is used as oxidant, is more than two times greater than that of the cell using conventionally prepared MEA, and more than three times greater when pure oxygen is used as oxidant. This could be attributed to the easier mass transportation due to the thinner catalyst layer and the better contact between the catalyst layer and the electrolyte membrane in the former case, even if, according to in situ CO stripping voltammetry results in the fuel cell anode environment, the surface composition of PtRu anode has been changed.

Song, S. Q.; Liang, Z. X.; Zhou, W. J.; Sun, G. Q.; Xin, Q.; Stergiopoulos, V.; Tsiakaras, P.

140

Preparation and characterization of Pt\\/C and Pt Ru\\/C electrocatalysts for direct ethanol fuel cells  

Microsoft Academic Search

Nano-sized Pt and PtRu colloids are prepared by a microwave-assisted polyol process, and transferred to a toluene solution of decanthiol. Vulcan XC-72 is then added to the toluene solution to adsorb the thiolated Pt and PtRu colloids. Transmission electron microscopy examinations show nearly spherical particles and narrow size distributions for both supported and unsupported metals. The carbon-supported Pt and PtRu

Zhaolin Liu; Xing Yi Ling; Xiaodi Su; Jim Yang Lee; Leong Ming Gan

2005-01-01

141

Comparative Toxicity of Nanoparticulate CuO and ZnO to Soil Bacterial Communities  

PubMed Central

The increasing industrial application of metal oxide Engineered Nano-Particles (ENPs) is likely to increase their environmental release to soils. While the potential of metal oxide ENPs as environmental toxicants has been shown, lack of suitable control treatments have compromised the power of many previous assessments. We evaluated the ecotoxicity of ENP (nano) forms of Zn and Cu oxides in two different soils by measuring their ability to inhibit bacterial growth. We could show a direct acute toxicity of nano-CuO acting on soil bacteria while the macroparticulate (bulk) form of CuO was not toxic. In comparison, CuSO4 was more toxic than either oxide form. Unlike Cu, all forms of Zn were toxic to soil bacteria, and the bulk-ZnO was more toxic than the nano-ZnO. The ZnSO4 addition was not consistently more toxic than the oxide forms. Consistently, we found a tight link between the dissolved concentration of metal in solution and the inhibition of bacterial growth. The inconsistent toxicological response between soils could be explained by different resulting concentrations of metals in soil solution. Our findings suggested that the principal mechanism of toxicity was dissolution of metal oxides and sulphates into a metal ion form known to be highly toxic to bacteria, and not a direct effect of nano-sized particles acting on bacteria. We propose that integrated efforts toward directly assessing bioavailable metal concentrations are more valuable than spending resources to reassess ecotoxicology of ENPs separately from general metal toxicity.

Rousk, Johannes; Ackermann, Kathrin; Curling, Simon F.; Jones, Davey L.

2012-01-01

142

Fabrication of nanoparticulate porous LaOF films through film growth and thermal decomposition of ion-modified lanthanum diacetate hydroxide.  

PubMed

This paper first reports fabrication of macro/nanotextured rare-earth oxyfluoride films. Usage of ion-modified lanthanum diacetate hydroxide (LDAH) as self-templates was successful in producing nanoparticulate lanthanum oxyfluoride (LaOF) films. LDAH template films were deposited on glass substrates through a chemical bath deposition in solutions composed of lanthanum acetate sesquihydrate, methanol, trifluoroacetic acid, and aqueous ammonia. The LDAH films had a unique, nestlike morphology owing to a two-dimensional hexagonal crystal growth. Modification of LDAH with trifluoroacetate ions led to formation of LaOF after pyrolyzing the template films at temperatures of 400-600 degrees C in air. The resultant LaOF films had a nanoparticulate porous microstructure, maintaining the morphology of the original LDAH template films. It was also successful to incorporate Eu3+ ions into LaOF through deposition of the LDAH film in a solution containing europium acetate tetrahydrate. The characteristic photoluminescence from Eu(3+) was observed with an ultraviolet-light excitation at 273 nm, indicating that Eu3+ was homogeneously distributed in LaOF host crystals. Thus the ion-modification of LDAH was also demonstrated to be a useful method for preparing nanostructured rare-earth oxyfluoride materials havingvarious cationic compositions. PMID:15875413

Hosono, Eiji; Fujihara, Shinobu; Kimura, Toshio

2004-04-27

143

Synthese de nanoparticules plasmoniques par laser femtoseconde en milieu liquide pour des applications biomedicales  

NASA Astrophysics Data System (ADS)

The femtosecond laser synthesis of plasmonic nanoparticles (Au, Ag, Cu, AuAg, AuCu) is described. The approach relies on the fs laser ablation of a target immersed in a liquid, followed by the laser-induced fragmentation and growth of nanoparticles in solution. This two-step methodology significantly enhances the production rate, the reproducibility and the size control of nanoparticles in comparison to the direct laser ablation based technique. For gold, the laser-induced growth of nanometric seeds initially formed by laser ablation in the presence of a stabilizing agent allows the synthesis of functionalized nanoparticles with sizes ranging from 3-76 nm and coefficients of variation (COV) varying between 15-30%. In comparison to the direct laser ablation, the size control is much simpler, as it uniquely depends on the gold to stabilizing agent molecular concentration ratio. The approach has been described for dextran and polyethylene glycol (PEG), but can be extended to all stabilizing agents and open new avenues in the formation of various novel bioconjugates. The fs laser ablation and fragmentation also allow the synthesis of stable and low dispersed Au nanoparticles in pure water. These nanoparticles are unique for sensing applications with high sensitivity based on surface enhanced Raman scattering (SERS), since they greatly reduce the noise associated with surface contaminants and byproducts found in solution. The formation of various nanospheres with predetermined size, shape and composition (AuxAg(1-x), AuxCu(1-x) ) is also reported by the use of a fs irradiation of a mixture of two pure metallic ix colloidal solutions in a very simple chemical environment, e.g. water and a stabilizing agent. From a chemical point of view, oxidation of silver nanoparticles is significantly reduced by the incorporation of a small amount of gold and is completely inhibited for a gold atomic fraction larger than 0.4-0.5. The bifunctional nature related to the partial oxidation of the gold nanoparticle surface allows a wide range of stabilization mechanisms. The stabilization by hydrophobic-hydrophobic interaction, by hydrogen bonds formation, by chemisorptions of thiols and by electrostatic interactions is evaluated. A new class of stabilizing agents, biopolymers, is also introduced. The addition of these polymers during the laser ablation, fragmentation or growth process enables in situ surface functionalization and efficient size control. The biocompatibility of these stabilizers also allows the direct introduction of nanoparticles in in vitro or in vivo applications without further purification. Significant efforts have also been undertaken to check the possible degradation of the polymers used during the laser process. These studies demonstrate a low degradation via an oxidation mechanism, involving the production of free radicals and oxidizing species by dissociation of water molecules during the laser process. Finally, the mechanisms of laser ablation in liquids and a growth model for the nanoparticles are proposed based on experimental results from literature and this thesis. The formation of nanoparticles is described by three distinct phases. First, a fast nucleation and condensation of the ejected species occur in the plasma and are caused by extremely high cooling rates, which lead to a strong supersaturation. This short nucleation and condensation phase is followed by a marked growth of the liquid (and still hot) nuclei by coalescence. After solidification, these nuclei should have sizes below 2 nm and be mostly condensed at the liquid-vapor interface of the growing cavitation bubble. Without the presence of stabilizing agent, growth by atomic diffusion and coalescence continue inside the cavitation bubble and should be accelerated following its collapse. Nanoparticles and unreacted monomers are then propelled out of the ablation zone by the secondary shock wave associated with the collapse of the cavitation bubble and further grow in solution. This cycle is repeated for each laser pulse and interaction between species

Besner, Sebastien

144

Mecanismes de deformation de nanoparticules d'Au par irradiation ionique  

NASA Astrophysics Data System (ADS)

In the present thesis, we study the anisotropic deformation of gold nanoparticles embedded in amorphous silica or crystalline aluminum arsenide, under ion bombardment. We try to comprehend the mechanism responsible for this deformation and to remove any ambiguity related to the explanation of this phenomenon. A hybrid process combining sputtering and plasma enhanced chemical vapour deposition was used to fabricate Au/SiO2 layers on fused silica substrates. Structures with single and multilayer were obtained. Heating during or after deposition activates the Au atom agglomeration and favours the growth of the nanoparticles. Also, a Au/AlAs nanocomposite was obtained by ion implantation of AlAs films, followed by rapid thermal annealing. The samples of the two nanocomposites, cooled with liquid nitrogen, were irradiated with 2 to 40 MeV Cu, Si, Au or In ion beams, at fluences ranging from 1x10 13 to 4x1015 ions/cm2, using a Tandem or Tandetron accelerator. The structural and morphological properties of the Au/SiO2 nanocomposite were extracted by optical means; the frequency and the width of surface plasmon resonance band depend on the nanoparticle shape and size, their concentration, the inter-particle distance and the dielectric properties of material in which the particles are embedded. The aluminum arsenide crystallinity was studied by two techniques: Raman spectroscopy and Rutherford backscattering spectrometry in channelling configuration (RBS/ channelling). The Au concentration in the nanocomposite layers was deducted from RBS results. The size distribution and metallic nanoparticles shape transformation in both nanocomposites were observed by electronic transmission microscopy. The results obtained within the framework of this work are the subject of three journal papers. The first publication shows the possibility of manipulating the width and spectral position of the gold nanoparticle absorption band in Au/SiO2 nanocomposites by modifying their structure (form, size and inter-particle distance). The obtained Au nanoparticles are nearly spherical. The surface plasmon (PS) absorption band corresponding to the distant particles is located at 520 nm. After ion irradiation, the spherical nanoparticles transform into ellipsoids aligned along the ion beam. The absorption band splits into two bands: transversal and longitudinal. The band corresponding to the ellipsoids small axis (transversal) is blue-shifted and that corresponding to the long axis (longitudinal) is red-shifted indicating the elongation of particles in the beam direction. The second paper is consecrated to the crucial role of the plastic deformation of the matrix and to the importance of the metal atomic mobility in the anisotropic nanoparticles deformation in Au/SiO 2 nanocomposites. Our measurements show that a threshold value of 2 keV/nm (electronic stopping power) is necessary for the deformation of Au nanoparticles. This value is close to that required for silica deformation. Mobility of the Au atoms at the time of the ion passage is confirmed by temperature calculation within the ionic track. The third paper treats the attempt of formation and deformation of Au nanoparticles in crystalline aluminum arsenide matrix known by its high resistance to amorphisation and deformation under ionic bombardment. The principal result of the last article confirms the essential role of the matrix. It proves that the anisotropic deformation of surrounding material is indispensable for gold nanoparticles deformation. The experimental results mentioned above and temperature calculations within ionic tracks allowed us to propose the following anisotropic deformation scenario of Au nanoparticles embedded in Au/SiO2 nanocomposite: (1) Each ion crossing the silica melts (very briefly) a narrow cylinder around its trajectory forming thus a latent track. This is consistent with the observed threshold value in the electronic stopping power. (2) The cumulative effect of many separate ion impacts leads to the anisotropic growth of the silica matrix which contracts in the direct

Harkati Kerbouah, Chahineze

145

Control Banding Nanotool: Evaluation of a qualitative risk assessment method for the control of nanoparticulate exposures  

SciTech Connect

Control Banding strategies offer a simplified control of worker exposures when there is an absence of firm toxicological and exposure information. The nanotechnology industry fits this classification as there are overwhelming uncertainties of work-related health risks posed by nanomaterials. Many experts have suggested Control Banding as a solution for these issues. A recent survey shows a majority of nanomaterial users are not performing a basic risk assessment of their product in use. A Control Banding Nanotool has been developed and implemented to afford a qualitative risk assessment toward the control of nanoparticle exposures. The international use of the Control Banding Nanotool reflects on both its need and its possibilities. By developing this dynamic Control Banding Nanotool within the realm of the scientific information available, this application of Control Banding appears to be a useful approach for assessing the risk of nanomaterial operations. This success can be seen in providing recommendations for appropriate engineering controls, facilitating the allocation of resources to the activities that most need them, and initiating an appropriate discussion of these risks with nonexperts. Experts have requested standardization of toxicological parameters, affording better utility and consistency of research. This database of toxicological research findings should be harnessed and presented in a format feeding directly into the Control Banding Nanotool severity and probability risk matrix. Making the latest research available for experts and practitioners alike will provide the best protection of workers in the nanotechnology industries. This presentation will also show the science behind the simplified Control Banding Nanotool approach, its structure, weighting of risks, utility for exposure mitigation, and the research needs to bolster its effectiveness.

Zalk, D; Paik, S; Swuste, P

2009-01-27

146

Direct writing of metal nanostructures: lithographic tools for nanoplasmonics research.  

PubMed

Continued progress in the fast-growing field of nanoplasmonics will require the development of new methods for the fabrication of metal nanostructures. Optical lithography provides a continually expanding tool box. Two-photon processes, as demonstrated by Shukla et al. (doi: 10.1021/nn103015g), enable the fabrication of gold nanostructures encapsulated in dielectric material in a simple, direct process and offer the prospect of three-dimensional fabrication. At higher resolution, scanning probe techniques enable nanoparticle particle placement by localized oxidation, and near-field sintering of nanoparticulate films enables direct writing of nanowires. Direct laser "printing" of single gold nanoparticles offers a remarkable capability for the controlled fabrication of model structures for fundamental studies, particle-by-particle. Optical methods continue to provide a powerful support for research into metamaterials. PMID:21417494

Leggett, Graham J

2011-03-22

147

Occurrence and behaviour of dissolved, nano-particulate and micro-particulate iron in waste waters and treatment systems: new insights from electrochemical analysis.  

PubMed

Cyclic-, Differential Pulse- and Steady-state Microdisc Voltammetry (CV, DPV, SMV) techniques have been used to quantify the occurrence and fate of dissolved Fe(ii)/Fe(iii), nano-particulate and micro-particulate iron over a 12 month period in a series of net-acidic and net-alkaline coal mine drainages and passive treatment systems. Total iron in the mine waters is typically 10-100 mg L(-1), with values up to 2100 mg L(-1). Between 30 and 80% of the total iron occurs as solid phase, of which 20 to 80% is nano-particulate. Nano-particulate iron comprises 20 to 70% of the nominally "dissolved" (i.e. <0.45 ?m) iron. Since coagulation and sedimentation are the only processes required to remove solid phase iron, these data have important implications for the generation or consumption of acidity during water treatment. In most waters, the majority of truly dissolved iron occurs as Fe(ii) (average 64 ± 22%). Activities of Fe(ii) do not correlate with pH and geochemical modelling shows that no Fe(ii) mineral is supersaturated. Removal of Fe(ii) must proceed via oxidation and hydrolysis. Except in waters with pH < 4.4, activities of Fe(iii) are strongly and negatively correlated with pH. Geochemical modelling suggests that the activity of Fe(iii) is controlled by the solubility of hydrous ferric oxides and oxyhydroxysulfates, supported by scanning and transmission electron microscopic analysis of solids. Nevertheless, the waters are generally supersaturated with respect to ferrihydrite and schwertmannite, and are not at redox equilibrium, indicating the key role of oxidation and hydrolysis kinetics on water treatment. Typically 70-100% of iron is retained in the treatment systems. Oxidation, hydrolysis, precipitation, coagulation and sedimentation occur in all treatment systems and - independent of water chemistry and the type of treatment system - hydroxides and oxyhydroxysulfates are the main iron sinks. The electrochemical data thus reveal the rationale for incomplete iron retention in individual systems and can thus inform future design criteria. The successful application of this low cost and rapid electrochemical method demonstrates its significant potential for real-time, on-site monitoring of iron-enriched waters and may in future substitute traditional analytical methods. PMID:22370608

Matthies, R; Aplin, A C; Horrocks, B R; Mudashiru, L K

2012-04-01

148

Catalyst inks and method of application for direct methanol fuel cells  

DOEpatents

Inks are formulated for forming anode and cathode catalyst layers and applied to anode and cathode sides of a membrane for a direct methanol fuel cell. The inks comprise a Pt catalyst for the cathode and a Pt--Ru catalyst for the anode, purified water in an amount 4 to 20 times that of the catalyst by weight, and a perfluorosulfonic acid ionomer in an amount effective to provide an ionomer content in the anode and cathode surfaces of 20% to 80% by volume. The inks are prepared in a two-step process while cooling and agitating the solutions. The final solution is placed in a cooler and continuously agitated while spraying the solution over the anode or cathode surface of the membrane as determined by the catalyst content.

Zelenay, Piotr (Los Alamos, NM); Davey, John (Los Alamos, NM); Ren, Xiaoming (Los Alamos, NM); Gottesfeld, Shimshon (Los Alamos, NM); Thomas, Sharon C. (Vancouver, CA)

2004-02-24

149

Highly-optimized membrane electrode assembly for direct methanol fuel cell prepared by sedimentation method  

NASA Astrophysics Data System (ADS)

An electrode for a direct methanol fuel cell (DMFC) is prepared by means of the sedimentation method. A suspension containing Pt black, PTFE and water was filtered through a polycarbonate film and a thin catalyst layer remains on this film. This catalyst layer is then transferred to a gas-diffusion layer by applying a pressure to the assembly and then peeling off the filter film. For the anode catalyst layer, the suspension contained Pt-Ru black and water. The preparation process is optimized and single-cell performance is examined under different operating conditions. Operated at 60 °C, the output power density of the membrane electrode assembly (MEA) fabricated by the sedimentation method is 70% higher than that for an assembly prepared by the conventional brushing technique.

Liu, Jing Hua; Jeon, Min Ku; Choi, Won Choon; Woo, Seong Ihl

150

Selective electrocatalysts toward a prototype of the membraneless direct methanol fuel cell  

PubMed Central

Mastery over the structure of nanomaterials enables control of their properties to enhance their performance for a given application. Herein we demonstrate the design and fabrication of Pt-based nanomaterials with enhanced catalytic activity and superior selectivity toward the reactions in direct methanol fuel cells (DMFCs) upon the deep understanding of the mechanisms of these electrochemical reactions. In particular, the ternary Au@Ag2S-Pt nanocomposites display superior methanol oxidation reaction (MOR) selectivity due to the electronic coupling effect among different domains of the nanocomposites, while the cage-bell structured Pt-Ru nanoparticles exhibit excellent methanol tolerance for oxygen reduction reaction (ORR) at the cathode because of the differential diffusion of methanol and oxygen in the porous Ru shell of the cage-bell nanoparticles. The good catalytic selectivity of these Pt-based nanomaterials via structural construction enables a DMFC to be built without a proton exchange membrane between the fuel electrode and the oxygen electrode.

Feng, Yan; Yang, Jinhua; Liu, Hui; Ye, Feng; Yang, Jun

2014-01-01

151

Polymer electrolyte direct methanol fuel cells: an option for transportation applications  

SciTech Connect

PEFCs most frequently considered for electric vehicles have been based on either hydrogen carried aboard, or steam-reforming of methanol on board to produce H2 + CO2. Direct methanol fuel cells (DMFCs), which use a liquid methanol fuel feed, completely avoid the complexity and weight penalties of the reformer, but have not been considered a serious option until recently, because of much lower power densities. Recent advances in DMFCs have been dramatic, however, with the DMFC reaching power densities which are significant fractions of those provided by reformate/air fuel cells. Use of established Pt-Ru anode electrocatalysts and Pt cathode electrocatalysts in polymer electrolyte DMFCs has resulted in enhanced DMFC performance, particularly when operated above 100 C and when catalyst layer composition and structure are optimized. The higher DMFC power densities recently achieved provide a new basis for considering DMFCs for transportation applications.

Gottesfeld, S.; Cleghorn, S.J.C.; Ren, X.; Springer, T.E.; Wilson, M.S.; Zawodzinski, T.A.

1996-10-01

152

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

153

A direct 2-propanol polymer electrolyte fuel cell  

NASA Astrophysics Data System (ADS)

We report the performance of a polymer electrolyte membrane direct 2-propanol fuel cell (DPFC). The cell consisted of a Pt-Ru (atomic ratio of 1:1) black anode, a Pt black cathode, and a Nafion ®-117 membrane electrolyte. The cell was operated at 90 °C with aqueous 2-propanol as fuel and with oxygen as oxidant. The performance of the cell operating on 2-propanol is substantially higher than when it was operating on methanol at current densities lower than ˜200 mA/cm 2. The electrical efficiency of the direct 2-propanol fuel cell is nearly 1.5 times that of the direct methanol fuel cell at power densities below 128 mW/cm 2. Studies on the effects of electrocatalyst loading, of 2-propanol concentration, and of oxygen pressure on cell performance indicate that the cells operating on 2-propanol require lower anode and cathode loadings than cells operating on methanol. Cathode poisoning by 2-propanol is less severe than by methanol. Hydrogen gas evolution observed at the anode at low current densities indicated that catalytic dehydrogenation of 2-propanol occurred over the anode catalyst. A rapid voltage drop occurred at high current densities and after operating the cell for extended periods of time at constant current. The rapid voltage drop is an anode phenomenon.

Cao, Dianxue; Bergens, Steven H.

154

On-line FTIR spectroscopic investigations of methanol oxidation in a direct methanol fuel cell  

SciTech Connect

A real-time Fourier transform infrared spectroscopy (FTIRS) analysis of the products of methanol oxidation in a prototype direct-methanol fuel cell operating at high temperatures (150 to 185 C) is reported here. The methanol oxidation products on platinum black and platinum-ruthenium catalyst surfaces were determined as a function of the fuel cell operating temperature, current density, and methanol/water mole ratio. Neither formaldehyde nor formic acid was detected in anode exhaust gas at all cell operating conditions. The product distributions of methanol oxidation obtained by on-line FTIRS are consistent with previous results obtained by on-line mass spectroscopy under similar conditions. With pure methanol in anode feed, methanaldimethylacetal was found to be the main product, methyl formate and CO{sub 2} were also found. However, when water was present in the anode feed, the main product was CO{sub 2}, and the formation of methanal-dimethylacetal and methyl formate decreased significantly with increase of the water/methanol mole ratio. Increase of cell operating temperature enhanced the formation of CO{sub 2} and decreased the formation of methanaldimethylacetal and methyl formate. Pt/Ru catalyst is more active for methanol oxidation and has a higher selectivity toward CO{sub 2} formation than Pt-black. Nearly complete methanol oxidation, i.e., the product was almost exclusively CO{sub 2}, was achieved using a Pt/Ru catalyst and a water/methanol mole ratio of 2 or higher in the anode feed at a temperature of 185 C or above.

Lin, W.F.; Wang, J.T.; Savinell, R.F. [Case Western Reserve Univ., Cleveland, OH (United States)

1997-06-01

155

PtRu/Ti anodes with varying Pt ratio: Ru ratio prepared by electrodeposition for the direct methanol fuel cell.  

PubMed

PtRu/Ti anodes with varying Pt ratio Ru ratio were prepared by electrodeposition of a thin PtRu catalyst layer onto Ti mesh for a direct methanol fuel cell (DMFC). The morphology and structure of the catalyst layers were analyzed by SEM, EDX and XRD. The catalyst coating layer shows an alloy character. The relative activities of the PtRu/Ti electrodes were assessed and compared in half cell and single DMFC experiments. The results show that these electrodes are very active for the methanol oxidation and that the optimum Ru surface coverage was ca. 9 at.% for DMFC operating at 20 degrees C and 11 at.% at 60 degrees C. The PtRu/Ti anode shows a performance comparable to that of the conventional carbon-based anode in a DMFC operating with 0.25 M or 0.5 M methanol solution and atmosphere oxygen gas at 90 degrees C. PMID:16763704

Shao, Zhi-Gang; Zhu, Fuyun; Lin, Wen-Feng; Christensen, Paul A; Zhang, Huamin

2006-06-21

156

Design, Characterization, and Aerosol Dispersion Performance Modeling of Advanced Spray-Dried Microparticulate/Nanoparticulate Mannitol Powders for Targeted Pulmonary Delivery as Dry Powder Inhalers  

PubMed Central

Abstract Background: The purpose was to design and characterize inhalable microparticulate/nanoparticulate dry powders of mannitol with essential particle properties for targeted dry powder delivery for cystic fibrosis mucolytic treatment by dilute organic solution spray drying, and, in addition, to tailor and correlate aerosol dispersion performance delivered as dry powder inhalers based on spray-drying conditions and solid-state physicochemical properties. Methods: Organic solution advanced spray drying from dilute solution followed by comprehensive solid-state physicochemical characterization and in vitro dry powder aerosolization were used. Results: The particle size distribution of the spray-dried (SD) powders was narrow, unimodal, and in the range of ?500?nm to 2.0??m. The particles possessed spherical particle morphology, relatively smooth surface morphology, low water content and vapor sorption (crystallization occurred at exposure above 65% relative humidity), and retention of crystallinity by polymorphic interconversion. The emitted dose, fine particle fraction (FPF), and respirable fraction (RF) were all relatively high. The mass median aerodynamic diameters were below 4??m for all SD mannitol aerosols. Conclusion: The in vitro aerosol deposition stage patterns could be tailored based on spray-drying pump rate. Positive linear correlation was observed between both FPF and RF values with spray-drying pump rates. The interplay between various spray-drying conditions, particle physicochemical properties, and aerosol dispersion performance was observed and examined, which enabled tailoring and modeling of high aerosol deposition patterns.

Li, Xiaojian; Vogt, Frederick G.; Hayes, Don

2014-01-01

157

Laser welding of nanoparticulate TiO2 and transparent conducting oxide electrodes for highly efficient dye-sensitized solar cell  

NASA Astrophysics Data System (ADS)

Poor interfacial contact is often encountered in nanoparticulate film-based devices. The dye-sensitized solar cell (DSSC) is a representative case in which a nanoporous TiO2 electrode needs to be prepared on the transparent conducting oxide (TCO)-coated glass substrate. In this study, we demonstrate that the inter-electrode contact resistance accounts for a considerable portion of the total resistance of a DSSC and its efficiency can be greatly enhanced by welding the interface with a laser. TiO2 films formed on the TCO-coated glass substrate were irradiated with a pulsed ultraviolet laser beam at 355 nm this transmits through the TCO and glass but is strongly absorbed by TiO2. Electron microscopy analysis and impedance measurements showed that a thin continuous TiO2 layer is formed at the interface as a result of the local melting of TiO2 nanoparticles and this layer completely bridges the gap between the two electrodes, improving the current flow with a reduced contact resistance. We were able to improve the efficiency by 35-65% with this process. DSSCs fabricated using a homemade TiO2 paste revealed an efficiency improvement from ? = 3.3% to 5.4%, and an increase from 8.2% to 11.2% was achieved with the TiO2 electrodes made from a commercial paste.

Kim, Jinsoo; Kim, Jonghyun; Lee, Myeongkyu

2010-08-01

158

Initial in vitro screening approach to investigate the potential health and environmental hazards of Envirox(TM) - a nanoparticulate cerium oxide diesel fuel additive  

PubMed Central

Nanotechnology is the new industrial revolution of the 21st Century as the various processes lead to radical improvements in medicine, manufacturing, energy production, land remediation, information technology and many other everyday products and applications. With this revolution however, there are undoubted concerns for health, safety and the environment which arise from the unique nature of materials and processes at the nanometre scale. The in vitro assays used in the screening strategy are all validated, internationally accepted protocols and provide a useful indication of potential toxicity of a chemical as a result of effects on various toxicological endpoints such as local site of contact (dermal) irritation, general cytotoxicity and mutagenicity. The initial in vitro screening strategy described in this paper to investigate the potential health implications, if any, which may arise following exposure to one specific application of nanoparticulate cerium oxide used as a diesel fuel borne catalyst, reflects a precautionary approach and the results will inform judgement on how best to proceed to ensure safe use.

Park, Barry; Martin, Patricia; Harris, Chris; Guest, Robert; Whittingham, Andrew; Jenkinson, Peter; Handley, John

2007-01-01

159

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

160

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

161

Organic-coated nanoparticulate zero valent iron for remediation of chemical oxygen demand (COD) and dissolved metals from tropical landfill leachate.  

PubMed

The use of nanoparticulate zero valent iron (NZVI) in the treatment of inorganic contaminants in landfill leachate and polluted plumes has been the subject of many studies, especially in temperate, developed countries. However, NZVI's potential for reduction of chemical oxygen demand (COD) and treatment of metal ion mixtures has not been explored in detail. We investigated the efficiency of NZVI synthesized in the presence of starch, mercaptoacetic, mercaptosuccinic, or mercaptopropenoic acid for the reduction of COD, nutrients, and metal ions from landfill leachate in tropical Sri Lanka. Synthesized NZVI were characterized with X-ray diffraction (XRD), transmission electron microscopy, X-ray photoelectron spectroscopy, scanning electron microscopy (SEM), thermal gravimetric analysis, Fourier transform infrared spectroscopy (FTIR) and Brunauer-Emmett-Teller. Of the samples tested, Starch-NZVI (S-NZVI) and mercaptoacetic-NZVI (MA-NZVI) performed well for treatment both COD and metal mixture. The removal percentages for COD, nitrate-nitrogen, and phosphate from S-NZVI were 50, 88, and 99 %, respectively. Heavy metal removal was higher in S-NZVI (>95 %) than others. MA-NZVI, its oxidation products, and functional groups of its coating showed the maximum removal amounts for both Cu (56.27 mg g(-1)) and Zn (28.38 mg g(-1)). All mercapto-NZVI showed well-stabilized nature under FTIR and XRD investigations. Therefore, we suggest mercapto acids as better agents to enhance the air stability for NZVI since chemically bonded thiol and carbonyl groups actively participation for stabilization process. PMID:24535668

Wijesekara, S S R M D H R; Basnayake, B F A; Vithanage, Meththika

2014-06-01

162

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

163

Tungsten carbides as potential alternative direct methanol fuel cell anode electrocatalysts  

NASA Astrophysics Data System (ADS)

The reduction of precious metal loading and the improvement of sluggish kinetics at the anode electrocatalyst are two primary concerns for economical development of direct methanol fuel cells (DMFC). The purpose of this research is to examine the feasibility of using tungsten carbides as alternative fuel cell anode electrocatalysts. The anodic chemistry of the direct methanol fuel cell requires the oxidation of methanol and the decomposition of water to produce protons, electrons, and gas-phase CO2. Currently, the most effective anode electrocatalyst for DMFC is the Pt/Ru bimetallic catalyst, which efficiently oxidizes methanol, as well as decomposes water for the oxidation and removal of adsorbed CO species. Although the Pt/Ru bimetallic system exhibits desirable electrochemical activities, both Pt and Ru are expensive due to limited supplies. In addition, strong chemisorption of CO on Pt and Ru makes the electrocatalyst susceptible to CO poisoning, blocking the active sites for methanol oxidation. This work began by examining the reactions of methanol, water, and CO on carbide-modified tungsten (C/W) single crystal surfaces, with and without submonolayer coverages of Pt. These fundamental surface science results demonstrated the potential for tungsten carbides to be used as anode catalysts in DMFC, exhibiting decomposition of both methanol and water along with significantly lowered CO desorption temperatures. Additionally, submonolayer Pt-modification of the C/W surfaces resulted in a synergistic effect, eliminating the undesired reaction pathway on the C/W surface that produced gas-phase CH4. To bridge the materials gap between model single crystal surfaces and the more realistic thin film electrocatalysts, polycrystalline tungsten carbide thin films were created via physical vapor deposition (PVD) and carburization of polycrystalline tungsten foil. Fundamental surface science techniques were applied to the PVD films to examine the reaction pathways of DMFC pertinent molecules on the surface, ensuring similar surface reactivity and selectivity to the single crystal surfaces. Finally, cyclic voltammetry (CV) measurements, both ex situ and in situ coupled with X-ray photoelectron spectroscopy (XPS), have been applied to examine the electrocatalyst stability and methanol oxidation rates in an electrochemical environment.

Zellner, Michael

164

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

165

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.

USKOKOVIC, VUK; DESAI, TEJAL A.

2014-01-01

166

Synthesis of monolithic nanoparticulate ZrO2 in a new polymorph of orthorhombic crystal structure at ambient pressure  

NASA Astrophysics Data System (ADS)

A new polymorph of self-stabilized o-ZrO2 of orthorhombic crystal structure has been synthesized at ambient pressure. It has the lattice parameters a = 0.3340, b = 0.5535, and c = 0.6364 nm in the Pmnb space group. A single phase of o-ZrO2 forms in 2 h of heating of a porous ZrO(OH)2 . xH2O precursor (amorphous) at 500 °C in air. The kind of precursor used in this novel o-ZrO2 synthesis is derived by a simple hydrolysis of aqueous ZrOCl2 . 8H2O in reaction with ammonia liquor at a controlled temperature of 5 °C. At this temperature, ZrO(OH)2 molecules as soon as they form (ZrOCl2 + 2NH4OH ZrO(OH)2 + 2NH4Cl) recombine with one another through H-bonded H2O to form a ZrO(OH)2 . xH2O polymer gel. In flowing air at 20-40 °C, some of the H2O evaporates leaving behind porous ZrO(OH)2 . xH2O with NH4Cl impurities. The o-ZrO2 sample, 15 nm average crystallite size, transforms to monoclinic m-ZrO2, with a concomitant growth of 23 nm crystallites at temperatures as high as 800 °C. A kinetically different process operates in the direct heating of ZrO(OH)2 . xH2O gel, forming a tetragonal ZrO2 or m-ZrO2.

Ram, S.; Mondal, A.

2004-03-01

167

Performance of PEM Liquid-Feed Direct Methanol-Air Fuel Cells  

NASA Technical Reports Server (NTRS)

A direct methanol-air fuel cell operating at near atmospheric pressure, low-flow rate air, and at temperatures close to 60oC would tremendously enlarge the scope of potential applications. While earlier studies have reported performance with oxygen, the present study focuses on characterizing the performance of a PEM liquid feed direct methanol-air cell consisting of components developed in house. These cells employ Pt-Ru catalyst in the anode, Pt at the cathode and Nafion 117 as the PEM. The effect of pressure, flow rate of air and temperature on cell performance has been studied. With air, the performance level is as high as 0.437 V at 300 mA/cm2 (90oC, 20 psig, and excess air flow) has been attained. Even more significant is the performance level at 60oC, 1 atm and low flow rates of air (3-5 times stoichiometric), which is 0.4 V at 150 mA/cm2. Individual electrode potentials for the methanol and air electrode have been separated and analyzed. Fuel crossover rates and the impact of fuel crossover on the performance of the air electrode have also been measured. The study identifies issues specific to the methanol-air fuel cell and provides a basis for improvement strategies.

Narayanan, S. R.

1995-01-01

168

Preparation and performance of a Nafion ®/montmorillonite nanocomposite membrane for direct methanol fuel cell  

NASA Astrophysics Data System (ADS)

Direct methanol fuel cells (DMFC) have major technical problems, e.g. slow methanol oxidation kinetics and high methanol crossover, to use as power sources for several applications. To overcome these problems it has been proposed to increase the fuel cell operating temperature to over 100-150 °C and to reduce the methanol permeability. In this work, we made Nafion ®/montmorillonite (MMT) nanocomposite membranes and carried out diverse tests. The nanocomposite membranes were produced by direct melt intercalation of perfluorosulfonylfluoride copolymer resin (Nafion ® resin) into the montmorillonite and modified montmorillonite (m-MMT) which was organized by dodecylamine. The membrane-electrode assembly (MEA) has been made using a hot pressing method and the electrode prepared using PtRu black and Pt black catalysts for anode and cathode, respectively. The morphology of the nanocomposite membranes has been investigated using SEM and TEM. The nanocomposite membranes and MMT and m-MMT were analyzed using by FT-IR and X-ray diffraction (XRD). The thermal and mechanical properties of those membranes were also investigated and the methanol permeability was measured by gas chromatography (GC). The performance of the MEA using the nanocomposite membrane was evaluated by single cell test. The results show that the performance of the MEA using the nanocomposite membrane was higher than that of a commercial Nafion ® membrane at high operating temperature.

Jung, D. H.; Cho, S. Y.; Peck, D. H.; Shin, D. R.; Kim, J. S.

169

Advance Directives  

MedlinePLUS

... saved articles window. My Saved Articles » My ACS » Advance Directives Download Printable Version [PDF] » An advance health care ... to get started. Why do you need an advance directive? What is an advance directive? Types of advance ...

170

Multiferroic nanoparticulate thin film composites by Co implantation of ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystal targets  

NASA Astrophysics Data System (ADS)

Two-phase magnetostrictive-piezoelectric thin film composites are key materials to the development of a range of potentially disruptive magnetoelectric technologies, such as electrical-writing magnetic-reading random access memories. However, multiferroic thin film composites prepared so far show neither magnetoelectric switching nor magnetoelectric responses comparable to those of related bulk ceramic materials and cermets. Here we show that ion implantation of magnetic species into ferroelectric single crystal targets can be an effective alternative means of obtaining nanoparticulate thin film composites of this type. Concept is proved by the implantation of Co into a Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystal with ultrahigh piezoelectricity. Formation of an ensemble of ferromagnetic nanoparticles embedded in an amorphized layer within the ferroelectric crystal is clearly shown.

Torres, María; Ricote, Jesús; Amorín, Harvey; Jaafar, Miriam; Holgado, Susana; Piqueras, Juan; Asenjo, Agustina; García-Hernández, Mar; Algueró, Miguel

2011-12-01

171

Selective electrocatalysts toward a prototype of the membraneless direct methanol fuel cell.  

PubMed

Mastery over the structure of nanomaterials enables control of their properties to enhance their performance for a given application. Herein we demonstrate the design and fabrication of Pt-based nanomaterials with enhanced catalytic activity and superior selectivity toward the reactions in direct methanol fuel cells (DMFCs) upon the deep understanding of the mechanisms of these electrochemical reactions. In particular, the ternary Au@Ag2S-Pt nanocomposites display superior methanol oxidation reaction (MOR) selectivity due to the electronic coupling effect among different domains of the nanocomposites, while the cage-bell structured Pt-Ru nanoparticles exhibit excellent methanol tolerance for oxygen reduction reaction (ORR) at the cathode because of the differential diffusion of methanol and oxygen in the porous Ru shell of the cage-bell nanoparticles. The good catalytic selectivity of these Pt-based nanomaterials via structural construction enables a DMFC to be built without a proton exchange membrane between the fuel electrode and the oxygen electrode. PMID:24448514

Feng, Yan; Yang, Jinhua; Liu, Hui; Ye, Feng; Yang, Jun

2014-01-01

172

Single wall carbon nanotube supports for portable direct methanol fuel cells.  

PubMed

Single-wall and multiwall carbon nanotubes are employed as carbon supports in direct methanol fuel cells (DMFC). The morphology and electrochemical activity of single-wall and multiwall carbon nanotubes obtained from different sources have been examined to probe the influence of carbon support on the overall performance of DMFC. The improved activity of the Pt-Ru catalyst dispersed on carbon nanotubes toward methanol oxidation is reflected as a shift in the onset potential and a lower charge transfer resistance at the electrode/electrolyte interface. The evaluation of carbon supports in a passive air breathing DMFC indicates that the observed power density depends on the nature and source of carbon nanostructures. The intrinsic property of the nanotubes, dispersion of the electrocatalyst and the electrochemically active surface area collectively influence the performance of the membrane electrode assembly (MEA). As compared to the commercial carbon black support, single wall carbon nanotubes when employed as the support for anchoring the electrocatalyst particles in the anode and cathode sides of MEA exhibited a approximately 30% enhancement in the power density of a single stack DMFC operating at 70 degrees C. PMID:16471506

Girishkumar, G; Hall, Timothy D; Vinodgopal, K; Kamat, Prashant V

2006-01-12

173

Direct Variation  

NSDL National Science Digital Library

This learning unit from Regents Prep Exam Center introduces the topic of direct variation equations. The material includes a lesson plan, practice problems and a teacher's guide. Students will learn the basics of what a direct variation equation is and the formula for direct variation.

2012-01-01

174

Investigation of nano Pt and Pt-based alloys electrocatalysts for direct methanol fuel cells and their properties  

NASA Astrophysics Data System (ADS)

The electrocatalysts used in micro direct methanol fuel cell (?DMFC), such as Pt/C and Pt alloy/C, prepared by liquid-phase NaBH4 reduction method have been investigated. XC-72 (Cobalt corp. Company, U.S.A) is chosen as the activated carrier for the electrocatalysts to keep the catalysts powder in the range of several nanometers. The XRD, SEM, EDX analyses indicated that the catalysts had small particle size in several nanometers, in excellent dispersed phase and the molar ratio of the precious metals was found to be optimal. The performances of the DMFCs using cathodic catalyst with Pt percentage of 30wt% and different anodic catalysts (Pt-Ru, Pt-Ru-Mo) were tested. The polarization curves and power density curves of the cells were measured to determine the optimal alloy composition and condition for the electrocatalysts. The results showed that the micro direct methanol fuel cell with 30wt% Pt/C as the cathodic catalyst and n(Pt):n(Ru):n(Mo) = 3:2:2 PtRuMo/C as the anodic catalyst at room temperature using 2.0mol/L methanol solution has the best performances.

Suo, Chunguang; Zhang, Wenbin; Shi, Xinghua; Ma, Chuxia

2014-03-01

175

Analysis of the electrochemical characteristics of a direct methanol fuel cell based on a Pt-Ru/C anode catalyst  

SciTech Connect

A vapor-feed direct methanol fuel cell based on a Nafion 117{reg_sign} solid polymer electrolyte was investigated. Pt-Ru/C and Pt/C catalysts were employed for methanol oxidation and oxygen reduction, respectively. The structure, surface, and morphology of the catalysts were investigated by X-ray powder diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Crystalline face-centered cubic phases were found in the Pt and Pt-Ru catalysts. The alloy composition in the Pt-Ru/C catalyst was different from the nominal composition, probably due to the formation of surface RuO{sub x} species, as indicated by X-ray photoelectron spectroscopy. Transmission electron microscopy observation showed an increase of the average particle size and particle agglomeration in the Pt-Ru/C catalyst compared to the Pt/C catalyst. The membrane/electrode assembly was prepared by using a paste process method. Scanning electron microscopy and energy dispersive X-ray analyses showed good adhesion of catalyst layers to the membrane and a homogeneous distribution of the ionomer inside the catalyst. AC-impedance and galvanostatic steady-state polarization techniques were used to investigate the electrochemical performance of the direct methanol fuel cell.

Arico, A.S.; Creti, P.; Mantegna, R.; Giordano, N.; Antonucci, V. [CNR Inst. for Transformation and Storage of Energy, Messina (Italy); Kim, H. [Seoul National Univ. (Korea, Republic of). Dept. of Chemistry

1996-12-01

176

Direct formic acid fuel cells  

NASA Astrophysics Data System (ADS)

The performance of formic acid fuel oxidation on a solid PEM fuel cell at 60 °C is reported. We find that formic acid is an excellent fuel for a fuel cell. A model cell, using a proprietary anode catalyst produced currents up to 134 mA/cm 2 and power outputs up to 48.8 mW/cm 2. Open circuit potentials (OCPs) are about 0.72 V. The fuel cell runs successfully over formic acid concentrations between 5 and 20 M with little crossover or degradation in performance. The anodic polarization potential of formic acid is approximately 0.1 V lower than that for methanol on a standard Pt/Ru catalyst. These results show that formic acid fuel cells are attractive alternatives for small portable fuel cell applications.

Rice, C.; Ha, S.; Masel, R. I.; Waszczuk, P.; Wieckowski, A.; Barnard, Tom

177

Study of catalysis for solid oxide fuel cells and direct methanol fuel cells  

NASA Astrophysics Data System (ADS)

Fuel cells offer the enticing promise of cleaner electricity with lower environmental impact than traditional energy conversion technologies. Driven by the interest in power sources for portable electronics, and distributed generation and automotive propulsion markets, active development efforts in the technologies of both solid oxide fuel cell (SOFC) and direct methanol fuel cell (DMFC) devices have achieved significant progress. However, current catalysts for fuel cells are either of low catalytic activity or extremely expensive, presenting a key barrier toward the widespread commercialization of fuel cell devices. In this thesis work, atomic layer deposition (ALD), a novel thin film deposition technique, was employed to apply catalytic Pt to SOFC, and investigate both Pt skin catalysts and Pt-Ru catalysts for methanol oxidation, a very important reaction for DMFC, to increase the activity and utilization levels of the catalysts while simultaneously reducing the catalyst loading. For SOFCs, we explored the use of ALD for the fabrication of electrode components, including an ultra-thin Pt film for use as the electrocatalyst, and a Pt mesh structure for a current collector for SOFCs, aiming for precise control over the catalyst loading and catalyst geometry, and enhancement in the current collect efficiency. We choose Pt since it has high chemical stability and excellent catalytic activity for the O2 reduction reaction and the H2 oxidation reaction even at low operating temperatures. Working SOFC fuel cells were fabricated with ALD-deposited Pt thin films as an electrode/catalyst layer. The measured fuel cell performance reveals that comparable peak power densities were achieved for ALD-deposited Pt anodes with only one-fifth of the Pt loading relative to a DC-sputtered counterpart. In addition to the continuous electrocatalyst layer, a micro-patterned Pt structure was developed via the technique of area selective ALD. By coating yttria-stabilized zirconia, a typical solid oxide electrolyte, with patterned (octadecyltrichlorosilane) ODTS self-assembled monolayers (SAMs), Pt thin films were grown selectively on the SAM-free surface regions. Features with sizes as small as 2 mum were deposited by this combined ALD-muCP method. The micro-patterned Pt structure deposited by area selective ALD was applied to SOFCs as a current collector grid/patterned catalyst. An improvement in the fuel cell performance by a factor of 10 was observed using the Pt current collector grids/patterned catalyst integrated onto cathodic La0.6Sr 0.4Co0.2Fe0.8O3-delta. For possible catalytic anodes in DMFCs employing a 1:1 stoichiometric methanol-water reforming mixture, two strategies were employed in this thesis. One approach is to fabricate skin catalysts, where ALD Pt films of various thicknesses were used to coat sputtered Ru films forming Pt skin catalysts for study of methanol oxidation. Another strategy is to replace or alloy Pt with Ru; for this effort, both dc-sputtering and atomic layer deposition were employed to fabricate Pt-Ru catalysts of various Ru contents. The electrochemical behavior of all of the Pt skin catalysts, the DC co-sputtered Pt-Ru catalysts and the ALD co-deposited Pt-Ru catalysts were evaluated at room temperature for methanol oxidation using cyclic voltammetry and chronoamperometry in highly concentrated 16.6 M MeOH, which corresponds to the stoichiometric fuel that will be employed in next generation DMFCs that are designed to minimize or eliminate methanol crossover. The catalytic activity of sputtered Ru catalysts toward methanol oxidation is strongly enhanced by the ALD Pt overlayer, with such skin layer catalysts displaying superior catalytic activity over pure Pt. For both the DC co-sputtered catalysts and ALD co-deposited catalysts, the electrochemical studies illustrate that the optimal stoichiometry ratio for Pt to Ru is approximately 1:1, which is in good agreement with most literature.

Jiang, Xirong

178

Directing 101.  

ERIC Educational Resources Information Center

Providing an introduction to anyone considering directing as a field of study or career, this book takes a broad look at the process of directing and encourages students and professionals alike to look outside of the movie industry for inspiration. Chapters in the book discuss selecting and acquiring material; budgeting and financing; casting and…

Pintoff, Ernest

179

Electrical enhancement of direct methanol fuel cells by metal-plasma ion implantation Pt-Ru/C multilayer catalysts.  

PubMed

Direct methanol fuel cells (DMFC) have been widely studied owing to their simple cell configuration, high volume energy density, short start-up time, high operational reliability and other favorable characteristics. However, major limitations include high production cost, poisoning of the catalyst and methanol crossover. This study adopts a simple technique for preparing Pt-Ru/C multilayer catalysts, including magnetron sputtering (MS) and metal-plasma ion implantation (MPII). The Pt catalysts were sputtered onto the gas diffusion layer (GDL), followed by the implantation of Ru catalysts using MPII (at an accelerating voltage of 20 kV and an implantation dose of 1 x 10(16) ions/cm2). Pt-Ru is repeatedly processed to prepare Pt-Ru/C multilayer catalysts. The catalyst film structure and microstructure were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electronic microscopy (SEM), respectively. The cell performance was tested using a potential stat/galvano-stat. The results reveal that the membrane electrode assembly (MEA) of four multilayer structures enhances the cell performance of DMFC. The measured power density is 2.2 mW/cm2 at a methanol concentration of 2 M, with an OCV of 0.493 V. PMID:19441400

Weng, Ko-Wei; Chen, Yung-Lin; Chen, Ya-Chi; Lin, Tai-Nan

2009-02-01

180

Advance Directives  

Cancer.gov

A fact sheet about advance directives, which are legal documents that allow people to communicate their decisions about medical care to family, friends, and health care professionals in the event that they are unable to make those decisions themselves.

181

Improved Anode for a Direct Methanol Fuel Cell  

NASA Technical Reports Server (NTRS)

A modified chemical composition has been devised to improve the performance of the anode of a direct methanol fuel cell. The main feature of the modified composition is the incorporation of hydrous ruthenium oxide into the anode structure. This modification can reduce the internal electrical resistance of the cell and increase the degree of utilization of the anode catalyst. As a result, a higher anode current density can be sustained with a smaller amount of anode catalyst. These improvements can translate into a smaller fuel-cell system and higher efficiency of conversion. Some background information is helpful for understanding the benefit afforded by the addition of hydrous ruthenium oxide. The anode of a direct methanol fuel cell sustains the electro-oxidation of methanol to carbon dioxide in the reaction CH3OH + H2O--->CO2 + 6H(+) + 6e(-). An electrocatalyst is needed to enable this reaction to occur. The catalyst that offers the highest activity is an alloy of approximately equal numbers of atoms of the noble metals platinum and ruthenium. The anode is made of a composite material that includes high-surface-area Pt/Ru alloy particles and a proton-conducting ionomeric material. This composite is usually deposited onto a polymer-electrolyte (proton-conducting) membrane and onto an anode gas-diffusion/current-collector sheet that is subsequently bonded to the proton-conducting membrane by hot pressing. Heretofore, the areal density of noble-metal catalyst typically needed for high performance has been about 8 mg/cm2. However, not all of the catalyst has been utilized in the catalyzed electro-oxidation reaction. Increasing the degree of utilization of the catalyst would make it possible to improve the performance of the cell for a given catalyst loading and/or reduce the catalyst loading (thereby reducing the cost of the cell). The use of carbon and possibly other electronic conductors in the catalyst layer has been proposed for increasing the utilization of the catalyst by increasing electrical connectivity between catalyst particles. However, the relatively low density of carbon results in thick catalyst layers that impede the mass transport of methanol to the catalytic sites. Also, the electrical conductivity of carbon is less than 1/300th of typical metals. Furthermore, the polymer-electrolyte membrane material is acidic and most metals are not chemically stable in contact with it. Finally, a material that conducts electrons (but not protons) does not contribute to the needed transport of protons produced in the electro-oxidation reaction.

Valdez, Thomas; Narayanan, Sekharipuram

2005-01-01

182

Direction 2000.  

ERIC Educational Resources Information Center

Describes the Direction 2000 program at Mary Ward Catholic Secondary School in Toronto, which features large subject resource areas instead of classrooms, a schoolwide computer network developed in conjunction with Unisys Canada, computer education across the curriculum, and an automated approach to information retrieval. (DMM)

Schmidt, Wendy; Sisca, Laila

1992-01-01

183

Electrochemical oxidation of borohydride at nano-gold-based electrodes: Application in direct borohydride fuel cells  

Microsoft Academic Search

Nano-particulate gold-based materials along with commercial gold supported over carbon were investigated as possible alternative electrocatalysts for the oxidation of borohydride in alkaline media. Cyclic voltammetry experiments conducted on these materials show very high activity for the nano-particulate materials compared to the commercial materials despite a lower loading of gold (0.8mgcm?2 compared to 1.0mgcm?2) and lower interface area in the

Fazlil A. Coowar; Girts Vitins; Gary O. Mepsted; Susan C. Waring; Jacqueline A. Horsfall

2008-01-01

184

Direct Contact  

Microsoft Academic Search

\\u000a Early fictional depictions of direct contact with extraterrestrials, like those by Lasswitz and Wells, assumed that spacecraft\\u000a could carry living beings across interplanetary distances. Now we know that such journeys are possible for a civilization\\u000a at our level of technological development. We already have landed men on Earth’s moon and are planning to transport humans\\u000a to Mars. We also know

Michael A. G. Michaud

185

Improved Cathode Structure for a Direct Methanol Fuel Cell  

NASA Technical Reports Server (NTRS)

An improved cathode structure on a membrane/electrode assembly has been developed for a direct methanol fuel cell, in a continuing effort to realize practical power systems containing such fuel cells. This cathode structure is intended particularly to afford better cell performance at a low airflow rate. A membrane/electrode assembly of the type for which the improved cathode structure was developed (see Figure 1) is fabricated in a process that includes brush painting and spray coating of catalyst layers onto a polymer-electrolyte membrane and onto gas-diffusion backings that also act as current collectors. The aforementioned layers are then dried and hot-pressed together. When completed, the membrane/electrode assembly contains (1) an anode containing a fine metal black of Pt/Ru alloy, (2) a membrane made of Nafion 117 or equivalent (a perfluorosulfonic acid-based hydrophilic, proton-conducting ion-exchange polymer), (3) a cathode structure (in the present case, the improved cathode structure described below), and (4) the electrically conductive gas-diffusion backing layers, which are made of Toray 060(TradeMark)(or equivalent) carbon paper containing between 5 and 6 weight percent of poly(tetrafluoroethylene). The need for an improved cathode structure arises for the following reasons: In the design and operation of a fuel-cell power system, the airflow rate is a critical parameter that determines the overall efficiency, cell voltage, and power density. It is desirable to operate at a low airflow rate in order to obtain thermal and water balance and to minimize the size and mass of the system. The performances of membrane/electrode assemblies of prior design are limited at low airflow rates. Methanol crossover increases the required airflow rate. Hence, one way to reduce the required airflow rate is to reduce the effect of methanol crossover. Improvement of the cathode structure - in particular, addition of hydrophobic particles to the cathode - has been demonstrated to mitigate the effects of crossover and decrease the airflow required.

Valdez, Thomas; Narayanan, Sekharipuram

2005-01-01

186

Nanostructured self-assembly materials from neat and aqueous solutions of C18 lipid pro-drug analogues of Capecitabine?a chemotherapy agent. Focus on nanoparticulate cubosomes? of the oleyl analogue  

SciTech Connect

A series of prodrug analogues based on the established chemotherapy agent, 5-fluorouracil, have been prepared and characterized. C18 alkyl and alkenyl chains with increasing degree of unsaturation were attached to the N{sup 4} position of the 5-fluorocytosine (5-FC) base via a carbamate bond. Physicochemical characterization of the prodrug analogues was carried out using a combination of differential scanning calorimetry, cross-polarized optical microscopy, X-ray diffraction and small-angle X-ray scattering. The presence of a monounsaturated oleyl chain was found to promote lyotropic liquid crystalline phase formation in excess water with a fluid lamellar phase observed at room temperature and one or more bicontinuous cubic phases at 37 C. The bulk phase was successfully dispersed into liposomes or cubosomes at room and physiological temperature respectively. In vitro toxicity of the nanoparticulate 5-FCOle dispersions was evaluated against several normal and cancer cell types over a 48 h period and exhibited an IC{sub 50} of 100 {micro}M against all cell types. The in vivo efficacy of 5-FCOle cubosomes was assessed against the highly aggressive mouse 4T1 breast cancer model and compared to Capecitabine (a water-soluble commercially available 5-FU prodrug) delivered at the same dosages. After 21 days of treatment, the 0.5 mmol 5-FCOle treatment group exhibited a significantly smaller average tumour volume than all other treatment groups including Capecitabine at similar dosage. These results exemplify the potential of self-assembled amphiphile prodrugs for delivery of bioactives in vivo.

Gong, Xiaojuan; Moghaddam, Minoo J.; Sagnella, Sharon M.; Conn, Charlotte E.; Mulet, Xavier; Danon, Stephen J.; Waddington, Lynne J.; Drummond, Calum J.

2012-02-06

187

Recent advances in direct methanol fuel cells at Los Alamos National Laboratory  

NASA Astrophysics Data System (ADS)

This paper describes recent advances in the science and technology of direct methanol fuel cells (DMFCs) made at Los Alamos National Laboratory (LANL). The effort on DMFCs at LANL includes work devoted to portable power applications, funded by the Defense Advanced Research Project Agency (DARPA), and work devoted to potential transport applications, funded by the US DOE. We describe recent results with a new type of DMFC stack hardware that allows to lower the pitch per cell to 2 mm while allowing low air flow and air pressure drops. Such stack technology lends itself to both portable power and potential transport applications. Power densities of 300 W/l and 1 kW/l seem achievable under conditions applicable to portable power and transport applications, respectively. DMFC power system analysis based on the performance of this stack, under conditions applying to transport applications (joint effort with U.C. Davis), has shown that, in terms of overall system efficiency and system packaging requirements, a power source for a passenger vehicle based on a DMFC could compete favorably with a hydrogen-fueled fuel cell system, as well as with fuel cell systems based on fuel processing on board. As part of more fundamental studies performed, we describe optimization of anode catalyst layers in terms of PtRu catalyst nature, loading and catalyst layer composition and structure. We specifically show that, optimized content of recast ionic conductor added to the catalyst layer is a sensitive function of the nature of the catalyst. Other elements of membrane/electrode assembly (MEA) optimization efforts are also described, highlighting our ability to resolve, to a large degree, a well-documented problem of polymer electrolyte DMFCs, namely "methanol crossover". This was achieved by appropriate cell design, enabling fuel utilization as high as 90% in highly performing DMFCs.

Ren, Xiaoming; Zelenay, Piotr; Thomas, Sharon; Davey, John; Gottesfeld, Shimshon

188

Future direction of direct writing  

NASA Astrophysics Data System (ADS)

Direct write technology using special inks consisting of finely dispersed metal nanoparticles in liquid is receiving an undivided attention in recent years for its wide range of applicability in modern electronic industry. The application of this technology covers radio frequency identification-tag (RFID-tag), flexible-electronics, organic light emitting diodes (OLED) display, e-paper, antenna, bumpers used in flip-chip, underfilling, frit, miniresistance applications and biological uses, artificial dental applications and many more. In this paper, the authors have reviewed various direct write technologies on the market and discussed their advantages and shortfalls. Emphasis has given on microdispensing deposition write (MDDW), maskless mesoscale materials deposition (M3D), and ink-jet technologies. All of these technologies allow printing various patterns without employing a mask or a resist with an enhanced speed with the aid of computer. MDDW and M3D are capable of drawing patterns in three-dimension and MDDW, in particular, is capable of writing nanoinks with high viscosity. However, it is still far away for direct write to be fully implemented in the commercial arena. One of the hurdles to overcome is in manufacturing conductive inks which are chemically and physically stable, capable of drawing patterns with acceptable conductivity, and also capable of drawing patterns with acceptable adhesiveness with the substrates. The authors have briefly discussed problems involved in manufacturing nanometal inks to be used in various writing devices. There are numerous factors to be considered in manufacturing such inks. They are reducing agents, concentrations, oxidation, compact ability allowing good conductivity, and stability in suspension.

Kim, Nam-Soo; Han, Kenneth N.

2010-11-01

189

Direct visualization of gastrointestinal tract with lanthanide-doped BaYbF5 upconversion nanoprobes.  

PubMed

Nanoparticulate contrast agents have attracted a great deal of attention along with the rapid development of modern medicine. Here, a binary contrast agent based on PAA modified BaYbF5:Tm nanoparticles for direct visualization of gastrointestinal (GI) tract has been designed and developed via a one-pot solvothermal route. By taking advantages of excellent colloidal stability, low cytotoxicity, and neglectable hemolysis of these well-designed nanoparticles, their feasibility as a multi-modal contrast agent for GI tract was intensively investigated. Significant enhancement of contrast efficacy relative to clinical barium meal and iodine-based contrast agent was evaluated via X-ray imaging and CT imaging in vivo. By doping Tm(3+) ions into these nanoprobes, in vivo NIR-NIR imaging was then demonstrated. Unlike some invasive imaging modalities, non-invasive imaging strategy including X-ray imaging, CT imaging, and UCL imaging for GI tract could extremely reduce the painlessness to patients, effectively facilitate imaging procedure, as well as rationality economize diagnostic time. Critical to clinical applications, long-term toxicity of our contrast agent was additionally investigated in detail, indicating their overall safety. Based on our results, PAA-BaYbF5:Tm nanoparticles were the excellent multi-modal contrast agent to integrate X-ray imaging, CT imaging, and UCL imaging for direct visualization of GI tract with low systemic toxicity. PMID:23849344

Liu, Zhen; Ju, Enguo; Liu, Jianhua; Du, Yingda; Li, Zhengqiang; Yuan, Qinghai; Ren, Jinsong; Qu, Xiaogang

2013-10-01

190

Freeze Drying: Potential for Powdered Nanoparticulate Product  

Microsoft Academic Search

Nanoparticles were prepared by using an emulsion solvent evaporation method. Further, the drying of an anti-cancer drug of proprietary nature (nanosized) was carried out by a freeze-drying technique to get a free-flowing powder. A systematic approach was developed to study the freeze-drying technique for polymeric nanoparticles. Initially, the freeze-thawing experiments were carried out with varying concentrations of cryoprotectants to screen

V. V. Patil; P. P. Dandekar; V. B. Patravale; B. N. Thorat

2010-01-01

191

Syntheses of perovskite oxides nanoparticles La 1? x Sr x MO 3? ? (M = Co and Cu) as anode electrocatalyst for direct methanol fuel cell  

Microsoft Academic Search

Conventionally, noble metals such as Pt and Pt–Ru bimetallic system were utilized as electrocatalyst for methanol oxidation in acid and alkaline media. However, during the oxidation reaction, these noble metals are poisoned by the methanol oxidation intermediates, such as CO or COH species. Therefore, the utilization of electrochemically active conducting metal oxide (substituted perovskite oxide) may be a solution for

Ho-Chieh Yu; Kuan-Zong Fung; Tz-Chiang Guo; Wen-Li Chang

2004-01-01

192

Advance care directives  

MedlinePLUS

Living will; Power of attorney; DNR - advance directive; Do not resuscitate - advance directive ... of medical care you should receive. Using an advance directive, you can tell your doctor what medical treatment ...

193

Direct Current Transformer.  

National Technical Information Service (NTIS)

A direct current transformer was built in which the primary consists of an elongated strip of superconductive material, across the ends of which is applied a direct current potential. Parallel and closely spaced to the primary is positioned a transformer ...

E. W. Urban S. M. Khanna

1977-01-01

194

Directed Fluid Sheets.  

National Technical Information Service (NTIS)

This paper is concerned mainly with incompressible inviscid fluid sheets but the incompressible linearly viscous fluid sheet is also considered. The development is based on a direct formulation using the two-dimensional theory of directed media called Cos...

A. E. Green P. M. Naghdi

1976-01-01

195

Advance Directives (Psychiatric)  

MedlinePLUS

... org/ (800) 950-NAMI; info@nami.org ©2014 Advance Directives by Ronald S. Honberg National Director for Policy and ... psychosurgery from their scope. Laws specifically authorizing psychiatric advance directives have been enacted in twelve states. The first ...

196

Directional shear force microscopy  

SciTech Connect

We describe a technique, based on shear force microscopy, that allows one to detect shear forces in a chosen direction at the nanometer scale. The lateral direction of an oscillating probe tip is determined by selecting which of the four quadrants are excited on the piezo driver. The shear forces depend directly on this lateral direction if structural anisotropies are present, as confirmed with polydiacetylene monolayers.

Burns, A. R.; Carpick, R. W.

2001-01-15

197

Directed energy architectures  

SciTech Connect

This report discusses the roles directed energy could play in strategic defense, assesses their likely effectiveness, and outlines the important complementarity between directed and kinetic energy, which appears to be pivotal to the development of robust defenses. Directed energy concepts could provide adequate kill rates that are relatively insensitive to fast, compact launches. Midcourse applications are based on the robust discrimination ability of directed energy weapons.

Canavan, G.H.

1988-05-01

198

Directed energy architectures  

Microsoft Academic Search

This report discusses the roles directed energy could play in strategic defense, assesses their likely effectiveness, and outlines the important complementarity between directed and kinetic energy, which appears to be pivotal to the development of robust defenses. Directed energy concepts could provide adequate kill rates that are relatively insensitive to fast, compact launches. Midcourse applications are based on the robust

Canavan

1988-01-01

199

Preparation of platinum–ruthenium onto solid polymer electrolyte membrane and the application to a DMFC anode  

Microsoft Academic Search

The ‘impregnation–reduction method’ has been investigated as a tool for the preparation of a direct methanol fuel cell (DMFC) anode. In this method, PtRu electrocatalysts were directly bonded onto a polymer electrolyte membrane by the chemical reduction of a mixture of Pt and Ru complexes impregnated in the membrane. The deposited PtRu particles were embedded in the 3–4 ?m region

Naoko Fujiwara; Kazuaki Yasuda; Tsutomu Ioroi; Zyun Siroma; Yoshinori Miyazaki

2002-01-01

200

Direct bonding and beyond  

NASA Astrophysics Data System (ADS)

We present a number of recent evaluations of direct bonding, a glueless bonding technology, performed under ambient conditions. If combined with bond-strengthening, this geometry-conserving technology is well suited for an application in far ultraviolet immersion lithography. Our term beyond direct bonding refers to taking at least one additional technological step beyond direct bonding, involving chemical interface engineering, advanced silicon-on-insulator (SOI) technology, whereby the unwanted influence of dilatation mismatch is obviated. The combination of successive direct bonding, nanopillar lattice structures and silicon-technological engineering makes it possible for us to arrange quantum dots, wires, and planes in a transversal cascade. We also address the interrelationship between direct bonding and elasticity, as well as plasticity; the latter is in relation to direct bonded glass wafers that are thermally treated to create the geometric shape, e.g., required for specific lab-on-a-chip components with a three-dimensional overall configuration.

Haisma, Jan; Hattu, Nico; (Dook) Pulles, J. T. C. M.; Steding, Esther; Vervest, Jan C. G.

2007-09-01

201

Direct bonding and beyond  

Microsoft Academic Search

We present a number of recent evaluations of direct bonding, a glueless bonding technology, performed under ambient conditions. If combined with bond-strengthening, this geometry-conserving technology is well suited for an application in far ultraviolet immersion lithography. Our term beyond direct bonding refers to taking at least one additional technological step beyond direct bonding, involving chemical interface engineering, advanced silicon-on-insulator (SOI)

Jan Haisma; Nico Hattu; Esther Steding; Jan C. G. Vervest

2007-01-01

202

Watson's ANOVA for Directions.  

National Technical Information Service (NTIS)

Watson's ANOVA technique for analyzing unit vectors in p dimensions has been usually used with directional data, with p=2 or 3. It is shown how the one-way ANOVA can be extended to a multiway layout, and an example is given using coal-cleat directions. Th...

M. A. Stephens

1992-01-01

203

Modelling Directional Solidification  

NASA Technical Reports Server (NTRS)

The long range goal of this program has been to develop an improved understanding of phenomena of importance to directional solidification, in order to enable explanation and prediction of differences in behavior between solidification on Earth and in space. Current emphasis is on determining the influence of perturbations on directional solidification.

Wilcox, William R.; Regel, Liya L.; Zhou, Jian; Yuan, Weijun

1992-01-01

204

Direct Support Workforce Development.  

ERIC Educational Resources Information Center

The fourteen brief articles in this theme issue all examine challenges in the development of direct support staff working with people who have developmental disabilities. The articles also include the views of direct support providers and people with developmental disabilities themselves, as well as examples of strategies used by provider agencies…

Impact, 1998

1998-01-01

205

Direct current transformer  

NASA Technical Reports Server (NTRS)

A direct current transformer in which the primary consists of an elongated strip of superconductive material, across the ends of which is direct current potential is described. Parallel and closely spaced to the primary is positioned a transformer secondary consisting of a thin strip of magnetoresistive material.

Khanna, S. M.; Urban, E. W. (inventors)

1979-01-01

206

Packing Directed Circuits Fractionally  

Microsoft Academic Search

LetG be a digraph, and letk=1, such that no “fractional” packing of directed circuits ofG has value >k, when every vertex is given “capacity” 1. We prove there is a set ofO (k logk logk) vertices meeting all directed circuits ofG.

Paul D. Seymour

1995-01-01

207

Directed energy overview  

Microsoft Academic Search

Directed energy weapons can add significantly to the effectiveness of a Strategic Defense System (SDS) by complementing the capabilty of phase I kinetic energy weapons. Component development for each of the directed energy concepts is progressing well. The chemical laser and neutral particle beam programs are nearing the stage where component integration tests are essential for establishing engineering proof-of-principle. For

Neil Griff

1990-01-01

208

Variable Direction Force Coupler.  

National Technical Information Service (NTIS)

A variable direction force coupler is described for transmitting a reciprocating force along a selectable curved path. The coupler consists of a flexible tube filled with rigid balls, including force transmission members at each end which are adapted to c...

W. H. Hespenhide

1970-01-01

209

Directional Gear Ratio Transmission.  

National Technical Information Service (NTIS)

Epicyclic gear transmissions which transmit output at a gear ratio dependent only upon the input's direction are considered. A transmission housing envelops two epicyclic gear assemblies, and has shafts extending from it. One shaft is attached to a sun ge...

A. E. Lefever

1982-01-01

210

AISI direct steelmaking program  

SciTech Connect

AISI with co-funding from DOE has initiated a research and development program aimed at the development of a new process for direct steelmaking, and the program is discussed in this document. The project is expected to cost about $30 million over a three-year period, with the government providing approximately 77 percent of the funds and AISI the balance. In contrast to current steelmaking processes which are largely open and batch, the direct steelmaking process would be closed and continuous. Further, it would use coal directly, thereby avoiding the need for coke ovens. The second year of the Direct Steelmaking Program (November 29, 1989, through November 28, 1990) was a year of significant accomplishment. The various research programs proceeded essentially on schedule and the pilot plant, the centerpiece of the program, was completed about three months behind schedule but began operation in almost a picture-perfect manner. This report presents the last years accomplishments.

Aukrust, E.

1991-01-09

211

THE DIRECTED DAYDREAM TECHNIQUE  

Microsoft Academic Search

SCENES ARE SUGGESTED TO THE PATIENT AS BASES FOR DAYDREAMING. THE 5 BASIC PRINCIPLES OF DIRECTED DAYDREAM THERAPY ARE SYMBOL CONFRONTATION, FEEDING, RECONCILIATION, MAGIC FLUIDS, AND EXHAUSTING AND KILLING. ILLUSTRATIVE CASE EXCERPTS ARE GIVEN.

MAX HAMMER

1967-01-01

212

The Directed Case Method  

NSDL National Science Digital Library

Many instructors think that by incorporating case study analysis into the science classroom they will sacrifice course content. The directed case method, however, is a proven strategy for deepening and solidifying understanding of facts and concepts when

Curtin, Leslie N.; Cliff, William H.

2000-09-01

213

Magnetostrictive Direct Drive Motors.  

National Technical Information Service (NTIS)

Developing magnetostrictive direct drive research motors to power robot joints is discussed. These type motors are expected to produce extraordinary torque density, to be able to perform microradian incremental steps and to be self-braking and safe with t...

D. Naik P. H. Dehoff

1990-01-01

214

Directed TreeWidth  

Microsoft Academic Search

We generalize the concept of tree-width to directed graphs and prove that every directed graph with no “haven” of large order has small tree-width. Conversely, a digraph with a large haven has large tree-width. We also show that the Hamilton cycle problem and other NP-hard problems can be solved in polynomial time when restricted to digraphs of bounded tree-width.

Thor Johnson; Neil Robertson; Paul D. Seymour; Robin Thomas

2001-01-01

215

Direct conversion technology  

Microsoft Academic Search

The overall objective of the Direct Conversion Technology task is to develop an experimentally verified technology base for promising direct conversion systems that have potential application for energy conservation in the end-use sectors. This report contains progress of research on the Alkali Metal Thermal-to-Electric Converter (AMTEC), and on the Two-Phase Liquid-Metal Magnetohydrodynamic Electrical Generator (LMMHD) for the period January 1,

Paul F. Massier; C. P. Bankston; R. Williams; M. Underwood; B. Jeffries-Nakamura; G. Fabris

1989-01-01

216

Direct conversion technology  

Microsoft Academic Search

The overall objective of the Direct Conversion Technology task is to develop an experimentally verified technology base for promising direct thermal-to-electric energy conversion systems that have potential application for energy conservation in the end-use sectors. This report contains progress of research on the Alkali Metal Thermal-to-Electric Converter (AMTEC), and on the Two-Phase Liquid-Metal MHD Electrical Generator (LMMHD) for the period

P. F. Massier; C. P. Bankston; G. Fabris; L. D. Kirol

1988-01-01

217

BIOCHEMISTRY: Directing Biosynthesis  

NSDL National Science Digital Library

Access to the article is free, however registration and sign-in are required. Genetic engineering is revealing biosynthetic pathways for the synthesis of small molecules and avenues toward cheaper syntheses. Projects aiming to direct the biosynthesis of small molecules may seek to make new compounds, make natural compounds in unnatural organisms, or alter the metabolic flux through a particular biosynthetic pathway. This Perspective presents three examples that illustrate the state of directed biosynthesis and highlight its future prospects.

Michael A. Fischbach (Harvard Medical School; Harvard University;Department of Biological Chemistry and Molecular Pharmacology; HHMI and the Department of Chemistry and Chemical Biology); Christopher T. Walsh (Harvard Medical School;Department of Biological Chemisty and Molecular Pharmacology)

2006-10-27

218

Refrigerant directly cooled capacitors  

DOEpatents

The invention is a direct contact refrigerant cooling system using a refrigerant floating loop having a refrigerant and refrigeration devices. The cooling system has at least one hermetic container disposed in the refrigerant floating loop. The hermetic container has at least one electronic component selected from the group consisting of capacitors, power electronic switches and gating signal module. The refrigerant is in direct contact with the electronic component.

Hsu, John S. (Oak Ridge, TN); Seiber, Larry E. (Oak Ridge, TN); Marlino, Laura D. (Oak Ridge, TN); Ayers, Curtis W. (Kingston, TN)

2007-09-11

219

Directional acoustic underwater thruster  

Microsoft Academic Search

This paper described a novel directional underwater thruster which could change thrust directions without any moving parts. When the underwater thruster moved along a non-vertical angle, it could produce straight backward thrust of 2.3mN and lateral thrust of 0.6mN in parallel on the device surface, with the total thrust\\/weight ration of 2:1. Water jet was streamed out by high intensity

Z. Wang; J. Zhu; X. Qiu; R. Tang; C. Yu; J. Oiler; E. Kim; H. Yu

2011-01-01

220

Estimating directional epistasis  

PubMed Central

Epistasis, i.e., the fact that gene effects depend on the genetic background, is a direct consequence of the complexity of genetic architectures. Despite this, most of the models used in evolutionary and quantitative genetics pay scant attention to genetic interactions. For instance, the traditional decomposition of genetic effects models epistasis as noise around the evolutionarily-relevant additive effects. Such an approach is only valid if it is assumed that there is no general pattern among interactions—a highly speculative scenario. Systematic interactions generate directional epistasis, which has major evolutionary consequences. In spite of its importance, directional epistasis is rarely measured or reported by quantitative geneticists, not only because its relevance is generally ignored, but also due to the lack of simple, operational, and accessible methods for its estimation. This paper describes conceptual and statistical tools that can be used to estimate directional epistasis from various kinds of data, including QTL mapping results, phenotype measurements in mutants, and artificial selection responses. As an illustration, I measured directional epistasis from a real-life example. I then discuss the interpretation of the estimates, showing how they can be used to draw meaningful biological inferences.

Le Rouzic, Arnaud

2014-01-01

221

Directed network modules  

NASA Astrophysics Data System (ADS)

A search technique locating network modules, i.e. internally densely connected groups of nodes in directed networks is introduced by extending the clique percolation method originally proposed for undirected networks. After giving a suitable definition for directed modules we investigate their percolation transition in the Erdos Rényi graph both analytically and numerically. We also analyse four real-world directed networks, including Google's own web-pages, an email network, a word association graph and the transcriptional regulatory network of the yeast Saccharomyces cerevisiae. The obtained directed modules are validated by additional information available for the nodes. We find that directed modules of real-world graphs inherently overlap and the investigated networks can be classified into two major groups in terms of the overlaps between the modules. Accordingly, in the word-association network and Google's web-pages, overlaps are likely to contain in-hubs, whereas the modules in the email and transcriptional regulatory network tend to overlap via out-hubs.

Palla, Gergely; Farkas, Illés J.; Pollner, Péter; Derényi, Imre; Vicsek, Tamás

2007-06-01

222

Direct conversion technology  

NASA Astrophysics Data System (ADS)

The overall objective of the Direct Conversion Technology task is to develop an experimentally verified technology base for promising direct conversion systems that have potential application for energy conservation in the end-use sectors. This report contains progress of research on the Alkali Metal Thermal-to-Electric Converter (AMTEC), and on the Two-Phase Liquid-Metal Magnetohydrodynamic Electrical Generator (LMMHD) for the period January 1, 1989 through December 31, 1989. Research on these concepts was initiated during October 1987. Reports prepared on previous occasions contain discussions on the following other direct conversion concepts: thermoelectric, pyroelectric, thermionic, thermophotovoltaic, thermoacoustic, thermomagnetic, thermoelastic (nitinol heat engines); and also, more complete discussions of AMTEC and LMMHD systems.

Massier, Paul F.; Bankston, C. P.; Williams, R.; Underwood, M.; Jeffries-Nakamura, B.; Fabris, G.

1989-12-01

223

Directional acoustic underwater thruster.  

PubMed

This study describes a tested prototype for a controllable directional underwater thruster with no moving parts. During operation, a high-intensity acoustic wave creates directional water jets and the device moves itself in the opposite direction. When the underwater thruster moves along a non-vertical angle, it can produce straight backward thrust of 2.3 mN and lateral thrust of 0.6 mN in parallel with the device surface, with a total thrust-to-weight ratio of 2:1. To enhance the acoustic streaming effect, a self-focusing acoustic transducer (SFAT) with air reflectors is used to focus the acoustic wave. PMID:21693390

Wang, Ziyu; Qiu, Xiaotun; Zhu, Jie; Oiler, Jon; Chen, Shih-Jui; Shi, Jing; Kim, Eun; Yu, Hongyu

2011-06-01

224

Directed energy overview  

NASA Astrophysics Data System (ADS)

Directed energy weapons can add significantly to the effectiveness of a Strategic Defense System (SDS) by complementing the capabilty of phase I kinetic energy weapons. Component development for each of the directed energy concepts is progressing well. The chemical laser and neutral particle beam programs are nearing the stage where component integration tests are essential for establishing engineering proof-of-principle. For the somewhat less mature ground-based free electron laser technology, device development will be emphasized during the next several years. Development of the acquisition, tracking and pointing (ATP) program will continue at a fast pace, with an exciting proof-of-principle test to occur in space in early 1990. The directed energy program remains on track to provide information to support a national decision on strategic defense in the 1991/1993 timeframe.

Griff, Neil

1990-06-01

225

Direct detection of WIMPs  

NASA Astrophysics Data System (ADS)

A generic weakly interacting massive particle (WIMP) is one of the most attractive candidates to account for the cold dark matter in our Universe, since it would be thermally produced with the correct abundance to account for the observed dark matter density. WIMPs can be searched for directly through their elastic scattering with a target material, and a variety of experiments are currently operating or planned with this aim. In these notes we overview the theoretical calculation of the direct detection rate of WIMPs as well as the different detection signals. We discuss the various ingredients (from particle physics and astrophysics) that enter the calculation and review the theoretical predictions for the direct detection of WIMPs in particle physics models.

Cerdeño, D. G.; Green, A. M.

226

Directional spherical multipole wavelets  

SciTech Connect

We construct a family of admissible analysis reconstruction pairs of wavelet families on the sphere. The construction is an extension of the isotropic Poisson wavelets. Similar to those, the directional wavelets allow a finite expansion in terms of off-center multipoles. Unlike the isotropic case, the directional wavelets are not a tight frame. However, at small scales, they almost behave like a tight frame. We give an explicit formula for the pseudodifferential operator given by the combination analysis-synthesis with respect to these wavelets. The Euclidean limit is shown to exist and an explicit formula is given. This allows us to quantify the asymptotic angular resolution of the wavelets.

Hayn, Michael; Holschneider, Matthias [Institute for Mathematics, University Potsdam, Am Neuen Palais 10, 144 69 Potsdam (Germany)

2009-07-15

227

Directed flux motor  

NASA Technical Reports Server (NTRS)

A directed flux motor described utilizes the directed magnetic flux of at least one magnet through ferrous material to drive different planetary gear sets to achieve capabilities in six actuated shafts that are grouped three to a side of the motor. The flux motor also utilizes an interwoven magnet configuration which reduces the overall size of the motor. The motor allows for simple changes to modify the torque to speed ratio of the gearing contained within the motor as well as simple configurations for any number of output shafts up to six. The changes allow for improved manufacturability and reliability within the design.

Wilson, Andrew (Inventor); Punnoose, Andrew (Inventor); Strausser, Katherine (Inventor); Parikh, Neil (Inventor)

2011-01-01

228

Direct Conversion Technology  

SciTech Connect

The overall objective of the Direct Conversion Technology task is to develop an experimentally verified technology base for promising direct conversion systems that have potential application for energy conservation in the end-use sectors. Initially, two systems were selected for exploratory research and advanced development. These are Alkali Metal Thermal-to-Electric Converter (AMTEC) and Two-Phase Liquid Metal MD Generator (LMMHD). This report describes progress that has been made during the first six months of 1992 on research activities associated with these two systems. (GHH)

Back, L.H.; Fabris, G.; Ryan, M.A.

1992-07-01

229

The Four Directions  

ERIC Educational Resources Information Center

This article presents the Native American cultural symbol, the Four Directions, as a sign that is culturally evident and inter-tribally significant. Through understanding the significance of the symbol, a deeper understanding is possible for non-Natives, especially an understanding of the Native Americans' relationship between their artwork and…

Willis, Steve

2005-01-01

230

Direct Satellite Broadcasting.  

National Technical Information Service (NTIS)

The Symposium on Direct Satellite Broadcasting (DSB), held in Dublin 23-25 May 1977, included 17 papers discussing the potentialities and problems of this new medium, which is to bring television to private homes via either 1-meter paraboloidal dishes or ...

N. M. Blachman

1977-01-01

231

Directional borehole radar calibration  

Microsoft Academic Search

We are developing an innovative low-noise directional borehole radar system. Harsh and changing operating environments are a challenge to the low-noise sensitive electronic design. Additionally a system with such high sensitivity is susceptible to temperature changes and to component parameter variations. Therefore a calibration module was developed to calibrate the overall measurement system with a test signal generator. This calibration

O. Borchert; K. Behaimanot; A. Glasmachers

2009-01-01

232

Implementing the WEEE Directive  

Microsoft Academic Search

During the 1980s, industrialised countries in Europe experienced a shortage of landfills. This lead National Governments and EU authorities to investigate regulations to direct waste streams to recycling and incineration. Besides packaging, cars and batteries, waste from electronic and electric products was identified as a major component of the generic waste stream which could be easily diverted to alternative processes

K. Hieronymi

2001-01-01

233

The Directed Case Method.  

ERIC Educational Resources Information Center

Provides an example of a directed case on human anatomy and physiology. Uses brief real life newspaper articles and clinical descriptions of medical reference texts to describe an actual, fictitious, or composite event. Includes interrelated human anatomy and physiology topics in the scenario. (YDS)

Cliff, William H.; Curtin, Leslie Nesbitt

2000-01-01

234

Dragonfly directional sensor  

NASA Astrophysics Data System (ADS)

This paper discusses the concept and hardware development of an all fiber-based, solid state, coherent array directional sensor that can locate and track bright objects against a darker background. This sensor is not an imager. It relies on the inherent structure of the global fiber distribution. Methods for characterizing and calibrating hardware embodiments are also presented.

Geary, Joe; Blackwell, Lisa; Edwards, Tim; Dargie, Mike

2013-02-01

235

Is Direct Mail Dead?  

ERIC Educational Resources Information Center

Varied approaches taken to bringing vitality to direct mail fundraising campaigns are described for 10 institutions: Northern Arizona University, Georgetown University (District of Columbia); Miami University (Ohio), Kansas University, Pennsylvania State University, St. Ignatius High School (Ohio); Metropolitan State University (Minnesota),…

Hauk, Jeff; Burdenski, Robert A.

1998-01-01

236

Generalized Partial Directed Coherence  

Microsoft Academic Search

This paper re-examines the definition of partial directed coherence (PDC) which was recently introduced as a linear frequency-domain quantifier of the multivariate relationship between simultaneously observed time series for application in functional connectivity inference in neuroscience. The present reappraisal aims at improving PDC's performance under scenarios that involve severely unbalanced predictive modelling errors (innovations noise). The present modification turns out

L. A. Baccald; F. de Medicina

2007-01-01

237

CGH Future Directions  

Cancer.gov

Looking ahead, we have three major future directions that we believe will help us push forward in achieving NCI’s goal of advancing global cancer research, building expertise, and leveraging resources across nations to address the challenges of cancer and reduce cancer deaths worldwide.

238

Laser assisted direct manufacturing  

Microsoft Academic Search

Direct Laser Manufacturing (DLM) with coaxial powder injection (TRUMPF DMD 505 installation) was applied for fabrication of 3D objects from metallic and ceramic powder. One of the advantages of DLM is the possibility to build functionally graded objects in one-step manufacturing cycle by application of a 2-channel powder feeder. Several models with different types of material gradients (smooth, sharp, periodic)

Ph. Bertrand; I. Smurov

2007-01-01

239

Core Directions in HRD.  

ERIC Educational Resources Information Center

This document consists of four papers presented at a symposium on core directions in human resource development (HRD) moderated by Verna Willis at the 1996 conference of the Academy of Human Resource Development. "Reengineering the Organizational HRD Function: Two Case Studies" (Neal Chalofsky) reports an action research study in which the…

1996

240

Direct anonymous attestation  

Microsoft Academic Search

This paper describes the direct anonymous attestation scheme (DAA). This scheme was adopted by the Trusted Computing Group (TCG) as the method for remote authentication of a hardware module, called Trusted Platform Module (TPM), while preserving the privacy of the user of the platform that contains the module. DAA can be seen as a group signature without the feature that

Ernest F. Brickell; Jan Camenisch; Liqun Chen

2004-01-01

241

Directional gamma detector  

DOEpatents

An improved directional gamma radiation detector has a collector sandwiched etween two layers of insulation of varying thicknesses. The collector and insulation layers are contained within an evacuated casing, or emitter, which releases electrons upon exposure to gamma radiation. Delayed electrons and electrons entering the collector at oblique angles are attenuated as they pass through the insulation layers on route to the collector.

LeVert, Francis E. (Downers Grove, Knoxville, TN); Cox, Samson A. (Downers Grove, IL)

1981-01-01

242

Fermilab Library directions  

Microsoft Academic Search

In this document, we indicate our current thinking about the directions of the Fermilab Library. The ideas relate to the preprint management issue in a number of ways. The ideas are subject to revision as we come to understand what is possible as well as what is needed by the Laboratory community. This document should therefore be regarded as our

P. Garrett; D. Ritchie

1990-01-01

243

Directional solidification of superalloys  

US Patent & Trademark Office Database

This invention relates to the directional solidification of superalloys, in particular nickel-based superalloys, by imposition of a predetermined temperature profile in the solidification front and, depending on the desired results, a predetermined rate of advance of said solidification front, whereas castings of markedly superior fatigue resistance are produced.

1990-10-23

244

Coatings for Directional Eutectics.  

National Technical Information Service (NTIS)

Coating compositions were evaluated for oxidation protection of directionally solidified composite alloy NiTaC-13. These coatings included three NiCrAlY compositions (30-5-1, 25-10-1 and 20-15-1), two FeCrAlY compositions (30-5-1 and 25-10-1), a CoCrAlY c...

M. R. Jackson J. R. Rairden L. V. Hampton

1974-01-01

245

Directional solidification of superalloys  

NASA Technical Reports Server (NTRS)

This invention relates to the directional solidification of superalloys, in particular nickel-based superalloys, by imposition of a predetermined temperature profile in the solidification front and, depending on the desired results, a predetermined rate of advance of said solidification front, whereas castings of markedly superior fatigue resistance are produced.

Schmidt, Deborah Diane (inventor); Alter, Wendy Sue (inventor); Hamilton, William David (inventor)

1990-01-01

246

[Direct biosynthesis of ethylene].  

PubMed

Ethylene is the most widely used petrochemical feedstock globally. The development of bio-ethylene is essential due to limited fossil fuels and rising oil prices. Bio-ethylene is produced primarily by the dehydration of ethanol, but can alternatively be directly produced from ethylene biosynthesis pathways in plants, algae, or microorganisms by using cheap and renewable substrates. This review addressed the biosynthesis of ethylene in plants and microorganisms, the characterization of key enzymes, genetic engineering strategies for ethylene biosynthesis in microorganisms, and evaluated its perspective and successful cases toward the industrial application. The direct production of bio-ethylene from a biological process in situ is promising to supplement and even replace the petrochemical ethylene production. PMID:24432658

Sun, Zhilan; Chen, Yifeng

2013-10-01

247

Irradiation direction from texture.  

PubMed

We present a theory of image texture resulting from the shading of corrugated (three-dimensional textured) surfaces, Lambertian on the micro scale, in the domain of geometrical optics. The derivation applies to isotropic Gaussian random surfaces, under collimated illumination, in normal view. The theory predicts the structure tensors from either the gradient or the Hessian of the image intensity and allows inferences of the direction of irradiation of the surface. Although the assumptions appear prima facie rather restrictive, even for surfaces that are not at all Gaussian, with the bidirectional reflectance distribution function far from Lambertian and vignetting and multiple scattering present, we empirically recover the direction of irradiation with an accuracy of a few degrees. PMID:14570101

Koenderink, Jan J; Pont, Sylvia C

2003-10-01

248

Direct heating surface combustor  

NASA Technical Reports Server (NTRS)

The combustor utilizes a non-adiabatic flame to provide low-emission combustion for gas turbines. A fuel-air mixture is directed through a porous wall, the other side of which serves as a combustion surface. A radiant heat sink disposed adjacent to and spaced from the combustion surface controls the combustor flame temperature in order to prevent the formation of oxides of nitrogen. A secondary air flow cools the heat sink. Additionally, up to 100% of secondary air flow is mixed with the combustion products at the direct heating surface combustor to dilute such products thereby reducing exit temperature. However, if less than 100% secondary air is mixed to the combustor, the remainder may be added to the combustion products further downstream.

Beremand, D. G.; Shire, L. I.; Mroz, T. S. (inventors)

1978-01-01

249

Modelling directional solidification  

NASA Technical Reports Server (NTRS)

An improved understanding of the phenomena of importance to directional solidification is attempted to enable explanation and prediction of differences in behavior between solidification on Earth and in space. Emphasis is now on experimentally determining the influence of convection and freezing rate fluctuations on compositional homogeneity and crystalline perfection. A correlation is sought between heater temperature profiles, buoyancy-driven convection, and doping inhomogeneities using naphthalene doped with anthracene. The influence of spin-up/spin-down is determined on compositional homogeneity and microstructure of indium gallium antimonide. The effect is determined of imposed melting - freezing cycles on indium gallium antimonide. The mechanism behind the increase of grain size caused by using spin-up/spin-down in directional solidification of mercury cadimum telluride is sought.

Wilcox, William R.

1987-01-01

250

New direct thrombin inhibitors  

Microsoft Academic Search

Direct thrombin inhibitors (DTIs) are a class of anticoagulants that bind selectively to thrombin and block its interaction\\u000a with its substrates. Dabigatran etexilate and AZD0837, the new generation of DTIs, are now under intense development, and\\u000a are potentially of great interest for internists. Dabigatran etexilate is a potent, non-peptidic small molecule that specifically\\u000a and reversibly inhibits both free and clot-bound

Alessandro Squizzato; Francesco Dentali; Luigi Steidl; Walter Ageno

2009-01-01

251

Fingerprint Directional Image Enhancement  

Microsoft Academic Search

\\u000a This work presents an efficient algorithm to enhance the directional image. Orientation, as a global feature of fingerprint,\\u000a is very important to image preprocessing methods used in automatic fingerprint identification system (AFIS). Proposed algorithm\\u000a consists of two weighted averaging stages over a neighborhood. In the first stage the 2D gaussian kernel is used as a weight\\u000a and in the second

Lukasz Wieclaw

2010-01-01

252

Classical direct interstring action  

Microsoft Academic Search

We generalize the classical action-at-a-distance theory between point particles to include one-dimensionally extended objects (strings) in space-time. We build parametrization-invariant couplings which lead to equations of motion for strings in each others' influence. The direct coupling of the area elements of the world sheets of the strings is considered in detail, from which we define an antisymmetric adjunct field. We

Michael Kalb; P. Ramond

1974-01-01

253

Topologies on directed graphs  

NASA Technical Reports Server (NTRS)

Given a directed graph, a natural topology is defined and relationships between standard topological properties and graph theoretical concepts are studied. In particular, the properties of connectivity and separatedness are investigated. A metric is introduced which is shown to be related to separatedness. The topological notions of continuity and homeomorphism. A class of maps is studied which preserve both graph and topological properties. Applications involving strong maps and contractions are also presented.

Lieberman, R. N.

1972-01-01

254

Direct and Inverse Variation  

NSDL National Science Digital Library

"Lesson 1 of two lessons teaches students about direct variation by allowing them to explore a simulated oil spill using toilet paper tissues (to represent land) and drops of vegetable oil (to simulate a volume of oil). Lesson 2 teaches students about inverse variation by exploring the relationship between the heights of a fixed amount of water poured into cylindrical containers of different sizes as compared to the area of the containers' bases." from Insights into Algebra 1 - Annenberg Foundation.

Media, Annenberg

2009-12-23

255

Modelling direction solidification  

NASA Technical Reports Server (NTRS)

The overall objective of this program is to develop an improved understanding of some phenomena of importance to directional solidification. The aim of this research is also to help predict differences in behavior between solidification on Earth and solidification in space. In this report, the validity of the Burton-Primslichter equation is explored. The influence of operating variables on grain and twin generation and propagation in single crystals of In sub (x) Ga sub (1-x) Sb is also investigated.

Wilcox, W. R.

1986-01-01

256

Future directions for QCD  

SciTech Connect

New directions for exploring QCD at future high-energy colliders are sketched. These include jets within jets. BFKL dynamics, soft and hard diffraction, searches for disoriented chiral condensate, and doing a better job on minimum bias physics. The new experimental opportunities include electron-ion collisions at HERA, a new collider detector at the C0 region of the TeVatron, and the FELIX initiative at the LHC.

Bjorken, J.D.

1996-10-01

257

Pneumatic Directional Control Valves  

NSDL National Science Digital Library

This learning object examines pneumatic directional control valves in two-way, three-way, and four-way valves. The presentation is interactive, as it allows the user to focus of certain valve types and cater their learning towards those. The site employs flash based animations, and also many other diagrams to address certain points. Overall, this site has nice presentation and allows presents a great deal of information.

Bartelt, Terry L.; Tomlin, Bonnie

2008-11-24

258

Direct syntheses of La{sub n+1}Ni{sub n}O{sub 3n+1} phases (n=1, 2, 3 and {infinity}) from nanosized co-crystallites  

SciTech Connect

A new direct route for the 'bottom up' syntheses of phases in the La{sub n+1}Ni{sub n}O{sub 3n+1} series (n=1, 2, 3 and {infinity}) has been achieved via single-step heat treatments of nanosized co-crystallized precursors. The co-crystallized precursors were prepared using a continuous hydrothermal flow synthesis system that uses a superheated water flow at ca. 400 deg. C and 24.1 MPa to produce nanoparticulate slurries. Overall, a significant reduction in time and number of steps for the syntheses of La{sub 3}Ni{sub 2}O{sub 7} and La{sub 4}Ni{sub 3}O{sub 10} was achieved compared with more conventional synthesis methods, which typically require multiple homogenization and reheating steps over several days. - Graphical abstract: Scanning electron micrograph of La{sub 4}Ni{sub 3}O{sub 10} (bar=1 {mu}m) made by a single heat treatment at 1075 deg. C in air for 12 h of a 4:3 La:Ni ratio co-crystallite mixture of the metal hydroxides.

Weng Xiaole; Boldrin, Paul [Department of Chemistry, Christopher Ingold Laboratories, University College London, 20 Gordon Street, London WC1H 0AJ (United Kingdom); School of Engineering and Material Sciences, Queen Mary University of London, London E1 4NS (United Kingdom); Abrahams, Isaac [Centre for Materials Research, School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS (United Kingdom); Skinner, Stephen J. [Department of Materials, Imperial College London, South Kensington, London SW7 2AZ (United Kingdom); Kellici, Suela [Department of Chemistry, Christopher Ingold Laboratories, University College London, 20 Gordon Street, London WC1H 0AJ (United Kingdom); Darr, Jawwad A. [Department of Chemistry, Christopher Ingold Laboratories, University College London, 20 Gordon Street, London WC1H 0AJ (United Kingdom)], E-mail: j.a.darr@ucl.ac.uk

2008-05-15

259

Direct conversion technology  

NASA Astrophysics Data System (ADS)

The overall objective of the Direct Conversion Technology task is to develop an experimentally verified technology base for promising direct thermal-to-electric energy conversion systems that have potential application for energy conservation in the end-use sectors. This report contains progress of research on the Alkali Metal Thermal-to-Electric Converter (AMTEC), and on the Two-Phase Liquid-Metal MHD Electrical Generator (LMMHD) for the period January 1988 through December 1988. Research on these concepts was initiated during October 1987. In addition, status reviews and assessments are presented for thermomagnetic converter concepts and for thermoelastic converters (Nitinol heat engines). Reports prepared on previous occasions contain discussions on the following other direct conversion concepts: thermoelectric, pyroelectric, thermionic thermophotovoltaic and thermoacoustic; and also, more complete discussions of AMTEC and LMMHD systems. A tabulated summary of the various systems which have been reviewed thus far has been prepared. Some of the important technical research needs are listed and a schematic of each system is shown.

Massier, P. F.; Bankston, C. P.; Fabris, G.; Kirol, L. D.

1988-12-01

260

Direct observation detonator operation  

NASA Astrophysics Data System (ADS)

The analysis of detonator-timing performance has involved the use of rotating-mirror cameras (RMC) used in the streak mode and high-speed film. Fiducial timing marks are applied to the film to provide temporal references. The use of a RMC for detonator analysis requires aligning the camera, performing an exposure test, capturing light from the detonation and then processing the film. This procedure can take up to an hour for two technicians. After the film is possessed another technician compares each light streak on the film with the fiducial timing marks also recorded on the film. Capturing light from a detonator and recording it directly to a digitizer can improve detonator-timing measurement in several ways. The digitized signals can then be directly analyzed with software. The direct recording method reduces the need for expensive rotating mirror cameras, film processing and subjective optical measurement comparison. Furthermore, an extensive support facility requiring several specialized technicians is reduced to a single technician in a modest laboratory. This technician is then capable of performing several tests an hour. Tests were preformed to measure light intensity at detonation. An optical method of capturing the light was designed using a remote microscope coupled to optical fiber to bring the light to an optical/electrical converter and a digitizer then records the signal. This system is presently used in parallel with a RMC. The results are compared for accuracy.

Hall, Charles R.

2001-11-01

261

Direct-Contact Heat Exchanger.  

National Technical Information Service (NTIS)

The working principle of direct contact heat exchanger, where heat transfer takes place between two immiscible fluids coming into direct contact, is described. Typical direct contact devices are outlined. A better understanding of the principles involved ...

A. Bricard

1991-01-01

262

Psychiatric Advance Directives: Getting Started  

MedlinePLUS

... Home Getting Started National Resource Center on Psychiatric Advance Directives - Getting Started Getting Started Psychiatric advance directives (PADs) are relatively new legal instruments that may ...

263

Directed energy planetary defense  

NASA Astrophysics Data System (ADS)

Asteroids and comets that cross Earth's orbit pose a credible risk of impact, with potentially severe disturbances to Earth and society. Numerous risk mitigation strategies have been described, most involving dedicated missions to a threatening object. We propose an orbital planetary defense system capable of heating the surface of potentially hazardous objects to the vaporization point as a feasible approach to impact risk mitigation. We call the system DE-STAR for Directed Energy System for Targeting of Asteroids and exploRation. DE-STAR is a modular phased array of kilowatt class lasers powered by photovoltaic's. Modular design allows for incremental development, test, and initial deployment, lowering cost, minimizing risk, and allowing for technological co-development, leading eventually to an orbiting structure that would be developed in stages with both technological and target milestones. The main objective of DE-STAR is to use the focused directed energy to raise the surface spot temperature to ~3,000K, allowing direct vaporization of all known substances. In the process of heating the surface ejecting evaporated material a large reaction force would alter the asteroid's orbit. The baseline system is a DE-STAR 3 or 4 (1-10km array) depending on the degree of protection desired. A DE-STAR 4 allows for asteroid engagement starting beyond 1AU with a spot temperature sufficient to completely evaporate up to 500-m diameter asteroids in one year. Small asteroids and comets can be diverted/evaporated with a DESTAR 2 (100m) while space debris is vaporized with a DE-STAR 1 (10m).

Lubin, Philip; Hughes, Gary B.; Bible, Johanna; Bublitz, Jesse; Arriola, Josh; Motta, Caio; Suen, Jon; Johansson, Isabella; Riley, Jordan; Sarvian, Nilou; Clayton-Warwick, Deborah; Wu, Jane; Milich, Andrew; Oleson, Mitch; Pryor, Mark; Krogen, Peter; Kangas, Miikka

2013-09-01

264

Direct to Digital Holography  

SciTech Connect

In this CRADA, Oak Ridge National Laboratory (ORNL) assisted nLine Corporation of Austin, TX in the development of prototype semiconductor wafer inspection tools based on the direct-to-digital holographic (DDH) techniques invented at ORNL. Key components of this work included, development of the first prototype named the Visible Alpha Tool (VAT) that uses visible spectrum illumination of 532 nm, assist in design of second prototype tool named the DUV Alpha Tool (DAT) using deep UV (266 nm) illumination, and continuing support of nLine in the development of higher throughput commercial tools.

Bingham, P.R.; Tobin, K.W.

2003-06-15

265

The Direction of Gravity  

NASA Astrophysics Data System (ADS)

Given a uniformly dense sphere with a hole through its center, gravity is supposed to cause an object dropped into the hole to oscillate between the extremities. This is a prediction of both Newton's and Einstein's theories of gravity. Though every physicist knows what is supposed to happen, nobody has ever seen it happen. Failure to back up the predicted oscillation with empirical evidence is not due to insurmountable technical obstacles; a laboratory experiment to test it is quite feasible. According to the ideals of science, we should not be satis ed with analogies or extrapolations suggesting that the prediction is correct. We should, if possible, get the answer directly from Nature.

Benish, R.

2011-06-01

266

Direct electroplating on nonconductors  

SciTech Connect

Recently proposed processes for direct electroplating on nonconductive substrates offer numerous advantages. The industrial implementation of such processes is, however, hampered by lack of understanding. Presented here is a model for this class of processes based on three synergistic mechanisms: (i) stepwise propagation through the seed clusters that serve as sequentially activated microelectrodes, (ii) preferential accessibility to current of the sharp edge, and (iii) kinetics-based enhancement due to the fast propagation of an additive-free edge. The model has been computer simulated and verified by experiments of copper electroplating on nonconductive substrates.

Weng, D.; Landau, U. [Case Western Reserve Univ., Cleveland, OH (United States). Dept. of Chemical Engineering

1995-08-01

267

Omni-directional railguns  

DOEpatents

A device for electromagnetically accelerating projectiles. The invention features two parallel conducting circular plates, a plurality of electrode connections to both upper and lower plates, a support base, and a projectile magazine. A projectile is spring-loaded into a firing position concentrically located between the parallel plates. A voltage source is applied to the plates to cause current to flow in directions defined by selectable, discrete electrode connections on both upper and lower plates. Repulsive Lorentz forces are generated to eject the projectile in a 360 degree range of fire.

Shahinpoor, Mohsen (9521 Avenida Del Oso NE., Albuquerque, NM 87111)

1995-01-01

268

Omni-directional railguns  

DOEpatents

A device is disclosed for electromagnetically accelerating projectiles. The invention features two parallel conducting circular plates, a plurality of electrode connections to both upper and lower plates, a support base, and a projectile magazine. A projectile is spring-loaded into a firing position concentrically located between the parallel plates. A voltage source is applied to the plates to cause current to flow in directions defined by selectable, discrete electrode connections on both upper and lower plates. Repulsive Lorentz forces are generated to eject the projectile in a 360 degree range of fire. 4 figs.

Shahinpoor, M.

1995-07-25

269

Direct solar pumped laser  

SciTech Connect

A direct solar pumped laser operates on emission from the phosphorescent T1 -> SO transition of a suitable dye molecule used in liquid or solid solution. The first excited singlet electronic state s1 is excited from the ground state so by light from solar concentrators absorbed in the absorption bands of the strong spin-allowed transitions sp <- so, P > or = 1, where the primary absorption band is usually P 1. Excitation of dye molecules to the first triplet state t1 occurs via intersystem crossing from s1 to the triplet state manifold.

Volkin, H.C.

1981-07-28

270

Mandating advance directives.  

PubMed

As the population ages, end-of-life care (EOLC) costs become an increasingly pressing subject. Advance directives (ADs) are legal documents that allow individuals to convey their decisions about EOLC. Although ADs have been shown to reduce EOLC costs, most people do not have ADs. To address this issue, we propose that Congress instruct the Centers for Medicare and Medicaid Services to collect ADs from Medicare beneficiaries. Because ADs can improve care and reduce unnecessary spending, this solution would likely be attractive to a broad coalition of support from providers, insurers, and the public. PMID:24293349

Eltorai, Adam E M; Besdine, Richard W

2014-06-01

271

Omni-directional railguns  

SciTech Connect

This invention is comprised of a device for electromagetically accelerating projectiles. The invention features two parallel conducting circular plates, a plurality of electrode connections to both upper and lower plates, a support base, and a projectile magazine. A projectile is spring-loaded into a firing position concentrically located between the parallel plates. A voltage source is applied to the plates to cause current to flow in directions defined by selectable, discrete electrode connections on both upper and lower plates. Repulsive Lorentz forces are generated to eject the projectile in a 360 degree range of fire.

Shahinpoor, M.

1994-12-31

272

Direct to Digital Holography  

SciTech Connect

In this CRADA, Oak Ridge National Laboratory (ORNL) assisted nLine Corporation of Austin, TX in the development of prototype semiconductor wafer inspection tools based on the direct-to-digital holographic (DDH) techniques invented at ORNL. Key components of this work included, testing of DDH for detection of defects in High Aspect Ratio (HAR) structures, development of image processing techniques to enhance detection capabilities through the use of both phase and intensity, and development of methods for autofocus on the DDH tools.

Bingham, P.R.; Tobin, K.W.

2002-06-15

273

New directions in retinal research.  

PubMed

Direction-selective retinal ganglion cells (DSGCs) respond to image motion in a "preferred" direction but not the opposite "null" direction. Extracellular spike recordings from rabbit DSGCs suggested that the key mechanism underlying the directional responses is spatially offset inhibition projecting in the null direction. Recent patch-clamp recordings have shown that this inhibition, which acts directly on the DSGC, is already direction selective. Dual recordings established that the inhibition arises from starburst amacrine cells (SBACs) located on the null side of the DSGC but not from those on the preferred side. Thus, for each radially symmetric SBAC, processes pointing in different directions would provide the null-direction inhibition to subtypes of DSGCs with different preferred directions. Ca2+ imaging revealed that the SBAC terminal processes respond more strongly to image motion away from the soma than towards the soma, therefore accounting for the direction selectivity of the inhibitory input to the DSGCs. PMID:12850434

Taylor, W Rowland; Vaney, David I

2003-07-01

274

Remote direct memory access  

DOEpatents

Methods, parallel computers, and computer program products are disclosed for remote direct memory access. Embodiments include transmitting, from an origin DMA engine on an origin compute node to a plurality target DMA engines on target compute nodes, a request to send message, the request to send message specifying a data to be transferred from the origin DMA engine to data storage on each target compute node; receiving, by each target DMA engine on each target compute node, the request to send message; preparing, by each target DMA engine, to store data according to the data storage reference and the data length, including assigning a base storage address for the data storage reference; sending, by one or more of the target DMA engines, an acknowledgment message acknowledging that all the target DMA engines are prepared to receive a data transmission from the origin DMA engine; receiving, by the origin DMA engine, the acknowledgement message from the one or more of the target DMA engines; and transferring, by the origin DMA engine, data to data storage on each of the target compute nodes according to the data storage reference using a single direct put operation.

Archer, Charles J.; Blocksome, Michael A.

2012-12-11

275

Direct Production of Copper  

NASA Astrophysics Data System (ADS)

The use of commercially pure oxygen in flash smelting a typical chalcopyrite concentrate or a low grade comminuted matte directly to copper produces a large excess of heat. The heat balance is controlled by adjusting the calorific value of the solid feed. A portion of the sulfide material is roasted to produce a calcine which is blended with unroasted material, and the blend is then autogeneously smelted with oxygen and flux directly to copper. Either iron silicate or iron calcareous slags are produced, both being subject to a slag cleaning treatment. Practically all of the sulfur is contained in a continuous stream of SO2 gas, most of which is strong enough for liquefaction. A particularly attractive feature of these technologies is that no radically new metallurgical equipment needs to be developed. The oxygen smelting can be carried out not only in the Inco type flash furnace but in other suitable smelters such as cyclone furnaces. Another major advantage stems from abolishion of the ever-troublesome converter aisle, which is replaced with continuous roasting of a fraction of the copper sulfide feed.

Victorovich, G. S.; Bell, M. C.; Diaz, C. M.; Bell, J. A. E.

1987-09-01

276

Direct-contact heat exchanger  

NASA Astrophysics Data System (ADS)

The working principle of direct contact heat exchanger, where heat transfer takes place between two immiscible fluids coming into direct contact, is described. Typical direct contact devices are outlined. A better understanding of the principles involved and the development of computational models for multiphase subsytems are concluded as stimulus for direct contact heat and mass transfer applications.

Bricard, A.

277

Direct-contact heat exchanger  

Microsoft Academic Search

The working principle of direct contact heat exchanger, where heat transfer takes place between two immiscible fluids coming into direct contact, is described. Typical direct contact devices are outlined. A better understanding of the principles involved and the development of computational models for multiphase subsytems are concluded as stimulus for direct contact heat and mass transfer applications.

A. Bricard

1991-01-01

278

Microfluidic Compartmentalized Directed Evolution  

PubMed Central

Summary Directed evolution studies often make use of water-in-oil compartments, which conventionally are prepared by bulk emulsification, a crude process that generates non-uniform droplets and can damage biochemical reagents. A microfluidic emulsification circuit was devised that generates uniform water-in-oil droplets (21.9 ± 0.8 ?m radius) with high throughput (107–108 droplets per hour). The circuit contains a radial array of aqueous flow nozzles that intersect a surrounding oil flow channel. This device was used to evolve RNA enzymes with RNA ligase activity, selecting enzymes that could resist inhibition by neomycin. Each molecule in the population had the opportunity to undergo 108-fold selective amplification within its respective compartment. Then the progeny RNAs were harvested and used to seed new compartments. During five rounds of this procedure, the enzymes acquired mutations that conferred resistance to neomycin and caused some enzymes to become dependent on neomycin for optimal activity.

Paegel, Brian M.; Joyce, Gerald F.

2010-01-01

279

Laser assisted direct manufacturing  

NASA Astrophysics Data System (ADS)

Direct Laser Manufacturing (DLM) with coaxial powder injection (TRUMPF DMD 505 installation) was applied for fabrication of 3D objects from metallic and ceramic powder. One of the advantages of DLM is the possibility to build functionally graded objects in one-step manufacturing cycle by application of a 2-channel powder feeder. Several models with different types of material gradients (smooth, sharp, periodic) and multi-layered structures were manufactured from SS, stellite (Cobalt alloy), Cu and W alloys. Technology of Selective Laser Melting (SLM) was applied for manufacturing of net shaped objects from different powders (PHENIX PM-100 machine) : Inox 904L, Ni625, Cu/Sn, W and Zr02-Y2O3. Performance and limitations of SLM technology for fabrication of elements for chemical and mechanical industries are analysed. Two-component objects (Stainless steel /Cu - H13/CuNi) were fabricated in a two-step manufacturing cycle.

Bertrand, Ph.; Smurov, I.

2007-07-01

280

Fiber optic TV direct  

NASA Technical Reports Server (NTRS)

The objective of the operational television (OTV) technology was to develop a multiple camera system (up to 256 cameras) for NASA Kennedy installations where camera video, synchronization, control, and status data are transmitted bidirectionally via a single fiber cable at distances in excess of five miles. It is shown that the benefits (such as improved video performance, immunity from electromagnetic interference and radio frequency interference, elimination of repeater stations, and more system configuration flexibility) can be realized if application of the proven fiber optic transmission concept is used. The control system will marry the lens, pan and tilt, and camera control functions into a modular based Local Area Network (LAN) control network. Such a system does not exist commercially at present since the Television Broadcast Industry's current practice is to divorce the positional controls from the camera control system. The application software developed for this system will have direct applicability to similar systems in industry using LAN based control systems.

Kassak, John E.

1991-01-01

281

Site directed recombination  

DOEpatents

Enhanced homologous recombination is obtained by employing a consensus sequence which has been found to be associated with integration of repeat sequences, such as Alu and ID. The consensus sequence or sequence having a single transition mutation determines one site of a double break which allows for high efficiency of integration at the site. By introducing single or double stranded DNA having the consensus sequence flanking region joined to a sequence of interest, one can reproducibly direct integration of the sequence of interest at one or a limited number of sites. In this way, specific sites can be identified and homologous recombination achieved at the site by employing a second flanking sequence associated with a sequence proximal to the 3'-nick.

Jurka, Jerzy W. (Los Altos, CA)

1997-01-01

282

Directed polymerase evolution.  

PubMed

Polymerases evolved in nature to synthesize DNA and RNA, and they underlie the storage and flow of genetic information in all cells. The availability of these enzymes for use at the bench has driven a revolution in biotechnology and medicinal research; however, polymerases did not evolve to function efficiently under the conditions required for some applications and their high substrate fidelity precludes their use for most applications that involve modified substrates. To circumvent these limitations, researchers have turned to directed evolution to tailor the properties and/or substrate repertoire of polymerases for different applications, and several systems have been developed for this purpose. These systems draw on different methods of creating a pool of randomly mutated polymerases and are differentiated by the process used to isolate the most fit members. A variety of polymerases have been evolved, providing new or improved functionality, as well as interesting new insight into the factors governing activity. PMID:24211837

Chen, Tingjian; Romesberg, Floyd E

2014-01-21

283

Speech research directions  

SciTech Connect

This paper presents an overview of the current activities in speech research. The authors discuss the state of the art in speech coding, text-to-speech synthesis, speech recognition, and speaker recognition. In the speech coding area, current algorithms perform well at bit rates down to 9.6 kb/s, and the research is directed at bringing the rate for high-quality speech coding down to 2.4 kb/s. In text-to-speech synthesis, what we currently are able to produce is very intelligible but not yet completely natural. Current research aims at providing higher quality and intelligibility to the synthetic speech that these systems produce. Finally, today's systems for speech and speaker recognition provide excellent performance on limited tasks; i.e., limited vocabulary, modest syntax, small talker populations, constrained inputs, etc.

Atal, B.S.; Rabiner, L.R.

1986-09-01

284

Magnetostrictive direct drive motors  

NASA Technical Reports Server (NTRS)

Developing magnetostrictive direct drive research motors to power robot joints is discussed. These type motors are expected to produce extraordinary torque density, to be able to perform microradian incremental steps and to be self-braking and safe with the power off. Several types of motor designs have been attempted using magnetostrictive materials. One of the candidate approaches (the magnetostrictive roller drive) is described. The method in which the design will function is described as is the reason why this approach is inherently superior to the other approaches. Following this, the design will be modelled and its expected performance predicted. This particular candidate design is currently undergoing detailed engineering with prototype construction and testing scheduled for mid 1991.

Naik, Dipak; Dehoff, P. H.

1990-01-01

285

Comprehension of Navigation Directions  

NASA Technical Reports Server (NTRS)

Subjects were shown navigation instructions varying in length directing them to move in a space represented by grids on a computer screen. They followed the instructions by clicking on the grids in the locations specified. Some subjects repeated back the instructions before following them, some did not, and others repeated back the instructions in reduced form, including only the critical words. The commands in each message were presented simultaneously for half of the subjects and sequentially for the others. For the longest messages, performance was better on the initial commands and worse on the final commands with simultaneous than with sequential presentation. Instruction repetition depressed performance, but reduced repetition removed this disadvantage. Effects of presentation format were attributed to visual scanning strategies. The advantage for reduced repetition was attributable either to enhanced visual scanning or to reduced output interference. A follow-up study with auditory presentation supported the visual scanning explanation.

Healy, Alice F.; Schneider, Vivian I.

2002-01-01

286

Conclusions and Policy Directions,  

SciTech Connect

This chapter briefly revisits the constraints and opportunities of mitigation and adaptation, and highlights and the multiple linkages, synergies and trade-offs between mitigation, adaptation and urban development. The chapter then presents future policy directions, focusing on local, national and international principles and policies for supporting and enhancing urban responses to climate change. In summary, policy directions for linking climate change responses with urban development offer abundant opportunities; but they call for new philosophies about how to think about the future and how to connect different roles of different levels of government and different parts of the urban community. In many cases, this implies changes in how urban areas operate - fostering closer coordination between local governments and local economic institutions, and building new connections between central power structures and parts of the population who have often been kept outside of the circle of consultation and discourse. The difficulties involved in changing deeply set patterns of interaction and decision-making in urban areas should not be underestimated. Because it is so difficult, successful experiences need to be identified, described and widely publicized as models for others. However, where this challenge is met, it is likely not only to increase opportunities and reduce threats to urban development in profoundly important ways, but to make the urban area a more effective socio-political entity, in general - a better city in how it works day to day and how it solves a myriad of problems as they emerge - far beyond climate change connections alone. It is in this sense that climate change responses can be catalysts for socially inclusive, economically productive and environmentally friendly urban development, helping to pioneer new patterns of stakeholder communication and participation.

Wilbanks, Thomas J [ORNL; Romero-Lankao, Paty [National Center for Atmospheric Research (NCAR); Gnatz, P [National Center for Atmospheric Research (NCAR)

2011-01-01

287

Direct Georeferencing of Uavs  

NASA Astrophysics Data System (ADS)

UAV systems have become an attractive data acquisition platform in emerging applications. As measuring instrument they extend the lineup of possible surveying methods in the field of geomatics. However, most of UAVs are equipped with low-cost navigation sensors such as GPS or INS, allowing a positioning accuracy of 3 to 5 m. As a result the acquired position- and orientation data fea- tures a low accuracy which implicates that it cannot be used in applications that require high precision data on cm-level (e.g. direct georeferencing). In this paper we will analyze the potential of differential post-processing of GPS data from UAV in order to im- prove the positioning accuracy for applications basing on direct georeferencing. Subsequently, the obtained results are compared and verified with a track of the octocopter carried out with a total station simultaneously to the GPS data acquisition. The results show that the differential post-processing essentially improved the accuracy of the Falcon position data. Thereby the average offset be- tween the data sets (GPS data, track) and the corresponding standard deviation is 0.82 m and 0.45 m, respectively. However, under ideal conditions it is even possible to improve this positioning accuracy to the cm-range. Furthermore, there are still several sources of error such as the offset between the GPS antenna of the Falcon 8 and the prism which is used for the track. Considering this fact there is further room for improvement regarding the here discussed positioning method.

Bláha, M.; Eisenbeiss, H.; Grimm, D.; Limpach, P.

2011-09-01

288

Optimised nanoformulation of bromocriptine for direct nose-to-brain delivery: biodistribution, pharmacokinetic and dopamine estimation by ultra-HPLC/mass spectrometry method.  

PubMed

Objective: The present work evaluated whether the prepared nanoparticles (NPs) would be able to target the drug to the brain by a non-invasive nasal route enhancing its bioavailability. Methods: Bromocriptine (BRC) chitosan NPs (CS NPs) were prepared by ionic gelation method. The biodistribution, pharmacokinetic parameters and dopamine concentration was analysed by ultra-HPLC/mass spectrometry method. The histopathological examination in haloperidol-induced Parkinson's disease in mice model following intranasal (i.n.) administration was evaluated. Results: BRC was found stable in all exposed conditions and the percentage accuracy observed for intra-day and inter-day batch samples ranged from 90.5 to 107% and 95.3 to 98.9% for plasma and brain homogenates, respectively. BRC-loaded CS NPs showed greater retention into the nostrils (42 ± 8.5% radioactivity) for about 4 h, whereas the 44 ± 7.5% could be retained up to 1 h for BRC solution. The brain:blood ratios of 0.96 ± 0.05 > 0.73 ± 0.15 > 0.25 ± 0.05 of BRC-loaded CS NPs (i.n.) > BRC solution (i.n.) > BRC-loaded CS NPs (intravenous), respectively, at 0.5 h indicated direct nose-to-brain transport bypassing blood-brain barrier. BRC-loaded CS NPs administered intranasally showed significantly high dopamine concentration (20.65 ± 1.08 ng/ml) as compared to haloperidol-treated mice (10.94 ± 2.16 ng/ml) (p < 0.05). Histopathology of brain sections showed selective degeneration of the dopaminergic neurons in haloperidol-treated mice which was markedly reverted by BRC-loaded CS NPs. Conclusion: Nanoparticulate drug delivery system could be potentially used as a nose-to-brain drug delivery carrier for the treatment of Parkinson's disease. PMID:24655115

Md, Shadab; Haque, Shadabul; Fazil, Mohammad; Kumar, Manish; Baboota, Sanjula; Sahni, Jasjeet K; Ali, Javed

2014-06-01

289

Measuring Dark Matter Distribution in Directional Direct Detection  

NASA Astrophysics Data System (ADS)

Direct detection of dark matter with directional sensitivity offers not only measurement of both recoil energy and direction of dark matter, but also a way to understand dark matter distribution in the Galaxy. Maxwell distribution is usually supposed as the distribution near the Earth, however, result of N-body simulations suggest deviation from that due to tidal stream in the Galaxy. We explore the possibility of distinguishing the distribution by direct detection using nuclear emulsions.

Nagao, Keiko I.

2013-12-01

290

Multiple direction vibration fixture  

DOEpatents

An apparatus for simulating a rocket launch environment on a test item undergoing centrifuge testing by subjecting the item simultaneously or separately to vibration along an axis of centripetal force and along an axis perpendicular to the centripetal force axis. The apparatus includes a shaker motor supported by centrifuge arms and a right angle fixture pivotally connected to one of the shaker motor mounts. When the shaker motor vibrates along the centripetal force axis, the vibrations are imparted to a first side of the right angle fixture. The vibrations are transmitted 90 degrees around the pivot and are directed to a second side of the right angle fixture which imparts vibrations perpendicular to the centripetal force axis. The test item is in contact with a third side of the right angle fixture and receives both centripetal-force-axis vibrations and perpendicular axis vibrations simultaneously. A test item can be attached to the third side near the flexible coupling or near the air bag to obtain vibrations along the centripetal force axis or transverse to the centripetal force axis.

Cericola, Fred (Albuquerque, NM); Doggett, James W. (Albuquerque, NM); Ernest, Terry L. (Albuquerque, NM); Priddy, Tommy G. (Rockville, MD)

1991-01-01

291

Coatings for directional eutectics  

NASA Technical Reports Server (NTRS)

Coatings developed to provide oxidation protection for the directionally-solidified eutectic alloy NiTaC-B (4.4 weight percent Cr) were evaluated. Of seven Co-, Fe- and Ni-base coatings that were initially investigated, best resistance to cyclic oxidation was demonstrated by duplex coatings fabricated by depositing a layer of NiCrAl(Y) by vacuum evaporation from an electron beam source followed by deposition of an Al overlayer using the pack cementation process. It was found that addition of carbon to the coating alloy substantially eliminated the problem of fiber denudation in TaC-type eutectic alloys. Burner rig cycled NiTaC-B samples coated with Ni-20Cr-5Al-0.1C-0.1Y+Al and rupture-tested at 1100 deg C performed as well as or better than uncoated, vacuum cycled and air-tested NiTaC-13; however, a slight degradation with respect to uncoated material was noted in air-stress rupture tests at 870 deg C for both cycled and uncycled samples.

Rairden, J. R.; Jackson, M. R.

1976-01-01

292

New Directions in Biotechnology  

NASA Technical Reports Server (NTRS)

The macromolecule crystallization program within NASA is undergoing considerable pressure, particularly budgetary pressure. While it has shown some successes, they have not lived up to the expectations of others, and technological advances may rapidly overtake the natural advantages offered by crystallization in microgravity. Concomitant with the microgravity effort has been a research program to study the macromolecule crystallization process. It was believed that a better understanding of the process would lead to growth of improved crystals for X-ray diffraction studies. The results of the various research efforts have been impressive in improving our understanding of macromolecule crystallization, but have not led to any improved structures. Macromolecule crystallization for structure determination is "one of", the job being unique for every protein and finished once a structure is obtained. However, the knowledge gained is not lost, but instead lays the foundation for developments in new areas of biotechnology and nanotechnology. In this it is highly analogous to studies into small molecule crystallization, the results of which have led to our present day microelectronics-based society. We are conducting preliminary experiments into areas such as designed macromolecule crystals, macromolecule-inorganic hybrid structures, and macromolecule-based nanotechnology. In addition, our protein crystallization studies are now being directed more towards industrial and new approaches to membrane protein crystallization.

2003-01-01

293

Direct cupration of fluoroform.  

PubMed

We have found the first reaction of direct cupration of fluoroform, the most attractive CF(3) source for the introduction of the trifluoromethyl group into organic molecules. Treatment of CuX (X = Cl, Br, I) with 2 equiv of MOR (M = K, Na) in DMF or NMP produces novel alkoxycuprates that readily react with CF(3)H at room temperature and atmospheric pressure to give CuCF(3) derivatives. The CuCl and t-BuOK (1:2) combination provides best results, furnishing the CuCF(3) product within seconds in nearly quantitative yield. As demonstrated, neither CF(3)(-) nor CF(2) mediate the Cu-CF(3) bond formation, which accounts for its remarkably high selectivity. The fluoroform-derived CuCF(3) solutions can be efficiently stabilized with TREAT HF to produce CuCF(3) reagents that readily trifluoromethylate organic and inorganic electrophiles in the absence of additional ligands such as phenanthroline. A series of novel Cu(I) complexes have been structurally characterized, including K(DMF)[Cu(OBu-t)(2)] (1), Na(DMF)(2)[Cu(OBu-t)(2)] (2), [K(8)Cu(6)(OBu-t)(12)(DMF)(8)(I)](+) I(-) (3), and [Cu(4)(CF(3))(2)(C(OBu-t)(2))(2)(?(3)-OBu-t)(2)] (7). PMID:22136628

Zanardi, Alessandro; Novikov, Maxim A; Martin, Eddy; Benet-Buchholz, Jordi; Grushin, Vladimir V

2011-12-28

294

Directional solidification under stress  

NASA Astrophysics Data System (ADS)

Directional solidification under uniaxial stress is analyzed. In the absence of stress, it is well known that the moving planar front undergoes a morphological Mullins-Sekerka (MS) instability. Under uniaxial stress, even an interface at rest develops an instability known by the names of Asaro, Tiller, and Grinfeld (ATG). This paper analyzes the coupling between these two instabilities, a situation on which we have recently given a brief account [Durand et al., Phys. Rev. Lett. 76, 3013 (1996)]. We discover that under favorable circumstances a weak uniaxial stress of the order of 1 bar leads to a dramatic change of the Mullins-Sekerka instability. The threshold, together with the microstructure scale, are shifted by amounts going up to one (or several) decade(s). This effect should open new lines of both experimental and theoretical inquiries. A weakly nonlinear analysis is presented by means of a Landau expansion. It is known that the MS bifurcation is subcritical for a small enough solute partition coefficient, and is supercritical otherwise. The ATG instability is always subcritical. The nonlinear evolution of the ATG instability leads to cusps which grow unstably, leading ultimately to the fracture threshold. It is shown here that due to a subtle coupling between both instabilities, the MS bifurcation in its supercritical regime may cause the MS-ATG coupled bifurcation to be supercritical. Discussions and outlooks are presented. In particular it is appealing to speculate that the creation of giant causeways in igneous rocks can be interpreted within the present context.

Cantat, Isabelle; Kassner, Klaus; Misbah, Chaouqi; Müller-Krumbhaar, Heiner

1998-11-01

295

Coatings for directional eutectics  

NASA Technical Reports Server (NTRS)

Significant advances have been made in the development of an environmentally stable coating for a very high strength, directionally solidified eutectic alloy designated NiTaC-13. Three duplex (two-layer) coatings survived 3,000 hours on a cyclic oxidation test (1,100 C to 90 C). These coatings were fabricated by first depositing a layer of NiCrAl(Y) by vacuum evaporation from an electron beam heated source, followed by depositing an aluminizing overlayer. The alloy after exposure with these coatings was denuded of carbide fibers at the substrate/coating interface. It was demonstrated that TaC fiber denudation can be greatly retarded by applying a carbon-bearing coating. The coating was applied by thermal spraying followed by aluminization. Specimens coated with NiCrAlCY+Al survived over 2,000 hours in the cyclic oxidation test with essentially no TaC denudation. Coating ductility was studied for coated and heat-treated bars, and stress rupture life at 871 C and 1,100 C was determined for coated and cycled bars.

Rairden, J. R.; Jackson, M. R.

1976-01-01

296

Magnetostrictive direct drive motor  

NASA Technical Reports Server (NTRS)

Highly magnetostrictive materials such as Tb.3Dy.7Fe2, commercially known as TERFENOL-D, have been used to date in a variety of devices such as high power actuators and linear motors. The larger magnetostriction available in twinned single crystal TERFENOL-D, approx. 2000 ppm at moderate magnetic field strengths, makes possible a new generation of magnetomechanical devices. NASA researchers are studying the potential of this material as the basis for a direct microstepping rotary motor with torque densities on the order of industrial hydraulics and five times greater than that of the most efficient, high power electric motors. Such a motor would be a micro-radian stepper, capable of precision movements and self-braking in the power-off state. Innovative mechanical engineering techniques are juxtaposed on proper magnetic circuit design to reduce losses in structural flexures, inertias, thermal expansions, eddy currents, and magneto-mechanical coupling, thus optimizing motor performance and efficiency. Mathematical models are presented, including magnetic, structural, and both linear and nonlinear dynamic calculations and simulations. In addition, test results on prototypes are presented.

Naik, Dipak; Dehoff, P. H.

1991-01-01

297

Ergonomics--future directions.  

PubMed

The International Ergonomics Association plays a leadership role in shaping the future of ergonomics. Having formed nearly 50 years ago for researchers to meet and exchange their findings, it still provides a wide range of opportunities for promoting research and teaching. In 2006, the IEA is also an outward looking organisation with linkages to governments, international agencies and other professional associations. We have many opportunities to extend our engagement with industry and the community through the IEA communication strategy and Technical Committees. Whilst the IEA now has 20 Technical Committees that demonstrate the diversity of ergonomics research there is a growing trend towards integration of specialist areas. The emergence of a holistic approach to research and application of ergonomics is making a new direction for the ergonomics profession. Apart from the role of a technical specialist, the Ergonomist is also a team member with a range of other stakeholders. To be effective in practice, the Ergonomist needs to be a good communicator and "agent of change" who can mentor others to develop simple cost effective interventions. Research is fundamental to the science of ergonomics. Evaluation of interventions remains a major component of future ergonomics research. Sustainable positive outcomes based on a holistic approach will result in a broad uptake of ergonomics findings. In industry future challenges relating to psychological health in developed countries and the informal sector in developing countries are emerging as new areas for research and application of ergonomics. PMID:18572792

Caple, David C

2007-12-01

298

Directly Driven Ion Outflow  

NASA Technical Reports Server (NTRS)

We examine ionospheric outflows in the high altitude magnetospheric polar cap during the POLAR satellite's apogee on April 19, 1996 using the Thermal Ion Dynamics Experiment (TIDE) instrument. The elevated levels of O(+) observed in this pass may be due to the geophysical conditions during and prior to the apogee pass. In addition to the high abundance of O(+) relative to H(+), several other aspects of this data are noteworthy. We observe relationships between the density, velocity, and temperature which appear to be associated with perpendicular heating and the mirror force, rather than adiabatic expansion. The H(+) outflow is at a fairly constant flux which is consistent with being source limited by charge exchange at lower altitudes. Local centrifugal acceleration in the polar cap is found to be insufficient to account for the main variations we observe in the outflow velocity. The solar wind speed is high during this pass approximately 700 kilometers per second, and there are Alfve'n waves present in the solar wind such that the solar wind speed and IMF Bx are correlated. In this pass both the H(+) and O(+) outflow velocities correlate with both the solar wind speed and IMF fluctuations. Polar cap magnetometer and Hydra electron data show the same long period wave structure as found in the solar wind and polar cap ion outflow. In addition, the polar cap Poynting flux along the magnetic field direction correlates well with the H(+) temperature (R=0.84). We conclude that the solar wind can drive polar cap ion outflow particularly during polar squalls by setting up a parallel drop that is tens of eV which then causes the ion outflow velocity of O(+) and H(+), the electrons, and magnetic perturbations to vary in a similar fashion.

Elliott, H. A.; Comfort, R. H.; Craven, P. D.; Moore, T. E.; Russell, C. T.; Rose, M. Franklin (Technical Monitor)

2001-01-01

299

[Advance medical directives].  

PubMed

A patient's rights to autonomy and to participate in the decision making process is a fundamental ethical principle. However, for the non-competent patient, participation in decision-making is more problematic. A survey carried out in Israel found that less than half of the offspring of terminally ill elderly patients knew the request of their parents regarding life-supporting measures. A solution to this problem is the use of medical advance directives (MADs). In the U.S.A (in 1991) it was required by a federal law to inform every hospitalized patient of his right to use MADs. The experience from the use of MADs in the USA during the last 10 years show that: 1) Most lay persons as well as medical staff support the use of MADs 2) The rate of the use of MADs is about 20%, and among long term care hospitalized patients it is even higher. 3) Sex, age, level of education, morbidity and income were found to be significant factors. 4) Education on the use of the MADs raised the rate of use. 5) Most of the patients who had MADs did not discuss the issue of life supporting treatment with their physicians. 6) Patients who had MADs received less aggressive treatment with reduced medical cost. 7) There is a preference to write generic MADs. Arguments supporting the use of MADs state that they: extend patient autonomy; relieve patient anxiety regarding unwanted treatment; relieve physicians' anxiety concerning legal liability; reduce interfamily conflicts, and they also lower health care costs. Arguments opposing the use claim that they: violate sanctity of life; promote an adversarial physician-patient relationship; may lead to euthanasia; fail to express the patient's current wishes and may even counteract physicians' values. On the basis of experience in the USA and the positive attitude regarding MADs, it appears that MADs can also be applicable in Israel. PMID:11905092

Sonnenblick, Moshe

2002-02-01

300

Identification of Directional Couplings  

NASA Astrophysics Data System (ADS)

An important piece of information, which can be extracted from parameters of empirical models, is quantitative characteristics of couplings between processes under study. The problem of coupling detection is encountered in multiple fields including physics (Bezruchko et al., 2003), geophysics (Maraun and Kurths, 2005; Mokhov and Smirnov, 2006, 2008; Mosedale et al., 2006; Palus and Novotna, 2006; Verdes, 2005; Wang et al., 2004), cardiology (Rosenblum et al., 2002; Palus and Stefanovska, 2003) and neurophysiology (Arnhold et al., 1999; Brea et al., 2006; Faes et al., 2008; Friston et al., 2003; Kreuz et al., 2007; Kiemel et al., 2003; Le Van Quyen et al., 1999; Mormann et al., 2000; Osterhage et al., 2007; Pereda et al., 2005; Prusseit and Lehnertz, 2008; Smirnov et al., 2005; Romano et al., 2007; Schelter et al., 2006; Schiff et al., 1996; Sitnikova et al., 2008; Smirnov et al., 2008, Staniek and Lehnertz, 2008; Tass, 1999; Tass et al., 2003). Numerous investigations are devoted to synchronisation, which is an effect of interaction between non-linear oscillatory systems (see, e.g., Balanov et al., 2008; Boccaletti et al., 2002; Hramov and Koronovskii, 2004; Kreuz et al., 2007; Maraun and Kurths, 2005; Mormann et al., 2000; Mosekilde et al., 2002; Osipov et al., 2007; Palus and Novotna, 2006; Pikovsky et al., 2001; Prokhorov et al., 2003; Tass et al., 2003). In the last decade, more careful attention is paid to directional coupling analysis. Such characteristics might help, e.g., to localise an epileptic focus (a pathologic area) in the brain from electroencephalogram (EEG) or magnetoencephalogram (MEG) recordings: hypothetically, an increasing influence of an epileptic focus on adjacent areas leads to the seizure onset for some kinds of epilepsy.

Bezruchko, Boris P.; Smirnov, Dmitry A.

301

Direct Methane Conversion: An Assessment.  

National Technical Information Service (NTIS)

If its were possible to convert methane directly to methanol or higher hydrocarbons with high conversion and selectivity, both the steam reforming and methanol synthesis steps could be eliminated. This direct conversion approach has the potential for cons...

D. Gray G. Tomlinson J. Shen

1988-01-01

302

Optimal Selection for Direct Mail  

Microsoft Academic Search

Direct marketing (mail) is a growing area of marketing practice, yet the academic journals contain very little research on this topic. The most important issue for direct marketers is how to sample targets from a population for a direct mail campaign. Although some selection methods are described in the literature, there seems to be not a single paper discussing the

Jan Roelf Bult; Tom Wansbeek

1995-01-01

303

Image Segmentation with Directed Trees  

Microsoft Academic Search

This correspondence presents a simple algorithm to detect and label homogeneous areas in an image, using directed trees for region labeling. The scheme constructs directed trees with the image points as nodes, guided by an edge value computed at every point. These directed trees segment the image into disjoint regions. Because of a valley seeldng property of the tree construction

P. M. Narendra; M. Goldberg

1980-01-01

304

Direct methane conversion: An assessment  

Microsoft Academic Search

If its were possible to convert methane directly to methanol or higher hydrocarbons with high conversion and selectivity, both the steam reforming and methanol synthesis steps could be eliminated. This direct conversion approach has the potential for considerable savings in cost if technically sound processes can be developed. Interest in direct methane or natural gas conversion has recently intensified worldwide.

D. Gray; G. Tomlinson; J. Shen

1988-01-01

305

Determinants of molecular motor directionality  

Microsoft Academic Search

Work over the past two years has led to a breakthrough in our understanding of the molecular basis of the directionality of the kinesin motor proteins. This breakthrough has come first from the reversal of directionality of the kinesin-related motor Ncd, followed closely by the reversal of kinesin’s directionality and the finding that the Ncd ‘neck’ can convert Ncd or

Sharyn A. Endow

1999-01-01

306

Strategic Defense Initiative Organization. Directive  

SciTech Connect

The Directive reissues DoD Directive 5141.5, February 21, 1986, and establishes, pursuant to the authority vested in the Secretary of Defense under Title 10, United States Code, and National Security Decision Directive 119, January 6, 1984, the Strategic Defense Initiative Organization as an agency of the Department of Defense with responsibilities, functions, relationships, and authorities as prescribed herein.

Furtner, R.

1987-06-04

307

Motor directional tuning across brain areas: directional resonance and the role of inhibition for directional accuracy.  

PubMed

Motor directional tuning (Georgopoulos et al., 1982) has been found in every brain area in which it has been sought for during the past 30-odd years. It is typically broad, with widely distributed preferred directions and a population signal that predicts accurately the direction of an upcoming reaching movement or isometric force pulse (Georgopoulos et al., 1992). What is the basis for such ubiquitous directional tuning? How does the tuning come about? What are the implications of directional tuning for understanding the brain mechanisms of movement in space? This review addresses these questions in the light of accumulated knowledge in various sub-fields of neuroscience and motor behavior. It is argued (a) that direction in space encompasses many aspects, from vision to muscles, (b) that there is a directional congruence among the central representations of these distributed "directions" arising from rough but orderly topographic connectivities among brain areas, (c) that broad directional tuning is the result of broad excitation limited by recurrent and non-recurrent (i.e., direct) inhibition within the preferred direction loci in brain areas, and (d) that the width of the directional tuning curve, modulated by local inhibitory mechanisms, is a parameter that determines the accuracy of the directional command. PMID:23720612

Mahan, Margaret Y; Georgopoulos, Apostolos P

2013-01-01

308

Motor directional tuning across brain areas: directional resonance and the role of inhibition for directional accuracy  

PubMed Central

Motor directional tuning (Georgopoulos et al., 1982) has been found in every brain area in which it has been sought for during the past 30-odd years. It is typically broad, with widely distributed preferred directions and a population signal that predicts accurately the direction of an upcoming reaching movement or isometric force pulse (Georgopoulos et al., 1992). What is the basis for such ubiquitous directional tuning? How does the tuning come about? What are the implications of directional tuning for understanding the brain mechanisms of movement in space? This review addresses these questions in the light of accumulated knowledge in various sub-fields of neuroscience and motor behavior. It is argued (a) that direction in space encompasses many aspects, from vision to muscles, (b) that there is a directional congruence among the central representations of these distributed “directions” arising from rough but orderly topographic connectivities among brain areas, (c) that broad directional tuning is the result of broad excitation limited by recurrent and non-recurrent (i.e., direct) inhibition within the preferred direction loci in brain areas, and (d) that the width of the directional tuning curve, modulated by local inhibitory mechanisms, is a parameter that determines the accuracy of the directional command.

Mahan, Margaret Y.; Georgopoulos, Apostolos P.

2013-01-01

309

A Novel Direction-Finding Algorithm for Directional Borehole Radar  

Microsoft Academic Search

A directional borehole radar system has been developed for the purpose of 3-D imaging of subsurface targets in a single-hole measurement. The radar system is equipped with a uniform circular array consisting of four dipole antennas as a receiver in order to realize azimuth bearing sensitivity. We propose a new direction-finding (DF) algorithm that is suitable for directional borehole radar

Takuya Takayama; Motoyuki Sato

2007-01-01

310

78 FR 32533 - Proposed Collection of Information: Direct Deposit, Go Direct, and Direct Express Sign-Up Forms  

Federal Register 2010, 2011, 2012, 2013

...Collection of Information: Direct Deposit, Go Direct, and Direct Express Sign-Up Forms...Deposit Sign-Up Form'', Form 1200 ``Go Direct Sign-Up Form for Direct Deposit...Title: Direct Deposit Sign-Up Form, and Go Direct Sign-Up Form, and Direct...

2013-05-30

311

Nano-particulate dispersion and reinforcement of nanostructured composite materials  

NASA Astrophysics Data System (ADS)

This research investigated the feasibility of reinforcing polymer composites using 30 nm SiC nanoparticles in a vinyl ester resin. The SiC nanoparticles were examined using transmission electron microscopy and thermogravimetric analysis. Gamma-methacryloxy propyl trimethoxy silane (MPS) was chosen as the coupling agent. Both mixing procedures with (1) the nanoparticles pretreated with a dilute MPS solution in an acid 5% (v/v) water-ethanol mixture and (2) the MPS sonicated as an integral blend with the filled vinyl ester, were attempted. Fourier transform infrared spectroscopy was used to study the silanol condensation between MPS and the SiC nanoparticles. The results show that ultrasonic mixing did not fully disperse the particles. Hence the composite strength did not improve although the modulus increased. The use of MPS improved the dispersion quality and hence the composite strength. The rheological behavior of SiC nanoparticle-filled vinyl ester resin systems was evaluated in terms of the Bingham, power law, Herschel-Bulkley, and Casson models. Even when the particle loading was less then 4% by weight, the viscosity of the nanoparticle suspension was found to increase much more than that of a microparticle suspension. This phenomenon may be the result of association between nanoparticles and polymer molecules, effectively making the nanoparticles larger. The resulting reduction in the mobility of polymer molecules also led to delayed curing. The maximum particle loading corresponding to infinite viscosity was determined as 0.1 volume fraction using the (1 - eta r-1/2) - ? dependence. The experimental optimum fractional weight per cent of the dispersants (wt. % dispersant/wt. % SiC) was found to be around 40% for 30 nm SiC nanoparticles, which is in close agreement with the theoretically calculated monolayer coverage dosage of 67%.

Yong, Virginia Hiu-Hung

2005-12-01

312

Metal-Enhanced Fluorescence from Nanoparticulate Zinc Films  

PubMed Central

A detailed study of metal-enhanced fluorescence (MEF) from fluorophores in the blue-to- red spectral region placed in close proximity to thermally evaporated zinc nanostructured films is reported. The zinc nanostructured films were deposited onto glass microscope slides as individual particles and were 1–10 nm in height and 20–100 nm in width, as characterized by Atomic Force Microscopy. The surface plasmon resonance peak of the zinc nanostructured films was ? 400 nm. Finite-difference time-domain calculations for single and multiple nanostructures organized in a staggered fashion on a solid support predict, as expected, that the electric fields are concentrated both around and between the nanostructures. Additionally, Mie scattering calculations show that the absorption and scattering components of the extinction spectrum are dominant in the UV and visible spectral ranges, respectively. Enhanced fluorescence emission accompanied by no significant changes in excited state lifetimes of fluorophores with emission wavelengths in the visible blue-to-red spectral range near-to zinc nanostructured films were observed, implying that MEF from zinc nanostructured films is mostly due to an electric field enhancement effect.

Aslan, Kadir; Previte, Michael J.R.; Zhang, Yongxia; Geddes, Chris D.

2009-01-01

313

Dual-nanoparticulate-reinforced aluminum matrix composite materials  

Microsoft Academic Search

Aluminum (Al) matrix composite materials reinforced with carbon nanotubes (CNT) and silicon carbide nanoparticles (nano-SiC) were fabricated by mechanical ball milling, followed by hot-pressing. Nano-SiC was used as an active mixing agent for dispersing the CNTs in the Al powder. The hardness of the produced composites was dramatically increased, up to eight times higher than bulk pure Al, by increasing

Hansang Kwon; Seungchan Cho; Marc Leparoux; Akira Kawasaki

2012-01-01

314

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.

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

2012-01-01

315

Determination of the effective refractive index of nanoparticulate ITO layers.  

PubMed

Nanoparticles of transparent conducting oxides, such as indium tin oxide, can be used in printing techniques to generate functional layers for various optoelectronic devices. Since these deposition methods do not create fully consolidated films, the optical properties of such layers are expected to be notably different from those of the bulk material and should be characterized on their own. In this work we present a way to measure the effective refractive index of a particulate ITO layer by refraction of light. The obtained data points are used to identify an accurate layer model for spectroscopic ellipsometry. In this way the complex refractive index of the particle layer is determined in a wide spectral range from ultra violet to near infrared. PMID:24104162

Baum, M; Alexeev, I; Latzel, M; Christiansen, S H; Schmidt, M

2013-09-23

316

Thick film magnetic nanoparticulate composites and method of manufacture thereof  

NASA Technical Reports Server (NTRS)

Thick film magnetic/insulating nanocomposite materials, with significantly reduced core loss, and their manufacture are described. The insulator coated magnetic nanocomposite comprises one or more magnetic components, and an insulating component. The magnetic component comprises nanometer scale particles (about 1 to about 100 nanometers) coated by a thin-layered insulating phase. While the intergrain interaction between the immediate neighboring magnetic nanoparticles separated by the insulating phase provides the desired soft magnetic properties, the insulating material provides high resistivity, which reduces eddy current loss.

Ma, Xinqing (Inventor); Zhang, Yide (Inventor); Ge, Shihui (Inventor); Zhang, Zongtao (Inventor); Yan, Dajing (Inventor); Xiao, Danny T. (Inventor)

2009-01-01

317

Dual-nanoparticulate-reinforced aluminum matrix composite materials.  

PubMed

Aluminum (Al) matrix composite materials reinforced with carbon nanotubes (CNT) and silicon carbide nanoparticles (nano-SiC) were fabricated by mechanical ball milling, followed by hot-pressing. Nano-SiC was used as an active mixing agent for dispersing the CNTs in the Al powder. The hardness of the produced composites was dramatically increased, up to eight times higher than bulk pure Al, by increasing the amount of nano-SiC particles. A small quantity of aluminum carbide (Al(4)C(3)) was observed by TEM analysis and quantified using x-ray diffraction. The composite with the highest hardness values contained some nanosized Al(4)C(3). Along with the CNT and the nano-SiC, Al(4)C(3) also seemed to play a role in the enhanced hardness of the composites. The high energy milling process seems to lead to a homogeneous dispersion of the high aspect ratio CNTs, and of the nearly spherical nano-SiC particles in the Al matrix. This powder metallurgical approach could also be applied to other nanoreinforced composites, such as ceramics or complex matrix materials. PMID:22571898

Kwon, Hansang; Cho, Seungchan; Leparoux, Marc; Kawasaki, Akira

2012-06-01

318

Dual-nanoparticulate-reinforced aluminum matrix composite materials  

NASA Astrophysics Data System (ADS)

Aluminum (Al) matrix composite materials reinforced with carbon nanotubes (CNT) and silicon carbide nanoparticles (nano-SiC) were fabricated by mechanical ball milling, followed by hot-pressing. Nano-SiC was used as an active mixing agent for dispersing the CNTs in the Al powder. The hardness of the produced composites was dramatically increased, up to eight times higher than bulk pure Al, by increasing the amount of nano-SiC particles. A small quantity of aluminum carbide (Al4C3) was observed by TEM analysis and quantified using x-ray diffraction. The composite with the highest hardness values contained some nanosized Al4C3. Along with the CNT and the nano-SiC, Al4C3 also seemed to play a role in the enhanced hardness of the composites. The high energy milling process seems to lead to a homogeneous dispersion of the high aspect ratio CNTs, and of the nearly spherical nano-SiC particles in the Al matrix. This powder metallurgical approach could also be applied to other nanoreinforced composites, such as ceramics or complex matrix materials.

Kwon, Hansang; Cho, Seungchan; Leparoux, Marc; Kawasaki, Akira

2012-06-01

319

Differences in catalytic properties between mesoporous and nanoparticulate platinum  

NASA Astrophysics Data System (ADS)

Conventional Pt/Al2O3 catalysts prepared by wet-impregnation are composed of Pt nanoparticles exposing convex and facetted surfaces deposited on high-surface area ?-Al2O3 supports. A hexagonal phase mesoporous Pt material (denoted H1-Pt) prepared by chemical reduction in the aqueous domains of a lyotropic liquid crystalline template exposes however mainly a concave surface with expected different catalytic properties. A series of Pt/Al2O3 catalysts were prepared using H1-Pt, Pt-black or wet-impregnated Pt, and the samples were characterized by SEM-EDX and TEM, and finally evaluated for CO oxidation. The H1-Pt/Al2O3 catalyst showed an ignition profile for CO oxidation at lower temperatures and thus appeared less sensitive to CO poisoning than the two other types of samples. This difference may be related to the differences in surface curvature.

Saramat, A.; Andersson, M.; Hant, S.; Thormählen, P.; Skoglundh, M.; Attard, G. S.; Palmqvist, A. E. C.

2007-07-01

320

Pharmacokinetic change of nanoparticulate formulation "Lactosome" on multiple administrations.  

PubMed

Lactosome, which is a polymer micelle composed of poly(lactic acid)-b-poly(sarcosine), was applied successfully for solid tumor imaging. Lactosome is considered to escape from the reticuloendothelial system recognition, and shows prolonged in vivo blood clearance time. In vivo disposition of Lactosome, however, changed upon multiple dosages. Lactosome at the 2nd dosage was cleared from the blood stream by trapping at liver. This accelerated blood clearance (ABC) phenomenon is explained by production of anti-Lactosome IgM and IgG(3) through the immune response related with B-lymphocyte cells. The memory effect of B-lymphocyte cells lasted nearly for six months in mouse. The epitope moiety of Lactosome is concluded to be poly(sarcosine) based on the competitive inhibition assay. Since the ABC phenomenon was also reported with PEGylated liposome, nanoparticles in general may be potential in triggering the immune system. PMID:22841811

Hara, Eri; Makino, Akira; Kurihara, Kensuke; Yamamoto, Fumihiko; Ozeki, Eiichi; Kimura, Shunsaku

2012-11-01

321

Photoproduction of iodine with nanoparticulate semiconductors and insulators  

PubMed Central

The crystal structures of different forms of TiO2 and those of BaTiO3, ZnO, SnO2, WO3, CuO, Fe2O3, Fe3O4, ZrO2 and Al2O3 nanoparticles have been deduced by powder X-ray diffraction. Their optical edges have been obtained by UV-visible diffuse reflectance spectra. The photocatalytic activities of these oxides and also those of SiO2 and SiO2 porous to oxidize iodide ion have been determined and compared. The relationships between the photocatalytic activities of the studied oxides and the illumination time, wavelength of illumination, concentration of iodide ion, airflow rate, photon flux, pH, etc., have been obtained. Use of acetonitrile as medium favors the photogeneration of iodine.

2011-01-01

322

Paclitaxel loaded PEGylated gleceryl monooleate based nanoparticulate carriers in chemotherapy.  

PubMed

A PEGylated drug delivery system of paclitaxel (PTX), based on glyceryl monooleate (GMO) was prepared by optimizing various parameters to explore its potential in anticancer therapy. The prepared system was characterized through polarized light microscopy, TEM, AFM and SAXS to reveal its liquid crystalline nature. As GMO based LCNPs exhibit high hemolytic toxicity and faster release of entrapped drug (66.2 ± 2.5% in 24 h), PEGylation strategy was utilized to increase the hemocompatibility (reduction in hemolysis from 60.3 ± 10.2 to 4.4 ± 1.3%) and control the release of PTX (43.6 ± 3.2% released in 24 h). The cytotoxic potential and cellular uptake was assessed in MCF-7 cell lines. Further, biodistribution studies were carried out in EAT (Ehrlich Ascites tumor) bearing mice using (99m)Tc-(Technetium radionuclide) labeled formulations and an enhanced circulation time and tumor accumulation (14 and 8 times, respectively) were observed with PEGylated carriers over plain ones, at 24 h. Finally, tumor growth inhibition experiment was performed and after 15 days, control group exhibited 15 times enhancement in tumor volume, while plain and PEGylated systems exhibited only 8 and 4 times enhancement, respectively, as compared to initial tumor volume. The results suggest that PEGylation enhances the hemocompatibility and efficacy of GMO based system that may serve as an efficient i.v. delivery vehicle for paclitaxel. PMID:22809646

Jain, Vikas; Swarnakar, Nitin K; Mishra, Prabhat R; Verma, Ashwni; Kaul, Ankur; Mishra, Anil K; Jain, Narendra K

2012-10-01

323

NOVEL NANOPARTICULATE CATALYSTS FOR IMPROVED VOC TREATMENT DEVICES - PHASE I  

EPA Science Inventory

Catalytic oxidation of VOCs is increasingly used for treatment of large-volume emissions at relatively dilute VOC levels. The best performing catalytic oxidation devices for attainment of very high VOC destruction levels employ precious metal catalysts, the costs of which a...

324

Nanoparticulate gellants for metallized gelled liquid hydrogen with aluminum  

NASA Technical Reports Server (NTRS)

Gelled liquid hydrogen was experimentally formulated using sol-gel technology. As a follow-on to work with cryogenic simulants, hydrogen was gelled with an alkoxide material: BTMSE. Initial results demonstrated that gellants with a specific surface area of 1000 m(exp 2)/g could be repeatably fabricated. Gelled hexane and metallized gelled hexane (with 13.8-wt% Al) were produced. Propellant settling testing was conducted for acceleration levels of 2 to 10 times normal gravity and a minimum gellant percentage was determined for stable gelled hexane and metalized gelled hexane. A cryogenic capillary rheometer was also designed, constructed, and used to determine the viscosity of gelled hydrogen. Small volumes of liquid hydrogen were gelled with a 7- to 8-wt% gellant level. The gelled H2 viscosity was 1.5 to 3.7 times that of liquid hydrogen: 0.048 to 0.116 mPa-s versus 0.03 mPa-s for liquid H2 (at 16 K and approximately 1 atm pressure).

Palaszewski, Bryan; Starkovich, John; Adams, Scott

1996-01-01

325

Nanoparticulate systems for the delivery of antisense oligonucleotides  

Microsoft Academic Search

Antisense oligonucleotides are molecules that are able to inhibit gene expression being therefore potentially active for the treatment of viral infections or cancer. However, because of their poor stability in biological medium and their weak intracellular penetration, colloidal drugs carriers such as nanoparticles were developed for the delivery of oligonucleotides (ODN). ODN associated to nanoparticles were shown to be protected

Gregory Lambert; Elias Fattal; Patrick Couvreur

2001-01-01

326

Mannosylated nanoparticulate carriers of rifabutin for alveolar targeting.  

PubMed

The objective of the present study was to evaluate the prospective of engineered nanoparticles for selective delivery of an antituberculosis drug, rifabutin, to alveolar tissues. Drug-loaded solid lipid nanoparticles (SLNs) were synthesized and efficiently mannosylated. The formation of uncoated and coated SLNs was characterized by FTIR spectroscopy and SEM studies. A variety of physicochemical parameters such as drug loading, particle size, polydispersity index, zeta potential, and in vitro drug release were determined. The toxicity and targeting potential of the prepared formulation were assessed with alveolar macrophage uptake, hematological studies, and in vivo studies of uncoated and coated SLNs. Ex vivo cellular uptake studies of SLNs formulations in alveolar macrophages depicted almost six times enhanced uptake due to mannose coating. The hematological studies proved mannose-conjugated system to be less immunogenic and suitable for sustained delivery as evaluated against uncoated formulation. Further, the serum level and organ distribution studies demonstrated efficiency of the system for prolonged circulation and spatial delivery of rifabutin to alveolar tissues. Finally, it was concluded that mannose-conjugated SLNs can be exploited for effective and targeted delivery of rifabutin compared to its uncoated formulation and ultimately increasing the therapeutic margin of safety while reducing the side effects. PMID:19938949

Nimje, Navneet; Agarwal, Abhinav; Saraogi, Gaurav Kant; Lariya, Narendra; Rai, Gopal; Agrawal, Himanshu; Agrawal, G P

2009-12-01

327

Nanoparticulated magnetic drug delivery systems: Preparation and magnetic characterization  

NASA Astrophysics Data System (ADS)

This paper describes how magnetic resonance can be successfully used as a tool to help customize and quantify nanosized magnetic particles while labeling cells and administered in animals for targeting different biological sites. Customization of magnetic nanoparticles is addressed here in terms of production of complex magnetic drug delivery systems whereas quantification of magnetic nanoparticle in different biological compartments emerges as a key experimental information to assess time-dependent magnetic nanoparticle biodistribution profiles. Examples of using magnetic resonance in unfolding information regarding the pharmacokinetics of intravenously-injected surface-functionalized magnetic nanoparticles in animals are included in the paper.

Morais, P. C.

2010-03-01

328

Dynamic behaviors in directed networks  

SciTech Connect

Motivated by the abundance of directed synaptic couplings in a real biological neuronal network, we investigate the synchronization behavior of the Hodgkin-Huxley model in a directed network. We start from the standard model of the Watts-Strogatz undirected network and then change undirected edges to directed arcs with a given probability, still preserving the connectivity of the network. A generalized clustering coefficient for directed networks is defined and used to investigate the interplay between the synchronization behavior and underlying structural properties of directed networks. We observe that the directedness of complex networks plays an important role in emerging dynamical behaviors, which is also confirmed by a numerical study of the sociological game theoretic voter model on directed networks.

Park, Sung Min [Center of Complex Systems, Samsung Economic Research Institute, Seoul 140-702 (Korea, Republic of); Kim, Beom Jun [Department of Physics, BK21 Physics Research Division, and Institute of Basic Science, Sungkyunkwan University, Suwon 440-746 (Korea, Republic of)

2006-08-15

329

Clustering signatures classify directed networks  

NASA Astrophysics Data System (ADS)

We use a clustering signature, based on a recently introduced generalization of the clustering coefficient to directed networks, to analyze 16 directed real-world networks of five different types: social networks, genetic transcription networks, word adjacency networks, food webs, and electric circuits. We show that these five classes of networks are cleanly separated in the space of clustering signatures due to the statistical properties of their local neighborhoods, demonstrating the usefulness of clustering signatures as a classifier of directed networks.

Ahnert, S. E.; Fink, T. M. A.

2008-09-01

330

Numerical Analysis of Dynamic Direct Tension and Direct Compression Tests.  

National Technical Information Service (NTIS)

This report summarizes the results of a comprehensive numerical analysis of direct tension and direct compression tests of plain concrete performed at strain rates between 1 and 10 to the 2nd power on a Split Hopkinson Pressure Bar (SHPB). The objective o...

J. W. Tedesco M. L. Hughes B. P. O'Neil

1993-01-01

331

Packing Rooted Directed Cuts in a Weighted Directed Graph.  

National Technical Information Service (NTIS)

A simple algorithm is described for constructing a maximum packing of cuts directed away from a distinguished vertex, called the root, in a directed graph each of whose edges has a nonnegative weight, and it is shown that the maximum packing value is equa...

D. R. Fulkerson

1972-01-01

332

Directed Discovery of Crystal Structures  

NSDL National Science Digital Library

David Mogk and Kent Ratajeski Department of Earth Sciences, Montana State University, Bozeman, MT Published Jan. 25, 2005 Description This contribution is modified from a published exercise "Directed ...

333

Direct cooled power electronics substrate  

DOEpatents

The disclosure describes directly cooling a three-dimensional, direct metallization (DM) layer in a power electronics device. To enable sufficient cooling, coolant flow channels are formed within the ceramic substrate. The direct metallization layer (typically copper) may be bonded to the ceramic substrate, and semiconductor chips (such as IGBT and diodes) may be soldered or sintered onto the direct metallization layer to form a power electronics module. Multiple modules may be attached to cooling headers that provide in-flow and out-flow of coolant through the channels in the ceramic substrate. The modules and cooling header assembly are preferably sized to fit inside the core of a toroidal shaped capacitor.

Wiles, Randy H [Powell, TN; Wereszczak, Andrew A [Oak Ridge, TN; Ayers, Curtis W. (Kingston, TN) [Kingston, TN; Lowe, Kirk T. (Knoxville, TN) [Knoxville, TN

2010-09-14

334

Scatterometer directional response during rain  

NASA Technical Reports Server (NTRS)

Rainfall modification of directional scatterometer response from the sea surface was simulated in wind-wave tank experiments. Data show that for the range of conditions in laboratory experiments, rain enhances radar cross section for all azimuthal angles relative to wind direction. This result broadens previous measurements, which showed that scatterometer response increases with increasing rainfall for radars pointing upwind. But more to the point, the data also show that the directional dynamic-range of scatterometry diminishes rapidly as rainfall rate increases. Thus, while it may be possible to determine wind speed and direction during rain, it will require adequate system sensitivity.

Bliven, L.; Norcross, G.; Giovanangeli, J.-P.

1989-01-01

335

Problematic Directives in Pedagogical Interaction  

ERIC Educational Resources Information Center

Directives are integral to teachers' pedagogical repertoire, and their efficacy crucial to optimizing learning outcomes. Based on data from a videotaped tutoring session collected at an after-school early literacy program, we describe the specific ways in which certain practices of directives can hinder learner participation and compromise…

Waring, Hansun Zhang; Hruska, Barbara L.

2012-01-01

336

Symmetrizations for clustering directed graphs  

Microsoft Academic Search

Graph clustering has generally concerned itself with clustering undirected graphs; however the graphs from a number of important domains are essentially directed, e.g. networks of web pages, research papers and Twitter users. This paper investigates various ways of symmetrizing a directed graph into an undirected graph so that previous work on clustering undirected graphs may subsequently be leveraged. Recent work

Venu Satuluri; Srinivasan Parthasarathy

2011-01-01

337

Direct mediation, duality and unification  

Microsoft Academic Search

It is well-known that in scenarios with direct gauge mediation of supersymmetry breaking the messenger fields significantly affect the running of Standard Model couplings and introduce Landau poles which are difficult to avoid. Among other things, this appears to remove any possibility of a meaningful unification prediction and is often viewed as a strong argument against direct mediation. We propose

Steven Abel; Valentin V. Khoze

2008-01-01

338

A Directional Borehole Radar System  

Microsoft Academic Search

In this paper we present the simulation and design of a directional borehole radar. In addition we discuss an imaging method for the radar system. The antenna system contains an electric dipole which is in one direction shielded by a cylindrical perfectly conducting reflector. The radiation pattern of the reflected wavefield is computed by first solving the integral equation. This

Koen W. A. van Dongen; Ronald van Waard; Stefan van der Baan; Peter M. van den Berg; Jacob T. Fokkema

2002-01-01

339

Epidemic threshold in directed networks  

NASA Astrophysics Data System (ADS)

Epidemics have so far been mostly studied in undirected networks. However, many real-world networks, such as the online social network Twitter and the world wide web, on which information, emotion, or malware spreads, are directed networks, composed of both unidirectional links and bidirectional links. We define the directionality ? as the percentage of unidirectional links. The epidemic threshold ?c for the susceptible-infected-susceptible (SIS) epidemic is lower bounded by 1/?1 in directed networks, where ?1, also called the spectral radius, is the largest eigenvalue of the adjacency matrix. In this work, we propose two algorithms to generate directed networks with a given directionality ?. The effect of ? on the spectral radius ?1, principal eigenvector x1, spectral gap (?1-?2), and algebraic connectivity ?N-1 is studied. Important findings are that the spectral radius ?1 decreases with the directionality ?, whereas the spectral gap and the algebraic connectivity increase with the directionality ?. The extent of the decrease of the spectral radius depends on both the degree distribution and the degree-degree correlation ?D. Hence, in directed networks, the epidemic threshold is larger and a random walk converges to its steady state faster than that in undirected networks with the same degree distribution.

Li, Cong; Wang, Huijuan; Van Mieghem, Piet

2013-12-01

340

Directional Dogbone Flextensional Sonar Transducer.  

National Technical Information Service (NTIS)

In order to transmit energy in one direction, sonar flextensional transducers are combined into arrays of elements that are spaced a 1/4 wavelength apart. The directionality (front-to- back pressure ratio) is a modest of 6 dB. A single projector that is 1...

S. C. Butler

2010-01-01

341

Defense Nuclear Agency (DNA). Directive  

SciTech Connect

Under the authority vested in the Secretary of Defense by Title 10, United States Code, the Directive reissues DoD Directive 5105.31, November 3, 1971, to update the responsibilities, functions, relationship, and authorities of the Defense Nuclear Agency.

Furtner, R.

1987-03-18

342

Efficient Placement of Directional Antennas  

SciTech Connect

Directional antenna is an technology for the proliferation of wireless networks. In centralized wireless network, wireless devices communicate through base stations. Directed antennas are placed on base stations and form a backbone of communication. The communication between base stations and wireless devices can be interfered due to a large number of wireless device. Methodically positioning and orienting directed antennas can help to reduce the interference while saving energy. An integer linear programming is developed for siting and directing antennas on multiple base stations, and this formulation can be extended to model non-overlapping channels. Through the integer programming formulation, optimal antenna positions can be used to analyze the performance of directed antennas with different parameters like the number base stations and the number of non-overlapping channels.

Pan, Feng [Los Alamos National Laboratory; Kasiviswanathan, Shiva [Los Alamos National Laboratory

2010-09-20

343

Direct Manipulation in Virtual Reality  

NASA Technical Reports Server (NTRS)

Virtual Reality interfaces offer several advantages for scientific visualization such as the ability to perceive three-dimensional data structures in a natural way. The focus of this chapter is direct manipulation, the ability for a user in virtual reality to control objects in the virtual environment in a direct and natural way, much as objects are manipulated in the real world. Direct manipulation provides many advantages for the exploration of complex, multi-dimensional data sets, by allowing the investigator the ability to intuitively explore the data environment. Because direct manipulation is essentially a control interface, it is better suited for the exploration and analysis of a data set than for the publishing or communication of features found in that data set. Thus direct manipulation is most relevant to the analysis of complex data that fills a volume of three-dimensional space, such as a fluid flow data set. Direct manipulation allows the intuitive exploration of that data, which facilitates the discovery of data features that would be difficult to find using more conventional visualization methods. Using a direct manipulation interface in virtual reality, an investigator can, for example, move a data probe about in space, watching the results and getting a sense of how the data varies within its spatial volume.

Bryson, Steve

2003-01-01

344

Module bay with directed flow  

DOEpatents

A module bay requires less cleanroom airflow. A shaped gas inlet passage can allow cleanroom air into the module bay with flow velocity preferentially directed toward contaminant rich portions of a processing module in the module bay. Preferential gas flow direction can more efficiently purge contaminants from appropriate portions of the module bay, allowing a reduced cleanroom air flow rate for contaminant removal. A shelf extending from an air inlet slit in one wall of a module bay can direct air flowing therethrough toward contaminant-rich portions of the module bay, such as a junction between a lid and base of a processing module.

Torczynski, John R. (Albuquerque, NM)

2001-02-27

345

Directional fast-neutron detector  

DOEpatents

A plurality of omnidirectional radiation detectors are arranged in a close packed symmetrical pattern to form a segmented detector. The output radiation counts from these detectors are arithmetically combined to provide the direction of a source of incident radiation. Directionality is achieved without the use of shielding to provide collimation and background reduction effects. Indeed, output counts from paired detectors are simply subtracted to yield a vector direction toward the radiation source. The counts from all of the detectors can be combined to yield an output signal functionally related to the radiation source strength.

Byrd, Roger C. (Albuquerque, NM)

1994-01-01

346

2008 world direct reduction statistics  

SciTech Connect

This supplement discusses total direct reduced iron (DRI) production for 2007 and 2008 by process. Total 2008 production by MIDREX(reg sign) direct reduction process plants was over 39.8 million tons. The total of all coal-based processes was 17.6 million tons. Statistics for world DRI production are also given by region for 2007 and 2008 and by year (1970-2009). Capacity utilization for 2008 by process is given. World DRI production by region and by process is given for 1998-2008 and world DRI shipments are given from the 1970s to 2008. A list of world direct reduction plants is included.

NONE

2009-07-01

347

Improved Properties by Direct Quenching.  

National Technical Information Service (NTIS)

The advantages on mechanical properties by quenching directly after hot deformation and tempering are discussed in detail, and it is shown that increased precipitation strengthening efficiency is achieved by the process in comparison with the conventional...

G. Tither J. Kewell M. G. Frost

1972-01-01

348

Direct Detectors for Electron Microscopy  

NASA Astrophysics Data System (ADS)

There is interest in improving the detectors used to capture images in transmission electron microscopy. Detectors with an improved modulation transfer function at high spatial frequencies allow for higher resolution in images at lower magnification, which leads to an increased effective field of view. Detectors with improved detective quantum efficiency are important for low dose applications. One way in which these performance enhancements can be achieved is through direct detection, where primary electrons are converted directly into suitable electrical signals by the detector rather than relying on an indirect electron to photon conversion before detection. In this paper we present the characterisation of detector performance for a number of different direct detection technologies, and compare these technologies to traditional indirect detectors. Overall our results show that direct detection enables a significant improvement in all aspects of detector performance.

Clough, R. N.; Moldovan, G.; Kirkland, A. I.

2014-06-01

349

Direct Methane Conversion: An Assessment.  

National Technical Information Service (NTIS)

This report documents technical analyses of the following direct methane conversion approaches: oxidative coupling, partial oxidation and oxyhydrochlorination. System efficiencies are compared to the performance of conventional steam reforming, methanol s...

D. Gray G. Tomlinson

1988-01-01

350

Direct Methane Conversion Process Evaluations.  

National Technical Information Service (NTIS)

The first task in this study is to screen direct methane conversion processes and select three for process design and cost evaluation. Criteria used are: degree of definition; economic potential; projected thermal efficiency; number of steps involved; and...

J. M. C. T. Fox

1988-01-01

351

Direct Broadcast Satellite: Radio Program  

NASA Technical Reports Server (NTRS)

NASA is committed to providing technology development that leads to the introduction of new commercial applications for communications satellites. The Direct Broadcast Satellite-Radio (DBS-R) Program is a joint effort between The National Aeronautics and Space Administration (NASA) and The United States Information Agency/Voice of America (USIA/VOA) directed at this objective. The purpose of this program is to define the service and develop the technology for a direct-to-listener satellite sound broadcasting system. The DBS-R Program, as structured by NASA and VOA, is now a three-phase program designed to help the U.S. commercial communications satellite and receiver industry bring about this new communications service. Major efforts are being directed towards frequency planning hardware and service development, service demonstration, and experimentation with new satellite and receiver technology.

Hollansworth, James E.

1992-01-01

352

Direct Simulation of Turbulent Combustion.  

National Technical Information Service (NTIS)

Direct Numerical Simulation (DNS) results obtained for premixed turbulent flames are presented and discussed to provide a description of the DNS possibilities and limitations. Numerical issues and boundary conditions are discussed. The basis of flamelet m...

T. J. Poinsot

1992-01-01

353

Direct nuclear-powered lasers  

NASA Technical Reports Server (NTRS)

The development of direct nuclear pumped lasers is reviewed. Theoretical and experimental investigations of various methods of converting the energy of nuclear fission fragments to laser power are summarized. The development of direct nuclear pumped lasers was achieved. The basic processes involved in the production of a plasma by nuclear radiation were studied. Significant progress was accomplished in this area and a large amount of basic data on plasma formation and atomic and molecular processes leading to population inversions is available.

Jalufka, N. W.

1983-01-01

354

Numerical analysis of dynamic direct tension and direct compression tests  

NASA Astrophysics Data System (ADS)

This report summarizes the results of a comprehensive numerical analysis of direct tension and direct compression tests of plain concrete performed at strain rates between 1 and 10 to the 2nd power on a Split Hopkinson Pressure Bar (SHPB). The objective of this study was to investigate failure mechanisms in plain concrete specimens at high strain rates. Both an elastic and inelastic concrete material model were employed in all numerical analyses. The modes of failure predicted by the numerical analyses are consistent with those observed in experimental studies. In all instances, the mode of failure was significantly influenced by the rate of loading.

Tedesco, Joseph W.; Hughes, Mary L.; Oneil, Brian P.

1993-01-01

355

"Let Me Be Direct": Using Direct Assessments with Student Leaders  

ERIC Educational Resources Information Center

A primary goal of assessment is to deliver truthful and clear information that can be used to inform and improve outcomes. Although there are multiple ways to achieve this goal, common approaches can be broken down into two major categories: (1) direct assessment; and (2) indirect assessment. Indirect assessment typically relies on general…

Lindsay, Nathan; Hourigan, Aimee; Smist, Jennifer; Wray, Larry

2013-01-01

356

Dark Matter (mostly Direct) Detection  

NASA Astrophysics Data System (ADS)

After briefly summarizing the motivations for the ?-CDM model, I will argue rather provocatively that the many candidates already reported by indirect detection experiments are a strong indication that it is nearly impossible to distinguish a WIMP annihilation signal from astrophysical background using the indirect detection method. This structural uncertainty argues strongly in favor of direct detection of WIMP interactions in the controlled environment of the laboratory and I will describe the main strategies developed to detect WIMPs using the direct detection technique in underground sites, protected from the cosmic-ray induced background. I will show that most of the present experimental efforts is now focused on three identification techniques of nuclear recoils, i.e. charge-phonon, light-phonon and charge-scintillation simultaneous detection. Finally, since direct detection has also its own candidate, I will comment on the DAMA annual modulation candidate, and on the lessons that can be learned from the long controversy over this result.

Chardin, G.

2010-06-01

357

Directions for improved fusion reactors  

SciTech Connect

Conceptual fusion reactor studies over the past 10 to 15 years have projected systems that may be too large, complex, and costly to be of commercial interest. One main direction for improved fusion reactors points towards smaller, higher-power-density approaches. First-order economic issues (i.e., unit direct cost and cost of electricity) are used to support the need for more compact fusion reactors. A generic fusion physics/engineering/costing model is used to provide a quantiative basis for these arguments for specific fusion concepts.

Krakowski, R.A.; Miller, R.L.; Delene, J.G.

1986-01-01

358

Directional drilling and earth curvature  

SciTech Connect

This paper provides a review of current practices for calculating directional drilling placement in the light of modern extended-reach applications. The review highlights the potential for gross errors in the application of geodetic reference information and errors inherent in the calculation method. Both types of error are quantified theoretically and illustrated with a real example. The authors borrow established land surveying calculation methods to develop a revised best practice for directional drilling. For the elimination of gross errors they prescribe increased awareness and a more disciplined approach to the handling of positional data.

Williamson, H.S.; Wilson, H.F.

2000-03-01

359

Biocatalyst Development by Directed Evolution  

PubMed Central

Biocatalysis has emerged as a great addition to traditional chemical processes for production of bulk chemicals and pharmaceuticals. To overcome the limitations of naturally occurring enzymes, directed evolution has become the most important tool for improving critical traits of biocatalysts such as thermostability, activity, selectivity, and tolerance towards organic solvents for industrial applications. Recent advances in mutant library creation and high-throughput screening have greatly facilitated the engineering of novel and improved biocatalysts. This review provides an update of the recent developments in the use of directed evolution to engineer biocatalysts for practical applications.

Wang, Meng; Si, Tong; Zhao, Huimin

2012-01-01

360

Sparse Direct Methods: An Introduction  

NASA Astrophysics Data System (ADS)

The solution of large-scale linear systems lies at the heart of many computations in science, engineering, industry, and (more recently) finance. In this paper, we give a brief introduction to direct methods based on Gaussian elimination for the solution of such systems. We discuss the methods with reference to the sparse direct solvers that are available in the Harwell Subroutine Library. We briefly consider large sparse eigenvalue problems and show how the efficient solution of such problems depends upon the efficient solution of sparse linear systems.

Scott, J. A.

361

A Cell's Sense of Direction  

NSDL National Science Digital Library

In eukaryotic cells directional sensing is mediated by heterotrimeric guanine nucleotideâÂÂbinding protein (G protein)âÂÂlinked signaling pathways. In Dictyostelium discoideum amoebae and mammalian leukocytes, the receptors and G-protein subunits are uniformly distributed around the cell perimeter. Chemoattractants induce the transient appearance of binding sites for several pleckstrin homology domainâÂÂcontaining proteins on the inner face of the membrane. In gradients of attractant these sites are persistently present on the side of the cell facing the higher concentration, even in the absence of a functional actin cytoskeleton or cell movement. Thus, the cell senses direction by spatially regulating the activity of the signal transduction pathway.

Carole A. Parent (Johns Hopkins University School of Medicine;Department of Biological Chemistry); Peter N. Devreotes (Johns Hopkins University School of Medicine;Department of Biological Chemistry)

1999-04-30

362

Direct measurement of intracellular pressure.  

PubMed

A method to directly measure the intracellular pressure of adherent, migrating cells is described in this unit. This approach is based on the servo-null method where a microelectrode is introduced into the cell to directly measure the physical pressure of the cytoplasm. We also describe the initial calibration of the microelectrode, as well as the application of the method to cells migrating inside three-dimensional (3-D) extracellular matrix (ECM). Curr. Protoc. Cell Biol. 63:12.9.1-12.9.9. © 2014 by John Wiley & Sons, Inc. PMID:24894836

Petrie, Ryan J; Koo, Hyun

2014-01-01

363

Directional harmonics in Doppler effect  

NASA Astrophysics Data System (ADS)

A mathematical theory is presented which shows that a moving reflector of waves gives rise to harmonics of the Doppler shift in the input impedance of the transmission medium. The analysis can be used to explain new 'direction of motion' detection phenomena.

Lazarus, M. J.; Somekh, M. G.; Novak, S.; Pantoja, F. R.

1981-01-01

364

Following Directions - Ndakinna Wilderness Project  

NSDL National Science Digital Library

In this lesson, students watch a video segment, take notes and follow directions to create both a diagram with captions and a drawing that communicates information about camouflaging. Learners critically analyze texts by identifying which details are important to note. Note taking allows learners to focus, organize and clarify their thinking and understanding of texts.

2010-01-01

365

Directions for Defense Digital Libraries.  

ERIC Educational Resources Information Center

Describes directions, challenges, and objectives of the information management program of the United States Defense Advanced Research Projects Agency (DARPA). The program envisions the rigor and organization normally associated with a research library to be virtually rendered and extended in the networked world of distributed information. (AEF)

Larsen, Ronald L.

1998-01-01

366

Direct simulation of turbulent combustion  

NASA Technical Reports Server (NTRS)

Understanding and modeling of turbulent combustion are key problems in the computation of numerous practical systems. Because of the lack of analytical theories in this field and of the difficulty of performing precise experiments, direct simulation appears to be one of the most attractive tools to use in addressing this problem. From Sep. 1989 - Sep. 1990, the following problems were studied using direct simulation but also experiments and theoretical models: (1) the influence of curvature on premixed flame fronts; (2) the construction of a model for the flame stretch based on direct simulation and multifractal analysis; and (3) the simulation of the interaction between random flow field and a flame front. The general objective was to improve knowledge of turbulent combustion but also to use this information for turbulent combustion models. The transfer of direct simulation results towards models is also in progress. A submodel to evaluate the flame stretch was derived from the present study and incorporated in the Coherent Flame model used in France for piston and aircraft engines.

Poinsot, Thierry J.

1991-01-01

367

Laboratory-Directed Protein Evolution  

PubMed Central

Systematic approaches to directed evolution of proteins have been documented since the 1970s. The ability to recruit new protein functions arises from the considerable substrate ambiguity of many proteins. The substrate ambiguity of a protein can be interpreted as the evolutionary potential that allows a protein to acquire new specificities through mutation or to regain function via mutations that differ from the original protein sequence. All organisms have evolutionarily exploited this substrate ambiguity. When exploited in a laboratory under controlled mutagenesis and selection, it enables a protein to “evolve” in desired directions. One of the most effective strategies in directed protein evolution is to gradually accumulate mutations, either sequentially or by recombination, while applying selective pressure. This is typically achieved by the generation of libraries of mutants followed by efficient screening of these libraries for targeted functions and subsequent repetition of the process using improved mutants from the previous screening. Here we review some of the successful strategies in creating protein diversity and the more recent progress in directed protein evolution in a wide range of scientific disciplines and its impacts in chemical, pharmaceutical, and agricultural sciences.

Yuan, Ling; Kurek, Itzhak; English, James; Keenan, Robert

2005-01-01

368

Reflections, Perceptions, and Future Directions.  

ERIC Educational Resources Information Center

This response by the original author to critiques of his review of his own work in gifted education suggests possible new directions for the field. These include: the relationship between general and gifted education, the under representation of minority students as the "time bomb" of gifted education, achieving a balance between curricular…

Renzulli, Joseph S.

1999-01-01

369

Future Directions for Machine Learning  

Microsoft Academic Search

Summary In this paper we discuss possible future directions of research for soft computing in the context of artificial intelligence machine learning. Fundamental issues are presented with basic ideas emphasised rather than detailed accounts of algorithms and procedures. The use of fuzzy sets for machine learning, computer intelligence and creativity are discussed in relation to the central problems of creating

J. F. Baldwin

370

Directing Performers for the Cameras.  

ERIC Educational Resources Information Center

An excellent way for an undergraduate, novice director of television and film to pick up background experience in directing performers for cameras is by participating in nonbroadcast-film activities, such as theatre, dance, and variety acts, both as performer and as director. This document describes the varieties of activities, including creative,…

Wilson, George P., Jr.

371

Direction discriminating hearing aid system  

NASA Technical Reports Server (NTRS)

A visual display was developed for people with substantial hearing loss in either one or both ears. The system consists of three discreet units; an eyeglass assembly for the visual display of the origin or direction of sounds; a stationary general purpose noise alarm; and a noise seeker wand.

Jhabvala, M.; Lin, H. C.; Ward, G.

1991-01-01

372

A Note on Direct Costing  

Microsoft Academic Search

In many organizations the engineer plays an important role in making cost studies, establishing budgets, and setting cost standards. As a result, he becomes involved with a wide variety of cost data and with accounting procedures for treatin3 such data. This being the case, the growing utilization of direct costing in manufacturing concerns has considerable significance for many engineers. The

David V. Heebink

1963-01-01

373

Directed information dissemination in VANET  

Microsoft Academic Search

We assume that there exists an inter vehicular network using OLSR where accident information can be propagated to all nodes using on-going OLSR control packets. In order to ensure relevancy of the information, we want to be able to control the direction to which the information should or should not be sent. In this paper, we discuss our scheme to

A. K. M. Mahtab Hossain; Preechai Mekbungwan; Kanchana Kanchanasut

2011-01-01

374

Developments in Direct Drilling Techniques.  

National Technical Information Service (NTIS)

The report outlines methods and techniques of measuring in-groove r.h.% in the direct drilled seed micro-environment, as an indirect performance assessment tool for evaluating seed drill openers. A number of laboratory and field experiments, which used va...

M. A. Choudhary C. J. Baker

1985-01-01

375

Direct-Coupled-Resonator Filters  

Microsoft Academic Search

A new analysis is given of direct-coupled-resonator filters that results in excellent response at much greater bandwidths than has previously been possible. The method relies on the fact that the coupling elements can be made into perfect impedance inverters, or \\

Seymour Cohn

1957-01-01

376

DIRECTIONS TOWARDS FUTURE GREEN INTERNET  

Microsoft Academic Search

This paper presents several technical directions towards re- alizing future green Internet. The threat of man-made cli- mate change has become a key issue in the world and is cur- rently forcing various industries including ICT to reduce both energy consumption and carbon emissions. This paper de- scribes power consumption and carbon emissions caused by ICT and their forecast in

Hideaki Imaizumi; Hiroyuki Morikawa

377

Direct methods for recovering motion  

Microsoft Academic Search

We have developed direct methods for recovering the motion of an observer in a static environment in th e case of pure rotation, pure translation, and arbitrary motion when the rotation is known . Some of thes e methods are based on the minimization of the difference between the observed time derivative of bright - ness and that predicted from

Berthold K. P. Horn; E. J. WELDON JR

1988-01-01

378

New Directions in Teacher Education.  

ERIC Educational Resources Information Center

Approximately one-third of Microelectronics Education Programme (MEP) funding is directed toward in-service teacher education. Three levels of competence (familiarization, understanding, applications) are fostered in each of four domains: electronics/control technology; computer as instrument; computer as learning; and electronic communications.…

Anderson, John

1982-01-01

379

Direct flow crystal growth system  

DOEpatents

A crystal is grown in a constantly filtered solution which is flowed directly into the growing face of a crystal. In a continuous flow system, solution at its saturation temperature is removed from a crystal growth tank, heated above its saturation temperature, filtered, cooled back to its saturation temperature, and returned to the tank.

Montgomery, Kenneth E. (Tracy, CA) [Tracy, CA; Milanovich, Fred P. (Lafayette, CA) [Lafayette, CA

1992-01-01

380

Training of Direct Service Staff.  

ERIC Educational Resources Information Center

This newsletter theme issue features articles on training of direct service staff working with persons with developmental disabilities in employment, education, and residential settings. The articles examine job training, delivery systems, training models, and implications of current approaches. The newsletter includes three articles presenting…

Wallace, Teri, Ed.; And Others

1992-01-01

381

Direct calculation of ionization energies  

Microsoft Academic Search

The advantages of the propagator formalism, as a direct method of calculating ionization energies, are stressed. The propagator equations are derived for closed-shell systems using an operator method instead of the usual diagrammatic derivations. The equations enable the development of an interpretation of the ionization energies in terms of conceptually simple quantities, such as pair correlation energies and associated relaxation

B. T. Pickup; O. Goscinski

1973-01-01

382

Efficient Goal-Directed Exploration  

Microsoft Academic Search

If a state space is not completely known in advance, then search algorithms have to explore it sufficiently to locate a goal state and a path leading to it, performing therefore what we call goal-directed exploration. Two paradigms of this process are pure exploration and heuristic-driven exploita- tion: the former approaches explore the state space using only knowledge of the

Yury V. Smirnov; Sven Koenig; Manuela M. Veloso; Reid G. Simmons

1996-01-01

383

Direct Time Resolution of Sonoluminescence.  

National Technical Information Service (NTIS)

Sonoluminescence is the synchronous emissions of pulses of light that are observed to originate from a gas bubble trapped at the pressure antinode of a resonant sound field in a liquid. The duration of the pulse has been directly measured by launching the...

G. R. Abel

1993-01-01

384

Postsecondary, Teacher Directed Comprehension Strategies.  

ERIC Educational Resources Information Center

Examines the theoretical and research perspectives (including metacognition, schema theory, and text structure) related to the direct instruction of comprehension at the college level for developmental readers. Concludes that many such strategies are not grounded in solid research bases and recommends that future research focus on the…

Mealey, Donna L.; Nist, Sherrie L.

1989-01-01

385

Direct detection of dark matter axions with directional sensitivity  

NASA Astrophysics Data System (ADS)

We study the directional effect of the expected axion dark matter signal in a resonant cavity of an axion haloscope detector, for cavity geometries not satisfying the condition that the axion de Broglie wavelength ?a is sufficiently larger than the cavity dimensions L for a fully coherent conversion, i.e. ?agtrsim2?L. We focus on long thin cavities immersed in dipole magnets and find, for appropriately chosen cavity lengths, an O(1) modulation of the signal with the cavity orientation with respect the momentum distribution of the relic axion background predicted by the isothermal sphere model for the galactic dark matter halo. This effect can be exploited to design directional axion dark matter detectors, providing an unmistakable signature of the extraterrestrial origin of a possible positive detection. Moreover, the precise shape of the modulation may give information of the galactic halo distribution and, for specific halo models, give extra sensitivity for higher axion masses.

Irastorza, Igor G.; García, Juan A.

2012-10-01

386

Sampling properties of directed networks  

NASA Astrophysics Data System (ADS)

For many real-world networks only a small “sampled” version of the original network may be investigated; those results are then used to draw conclusions about the actual system. Variants of breadth-first search (BFS) sampling, which are based on epidemic processes, are widely used. Although it is well established that BFS sampling fails, in most cases, to capture the IN component(s) of directed networks, a description of the effects of BFS sampling on other topological properties is all but absent from the literature. To systematically study the effects of sampling biases on directed networks, we compare BFS sampling to random sampling on complete large-scale directed networks. We present new results and a thorough analysis of the topological properties of seven complete directed networks (prior to sampling), including three versions of Wikipedia, three different sources of sampled World Wide Web data, and an Internet-based social network. We detail the differences that sampling method and coverage can make to the structural properties of sampled versions of these seven networks. Most notably, we find that sampling method and coverage affect both the bow-tie structure and the number and structure of strongly connected components in sampled networks. In addition, at a low sampling coverage (i.e., less than 40%), the values of average degree, variance of out-degree, degree autocorrelation, and link reciprocity are overestimated by 30% or more in BFS-sampled networks and only attain values within 10% of the corresponding values in the complete networks when sampling coverage is in excess of 65%. These results may cause us to rethink what we know about the structure, function, and evolution of real-world directed networks.

Son, S.-W.; Christensen, C.; Bizhani, G.; Foster, D. V.; Grassberger, P.; Paczuski, M.

2012-10-01

387

Sampling properties of directed networks.  

PubMed

For many real-world networks only a small "sampled" version of the original network may be investigated; those results are then used to draw conclusions about the actual system. Variants of breadth-first search (BFS) sampling, which are based on epidemic processes, are widely used. Although it is well established that BFS sampling fails, in most cases, to capture the IN component(s) of directed networks, a description of the effects of BFS sampling on other topological properties is all but absent from the literature. To systematically study the effects of sampling biases on directed networks, we compare BFS sampling to random sampling on complete large-scale directed networks. We present new results and a thorough analysis of the topological properties of seven complete directed networks (prior to sampling), including three versions of Wikipedia, three different sources of sampled World Wide Web data, and an Internet-based social network. We detail the differences that sampling method and coverage can make to the structural properties of sampled versions of these seven networks. Most notably, we find that sampling method and coverage affect both the bow-tie structure and the number and structure of strongly connected components in sampled networks. In addition, at a low sampling coverage (i.e., less than 40%), the values of average degree, variance of out-degree, degree autocorrelation, and link reciprocity are overestimated by 30% or more in BFS-sampled networks and only attain values within 10% of the corresponding values in the complete networks when sampling coverage is in excess of 65%. These results may cause us to rethink what we know about the structure, function, and evolution of real-world directed networks. PMID:23214649

Son, S-W; Christensen, C; Bizhani, G; Foster, D V; Grassberger, P; Paczuski, M

2012-10-01

388

Rapid preparation of Pt-Ru/graphitic carbon nanofiber nanocomposites as DMFC anode catalysts using microwave processing.  

PubMed

Pt-Ru/graphitic carbon nanofiber (GCNF) nanocomposites have been prepared on two different GCNF supports, with the use of a bimetallic precursor as a source of metal and microwave processing for thermal treatments. Pt-Ru nanoparticles appear as the major metal-containing component of these nanocomposites along with variable trace amounts of Ru metal. Use of microwave heating permits rapid preparation of these nanocomposites and affords metal nanoclusters of nearly uniform size. The performance of these nanocomposites as anode electrocatalysts in direct-methanol fuel cells (DMFCs) is compared with that of unsupported Pt-Ru colloid at identical total metal loading. The Pt-Ru/narrow tubular herringbone GCNF nanocomposite shows DMFC performance comparable to that recorded for an unsupported Pt-Ru colloid. PMID:14503410

Steigerwalt, Eve S; Deluga, Gregg A; Lukehart, C M

2003-06-01

389

Fault Branching and Rupture Directivity  

NASA Astrophysics Data System (ADS)

Can the rupture directivity of past earthquakes be inferred from fault geometry? Nakata et al. [J. Geogr., 1998] propose to relate the observed surface branching of fault systems with directivity. Their work assumes that all branches are through acute angles in the direction of rupture propagation. However, in some observed cases rupture paths seem to branch through highly obtuse angles, as if to propagate ``backwards". Field examples of that are as follows: (1) Landers 1992. When crossing from the Johnson Valley to the Homestead Valley (HV) fault via the Kickapoo (Kp) fault, the rupture from Kp progressed not just forward onto the northern stretch of the HV fault, but also backwards, i.e., SSE along the HV [Sowers et al., 1994, Spotila and Sieh, 1995, Zachariasen and Sieh, 1995, Rockwell et al., 2000]. Measurements of surface slip along that backward branch, a prominent feature of 4 km length, show right-lateral slip, decreasing towards the SSE. (2) At a similar crossing from the HV to the Emerson (Em) fault, the rupture progressed backwards along different SSE splays of the Em fault [Zachariasen and Sieh, 1995]. (3). In crossing from the Em to Camp Rock (CR) fault, again, rupture went SSE on the CR fault. (4). Hector Mine 1999. The rupture originated on a buried fault without surface trace [Li et al., 2002; Hauksson et al., 2002] and progressed bilaterally south and north. In the south it met the Lavic Lake (LL) fault and progressed south on it, but also progressed backward, i.e. NNW, along the northern stretch of the LL fault. The angle between the buried fault and the northern LL fault is around -160o, and that NNW stretch extends around 15 km. The field examples with highly obtuse branch angles suggest that there may be no simple correlation between fault geometry and rupture directivity. We propose that an important distinction is whether those obtuse branches actually involved a rupture path which directly turned through the obtuse angle (while continuing also on the main fault), or rather involved arrest by a barrier on the original fault and jumping [Harris and Day, JGR, 1993] to a neighboring fault on which rupture propagated bilaterally to form what appears as a backward-branched structure. Our studies [Poliakov et al., JGR in press, 2002; Kame et al, EOS, 2002] of stress fields around a dynamically moving mode II crack tip show a clear tendency to branch from the straight path at high rupture speeds, but the stress fields never allow the rupture path to directly turn through highly obtuse angles, and hence that mechanism is unlikely. In contrast, study of fault maps in the vicinity of the Kp to HV fault transition [Sowers et al., 1994], discussed as case (1) above, strongly suggest that the large-angle branching occurred as a jump, which we propose as the likely general mechanism. Implications for the Nakata et al. [1998] aim of inferring rupture directivity from branch geometry is that this will be possible only when rather detailed characterization (by surface geology, seismic relocation, trapped waves) of fault connectivity can be carried out in the vicinity of the branching junction, to ascertain whether direct turning of the rupture path through an angle, or jumping and then propagating bilaterally, were involved in prior events. They have opposite implications for how we would associate past directivity with a (nominally) branched fault geometry.

Dmowska, R.; Rice, J. R.; Kame, N.

2002-12-01

390

Direction Counts: A Comparative Study of Spatially Directional Counting Biases in Cultures with Different Reading Directions  

ERIC Educational Resources Information Center

Western adults associate small numbers with left space and large numbers with right space. Where does this pervasive spatial-numerical association come from? In this study, we first recorded directional counting preferences in adults with different reading experiences (left to right, right to left, mixed, and illiterate) and observed a clear…

Shaki, Samuel; Fischer, Martin H.; Gobel, Silke M.

2012-01-01

391

Advance Directives for Mental Health Treatment  

Microsoft Academic Search

Advance directives are designed to establish a person's preferences for treatment if the person becomes incompetent in the future or unable to communicate those preferences to treatment providers. Mental health advance directives are similar to the more commonly used directives for end-of-life medical decisions. A patient must be competent to execute a mental health advance directive, and the directive must

Debra S. Srebnik; John Q. La Fond

392

Entrance Counseling Guide for Direct Loan Borrowers  

ERIC Educational Resources Information Center

This guide describes the four types of loans offered by the Direct Loan Program[SM]: (1) Direct Subsidized Loans; (2) Direct Unsubsidized Loans; (3) Direct PLUS Loans; and (4) Direct Consolidation Loans. Among the topics covered in the guide are: Use of Your Loan Money, The Master Promissory Note, How Your Loans Will Be Disbursed (Paid Out),…

Federal Student Aid, US Department of Education, 2010

2010-01-01

393

Prototype Borehole Directional Radar System  

SciTech Connect

This report summarizes the progress of the Borehole Directional Radar (BDR) System, which is a high-power, high-resolution tool that is being developed to locate lithologic layers or fractures away from a wellbore. The key to the tool's potential is its ability to accurately measure distance and direction of a lithologic discontinuity underground. The results of two field tests in 1988 are presented. The report also discusses the deficiencies of the current system, and a proposed upgrade. Finally, possible other applications of the BDR System are outlined, including (1) locating gas and oil reservoirs below a salt dome, (2) determining the integrity of underground structures (e.g., Strategic Petroleum Reserve, Nuclear Waste Repository Site), and (3) verifying underground nuclear tests. 25 refs., 14 figs.

Chang, Hsi-Tien

1989-09-01

394

Asymmetrically Coupled Directed Percolation Systems  

NASA Astrophysics Data System (ADS)

We introduce a dynamical model of coupled directed percolation systems with two particle species. The two species A and B are coupled asymmetrically in that A particles branch B particles, whereas B particles prey on A particles. This model may describe epidemic spreading controlled by reactive immunization agents. We study nonequilibrium phase transitions with attention focused on the multicritical point where both species undergo the absorbing phase transition simultaneously. In one dimension, we find that the inhibitory coupling from B to A is irrelevant and the model belongs to the unidirectionally coupled directed percolation class. On the contrary, a mean-field analysis predicts that the inhibitory coupling is relevant and a new universality appears with a variable dynamic exponent. Numerical simulations on small-world networks confirm our predictions.

Noh, Jae Dong; Park, Hyunggyu

2005-04-01

395

ODE Direction Field Plotter Model  

NSDL National Science Digital Library

The Direction Field Plotter Model shows a graphical representation of the solutions to a first-order differential equation dx/dt=f(x,t) by plotting a grid of line segments with components that show the rate of change of the solution x(t) at each gridpoint. This slope field visualization uses normalized line segments to provide a qualitatively feel for the solution geometry. The solution curves can be sketched by connecting adjacent line segments. Clicking on an (x,t) point shows the exact solution starting at that point. The Direction Field Plotter Model was developed using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the jar file will run the program if Java is installed. You can modify this simulation if you have EJS installed by right-clicking within the map and selecting "Open Ejs Model" from the pop-up menu item.

Christian, Wolfgang; Franciscouembre

2012-08-21

396

The value of direct messaging.  

PubMed

Direct secure messaging (DSM) is a way to send patient information in an encrypted form among physicians, among provider organizations, and to state agencies. Improving efficiency of communication between physicians through DSM also improves productivity-not only for physician users, but also for the practices and organizations they serve. However, use of DSM must expand for users and their organizations to achieve full benefits. PMID:24611231

Wagner, Karen

2014-02-01

397

Human smooth pursuit direction discrimination  

Microsoft Academic Search

The smooth pursuit system is usually studied using single moving objects as stimuli. However, the visual motion system can respond to stimuli that must be integrated spatially and temporally (Williams DG, Sekuler R. Vision Res 1984;24:55–62; Watamaniuk SNJ, Sekuler R, Williams DW. Vision Res 1989;29:47–59). For example, when each dot of a random-dot cinematogram (RDC) is assigned a new direction

Scott N. J Watamaniuk; Stephen J Heinen

1999-01-01

398

Relativistic propulsion using directed energy  

NASA Astrophysics Data System (ADS)

We propose a directed energy orbital planetary defense system capable of heating the surface of potentially hazardous objects to the evaporation point as a futuristic but feasible approach to impact risk mitigation. The system is based on recent advances in high efficiency photonic systems. The system could also be used for propulsion of kinetic or nuclear tipped asteroid interceptors or other interplanetary spacecraft. A photon drive is possible using direct photon pressure on a spacecraft similar to a solar sail. Given a laser power of 70GW, a 100 kg craft can be propelled to 1AU in approximately 3 days achieving a speed of 0.4% the speed of light, and a 10,000 kg craft in approximately 30 days. We call the system DE-STAR for Directed Energy System for Targeting of Asteroids and exploRation. DE-STAR is a modular phased array of solid-state lasers, powered by photovoltaic conversion of sunlight. The system is scalable and completely modular so that sub elements can be built and tested as the technology matures. The sub elements can be immediately utilized for testing as well as other applications including space debris mitigation. The ultimate objective of DE-STAR would be to begin direct asteroid vaporization and orbital modification starting at distances beyond 1 AU. Using phased array technology to focus the beam, the surface spot temperature on the asteroid can be raised to more than 3000K, allowing evaporation of all known substances. Additional scientific uses of DE-STAR are also possible.

Bible, Johanna; Johansson, Isabella; Hughes, Gary B.; Lubin, Philip M.

2013-09-01

399

Azimuthal anisotropy of direct photons  

SciTech Connect

The electromagnetic bremsstrahlung produced by a quark interacting with nucleons or nuclei is azimuthally asymmetric. In the light-cone dipole approach this effect is related to the orientation dependent dipole cross section. Such a radiation anisotropy is expected to contribute to the azimuthal asymmetry of direct photons in pA and AA collisions, as well as in deep-inelastic scattering and in the production of dileptons.

Kopeliovich, B. Z. [Departamento de Fisica y Centro de Estudios Subatomicos, Universidad Tecnica Federico Santa Maria, Casilla 110-V, Valparaiso (Chile); Joint Institute for Nuclear Research, Dubna (Russian Federation); Pirner, H. J. [Institute for Theoretical Physics, University of Heidelberg, Philosophenweg 19, D-69120 Heidelberg (Germany); Rezaeian, A. H.; Schmidt, Ivan [Departamento de Fisica y Centro de Estudios Subatomicos, Universidad Tecnica Federico Santa Maria, Casilla 110-V, Valparaiso (Chile)

2008-02-01

400

Direct generation of optical vortices  

NASA Astrophysics Data System (ADS)

A detailed scheme is established for the direct generation of optical vortices, signifying light endowed with orbital angular momentum. In contrast to common techniques based on the tailored conversion of the wave front in a conventional beam, this method provides for the direct spontaneous emission of photons with the requisite field structure. This form of optical emission results directly from the electronic relaxation of a delocalized exciton state that is supported by a ringlike array of three or more nanoscale chromophores. An analysis of the conditions leads to a general formulation revealing a requirement for the array structure to adhere to one of a restricted set of permissible symmetry groups. It is shown that the coupling between chromophores within each array leads to an energy level splitting of the exciton structure, thus providing for a specific linking of exciton phase and emission wavelength. For emission, arrays conforming to one of the given point-group families' doubly degenerate excitons exhibit the specific phase characteristics necessary to support vortex emission. The highest order of exciton symmetry, corresponding to the maximum magnitude of electronic orbital angular momentum supported by the ring, provides for the most favored emission. The phase properties of the emission produced by the relaxation of such excitons are exhibited on plots which reveal the azimuthal phase progression around the ring, consistent with vortex emission. It is proven that emission of this kind produces electromagnetic fields that map with complete fidelity onto the phase structure of a Laguerre-Gaussian optical mode with the corresponding topological charge. The prospect of direct generation paves the way for practicable devices that need no longer rely on the modification of a conventional laser beam by a secondary optical element. Moreover, these principles hold promise for the development of a vortex laser, also based on nanoscale exciton decay, enabling the production of coherent radiation with a tailor-made helical wave front.

Williams, Mathew D.; Coles, Matt M.; Bradshaw, David S.; Andrews, David L.

2014-03-01

401

Direct search for light gluinos  

Microsoft Academic Search

We present the results for a direct search for light gluinos through the appearance of ??3?0 with high transverse momentum in the vacuum tank of the NA48 experiment at CERN. We find one event within a lifetime range of 10?9–10?3 s and another one between 10?10–10?9 s. Both events are consistent with the expected background from neutrons in the beam,

V. Fanti; A. Lai; L. Musa; D. Marras; A. Nappi; B. Hay; R. W. Moore; K. N. Moore; D. J. Munday; M. D. Needham; M. A. Parker; T. O. White; S. A. Wotton; J. Andersen; G. Barr; G. Bocquet; J. Bremer; A. Ceccucci; D. Cundy; N. Doble; G. Fischer; W. Funk; L. Gatignon; A. Gianoli; G. Govi; P. Grafström; W. Kubischta; S. Luitz; G. Kesseler; J. P. Matheys; A. Norton; S. Palestini; B. Panzer-Steindel; D. Schinzel; H. Taureg; M. Velasco; O. Vossnack; H. Wahl; G. Wirrer; V. Kekelidze; A. Mestvirishvili; I. Potrebenikov; G. Tatichvili; A. Tkatchev; A. Zinchenko; O. Boyle; V. J. Martin; I. G. Knowles; H. L. C. Parsons; P. Dalpiaz; J. Duclos; P. L. Frabetti; M. Martini; F. Petrucci; M. Porcu; M. Savrié; A. Bizzeti; M. Calvetti; G. Graziani; E. Iacopini; M. Lenti; A. Michetti; H. G. Becker; H. Blümer; P. Buchholz; D. Coward; C. Ebersberger; H. Fox; A. Kalter; K. Kleinknecht; U. Koch; L. Köpke; B. Renk; J. Scheidt; V. Schönharting; I. Schué; R. Wilhelm; A. Winharting; M. Wittgen; J. C. Chollet; S. Crépé; L. Iconomidou-Fayard; L. Fayard; J. Ocariz; G. Unal; D. Vattolo; I. Wingerter; G. Anzivino; P. Cenci; P. Lubrano; M. Pepe; B. Gorini; P. Calafiura; R. Carosi; C. Cerri; M. Cirilli; F. Costantini; R. Fantechi; S. Giudici; I. Mannelli; V. Marzulli; G. Pierazzini; M. Sozzi; J. B. Cheze; J. Cogan; M. De Beer; P. Debu; A. Formica; R. Granier-De-Cassagnac; P. Hristov; E. Mazzucato; B. Peyaud; S. Schanne; R. Turlay; B. Vallage; I. Augustin; M. Bender; M. Holder; M. Ziolkowski; R. Arcidiacono; C. Biino; F. Marchetto; E. Menichetti; J. Nassalski; E. Rondio; M. Szleper; W. Wislicki; S. Wronka; H. Dibon; M. Jeitler; M. Markytan; I. Mikulec; G. Neuhofer; M. Pernicka; A. Taurok

1999-01-01

402

Direct search for light gluinos  

Microsoft Academic Search

We present the results for a direct search for light gluinos through the appearance of $\\\\eta\\\\rightarrow 3\\\\pin$ with high transverse momentum in the vacuum tank of the NA48 experiment at CERN. We find one event within a lifetime range of $10^{-9}-10^{-3}$\\\\,s and another one between $10^{-10}-10^{-9}$\\\\,s. Both events are consistent with the expected background from neutrons in the beam, produced

V Fanti; A Lai; L Musa; D Marras; A Nappi; B Hay; R W Moore; K N Moore; D J Munday; M D Needham; M A Parker; T O White; S A Wotton; J Andersen; Giles David Barr; G Bocquet; J Bremer; Augusto Ceccucci; Donald C Cundy; Niels T Doble; G Fischer; W Funk; L Gatignon; A Gianoli; A Gonidec; G Govi; P Grafström; Werner Kubischta; S Luitz; G Kesseler; J P Matheys; Alan Robert Norton; S Palestini; B Panzer-Steindel; D Schinzel; Hans Taureg; M Velasco; O Vossnack; H Wahl; G Wirrer; V D Kekelidze; A Mestvirishvili; Yu K Potrebenikov; G T Tatishvili; A L Tkachev; A I Zinchenko; O Boyle; V J Martin; I G Knowles; H Parsons; Pietro Dalpiaz; J Duclos; P L Frabetti; M Martini; F Petrucci; M Porcu; M Savrié; A Bizzeti; M Calvetti; G Graziani; E Iacopini; M Lenti; A Michetti; H G Becker; H Blümer; P Buchholz; D H Coward; C Ebersberger; H Fox; A Kalter; K Kleinknecht; U Koch; L Köpke; B Renk; J Scheidt; J Schmidt; V Schönharting; Yu Schué; R Wilhelm; A Winharting; M Wittgen; J C Chollet; S Crépé; L Iconomidou-Fayard; Louis Fayard; J Ocariz; G Unal; D Vattolo; I Wingerter-Seez; Giuseppina Anzivino; P Cenci; P Lubrano; M Pepé; B Gorini; P Calafiura; R Carosi; C Cerri; M Cirilli; F Costantini; R Fantechi; Sergio Giudici; I Mannelli; V M Marzulli; G M Pierazzini; M Sozzi; J B Chèze; J Cogan; M De Beer; P Debu; A Formica; R Granier de Cassagnac; P Z Khristov; E Mazzucato; B Peyaud; S Schanne; René Turlay; B Vallage; I Augustin; M Bender; M Holder; M Ziolkowski; R Arcidiacono; C Biino; F Marchetto; E Menichetti; J P Nassalski; Ewa Rondio; M Szleper; W Wislicki; S Wronka; Heinz Dibon; Manfred Jeitler; Manfred Markytan; I Mikulec; Günther Neuhofer; Manfred Pernicka; Anton Taurok

1998-01-01

403

Directional Darwinian Selection in proteins  

PubMed Central

Background Molecular evolution is a very active field of research, with several complementary approaches, including dN/dS, HON90, MM01, and others. Each has documented strengths and weaknesses, and no one approach provides a clear picture of how natural selection works at the molecular level. The purpose of this work is to present a simple new method that uses quantitative amino acid properties to identify and characterize directional selection in proteins. Methods Inferred amino acid replacements are viewed through the prism of a single physicochemical property to determine the amount and direction of change caused by each replacement. This allows the calculation of the probability that the mean change in the single property associated with the amino acid replacements is equal to zero (H0: ? = 0; i.e., no net change) using a simple two-tailed t-test. Results Example data from calanoid and cyclopoid copepod cytochrome oxidase subunit I sequence pairs are presented to demonstrate how directional selection may be linked to major shifts in adaptive zones, and that convergent evolution at the whole organism level may be the result of convergent protein adaptations. Conclusions Rather than replace previous methods, this new method further complements existing methods to provide a holistic glimpse of how natural selection shapes protein structure and function over evolutionary time.

2013-01-01

404

BNL Direct Wind Superconducting Magnets  

SciTech Connect

BNL developed Direct Wind magnet technology is used to create a variety of complex multi-functional multi-layer superconducting coil structures without the need for creating custom production tooling and fixturing for each new project. Our Direct Wind process naturally integrates prestress into the coil structure so external coil collars and yokes are not needed; the final coil package transverse size can then be very compact. Direct Wind magnets are produced with very good field quality via corrections applied during the course of coil winding. The HERA-II and BEPC-II Interaction Region (IR) magnet, J-PARC corrector and Alpha antihydrogen magnetic trap magnets and our BTeV corrector magnet design are discussed here along with a full length ILC IR prototype magnet presently in production and the coils that were wound for an ATF2 upgrade at KEK. A new IR septum magnet design concept for a 6.2 T combined-function IR magnet for eRHIC, a future RHIC upgrade, is introduced here.

Parker, B.; Anerella, M.; Escallier, J.; Ghosh, A.; Jain, A.; Marone, A.; Muratore, A.; Wanderer, P.

2011-09-12

405

Optimized Direct-Drive Uniformity  

NASA Astrophysics Data System (ADS)

The means of optimizing direct-drive illumination uniformity in laser fusion implosions will be discussed. To provide the most-uniform drive, the target must be illuminated by smooth single beams, symmetrically placed on target, with the optimum beam shape. On the 60-beam OMEGA laser system these near-optimum, direct-drive illumination conditions have been achieved by smoothing each beam with 1-THz smoothing by spectral dispersion (SSD), which incorporates distributed phase plates (DPP's) and polarization smoothing (PS), and by the modified soccer-ball orientation of the beams. The current beam smoothing provides for unprecedented levels of direct-drive uniformity, approaching ?_rms ˜ 2% up to ? = 200 after ˜300 ps. The sensitivity of the illumination to beam shape has been studied, and a new set of DPP's have been designed and are being built to further optimize the uniformity on OMEGA. Also, the sensitivity of the drive to beam balance, beam pointing, and target positioning has been studied both by calculation and by performing target implosions allowing quantitative limits to be placed on all contributors. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460.

Marshall, F. J.; McKenty, P. W.; Kessler, T. J.; Forties, R.; Kelly, J. A.; Waxer, L. J.

2002-11-01

406

Wellbore inertial directional surveying system  

DOEpatents

A wellbore inertial directional surveying system for providing a complete directional survey of an oil or gas well borehole to determine the displacement in all three directions of the borehole path relative to the well head at the surface. The information generated by the present invention is especially useful when numerous wells are drilled to different geographical targets from a single offshore platform. Accurate knowledge of the path of the borehole allows proper well spacing and provides assurance that target formations are reached. The tool is lowered down into a borehole on an electrical cable. A computer positioned on the surface communicates with the tool via the cable. The tool contains a sensor block which is supported on a single gimbal, the rotation axis of which is aligned with the cylinder axis of the tool and, correspondingly, the borehole. The gyroscope measurement of the sensor block rotation is used in a null-seeking servo loop which essentially prevents rotation of the sensor block about the gimbal axis. Angular rates of the sensor block about axes which are perpendicular to te gimbal axis are measured by gyroscopes in a manner similar to a strapped-down arrangement. Three accelerometers provide acceleration information as the tool is lowered within the borehole. The uphole computer derives position information based upon acceleration information and angular rate information. Kalman estimation techniques are used to compensate for system errors. 25 figures.

Andreas, R.D.; Heck, G.M.; Kohler, S.M.; Watts, A.C.

1982-09-08

407

Wellbore inertial directional surveying system  

DOEpatents

A wellbore inertial directional surveying system for providing a complete directional survey of an oil or gas well borehole to determine the displacement in all three directions of the borehole path relative to the well head at the surface. The information generated by the present invention is especially useful when numerous wells are drilled to different geographical targets from a single off-shore platform. Accurate knowledge of the path of the borehole allows proper well spacing and provides assurance that target formations are reached. The tool is lowered down into a borehole on the electrical cable. A computer positioned on the surface communicates with the tool via the cable. The tool contains a sensor block which is supported on a single gimbal, the rotation axis of which is aligned with the cylinder axis of the tool and, correspondingly, the borehole. The gyroscope measurement of the sensor block rotation is used in a null-seeking servo loop which essentially prevents rotation of the sensor block aboutthe gimbal axis. Angular rates of the sensor block about axes which are perpendicular to the gimbal axis are measured by gyroscopes in a manner similar to a strapped-down arrangement. Three accelerometers provide acceleration information as the tool is lowered within the borehole. The uphole computer derives position information based upon acceleration information and anular rate information. Kalman estimation techniques are used to compensate for system errors.

Andreas, Ronald D. (Albuquerque, NM); Heck, G. Michael (Albuquerque, NM); Kohler, Stewart M. (Albuquerque, NM); Watts, Alfred C. (Albuquerque, NM)

1991-01-01

408

Protrusion fluctuations direct cell motion.  

PubMed

Many physiological phenomena involve directional cell migration. It is usually attributed to chemical gradients in vivo. Recently, other cues have been shown to guide cells in vitro, including stiffness/adhesion gradients or micropatterned adhesive motifs. However, the cellular mechanism leading to these biased migrations remains unknown, and, often, even the direction of motion is unpredictable. In this study, we show the key role of fluctuating protrusions on ratchet-like structures in driving NIH3T3 cell migration. We identified the concept of efficient protrusion and an associated direction index. Our analysis of the protrusion statistics facilitated the quantitative prediction of cell trajectories in all investigated conditions. We varied the external cues by changing the adhesive patterns. We also modified the internal cues using drug treatments, which modified the protrusion activity. Stochasticity affects the short- and long-term steps. We developed a theoretical model showing that an asymmetry in the protrusion fluctuations is sufficient for predicting all measures associated with the long-term motion, which can be described as a biased persistent random walk. PMID:24988339

Caballero, David; Voituriez, Raphaël; Riveline, Daniel

2014-07-01

409

Direct Arthroscopic Distal Clavicle Resection  

PubMed Central

Degenerative change involving the acromioclavicular (AC) is frequently seen as part of a normal aging process. Occasionally, this results in a painful clinical condition. Although AC joint symptoms commonly occur in conjunction with other shoulder pathology, they may occur in isolation. Treatment of isolated AC joint osteoarthritis is initially non-surgical. When such treatment fails to provide lasting relief, surgical treatment is warranted. Direct (superior) arthroscopic resection of the distal (lateral) end of the clavicle is a successful method of treating the condition, as well as other isolated conditions of the AC joint. The following article reviews appropriate patient evaluation, surgical indications and technique.

Lervick, Gregory N

2005-01-01

410

Directional Solidification of Eutectic Ceramics  

NASA Technical Reports Server (NTRS)

Two major problems associated with structural ceramics are lack of damage tolerance and insufficient strength and creep resistance at very high temperatures of interest for aerospace application. This work demonstrated that the directionally solidified eutectics can have unique poly-phase microstructures and mechanical properties superior to either constituent alone. The constraining effect of unique eutectic microstructures result in higher resistance to slow crack growth and creep. Prospect of achieving superior properties through controlled solidification are presented and this technology can also be beneficial to produce new class of materials.

Sayir, Ali

2001-01-01

411

Future directions for ITM imaging  

NASA Astrophysics Data System (ADS)

Remote sensing of the Earth's ionosphere-thermosphere-mesosphere photon emissions has been one of the workhorse tools for Aeronomic research. With the access of space in the 1960s, the window of wavelengths opened wider. As a consequence new insights have been gained of the relationship and coupling of the space above and the atmosphere below this region. Even as this area of research has matured, significant and compelling questions remain unresolved. This talk will address significant and compelling questions that remain open and what role remote sensing plays in helping resolve them. Possible directions for future technology and implementation strategy will be explored.

Spann, J.

2005-12-01

412

Directed Discovery of Crystal Structures  

NSDL National Science Digital Library

This contribution is modified from a published exercise "Directed Discovery of Crystal Structures Using Ball-and-Stick Models" [Mogk, 1997] . While the published exercise is based on student exploration of traditional ball-and-stick models of crystal structures, this modified version uses a similar "discovery-based" approach and the latest online crystallographic information and visualization software to teach the spatial relationships and crystal-chemical rules that govern the crystal structures of common minerals and crystalline solids. A few changes in the content have been made from the published exercise, mainly to accommodate the new digital media.

Mogk, Dave; Ratajeski, Kent

413

Fatness and fertility: which direction?  

PubMed

Metabolic status has long been thought to determine reproductive status, with abnormal metabolic phenotypes altering reproductive cascades, such as the onset of puberty. In this issue of the JCI, Tolson and colleagues provide evidence that kisspeptin, a hormone that promotes sexual maturation, regulates metabolism. Female mice lacking the kisspeptin receptor (KISS1R) gained more weight than control animals, and this weight gain was caused not by increased food consumption, but by an overall decrease in energy and metabolism. While this study provides a direct link between the kisspeptin pathway and metabolic output, more work will need to be done to determine whether alterations in this pathway contribute to human obesity. PMID:24937420

Seminara, Stephanie B

2014-07-01

414

Direct application of geothermal energy  

SciTech Connect

An overall treatment of direct geothermal applications is presented with an emphasis on the above-ground engineering. The types of geothermal resources and their general extent in the US are described. The potential market that may be served with geothermal energy is considered briefly. The evaluation considerations, special design aspects, and application approaches for geothermal energy use in each of the applications are considered. The present applications in the US are summarized and a bibliography of recent studies and applications is provided. (MHR)

Reistad, G.M.

1980-01-01

415

Direct cosmic-ray detection  

NASA Astrophysics Data System (ADS)

One century after the discovery of cosmic rays, many questions remain open on their origin, nature, and transport. Experiments to detect them directly have constantly improved, and are today of highly diversified designs. Indeed, precise measurements of cosmic rays in an energy range from ˜104 to ˜1015eV allow one to study the mechanism of acceleration of primary cosmic rays up to very high energy, to characterise their possible sources, and to clarify their interactions with the interstellar medium. Such measurements of elemental cosmic-ray spectra require complementary and redundant charge- and energy-identification detectors, such as the balloon-borne Cosmic-Ray Energetics And Mass (CREAM) experiment, which measures cosmic rays from 1012 to 1015 eV for all elements up to and including iron. Here I present the current status of direct cosmic-ray measurements, with the focus on the latest CREAM results. Finally, I briefly discuss the cosmic-ray identification above the knee.

Putze, Antje

2012-01-01

416

Staged direct injection diesel engine  

DOEpatents

A diesel engine having staged injection for using lower cetane number fuels than No. 2 diesel fuel. The engine includes a main fuel injector and a pilot fuel injector. Pilot and main fuel may be the same fuel. The pilot injector injects from five to fifteen percent of the total fuel at timings from 20.degree. to 180.degree. BTDC depending upon the quantity of pilot fuel injected, the fuel cetane number and speed and load. The pilot fuel injector is directed toward the centerline of the diesel cylinder and at an angle toward the top of the piston, avoiding the walls of the cylinder. Stratification of the early injected pilot fuel is needed to reduce the fuel-air mixing rate, prevent loss of pilot fuel to quench zones, and keep the fuel-air mixture from becoming too fuel lean to become effective. In one embodiment, the pilot fuel injector includes a single hole for injection of the fuel and is directed at approximately 48.degree. below the head of the cylinder.

Baker, Quentin A. (San Antonio, TX)

1985-01-01

417

Radial lean direct injection burner  

SciTech Connect

A burner for use in a gas turbine engine includes a burner tube having an inlet end and an outlet end; a plurality of air passages extending axially in the burner tube configured to convey air flows from the inlet end to the outlet end; a plurality of fuel passages extending axially along the burner tube and spaced around the plurality of air passage configured to convey fuel from the inlet end to the outlet end; and a radial air swirler provided at the outlet end configured to direct the air flows radially toward the outlet end and impart swirl to the air flows. The radial air swirler includes a plurality of vanes to direct and swirl the air flows and an end plate. The end plate includes a plurality of fuel injection holes to inject the fuel radially into the swirling air flows. A method of mixing air and fuel in a burner of a gas turbine is also provided. The burner includes a burner tube including an inlet end, an outlet end, a plurality of axial air passages, and a plurality of axial fuel passages. The method includes introducing an air flow into the air passages at the inlet end; introducing a fuel into fuel passages; swirling the air flow at the outlet end; and radially injecting the fuel into the swirling air flow.

Khan, Abdul Rafey; Kraemer, Gilbert Otto; Stevenson, Christian Xavier

2012-09-04

418

Direct Statistical Simulation of Climate  

NASA Astrophysics Data System (ADS)

Non-equilibrium statistical mechanics opens up the possibility of modeling climate directly,footnotetextE. N. Lorenz, The Nature and Theory of the General Circulation of the Atmosphere, vol. 218. World Meteorological Organization (1967). bypassing the traditional approach of accumulating statistics from lengthy numerical simulations. One way to implement such Direct Statistical Simulation (DSS) is by systematic expansion in equal-time cumulants.footnotetextJ. B. Marston, E. Conover, and T. Schneider, J. Atmos. Sci. 65, 1955 (2008). Essential physics of the general circulation can be illustrated with idealized 1- and 2-layer models of the atmosphere.footnotetextJ. B. Marston, Ann. Rev. Cond. Matt. Phys. 3, 285 (2012). A truncation at second order in the hierarchy of cumulants is equivalent to retaining the interaction between zonal mean flows and eddies. Eddy-eddy interactions appear at higher orders, but care must be taken to keep the higher-order expansions realizable with non-negative probability distribution functions. Live demonstrations of models, and their statistical mechanical solution, will be performed. Possible effects of polar amplification of warming, due to the melting of arctic sea ice, on the mid-latitude jet stream will be illustrated.

Marston, Brad

2013-03-01

419

Illumination direction from texture shading.  

PubMed

We investigate the ability of human observers to judge the direction of illumination from image texture. Photographs of 61 real surfaces were used, taken from the Columbia-Utrecht Reflectance and Texture (Curet) database (http:/www.cs.columbia.edu/CAVE/curet). All samples were normally viewed but obliquely illuminated, the elevation of the source being 22.5 degrees, 45.0 degrees, or 67.5 degrees. The illumination was with a collimated, parallel beam. Stimuli were presented in random orientation, and observers had to judge both the elevation and the azimuth of the source. Observers judged the azimuth within approximately 15 degrees, except for the fact that they committed random (with approximately 50% probability) sign flips (180 degrees flips). Connected with this finding is the fact that observers judged the illumination to be from above rather than below in the overwhelming majority of cases, despite the fact that each case occurred with equal probability. The elevation of the illumination can be judged to some extent but is not far above chance level. The data are in good agreement with a simple model that bases the estimate of illumination direction on the second-order statistics of local luminance gradients. This locates the locus of the probable mechanism very early in the visual stream. PMID:12801166

Koenderink, Jan J; van Doorn, Andrea J; Kappers, Astrid M L; te Pas, Susan F; Pont, Sylvia C

2003-06-01

420

Direct visualization of magnetoelectric domains  

NASA Astrophysics Data System (ADS)

The coupling between the magnetic and electric dipoles in multiferroic and magnetoelectric materials holds promise for conceptually novel electronic devices. This calls for the development of local probes of the magnetoelectric response, which is strongly affected by defects in magnetic and ferroelectric ground states. For example, multiferroic hexagonal rare earth manganites exhibit a dense network of boundaries between six degenerate states of their crystal lattice, which are locked to both ferroelectric and magnetic domain walls. Here we present the application of a magnetoelectric force microscopy technique that combines magnetic force microscopy with in situ modulating high electric fields. This method allows us to image the magnetoelectric response of the domain patterns in hexagonal manganites directly. We find that this response changes sign at each structural domain wall, a result that is corroborated by symmetry analysis and phenomenological modelling, and provides compelling evidence for a lattice-mediated magnetoelectric coupling. The direct visualization of magnetoelectric domains at mesoscopic scales opens up explorations of emergent phenomena in multifunctional materials with multiple coupled orders.

Geng, Yanan; Das, Hena; Wysocki, Aleksander L.; Wang, Xueyun; Cheong, S.-W.; Mostovoy, M.; Fennie, Craig J.; Wu, Weida

2014-02-01

421

Direct Current Electrical Motor Model  

NSDL National Science Digital Library

The Direct Current Electrical Motor Model illustrates a simple direct current (DC) motor. The model shows an external magnet (called the stator because itâs fixed in place) and a turning coil of wire called an armature ( rotor or coil, because it rotates). The armature, carrying current provided by the battery, is an electromagnet, because a current-carrying wire generates a magnetic field; invisible magnetic field lines are circulating all around the wire of the armature. The key to producing motion is positioning the electromagnet within the magnetic field of the permanent magnet (its field runs from its north to south poles). The armature experiences a force described by the left hand rule. This interplay of magnetic fields and moving charged particles (the electrons in the current) results in the magnetic force (depicted by the green arrows) that makes the armature spin because of the torque. Use the slider current I to see what happens when the flow of current is reversed. The checkbox current flow & electron flow alows different visualization since I = d(Q)/dt and Q= number of charge*e. The Play & Pause button allows freezing the 3D view for visualizing these forces, for checking for consistency with the left hand rule .

Hwang, Fu-Kwun; Wee, Loo K.

2011-11-23

422

Direct visualization of magnetoelectric domains.  

PubMed

The coupling between the magnetic and electric dipoles in multiferroic and magnetoelectric materials holds promise for conceptually novel electronic devices. This calls for the development of local probes of the magnetoelectric response, which is strongly affected by defects in magnetic and ferroelectric ground states. For example, multiferroic hexagonal rare earth manganites exhibit a dense network of boundaries between six degenerate states of their crystal lattice, which are locked to both ferroelectric and magnetic domain walls. Here we present the application of a magnetoelectric force microscopy technique that combines magnetic force microscopy with in situ modulating high electric fields. This method allows us to image the magnetoelectric response of the domain patterns in hexagonal manganites directly. We find that this response changes sign at each structural domain wall, a result that is corroborated by symmetry analysis and phenomenological modelling, and provides compelling evidence for a lattice-mediated magnetoelectric coupling. The direct visualization of magnetoelectric domains at mesoscopic scales opens up explorations of emergent phenomena in multifunctional materials with multiple coupled orders. PMID:24292421

Geng, Yanan; Das, Hena; Wysocki, Aleksander L; Wang, Xueyun; Cheong, S-W; Mostovoy, M; Fennie, Craig J; Wu, Weida

2014-02-01

423

Self-Directed Learning: Emerging Theory & Practice.  

ERIC Educational Resources Information Center

This book contains the following collection of papers: "Self-Directed Learning: Emerging Theory and Practice" (Long); "Self-Directed Orientation toward Learning: A Learning Style" (Bonham); "Self-Direction and Problem Solving: Theory and Method" (Peters); "Facilitating Self-Directed Learning: Not a Contradiction in Terms" (Garrison); "Development…

Long, Huey B.; And Others

424

Direct conversion of methane into oxygenates  

Microsoft Academic Search

Direct conversion of methane into useful chemicals remains as a big challenge in catalysis in the 21st century. A large number of studies have contributed to the direct conversion of methane in the past decade. Although there is still no direct process with commercial viability at this moment, many new methods and catalysts have been developed for the direct activation

Kiyoshi Otsuka; Ye Wang

2001-01-01

425

Design and modeling magnetorheological directional control valve  

Microsoft Academic Search

Directional control valves are designed to control direction of flow, while actuators maintain required speeds and precise positions. Magnetorheological (MR) fluid is a controllable fluid. Utilizing the MR fluid properties, direct interface between magnetic fields and fluid power is possible, without the need for mechanical moving parts like spools. This study proposes a design of a four-way three-position MR directional

Maher Yahya Salloom; Zahurin Samad

2012-01-01

426

Statistics of wind direction and its increments  

Microsoft Academic Search

has been no comprehensive study of the statistics of wind direction changes or increments. In this paper, we study the statistics of wind direction as well as of the changes in wind direction. In the spirit of Ref. 9, we find that the wind direction can be split into a large- scale drift and small-scale fluctuations around it. We find

Eric van Doorn; Brindesh Dhruva; Katepalli R. Sreenivasan; Victor Cassella

2008-01-01

427

A fingerprint classification technique using directional images  

Microsoft Academic Search

We present a fast, automated, feature-based technique for classifying fingerprints. The technique extracts the singular points (delta and core points) in fingerprints obtained from directional histograms. The technique enhances the digitized image using adaptive clipping and image matching, finds the directional image by checking the orientations of individual pixels, computes directional histograms using overlapping blocks in the directional image, and

Meltem Ballan; F. Ayhan Sakarya; Brian L. Evans

1997-01-01

428

Direct electrochemistry of pentachlorophenol hydroxylase  

NASA Astrophysics Data System (ADS)

The direct electrochemistry of flavin-containing monooxygenase, pentachlorophenol hydroxlase (PCPH), has been investigated under a variety of conditions. PCPH underwent a two-electron process on the electrodes, which correspond to the reduction/oxidation of FAD/FADH2 within the enzyme. The electrochemical response of PCPH relies on the interface of the electrode and the enzyme solution. Three types of interaction of the enzyme molecule with the electrodes were observed: at a bare edge-plane graphite electrode, diffusion-controlled process was observed, suggesting the interaction is weak. In the presence of the cations, the interaction became stronger, so that the voltammetric response changed from a diffusion control to an adsorption control An intermediate case was observed at a poly(L- lysine) modified EPG electrode.

Xie, Wei-hong; Allen, H.; Hill, O.; Wong, Luet L.

2001-09-01

429

Direct synthesis of calcium borohydride  

DOEpatents

A method is disclosed for directly preparing an alkaline earth metal borohydride, i.e. Ca(BH.sub.4).sub.2, from the alkaline earth metal hydride and the alkaline earth metal boride. The borohydride thus prepared is doped with a small portion of a metal chloride catalyst compound, such as RuCl.sub.3, TiCl.sub.3, or a mixture of TiCl.sub.3 and palladium metal. The process provides for mechanically mixing the dry reagents under an inert atmosphere followed by charging the mixed materials with high pressure hydrogen at about 70 MPa while heating the mixture to about 400.degree. C. The method is relatively simple and inexpensive and provides reversible hydride compounds which are free of the usual contamination introduced by prior art wet chemical methods.

Ronnebro, Ewa Carin Ellinor (Dublin, CA) [Dublin, CA; Majzoub, Eric H. (Pleasanton, CA) [Pleasanton, CA

2009-10-27

430

Theory of directional pulse propagation  

SciTech Connect

We construct combined electric and magnetic field variables which independently represent energy flows in the forward and backward directions, respectively, and use these to reformulate Maxwell's equations. These variables enable us to not only judge the effect and significance of backward-traveling field components, but also to discard them when appropriate. They thereby have the potential to simplify numerical simulations, leading to potential speed gains of up to 100% over standard finite difference time-domain (FDTD) or pseudospectral spatial-domain (PSSD) simulations. We present results for various illustrative situations, including an example application to second harmonic generation in periodically poled lithium niobate. These field variables are also used to derive both envelope equations useful for narrow-band pulse propagation, and a second order wave equation. Alternative definitions are also presented.

Kinsler, P.; Radnor, S. B. P.; New, G. H. C. [Department of Physics, Imperial College London, Prince Consort Road, London SW7 2BW (United Kingdom)

2005-12-15

431

Direct synthesis of magnesium borohydride  

DOEpatents

A method is disclosed for directly preparing an alkaline earth metal borohydride, i.e. Mg(BH.sub.4).sub.2, from the alkaline earth metal boride MgB.sub.2 by hydrogenating the MgB.sub.2 at an elevated temperature and pressure. The boride may also be doped with small amounts of a metal chloride catalyst such as TiCl.sub.3 and/or NiCl.sub.2. The process provides for charging MgB.sub.2 with high pressure hydrogen above at least 70 MPa while simultaneously heating the material to about 350.degree. C. to about 400.degree. C. The method is relatively simple and inexpensive and provides a reversible hydride compound having a hydrogen capacity of at least 11 wt %.

Ronnebro, Ewa Carin Ellinor (Kennewick, WA); Severa, Godwin (Honolulu, HI); Jensen, Craig M. (Kailua, HI)

2012-04-03

432

High gradient directional solidification furnace  

NASA Astrophysics Data System (ADS)

A high gradient directional solidification furnace is disclosed which includes eight thermal zones throughout the length of the furnace. In the hot end of the furnace, furnace elements provide desired temperatures. These elements include Nichrome wire received in a grooved tube which is encapsulated y an outer alumina core. A booster heater is provided in the hot end of the furnace which includes toroidal tungsten/rhenium wire which has a capacity to put heat quickly into the furnace. An adiabatic zone is provided by an insulation barrier to separate the hot end of the furnace from the cold end. The old end of the furnace is defined by additional heating elements. A heat transfer plate provides a means by which heat may be extracted from the furnace and conducted away through liquid cooled jackets. By varying the input of heat via the booster heater and output of heat via the heat transfer plate, a desired thermal gradient profile may be provided.

Aldrich, B. R.; Whitt, W. D.

1985-10-01

433

Statistical properties of directed avalanches  

NASA Astrophysics Data System (ADS)

A two-dimensional directed stochastic sandpile model is studied both numerically and analytically. One of the known analytical approaches is extended by considering general stochastic toppling rules. The probability density distribution for the first-passage time of stochastic process described by a nonlinear Langevin equation with power-law dependence of the diffusion coefficient is obtained. Large-scale Monte Carlo simulations are performed with the aim to analyze statistical properties of the avalanches, such as the asymmetry between the initial and final stages, scaling of voids and the width of the thickest branch. Comparison with random walks description is drawn and different plausible scenarios for the avalanche evolution and the scaling exponents are suggested.

Bunzarova, N. Zh.

2010-09-01

434

High gradient directional solidification furnace  

NASA Technical Reports Server (NTRS)

A high gradient directional solidification furnace is disclosed which includes eight thermal zones throughout the length of the furnace. In the hot end of the furnace, furnace elements provide desired temperatures. These elements include Nichrome wire received in a grooved tube which is encapsulated y an outer alumina core. A booster heater is provided in the hot end of the furnace which includes toroidal tungsten/rhenium wire which has a capacity to put heat quickly into the furnace. An adiabatic zone is provided by an insulation barrier to separate the hot end of the furnace from the cold end. The old end of the furnace is defined by additional heating elements. A heat transfer plate provides a means by which heat may be extracted from the furnace and conducted away through liquid cooled jackets. By varying the input of heat via the booster heater and output of heat via the heat transfer plate, a desired thermal gradient profile may be provided.

Aldrich, B. R.; Whitt, W. D. (inventor)

1985-01-01

435

Direct band gap silicon allotropes.  

PubMed

Elemental silicon has a large impact on the economy of the modern world and is of fundamental importance in the technological field, particularly in solar cell industry. The great demand of society for new clean energy and the shortcomings of the current silicon solar cells are calling for new materials that can make full use of the solar power. In this paper, six metastable allotropes of silicon with direct or quasidirect band gaps of 0.39-1.25 eV are predicted by ab initio calculations at ambient pressure. Five of them possess band gaps within the optimal range for high converting efficiency from solar energy to electric power and also have better optical properties than the Si-I phase. These Si structures with different band gaps could be applied to multiple p-n junction photovoltaic modules. PMID:24971657

Wang, Qianqian; Xu, Bo; Sun, Jian; Liu, Hanyu; Zhao, Zhisheng; Yu, Dongli; Fan, Changzeng; He, Julong

2014-07-16

436

Combination of earthquake direction effects  

NASA Astrophysics Data System (ADS)

The correct application of the square root of the sum of the squares (SRSS) rule is presented for obtaining the combined responses of a subsystem to seismic excitations given by orthogonal earthquake components represented by system response spectra. Alternate methods of applying the SRSS, which are sometimes used either for simplicity or due to different interpretation, are evaluated and compared with the correct method. The evaluations consider the following four cases: (1) the correct method which combines the responses in a particular direction given by each earthquake component as a last step, (2) a generally unconservative method whereby both the system response spectra and the resulting subsystem responses are combind by the SRSS, (3) a method which can be unconservative for unequal earthquake components where the system response spectra are combined by the absolute sum and the resulting responses by the SRSS, and (4) a conservative method which combines the system response spectra by the SRSS but adds the resulting responses absolutely.

Morrone, A.

437

Interpolation by directed distance morphing  

NASA Astrophysics Data System (ADS)

Shape-based interpolation (SBI) is used for interpolation between binary serial slice images. Although SBI approximates the interslice geometry more accurately than traditional techniques such as linear (L) or cubic spline (CS) interpolation, SBI produces only a binary result. This paper extends SBI to interpolation of grayscale images (SBIG) using simulated 3D distance maps to produce a grayscale image volume. Results of SBIG are superior visually (sharper detail, no artificial intensities) and quantitatively to L or CS. This is particularly evident in sagittal and coronal reconstructions. Clipping artifacts due to nonoverlapping structures or rapid changes in image brightness are minimized using simulated 3D maps. However, when objects between slices do not overlap, shape-based interpolation results in compressed or nonexistent geometry in some or all of the interpolated slices. The nonoverlapping problem is described and quantified. A new interpolation algorithm, directed distance morphing, is introduced and used to address the nonoverlapping problem.

Barrett, William A.; Bess, Eric

1994-09-01

438

Method for directional hydraulic fracturing  

DOEpatents

A method for directional hydraulic fracturing using borehole seals to confine pressurized fluid in planar permeable regions, comprising: placing a sealant in the hole of a structure selected from geologic or cemented formations to fill the space between a permeable planar component and the geologic or cemented formation in the vicinity of the permeable planar component; making a hydraulic connection between the permeable planar component and a pump; permitting the sealant to cure and thereby provide both mechanical and hydraulic confinement to the permeable planar component; and pumping a fluid from the pump into the permeable planar component to internally pressurize the permeable planar component to initiate a fracture in the formation, the fracture being disposed in the same orientation as the permeable planar component.

Swanson, David E. (West St. Paul, MN); Daly, Daniel W. (Crystal, MN)

1994-01-01

439

Statistical properties of directed avalanches.  

PubMed

A two-dimensional directed stochastic sandpile model is studied both numerically and analytically. One of the known analytical approaches is extended by considering general stochastic toppling rules. The probability density distribution for the first-passage time of stochastic process described by a nonlinear Langevin equation with power-law dependence of the diffusion coefficient is obtained. Large-scale Monte Carlo simulations are performed with the aim to analyze statistical properties of the avalanches, such as the asymmetry between the initial and final stages, scaling of voids and the width of the thickest branch. Comparison with random walks description is drawn and different plausible scenarios for the avalanche evolution and the scaling exponents are suggested. PMID:21230034

Bunzarova, N Zh

2010-09-01

440

Directional genome walking using PCR.  

PubMed

We describe here a PCR-based "directional genome walking" protocol. The basic procedure for the amplification consists of two rounds of PCR. A primary PCR was performed, on the genomic DNA using a biotinylated primer specific to a known sequence in the genome along with four universal walker primers that were designed with partial degeneracy. The biotinylated primary PCR products were immobilized on streptavidin-linked paramagnetic beads. This step removed all nonspecific amplification products, and the purified template was used for the second PCR using a nested primer and the walker primer-2 to increase specificity. This technique is potentially useful for cloning promoter regions and has been successfully used to isolate 5'-flanking genomic regions of many cDNA clones previously isolated by us. PMID:12398192

Mishra, R N; Singla-Pareek, S L; Nair, S; Sopory, S K; Reddy, M K

2002-10-01

441

Direct reconstruction of dark energy.  

PubMed

An important issue in cosmology is reconstructing the effective dark energy equation of state directly from observations. With so few physically motivated models, future dark energy studies cannot only be based on constraining a dark energy parameter space. We present a new nonparametric method which can accurately reconstruct a wide variety of dark energy behavior with no prior assumptions about it. It is simple, quick and relatively accurate, and involves no expensive explorations of parameter space. The technique uses principal component analysis and a combination of information criteria to identify real features in the data, and tailors the fitting functions to pick up trends and smooth over noise. We find that we can constrain a large variety of w(z) models to within 10%-20% at redshifts z?1 using just SNAP-quality data. PMID:20867085

Clarkson, Chris; Zunckel, Caroline

2010-05-28

442

Identifying Contienents, Oceans, and Directions  

NSDL National Science Digital Library

Utah Core Curriculum Social Studies Standard #6: Students use map skills to analyze the influence of physical features of th building of communities in the United States. Objective #1: Examine Maps and Globes Indicator #1: Identify Oceans and Continents of the World. Using the following activities and instructions you will be able to learn about the 5 oceans and the 7 continents. You will also be able to find them on a map get better understanding of the four directions. As we discussed last time in class the five oceans of the world are: Artic Ocean Atlantic Ocean Pacific Ocean Indian Ocean Southern Ocean (discovered in 2000) Click on the link below and print out the worksheet. This will help you locate the oceans and recognize their placement. Complete the worksheet to the best of our ...

Ms.bingham

2007-11-06

443

Directed Therapy for Exfoliation Syndrome  

PubMed Central

Exfoliation syndrome (XFS) is an age-related disorder of the extracellular matrix that leads the production of abnormal fibrillar material that leads to elevated intraocular pressure and a relatively severe glaucoma. Exfoliation material is deposited in numerous ocular tissues and extraocular organs. XFS is associated with ocular ischemia, cerebrovascular disease, neurodegenerative disease and cardiovascular disease. Current modalities of treatment include intraocular pressure lowering with topical antihypertensives, laser trabeculoplasty and filtration surgery. The disease paradigm for XFS should be expanded to include directed therapy designed specifically to target the underlying disease process. Potential targets include preventing the formation or promoting the depolymerization of exfoliation material. Novel therapies targeting trabecular meshwork may prove particularly useful in the care of exfoliative glaucoma. The systemic and ocular associations of XFS underscore the need for a comprehensive search for neuroprotective agents in its treatment.

Angelilli, Allison; Ritch, Robert

2009-01-01

444