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排序方式: 共有413条查询结果,搜索用时 11 毫秒
41.
Lowe Terry C. Bishop Alan Burns Carol Hartford Allen Parkin Don Trewhella Jill 《Journal of nanoparticle research》2000,2(3):249-266
Research in the emerging field of nanoscale science and technology has grown steadily at Los Alamos National Laboratory since 1990. This article summarizes some of this work, examining research highlights within the seven key categories of nanoscience in which Los Alamos has ongoing projects, capabilities, and facilities: (1) Materials and chemistry, (2) Theory and modeling, (3) Bioscience, (4) Investigative tools and facilities, (5) Sensors and devices, (6) Synthesis and fabrication, and (7) Education and outreach. Future research horizons are indicated throughout while institutional strategies for advancing nanoscale science are summarized at the end. 相似文献
42.
C. Meier V. Schünemann A.X. Trautwein G. Fuchs D. Lowe M. Boll 《Hyperfine Interactions》2000,126(1-4):69-73
The enzyme benzoyl-CoA reductase (BCR) has been studied by Mössbauer spectroscopy in fields up to 7 T and at temperature down to 4.2 K. It has been shown that the oxidized BCR contains three diamagnetic [4Fe-4S]2+ centers. Treatment of BCR with dithionite or deazaflavin reduces only one of the three centers from [4Fe-4S]2+ to [4Fe-4S]1+. The latter exhibits Mössbauer spectra at 4.2 K in applied fields characteristic for Fe2.5+Fe2.5+ (S=9/2) and Fe2+Fe2+ (S=4) pairs, both coupled antiferromagnetically to total spin S=1/2. 相似文献
43.
44.
Jamie Hunter Scott Rice Robert Lowe Christopher M. Pask Stuart Warriner Visuvanathar Sridharan 《Tetrahedron letters》2017,58(46):4400-4402
2′-Hydroxyacetophenone was alkylated with a range of substituted benzyl and heteroaryl alcohols to afford the corresponding C-alkylated products in good yields under microwave irradiation. The C-alkylated products were reacted with bromoacetonitrile to afford 2-amino-3-benzyl 1,4-naphthoquinone derivatives in moderate yields. 相似文献
45.
An unusually high yielding fluorination of aminopyralid (3) using F-TEDA (SELECTFLUOR™) in warm water, followed by kinetic resolution (via iterative esterification/saponification) of the crude fluorination product with dry HCl in methanol produced pure ring-fluorinated pyridine 2 in an overall yield of 31% for the two steps. 相似文献
46.
Enikö Kádár David M. Lowe Montserrat Solé Andrew S. Fisher Awadhesh N. Jha James W. Readman Thomas H. Hutchinson 《Analytical and bioanalytical chemistry》2010,396(2):657-666
Nano-Fe particle uptake was experimentally examined in vitro using excised gills and blood cells of the edible blue mussel
Mytilus sp. Whole gills were exposed to both Fe2O3 nanoparticles and a solution of the hydrated FeCl3 salt, for up to 12 h, and blood cells for 30 min. Equimolar Fe+3 in the nano- and the soluble form was estimated under the assumption of dense spherical particles accommodating the same
number of Fe+3 as in the dissolved salt solution, namely: 1,000 μg L−1 Fe2O3 equivalent to 100 μg L−1 FeCl3·6H2O. Putative toxic impact of nano-Fe in gill epithelia and blood cells was assessed by an array of techniques including light-
and electron microscopy, biomarkers for oxidative stress (lipid peroxidation levels), neurotoxic effects (acetylcholinesterase
activity) and cytotoxicity (neutral red retention). Total and filtered fractions (20 and 200 nm, respectively) of Fe were
analysed by ICP-OES. Our results provide evidence for the following: (1) much of both the soluble (95%) and the nano-Fe (90%)
were removed from the water column within 12 h; (2) dissolved- and nano-Fe seemed to follow different routes of uptake within
the gill epithelium; (3) both nano-Fe and soluble FeCl3 caused similar impairment of lysosomal stability in circulating blood cells; (4) lipid peroxidation in gills exposed to the
two distinct forms of Fe was increased, while acetylcholinesterase activity was unaffected. In these short-term in vitro studies,
there appears to be little difference in toxic response between exposure to the Fe salt and the nano-Fe indicating that, in
this case, the nanoparticles do not invoke special properties affecting biological function in gills. However, with the use
of nano-Fe as a food additive, clearly longer-term in vivo studies are warranted. 相似文献
47.
Xi X Cegla FB Lowe M Thiemann A Nowak T Mettin R Holsteyns F Lippert A 《Ultrasonics》2011,51(8):1014-1025
The use of bubbles in applications such as surface chemistry, drug delivery, and ultrasonic cleaning etc. has been enormously popular in the past two decades. It has been recognized that acoustically-driven bubbles can be used to disturb the flow field near a boundary in order to accelerate physical or chemical reactions on the surface. The interactions between bubbles and a surface have been studied experimentally and analytically. However, most of the investigations focused on violently oscillating bubbles (also known as cavitation bubble), less attention has been given to understand the interactions between moderately oscillating bubbles and a boundary. Moreover, cavitation bubbles were normally generated in situ by a high intensity laser beam, little experimental work has been carried out to study the translational trajectory of a moderately oscillating bubble in an acoustic field and subsequent interactions with the surface. This paper describes the design of an ultrasonic test cell and explores the mechanism of bubble manipulation within the test cell. The test cell consists of a transducer, a liquid medium and a glass backing plate. The acoustic field within the multi-layered stack was designed in such a way that it was effectively one dimensional. This was then successfully simulated by a one dimensional network model. The model can accurately predict the impedance of the test cell as well as the mode shape (distribution of particle velocity and stress/pressure field) within the whole assembly. The mode shape of the stack was designed so that bubbles can be pushed from their injection point onto a backing glass plate. Bubble radial oscillation was simulated by a modified Keller–Miksis equation and bubble translational motion was derived from an equation obtained by applying Newton’s second law to a bubble in a liquid medium. Results indicated that the bubble trajectory depends on the acoustic pressure amplitude and initial bubble size: an increase of pressure amplitude or a decrease of bubble size forces bubbles larger than their resonant size to arrive at the target plate at lower heights, while the trajectories of smaller bubbles are less influenced by these factors. The test cell is also suitable for testing the effects of drag force on the bubble motion and for studying the bubble behavior near a surface. 相似文献
48.
A common source of error in particle image velocimetry (PIV) is the presence of bright spots within the images. These bright
spots are characterized by grayscale intensities much greater than the mean intensity of the image and are typically generated
by intense scattering from seed particles. The displacement of bright spots can dominate the cross-correlation calculation
within an interrogation window, and may thereby bias the resulting velocity vector. An efficient and easy-to-implement image-enhancement
procedure is described to improve PIV results when bright spots are present. The procedure, called Intensity Capping, imposes
a user-specified upper limit to the grayscale intensity of the images. The displacement calculation then better represents
the displacement of all particles in an interrogation window and the bias due to bright spots is reduced. Four PIV codes and a large set of experimental
and simulated images were used to evaluate the performance of Intensity Capping. The results indicate that Intensity Capping
can significantly increase the number of valid vectors from experimental image pairs and reduce displacement error in the
analysis of simulated images. A comparison with other PIV image-enhancement techniques shows that Intensity Capping offers
competitive performance, low computational cost, ease of implementation, and minimal modification to the images. 相似文献
49.
Akira Miura Michael Lowe Chinmayee V. Subban Shinichi Kikkawa Richard G. Hennig Francis J. DiSalvo 《Journal of solid state chemistry》2011,184(1):7-11
A new silver nitride, AgTaN2, was synthesized from NaTaN2 by a cation-exchange reaction, using a AgNO3-NH4NO3 flux at 175 °C. Its crystal structure type is delafossite (R3¯m) with hexagonal lattice parameters of a=3.141(3) Å, c=18.81(2) Å, in which silver is linearly coordinated to nitrogen. Energy dispersive X-ray analysis and combustion nitrogen/oxygen analysis gave a composition with atomic ratios of Ag:Ta:N:O as 1.0:1.2(1):2.1(1):0.77(4), which is somewhat Ta rich and indicates some oxide formation. The X-ray photoelectron spectroscopy analysis showed a Ta- and O-rich surface and transmission electron microscope observation exhibited aggregates of ca. 4-5 nm-sized particles on the surface, which are probably related to the composition deviation from a AgTaN2. The lattice parameters of stoichiometric AgTaN2 calculated by density functional theory agree with the experimental ones, but the possibility of some oxygen incorporation and/or silver deficiency is not precluded. 相似文献
50.
Surman AJ Bonnet CS Lowe MP Kenny GD Bell JD Tóth E Vilar R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(1):223-230
This study shows that the relaxivity and optical properties of functionalised lanthanide‐DTPA‐bis‐amide complexes (lanthanide=Gd3+ and Eu3+, DTPA=diethylene triamine pentaacetic acid) can be successfully modulated by addition of specific anions, without direct Ln3+/anion coordination. Zinc(II)‐dipicolylamine moieties, which are known to bind strongly to phosphates, were introduced in the amide “arms” of these ligands, and the interaction of the resulting Gd–Zn2 complexes with a range of anions was screened by using indicator displacement assays (IDAs). Considerable selectivity for polyphosphorylated species (such as pyrophosphate and adenosine‐5′‐triphosphate (ATP)) over a range of other anions (including monophosphorylated anions) was apparent. In addition, we show that pyrophosphate modulates the relaxivity of the gadolinium(III) complex, this modulation being sufficiently large to be observed in imaging experiments. To establish the binding mode of the pyrophosphate and gain insight into the origin of the relaxometric modulation, a series of studies including UV/Vis and emission spectroscopy, luminescence lifetime measurements in H2O and D2O, 17O and 31P NMR spectroscopy and nuclear magnetic resonance dispersion (NMRD) studies were carried out. 相似文献