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Recent experiments suggest that the Ising pyrochlore magnets Ho2Ti2O7 and Dy2Ti2O7 display qualitative properties of the nearest-neighbor "spin ice" model. We discuss the dipolar energy scale present in both these materials and discuss how spin-ice behavior can occur despite the presence of long-range dipolar interactions. We present results of numerical simulations and a mean field analysis of Ising pyrochlore systems. Based on our quantitative theory, we suggest that the spin-ice behavior in these systems is due to long-range dipolar interactions, and that the nearest-neighbor exchange in Dy2Ti2O7 is antiferromagnetic. 相似文献
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Galarreta BC Norton PR Lagugné-Labarthet F 《Langmuir : the ACS journal of surfaces and colloids》2011,27(4):1494-1498
A two-dimensional array of gold nanotriangles inscribed onto glass coverslips were optimized for the surface-enhanced Raman detection of streptavidin/biotin monolayer assemblies. The nanostructures were fabricated by electron beam lithography, and its optical parameters were optimized to be probed under a Raman microscope with a linearly polarized He-Ne laser with an excitation wavelength of λ = 632.8 nm. The platforms were first tested against a monolayer of biotinylated alkanethiols (BAT) functionalized over the gold nanostructure, showing that good-quality spectra could be acquired with a short acquisition time. The supramolecular interaction of streptavidin (strep) with BAT showed subsequent modification of the Raman spectrum that implies a change in the secondary structure of the host biomolecule (streptavidin). Compared to gold surfaces without nanoscale structures, the local enhancement that results from our nanostructured surfaces allows one to detect the vibrational signal of monolayers within a time on the order of seconds and under modest laser intensity, further demonstrating the utility of using plasmonic metallic nanostructures for molecular recognition. 相似文献
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We obtain exact cosmological solutions of a higher derivative theory described by the Lagrangian L=R+2αR
2 in the presence of interacting scalar field. The interacting scalar field potential required for a known evolution of the
FRW universe in the framework of the theory is obtained using a technique different from the usual approach to solve the Einstein
field equations. We follow here a technique to determine potential similar to that used by Ellis and Madsen in Einstein gravity.
Some new and interesting potentials are noted in the presence of R
2 term in the Einstein action for the known behaviours of the universe. These potentials in general do not obey the slow rollover
approximation. 相似文献
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We compare the orbital angular momentum of the ‘quark’ in the scalar diquark model as well as that of the electron in QED (to order α) obtained from the Jaffe–Manohar decomposition to that obtained from the Ji relation. We estimate the importance of the vector potential in the definition of orbital angular momentum. 相似文献
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Sarvesh Varma Jessica McLachlan Amanda M. Leclair Betty C. Galarreta Peter R. Norton François Lagugné-Labarthet 《Analytical and bioanalytical chemistry》2010,396(3):1159-1165
This paper presents a novel method for cell positioning on a substrate which combines the optical quality of glass and the
cell-repelling property of fluoropolymers. The process employs plasma lithography, which utilizes the high-resolution patterning
of photolithography along with the versatility of the plasma polymerization. When mammalian cells were grown over these substrates,
they avoided the fluoropolymer regions and grew almost exclusively within the exposed glass areas (windows). The patterned
surface reproduces the initial design of the mask, offering the possibility to control cell distances and interactions with
a versatile arrangement whilst keeping the optical quality of glass for microscopy observation, in particular, when a pristine
substrate in needed. This approach opens up possibilities for analysis of biological processes, such as studying cell interactions,
with the integration of optical or electrical sensors. 相似文献
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AbstractA series of seven coumarinyl-amino acid ester conjugates have been synthesized and characterized by NMR (1H and 13C) and mass spectra. Further, the compounds were investigated for their therapeutic applications such as anti-inflammatory and antioxidant activities. Among the synthesized compounds most of the analogs showed good efficiency compared with the standard. 相似文献
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Microfluidic channel with embedded SERS 2D platform for the aptamer detection of ochratoxin A 总被引:1,自引:0,他引:1
Betty C. Galarreta Mohammadali Tabatabaei Valérie Guieu Eric Peyrin François Lagugné-Labarthet 《Analytical and bioanalytical chemistry》2013,405(5):1613-1621
A selective aptameric sequence is adsorbed on a two-dimensional nanostructured metallic platform optimized for surface-enhanced Raman spectroscopy (SERS) measurements. Using nanofabrication methods, a metallic nanostructure was prepared by electron-beam lithography onto a glass coverslip surface and embedded within a microfluidic channel made of polydimethylsiloxane, allowing one to monitor in situ SERS fingerprint spectra from the adsorbed molecules on the metallic nanostructures. The gold structure was designed so that its localized surface plasmon resonance matches the excitation wavelength used for the Raman measurement. This optofluidic device is then used to detect the presence of a toxin, namely ochratoxin-A (OTA), in a confined environment, using very small amounts of chemicals, and short data acquisition times, by taking advantage of the optical properties of a SERS platform to magnify the Raman signals of the aptameric monolayer system and avoiding chemical labeling of the aptamer or the OTA target. Fig
Aptamer detection of OTA within a SERS/microfluidic channel 相似文献
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