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21.
The recent development of X‐ray Photoelectron Spectroscopy (XPS) instrumentation with spatial resolution down to several microns has advanced the capability of elemental and chemical state imaging. XPS imaging analysis has been applied in understanding the delamination problems of siloxane coatings on polymethyl‐methacrylate (PMMA) polymer. It was found that delamination occurred by interfacial failure, and the coating suffered complete delamination from a PMMA substrate. This example offered an opportunity for the investigation of X‐ray damage on polymers encountered in XPS imaging analysis. This paper also demonstrated how to construct a constrained peak model with the aid of chemical knowledge and supporting evidence of the sample. Monte Carlo error analysis was used to determine the validity of the peak fit models used. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
22.
Neal JS Milosević MV Bending SJ Potenza A San Emeterio L Marrows CH 《Physical review letters》2007,99(12):127001
Hall probe microscopy has been used to image vortex-antivortex molecules induced in superconducting Pb films by the stray fields from square arrays of magnetic dots. We have directly observed spontaneous vortex-antivortex pairs and studied how they interact with added free (anti)fluxons in an applied magnetic field. We observe a variety of phenomena arising from competing symmetries which either drive added antivortices to join antivortex shells around dots or stabilize the translationally symmetric antivortex lattice between the dots. Added vortices annihilate antivortex shells, leading first to a stable "nulling state" with no free fluxons and then, at high densities, to vortex shells around the dots stabilized by the asymmetric antipinning potential. Our experimental findings are in good agreement with Ginzburg-Landau calculations. 相似文献
23.
In Situ Synthesis of Alkenyl Tetrazines for Highly Fluorogenic Bioorthogonal Live‐Cell Imaging Probes
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Dr. Haoxing Wu Dr. Jun Yang Dr. Jolita Šečkutė Prof. Neal K. Devaraj 《Angewandte Chemie (International ed. in English)》2014,53(23):5805-5809
In spite of the wide application potential of 1,2,4,5‐tetrazines, particularly in live‐cell and in vivo imaging, a major limitation has been the lack of practical synthetic methods. Here we report the in situ synthesis of (E)‐3‐substituted 6‐alkenyl‐1,2,4,5‐tetrazine derivatives through an elimination–Heck cascade reaction. By using this strategy, we provide 24 examples of π‐conjugated tetrazine derivatives that can be conveniently prepared from tetrazine building blocks and related halides. These include tetrazine analogs of biological small molecules, highly conjugated buta‐1,3‐diene‐substituted tetrazines, and a diverse array of fluorescent probes suitable for live‐cell imaging. These highly conjugated probes show very strong fluorescence turn‐on (up to 400‐fold) when reacted with dienophiles such as cyclopropenes and trans‐cyclooctenes, and we demonstrate their application for live‐cell imaging. This work provides an efficient and practical synthetic methodology for tetrazine derivatives and will facilitate the application of conjugated tetrazines, particularly as fluorogenic probes for live‐cell imaging. 相似文献
24.
Dr. Roberto J. Brea Christian M. Cole Prof. Neal K. Devaraj 《Angewandte Chemie (International ed. in English)》2014,53(51):14102-14105
Phospholipid vesicles are of intense fundamental and practical interest, yet methods for their de novo generation from reactive precursors are limited. A non‐enzymatic and chemoselective method to spontaneously generate phospholipid membranes from water‐soluble starting materials would be a powerful tool for generating vesicles and studying lipid membranes. Here we describe the use of native chemical ligation (NCL) to rapidly prepare phospholipids spontaneously from thioesters. While NCL is one of the most popular tools for synthesizing proteins and nucleic acids, to our knowledge this is the first example of using NCL to generate phospholipids de novo. The lipids are capable of in situ synthesis and self‐assembly into vesicles that can grow to several microns in diameter. The selectivity of the NCL reaction makes in situ membrane formation compatible with biological materials such as proteins. This work expands the application of NCL to the formation of phospholipid membranes. 相似文献
25.
Hendargo HC Bower BA Reinstein AS Shepherd N Tao YK Izatt JA 《Optics Communications》2011,284(19):4847-4851
Spectral domain phase microscopy (SDPM) is an extension of spectral domain optical coherence tomography (SDOCT) that exploits the extraordinary phase stability of spectrometer-based systems with common-path geometry to resolve sub-wavelength displacements within a sample volume. This technique has been implemented for high resolution axial displacement and velocity measurements in biological samples, but since axial displacement information is acquired serially along the lateral dimension, it has been unable to measure fast temporal dynamics in extended samples. Depth-Encoded SDPM (DESDPM) uses multiple sample arms with unevenly spaced common path reference reflectors to multiplex independent SDPM signals from separate lateral positions on a sample simultaneously using a single interferometer, thereby reducing the time required to detect unique optical events to the integration period of the detector. Here, we introduce DESDPM and demonstrate the ability to acquire useful phase data concurrently at two laterally separated locations in a phantom sample as well as a biological preparation of spontaneously beating chick cardiomyocytes. DESDPM may be a useful tool for imaging fast cellular phenomena such as nervous conduction velocity or contractile motion. 相似文献
26.
Craig F Ferris Tara Stolberg Praveen Kulkarni Murali Murugavel Robert Blanchard D Caroline Blanchard Marcelo Febo Mathew Brevard Neal G Simon 《BMC neuroscience》2008,9(1):111
Background
With the advent of functional magnetic resonance imaging (fMRI) in awake animals it is possible to resolve patterns of neuronal activity across the entire brain with high spatial and temporal resolution. Synchronized changes in neuronal activity across multiple brain areas can be viewed as functional neuroanatomical circuits coordinating the thoughts, memories and emotions for particular behaviors. To this end, fMRI in conscious rats combined with 3D computational analysis was used to identifying the putative distributed neural circuit involved in aggressive motivation and how this circuit is affected by drugs that block aggressive behavior. 相似文献27.
28.
Measurements of γ-ray excitation functions, γ-γ coincidence spectra and γ-ray angular distributions have been made. following the reactions 61Ni(α, n)64Zn, 62Ni(α, n)65Zn, 56Fe(14N, αnp)64Zn, 56Fe(12C, 2pn)65Zn, and 54Fe(12C, 2p)64Zn. Among the new levels observed in 64Zn are those at 5624 keV, 6765 keV, 6940 keV, and 6124 keV, the last one with a suggested assignment of (9?). In 65Zn. ten new levels probably in the positive-parity chain, with spin up to (), and a few others, have been found. Comparison of the 65Zn positive-parity levels with the 64Zn ground-state band supports the concept of a single neutron in the orbital weakly coupled to a core essentially identical to 64Zn. Many high-spin states in 64Zn itself can be aggregated into bands whose band heads are suggestive of two-quasiparticle states involving one excitation. 相似文献
29.
A resonance is observed in the 27Al(p, γ)28Si reaction at Ep=2876±2 keV, which corresponds to an excitation energy of 14356±2 keV. The 14.36 MeV level decays to a new level at 11577±2 keV, which is turn decays to the known level at 9701.8±0.5 keV. With previous information on the 9.70 MeV level and the present γ-ray angular distributions, obtained from singles spectra as recorded by a 40 cm3 Ge(Li) detector, the spins of the three levels can be limited to J=5, 6; J=6; and J=5, respectively. Transition strength arguments based on measurements of the strength of the 2876 keV resonance and the lifetime of the 11.58 MeV level indicate that the 14.36 MeV level has Jπ=6?, T=1 and that the 11.58 MeV level has Jπ=6?, T=0. 相似文献
30.
Summary The problem of the missing matter in the Universe is reviewed and discussed in terms of massive neutrinos. The primordial
abundances of light elements produced during the big bang nucleosynthesis can be used to determine firm bounds on the number
of neutrino flavours and on the ratio of baryon to photon densities in the Universe. These limits imply that nonbaryonic matter
is the dominant constituent of large-scale cosmic structures, being massive neutrinos the best guess for such a matter. In
order that the Universe be closed, a value of the neutrino rest mass is derived, which agrees with the bounds obtained from
the dynamics of galaxies and clusters of galaxies. It is also shown that density perturbations can hardly grow in a nucleon-dominated
Universe, and massive neutrinos may be the seed for nucleon condensations. All these astrophysical and cosmological considerations
suggest a lower and an upper bound of the neutrino rest mass.
Paper presented at the Congress ?Galactic and Extragalactic Dark Matter?, Roma, 28 to 30 June 1983. 相似文献