Zinc oxide nanoparticles were prepared by irradiation of aqueous solutions containing zinc(II) ions, propan-2-ol, polyvinyl alcohol, and hydrogen peroxide. Zinc oxide was found in solid phase either directly after irradiation, or after additional heat treatment. Various physicochemical parameters, including scintillation properties of prepared materials, were studied. After decomposition of impurities and annealing of oxygen vacancies, the samples showed intensive emission in visible spectral range and well-shaped exciton luminescence at 390–400 nm. The best scintillating properties had zinc oxide prepared from aqueous solutions containing zinc formate as initial precursor and hydrogen peroxide. Size of the crystalline particles ranged from tens to hundreds nm, depending on type of irradiated solution and post-irradiation thermal treatment. 相似文献
This Review summarizes the latest advances in the field of rylene dyes and rylene nanoemitters for applications in photonics, and describes the influence of the dye design on the optical properties, the self-assembly, the molecular interactions, as well as the labeling specificity of the compounds. The interplay between tailored (macro)molecular design and bulk/single-molecule spectroscopy enables complex processes to be explained, for example, the kinetics of energy-transfer processes or (bio)catalysis. Such investigations are essential for the ultimate design of optimized nanoemitters, and require a close cooperation between spectroscopists and preparative organic chemists. 相似文献
As a unique tool to assess metabolic fluxes noninvasively, 13C magnetic resonance spectroscopy (MRS) could help to characterize and understand malignancy in human tumors. However, its low sensitivity has hampered applications in patients. The aim of this study was to demonstrate that with sensitivity-optimized localized 13C MRS and intravenous infusion of [1-13C]glucose under euglycemia, it is possible to assess the dynamic conversion of glucose into its metabolic products in vivo in human glioma tissue.
Materials and Methods
Measurements were done at 3 T with a broadband single RF channel and a quadrature 13C surface coil inserted in a 1H volume coil. A 1H/13C polarization transfer sequence was applied, modified for localized acquisition, alternatively in two (50 ml) voxels, one encompassing the tumor and the other normal brain tissue.
Results
After about 20 min of [1-13C]glucose infusion, a [3-13C]lactate signal appeared among several resonances of metabolic products of glucose in MR spectra of the tumor voxel. The resonance of [3-13C]lactate was absent in MR spectra from contralateral tissue. In addition, the intensity of [1-13C]glucose signals in the tumor area was about 50% higher than that in normal tissue, likely reflecting more glucose in extracellular space due to a defective blood–brain barrier. The signal intensity for metabolites produced in or via the tricarboxylic acid (TCA) cycle was lower in the tumor than in the contralateral area, albeit that the ratios of isotopomer signals were comparable.
Conclusion
With an improved 13C MRS approach, the uptake of glucose and its conversion into metabolites such as lactate can be monitored noninvasively in vivo in human brain tumors. This opens the way to assessing metabolic activity in human tumor tissue. 相似文献
Real-space renormalization group maps, e.g., the majority rule transformation, map Ising-type models to Ising-type models
on a coarser lattice. We show that each coefficient in the renormalized Hamiltonian in the lattice-gas variables depends on
only a finite number of values of the renormalized Hamiltonian. We introduce a method which computes the values of the renormalized
Hamiltonian with high accuracy and so computes the coefficients in the lattice-gas variables with high accuracy. For the critical
nearest neighbor Ising model on the square lattice with the majority rule transformation, we compute over 1,000 different
coefficients in the lattice-gas variable representation of the renormalized Hamiltonian and study the decay of these coefficients.
We find that they decay exponentially in some sense but with a slow decay rate. We also show that the coefficients in the
spin variables are sensitive to the truncation method used to compute them. 相似文献
We examine the diffraction properties of lattice dynamical systems of algebraic origin. It is well-known that diverse dynamical
properties occur within this class. These include different orders of mixing (or higher-order correlations), the presence
or absence of measure rigidity (restrictions on the set of possible shift-invariant ergodic measures to being those of algebraic
origin), and different entropy ranks (which may be viewed as the maximal spatial dimension in which the system resembles an
i.i.d. process). Despite these differences, it is shown that the resulting diffraction spectra are essentially indistinguishable,
thus raising further difficulties for the inverse problem of structure determination from diffraction spectra. Some of them
may be resolved on the level of higher-order correlation functions, which we also briefly compare. 相似文献
The results of a systematic study of the light sensitivity and long-term potential stability (30 days) of poly(pyrrole) (PPy),
poly(3-octylthiophene) (POT), poly(3,4-ethylenedioxythiophene) (PEDOT), poly(aniline) (PANI) and plasticised poly(vinyl chloride)
(PVC) containing 20% (m/m) PANI are reported. Thin films were prepared either electrochemically or by the solution casting technique. This fundamental
study is of importance because conducting polymers (CP) are commonly used as ion-to-electron transduction materials in all-solid-state
solid contact ion-selective electrodes. The potential stability test done in 0.1 M KCl (pH 7.5) simulates the extreme situation
when the CP-based SC becomes in direct contact with water. Films prepared of a nanodispersion of PANI showed both good potential
stability and insensitivity to light even under illumination with very intensive light (>105 lx). In contrary, it was observed that POT is very light-sensitive. Upon illumination with intensive light, the potential
responses of POT films prepared by solution casting and electropolymerisation were 315 and 590 mV, respectively. A room light
sensitivity of approximately −10 to −15 mV was observed for these films. The other CPs in this study were insensitive to room
light (∼150 lx), but were light-sensitive under illumination with intensive light. The potential drift of PPy(Cl) is below
−10 μV/h (3–30 days), whereas the other most stable CPs in this study had a slightly higher potential drift. 相似文献
Caught in the act : An alkyl alkene ZrIV complex (see picture; Cp=C5H5) has been synthesized and characterized for the first time. The alkene bonding mode is highly asymmetric, and C2 is quite carbocationic. There is also evidence for rotation about the C1? C2 bond. This extremely unusual complex provides an exemplar of previously unknown intermediates in Ziegler–Natta and carbocationic polymerization reactions of alkenes.
We prove that the semirings of 1-preserving and of 0,1-preserving endomorphisms of a semilattice are always subdirectly irreducible
and we investigate under which conditions they are simple. Subsemirings are also investigated in a similar way. 相似文献