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21.
It is shown that the time-dependent WKB expansion highlights some of the hidden properties of the Schrödinger equation and forms a natural bridge between that equation and the functional integral formulation of quantum mechanics. In particular it is shown that the leading (zero- and first-order in ) terms in the WKB expansion are essentially classical, and the relationship of this result to the classical nature of the WKB partition function, and of the anomalies in quantum field theory, is discussed. 相似文献
22.
Jahn A Vreeland WN Gaitan M Locascio LE 《Journal of the American Chemical Society》2004,126(9):2674-2675
Traditional liposome preparation methods are based on mixing of bulk phases, leading to inhomogeneous chemical and/or mechanical conditions during formation; hence liposomes are often polydisperse in size and lamellarity. Here we show the formation of liposomes that encapsulate reagents in a continuous two-phase flow microfluidic network with precision control of size from 100 to 300 nm by manipulation of liquid flow rates. We demonstrate that by creating a solvent-aqueous interfacial region in a microfluidic format that is homogeneous and controllable on the length scale of a liposome, we can facilitate the fine control of liposome size and polydispersity. 相似文献
23.
Anthony OKeefe Andreas J. Illies James R. Gilbert Michael T. Bowers 《Chemical physics》1983,82(3):471-478
High-resolution translational-energy spectroscopy (up to 0.1 eV) has been carried out on 8 V beams of NO? and NO2?. Several features in the spectrum of NO4 are assigned to the transitions within the triplet manifold of this ion. The observed transitions originate in several excited electronic states, indicating long lifetimes (> 10 μs) for the states involved. Two electronic transitions in NO2' have been observed at low energies which are attributed to excitations to the first two excited states of this ion. 相似文献
24.
The azido tetrazolo valence isomerism of twenty 9-methyl-s-triazolo[4,3-c]tetrazolo[1,5-a]pyrimidines with different substituents at position 5 has been studied by means of 1H NMR spectroscopy. All the compounds have been found to be tetrazoles in the solid state and in (CD3)2SO solution; in CF3COOH azido and tetrazolo isomers are in equilibrium. From equilibrium constants K and thermodynamic data determined it is concluded that in this series K depends on both electronic effects and steric requirements of the 5-substituents. A linear relation between K and σ was found for 5-arylderivatives because ΔS° keeps approximately constant and the substituent mainly operates on ΔH°. 相似文献
25.
Andreas Mandelis 《Chemical physics letters》1984,108(4):388-392
A new, powerful, and experimentally very convenient spectroscopic technique is described. The technique uses pyroelectric polyvinylidene difluoride (PVDF) thin film detectors in contact with solid or liquid samples. The instrumental and spectral characteristics of photopyroelectric spectroscopy (PPES) are presented, and its advantages over conventional photoacoustic spectroscopy (PAS) are discussed. 相似文献
26.
The addition of carboxylic acids to dimethylamino-propinal ( 1a ) and 4-dimethyl-amino-but-3-in-2-on ( 1b ) gives, after rearrangement of the very instable primary adducts ( 2 ), Z-3-acetoxy-N,N-dimethylacrylamides and -crotonamides 3 to 8 in excellent yields and in a stereospecific manner. Similarly, the adducts of HCl and HBr to the alkynes 1a and 1b may be rearranged at low temperature by traces of acid to cis/trans equilibria of 3-halo-acrylamides and -crotonamides 9 and 10 . - On the other hand, treatment of 3-alkoxy-3-dimethylaminoacrolein with traces of acid yields alkylesters of E-3-dimethylaminoacrylic acid ( 12 , X = OR). - The preparative aspects of the rearrangement are discussed, and a brief outline of the spectroscopic properties of the compounds 3 to 8 is given. 相似文献
27.
Seong J Rohrbacher A Li ZR Janda KC Tao FM Spiegelman F Halberstadt N 《The Journal of chemical physics》2004,120(16):7456-7463
The potential energy surface of He2Ne+ has been reinvestigated using a combination of ab initio and diatomics-in-molecule (DIM) calculations. In contrast to the reports of two recent studies the ion is found to have an asymmetric linear He-Ne-He structure, with no barrier to formation from the separated atoms on the ground-state surface. The He-Ne+ bond lengths at the potential minimum are 1.51 and 1.81 A, and the total bonding energy is 0.717 eV. Comparing the He2Ne+ energy to that of HeNe+, the bonding energy for the second helium atom is 0.06 eV, about 10% of that of the first He atom. The saddle point between the two equivalent minima is a symmetric structure, 0.0074 eV above the potential minimum. A symmetric geometry becomes the overall potential minimum if the 2s hole on the Ne is excluded from the reference states of a multireference configuration interaction calculation. A DIM potential was created for the HenNe+ family of ions. The DIM potential is consistent with the asymmetric He2Ne+ ion serving as a core; it predicts a slightly more asymmetric geometry than the ab initio results. Additional helium atoms form five-membered rings around the bonds of the core ion to fill the first shell and then add to the ends of the cluster. The asymmetric core ion and the highly compact structure help to account for the lack of apparent shell structure in the mass spectrometry of HenNe+ clusters. Finally, we recommend that the value De=0.63+/-0.04 eV be adopted for the ground state of HeNe+. 相似文献
28.
There are many methods available for the detection of nucleotide variations in genetic material. Most of these methods are applied after amplification of the target genome sequence by the polymerase chain reaction (PCR). Many efforts are currently underway to develop techniques that can detect single nucleotide variations in genes either by means of, or without the need for, PCR. Allele-specific PCR (asPCR), which reports nucleotide variations based on either the presence or absence of a PCR-amplified DNA product, has the potential to combine target amplification and analysis in one single step. The principle of asPCR is based on the formation of matched or mismatched primer-target complexes by using allele-specific primer probes. PCR amplification by a DNA polymerase from matched 3'-primer termini proceeds, whereas a mismatch should obviate amplification. Given the recent advancements in real-time PCR, this technique should, in principle, allow single nucleotide variations to be detected online. However, this method is hampered by low selectivity, which necessitates tedious and costly manipulations. Recently, we reported that the selectivity of asPCR can be significantly increased through the employment of chemically modified primer probes. Here we report further significant advances in this area. We describe the synthesis of various primer probes that bear polar 4'-C-modified nucleotide residues at their 3' termini, and their evaluation in real-time asPCR. We found that primer probes bearing a 4'-C-methoxymethylene modification have superior properties in the discrimination of single nucleotide variations by PCR. 相似文献
29.
Andreas Holzmeister 《European Polymer Journal》2007,43(12):4859-4867
Homogeneous nonwovens composed of polymer nanofibers of a given diameter are characterized by structural parameters such as the average pore sizes and internal surfaces as well as by transport properties, which are strongly correlated to the fiber diameter at a given porosity. Such nonwovens are used among others for filter applications, protective clothing or as scaffolds for tissue engineering. A frequent requirement is that, to be able to prepare nonwovens optimised for the specific application, one has to find ways to disrupt this strong correlation allowing independent modification of pore diameter, transport properties and internal surface or to induce local chemical and structural heterogeneities within the nonwoven. The route explored in this paper is based on the electrospinning of heterogeneous nonwovens composed of nanofibers with two different average diameters (by a ratio of up to 10 and more) on the one hand and/or different chemical nature on the other hand. Spinning parameters have been optimised to achieve this goal. In addition, nonwovens composed of fibers with circular cross-section and with ribbon-like cross-section have been prepared. 相似文献
30.
Reactive constituents have been investigated in a molecular beam generated in the cathode surface glow area and surface boundary layer. Mixtures of nitrogen and hydrogen form NHx(x=0–4) compounds, which are of relevance in heterogeneous, plasma vs. metal nitriding reactions. Ammonia decomposition leads to NHx(x=2–4). Strong cataphoretic enrichment of hydrogen has been observed in the cathode glow area. Heterogeneous reactions of NHx with iron lead to the formation of iron nitrides via intermediates such as FeNH2–3. In a pulsed d.c. glow discharge, increased sputtering and decreased hydrogen enrichment have been observed. 相似文献