High-precision heteronuclear three-bond coupling constants including3J(HN, C′),3J(HN, Cβ),3J(Hα,Cγ), and3J(Hβ, C′) are determined for the nonproline residues in uniformly13C-enrichedantamanide,cyclo-(-Val1-Pro2-Pro3-Ala4-Phe5-Phe6-Pro7-Pro8-Phe9- Phe10-), using quantitative numerical 2D NMR spectrum evaluation based on the product-operator formalism. The experimental basis comprises two-dimensional1H,13C-heteronuclear relayed E.COSY spectra [J. M. Schmidt, R. R. Ernst, S. Aimoto, and M. Kainosho,J. Biomol. NMR6,95 (1995)], the multiplet patterns of which are subjected to iterative least-squares 2D multiplet-simulation procedures. Accuracy and precision of the spectrum fit are assessed byFstatistics and analysis of variances (ANOVA) leading to confidence intervals for the optimized spin-system parameters. The long-range J coupling constants obtained and their standard deviations provide the experimental foundation for a later detailed analysis of φ and χ1dihedral-angle equilibrium conformations contributing to the flexible peptide structure. 相似文献
The highly hydrophobic fluorophore Laurdan (6-dodecanoyl-2-(dimethylaminonaphthalene)) has been widely used as a fluorescent
probe to monitor lipid membranes. Actually, it monitors the structure and polarity of the bilayer surface, where its fluorescent
moiety is supposed to reside. The present paper discusses the high sensitivity of Laurdan fluorescence through the decomposition
of its emission spectrum into two Gaussian bands, which correspond to emissions from two different excited states, one more
solvent relaxed than the other. It will be shown that the analysis of the area fraction of each band is more sensitive to
bilayer structural changes than the largely used parameter called Generalized Polarization, possibly because the latter does
not completely separate the fluorescence emission from the two different excited states of Laurdan. Moreover, it will be shown
that this decomposition should be done with the spectrum as a function of energy, and not wavelength. Due to the presence
of the two emission bands in Laurdan spectrum, fluorescence anisotropy should be measured around 480 nm, to be able to monitor
the fluorescence emission from one excited state only, the solvent relaxed state. Laurdan will be used to monitor the complex
structure of the anionic phospholipid DMPG (dimyristoyl phosphatidylglycerol) at different ionic strengths, and the alterations
caused on gel and fluid membranes due to the interaction of cationic peptides and cholesterol. Analyzing both the emission
spectrum decomposition and anisotropy it was possible to distinguish between effects on the packing and on the hydration of
the lipid membrane surface. It could be clearly detected that a more potent analog of the melanotropic hormone α-MSH (Ac-Ser1-Tyr2-Ser3-Met4-Glu5-His6-Phe7-Arg8-Trp9-Gly10-Lys11-Pro12-Val13-NH2) was more effective in rigidifying the bilayer surface of fluid membranes than the hormone, though the hormone significantly
decreases the bilayer surface hydration. 相似文献
Accurate and efficient grid based techniques for the solution of the time-dependent Schrödinger equation for few-electron diatomic molecules irradiated by intense, ultrashort laser pulses are described. These are based on hybrid finite-difference, Lagrange mesh techniques. The methods are applied in three scenarios, namely H2+ with fixed internuclear separation, H2+ with vibrating nuclei and H2 with fixed internuclear separation and illustrative results presented.Received: 19 November 2002, Published online: 24 April 2003PACS:
02.60.Cb Numerical simulation; solution of equations - 02.70.Bf Finite-difference methods - 33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states) - 33.80.-b Photon interactions with molecules 相似文献
A high-accuracy finite-difference beam-propagation method (HAFD-BPM) based on high-accuracy divided-difference formulas is
presented. The truncation error in this HAFD-BPM is reduced to o(Δr)4in the transverse direction, whereas the error in a conventional FD-BPM is typically o(Δr)2. Gaussian beam propagation in vacuum and nonlinear medium is simulated by this new method and conventional one. The comparison
between them in computing time and accuracy reveals the advantage of this new method. As an example, this method is applied
to the simulation of blow-up in self-focusing of a Gaussian beam.
PACS 42.65.Hw; 42.25.Bs; 02.70.Bf 相似文献
A novel dual-emitter vacuum Compton detector (D-VCD) with
higher gamma ray detecting efficiency is proposed. The emitters are
made of Ta--Al clad metal. The gamma ray sensitivity is studied by
Monte Carlo simulation using the MCNP code. A comparison
between calculations and results measured by using the 1.25~MeV
gamma ray of Co-60 is also performed. Experimental sensitivities for
two sample D-VCDs with the same materials and structures are
1.92×10^ - 20 and 2.02×10^ -
20~C.cm2/MeV separately, which are consistent with
the simulation result of 1.98×10^ -
20~C.cm2/MeV and are 4 times higher than that of
VCD with a single Fe emitter. According to the simulation results, in
a gamma energy range from 0.5 to 3~MeV, the maximum sensitivity
variance for the D-VCD is less than 15%, and less than 5% in a
range from 1 to 2~MeV in particular. The novel D-VCD is applicable to
the detection of intense pulse gamma rays. 相似文献
We observed hyperfine structures of the 4D5/2 state of 85Rb atoms and applied them to the frequency stabilization of a laser diode by using the double resonance optical pumping (DROP). The hyperfine structures of the 4D5/2 states of 85Rb atoms were highly resolved in the Rb vapor cell. We compared the DROP with the optical-optical double resonance (OODR) in the 5S1/2-5P3/2-4D5/2 ladder-type system of 85Rb atoms. When we stabilized the frequency of a laser diode to the hyperfine structure of the 5P3/2(F″ = 4)-4D5/2(F″ = 3) transition by using the DROP spectrum, the frequency stability was approximately 2.3 × 10− 12 after 100 s. 相似文献
For LiYF4:Ce3+, LiLuF4:Ce3+ and LuF3:Ce3+ crystals UV/visible emission and time-resolved VUV/UV excitation spectra were recorded at liquid helium temperature with spectral resolution of 0.1 nm for excitation spectra and better than 0.3 nm for emission spectra. Well resolved fine structures due to zero-phonon lines were clearly observed in both excitation and emission spectra for LiYF4:Ce3+ and LiLuF4:Ce3+. For LuF3:Ce3+ crystal no fine structure was detected in the spectra even at the highest spectral resolution. Under the host excitation, the fine structure for high-energy emission band of Ce3+ (5d-2F5/2) in LiLuF4:Ce3+ becomes well pronounced because of weaker reabsorption effect, as compared to Ce3+ 4f-5d absorption, due to small penetration depth for exciting radiation. As a result the crystal-field splitting for 2F7/2 and 2F5/2 levels of Ce3+ in LiLuF4 crystal was measured. First observation of zero-phonon lines at ∼81,550 and ∼82,900 cm−1 as well as vibronic side bands due to interconfigurational 4f14-4f135d transitions in Lu3+ is reported for excitation spectrum of LiLuF4:Ce3+. 相似文献
In this article, we calculate the masses and residues of the heavy baryons Ωc*(css) and Ωb*(bss) with spin–parity with the QCD sum rules. The numerical values are compatible with the experimental data and other theoretical estimations.
PACS 14.20.Lq, 14.20.Mr 相似文献
Quantitative optical spectroscopy measurements of the emission spectra of the N(B2∑u,)ν′→X2∑gν″ transition (first negative system) in an Ar-N2 microwave discharge at atmospheric pressure have allowed determination of the rate coefficient of the production of N molecules in the B2 ∑u, state with vibrational level ν′ = 0. The N(B2∑u, ν′) molecules are produced by the reaction in a surface-wave-induced microwave discharge (2450 MHz) sustained in an open-ended dielectric tube. The rate coefficient K (T) has been obtained for ν′ν″ = 0 for different gas temperatures by varying the incident microwave power. The K00(T) values are between 7.10?10 and 4.10?10 cm3 s?1 for the temperature range 2500 to 3450K. 相似文献
2 /p-Si MOS structures were prepared in 0.1 M K2SO4 electrolyte with a pH of 7 (the 0.1 M KOH solution was buffered with H2SO4) at current densities of 3, 5, and 7 mA/cm2 and with four different pH values of the electrolyte at 3 mA/cm2. It is found that thermal annealing at a relatively low temperature can be used to improve the anodic MOS characteristics.
Moreover, of the pH and current density it followed that the pH has a dominant role in the interface electrical properties.
The lowest interface state densities at the maximum and the midgap positions are 7.1×1011 and 2.7×1010 eV-1cm-2 for a sample made with pH=7, J=3 mA/cm2. The characteristics of this sample seem satisfactory for device applications of anodized p-Si.
Received: 8 July 1996/Accepted: 22 January 1997 相似文献
We perform a simulation with the aim of checking the existence of a well defined stationary state for a two dimensional system
of driven hard disks when energy dissipation takes place at the system boundaries and no bulk impurities are present.
PACS: 02.70.Ns, 05.60.-k, 47.27.ek 相似文献
The energies of formation, enthalpies, and entropies of the conformers of 1-(carboxy)-1-(N-methylamide)-2-(3′,5′-di-tert-butyl)-4-hydroxyphenyl)-propionic acid and sodium and potassium 1-(carboxy)-1-(N-methylamide)-2-(3′,5′-di-tert-butyl)-4-hydroxyphenyl)-propionates are calculated by quantum-chemical methods in the PM6 approximation. A doubling of signals
in the 1H NMR spectrum of the first conformer is observed, which merge into singlets when the compound is heated. Changes in the structure
of the conformers and donor-acceptor complexes (solvates) occur with the preservation of the metal-ligand coordination bond.
Calculations of the characteristics of 1-(carboxy)-1-(N-methylamide)-2-(3′,5′-di-tert-butyl)-4-hydroxyphenyl)-propionic acid and sodium and potassium 1-(carboxy)-1-(N-methylamide)-2-(3′,5′-di-tert-butyl)-4-hydroxyphenyl)-propionates in the PM6 approximation make it possible to predict the structure and properties of
the solvated structures. The energies of homolysis of the H-O bond D(OH) are calculated, and a linear dependence of the antioxidant activity on D(OH) for the structures of the studied compounds is demonstrated. The results make it possible to predict the properties of antioxidants
in the biological environment. 相似文献
The conductivity and thermal stability of NH+4, H+(H2O)nβ″ and ion-rich β-alumina single crystals have been measured by the complex impedance method in the 25–700°C temperature range. Both structures have similar properties, but ion-rich β-alumina shows a higher stability and a lower activation energy (β: 0.18 eV, β″ 0.24 eV below 400°C and 250°C respectively). The room temperature conductivity is about 3×10-5ω-1cm-1. The conducting properties and mechanisms are discussed and compared to other protonic or ionic conductors. 相似文献
Emission and absorption spectra of Tm3+ in single crystal K2YF5 with different concentrations are reported and analyzed. The non-exponential feature of the fluorescence decay of 1D2 level for the high concentration sample indicates the existence of a cross-relaxation process. Energy level simulation has been carried out by using a phenomenological model with 16 parameters accounting simultaneously for the free ion and crystal field (CF) effects. A good fit was achieved with a root mean square deviation σ=18 cm−1. The free ion and CF effects were then discussed by comparing the available data of K2YF5:Nd3+, LiYF4:Tm3+ and LiYF4:Nd3+. 相似文献
Crystalline structures and infrared-to-visible upconversion luminescence spectra have been investigated in 1 mol% Er3+, 10 mol% Yb3+ and 0-20 mol% Li+ codoped TiO2 [1Er10Yb(0-20)Li:TiO2] nanocrystals. The crystalline structures of 1Er10Yb(0-20)Li:TiO2 were divided into three parts by the addition of Yb3+ and Li+. Both green and red upconversion emissions were observed from the 2H11/2/4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+ in Er3+-Yb3+-Li+ codoped TiO2, respectively. The green and red upconversion emissions of 1Er:TiO2 were enhanced significantly by Yb3+ and Li+ codoping, in which the intensities of green and red emissions and the intensity ratio of green to red emissions (Igreen/Ired) were highly dependent on the crystalline structures. The significant enhanced upconversion emissions resulted from the energy migration between Er3+ and Yb3+ as well as the distortion of crystal field symmetry of Er3+ caused by the dissolving of Li+ at lower Li+ codoping concentration and the phase transformation at higher Li+ concentration. It is concluded that codoping with ions of smaller ionic radius like Li+ can efficiently improve the upconversion emissions of Er3+ or other rare-earth ions doped luminsecence materials. 相似文献