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991.
Pekka Juusola Pentti Minkkinen Lasse Leino Jarmo K. Laihia 《Monatshefte für Chemie / Chemical Monthly》2007,138(10):951-965
Summary. (E)- and (Z)-Urocanic acids are endogenous chemicals in the normal mammalian skin. The first and the second thermodynamic dissociation
constants (pK
a1 and pK
a2) of urocanic acid isomers were determined using UV spectrophotometry in aqueous solutions. The values with standard deviation
(pK
a1 = 3.43 ± 0.12 and pK
a2 = 5.80 ± 0.04) and (pK
a1 = 2.7 ± 0.3 and pK
a2 = 6.65 ± 0.04) were obtained to (E)- and (Z)-urocanic acids, respectively. The second dissociations were studied also by potentiometric titration in aqueous sodium chloride
solutions up to the isotonic salt concentration (0.154 mol dm−3), and the second thermodynamic dissociation constants as well as activity parameters for both isomers were determined at
temperature 25°C and for (E)-urocanic acid also at 37°C. The obtained pK
a2 values were close to those found by UV spectrophotometry. The equations for the calculation of the second stoichiometric
dissociation constants of urocanic acid isomers on molality and molarity scale in aqueous sodium chloride solutions were derived.
The obtained pK
a1 and pK
a2 values for (Z)-urocanic acid appear to be essentially lower than some previously reported values in literature.
An erratum to this article is available at . 相似文献
992.
The molar conductivities (Λ) of solutions of n-tetrabutylammonium tetraphenylborate (NBu4BPh4) in 3-pentanone have been measured in the temperature range from 283.15 to 329.15 K. The conductance data have been analyzed
using the Lee-Wheaton conductivity equation with the distance parameter (a) set at Bjerrum’s pairing distance, and the limiting molar conductivities (Λo) and the association equilibrium constants (K
A) have been derived. The limiting ion conductivities (λ_±o) have been evaluated according to the method of Krumgalz. The λ+
o values have been compared with λ+
o values calculated from the empirical equation of Gill. The thermodynamic functions, Gibbs energy (Δ G
A
o), enthalpy (Δ H
A
o) and entropy (Δ S
A
o) for the process of ion-pair formation as well as the activation energy of the ionic movement (ΔH
∗) have been evaluated. The obtained results are discussed in terms of ion-ion and ion-solvent interactions. 相似文献
993.
Abstract—In the presence of Mg2+ and adenosine triphosphate (ATP), a rapid. light-induced, light-scattering transient is observed from bovine rod outer segments (ROS). This light-scattering transient we have labelled 'A'. Ca2+ cannot replace Mg2+ . nor can guanosine triphosphate (GTP) replace ATP. 'A' is observed at ATP concentrations as low as a few μM.
The half-time of 'A', 60 ms at 20° and 20 ms at 37°, is consistent with a process possibly involved in visual transduction.
'A' has the action spectrum of rhodopsin bleaching and its amplitude is strictly proportional to the fraction of rhodopsin bleached per flash. 'A' can be regenerated by 11- cis retinal.
Inhibition studics with ATP analogues, which cannot be hydrolysed and fail to evoke an 'A' response, reveal that an ATP hydrolysis process has to precede illumination in order for 'A' to occur.
On the basis of the above findings. it is proposed that there is a Mg2+ dependent ATPase in ROS that allows the disk membrane to assume a new membrane state which, upon illumination, is altered. giving rise to the structural phenomenon monitored as light-scattering transient 'A'. 相似文献
The half-time of 'A', 60 ms at 20° and 20 ms at 37°, is consistent with a process possibly involved in visual transduction.
'A' has the action spectrum of rhodopsin bleaching and its amplitude is strictly proportional to the fraction of rhodopsin bleached per flash. 'A' can be regenerated by 11- cis retinal.
Inhibition studics with ATP analogues, which cannot be hydrolysed and fail to evoke an 'A' response, reveal that an ATP hydrolysis process has to precede illumination in order for 'A' to occur.
On the basis of the above findings. it is proposed that there is a Mg
994.
分辨率增强技术(RET)设计流程中聚集了各式各样的点工具和方法。当前对深亚波长可制造性(DFM)设计的要求迫使设计与制造行业必须建立十分密切的合作关系。同时也促使EDA行业提供一种平台,以促进这些行业间的密切交流。合理利用这一平台将会对产能和品质产生直接的影响。 相似文献
995.
Cardiac pacing is a medical device to help human to overcome arrhythmia and to recover the regular beats of heart. A helical
configuration of electrode tip is a new type of cardiac pacing lead distal tip. The helical electrode attaches itself to the
desired site of heart by screwing its helical tip into the myocardium. In vivo experiments on anesthetized dogs were carried
out to measure the acute interactions between helical electrode and myocardium during screw-in and pull-out processes. These
data would be helpful for electrode tip design and electrode/myocardium adherence safety evaluation. They also provide reliability
data for clinical site choice of human heart to implant and to fix the pacing lead. A special design of the helical tip using
strain gauges is instrumented for the measurement of the screw-in and pull-out forces. We obtained the data of screw-in torques
and pull-out forces for five different types of helical electrodes at nine designed sites on ten canine hearts. The results
indicate that the screw-in torques increased steplike while the torque–time curves presente saw-tooth fashion. The maximum
torque has a range of 0.3–1.9 N mm. Obvious differences are observed for different types of helical tips and for different
test sites. Large pull-out forces are frequently obtained at epicardium of left ventricle and right ventricle lateral wall,
and the forces obtained at right ventricle apex and outflow tract of right ventricle are normally small. The differences in
pull-out forces are dictated by the geometrical configuration of helix and regional structures of heart muscle. 相似文献
996.
The effects of relative density of metal foams on the stresses and deformation of beam under bending
The exact analytic solution of the pure bending beam of metallic foams is given. The effects of relative density of the material
on stresses and deformation are revealed with the Triantafillou and Gibson constitutive law (TG model) taken as the analysis
basis. Several examples for individual foams are discussed, showing the importance of compressibility of the cellular materials.
One of the objects of this study is to generalize Hill’s solution for incompressible plasticity to the case of compressible
plasticity, and a kinematics parameter is brought into the analysis so that the velocity field can be determined.
The English text was polished by Yunming Chen. 相似文献
997.
In this paper, the authors present airflow field characteristics of human upper airway and soft palate movement attitude during
breathing. On the basis of the data taken from the spiral computerized tomography images of a healthy person and a patient
with Obstructive Sleep Apnea-Hypopnea Syndrome (OSAHS), three-dimensional models of upper airway cavity and soft palate are
reconstructed by the method of surface rendering. Numerical simulation is performed for airflow in the upper airway and displacement
of soft palate by fluid-structure interaction analysis. The reconstructed three-dimensional models precisely preserve the
original configuration of upper airways and soft palate. The results of the pressure and velocity distributions in the airflow
field are quantitatively determined, and the displacement of soft palate is presented. Pressure gradients of airway are lower
for the healthy person and the airflow distribution is quite uniform in the case of free breathing. However, the OSAHS patient
remarkably escalates both the pressure and velocity in the upper airway, and causes higher displacement of the soft palate.
The present study is useful in revealing pathogenesis and quantitative mutual relationship between configuration and function
of the upper airway as well as in diagnosing diseases related to anatomical structure and function of the upper airway.
The project supported by the National Natural Science Foundation of China (10672036, 10472025 and 10421002), the Natural Science
Foundation of Liaoning Province (20032109).
English text was polished by Yunming Chen. 相似文献
998.
The effects of the Gaussian white noise excitation on structural safety due to erosion of safe basin in Duffing oscillator
with double potential wells are studied in the present paper. By employing the well-developed stochastic Melnikov condition
and Monte–Carlo method, various eroded basins are simulated in deterministic and stochastic cases of the system, and the ratio
of safe initial points (RSIP) is presented in some given limited domain defined by the system’s Hamiltonian for various parameters
or first-passage times. It is shown that structural safety control becomes more difficult when the noise excitation is imposed
on the system, and the fractal basin boundary may also appear when the system is excited by Gaussian white noise only. From
the RSIP results in given limited domain, sudden discontinuous descents in RSIP curves may occur when the system is excited
by harmonic or stochastic forces, which are different from the customary continuous ones in view of the first-passage problems.
In addition, it is interesting to find that RSIP values can even increase with increasing driving amplitude of the external
harmonic excitation when the Gaussian white noise is also present in the system.
The project supported by the National Natural Science Foundation of China (10302025 and 10672140).
The English text was polished by Yunming Chen. 相似文献
999.
In this paper, by capturing the atomic information and reflecting the behaviour governed by the nonlinear potential function,
an analytical molecular mechanics approach is proposed. A constitutive relation for single-walled carbon nanotubes (SWCNT’s)
is established to describe the nonlinear stress-strain curve of SWCNT’s and to predict both the elastic properties and breaking
strain of SWCNT’s during tensile deformation. An analysis based on the virtual internal bond (VIB) model proposed by P. Zhang
et al. is also presented for comparison. The results indicate that the proposed molecular mechanics approach is indeed an
acceptable analytical method for analyzing the mechanical behavior of SWCNT’s.
The project supported by the National Natural Science Foundation of China (10121202, 90305015 and 10328203), the Key Grant
Project of Chinese Ministry of Education (0306) and the Research Grants Council of the Hong Kong Special Administrative Region,
China (HKU 7195/04E). 相似文献
1000.