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931.
“Simple” energetic patterns, where simple means the use of parameters derived only from the stoichiometry of these species,
are relatively rarely discussed in the literature. In addition, entropy studies have been dominated by derivation of the absolute
quantity S° rather than the entropy of formation (TΔf
S
o). Relationships between the entropy of formation and different parameters such as negative value of the charge of the species,
the number of oxygen atoms, the natural logarithm of the molecular weight, the total number of atoms and the number of central
atoms that are gases were recently discussed by us for aqueous polynuclear oxyanions. As shown here hydrogen containing anions
do not follow this pattern. In this study, new approaches for the estimation of the entropy of formation of aqueous hydrogen
containing mono and polynuclear oxyanions are suggested, evaluated and recommended. 相似文献
932.
Dragan Mihailovic 《Monatshefte für Chemie / Chemical Monthly》2003,134(2):137-147
Ferromagnetism in fullerene-based systems doped with metallocenes is reviewed. These compounds form a ferromagnetic state
by spin-coupling between π electrons on fullerene units, while the metallocene molecules do not contribute to the spin ordering.
One of these compounds has the highest critical temperature (19 K) for this class of compound. The magnetic properties of
these materials are very strongly dependent on the crystallization conditions.
Corresponding author. E-mail: Dragan.Mihailovic@ijs.si
Received September 4, 2002; accepted September 6, 2002 相似文献
933.
Jonathan Rosenhead 《The Journal of the Operational Research Society》1978,29(2):105-111
A case study is presented of the application of robustness analysis to the choice of examination subjects to be made by a 14-year-old girl. The analysis is conducted in terms of the desirable future career options which may be preserved by different combinations of subjects, and also of the balance with topics selected for their intrinsic interest. The approach, which employs very limited technical apparatus, is justified on a number of grounds-in particular, the crucial importance of uncertainty, and the need for understanding and acceptance by a "client" very unlike the corporate manager. Some tentative conclusions are reached on the extension of such methods to other cases of decision-makers with little, if any, resources to control except their own lives. 相似文献
934.
Helmut Schneider 《The Journal of the Operational Research Society》1978,29(12):1181-193
This paper deals with a periodic review inventory system. Methods are discussed for determining the re-order point s of an (s, S) order policy, when a certain service level is required. The results differ from those presented for a (Q, s) model which is usually considered in literature and implemented in practice. Methods are discussed for determining the re-order point of an (s, S) policy when demand is normal or gamma distributed. A numerical investigation demonstrates the applicability of the described methods. In particular, it is shown that these methods are superior to a formula that is implemented in many inventory control systems. 相似文献
935.
Ji-Lai Li Cai-Yun Geng Xu-Ri Huang Chia-Chung Sun 《Theoretical chemistry accounts》2007,117(3):417-429
The reaction of atomic radical F with propyne has been studied theoretically using ab initio quantum chemistry methods and
transition state theory. The potential energy surface was calculated at the CCSD(T)/aug-cc-pVDZ (single-point) level using
the UMP2/6-311++G(d,p) optimized structures. Two reaction mechanisms including the addition–isomerization–elimination reaction
mechanism and the directed hydrogen abstraction reaction mechanism are considered. For the hydrogen abstraction reactions,
i.e., the most probable evolution pathway in the title reaction, the HF formation occurs via direct abstraction mechanism
dominantly and the H atom picked up by the atomic radical F should come mostly from the methyl group of normal propyne. On
the other hand, for the addition–isomerization–elimination mechanism, the most feasible pathway should be the atomic radical
F attacking on the C≡C triple bond in propyne (CH3C≡CH) to form a weakly-bound adduct A1 with no barrier, followed by F addition to the C≡C triple bond to form the low-lying
intermediate isomer 5. Subsequently, isomer 5 directly dissociates to P3 H2CCCHF + H via transition state TS5/P3. The other reaction pathways on the doublet PES are less competitive due to thermodynamical or kinetic factors. Furthermore,
based on the analysis of the kinetics of all channels through which the addition and abstraction reaction proceed, we expect
that the competitive power of reaction channels may vary with experimental conditions for the title reaction. The present
work will provide useful information for understanding the processes of atomic radical F reaction with other unsaturated hydrocarbons.
This material is available from author via E-mail. 相似文献
936.
A 4-Amino-2-mercaptopyrimidine self-assembled monolayer (AMP SAMs/Au) modified gold electrode was prepared. The electrochemical
behavior of acetaminophen on the AMP SAMs/Au was studied in Britton-Robinson (BR) buffer solution. Compared to a bare gold
electrode, the modified electrode exhibits a significant enhancement in the oxidation current response for acetaminophen.
The modified electrode was used for the determination of acetaminophen by square wave voltammetry. The oxidation current increased
linearly with the concentration of acetaminophen in the range of 2.0 × 10−6−4.0 × 10−3 M. The modified electrode made it possible to eliminate the interference of dopamine (DA), brucine, epinephrine (EP), and
norepinephrine (NE). The practical analytical utility was illustrated by the determination of acetaminophen in a commercially
available drug.
The text was submitted by the authors in English. 相似文献
937.
In this work a novel graphical method is applied to the presentation of intercomparison results. This is demonstrated with
the results of a recent intercomparison in measuring the 137Cs, 40K, and 90Sr activity concentration in milk powder. The “PomPlot”, an intuitive graphical method, is used for producing a summary overview
of the participants’ results of a common measurand. The “PomPlot” displays (relative) deviations of individual results from
the reference value on the horizontal axis and (relative) uncertainties on the vertical axis. 相似文献
938.
Xiu-Kui Qu Lan-Ying Zhu Ling Li Xi-Lian Wei Feng Liu De-Zhi Sun 《Journal of solution chemistry》2007,36(5):643-650
As a continuation of our previous investigation, interactions between cyclodextrin (β-CD), γ-cyclodextrin (γ-CD) and alkyl trimethylammonium bromides in aqueous solutions have been studied with titration calorimetry and 1H NMR at 298.15 K. The results are discussed in terms of the amphiphilic interaction of CD with surfactants and the iceberg
structure formed by water molecules existing around the hydrophobic tail of surfactant molecules. The stoichiometry of the β-CD–surfactant system is 1:1 whereas that of the γ-CD–surfactant system is 1:2. The corresponding formation enthalpy (negative) of the complexes of the two systems decreases
with an increase in the number of carbon atoms (n) in hydrophobic chain of surfactant molecule, C
n
H2n+1, whereas the entropy increases with the enlargement of n. 相似文献
939.
Polymorphism of paracetamol 总被引:1,自引:0,他引:1
G. L. Perlovich Tatyana V. Volkova Annette Bauer-Brandl 《Journal of Thermal Analysis and Calorimetry》2007,89(3):767-774
The thermodynamic relationship between crystal modifications of paracetamol was studied by alternative methods. Temperature
dependence of saturated vapor pressure for polymorphic modifications of the drug paracetamol (acetaminophen) was mea sured
and thermodynamic functions of the sublimation process calculated. Solution calorimetry was carried out for the two modifications
in the same solvent. Thermodynamic parameters for sublimation for form I (monoclinic) were found: ΔG
sub298=60.0 kJ mol−1; ΔH
sub298=117.9±0.7 kJ mol−1; ΔS
sub298=190±2 J mol−1 K−1. For the orthorhombic modification (form II), the saturated vapor pressure could only be studied at 391 K. Phase transition
enthalpy at 298 K, ΔH
tr298(I→II)=2.0±0.4 kJ mol−1, was derived as the difference between the solution enthalpies of the noted polymorphs in the same solution (methanol). Based
on ΔH
tr298 (I→II), differences between temperature dependencies of heat capacities of both modifications and the vapor pressure value
of form II at 391 K, the temperature dependence of saturated vapor pressure and thermodynamic sublimation parameters for modification
II were also estimated (ΔG
sub298=56.1 kJ mol−1; ΔH
sub298=115.9±0.9 kJ mol−1; ΔS
sub298=200±3 J mol−1 K−1). The results indicate that the modifications are monotropically related, which is in contrast to findings recently reported
found by classical thermochemical methods. 相似文献
940.
Reversed-phase liquid chromatography and argentation chromatography of the minor capsaicinoids 总被引:1,自引:0,他引:1
Thompson RQ Phinney KW Sander LC Welch MJ 《Analytical and bioanalytical chemistry》2005,381(7):1432-1440
An investigation of the liquid chromatography of the minor capsaicinoids in a commercial capsaicinoid mixture is reported. Twelve stationary phases including C8, C18, C30, phenyl, and cation-exchange chemistries were examined in combination with isocratic aqueous methanol and aqueous acetonitrile mobile phases. A phenyl stationary phase and aqueous acetonitrile mobile phase baseline-resolved 7 of 11 capsaicinoids, and selected ion chromatograms (LC–ESI-MS) demonstrated this was the most effective reversed-phase separation. Argentation chromatography with an alkyl or phenyl column and aqueous silver nitrate–methanol mobile phase revealed the presence of the 6-ene-8-methyl and 6-ene-9-methyl homocapsaicin isomers and the absence of 7-ene-9-methyl homocapsaicin. A mixed phenyl–cation-exchange stationary phase (charged with silver ion) enabled unique and useful separations of the capsaicinoids. 相似文献