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Bajdik J. Pintye-Hódi K. Novák Cs. Kelemen A. Regdon G. Erős I. 《Journal of Thermal Analysis and Calorimetry》2002,68(2):613-627
The extents of the protective effects of coating films on the surface of crystals were determined. Three different samples
were made with different quantities of coating fluid (Sepifilm LP 010 in 10% aqueous solution). Since the atomizing rate was
constant, the coating time increased in parallel with the volume of coating fluid applied. The direct measurement of film
thickness and smoothness is very difficult, and therefore indirect methods were used. Dimenhydrinate was chosen as model drug;
this is a heat-sensitive antihistamine with a low melting point. This temperature can be reached during the tableting process.
The behaviour of samples on exposure to heat was examined by differential scanning calorimetry. The water uptakes of the samples
were determined with an Enslin apparatus. Plasticity was studied with an instrumented tablet machine. These indirect methods
(thermal conductivity, water uptake and plasticity measurements) revealed connections between the results of the various experiments.
An overlong coating time decreased the protective effect of the coating film.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
Vincenzo Santagada Ferdinando FiorinoElisa Perissutti Beatrice SeverinoSara Terracciano Giuseppe CirinoGiuseppe Caliendo 《Tetrahedron letters》2003,44(6):1145-1148
A novel and convenient microwave-assisted dimerization of an active peptide compound using the DKPs as scaffold is described. The key reaction giving rise to the diketopiperazine scaffold is the intermolecular coupling. No epimerization was detected in the reactions used. Conventional and microwave heating of the reactions are compared. Synthesis by microwave irradiation gave the desired compounds in higher yields and in shorter reaction times than those obtained by conventional heating. 相似文献
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Temperature modulated differential calorimetry (TMDSC) is used to examine the crystal-crystal transitions of poly(tetrafluoroethylene). This study gives new information about the dynamic thermal behavior of such transitions. The involvement of reversible and irreversible processes during the phenomenon is observed, which are related to the order-disorder changes occurring during the transition.This study adds a new example to the response of TMDSC during first order transitions. 相似文献
6.
Onofrio Mario Di Vincenzo Plamen Koshlukov Roberto La Scala 《Advances in Applied Mathematics》2006,37(4):541
In this paper we describe completely the involutions of the first kind of the algebra UTn(F) of n×n upper triangular matrices. Every such involution can be extended uniquely to an involution on the full matrix algebra. We describe the equivalence classes of involutions on the upper triangular matrices. There are two distinct classes for UTn(F) when n is even and a single class in the odd case.Furthermore we consider the algebra UT2(F) of the 2×2 upper triangular matrices over an infinite field F of characteristic different from 2. For every involution *, we describe the *-polynomial identities for this algebra. We exhibit bases of the corresponding ideals of identities with involution, and compute the Hilbert (or Poincaré) series and the codimension sequences of the respective relatively free algebras.Then we consider the *-polynomial identities for the algebra UT3(F) over a field of characteristic zero. We describe a finite generating set of the ideal of *-identities for this algebra. These generators are quite a few, and their degrees are relatively large. It seems to us that the problem of describing the *-identities for the algebra UTn(F) of the n×n upper triangular matrices may be much more complicated than in the case of ordinary polynomial identities. 相似文献
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Then-th commutator for a,b in a ringR is defined inductively as follows: [a,b]1=[a,b]=ab−ba and[a,b]
n=[[a,b]−1,b]. We characterize the ringsR without non-zero nil right ideals in which[a,b]
nis nilpotent or regular for alla,b∈R. We also examine the case whereR is a semiprime ring with involution in which[t
1, t2]nis nilpotent or regular for all tracest
1,t2∈R. 相似文献
9.
DRIFTS study of surface reactivity to NO2 by zinc nanoparticle aggregates and zinc hollow nanofibers
Zinc nanostructures synthesized with different morphologies from the same evaporation/condensation technique are studied with concern to surface reactivity to NO2 by Diffuse Reflectance Infrared Fourier Transformed Spectroscopy (DRIFTS). Synthesis of nanopowders is obtained, according to previous work, by gas flow thermal evaporation at 540 °C of bulk Zn grains. Two types of Zn powders are obtained and studied in experiments. The first one is collected on the cold walls of the reactor as a deposit produced by thermophoretic effect. It is constituted by grains (∼10 μm) originated by the stratification of smaller aggregates (∼200 nm) and isolated primary particles (∼50 nm) born in the gas flow. The second type of powder is grown from the condensation of Zn chemical vapors within the expansion orifice of the quartz reactor after relatively long time (∼1 h) deposition process. It is constituted mainly by hollow Zn nanofibers with external and internal diameter about 100 and 60 nm. Preliminary characterization of the two types of powders is made by SEM, TEM, XRD. Thereafter, the two types of samples are studied by DRIFTS at variable temperature (VT). Comparison is made between the home-synthesized nanopowders with respect to commercial Zn standard dust. The Zn hollow nanofibers when exposed to NO2 are found to exhibit dramatic reactivity, which is not observed at all either in the case of clustered aggregate zinc or of commercial Zn dust powders. Results indicate that, at increasing temperature from RT to 300 °C, the hollow nanofibers surface reacts distinctively with adsorbant gas NO2, with contemporary formation of a progressively growing narrow absorption band at 2500 cm−1 and contemporary depression of a doublet (∼1600-1628 cm−1) band. In order to justify this striking spectral feature, we propose the occurring of a possible polymerization process at nanofibers surface where most probably as a consequence of pre-treatment and exposure to gas NO2 a very thin film of ZnO is formed. The possible role of huge specific surface of hollow nanofibers as inferred by preliminary SEM, TEM, XRD studies is discussed. 相似文献
10.