252 research outputs found
Note on the Preparation of Some Thiobarbiturates
It has been shown that barbituric acid derivatives can be prepared in good yield by gradually adding sodium methoxide as condensation catalyst to a cyanoacetic or malonic ester reacting with urea or its derivatives. The principle of the gradual addition of sodium methoxide as condensing agent has now been extended to condensations of some substituted cyanoacetic and malonic esters with thiourea
Thermodynamically self-consistent non-stochastic micromagnetic model for the ferromagnetic state
In this work, a self-consistent thermodynamic approach to micromagnetism is
presented. The magnetic degrees of freedom are modeled using the
Landau-Lifshitz-Baryakhtar theory, that separates the different contributions
to the magnetic damping, and thereby allows them to be coupled to the electron
and phonon systems in a self-consistent way. We show that this model can
quantitatively reproduce ultrafast magnetization dynamics in Nickel.Comment: 5 pages, 3 figure
Adaptively time stepping the stochastic Landau-Lifshitz-Gilbert equation at nonzero temperature: implementation and validation in MuMax3
Thermal fluctuations play an increasingly important role in micromagnetic
research relevant for various biomedical and other technological applications.
Until now, it was deemed necessary to use a time stepping algorithm with a
fixed time step in order to perform micromagnetic simulations at nonzero
temperatures. However, Berkov and Gorn have shown that the drift term which
generally appears when solving stochastic differential equations can only
influence the length of the magnetization. This quantity is however fixed in
the case of the stochastic Landau-Lifshitz-Gilbert equation. In this paper, we
exploit this fact to straightforwardly extend existing high order solvers with
an adaptive time stepping algorithm. We implemented the presented methods in
the freely available GPU-accelerated micromagnetic software package MuMax3 and
used it to extensively validate the presented methods. Next to the advantage of
having control over the error tolerance, we report a twenty fold speedup
without a loss of accuracy, when using the presented methods as compared to the
hereto best practice of using Heun's solver with a small fixed time step.Comment: 9 pages, 9 figure
Calorimetric Investigation of Grafting of Styrene and Methylmethacrylate onto Air-Preirradiated Polyethylene
All existing and widely used methods for measuring reaction
rate of polymerization processes suffer from basic disadvantages
including indirect measurement, insufficient accuracy and limited
applicability. Their unsuitability is especially pronounced in the
investigation of graft copolymerization reactions in which the
accuracy of measurement could be affected even by the different
properties of individual polymer samples.
In this work a new method, calorimetry, free of mentioned
disadvantages is generally proposed for investigation of polymerization
processes and particularly its application to radiation induced
grafting of styrene and methylmethacrylate onto polyethylene
is demonstrated.
Experimental results showed the possibility of calorimetry
to measure the grafting rate continuously and directly in the whole
conversion range with the accuracy much better than with any
other method used so far.
It was concluded that styrene grafting is non-diffusion-controlled,
whereas methylmethacrylate grafting is not diffusion-
independent. With both monomers the reaction kinetics was
found to be dependent on the type of polyethylene a s a consequence
of different mechanisms, i. e. in the initiation step two different
species, peroxy radicals and peroxides, take part. Its concentration
is different in two types of polyethylene used. In the case of high
density polyethylene both active species participate in the initiation
process equally, according to their different nature. However, in
low density polyethylene the concentration of peroxy radicals is
negligible compared to that of peroxides and therefore peroxides
have dominating role in the initiation step of grafting reaction. The
change of the viscosity of reaction medium in the course of reaction
as well as the structure of polymer in the case of high density
polyethylene influence the kinetics of grafting reaction
Preparation of Some lmino- and Cyano-imino-substituted Barbiturates
A number of imino- and cyano-iminobarbituric acid derivatives has been prepared in good yield by gradually adding sodium methoxide - as condensation catalyst - to some substituted cyanoacetic and malonic esters reacting with urea, dicyandiamide
and guanidine
O nusproduktima kod preparacije 5-etil-5-fenil-barbiturne kiseline
5-etil-5-fenil-barbiturna kiselina (luminal, fenobarfital) priprema se obicno kondenzacijom dietil etil-fenil-malonata (II) i uree u abs. etanolu uz Na-etoksid kao kondenzacino sredstvo. Relativno niska iskoristenja pripisuju se cijepanju dietil etil-fenil-malonata. Poznato je, naime, da disupstituirani malonski esteri u prisutnosti Na-etoksida dekarbetoksiliraju u odgovarajuce disupstituirane octene estere. Kod kondenzacije disupstituiranih malonata sa ureom uz Na-etoksid daje preostali malonat odgovarajuci barbiturat, a cijepanjem nastali acetat produkte reakcije sa ureom (ili amonijakom)
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