519 research outputs found
Design and Evaluation of Matrix Diffusion Controlled Transdermal Patches of Diltiazem Hydrochloride
Se desarrolló un sistema matricial de tipo dispersivo para la administración transdérmica de clorhidrato de Diltiazem
usando diferentes proporciones de colofonia con Eudragit RL PM y polivinil pirrolidona. El parche preparado con
colofonia y polivinil pirrolidona no era transparente y muestra una distribución irregular de polivinil pirrolidona,
lo que puede ser debido al carácter hidrófi lo de ésta. Se investigó el efecto de los polímeros sobre las propiedades
tecnológicas; es decir, la liberación del fármaco, la velocidad de transmisión del vapor de agua, la pérdida porcentual
de humedad y el grosor. El parche con colofonia: Eudragit RL PM (6:4) dio como resultado una liberación
de 2651 mcg en 24 horas. Con el objeto de mejorar la liberación, se incluyeron distintas proporciones de alcanfor
en la formulación. El parche con colofonia: Eudragit RL PM (6:4) y un 5% p/v de alcanfor dio como resultado
una liberación constante del fármaco a lo largo de un período de 24 horas. La formulación F8 resultó ser la más
satisfactoria en lo que a las propiedades tecnológicas se refi ere. Se llevaron a cabo estudios posteriores de permeación
e irritación de la piel en ratas y conejos respectivamente. Por lo tanto, se puede concluir que con el parche
de colofonia: Eudragit RL PM en proporción 6:4 con un 5% p/v de alcanfor, se alcanzan los objetivos deseables
en sistemas de administración transdérmica de fármacos tales como anular el efecto de primer paso, una amplia liberación y una frecuencia de administración reducida.A matrix dispersion type transdermal drug delivery system of Diltiazem Hydrochloride was developed using different
ratios of rosin with Eudragit RL PM and polyvinyl pyrrolidone. The patch prepared by the combination of rosin and
polyvinyl pyrrolidone was not transparent one, and shows an uneven distribution of polyvinyl pyrrolidone, which may
be due to the hydrophilic nature of polyvinyl pyrrolidone. The effect of the polymers on the technological properties,
i.e., drug release, water vapor transmission rate, percentage moisture loss and thickness were investigated. The patch
containing rosin: Eudragit RL PM (6:4) showed a release of 2651 mcg in 24 h. In order to improve the release various
proportions of camphor was included in the formulation. The patch containing rosin: Eudragit RL PM (6:4) with
5% w/v of camphor showed a sustained release of the drug extending over a period of 24 h. Formulation F8 emerged
as the most satisfactory formulation as far as the technological properties were concerned. Further skin permeation
and skin irritation studies were carried out on rat skin and rabbit respectively. Therefore it can be concluded that the
patch containing rosin: Eudragit RL PM in the ratio 6:4 with 5%w/v of camphor achieved the desired objectives of
transdermal drug delivery systems, such as overcoming of fi rst pass effect, extended release and reduced frequency of
administration
Formulation and evaluation of oral sustained release of Diltiazem Hydrochloride using rosin as matrix forming material
Rosin, a natural resin, was used as a hydrophobic matrix material for the controlled release, using diltiazem HCl as model drug. Matrix tablets were prepared by direct compression method using rosin as matrix forming material in different proportions and with different diluent combinations. The tablets prepared were flat faced, retained their shape throughout. The method of preparation of matrix system and its concentration were found to have pronounced effect on the release of diltiazem HCl. The release was found to follow both the first order kinetics and fickian diffusion. The drug delivery was analyzed using the paddle method according to USP XXIII. All the studies were done in phosphate buffer pH 7.4. The matrix tablets were evaluated for its thickness, hardness, friability, weight variation, drug content and invitro release studies. The results suggest that the rosin is useful in developing sustained release matrix tablets, prolong release of water soluble drug for up to 24h. Rosin thus promises considerable utility in the development of oral sustained release drug delivery systems
Competition of Mesoscales and Crossover to Tricriticality in Polymer Solutions
We show that the approach to asymptotic fluctuation-induced critical behavior
in polymer solutions is governed by a competition between a correlation length
diverging at the critical point and an additional mesoscopic length-scale, the
radius of gyration. Accurate light-scattering experiments on polystyrene
solutions in cyclohexane with polymer molecular weights ranging from 200,000 up
to 11.4 million clearly demonstrate a crossover between two universal regimes:
a regime with Ising asymptotic critical behavior, where the correlation length
prevails, and a regime with tricritical theta-point behavior determined by a
mesoscopic polymer-chain length.Comment: 4 pages in RevTeX with 4 figure
Towards a quantitative phase-field model of two-phase solidification
We construct a diffuse-interface model of two-phase solidification that
quantitatively reproduces the classic free boundary problem on solid-liquid
interfaces in the thin-interface limit. Convergence tests and comparisons with
boundary integral simulations of eutectic growth show good accuracy for
steady-state lamellae, but the results for limit cycles depend on the interface
thickness through the trijunction behavior. This raises the fundamental issue
of diffuse multiple-junction dynamics.Comment: 4 pages, 2 figures. Better final discussion. 1 reference adde
The resistive state in a superconducting wire: Bifurcation from the normal state
We study formally and rigorously the bifurcation to steady and time-periodic
states in a model for a thin superconducting wire in the presence of an imposed
current. Exploiting the PT-symmetry of the equations at both the linearized and
nonlinear levels, and taking advantage of the collision of real eigenvalues
leading to complex spectrum, we obtain explicit asymptotic formulas for the
stationary solutions, for the amplitude and period of the bifurcating periodic
solutions and for the location of their zeros or "phase slip centers" as they
are known in the physics literature. In so doing, we construct a center
manifold for the flow and give a complete description of the associated
finite-dimensional dynamics
Banning the bulb: institutional evolution and the phased ban of incandescent lighting in Germany
Much academic attention has been directed at analysing energy efficiency investments through the lens of ‘behavioural failure’. These studies have challenged the neoclassical framing of regulation which emphasises the efficiency benefits of price based policy, underpinned by the notion of rational individual self-mastery. The increasing use of a regulatory ban on electric lamps in many countries is one of the most recent and high profile flash points in this dialectic of ‘freedom-versus-the-state’ in the public policy discourse. This paper interrogates this debate through a study of electric lamp diffusion in Germany. It is argued that neoclassical theory and equilibrium analysis is inadequate as a tool for policy analysis as it takes the formation of market institutions, such as existing regulations, for granted. Further still, it may be prone to encourage idealistic debates around such grand narratives which may in practice simply serve those who benefit most from the status quo. Instead we argue for an evolutionary approach which we suggest offers a more pragmatic framing tool which focuses on the formation of market institutions in light of shifting social norms and political goals—in our case, progress towards energy efficiency and environmental goals
Relativistic description of electron scattering on the deuteron
Within a quasipotential framework a relativistic analysis is presented of the
deuteron current. Assuming that the singularities from the nucleon propagators
are important, a so-called equal time approximation of the current is
constructed. This is applied to both elastic and inelastic electron scattering.
As dynamical model the relativistic one boson exchange model is used.
Reasonable agreement is found with a previous relativistic calculation of the
elastic electromagnetic form factors of the deuteron. For the unpolarized
inelastic electron scattering effects of final state interactions and
relativistic corrections to the structure functions are considered in the
impulse approximation. Two specific kinematic situations are studied as
examples.Comment: (19 pages in revtex + 15 figures not included, available upon
request.) report THU-93-10
Generation of defects and disorder from deeply quenching a liquid to form a solid
We show how deeply quenching a liquid to temperatures where it is linearly
unstable and the crystal is the equilibrium phase often produces crystalline
structures with defects and disorder. As the solid phase advances into the
liquid phase, the modulations in the density distribution created behind the
advancing solidification front do not necessarily have a wavelength that is the
same as the equilibrium crystal lattice spacing. This is because in a deep
enough quench the front propagation is governed by linear processes, but the
crystal lattice spacing is determined by nonlinear terms. The wavelength
mismatch can result in significant disorder behind the front that may or may
not persist in the latter stage dynamics. We support these observations by
presenting results from dynamical density functional theory calculations for
simple one- and two-component two-dimensional systems of soft core particles.Comment: 25 pages, 11 figure
Red Queen Coevolution on Fitness Landscapes
Species do not merely evolve, they also coevolve with other organisms.
Coevolution is a major force driving interacting species to continuously evolve
ex- ploring their fitness landscapes. Coevolution involves the coupling of
species fit- ness landscapes, linking species genetic changes with their
inter-specific ecological interactions. Here we first introduce the Red Queen
hypothesis of evolution com- menting on some theoretical aspects and empirical
evidences. As an introduction to the fitness landscape concept, we review key
issues on evolution on simple and rugged fitness landscapes. Then we present
key modeling examples of coevolution on different fitness landscapes at
different scales, from RNA viruses to complex ecosystems and macroevolution.Comment: 40 pages, 12 figures. To appear in "Recent Advances in the Theory and
Application of Fitness Landscapes" (H. Richter and A. Engelbrecht, eds.).
Springer Series in Emergence, Complexity, and Computation, 201
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