259 research outputs found
Formation of Liesegang patterns: Simulations using a kinetic Ising model
A kinetic Ising model description of Liesegang phenomena is studied using
Monte Carlo simulations. The model takes into account thermal fluctuations,
contains noise in the chemical reactions, and its control parameters are
experimentally accessible. We find that noisy, irregular precipitation takes
place in dimension d=2 while, depending on the values of the control
parameters, either irregular patterns or precipitation bands satisfying the
regular spacing law emerge in d=3.Comment: 7 pages, 8 ps figures, RevTe
Derivation of the Matalon-Packter law for Liesegang patterns
Theoretical models of the Liesegang phenomena are studied and simple
expressions for the spacing coefficients characterizing the patterns are
derived. The emphasis is on displaying the explicit dependences on the
concentrations of the inner- and the outer-electrolytes. Competing theories
(ion-product supersaturation, nucleation and droplet growth, induced sol-
coagulation) are treated with the aim of finding the distinguishing features of
the theories. The predictions are compared with experiments and the results
suggest that the induced sol-coagulation theory is the best candidate for
describing the experimental observations embodied in the Matalon-Packter law.Comment: 9 pages, 7 figures, RevTe
Formation of Liesegang patterns: A spinodal decomposition scenario
Spinodal decomposition in the presence of a moving particle source is
proposed as a mechanism for the formation of Liesegang bands. This mechanism
yields a sequence of band positions x_n that obeys the spacing law
x_n~Q(1+p)^n. The dependence of the parameters p and Q on the initial
concentration of the reagents is determined and we find that the functional
form of p is in agreement with the experimentally observed Matalon-Packter law.Comment: RevTex, 4 pages, 4 eps figure
Band Formation during Gaseous Diffusion in Aerogels
We study experimentally how gaseous HCl and NH_3 diffuse from opposite sides
of and react in silica aerogel rods with porosity of 92 % and average pore size
of about 50 nm. The reaction leads to solid NH_4Cl, which is deposited in thin
sheet-like structures. We present a numerical study of the phenomenon. Due to
the difference in boundary conditions between this system and those usually
studied, we find the sheet-like structures in the aerogel to differ
significantly from older studies. The influence of random nucleation centers
and inhomogeneities in the aerogel is studied numerically.Comment: 7 pages RevTex and 8 figures. Figs. 4-8 in Postscript, Figs. 1-3 on
request from author
Delocalization Transition of a Rough Adsorption-Reaction Interface
We introduce a new kinetic interface model suitable for simulating
adsorption-reaction processes which take place preferentially at surface
defects such as steps and vacancies. As the average interface velocity is taken
to zero, the self- affine interface with Kardar-Parisi-Zhang like scaling
behaviour undergoes a delocalization transition with critical exponents that
fall into a novel universality class. As the critical point is approached, the
interface becomes a multi-valued, multiply connected self-similar fractal set.
The scaling behaviour and critical exponents of the relevant correlation
functions are determined from Monte Carlo simulations and scaling arguments.Comment: 4 pages with 6 figures, new comment
Serum total and bone alkaline phosphatase levels and their correlation with serum minerals over the lifespan of sheep
This study aimed to assess serum total alkaline phosphatase (ALP) and its
bone isoform (BALP) levels during the ageing and in different physiologic states
of sheep, in order to expand the knowledge about the variation of these biomarkers
over the sheep lifespan. Ninety female sheep were divided into nine
groups of various ages and physiological states (dry, lactation and pregnancy). Serum
ALP, BALP and mineral levels were determined by commercial immunoassay,
molecular absorbance spectrophotometry and chemical luminescence for
BALP determination. Serum ALP and BALP decreased as sheep aged, and no statistically
significant differences were obtained between ewes in different physiologic
states. The continuous decline of serum BALP concentration along the sheep
lifespan, namely in mature and old sheep, is a sign of decreasing bone turnover
associated with ageing. Serum calcium concentrations increased slightly until 2
years of age and then showed a tenuous but statistically significant decrease in
mature sheep, while serum phosphorus maintained an uninterrupted decrease as
sheep matured. The knowledge of serum values of bone biomarkers throughout
the sheep lifespan may be useful in preclinical orthopaedic research studies and
for animal science studies using sheep.Cristina P. Sousa acknowledges the Portuguese Foundation for Science and Technology for her PhD scholarship SFRH/BD/45018/2008
Tartrate-resistant acid phosphate as biomarker of bone turnover over the lifespan and different physiologic stages in sheep
Currently, the best resources for assessment of bone tissue using imaging techniques are expensive and available in few medical facilities, thus serum or urinary bone turnover biomarkers could be useful as early indicators of prognosis. However, there is a wide range of variability in bone turnover markers due to several factors, such as different ages and metabolic stages, thus it is important to have as much data published on the subject as possible. The aim of this study was therefore to generate a reference range for alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP) and validate the already published data.National Council for Scientific and Technological Development (CNPq - Brazil) PhD scholarship 202248/2015–1.info:eu-repo/semantics/publishedVersio
Bone turnover markers in sheep and goat: a review of the scientific literature
Bone turnover markers (BTMs) are product of bone cell activity and are generally divided in bone formation and bone resorption markers. The purpose of this review was to structure the available information on the use of BTMs in studies on small ruminants, especially for monitoring their variations related to diet, exercise, gestation and metabolic lactation state, circadian and seasonal variations, and also during skeletal growth. Pre-clinical and translational studies using BTMs with sheep and goats as animal models in orthopaedic research studies to help in the evaluation of the fracture healing process and osteoporosis research are also described in this review. The available information from the reviewed studies was systematically organized in order to highlight the most promising BTMs in small ruminant research, as well as provide a wide view of the use of sheep and goat as animal models in orthopaedic research, type of markers and commercial assay kits with cross-reactivity in sheep and goat, method of sample and storage of serum and urine for bone turnover markers determination and the usefulness and limitations of bone turnover markers in the different studies, therefore an effective tool for researchers that seek answers to different questions while using BTMs in small ruminants.José Arthur de A. Camassa acknowledges to the
Conselho Nacional de Desenvolvimento Científico
e Tecnológico (CNPq), Brazil, for his PhD
scholarship 202248/2015-1.info:eu-repo/semantics/publishedVersio
Overall and cancer related mortality among patients with ocular inflammation treated with immunosuppressive drugs: retrospective cohort study
Context Whether immunosuppressive treatment adversely affects survival is unclear
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