20,898 research outputs found
Observational Constraints on Silent Quartessence
We derive new constraints set by SNIa experiments (`gold' data sample of
Riess et al.), X-ray galaxy cluster data (Allen et al. Chandra measurements of
the X-ray gas mass fraction in 26 clusters), large scale structure (Sloan
Digital Sky Survey spectrum) and cosmic microwave background (WMAP) on the
quartessence Chaplygin model. We consider both adiabatic perturbations and
intrinsic non-adiabatic perturbations such that the effective sound speed
vanishes (Silent Chaplygin). We show that for the adiabatic case, only models
with equation of state parameter are allowed: this
means that the allowed models are very close to \LambdaCDM. In the Silent case,
however, the results are consistent with observations in a much broader range,
-0.3<\alpha<0.7.Comment: 7 pages, 12 figures, to be submitted to JCA
Welcome to the TERMIS-EU 2008 Porto meeting
info:eu-repo/semantics/publishedVersio
Endometriosis: A Rare Cause of Large Bowel Obstruction.
Large bowel obstruction can result in significant morbidity and mortality, especially in cases of acute complete obstruction. There are many possible causes, the most common in adults being colorectal cancer. Endometriosis is a benign disease, and the most affected extragenital location is the bowel, especially the rectosigmoid junction. However, transmural involvement and acute occlusion are very rare events. We report an exceptional case of acute large bowel obstruction as the initial presentation of endometriosis. The differential diagnosis of colorectal carcinoma may be challenging, and this case emphasizes the need to consider intestinal endometriosis in females at a fertile age presenting with gastrointestinal symptoms and an intestinal mass causing complete large bowel obstruction.info:eu-repo/semantics/publishedVersio
Biodegradable polymeric fiber structures in tissue engineering
Tissue engineering offers a promising new approach to create biological alternatives to repair or restore function
of damaged or diseased tissues. To obtain three-dimensional tissue constructs, stem or progenitor cells must be
combined with a highly porous three-dimensional scaffold, but many of the structures purposed for tissue engineering
cannot meet all the criteria required by an adequate scaffold because of lack of mechanical strength and
interconnectivity, as well as poor surface characteristics. Fiber-based structures represent a wide range of morphological
and geometric possibilities that can be tailored for each specific tissue-engineering application. The
present article overviews the research data on tissue-engineering therapies based on the use of biodegradable fiber
architectures as a scaffold
The effect of water uptake on the behaviour of hydrophilic cements in confined environments
Physiological fluids will be in contact with the implant components from the first moments after a surgery. Therefore, the study of the
effect of water on the properties of the bone cements that are part of the arthroplasty procedure is of critical importance to predict the
long-term performance of the whole system. In our research group, we have developed a novel concept, the hydrophilic, partially
degradable and bioactive cements which uptake considerably more water than standard bone cements. In this paper, we aimed to study the
effect of water uptake (WU) by these cements on their behaviour. The tests were carried out in confined cavities, which represent more
accurately the in vivo situation the cement will face (constrained by the bone and prosthesis surfaces). We observed that the equilibrium
WU decreased up to 60% (as compared to non-confined situations), depending of the formulation. This decrease resulted in a latent
tendency of the cements to swell, and the hindering of such swelling generated a swelling pressure against the constraining walls. The
pressure, and consequent press-fitting effect, could be controlled by a number of mechanisms, and resulted in higher stability of the
hydrophilic cements, expressed as an increase in the push-out force, required to extract the specimens from such constrained cavities. This
effect was only observed in hydrophilic cements, not in commercial, hydrophobic ones used as controls. We conclude that such cements
will provide an additional and very useful source of immediate adhesion in the short-term after surgery: water induced press fitting
A review on the polymer properties of hydrophilic, partially degradable and bioactive acrylic cements (HDBC)
Acrylic bone cements were developed around 50 years ago for the fixation of hip prostheses during arthroplasty. Over
the intervening years, a series of drawbacks have been disclosed that have fostered intensive research on the development
of novel or alternative formulations to the standard acrylic cements. Here, we will review the development and
characterization of a novel class of cements, the Hydrophilic, partially Degradable and Bioactive Cements (HDBCs), an
example of multifunctional cements. They were developed to have improved biocompatibility and initial fixation to the
prosthesis and to induce the growth of bone on the surface of the cement and within pores generated by the degradation of
the solid component. HDBCs have higher water uptake than typical acrylic cements, leading to press-fitting inside
constrained cavities. They are tougher, albeit less stiff and strong than hydrophobic cements, and their mechanical
properties may be easily adjusted by small changes in composition. Last, the simultaneous bioactive and degradable
character of HDBCs have been shown to allow in vitro growth of calcium phosphates into pores within the bulk of the
cement
Sugars : burden or biomaterials of the future?
During the past few years, the field of tissue engineering (TE) has been shifting from replacement to regenerative strategies. Following this tendency, the requirements for biomaterials to be used in TE have been also changing. While a few decades ago bioinert materials that do not provoke undesired body responses were in the focus of material sciences, nowadays third generation biomaterials mimicking the nanoscale mechanisms of the interactions between cells and their in vivo environment are the target of material design. Although these mechanisms involve different bioactive molecules, until now mainly strategies involving small peptide epitopes that copycat specific sequences of complex proteins have been exploited. The breakthroughs that such approaches brought to biomaterials and TE fields are undeniable. Nevertheless, the important role that carbohydrates play in tissue structuring and function is still poorly explored and exploited in this context and we believe that this is one of the missing pieces in the TE puzzle. Carbohydrates are an integral part of our life. We are literally covered by them: from bacteria to mammalian cells, the molecular landscape of the cell surface is coated with sugars forming the so-called glycocalyx. This strategic placement of the sugars makes them crucial for the development, growth, function and/or survival of an organism. It is believed that the structural diversity of carbohydrates is the key for understanding and controlling those processes because of the huge number of ligand structures, which sugars can display in molecular recognition systems. However, their main advantages: the intricacy and the large natural diversity have turned against the scientists and have hampered their study. As a result, the field of glycomics is much less developed compared to its counterparts genomics and proteomics within TE. Recent advances in carbohydrate synthesis, sensing technologies and processing methodologies are inducing rapid changes in this field and will be discussed in this paThe authors acknowledge the funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no. NMP4-SL-2009-229292
Finite-size effects in roughness distribution scaling
We study numerically finite-size corrections in scaling relations for
roughness distributions of various interface growth models. The most common
relation, which considers the average roughness . This illustrates how
finite-size corrections can be obtained from roughness distributions scaling.
However, we discard the usual interpretation that the intrinsic width is a
consequence of high surface steps by analyzing data of restricted
solid-on-solid models with various maximal height differences between
neighboring columns. We also observe that large finite-size corrections in the
roughness distributions are usually accompanied by huge corrections in height
distributions and average local slopes, as well as in estimates of scaling
exponents. The molecular-beam epitaxy model of Das Sarma and Tamborenea in 1+1
dimensions is a case example in which none of the proposed scaling relations
works properly, while the other measured quantities do not converge to the
expected asymptotic values. Thus, although roughness distributions are clearly
better than other quantities to determine the universality class of a growing
system, it is not the final solution for this task.Comment: 25 pages, including 9 figures and 1 tabl
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