Several constitutive theories have been proposed in the literature to model the viscoelastic response of soft tissue, including widely used rheological constitutive models. These models are characterized by certain parameters (“time constants”) that define the time scales over which the tissue relaxes. These parameters are primarily obtained from stress relaxation experiments using curve-fitting techniques. However, the question of how best to estimate these time constants remains open.
As a step towards answering this question, we develop an optimal experimental design approach based on ideas from information geometry, namely Fisher information and Kullback-Leibler divergence. Tissue is modeled as a standard linear solid and described using a one- or two-term Prony series. Treating the time constants as unknowns, we develop expressions for the Fisher information and Kullback-Leibler divergence that allow us to maximize information gain from experimental data. Based on the results of this study, we propose that the largest time constant estimated from a stress relaxation experiment for a linear viscoelastic material should be at most one-fifth of the total time of the experiment in order to maximize information gain.
The study of the propagation of multiple cracks is essential to modeling and predicting structural integrity. The interaction between two cracks depends on a number of factors such as the domain geometry, the relative crack sizes and the separation between the two crack tips. In this paper, we study the interaction between two dynamically propagating cracks. We use the phase field method to track the crack paths, since this method can handle complex crack behavior such as crack branching, without any ad hoc criteria for crack evolution. The results from our dynamic simulations indicate that, unlike crack inter- action under quasi-static or fatigue loading, the presence of another crack does not accelerate crack propagation when dynamic loads are applied. However, some similarities in the crack topologies are observed for both quasi-static and dynamic loading.
Lloyd C. Engelbrecht (born 1927) is Professor Emeritus of Art History at the University of Cincinnati. In collaboration with his late wife, June-Marie F. Engelbrecht (1930-2009), he has been researching, writing about and speaking about architect and designer Henry C. Trost (1860-1933) and his family firm of Trost & Trost.
On May 8, 2014, Lloyd Engelbrecht was invited to speak at the University of Texas at El Paso as part of a Trost symposium. The following is an excerpt from the official announcement of the symposium:
In celebration of Trost’s architectural legacy, UTEP Special Collections will host the “Trost Lecture Series” at 6 p.m. May 8  in the UTEP Library, Blumberg Auditorium, room 111.
The event will feature speakers Dr. Troy Ainsworth, executive director of El Camino Real de Tierra Adentro Trail Association (CARTA); Joe and Lanna Duncan, owners of the Trost-designed El Capitan Hotel in Van Horn, Texas and El Paisano Hotel in Marfa, Texas; and Dr. Lloyd Engelbrecht, co-author of Henry C. Trost: Architect of the Southwest.
A public exhibit featuring family photos, sketches, blueprints and photographs of the buildings Trost designed in El Paso and throughout the Southwest will be on display May 10 in the UTEP Library’s atrium on the third floor.
The lecture and exhibit were part of Trost Week, May 3-10, 2014, which was organized by the Texas Trost Society, a new nonprofit group that advocates for the preservation of Trost & Trost architecture.
Hyperelastic constitutive models of soft tissue mechanical behavior are extensively used in applications like computer-aided surgery, injury modeling, etc. While numerous constitutive models have been proposed in the literature, an objective method is needed to select a parsimonious model that represents the experimental data well and has good predictive capability. This is an important problem given the large variability in the data inherent to soft tissue mechanical testing.
In this work, we discuss a Bayesian approach to this problem based on Bayes factors. We propose a holistic framework for model selection, wherein we consider four different factors to reliably choose a parsimonious model from the candidate set of models. These are the qualitative fit of the model to the experimental data, evidence values, maximum likelihood values, and the landscape of the likelihood function. We consider three hyperelastic constitutive models that are widely used in soft tissue mechanics: Mooney-Rivlin, Ogden and exponential. Three sets of mechanical testing data from the literature for agarose hydrogel, bovine liver tissue, porcine brain tissue are used to calculate the model selection statistics. A nested sampling approach is used to evaluate the evidence integrals. In our results, we highlight the robustness of the proposed Bayesian approach to model selection compared to the likelihood ratio, and discuss the use of the four factors to draw a complete picture of the model selection problem.
Members of the fungal genus Pneumocystis colonize healthy mammalian hosts
without causing apparent disease, but colonization in immunocompromised hosts
may result in a potentially fatal pneumonia known as Pneumocystis pneumonia.
Although Pneumocystis are fungi, this genus has characteristics that make it atypical
among other fungi. Pneumocystis do not appear to synthesize the major fungal sterol,
ergosterol, and biochemical analyses have shown that they utilize cholesterol rather
than ergosterol as the bulk sterol. Pneumocystis carinii appears to scavenge exogenous sterols, including cholesterol, from its mammalian host. As a result, it has long been held that their ability to scavenge cholesterol from their hosts, and their inability to undergo sterol biosynthesis, makes them resistant to antifungal drugs that target ergosterol or ergosterol biosynthesis. However, genome scans and in vitro assays indicate the presence of sterol biosynthetic genes within the P. carinii genome, and targeted inhibition of these enzymes resulted in reduced viability of P. carinii,
suggesting that these enzymes are functional within the organism. Heterologous
expression of P. carinii sterol genes, along with biochemical analyses of the lipid
content of P. carinii cellular membranes, have provided an insight into sterol
biosynthesis and the sterol-scavenging mechanisms used by these fungi.
Organisms in the genus Pneumocystis are ubiquitous, opportunistic pathogenic fungi capable of causing a
lethal pneumonia in immunocompromised mammalian hosts. Pneumocystis spp. are unique members of the
fungal kingdom due to the absence of ergosterol in their cellular membranes. Although these organisms were
thought to obtain cholesterol by scavenging, transcriptional analyses indicate that Pneumocystis carinii encodes
gene homologs involved in sterol biosynthesis. To better understand the sterol pathway in these uncultivable
fungi, yeast deletion strains were used to interrogate the function and localization of P. carinii lanosterol synthase (ERG7). The expression of PcErg7p in an ERG7-null mutant of the yeast Saccharomyces cerevisiae did not alter its growth rate and produced a functional lanosterol synthase, as evidenced by the presence of
lanosterol detected by gas chromatographic analysis in levels comparable to that produced by the yeast enzyme. Western blotting and fluorescence microscopy revealed that, like the S. cerevisiae Erg7p, the PcErg7p localized to lipid particles in yeast. Using fluorescence microscopy, we show for the first time the presence of apparent lipid particles in P. carinii and the localization of PcErg7p to lipid particles in P. carinii. The detection of lipid particles in P. carinii and their association with PcErg7p therein provide strong evidence that the enzyme serves a similar function in P. carinii. Moreover, the yeast heterologous system should be a useful tool for further analysis of the P. carinii sterol pathway.
The previous study for which this one serves as an update concluded that there was good news for those who wished to live in racially integrated communities in Hamilton
County. The news remains good. At the 2010 census, fifty-four suburban Hamilton
County communities and Cincinnati neighborhoods, over one-third of the total,
containing 45% of the total population of the county, were at least modestly racially
integrated (Table 9).2 This continues trends that began as early as 1970 when seven
communities achieved integration that persisted for at least forty years. At the 1980
census, twelve achieved racial integration that lasted for at least thirty years. And at the 1990 census, ten became integrated with that persisting for at least the next twenty years. Together, twenty-nine communities have remained racially integrated for at least twenty years.
At the same time, the dissimilarity index (DI), a standard measure of residential
integration, showed improved black/white integration for both the city of Cincinnati and
Hamilton County as a whole (Table 1). Cincinnati’s DI dropped from 91.2 in 1950, its
highest point, to 64.8 in 2010. Hamilton County’s DI dropped from 82.8 in 1980, the
earliest for which we have data, to 71.3 in 2010. This means that increasing numbers of whites and blacks are living on the same blocks in a number of communities here.
The desirability of these integrated neighborhoods has apparently remained steady over time. Although both the city and the county have lost population, the integrated
neighborhoods have proportionally lost no greater population than the rest. Moreover, in the last decade, conventional wisdom to the contrary, several of the long-term integrated communities experienced increases in the white percentage of their population.
When we looked at socio-economic conditions throughout the county as measured by
seven indicators drawn from the census, we found a range of values for the integrated
communities. Some are clearly in quite good shape and improving and some show signs of decay. On a scale that aggregates five of these indicators, integrated communities on the average fell between the values for the city of Cincinnati as a whole and for suburban Hamilton County. This is particularly good news as the declining economy has certainly hurt the African Americans population more than the rest of the population. Because of this, the integrated communities might be expected to show a greater decline than the rest of the county, and while some of them have been hurt, on the average, they seem to be holding their own in comparison to the rest of the county.
Finally, the city of Cincinnati, which has long seen an increase in black population and a decrease in white population, in the 2000s saw a significant slow-down in the decline of white population and an actual decrease in black population. This suggests that the black/white ratio may stabilize in the city in the near future.
In the spring of 2001 the hilly uplands immediately northwest of the modern city of Durres were for the first time investigated using the techniques of intensive surface survey. In total, an area of six square kilometers was explored and twenty-nine sites were defined, most of them new. Remains of Greek antiquity were plentiful and include unpublished inscriptions and graves. One site may be the location of a previously unknown Archaic temple. Included in this article are descriptions of the areas investigated, a list of sites, and a catalogue of the most diagnostic artifacts recovered. Patterns of settlement and land use are discussed and compared to those recorded by other surveys in Albania.
Lloyd C. Engelbrecht (born 1927) is Professor Emeritus of Art History at the University of Cincinnati. His article, “Wood, Plywood and Veneer, Cranbrook, the New Bauhaus and the W. P. A.: the Origins of the Eames Chair of 1946,” had its origins in a paper presented at a symposium, “Bauhaus, New Bauhaus, W. P. A.: Chairs for Mid-Century,” October 17, 1981, at the Mid-America Conference of the College Art Association, meeting in Milwaukee. The article was expanded and eventually completed in 1987, but it was never published. The author asked that his late wife, June-Marie F. Engelbrecht (1930-2009), be given credit for her immense amount of help with the research and writing of the article.