165 research outputs found
Scaling of Fracture Strength in Disordered Quasi-Brittle Materials
This paper presents two main results. The first result indicates that in
materials with broadly distributed microscopic heterogeneities, the fracture
strength distribution corresponding to the peak load of the material response
does not follow the commonly used Weibull and (modified) Gumbel distributions.
Instead, a {\it lognormal} distribution describes more adequately the fracture
strengths corresponding to the peak load of the response. Lognormal
distribution arises naturally as a consequence of multiplicative nature of
large number of random distributions representing the stress scale factors
necessary to break the subsequent "primary" bond (by definition, an increase in
applied stress is required to break a "primary" bond) leading up to the peak
load. Numerical simulations based on two-dimensional triangular and diamond
lattice topologies with increasing system sizes substantiate that a {\it
lognormal} distribution represents an excellent fit for the fracture strength
distribution at the peak load. The second significant result of the present
study is that, in materials with broadly distributed microscopic
heterogeneities, the mean fracture strength of the lattice system behaves as
, and scales as as the lattice system size, , approaches
infinity.Comment: 24 pages including 11 figure
Fracture roughness in three-dimensional beam lattice systems
We study the scaling of three-dimensional crack roughness using large-scale beam lattice systems. Our results for prenotched samples indicate that the crack surface is statistically isotropic, with the implication that experimental findings of anisotropy of fracture surface roughness in directions parallel and perpendicular to crack propagation is not due to the scalar or vectorial elasticity of the model. In contrast to scalar fuse lattices, beam lattice systems do not exhibit anomalous scaling or an extra dependence of roughness on system size. The local and global roughness exponents (ζloc and ζ, respectively) are equal to each other, and the three-dimensional crack roughness exponent is estimated to be ζloc=ζ=0.48±0.03. This closely matches the roughness exponent observed outside the fracture process zone. The probability density distribution p[Δh(ℓ)] of the height differences Δh(ℓ)=[h(x+ℓ)−h(x)] of the crack profile follows a Gaussian distribution, in agreement with experimental results.Peer reviewe
An Efficient Block Circulant Preconditioner For Simulating Fracture Using Large Fuse Networks
{\it Critical slowing down} associated with the iterative solvers close to
the critical point often hinders large-scale numerical simulation of fracture
using discrete lattice networks. This paper presents a block circlant
preconditioner for iterative solvers for the simulation of progressive fracture
in disordered, quasi-brittle materials using large discrete lattice networks.
The average computational cost of the present alorithm per iteration is , where the stiffness matrix is partioned into
-by- blocks such that each block is an -by- matrix, and
represents the operational count associated with solving a block-diagonal
matrix with -by- dense matrix blocks. This algorithm using the block
circulant preconditioner is faster than the Fourier accelerated preconditioned
conjugate gradient (PCG) algorithm, and alleviates the {\it critical slowing
down} that is especially severe close to the critical point. Numerical results
using random resistor networks substantiate the efficiency of the present
algorithm.Comment: 16 pages including 2 figure
The role of marbling as an intrinsic characteristic at the point of meat purchase – the Taguchi approach
Meat quality is considered a complex concept depending on many characteristics that could be intrinsic or extrinsic. At the same time, intrinsic and extrinsic quality cues affect consumers' purchasing decisions. The importance of each quality cue was analysed and discussed in previous literature. Thus, colour and level of marbling of fresh meat were defined as key quality cues at the point of meat purchase. These characteristics are mostly related to pork and beef. The aim of this study was to identify quality characteristics that most closely match the consumer's preferences and at the same time could be related to quality losses. For that purpose, this paper gives a novel approach of the potential application of Taguchi loss function associated with quality characteristics and related losses for colour and level of marbling. This application can be implemented by providing a quality characteristic's proper target values and limits, which would make the meat production process more consistent
Health care in Bosnia and Herzegovina before, during, and after 1992–1995 war: a personal testimony
Market-based health care reform during democratic transition in Bosnia and Herzegovina was complicated by the 1992–1995 war, that devastated the country and greater part of its health care infrastructure. The course of the transition and consequences of war for the health system and health professionals are presented here from the perspective of the author. The description of real-life situations and their context is used to illustrate the problems physicians, as well as international community, were faced with and how they tried to cope with them during and after the war. Speaking openly about the mistakes that were made in those times is the first step in preventing them from happening again and an invitation for exchange of opinions and open academic discussion
Morphology of two dimensional fracture surface
We consider the morphology of two dimensional cracks observed in experimental
results obtained from paper samples and compare these results with the
numerical simulations of the random fuse model (RFM). We demonstrate that the
data obey multiscaling at small scales but cross over to self-affine scaling at
larger scales. Next, we show that the roughness exponent of the random fuse
model is recovered by a simpler model that produces a connected crack, while a
directed crack yields a different result, close to a random walk. We discuss
the multiscaling behavior of all these models.Comment: slightly revise
Liposome Co-sedimentation and Co-flotation Assays to Study Lipid-Protein Interactions
A large proportion of proteins are expected to interact with cellular membranes to carry out their physiological functions in processes such as membrane transport, morphogenesis, cytoskeletal organization, and signal transduction. The recruitment of proteins at the membrane-cytoplasm interface and their activities are precisely regulated by phosphoinositides, which are negatively charged phospholipids found on the cytoplasmic leaflet of cellular membranes and play critical roles in membrane homeostasis and cellular signaling. Thus, it is important to reveal which proteins interact with phosphoinositides and to elucidate the underlying mechanisms. Here, we present two standard in vitro methods, liposome co-sedimentation and co-flotation assays, to study lipid-protein interactions. Liposomes can mimic various biological membranes in these assays because their lipid compositions and concentrations can be varied. Thus, in addition to mechanisms of lipid-protein interactions, these methods provide information on the possible specificities of proteins toward certain lipids such as specific phosphoinositide species and can hence shed light on the roles of membrane interactions on the functions of membrane-associated proteins.Peer reviewe
Changes in chemical attributes during ripening of traditional fermented sausage, "Pirot ironed"
"Pirot ironed" is a traditional Serbian dry-fermented sausage manufactured in the southeast of Serbia. The changes in the chemical attributes of Pirot ironed sausage were followed during ripening. Samples were taken on the processing days 0, 7, 14, 21 and 28. Pirot ironed sausage was produced from the most valuable cuts of beef and chevon, without addition of starter cultures or fat tissues. Sausages were manufactured in a traditional drying/ripening chamber, where they were pressed every two days to acquire the typical flat form and to speed up the drying. The final water activity was 0.839. The lowest pH value recorded was 5.30 on the processing day 28. During ripening, the water content decreased significantly from 74.72% to 40.32%, while the protein and the fat amounts increased significantly from 19.12% to 45.79% and from 1.22% to 6.21%, respectively. Up to now, the properties of Pirot ironed sausage have not been recognized or published in scientific literature in spite of the long tradition and popularity of this meat product in Serbia
Single Cell Genome Amplification Accelerates Identification of the Apratoxin Biosynthetic Pathway from a Complex Microbial Assemblage
Filamentous marine cyanobacteria are extraordinarily rich sources of structurally novel, biomedically relevant natural products. To understand their biosynthetic origins as well as produce increased supplies and analog molecules, access to the clustered biosynthetic genes that encode for the assembly enzymes is necessary. Complicating these efforts is the universal presence of heterotrophic bacteria in the cell wall and sheath material of cyanobacteria obtained from the environment and those grown in uni-cyanobacterial culture. Moreover, the high similarity in genetic elements across disparate secondary metabolite biosynthetic pathways renders imprecise current gene cluster targeting strategies and contributes sequence complexity resulting in partial genome coverage. Thus, it was necessary to use a dual-method approach of single-cell genomic sequencing based on multiple displacement amplification (MDA) and metagenomic library screening. Here, we report the identification of the putative apratoxin. A biosynthetic gene cluster, a potent cancer cell cytotoxin with promise for medicinal applications. The roughly 58 kb biosynthetic gene cluster is composed of 12 open reading frames and has a type I modular mixed polyketide synthase/nonribosomal peptide synthetase (PKS/NRPS) organization and features loading and off-loading domain architecture never previously described. Moreover, this work represents the first successful isolation of a complete biosynthetic gene cluster from Lyngbya bouillonii, a tropical marine cyanobacterium renowned for its production of diverse bioactive secondary metabolites
Gene Expression Studies in Major Depression
The dramatic technical advances in methods to measure gene expression on a genome-wide level thus far have not been paralleled by breakthrough discoveries in psychiatric disorders—including major depression (MD)—using these hypothesis-free approaches. In this review, we first describe the methodologic advances made in gene expression analysis, from quantitative polymerase chain reaction to next-generation sequencing. We then discuss issues in gene expression experiments specific to MD, ranging from the choice of target tissues to the characterization of the case group. We provide a synopsis of the gene expression studies published thus far for MD, with a focus on studies using mRNA microarray methods. Finally, we discuss possible new strategies for the gene expression studies in MD that circumvent some of the addressed issues
- …