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Influence of fluoride on the mineralization of collagen via the polymer-induced liquid-precursor (PILP) process.
ObjectiveThe polymer-induced liquid-precursor (PILP) mineralization process has been shown to remineralize artificial dentin lesions to levels consistent with those of native dentin. However, nanoindentation revealed that the moduli of those remineralized lesions were only ∼50% that of native dentin. We hypothesize that this may be due to the PILP process having been previously optimized to obtain high amounts (∼70wt%) of intrafibrillar crystals, but without sufficient interfibrillar mineral, another significant component of dentin.MethodsFluoride was added to the PILP-mineralization of collagen from rat tail tendon at varying concentrations to determine if a better balance of intra- versus inter-fibrillar mineralization could be obtained, as determined by electron microscopy. Nanoindentation was used to determine if fluoridated apatite could improve the mechanical properties of the composites.ResultsFluoride was successfully incorporated into the PILP-mineralization of rat tail tendon and resulted in collagen-mineral composite systems with the mineral phase of hydroxyapatite containing various levels of fluoridation. As the fluoride concentration increased, the crystals became larger and more rod-like, with an increasing tendency to form on the fibril surfaces rather than the interior. Nanomechanical testing of the mineralized tendons revealed that fluoride addition did not increase modulus over PILP mineralization alone. This likely resulted from the separated nature of collagen fibrils that comprise tendon, which does not provide lateral reinforcement and therefore may not be suited for the compressive loads of nanoindentation.SignificanceThis work contributes to the development of minimally invasive approaches to caries treatment by determining if collagen can be functionally mineralized
Sequential Posted Price Mechanisms with Correlated Valuations
We study the revenue performance of sequential posted price mechanisms and
some natural extensions, for a general setting where the valuations of the
buyers are drawn from a correlated distribution. Sequential posted price
mechanisms are conceptually simple mechanisms that work by proposing a
take-it-or-leave-it offer to each buyer. We apply sequential posted price
mechanisms to single-parameter multi-unit settings in which each buyer demands
only one item and the mechanism can assign the service to at most k of the
buyers. For standard sequential posted price mechanisms, we prove that with the
valuation distribution having finite support, no sequential posted price
mechanism can extract a constant fraction of the optimal expected revenue, even
with unlimited supply. We extend this result to the the case of a continuous
valuation distribution when various standard assumptions hold simultaneously.
In fact, it turns out that the best fraction of the optimal revenue that is
extractable by a sequential posted price mechanism is proportional to ratio of
the highest and lowest possible valuation. We prove that for two simple
generalizations of these mechanisms, a better revenue performance can be
achieved: if the sequential posted price mechanism has for each buyer the
option of either proposing an offer or asking the buyer for its valuation, then
a Omega(1/max{1,d}) fraction of the optimal revenue can be extracted, where d
denotes the degree of dependence of the valuations, ranging from complete
independence (d=0) to arbitrary dependence (d=n-1). Moreover, when we
generalize the sequential posted price mechanisms further, such that the
mechanism has the ability to make a take-it-or-leave-it offer to the i-th buyer
that depends on the valuations of all buyers except i's, we prove that a
constant fraction (2-sqrt{e})/4~0.088 of the optimal revenue can be always be
extracted.Comment: 29 pages, To appear in WINE 201
Using self-definition to predict the influence of procedural justice on organizational, interpersonal, and job/task-oriented citizenship behaviors
An integrative self-definition model is proposed to improve our understanding of how procedural justice affects different outcome modalities in organizational behavior. Specifically, it is examined whether the strength of different levels of self-definition (collective, relational, and individual) each uniquely interact with procedural justice to predict organizational, interpersonal, and job/task-oriented citizenship behaviors, respectively. Results from experimental and (both single and multisource) field data consistently revealed stronger procedural justice effects (1) on organizational-oriented citizenship behavior among those who define themselves strongly in terms of organizational characteristics, (2) on interpersonal-oriented citizenship behavior among those who define themselves strongly in terms of their interpersonal relationships, and (3) on job/task-oriented citizenship behavior among those who define themselves weakly in terms of their distinctiveness or uniqueness. We discuss the relevance of these results with respect to how employees can be motivated most effectively in organizational settings
Evolutionary game theory in growing populations
Existing theoretical models of evolution focus on the relative fitness
advantages of different mutants in a population while the dynamic behavior of
the population size is mostly left unconsidered. We here present a generic
stochastic model which combines the growth dynamics of the population and its
internal evolution. Our model thereby accounts for the fact that both
evolutionary and growth dynamics are based on individual reproduction events
and hence are highly coupled and stochastic in nature. We exemplify our
approach by studying the dilemma of cooperation in growing populations and show
that genuinely stochastic events can ease the dilemma by leading to a transient
but robust increase in cooperationComment: 4 pages, 2 figures and 2 pages supplementary informatio
The edge of neutral evolution in social dilemmas
The functioning of animal as well as human societies fundamentally relies on
cooperation. Yet, defection is often favorable for the selfish individual, and
social dilemmas arise. Selection by individuals' fitness, usually the basic
driving force of evolution, quickly eliminates cooperators. However, evolution
is also governed by fluctuations that can be of greater importance than fitness
differences, and can render evolution effectively neutral. Here, we investigate
the effects of selection versus fluctuations in social dilemmas. By studying
the mean extinction times of cooperators and defectors, a variable sensitive to
fluctuations, we are able to identify and quantify an emerging 'edge of neutral
evolution' that delineates regimes of neutral and Darwinian evolution. Our
results reveal that cooperation is significantly maintained in the neutral
regimes. In contrast, the classical predictions of evolutionary game theory,
where defectors beat cooperators, are recovered in the Darwinian regimes. Our
studies demonstrate that fluctuations can provide a surprisingly simple way to
partly resolve social dilemmas. Our methods are generally applicable to
estimate the role of random drift in evolutionary dynamics.Comment: 17 pages, 4 figure
Sorting of chromosomes by magnetic separation
Chromosomes were isolated from Chinese hamster x human hybrid cell lines containing four and nine human chromosomes. Human genomic DNA was biotinylated by nick translation and used to label the human chromosomes by in situ hybridization in suspension. Streptavidin was covalently coupled to the surface of magnetic beads and these were incubated with the hybridized chromosomes. The human chromosomes were bound to the magnetic beads through the strong biotin-streptavidin complex and then rapidly separated from nonlabeled Chinese hamster chromosomes by a simple permanent magnet. The hybridization was visualized by additional binding of avidin-FITC (fluorescein) to the unoccupied biotinylated human DNA bound to the human chromosomes. After magnetic separation, up to 98% of the individual chromosomes attached to magnetic beads were classified as human chromosomes by fluorescence microscopy
Subnuclear localization, rates and effectiveness of UVC-induced unscheduled DNA synthesis visualized by fluorescence widefield, confocal and super-resolution microscopy
Unscheduled DNA synthesis (UDS) is the final stage of the process of repair of DNA lesions induced by UVC. We detected UDS using a DNA precursor, 5-ethynyl-2′-deoxyuridine (EdU). Using wide-field, confocal and super-resolution fluorescence microscopy and normal human fibroblasts, derived from healthy subjects, we demonstrate that the sub-nuclear pattern of UDS detected via incorporation of EdU is different from that when BrdU is used as DNA precursor. EdU incorporation occurs evenly throughout chromatin, as opposed to just a few small and large repair foci detected by BrdU. We attribute this difference to the fact that BrdU antibody is of much larger size than EdU, and its accessibility to the incorporated precursor requires the presence of denatured sections of DNA. It appears that under the standard conditions of immunocytochemical detection of BrdU only fragments of DNA of various length are being denatured. We argue that, compared with BrdU, the UDS pattern visualized by EdU constitutes a more faithful representation of sub-nuclear distribution of the final stage of nucleotide excision repair induced by UVC. Using the optimized integrated EdU detection procedure we also measured the relative amount of the DNA precursor incorporated by cells during UDS following exposure to various doses of UVC. Also described is the high degree of heterogeneity in terms of the UVC-induced EdU incorporation per cell, presumably reflecting various DNA repair efficiencies or differences in the level of endogenous dT competing with EdU within a population of normal human fibroblasts
Detection of chromosome aberrations in metaphase and interphase tumor cells by in situ hybridization using chromosome-specific library probes
Chromosome aberrations in two glioma cell lines were analyzed using biotinylated DNA library probes that specifically decorate chromosomes 1, 4, 7, 18 and 22 from pter to qter. Numerical changes, deletions and rearrangements of these chromosomes were radily visualized in metaphase spreads, as well as in early prophase and interphase nuclei. Complete chromosomes, deleted chromosomes and segments of translocated chromosomes were rapidly delineated in very complex karyotypes. Simultaneous hybridizations with additional subregional probes were used to further define aberrant chromosomes. Digital image analysis was used to quantitate the total complement of specific chromosomal DNAs in individual metaphase and interphase cells of each cell line. In spite of the fact that both glioma lines have been passaged in vitro for many years, an under-representation of chromosome 22 and an over-representation of chromosome 7 (specifically 7p) were observed. These observations agree with previous studies on gliomas. In addition, sequences of chromosome 4 were also found to be under-represented, especially in TC 593. These analyses indicate the power of these methods for pinpointing chromosome segments that are altered in specific types of tumors
A passion for respect: On understanding the role of human needs and morality
In the present paper, we stress the importance of the concept respect in a wide variety of social settings and provide a working definition of this concept by emphasizing how respect relates to the act of communicating full recognition to other people on the dimensions of belongingness and morality. Subsequently, in two separate parts, we discuss why respect is so desired and valued. The first part looks at respect as a means to fulfil important human social concerns (“respect as a means to an end”). The second part looks at the potential moral underpinnings of respect and thus interprets “respect as an end in itself.” Finally, it is suggested that both reasons to value respect explain respect effects as a function of the working selfconcept that is salient (i.e., pragmatic versus idealistic self)
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