693 research outputs found
Mathematical analysis of a model for the growth of the bovine corpus luteum
The corpus luteum (CL) is an ovarian tissue that grows in the wound space created by follicular rupture. It produces the progesterone needed in the uterus to maintain pregnancy. Rapid growth of the CL and progesterone transport to the uterus require angiogenesis, the creation of new blood vessels from pre-existing ones, a process which is regulated by proteins that include fibroblast growth factor 2 (FGF2).\ud
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In this paper we develop a system of time-dependent ordinary differential equations to model CL growth. The dependent variables represent FGF2, endothelial cells (ECs), luteal cells, and stromal cells (like pericytes), by assuming that the CL volume is a continuum of the three cell types. We assume that if the CL volume exceeds that of the ovulated follicle, then growth is inhibited. This threshold volume partitions the system dynamics into two regimes, so that the model may be classified as a Filippov (piecewise smooth) system.\ud
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We show that normal CL growth requires an appropriate balance between the growth rates of luteal and stromal cells. We investigate how angiogenesis influences CL growth by considering how the system dynamics depend on the dimensionless EC proliferation rate, p5. We find that weak (low p5) or strong (high p5) angiogenesis leads to ‘pathological’ CL growth, since the loss of CL constituents compromises progesterone production or delivery. However, for intermediate values of p5, normal CL growth is predicted. The implications of these results for cow fertility are also discussed. For example, inadequate angiogenesis has been linked to infertility in dairy cows
Insights into ultrafast demagnetization in pseudo-gap half metals
Interest in femtosecond demagnetization experiments was sparked by Bigot's
discovery in 1995. These experiments unveil the elementary mechanisms coupling
the electrons' temperature to their spin order. Even though first quantitative
models describing ultrafast demagnetization have just been published within the
past year, new calculations also suggest alternative mechanisms.
Simultaneously, the application of fast demagnetization experiments has been
demonstrated to provide key insight into technologically important systems such
as high spin polarization metals, and consequently there is broad interest in
further understanding the physics of these phenomena. To gain new and relevant
insights, we perform ultrafast optical pump-probe experiments to characterize
the demagnetization processes of highly spin-polarized magnetic thin films on a
femtosecond time scale. Previous studies have suggested shifting the Fermi
energy into the center of the gap by tuning the number of electrons and thereby
to study its influence on spin-flip processes. Here we show that choosing
isoelectronic Heusler compounds (Co2MnSi, Co2MnGe and Co2FeAl) allows us to
vary the degree of spin polarization between 60% and 86%. We explain this
behavior by considering the robustness of the gap against structural disorder.
Moreover, we observe that Co-Fe-based pseudo gap materials, such as partially
ordered Co-Fe-Ge alloys and also the well-known Co-Fe-B alloys, can reach
similar values of the spin polarization. By using the unique features of these
metals we vary the number of possible spin-flip channels, which allows us to
pinpoint and control the half metals electronic structure and its influence
onto the elementary mechanisms of ultrafast demagnetization.Comment: 17 pages, 4 figures, plus Supplementary Informatio
Mathematical analysis of a model for the growth of the bovine corpus luteum.
The corpus luteum (CL) is an ovarian tissue that grows in the wound space created by follicular rupture. It produces the progesterone needed in the uterus to maintain pregnancy. Rapid growth of the CL and progesterone transport to the uterus require angiogenesis, the creation of new blood vessels from pre-existing ones, a process which is regulated by proteins that include fibroblast growth factor 2 (FGF2). In this paper we develop a system of time-dependent ordinary differential equations to model CL growth. The dependent variables represent FGF2, endothelial cells (ECs), luteal cells, and stromal cells (like pericytes), by assuming that the CL volume is a continuum of the three cell types. We assume that if the CL volume exceeds that of the ovulated follicle, then growth is inhibited. This threshold volume partitions the system dynamics into two regimes, so that the model may be classified as a Filippov (piecewise smooth) system. We show that normal CL growth requires an appropriate balance between the growth rates of luteal and stromal cells. We investigate how angiogenesis influences CL growth by considering how the system dynamics depend on the dimensionless EC proliferation rate, ρ₅. We find that weak (low ρ₅) or strong (high ρ₅) angiogenesis leads to 'pathological' CL growth, since the loss of CL constituents compromises progesterone production or delivery. However, for intermediate values of ρ₅, normal CL growth is predicted. The implications of these results for cow fertility are also discussed. For example, inadequate angiogenesis has been linked to infertility in dairy cows
Quantum Information Processing and Relativistic Quantum Fields
It is shown that an ideal measurement of a one-particle wave packet state of
a relativistic quantum field in Minkowski spacetime enables superluminal
signalling. The result holds for a measurement that takes place over an
intervention region in spacetime whose extent in time in some frame is longer
than the light-crossing time of the packet in that frame. Moreover, these
results are shown to apply not only to ideal measurements but also to unitary
transformations that rotate two orthogonal one-particle states into each other.
In light of these observations, possible restrictions on the allowed types of
intervention are considered. A more physical approach to such questions is to
construct explicit models of the interventions as interactions between the
field and other quantum systems such as detectors. The prototypical
Unruh-DeWitt detector couples to the field operator itself and so most likely
respects relativistic causality. On the other hand, detector models which
couple to a finite set of frequencies of field modes are shown to lead to
superluminal signalling. Such detectors do, however, provide successful
phenomenological models of atom-qubits interacting with quantum fields in a
cavity but are valid only on time scales many orders of magnitude larger than
the light-crossing time of the cavity.Comment: 16 pages, 2 figures. Improved abstract and discussion of 'ideal'
measurements. References to previous work adde
Decay of a Yukawa fermion at finite temperature and applications to leptogenesis
We calculate the decay rate of a Yukawa fermion in a thermal bath using
finite temperature cutting rules and effective Green's functions according to
the hard thermal loop resummation technique. We apply this result to the decay
of a heavy Majorana neutrino in leptogenesis. Compared to the usual approach
where thermal masses are inserted into the kinematics of final states, we find
that deviations arise through two different leptonic dispersion relations. The
decay rate differs from the usual approach by more than one order of magnitude
in the temperature range which is interesting for the weak washout regime. We
discuss how to arrive at consistent finite temperature treatments of
leptogenesis.Comment: 16 pages, 5 figure
Absorption Enhancement in Organic-Inorganic Halide Perovskite Films with Embedded Plasmonic Gold Nanoparticles
We report on the numerical analysis of solar absorption enhancement in organic-inorganic halide perovskite films embedding plasmonic gold nanoparticles. The effect of particle size and concentration is analyzed in realistic systems in which random particle location within the perovskite film and the eventual formation of dimers are also taken into account. We find a maximum integrated solar absorption enhancement of ∼10% in perovskite films of 200 nm thickness and ∼6% in 300 nm films, with spheres of radii 60 and 90 nm, respectively, in volume concentrations of around 10% in both cases. We show that the presence of dimers boosts the absorption enhancement up to ∼12% in the thinnest films considered. Absorption reinforcement arises from a double contribution of plasmonic near-field and scattering effects, whose respective weight can be discriminated and evaluated from the simulations.Peer Reviewe
Systematic Review of Gut Microbiota and Major Depression
Background: Recently discovered relationships between the gastrointestinal microbiome and the brain have implications for psychiatric disorders, including major depressive disorder (MDD). Bacterial transplantation from MDD patients to rodents produces depression-like behaviors. In humans, case-control studies have examined the gut microbiome in healthy and affected individuals. We systematically reviewed existing studies comparing gut microbial composition in MDD and healthy volunteers.Methods: A PubMed literature search combined the terms “depression,” “depressive disorder,” “stool,” “fecal,” “gut,” and “microbiome” to identify human case-control studies that investigated relationships between MDD and microbiota quantified from stool. We evaluated the resulting studies, focusing on bacterial taxa that were different between MDD and healthy controls.Results: Six eligible studies were found in which 50 taxa exhibited differences (p < 0.05) between patients with MDD and controls. Patient characteristics and methodologies varied widely between studies. Five phyla—Bacteroidetes, Firmicutes, Actinobacteria, Fusobacteria, and Protobacteria—were represented; however, divergent results occurred across studies for all phyla. The largest number of differentiating taxa were within phylum Firmicutes, in which nine families and 12 genera differentiated the diagnostic groups. The majority of these families and genera were found to be statistically different between the two groups in two identified studies. Family Lachnospiraceae differentiated the diagnostic groups in four studies (with an even split in directionality). Across all five phyla, nine genera were higher in MDD (Anaerostipes, Blautia, Clostridium, Klebsiella, Lachnospiraceae incertae sedis, Parabacteroides, Parasutterella, Phascolarctobacterium, and Streptococcus), six were lower (Bifidobacterium, Dialister, Escherichia/Shigella, Faecalibacterium, and Ruminococcus), and six were divergent (Alistipes, Bacteroides, Megamonas, Oscillibacter, Prevotella, and Roseburia). We highlight mechanisms and products of bacterial metabolism as they may relate to the etiology of depression.Conclusions: No consensus has emerged from existing human studies of depression and gut microbiome concerning which bacterial taxa are most relevant to depression. This may in part be due to differences in study design. Given that bacterial functions are conserved across taxonomic groups, we propose that studying microbial functioning may be more productive than a purely taxonomic approach to understanding the gut microbiome in depression
Genetic influences on response to novel objects and dimensions of personality in Papio baboons
Behavioral variation within and between populations and species of the genus Papio has been studied extensively, but little is known about the genetic causes of individual- or population-level differences. This study investigates the influence of genetic variation on personality (sometimes referred to as temperament) in baboons and identifies a candidate gene partially responsible for the variation in that phenotype. To accomplish these goals, we examined individual variation in response to both novel objects and an apparent novel social partner (using a mirror test) among pedigreed baboons (n = 578) from the Southwest National Primate Research Center. We investigated the frequency and duration of individual behaviors in response to novel objects and used multivariate factor analysis to identify trait-like dimensions of personality. Exploratory factor analysis identified two distinct dimensions of personality within this population. Factor 1 accounts for 46.8 % of the variance within the behavioral matrix, and consists primarily of behaviors related to the boldness of the subject. Factor 2 accounts for 18.8 % of the variation, and contains several anxiety like behaviors. Several specific behaviors, and the two personality factors, were significantly heritable, with the factors showing higher heritability than most individual behaviors. Subsequent analyses show that the behavioral reactions observed in the test protocol are associated with animals\u27 social behavior observed later in their home social groups. Finally we used linkage analysis to map quantitative trait loci for the measured phenotypes. Single nucleotide polymorphisms in a positional candidate gene (SNAP25) are associated with variation in one of the personality factors, and CSF levels of homovanillic acid and 3-methoxy-4-hydroxyphenylglycol. This study documents heritable variation in personality among baboons and suggests that sequence variation in SNAP25 may influence differences in behavior and neurochemistry in these nonhuman primates
Switchgrass (\u3ci\u3ePanicum virgatum\u3c/i\u3e L.) polyubiquitin gene (\u3ci\u3ePvUbi1\u3c/i\u3e and \u3ci\u3ePvUbi2\u3c/i\u3e) promoters for use in plant transformation
Abstract Background
The ubiquitin protein is present in all eukaryotic cells and promoters from ubiquitin genes are good candidates to regulate the constitutive expression of transgenes in plants. Therefore, two switchgrass (Panicum virgatum L.) ubiquitin genes (PvUbi1 and PvUbi2) were cloned and characterized. Reporter constructs were produced containing the isolated 5\u27 upstream regulatory regions of the coding sequences (i.e. PvUbi1 and PvUbi2 promoters) fused to the uidA coding region (GUS) and tested for transient and stable expression in a variety of plant species and tissues. Results
PvUbi1 consists of 607 bp containing cis-acting regulatory elements, a 5\u27 untranslated region (UTR) containing a 93 bp non-coding exon and a 1291 bp intron, and a 918 bp open reading frame (ORF) that encodes four tandem, head -to-tail ubiquitin monomer repeats followed by a 191 bp 3\u27 UTR. PvUbi2 consists of 692 bp containing cis-acting regulatory elements, a 5\u27 UTR containing a 97 bp non-coding exon and a 1072 bp intron, a 1146 bp ORF that encodes five tandem ubiquitin monomer repeats and a 183 bp 3\u27 UTR. PvUbi1 and PvUbi2 were expressed in all examined switchgrass tissues as measured by qRT-PCR. Using biolistic bombardment, PvUbi1 and PvUbi2 promoters showed strong expression in switchgrass and rice callus, equaling or surpassing the expression levels of the CaMV 35S, 2x35S, ZmUbi1, and OsAct1 promoters. GUS staining following stable transformation in rice demonstrated that the PvUbi1 and PvUbi2 promoters drove expression in all examined tissues. When stably transformed into tobacco (Nicotiana tabacum), the PvUbi2+3 and PvUbi2+9 promoter fusion variants showed expression in vascular and reproductive tissues. Conclusions
The PvUbi1 and PvUbi2 promoters drive expression in switchgrass, rice and tobacco and are strong constitutive promoter candidates that will be useful in genetic transformation of monocots and dicots
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