3,980 research outputs found
Couple stresses and discrete potentials in the vertex model of cellular monolayers
The vertex model is widely used to simulate the mechanical properties of
confluent epithelia and other multicellular tissues. This inherently discrete
framework allows a Cauchy stress to be attributed to each cell, and its
symmetric component has been widely reported, at least for planar monolayers.
Here we consider the stress attributed to the neighbourhood of each tricellular
junction, evaluating in particular its leading-order antisymmetric component
and the associated couple stresses, which characterise the degree to which
individual cells experience (and resist) in-plane bending deformations. We
develop discrete potential theory for localised monolayers having disordered
internal structure and use this to derive the analogues of Airy and Mindlin
stress functions. These scalar potentials typically have broad-banded spectra,
highlighting the contributions of small-scale defects and boundary-layers to
global stress patterns. An affine approximation attributes couple stresses to
pressure differences between cells sharing a trijunction, but simulations
indicate an additional role for non-affine deformations.Comment: 8 figures, 1 tabl
ELECTROMYOGRAPHICAL ANALYSIS OF PLYOMETRIC EXERCISES
The purpose of this study was to evaluate integrated electromyographic (IEMG) activity of the quadriceps (Q), hamstring (H), and gastrocnemius (G) muscle groups during the performance of 10 randomly ordered plyometric (P) exercises. Subjects included 23 adults who routinely performed P. A one way Repeated Measures ANOVA indicated Q-IEMG activity was significantly different (p 0.05) were found for the G-IEMG for female subjects and those with vertical jumps less than 50 cm, or for the H muscle group. Bonferonni adjusted pairwise comparisons of main effects revealed differences in IEMG between specific P exercises
Plasma oxylipins and unesterified precursor fatty acids are altered by DHA supplementation in pregnancy: Can they help predict risk of preterm birth?
Oxidized lipids derived from omega-6 (n-6) and omega-3 (n-3) polyunsaturated fatty acids, collectively known as oxylipins, are bioactive signaling molecules that play diverse roles in human health and disease. Supplementation with n-3 docosahexaenoic acid (DHA) during pregnancy has been reported to decrease the risk of preterm birth in singleton pregnancies, which may be due to effects of DHA supplementation on oxylipins or their precursor n-6 and n-3 fatty acids. There is only limited understanding of the levels and trajectory of changes in plasma oxylipins during pregnancy, effects of DHA supplementation on oxylipins and unesterified fatty acids, and whether and how oxylipins and their unesterified precursor fatty acids influence preterm birth. In the present study we used liquid chromatography-tandem mass spectrometry to profile oxylipins and their precursor fatty acids in the unesterified pool using plasma samples collected from a subset of pregnant Australian women who participated in the ORIP (Omega-3 fats to Reduce the Incidence of Prematurity) study. ORIP is a large randomized controlled trial testing whether daily supplementation with n-3 DHA can reduce the incidence of early preterm birth compared to control. Plasma was collected at study entry (âpregnancy week 14) and again at âweek 24, in a subgroup of 48 ORIP participants-12 cases with spontaneous preterm (<37 weeks) birth and 36 matched controls with spontaneous term (â„40 weeks) birth. In the combined preterm and term pregnancies, we observed that in the control group without DHA supplementation unesterified AA and AA-derived oxylipins 12-HETE, 15-HETE and TXB2 declined between weeks 14-24 of pregnancy. Compared to control, DHA supplementation increased unesterified DHA, EPA, and AA, DHA-derived 4-HDHA, 10-HDHA and 19,20-EpDPA, and AA-derived 12-HETE at 24 weeks. In exploratory analysis independent of DHA supplementation, participants with concentrations above the median for 5-lipoxygenase derivatives of AA (5-HETE, Odds Ratio (OR) 8.2; p = 0.014) or DHA (4-HDHA, OR 8.0; p = 0.015) at 14 weeks, or unesterified AA (OR 5.1; p = 0.038) at 24 weeks had higher risk of spontaneous preterm birth. The hypothesis that 5-lipoxygenase-derived oxylipins and unesterified AA could serve as mechanism-based biomarkers predicting spontaneous preterm birth should be evaluated in larger, adequately powered studies
Why Was There a Harmful Algal Bloom in 2015: The Relative Growth of Toxic and Non-toxic Diatoms as a Function of Temperature
A coastwide bloom of the toxigenic diatom Pseudo-nitzschia in 2015 resulted in the largest recorded outbreak and unprecedented levels of the neurotoxin, domoic acid (DA), along the North American west coast. The scientific community has suggested that warmer ocean temperatures were the main cause of this harmful algal bloom (HAB), but little scientific evidence to support the relationship between temperature, and the growth and toxicity of Pseudo-nitzschia has been provided for local isolates of these diatoms. To gain insight into bloom dynamics, a laboratory study was conducted to examine the growth of toxic and non-toxic phytoplankton species at a range of temperatures. Non- (or low) toxic diatoms Pseudo-nitzschia fraudulenta, Skeletonema costatum, and Chaetoceros decipiens were isolated from the 2015 bloom, and cultured at eight temperature conditions (5.6, 6.8, 8.7, 10.8, 13.3, 15.2, 17.2, 19.0°C). A total of 48 cultures (6 tubes per condition), with duplicates at each temperature, were grown in a temperature gradient incubator and monitored for 31 days over three complete growth cycles (runs) of exponential and stationary growth. Specific growth rates, determined from daily measures of in vivo fluorescence, indicate that by Run 3, there was no growth at 5.6°C for Chaetoceros decipiens, and a large decline in the growth rate for Skeletonema costatum at 17.2 and 19.0°C. Pseudo-nitzschia fraudulenta demonstrated the greatest growth rates of all species from 10.8 to 19.0°C, and exhibited the broadest range of elevated growth rates. These temperature results indicate that Skeletonema costatum does not thrive in ocean temperatures above 15°C, and is outcompeted by other algae, including both species of Pseudo-nitzschia. Results of this study will greatly aid oceanographers in determining the dominant species in a coastal region as a function of ambient ocean temperature conditions
The reproductive biology of the porbeage shark (Lamna nasus) in the western North Atlantic Ocean
Reproductive organs from 393 male and 382 female porbeagles (Lamna nasus), caught in the western North Atlantic Ocean, were examined to determine size at maturity and reproductive cycle. Males ranged in size from 86 to 246 cm fork length (FL) and females ranged from 94 to 288 cm FL. Maturity in males was best described by an inflection in the relationship of clasper length to fork length when combined with clasper calcification. Males matured between 162 and 185 cm FL and 50% were mature at 174 cm FL. In females, all reproductive organ measurements related to body length showed a strong inflection around the size of maturity. Females matured between 210 and 230 cm FL and 50% were mature at 218 cm FL. After a protracted fall mating period (SeptemberâNovember), females give birth to an average of 4.0 young in spring (AprilâJune). As in other lamnids, young are nourished through oophagy. Evidence from this study indicated a one-year reproductive cycle and gestation period lasting 8â9 months
A Complexity View of Rainfall
We show that rain events are analogous to a variety of nonequilibrium
relaxation processes in Nature such as earthquakes and avalanches. Analysis of
high-resolution rain data reveals that power laws describe the number of rain
events versus size and number of droughts versus duration. In addition, the
accumulated water column displays scale-less fluctuations. These statistical
properties are the fingerprints of a self-organized critical process and may
serve as a benchmark for models of precipitation and atmospheric processes.Comment: 4 pages, 5 figure
Epidemic analysis of the second-order transition in the Ziff-Gulari-Barshad surface-reaction model
We study the dynamic behavior of the Ziff-Gulari-Barshad (ZGB) irreversible
surface-reaction model around its kinetic second-order phase transition, using
both epidemic and poisoning-time analyses. We find that the critical point is
given by p_1 = 0.3873682 \pm 0.0000015, which is lower than the previous value.
We also obtain precise values of the dynamical critical exponents z, \delta,
and \eta which provide further numerical evidence that this transition is in
the same universality class as directed percolation.Comment: REVTEX, 4 pages, 5 figures, Submitted to Physical Review
Assessing the influence of dopamine and mindfulness on the formation of routines in visual search
Given experience in cluttered but stable visual environments, our eyeâmovements form stereotyped routines that sample taskârelevant locations, while not mixingâup routines between similar taskâsettings. Both dopamine signaling and mindfulness have been posited as factors that influence the formation of such routines, yet quantification of their impact remains to be tested in healthy humans. Over two sessions, participants searched through grids of doors to find hidden targets, using a gazeâcontingent display. Within each session, door scenes appeared in either one of two colors, with each color signaling a differing set of likely target locations. We derived measures for how well target locations were learned (targetâaccuracy), how routine were sets of eyeâmovements (stereotypy), and the extent of interference between the two scenes (settingâaccuracy). Participants completed two sessions, where they were administered either levodopa (dopamine precursor) or placebo (vitamin C), under doubleâblind counterbalanced conditions. Dopamine and trait mindfulness (assessed by questionnaire) interacted to influence both targetâaccuracy and stereotypy. Increasing dopamine improved accuracy and reduced stereotypy for high mindfulness scorers, but induced the opposite pattern for low mindfulness scorers. Dopamine also disrupted settingâaccuracy invariant to mindfulness. Our findings show that mindfulness modulates the impact of dopamine on the targetâaccuracy and stereotypy of eyeâmovement routines, whereas increasing dopamine promotes interference between taskâsettings, regardless of mindfulness. These findings provide a link between nonâhuman and human models regarding the influence of dopamine on the formation of taskârelevant eyeâmovement routines and provide novel insights into behaviorâtrait factors that modulate the use of experience when building adaptive repertoires
An MHC class Ibârestricted CD8 T cell response confers antiviral immunity
Although immunity against intracellular pathogens is primarily provided by CD8 T lymphocytes that recognize pathogen-derived peptides presented by major histocompatibility complex (MHC) class Ia molecules, MHC class Ibârestricted CD8 T cells have been implicated in antiviral immunity. Using mouse polyoma virus (PyV), we found that MHC class Iaâdeficient (Kbâ/âDbâ/â) mice efficiently control this persistently infecting mouse pathogen. CD8 T cell depletion mitigates clearance of PyV in Kbâ/âDbâ/â mice. We identified the ligand for PyV-specific CD8 T cells in Kbâ/âDbâ/â mice as a nonamer peptide from the VP2 capsid protein presented by Q9, a member of the ÎČ2 microglobulinâassociated Qa-2 family. Using Q9-VP2 tetramers, we monitored delayed but progressive expansion of these antigen-specific CD8αÎČ T cells in Kbâ/âDbâ/â mice. Importantly, we demonstrate that Q9-VP2âspecific CD8 T cells more effectively clear wild-type PyV than a VP2 epitopenull mutant PyV. Finally, we show that wild-type mice also generate Q9-restricted VP2 epitopeâspecific CD8 T cells to PyV infection. To our knowledge, this is the first evidence for a defined MHC class Ibârestricted antiviral CD8 T cell response that contributes to host defense. This study motivates efforts to uncover MHC class Ibârestricted CD8 T cell responses in other viral infections, and given the limited polymorphism of MHC class Ib molecules, it raises the possibility of developing peptide-based viral vaccines having broad coverage across MHC haplotypes
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