The Effect of Resistivity on the Nonlinear Stage of the Magnetorotational Instability in Accretion Disks

We present three-dimensional magnetohydrodynamic simulations of the nonlinear evolution of the magnetorotational instability (MRI) with a non-zero Ohmic resistivity. The properties of the saturated state depend on the initial magnetic field configuration. In simulations with an initial uniform vertical field, the MRI is able to support angular momentum transport even for large resistivities through the quasi-periodic generation of axisymmetric radial channel solutions rather than through the maintenance of anisotropic turbulence. Simulations with zero net flux show that the angular momentum transport and the amplitude of magnetic energy after saturation are significantly reduced by finite resistivity, even at levels where the linear modes are only slightly affected. This occurs at magnetic Reynolds numbers expected in low, cool states of dwarf novae, these results suggest that finite resistivity may account for the low and high angular momentum transport rates inferred for these systems.Comment: 8 figures, accepted for publication in Ap

The Relationship of Stomatal Conductnace to Mechanical Strength in Leaves of Santa Monica Plants

The Santa Monica Mountains ecosystem has a high diversity of plants with different lifestyles that produce different physiological characteristics individual to all plants. Studies in Australia, another Mediterranean ecosystem, have shown that mechanical strength of leaves is relatable to soil stress. This experiment seeks to determine whether mechanical strengths of leaves correlate to stomatal conductance of leaves across different species in the Santa Monica Mountains. Four species of plants are tested for their stomatal conductance in the field, and the leaves are tested for tensile strength using Young’s Modulus for comparison across leaves. These data show that there was no comparable linear relationship across species, but also found that there were statistical differences in tensile strength and stomatal conductance for all species

Non-invasive anaerobic threshold measurement using fuzzy model interpolation

The interface between skeletal muscle activation through aerobic and anaerobic glycolysis is of key interest to sportspeople and athletes who participate in medium to long distance sports, such as middle- and long-distance running, cycling, swimming, rowing, kayaking and a variety of other events. To date, the gold standard for measuring anaerobic threshold (AT) is a structured test to exhaustion where blood lactate concentration is measured at regular intervals. However, the need for invasive testing, requiring trained personnel and specialist equipment, limits the availability of such tests. This paper proposes a non-invasive AT measurement method, which validates well against AT measured using lactate analysis. In addition, the proposed test has a relatively loose set of requirements on the exercise test protocol required and just requires a measure of exercise intensity and heart-rate. While the test is applicable to a range of sports, usage is demonstrated in this paper for a set of cyclists, using velocity as a measure of exercise intensity

The interaction of a giant planet with a disc with MHD turbulence I: The initial turbulent disc models

This is the first of a series of papers aimed at developing and interpreting simulations of protoplanets interacting with turbulent accretion discs. Here we study the disc models prior to the introduction of a protoplanet.We study models in which a Keplerian domain is unstable to the magnetorotational instability (MRI). Various models with B-fields having zero net flux are considered.We relate the properties of the models to classical viscous disc theory.All models attain a turbulent state with volume averaged stress parameter alpha ~ 0.005. At any particular time the vertically and azimuthally averaged value exhibited large fluctuations in radius. Time averaging over periods exceeding 3 orbital periods at the outer boundary of the disc resulted in a smoother quantity with radial variations within a factor of two or so. The vertically and azimuthally averaged radial velocity showed much larger spatial and temporal fluctuations, requiring additional time averaging for 7-8 orbital periods at the outer boundary to limit them. Comparison with the value derived from the averaged stress using viscous disc theory yielded schematic agreement for feasible averaging times but with some indication that the effects of residual fluctuations remained. The behaviour described above must be borne in mind when considering laminar disc simulations with anomalous Navier--Stokes viscosity. This is because the operation of a viscosity as in classical viscous disc theory with anomalous viscosity coefficient cannot apply to a turbulent disc undergoing rapid changes due to external perturbation. The classical theory can only be used to describe the time averaged behaviour of the parts of the disc that are in a statistically steady condition for long enough for appropriate averaging to be carried out.Comment: 10 pages, 23 figures, accepted for publication in MNRAS. A gzipped postscript version including high resolution figures is available at http://www.maths.qmul.ac.uk/~rp

Hyperhomocysteinemia decreases bone blood flow

Elevated plasma levels of homocysteine (Hcy), known as hyperhomocysteinemia (HHcy), are associated with osteoporosis. A decrease in bone blood flow is a potential cause of compromised bone mechanical properties. Therefore, we hypothesized that HHcy decreases bone blood flow and biomechanical properties. To test this hypothesis, male Sprague–Dawley rats were treated with Hcy (0.67 g/L) in drinking water for 8 weeks. Age-matched rats served as controls. At the end of the treatment period, the rats were anesthetized. Blood samples were collected from experimental or control rats. Biochemical turnover markers (body weight, Hcy, vitamin B12, and folate) were measured. Systolic blood pressure was measured from the right carotid artery. Tibia blood flow was measured by laser Doppler flow probe. The results indicated that Hcy levels were significantly higher in the Hcy-treated group than in control rats, whereas vitamin B12 levels were lower in the Hcy-treated group compared with control rats. There was no significant difference in folate concentration and blood pressure in Hcy-treated versus control rats. The tibial blood flow index of the control group was significantly higher (0.78 ± 0.09 flow unit) compared with the Hcy-treated group (0.51 ± 0.09). The tibial mass was 1.1 ± 0.1 g in the control group and 0.9 ± 0.1 in the Hcy-treated group. The tibia bone density was unchanged in Hcy-treated rats. These results suggest that Hcy causes a reduction in bone blood flow, which contributes to compromised bone biomechanical properties

Light enough to travel: migratory bats have smaller brains, but not larger hippocampi, than sedentary species

Migratory bird species have smaller brains than non-migratory species. The behavioural flexibility/migratory precursor hypothesis suggests that sedentary birds have larger brains to allow the behavioural flexibility required in a seasonally variable habitat. The energy trade-off hypothesis proposes that brains are heavy, energetically expensive and therefore, incompatible with migration. Here, we compared relative brain, neocortex and hippocampus volume between migratory and sedentary bats at the species-level and using phylogenetically independent contrasts. We found that migratory bats had relatively smaller brains and neocortices than sedentary species. Our results support the energy trade-off hypothesis because bats do not exhibit the same degree of flexibility in diet selection as sedentary birds. Our results also suggest that bat brain size differences are subtler than those found in birds, perhaps owing to bats' shorter migration distances. Conversely, we found no difference in relative hippocampus volume between migratory and sedentary species, underscoring our limited understanding of the role of the hippocampus in bats

Cancer-associated mutations reveal a novel role for EpCAM as an inhibitor of cathepsin-L and tumor cell invasion

BACKGROUND: EpCAM (Epithelial cell adhesion molecule) is often dysregulated in epithelial cancers. Prior studies implicate EpCAM in the regulation of oncogenic signaling pathways and epithelial-to-mesenchymal transition. It was recently demonstrated that EpCAM contains a thyroglobulin type-1 (TY-1) domain. Multiple proteins with TY-1 domains are known to inhibit cathepsin-L (CTSL), a cysteine protease that promotes tumor cell invasion and metastasis. Analysis of human cancer sequencing studies reveals that somatic EpCAM mutations are present in up to 5.1% of tested tumors. METHODS: The Catalogue of Somatic Mutations in Cancer (COSMIC) database was queried to tabulate the position and amino acid changes of cancer associated EpCAM mutations. To determine how EpCAM mutations affect cancer biology we studied C66Y, a damaging TY-1 domain mutation identified in liver cancer, as well as 13 other cancer-associated EpCAM mutations. In vitro and in vivo models were used to determine the effect of wild type (WT) and mutant EpCAM on CTSL activity and invasion. Immunoprecipitation and localization studies tested EpCAM and CTSL protein binding and determined compartmental expression patterns of EpCAM mutants. RESULTS: We demonstrate that WT EpCAM, but not C66Y EpCAM, inhibits CTSL activity in vitro, and the TY-1 domain of EpCAM is responsible for this inhibition. WT EpCAM, but not C66Y EpCAM, inhibits tumor cell invasion in vitro and lung metastases in vivo. In an extended panel of human cancer cell lines, EpCAM expression is inversely correlated with CTSL activity. Previous studies have demonstrated that EpCAM germline mutations can prevent EpCAM from being expressed at the cell surface. We demonstrate that C66Y and multiple other EpCAM cancer-associated mutations prevent surface expression of EpCAM. Cancer-associated mutations that prevent EpCAM cell surface expression abrogate the ability of EpCAM to inhibit CTSL activity and tumor cell invasion. CONCLUSIONS: These studies reveal a novel role for EpCAM as a CTSL inhibitor, confirm the functional relevance of multiple cancer-associated EpCAM mutations, and suggest a therapeutic vulnerability in cancers harboring EpCAM mutations

Walnut oil increases cholesterol efflux through inhibition of stearoyl CoA desaturase 1 in THP-1 macrophage-derived foam cells

Extent: 13p.Background: Walnuts significantly decrease total and low-density lipoprotein cholesterol in normo- and hypercholesterolemic individuals. No study to date has evaluated the effects of walnuts on cholesterol efflux, the initial step in reverse cholesterol transport, in macrophage-derived foam cells (MDFC). The present study was conducted to investigate the mechanisms by which walnut oil affects cholesterol efflux. Methods: The extract of English walnuts (walnut oil) was dissolved in DMSO and applied to cultured THP-1 MDFC cells (0.5 mg/mL). THP-1 MDFC also were treated with human sera (10%, v:v) taken from subjects in a walnut feeding study. Cholesterol efflux was examined by liquid scintillation counting. Changes in gene expression were quantified by real time PCR. Results: Walnut oil treatment significantly increased cholesterol efflux through decreasing the expression of the lipogenic enzyme stearoyl CoA desaturase 1 (SCD1) in MDFC. Alpha-linolenic acid (ALA), the major n-3 polyunsaturated fatty acids found in walnuts, recaptured SCD1 reduction in MDFC, a mechanism mediated through activation of nuclear receptor farnesoid-X-receptor (FXR). Postprandial serum treatment also increased cholesterol efflux in MDFC. When categorized by baseline C-reactive protein (CRP; cut point of 2 mg/L), subjects in the lower CRP sub-group benefited more from dietary intervention, including a more increase in cholesterol efflux, a greater reduction in SCD1, and a blunted postprandial lipemia. Conclusion: In conclusion, walnut oil contains bioactive molecules that significantly improve cholesterol efflux in MDFC. However, the beneficial effects of walnut intake may be reduced by the presence of a pro-inflammatory state.Jun Zhang, Jessica A Grieger, Penny M Kris-Etherton, Jerry T Thompson, Peter J Gillies, Jennifer A Fleming and John P Vanden Heuve