555 research outputs found

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

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    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

    Retroviral Expression of Transforming Growth Factor-Alpha Does Not Transform Fibroblasts or Keratinocytes

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    Transforming growth factor α (TGFα) is a peptide so named because it helps to impart anchorage-independent growth to normal rat kidney (NRK) cells in vitro and is secreted by many rodent and human tumor cells. To directly investigate the transforming properties of this factor, we constructed a replication-defective murine retrovirus that expresses the human sequence coding for TGFα. infection of NIH/3T3 cells with the TGFα retrovirus led to the integration of a transcriptionally active provirus and overexpression of biologically active TGFα, but failed to induce morphologic transformation. Similarly, the TGFα retrovirus failed to induce morphologic transformation of five other types of rodent fibroblasts.We also investigated the effect of TGFα expression on the growth of BALB/MK mouse keratinocytes, which require epidermal growth factor (EGF) for proliferation. We show that exogenously added TGFα is an extremely potent mitogen for BALB/MK cells. However, retroviral expression of TGFa in BALB/MK cells failed to relieve dependence on exogenously added EGF (or TGFα) for cell growth. These results suggest that overexpression of TGFα does not, by itself, transform rodent fibroblasts or keratinocytes

    Local Magnetohydrodynamical Models of Layered Accretion Disks

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    Using numerical MHD simulations, we have studied the evolution of the magnetorotational instability in stratified accretion disks in which the ionization fraction (and therefore resistivity) varies substantially with height. This model is appropriate to dense, cold disks around protostars or dwarf nova systems which are ionized by external irradiation of cosmic rays or high-energy photons. We find the growth and saturation of the MRI occurs only in the upper layers of the disk where the magnetic Reynolds number exceeds a critical value; in the midplane the disk remains queiscent. The vertical Poynting flux into the "dead", central zone is small, however velocity fluctuations in the dead zone driven by the turbulence in the active layers generate a significant Reynolds stress in the midplane. When normalized by the thermal pressure, the Reynolds stress in the midplane never drops below about 10% of the value of the Maxwell stress in the active layers, even though the Maxwell stress in the dead zone may be orders of magnitude smaller than this. Significant mass mixing occurs between the dead zone and active layers. Fluctuations in the magnetic energy in the active layers can drive vertical oscillations of the disk in models where the ratio of the column density in the dead zone to that in the active layers is <10. These results have important implications for the global evolution of a layered disk, in particular there may be residual mass inflow in the dead layer. We discuss the effects that dust in the disk may have on our results.Comment: Accepted by Ap.

    Political Competency: Understanding How College Students Develop Their Political Identity

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    Constructing models of how students come to understand their identity is a hallmark of student development theory. Yet, there is little published research or institutional attention devoted to the examination of students’ political identity development. In this article, the authors apply existing student development theories to this topic and describe ways that student affairs practitioners can facilitate student growth in this important dimension of adulthood

    Waterfowl Population Status, 2010

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    In the traditional survey area, which includes strata 1‒18, 20‒50, and 75‒77, the total duck population estimate was 40.9 ± 0.7 [SE] million birds. This estimate was similar to last year\u27s estimate of 42.0 ± 0.7 million birds and was 21% above the long-term average (1955‒2009). Estimated mallard (Anas platyrhynchos) abundance was 8.4 ± 0.3 million birds, which was similar to the 2009 estimate of 8.5 ± 0.2 million birds and 12% above the long-term average. Estimated abundance of gadwall (A. strepera; 3.0 ± 0.2 million) was similar to the 2009 estimate and 67% above the long-term average. Estimated abundance of American wigeon (A. americana; 2.4 ± 0.1 million) was similar to 2009 and the long-term average. The estimated abundance of green-winged teal (A. crecca) was 3.5 ± 0.2 million, which was similar to the 2009 estimate and 78% above their longterm average of 1.9 ± 0.02 million. The estimate of blue-winged teal abundance (A. discors) was 6.3 ± 0.4 million, which was 14% below the 2009 estimate and 36% above their long-term average of 4.7 ± 0.04 million. The estimate for northern pintails (A. acuta; 3.5 ± 0.2 million) was similar to the 2009 estimate, and 13% below the long-term average of 4.0 ± 0.04 million. Estimates of northern shovelers (A. clypeata; 4.1 ± 0.2 million) and redheads (Aythya americana; 1.1 ± 0.1 million) were similar to their 2009 estimates and were 76% and 63% above their long-term averages of 2.3 ± 0.02 million and 0.7 ± 0.01 million, respectively. The canvasback estimate (A. valisineria; 0.6 ± 0.05 million) was similar to the 2009 estimate and to the long-term average. The scaup estimate (A. affinis and A. marila combined; 4.2 ± 0.2 million) was similar to that of 2009 and 16% below the long-term average of 5.1 ± 0.05 million. Habitat conditions during the 2010 Waterfowl Breeding Population and Habitat Survey were characterized by average to below-average moisture, a mild winter, and early spring across the traditional and eastern survey areas. The total pond estimate (Prairie Canada and U.S. combined) was 6.7 ± 0.2 million. This was similar to the 2009 estimate and 34% above the long-term average (1974‒2009) of 5.0 ± 0.03 million ponds. The 2010 estimate of ponds in Prairie Canada was 3.7 ± 0.2 million. This was similar to last year\u27s estimate (3.6 ± 0.1 million) and to the long-term average (1961‒2009; 3.4 ± 0.03 million). The 2010 pond estimate for the north central U.S. was 2.9 ± 0.1 million, which was similar to last year\u27s estimate (2.9 ± 0.1 million) and 87% above the long-term average (1974‒2009; 1.6 ± 0.02 million). The projected mallard fall-flight index is 10.3 ± 0.9 million birds. The eastern survey area was restratifed in 2005 and is now composed of strata 51‒72. Estimates of mallards, scaup, scoters (black [Melanitta nigra], white-winged [M. fusca], and surf [M. perspicillata]), green-winged teal, American wigeon, bufflehead (Bucephala albeola), ring-necked duck (Aythya collaris), and goldeneyes (common [B. clangula] and Barrow\u27s [B. islandica]) were all similar to their 2009 estimates and long-term averages. The merganser (red-breasted [Mergus serrator], common [M. merganser], and hooded [Lophodytes cucullatus]) estimate was 386.4 thousand, which was 15% below the 2009 estimate, and 14% below the long-term average of 450.8 thousand. The American black duck (Anas rubripes) estimate was similar to the 2009 estimate and 7% below the long-term average of 478.9 thousand

    Mammaglobin as a potential molecular target for breast cancer drug delivery

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    <p>Abstract</p> <p>Background</p> <p>Mammaglobin (MAM) has been used as a specific molecular marker for breast cancer diagnosis. Recently, several groups of researchers proposed a number of therapeutic strategies targeting this molecule. Some of the strategies are based upon an essential but not demonstrated hypothesis – mammaglobin is associated with the surface of breast cancer cells, which strongly disputes the therapeutic strategies.</p> <p>Results</p> <p>We conducted a computer-based predictive analysis and identified a small fragment at the N-end of MAM as a potential transmembrane domain. We provided several evidences to demonstrate the presence of the membrane-associated MAM. We isolated the membrane protein components from known MAM positive breast cancer cells (MDA-MB361 and MDA-MB415). We showed that about 22–64% of MAM proteins, depending upon the types of the cancer cells, directly attached on the membrane of breast cancer cells, by Western blotting assays. To directly visualize the presence of the membrane-bound MAM protein, we incubated the MAM positive cancer cells with FITC labeled anti-MAM antibody, and observed clear fluorescent signals on the surface of the cells. In studying the MAM protein distribution in human breast cancer tissues, we first identified two immunostain patterns that are associated with the membrane-bound MAM: the membrane stain pattern and luminary surface stain pattern. To test whether the membrane-associated MAM can serve as a molecular target for drug delivery, we conjugated anti-MAM antibody to human low-density lipoprotein (LDL) and loaded doxorubicin (Dox) in the core of LDL. Specific binding and cytotoxicity of the MAM targeted and Dox loaded LDL was tested in the MAM positive breast cancer cells <it>in vitro</it>.</p> <p>Conclusion</p> <p>We first showed that some of MAM protein directly associated with the surface of breast cancer cells. The membrane-associated MAM protein may be utilized as a useful molecular marker for breast cancer targeted drug delivery.</p

    Incidence and prevalence of celiac disease and dermatitis herpetiformis in the UK over two decades: population-based study

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    OBJECTIVES: Few studies have quantified the incidence and prevalence of celiac disease (CD) and dermatitis herpetiformis (DH) nationally and regionally by time and age groups. Understanding this epidemiology is crucial for hypothesizing about causes and quantifying the burden of disease. METHODS: Patients with CD or DH were identified in the Clinical Practice Research Datalink between 1990 and 2011. Incidence rates and prevalence were calculated by age, sex, year, and region of residence. Incidence rate ratios (IRR) adjusted for age, sex, and region were calculated with Poisson regression. RESULTS: A total of 9,087 incident cases of CD and 809 incident cases of DH were identified. Between 1990 and 2011, the incidence rate of CD increased from 5.2 per 100,000 (95% confidence interval (CI), 3.8-6.8) to 19.1 per 100,000 person-years (95% CI, 17.8-20.5; IRR, 3.6; 95% CI, 2.7-4.8). The incidence of DH decreased over the same time period from 1.8 per 100,000 to 0.8 per 100,000 person-years (average annual IRR, 0.96; 95% CI, 0.94-0.97). The absolute incidence of CD per 100,000 person-years ranged from 22.3 in Northern Ireland to 10 in London. There were large regional variations in prevalence for CD but not DH. CONCLUSIONS: We found a fourfold increase in the incidence of CD in the United Kingdom over 22 years, with large regional variations in prevalence. This contrasted with a 4% annual decrease in the incidence of DH, with minimal regional variations in prevalence. These contrasts could reflect differences in diagnosis between CD (serological diagnosis and case finding) and DH (symptomatic presentation) or the possibility that diagnosing and treating CD prevents the development of DH
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