777 research outputs found

    Neutrino Oscillations in a Supersymmetric SO(10) Model with Type-III See-Saw Mechanism

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    The neutrino oscillations are studied in the framework of the minimal supersymmetric SO(10) model with Type-III see-saw mechanism by additionally introducing a number of SO(10) singlet neutrinos. The light Majorana neutrino mass matrix is given by a combination of those of the singlet neutrinos and the SU(2)LSU(2)_L active neutrinos. The minimal SO(10) model gives an unambiguous Dirac neutrino mass matrix, which enables us to predict the masses and the other parameters for the singlet neutrinos. These predicted masses take the values accessible and testable by near future collider experiments under the reasonable assumptions. More comprehensive calculations on these parameters are also given.Comment: 14 pages, 5 figures; the version to appear in JHE

    Topological signature of deterministic chaos in short nonstationary signals from an optical parametric oscillator

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    Although deterministic chaos has been predicted to occur in the triply resonant optical parametric oscillator (TROPO) fifteen years ago, experimental evidence of chaotic behavior in this system has been lacking so far, in marked contrast with most nonlinear systems, where chaos has been actively tracked and found. This situation is probably linked to the high sensitivity of the TROPO to perturbations, which adversely affects stationary operation at high power. We report the experimental observation in this system of a burst of irregular behavior of duration 80 microseconds. Although the system is highly nonstationary over this time interval, a topological analysis allows us to extract a clearcut signature of deterministic chaos from a time series segment of only 9 base cycles (3 microseconds). This result suggests that nonstationarity is not necessarily an obstacle to the characterization of chaos

    Criminal Justice Reform as HIV and TB Prevention in African Prisons

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    Katherine Todrys and Joseph Amon argue for criminal justice system reforms in sub-Saharan Africa to reduce HIV and TB transmission in prisons and to guarantee detainees' human rights and health

    Changes in Cell Morphology Are Coordinated with Cell Growth through the TORC1 Pathway

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    SummaryBackgroundGrowth rate is determined not only by extracellular cues such as nutrient availability but also by intracellular processes. Changes in cell morphology in budding yeast, mediated by polarization of the actin cytoskeleton, have been shown to reduce cell growth.ResultsHere we demonstrate that polarization of the actin cytoskeleton inhibits the highly conserved Target of Rapamycin Complex 1 (TORC1) pathway. This downregulation is suppressed by inactivation of the TORC1 pathway regulatory Iml1 complex, which also regulates TORC1 during nitrogen starvation. We further demonstrate that attenuation of growth is important for cell recovery after conditions of prolonged polarized growth.ConclusionsOur results indicate that extended periods of polarized growth inhibit protein synthesis, mass accumulation, and the increase in cell size at least in part through inhibiting the TORC1 pathway. We speculate that this mechanism serves to coordinate the ability of cells to increase in size with their biosynthetic capacity

    Cooperative oscillation of non-degenerate transverse modes in an optical system: multimode operation in parametric oscillators

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    We show experimentally that parametric interaction can induce a cooperative oscillation of non simultaneously resonant transverse modes in an optical parametric oscillator. More generally, this effect is expected to occur in any spatially extended system subjected to boundary conditions where nonlinear wave mixing of two nonresonant spatial modes can generate a resonant oscillation

    Rain-Fed Farming System at a Crossroads in Semi-Arid Areas of Tanzania: What Roles do Climate Variability and Change Play?

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    Positive changes, like adopting drought resistant crop varieties, in the rain-fed farming system (RFFS) in response to climate variability and change enhance system’s ability to support people’s living as opposed to negative changes, like lack of pastures, which put the system at risk of failure in supporting the living. Using participatory rural appraisal (PRA) and household survey, this paper examined the roles of climate variability and change in triggering changes in RFFS. Specifically, the paper: (i) assessed dominant crop and livestock farming system; (ii) assessed the change element of crop and livestock production systems; and (iii) examined factors for the changes in RFFS. A random sample of 388 households was used. Qualitative data analysis was done through content analysis. Binary logistic regression was used to assess factors that explain changes on RFFS. The results showed that dominant crops were different in each village. Secondly, some changes in crop varieties and in livestock grazing arrangements were noted in response to climate variability and change. Unlike the hypothesis (P>0.05), the results demonstrated that warming (ß = -10.61, Wald = 36.26, P ? 0.001) showed highest significant impact on likelihood of adopting new crop varieties relative to other factors. Similarly, drought (ß = 2.16, Wald = 6.82, P ? 0.009) showed highest impact on the likelihood of changing a grazing place. Yet, the changes were constrained by factors like natural resources protective policies, failure of crop varieties to withstand warming and drought, and poor land use management. Therefore, the RFFS was at a crossroads with implications on system sustainability and livelihoods. The government and private interventions should support farmers and agro-pastoralists to manage risks related to the changes in RFFS in response to climate variability and change. Keywords: Climate change, agro-pastoralism, livelihoods, semi-arid, Tanzani

    Killing the umpire: cooperative defects in mitotic checkpoint and BRCA2 genes on the road to transformation

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    Recent findings from mouse models of BRCA2 genetic lesions have provided intriguing insights and important questions concerning modes of tumor development in familial breast and ovarian cancers. Fibroblasts from mice homozygous for the BRCA2(Tr) allele grow poorly and display an array of chromosomal abnormalities that are consistent with a role for BRCA2 in DNA repair. This growth defect can be overcome and cellular transformation promoted by the expression of defective, dominant negative alleles of p53 and of the mitotic checkpoint gene Bub1, both of which are known to induce chromosome instability. These findings are mirrored in the genetic lesions sustained in tumors found in the rare BRCA2(Tr/Tr)mice that survive to adulthood, which include defects in p53 as well as the mitotic checkpoint proteins Bub1 and Mad3L. Together, these data hint that tumors in these mice evolve from an unusually intense selective pressure to remove DNA damage checkpoints, which in turn might be facilitated by chromosomal abolition of mitotic checkpoints and the consequent increase in shuffling of genetic information. How these genetic lesions co-operate to yield transformed cells and how these data relate to BRCA1 and BRCA2 defects in the human population are important questions raised by this work
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