The Experts below are selected from a list of 148020 Experts worldwide ranked by ideXlab platform

Robert Brandenberger - One of the best experts on this subject based on the ideXlab platform.

  • back reaction of perturbations in two scalar field inflationary models
    arXiv: High Energy Physics - Theory, 2003
    Co-Authors: Ghazal Geshnizjani, Robert Brandenberger
    Abstract:

    We calculate the back-reaction of long wavelength cosmological perturbations on a general relativistic measure of the Local Expansion rate of the Universe. Specifically, we consider a cosmological model in which matter is described by two scalar matter fields, one being the inflaton and the other one representing a matter field which is used as a clock. We analyze back-reaction in a phase of inflaton-driven slow-roll inflation, and find that the leading infrared back-reaction terms contributing to the evolution of the Expansion rate do not vanish when measured at a fixed value of the clock field. We also analyze the back-reaction of entropy modes in a specific cosmological model with negative square mass for the entropy field and find that back-reaction can become significant. Our work provides evidence that, in general, the back-reaction of infrared fluctuations could be Locally observable.

  • back reaction and Local cosmological Expansion rate
    Physical Review D, 2002
    Co-Authors: Ghazal Geshnizjani, Robert Brandenberger
    Abstract:

    We calculate the back reaction of cosmological perturbations on a general relativistic variable which measures the Local Expansion rate of the Universe. Specifically, we consider a cosmological model in which matter is described by a single field. We analyze back reaction both in a matter-dominated Universe and in a phase of scalar field-driven chaotic inflation. In both cases, we find that the leading infrared terms contributing to the back reaction vanish when the Local Expansion rate is measured at a fixed value of the matter field which is used as a clock, whereas they do not appear to vanish if the Expansion rate is evaluated at a fixed value of the background time. We discuss possible implications for more realistic models with a more complicated matter sector.

J Lingertat - One of the best experts on this subject based on the ideXlab platform.

  • Local Expansion method for fast plasma boundary identification in jet
    Nuclear Fusion, 1993
    Co-Authors: D P Obrien, J J Ellis, J Lingertat
    Abstract:

    A Local Expansion technique for the reconstruction of the plasma boundary is presented. The method is particularly accurate in identifying the separatrix in X-point configurations. It is applied to JET discharges and the results are compared with those of a full equilibrium code and with other independent diagnostics. It is found that the majority of the H-mode discharges at JET have been achieved in marginal limiter configurations. The method is sufficiently reliable and fast for real time shape control

  • Local Expansion method for fast plasma boundary identification in jet
    Nuclear Fusion, 1993
    Co-Authors: D P Obrien, J J Ellis, J Lingertat
    Abstract:

    A Local Expansion technique for the reconstruction of the plasma boundary is presented. The method is particularly accurate in identifying the separatrix in X-point configurations. It is applied to JET discharges and the results are compared with those of a full equilibrium code and with other independent diagnostics. It is found that the majority of the H-mode discharges at JET have been achieved in marginal limiter configurations. The method is sufficiently reliable and fast for real time shape control

Ghazal Geshnizjani - One of the best experts on this subject based on the ideXlab platform.

  • back reaction of perturbations in two scalar field inflationary models
    arXiv: High Energy Physics - Theory, 2003
    Co-Authors: Ghazal Geshnizjani, Robert Brandenberger
    Abstract:

    We calculate the back-reaction of long wavelength cosmological perturbations on a general relativistic measure of the Local Expansion rate of the Universe. Specifically, we consider a cosmological model in which matter is described by two scalar matter fields, one being the inflaton and the other one representing a matter field which is used as a clock. We analyze back-reaction in a phase of inflaton-driven slow-roll inflation, and find that the leading infrared back-reaction terms contributing to the evolution of the Expansion rate do not vanish when measured at a fixed value of the clock field. We also analyze the back-reaction of entropy modes in a specific cosmological model with negative square mass for the entropy field and find that back-reaction can become significant. Our work provides evidence that, in general, the back-reaction of infrared fluctuations could be Locally observable.

  • back reaction and Local cosmological Expansion rate
    Physical Review D, 2002
    Co-Authors: Ghazal Geshnizjani, Robert Brandenberger
    Abstract:

    We calculate the back reaction of cosmological perturbations on a general relativistic variable which measures the Local Expansion rate of the Universe. Specifically, we consider a cosmological model in which matter is described by a single field. We analyze back reaction both in a matter-dominated Universe and in a phase of scalar field-driven chaotic inflation. In both cases, we find that the leading infrared terms contributing to the back reaction vanish when the Local Expansion rate is measured at a fixed value of the matter field which is used as a clock, whereas they do not appear to vanish if the Expansion rate is evaluated at a fixed value of the background time. We discuss possible implications for more realistic models with a more complicated matter sector.

D P Obrien - One of the best experts on this subject based on the ideXlab platform.

  • Local Expansion method for fast plasma boundary identification in jet
    Nuclear Fusion, 1993
    Co-Authors: D P Obrien, J J Ellis, J Lingertat
    Abstract:

    A Local Expansion technique for the reconstruction of the plasma boundary is presented. The method is particularly accurate in identifying the separatrix in X-point configurations. It is applied to JET discharges and the results are compared with those of a full equilibrium code and with other independent diagnostics. It is found that the majority of the H-mode discharges at JET have been achieved in marginal limiter configurations. The method is sufficiently reliable and fast for real time shape control

  • Local Expansion method for fast plasma boundary identification in jet
    Nuclear Fusion, 1993
    Co-Authors: D P Obrien, J J Ellis, J Lingertat
    Abstract:

    A Local Expansion technique for the reconstruction of the plasma boundary is presented. The method is particularly accurate in identifying the separatrix in X-point configurations. It is applied to JET discharges and the results are compared with those of a full equilibrium code and with other independent diagnostics. It is found that the majority of the H-mode discharges at JET have been achieved in marginal limiter configurations. The method is sufficiently reliable and fast for real time shape control

Matthew P Murphy - One of the best experts on this subject based on the ideXlab platform.

  • articular cartilage regeneration by activated skeletal stem cells
    Nature Medicine, 2020
    Co-Authors: Gunsagar S Gulati, Matthew P Murphy, Lauren S Koepke, Michael T Lopez, Xinming Tong, Thomas H Ambrosi, Owen Marecic, Yuting Wang
    Abstract:

    Osteoarthritis (OA) is a degenerative disease resulting in irreversible, progressive destruction of articular cartilage1. The etiology of OA is complex and involves a variety of factors, including genetic predisposition, acute injury and chronic inflammation2-4. Here we investigate the ability of resident skeletal stem-cell (SSC) populations to regenerate cartilage in relation to age, a possible contributor to the development of osteoarthritis5-7. We demonstrate that aging is associated with progressive loss of SSCs and diminished chondrogenesis in the joints of both mice and humans. However, a Local Expansion of SSCs could still be triggered in the chondral surface of adult limb joints in mice by stimulating a regenerative response using microfracture (MF) surgery. Although MF-activated SSCs tended to form fibrous tissues, Localized co-delivery of BMP2 and soluble VEGFR1 (sVEGFR1), a VEGF receptor antagonist, in a hydrogel skewed differentiation of MF-activated SSCs toward articular cartilage. These data indicate that following MF, a resident stem-cell population can be induced to generate cartilage for treatment of Localized chondral disease in OA.

  • identification of the human skeletal stem cell
    Cell, 2018
    Co-Authors: Charles Chan, Gunsagar S Gulati, Rahul Sinha, Justin Vincent Tompkins, Michael Lopez, Ava C Carter, Ryan C Ransom, Andreas Reinisch, Taylor Wearda, Matthew P Murphy
    Abstract:

    Summary Stem cell regulation and hierarchical organization of human skeletal progenitors remain largely unexplored. Here, we report the isolation of a self-renewing and multipotent human skeletal stem cell (hSSC) that generates progenitors of bone, cartilage, and stroma, but not fat. Self-renewing and multipotent hSSCs are present in fetal and adult bones and can also be derived from BMP2-treated human adipose stroma (B-HAS) and induced pluripotent stem cells (iPSCs). Gene expression analysis of individual hSSCs reveals overall similarity between hSSCs obtained from different sources and partially explains skewed differentiation toward cartilage in fetal and iPSC-derived hSSCs. hSSCs undergo Local Expansion in response to acute skeletal injury. In addition, hSSC-derived stroma can maintain human hematopoietic stem cells (hHSCs) in serum-free culture conditions. Finally, we combine gene expression and epigenetic data of mouse skeletal stem cells (mSSCs) and hSSCs to identify evolutionarily conserved and divergent pathways driving SSC-mediated skeletogenesis. Video Abstract