6,674 research outputs found
Grand unification through gravitational effects
We systematically study the unification of gauge couplings in the presence of
(one or more) effective dimension-5 operators cHGG/4MPl, induced into the grand
unified theory by gravitational interactions at the Planck scale MPl. These
operators alter the usual condition for gauge coupling unification, which can,
depending on the Higgs content H and vacuum expectation value, result in
unification at scales MX significantly different than naively expected. We find
non-supersymmetric models of SU(5) and SO(10) unification, with natural Wilson
coefficients c, that easily satisfy the constraints from proton decay.
Furthermore, gauge coupling unification at scales as high as the Planck scale
seems feasible, possibly hinting at simultaneous unification of gauge and
gravitational interactions. In the Appendix we work out the group theoretical
aspects of this scenario for SU(5) and SO(10) unified groups in detail; this
material is also relevant in the analysis of non-universal gaugino masses
obtained from supergravity.Comment: 27 pages, 5 figures, 8 tables, 1 appendix, revtex; v2: introduction
and conclusion expanded, references added, minor changes, version published
in PR
Black hole entropy, curved space and monsters
We investigate the microscopic origin of black hole entropy, in particular
the gap between the maximum entropy of ordinary matter and that of black holes.
Using curved space, we construct configurations with entropy greater than their
area in Planck units. These configurations have pathological properties and we
refer to them as monsters. When monsters are excluded we recover the entropy
bound on ordinary matter . This bound implies that essentially all
of the microstates of a semiclassical black hole are associated with the growth
of a slightly smaller black hole which absorbs some additional energy. Our
results suggest that the area entropy of black holes is the logarithm of the
number of distinct ways in which one can form the black hole from ordinary
matter and smaller black holes, but only after the exclusion of monster states.Comment: 5 pages, revtex. Final version to appear Physics Letters
Child Sexual Abuse in Asian American Families: An Examination of Cultural Factors That Influence Prevalence, Identification, and Treatment
Child sexual abuse affects thousands of families each year. Issues pertaining to the prevalence, identification, and treatment of sexual abuse have been relatively well explored in the literature as they pertain to the dominant European American culture. These issues, however, are still relatively unexplored in terms of how sexual abuse affects Asian American families and the Asian American community. We review the relevant literature in Asian American families. These matters are explored in the context of Asian American values such as collectivity, conformity, inconspicuousness, middle position virtue, shame, self-control, and fatalism. Attitudes toward family, sexuality, and the mental health system are also discussed. Cultural and institutional barriers to underutilizing mental health services are also explored, and suggestions for overcoming these barriers are offered
Unitarity and the Hilbert space of quantum gravity
Under the premises that physics is unitary and black hole evaporation is
complete (no remnants, no topology change), there must exist a one-to-one
correspondence between states on future null and timelike infinity and on any
earlier spacelike Cauchy surface (e.g., slices preceding the formation of the
hole). We show that these requirements exclude a large set of semiclassical
spacetime configurations from the Hilbert space of quantum gravity. In
particular, the highest entropy configurations, which account for almost all of
the volume of semiclassical phase space, would not have quantum counterparts,
i.e. would not correspond to allowed states in a quantum theory of gravity.Comment: 7 pages, 3 figures, revtex; minor changes in v2 (version published in
Class. Quant. Grav.
An integrated strategic sourcing process for complex systems
Thesis (M.B.A.)--Massachusetts Institute of Technology, Sloan School of Management; and, (S.M.)--Massachusetts Institute of Technology, Engineering Systems Division; in conjunction with the Leaders for Manufacturing Program at MIT, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 85-88).Aerospace firms continue to outsource increasingly complex components and systems for access to talent, lower costs, and global presence. In addition to strong competition from Airbus and other emergent companies, Boeing is faced with the challenge of reducing financial risk and placing work internationally to offset foreign sales obligations. The organization has recognized a need for an integrated framework to consistently make sourcing decisions that limits subjectivity and positions the company for continued success. This thesis is based on a six-month internship study with the Future Production System team based in Seattle, WA and it examines the strategic sourcing decision process at Boeing Commercial Airplanes. A discussion-based strategic sourcing process utilizing a holistic range of factors is proposed to test whether an expensive, complex, and integrated system like a composite airplane wing should be outsourced or if it should be designed and produced internally. This workshop-based strategy development process develops weighted factors through a structured, cross-functional process where multiple proposals can be evaluated based on their performance against a set of quantitative and qualitative factors such as cost, quality, flow, knowledge management, stability, and risk. The development of a baseline sourcing proposal for a composite airplane wing demonstrated the process. Careful assumptions were made and data collected to ensure a realistic scenario for a future single-aisle plane. The documented baseline wing sourcing strategy includes recommendations for proximity, design integration, and production responsibilities.by David T. Hsu.S.M.M.B.A
Monsters, black holes and the statistical mechanics of gravity
We review the construction of monsters in classical general relativity.
Monsters have finite ADM mass and surface area, but potentially unbounded
entropy. From the curved space perspective they are objects with large proper
volume that can be glued on to an asymptotically flat space. At no point is the
curvature or energy density required to be large in Planck units, and quantum
gravitational effects are, in the conventional effective field theory
framework, small everywhere. Since they can have more entropy than a black hole
of equal mass, monsters are problematic for certain interpretations of black
hole entropy and the AdS/CFT duality.
In the second part of the paper we review recent developments in the
foundations of statistical mechanics which make use of properties of
high-dimensional (Hilbert) spaces. These results primarily depend on kinematics
-- essentially, the geometry of Hilbert space -- and are relatively insensitive
to dynamics. We discuss how this approach might be adopted as a basis for the
statistical mechanics of gravity. Interestingly, monsters and other highly
entropic configurations play an important role.Comment: 9 pages, 4 figures, revtex; invited Brief Review to be published in
Modern Physics Letters
A conserved circadian function for the Neurofibromatosis 1 gene
Summary: Loss of the Neurofibromatosis 1 (Nf1) protein, neurofibromin, in Drosophila disrupts circadian rhythms of locomotor activity without impairing central clock function, suggesting effects downstream of the clock. However, the relevant cellular mechanisms are not known. Leveraging the discovery of output circuits for locomotor rhythms, we dissected cellular actions of neurofibromin in recently identified substrates. Herein, we show that neurofibromin affects the levels and cycling of calcium in multiple circadian peptidergic neurons. A prominent site of action is the pars intercerebralis (PI), the fly equivalent of the hypothalamus, with cell-autonomous effects of Nf1 in PI cells that secrete DH44. Nf1 interacts genetically with peptide signaling to affect circadian behavior. We extended these studies to mammals to demonstrate that mouse astrocytes exhibit a 24-hr rhythm of calcium levels, which is also attenuated by lack of neurofibromin. These findings establish a conserved role for neurofibromin in intracellular signaling rhythms within the nervous system. : Bai et al. show that the gene mutated in the disease Neurofibromatosis 1 is required for maintaining levels or cycling of calcium in circadian neurons in Drosophila and in mammalian cells. These effects likely account for effects of Nf1 on circadian behavior in Drosophila and may be relevant in explaining sleep phenotypes in patients. Keywords: circadian rhythms, neurofibromatosis 1, Drosophila, peptide signaling, cycling of calcium, mouse astrocyte
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