260 research outputs found
Cosmological Perturbations from the No Boundary Euclidean Path Integral
We compute, from first principles, the quantum fluctuations about instanton
saddle points of the Euclidean path integral for Einstein gravity coupled to a
scalar field. The Euclidean two-point correlator is analytically continued into
the Lorentzian region where it describes the quantum mechanical vacuum
fluctuations in the state described by no boundary proposal initial conditions.
We concentrate on the density perturbations in open inflationary universes
produced from cosmological instantons, describing the differences between
non-singular Coleman-De Luccia and singular Hawking-Turok instantons. We show
how the Euclidean path integral uniquely specifies the fluctuations in both
cases.Comment: 21 pages, RevTex file, including five postscript figure file
âIt Takes Two Hands to Clapâ: How Gaddi Shepherds in the Indian Himalayas Negotiate Access to Grazing
This article examines the effects of state intervention on the workings of informal institutions that coordinate the communal use and management of natural resources. Specifically it focuses on the case of the nomadic Gaddi
shepherds and official attempts to regulate their access to grazing pastures in the Indian Himalayas. It is often predicted that the increased presence of the modern state critically undermines locally appropriate and community-based resource management arrangements. Drawing on the work of Pauline Peters and Francis Cleaver, I identify key instances of socially embedded âcommonâ management institutions and explain the evolution of these arrangements
through dynamic interactions between individuals, communities and the agents of the state. Through describing the âliving spaceâ of Gaddi shepherds across the annual cycle of nomadic migration with their flocks I explore the
ways in which they have been able to creatively reinterpret external interventions, and suggest how contemporary arrangements for accessing pasture at different moments of the annual cycle involve complex combinations of the
formal and the informal, the âtraditionalâ and the âmodernâ
Reinforcing medical authority: clinical ethics consultation and the resolution of conflicts in treatment decisions
Despite substantial efforts in the past 15Â years to professionalise the field of clinical ethics consultation, sociologists have not reâexamined past hypotheses about the role of such services in medical decisionâmaking and their effect on physician authority. In relation to those hypotheses, we explore two questions: (i)Â What kinds of issues does ethics consultation resolve? and (ii) what is the nature of the resolution afforded by these consults? We examined ethics consultation records created between 2011 and midâ2015 at a large tertiary care US hospital and found that in most cases, the problems addressed are not novel ethical dilemmas as classically conceived, but are instead disagreements between clinicians and patients or their surrogates about treatment. The resolution offered by a typical ethics consultation involves strategies to improve communication rather than the parsing of ethical obligations. In cases where disagreements persist, the proposed solution is most often based on technical clinical judgements, reinforcing the role of physician authority in patient care and the ethical decisions made about that care.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/154312/1/shil13003.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/154312/2/shil13003_am.pd
Colossal dielectric constants in transition-metal oxides
Many transition-metal oxides show very large ("colossal") magnitudes of the
dielectric constant and thus have immense potential for applications in modern
microelectronics and for the development of new capacitance-based
energy-storage devices. In the present work, we thoroughly discuss the
mechanisms that can lead to colossal values of the dielectric constant,
especially emphasising effects generated by external and internal interfaces,
including electronic phase separation. In addition, we provide a detailed
overview and discussion of the dielectric properties of CaCu3Ti4O12 and related
systems, which is today's most investigated material with colossal dielectric
constant. Also a variety of further transition-metal oxides with large
dielectric constants are treated in detail, among them the system La2-xSrxNiO4
where electronic phase separation may play a role in the generation of a
colossal dielectric constant.Comment: 31 pages, 18 figures, submitted to Eur. Phys. J. for publication in
the Special Topics volume "Cooperative Phenomena in Solids: Metal-Insulator
Transitions and Ordering of Microscopic Degrees of Freedom
Wall fluctuation modes and tensor CMB anisotropy in open inflation models
We calculate the spectrum of large angle cosmic microwave background (CMB)
anisotropies due to quantum fluctuations of the gravitational wave modes in
one-bubble open inflation models. We find the bubble-wall fluctuation modes,
which had been thought to exist discretely in previous analyses, are actually
contained in the continuous spectrum of gravitational wave modes when the
gravitational coupling is correctly taken into account. Then we find that the
spectrum of the tensor CMB anisotropy can be decomposed into the part due to
the wall fluctuation modes and that due to the usual gravitational wave modes
in a way which is almost model-independent, even when the gravitational
coupling is strong. We also discuss observational constraints on the model
parameters. We find that an appreciable portion of the parameter space is
excluded but the remaining allowable region is still wide enough to leave the
one-bubble scenario viable.Comment: 12 pages revtex file, 9 postscript figure
Variational formulas and cocycle solutions for directed polymer and percolation models
We discuss variational formulas for the law of large numbers limits of certain models of motion in a random medium: namely, the limiting time constant for last-passage percolation and the limiting free energy for directed polymers. The results are valid for models in arbitrary dimension, steps of the admissible paths can be general, the environment process is ergodic under spatial translations, and the potential accumulated along a path can depend on the environment and the next step of the path. The variational formulas come in two types: one minimizes over gradient-like cocycles, and another one maximizes over invariant measures on the space of environments and paths. Minimizing cocycles can be obtained from Busemann functions when these can be proved to exist. The results are illustrated through 1+1 dimensional exactly solvable examples, periodic examples, and polymers in weak disorder
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