1,034 research outputs found
Sheep in Wolf’s Clothing: The Role of Artifacts in Interpretive Schema Change
In this paper, we investigate the role of artifacts in a failed project that aimed at implementing a new culture of dealing with errors in a hospital by transferring safety standards from the aviation industry. We apply the interpretative method of objective hermeneutics to elucidate the role of artifacts as linking pins between diverging interpretive schemata and collective action during attempts to modify organizational routines. In particular, we show how the implementation of artifacts may serve as a means to satisfy a new espoused schema, while at the same time they are created and interpreted in ways that strengthen the old enacted schema. Although on the surface everyone would appreciate changes in treatment routines that help to avoid errors, the guiding norms of individual vigilance and self-centeredness, a culture that emphasizes hierarchy as a core value as well as the lack of sanctions for enacting the old schema led to a situation where the new espoused schema was never enacted. Instead, artifacts were used to stabilize a divergence between espoused and enacted schemata. Failure remained a cultural taboo.(VLID)342667
Pulsar Constraints on Neutron Star Structure and Equation of State
With the aim of constraining the structural properties of neutron stars and
the equation of state of dense matter, we study sudden spin-ups, glitches,
occurring in the Vela pulsar and in six other pulsars. We present evidence that
glitches represent a self-regulating instability for which the star prepares
over a waiting time. The angular momentum requirements of glitches in Vela
indicate that at least 1.4% of the star's moment of inertia drives these
events. If glitches originate in the liquid of the inner crust, Vela's
`radiation radius' must exceed ~12 km for a mass of 1.4 solar masses.
Observational tests of whether other neutron stars obey this constraint will be
possible in the near future.Comment: 5 pages, including figures. To appear in Physical Review Letter
Neutron Star Structure and the Neutron Radius of 208Pb
We study relationships between the neutron-rich skin of a heavy nucleus and
the properties of neutron-star crusts. Relativistic effective field theories
with a thicker neutron skin in Pb have a larger electron fraction and a
lower liquid-to-solid transition density for neutron-rich matter. These
properties are determined by the density dependence of the symmetry energy
which we vary by adding nonlinear couplings between isoscalar and isovector
mesons. An accurate measurement of the neutron radius in Pb---via
parity violating electron scattering---may have important implications for the
structure of neutron stars.Comment: 5 pages 3 figures, added additional evidence of model independence,
Phys. Rev. Letters in pres
Dirac theory within the Standard-Model Extension
The modified Dirac equation in the Lorentz-violating Standard-Model Extension
(SME) is considered. Within this framework, the construction of a hermitian
Hamiltonian to all orders in the Lorentz-breaking parameters is investigated,
discrete symmetries and the first-order roots of the dispersion relation are
determined, and various properties of the eigenspinors are discussed.Comment: 11 pages REVTe
The neutron radii of Lead and neutron stars
A new relation between the neutron skin of a heavy nucleus and the radius of
a neutron star is proposed: the larger the neutron skin of the nucleus the
larger the radius of the star. Relativistic models that reproduce a variety of
ground-state observables can not determine uniquely the neutron skin of a heavy
nucleus. Thus, a large range of neutron skins is generated by supplementing the
models with nonlinear couplings between isoscalar and isovector mesons. We
illustrate how the correlation between the neutron skin and the radius of the
star can be used to place important constraints on the equation of state and
how it may help elucidate the existence of a phase transition in the interior
of the neutron star.Comment: 4 pages including 4 encapsulated postscript figure
Gravitational physics with antimatter
The production of low-energy antimatter provides unique opportunities to
search for new physics in an unexplored regime. Testing gravitational
interactions with antimatter is one such opportunity. Here a scenario based on
Lorentz and CPT violation in the Standard- Model Extension is considered in
which anomalous gravitational effects in antimatter could arise.Comment: 5 pages, presented at the International Conference on Exotic Atoms
(EXA 2008) and the 9th International Conference on Low Energy Antiproton
Physics (LEAP 2008), Vienna, Austria, September 200
Selective Light-Triggered Release of DNA from Gold Nanorods Switches Blood Clotting On and Off
Blood clotting is a precise cascade engineered to form a clot with temporal and spatial control. Current control of blood clotting is achieved predominantly by anticoagulants and thus inherently one-sided. Here we use a pair of nanorods (NRs) to provide a two-way switch for the blood clotting cascade by utilizing their ability to selectively release species on their surface under two different laser excitations. We selectively trigger release of a thrombin binding aptamer from one nanorod, inhibiting blood clotting and resulting in increased clotting time. We then release the complementary DNA as an antidote from the other NR, reversing the effect of the aptamer and restoring blood clotting. Thus, the nanorod pair acts as an on/off switch. One challenge for nanobiotechnology is the bio-nano interface, where coronas of weakly adsorbed proteins can obscure biomolecular function. We exploit these adsorbed proteins to increase aptamer and antidote loading on the nanorods.National Science Foundation (U.S.) (Grant DMR #0906838
Bayesian Methods for Exoplanet Science
Exoplanet research is carried out at the limits of the capabilities of
current telescopes and instruments. The studied signals are weak, and often
embedded in complex systematics from instrumental, telluric, and astrophysical
sources. Combining repeated observations of periodic events, simultaneous
observations with multiple telescopes, different observation techniques, and
existing information from theory and prior research can help to disentangle the
systematics from the planetary signals, and offers synergistic advantages over
analysing observations separately. Bayesian inference provides a
self-consistent statistical framework that addresses both the necessity for
complex systematics models, and the need to combine prior information and
heterogeneous observations. This chapter offers a brief introduction to
Bayesian inference in the context of exoplanet research, with focus on time
series analysis, and finishes with an overview of a set of freely available
programming libraries.Comment: Invited revie
Gravity, Lorentz Violation, and the Standard Model
The role of the gravitational sector in the Lorentz- and CPT-violating
Standard-Model Extension (SME) is studied. A framework is developed for
addressing this topic in the context of Riemann-Cartan spacetimes, which
include as limiting cases the usual Riemann and Minkowski geometries. The
methodology is first illustrated in the context of the QED extension in a
Riemann-Cartan background. The full SME in this background is then considered,
and the leading-order terms in the SME action involving operators of mass
dimension three and four are constructed. The incorporation of arbitrary
Lorentz and CPT violation into general relativity and other theories of gravity
based on Riemann-Cartan geometries is discussed. The dominant terms in the
effective low-energy action for the gravitational sector are provided, thereby
completing the formulation of the leading-order terms in the SME with gravity.
Explicit Lorentz symmetry breaking is found to be incompatible with generic
Riemann-Cartan geometries, but spontaneous Lorentz breaking evades this
difficulty.Comment: 21 pages REVTeX, references added, accepted in Physical Review
Threshold analyses and Lorentz violation
In the context of threshold investigations of Lorentz violation, we discuss
the fundamental principle of coordinate invariance, the role of an effective
dynamical framework, and the conditions of positivity and causality. Our
analysis excludes a variety of previously considered Lorentz-breaking
parameters and opens an avenue for viable dispersion-relation investigations of
Lorentz violation.Comment: 9 page
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