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16,369
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"Long, J."
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Completely dark photons from gravitational particle production during the inflationary era
A
bstract
Starting with the de Broglie-Proca Lagrangian for a massive vector field, we calculate the number density of particles resulting from gravitational particle production (GPP) during inflation, with detailed consideration to the evolution of the number density through the reheating. We find plausible scenarios for the production of dark-photon dark matter of mass in a wide range, as low as a micro-electron volt to 10
14
GeV. Gravitational particle production does not depend on any coupling of the dark photon to standard-model particles.
Journal Article
A GENERAL FRAMEWORK FOR COMPARING PREDICTIONS AND MARGINAL EFFECTS ACROSS MODELS
Many research questions involve comparing predictions or effects across multiple models. For example, it may be of interest whether an independent variable's effect changes after adding variables to a model. Or, it could be important to compare a variable's effect on different outcomes or across different types of models. When doing this, marginal effects are a useful method for quantifying effects because they are in the natural metric of the dependent variable and they avoid identification problems when comparing regression coefficients across logit and probit models. Despite advances that make it possible to compute marginal effects for almost any model, there is no general method for comparing these effects across models. In this article, the authors provide a general framework for comparing predictions and marginal effects across models using seemingly unrelated estimation to combine estimates from multiple models, which allows tests of the equality of predictions and effects across models. The authors illustrate their method to compare nested models, to compare effects on different dependent or independent variables, to compare results from different samples or groups within one sample, and to assess results from different types of models.
Journal Article
Defining crime : a critique of the concept and its implication
\"Defining Crime explores the limitations of the legal definition of crime, how that politically based definition has shaped criminological research, and why criminologists must redefine crime to include scientific objectivity. Lynch, Stretesky, and Long argue that a scientific definition of crime must be detached from criminal law and the variation the political construction imposes. The authors propose an alternative definition of crime, explore its limitations, and how it can reshape criminological research. \"-- Provided by publisher.
Book
Ligand design strategies to increase stability of gadolinium-based magnetic resonance imaging contrast agents
Gadolinium(III) complexes have been widely utilised as magnetic resonance imaging (MRI) contrast agents for decades. In recent years however, concerns have developed about their toxicity, believed to derive from demetallation of the complexes in vivo, and the relatively large quantities of compound required for a successful scan. Recent efforts have sought to enhance the relaxivity of trivalent gadolinium complexes without sacrificing their stability. This review aims to examine the strategic design of ligands synthesised for this purpose, provide an overview of recent successes in gadolinium-based contrast agent development and assess the requirements for clinical translation.
Gadolinium(III) complexes are strong enhancers of magnetic resonance imaging (MRI) signals, thus are widely used as contrast agents despite their potential toxicity. Here, the authors review ligand design approaches aimed at improving the stability of Gd(III)-based MRI contrast agents.
Journal Article
Cosmological aspects of the clockwork axion
A
bstract
The clockwork axion refers to a family of aligned multi-axion models that lead to an exponential hierarchy between the scale of Peccei-Quinn symmetry breaking and the scale of the axion decay constant. The clockworking can bring the Peccei-Quinn-scale particles to within reach of collider experiments. In this work we are interested in whether cosmological observations impose any new constraints on the clockwork axion. If the universe reheats above the scale of Peccei-Quinn breaking, then the ensuing cosmological phase transition produces a network of topological defects, which have a qualitatively different behavior from the string-wall network in the usual axion models. We estimate the relic abundances of axion dark matter and dark radiation that arise from the emission of axions by the defect network, and we infer a constraint on the scale of Peccei-Quinn breaking and the mass spectrum. We find that the defect contribution to the axion
dark matter
relic abundance is generally negligible. However, the defect production of relativistic axion
dark radiation
becomes significant if the scale of Peccei-Quinn symmetry breaking is larger than 100 TeV, and measurements of Δ
N
eff
provide a new probe of this class of models.
Journal Article
Concrete economics : the Hamilton approach to economic growth and policy
\"Brilliantly written and argued, Concrete Economics shows exactly how the US government has shaped and directed the economy since the very inception of the country. This book does not rehash the sturdy and well-known arguments that to thrive, an entrepreneurial economy needs a social and policy environment characterized by a broad range of freedoms. Nor does it buy into the myth of the absolutely free market. Instead, Cohen and DeLong focus on the forgotten role played by the US government in initiating and enabling a redesign of the US economy. The government not only sets the ground rules for entrepreneurial activity but directs the surges of energy that mark a vibrant economy. It is as true for present-day Silicon Valley as it was for New England manufacturing at the dawn of the nineteenth century. This is not an argument based on abstract truths, complex correlations, or arcane discoveries, but rather on the facts of how the US economy succeeded so brilliantly. And that provides a blueprint for how the government, established companies, and new ventures can partner to yet again successfully reshape the economy. \"-- Provided by publisher.
Book
Gadolinium Deposition in Brain: Current Scientific Evidence and Future Perspectives
In the past 4 years, many publications described a concentration-dependent deposition of gadolinium in the brain both in adults and children, seen as high signal intensities in the globus pallidus and dentate nucleus on unenhanced T1-weighted images. Postmortem human or animal studies have validated gadolinium deposition in these T1-hyperintensity areas, raising new concerns on the safety of gadolinium-based contrast agents (GBCAs). Residual gadolinium is deposited not only in brain, but also in extracranial tissues such as liver, skin, and bone. This review summarizes the current evidence on gadolinium deposition in the human and animal bodies, evaluates the effects of different types of GBCAs on the gadolinium deposition, introduces the possible entrance or clearance mechanism of the gadolinium and potential side effects that may be related to the gadolinium deposition on human or animals, and puts forward some suggestions for further research.
Journal Article