16,377 research outputs found
A Nonlinear Model of the Business Cycle
The usual index of leading indicators has constant weights on its components and is therefore implicitly premised on the assumption that the dynamical properties of the economy remain the same over time and across phases of the business cycle. We explore the possibility that the business cycle has phases, for example, recessions, recoveries and normal growth, each with its unique dynamics. Based on this possibility we develop a nonlinear model of the business cycle that combines a number of previous approaches. We model the state of the economy as a latent variable with a threshold autoregression structure. In addition to dependence on its own lags the latent variable is also determined by observed economic and financial variables. In turn these variables are modeled as following a nonlinear vector autoregression with regimes defined by the latent business cycle variable. A Markov Chain Monte Carlo algorithm is developed to estimate the model. Special attention is paid to specification of prior distributions given the large dimension of the model. We also investigate using the business cycle chronology of the NBER to aid in the classification of the latent variable. The two main empirical objectives of the model are to provide more accurate predictions of economic variables particularly at turning points and to describe how the dynamics differ across business cycle phasesnonlinear, business cycle, Bayesian
Femtosecond probing of bimolecular reactions: The collision complex
Progress has been made in probing the femtosecond
dynamics of transition states of chemical reactions.(1) The
"half-collision" case of unimolecular reactions has been
experimentally investigated for a number of systems and
much theoretical work has already been developed.(2) For
bimolecular reactions, the case of full collision, the zero of
time is a problem which makes the femtosecond temporal
resolution of the dynamics a difficult task
Femtosecond real-time probing of reactions. VIII. The bimolecular reaction Br+I2
In this paper, we discuss the experimental technique for real-time measurement of the lifetimes of the collision complex of bimolecular reactions. An application to the atomâmolecule Br+I_2 reaction at two collision energies is made. Building on our earlier Communication [J. Chem. Phys. 95, 7763 (1991)], we report on the observed transients and lifetimes for the collision complex, the nature of the transition state, and the dynamics near threshold. Classical trajectory calculations provide a framework for deriving the global nature of the reactive potential energy surface, and for discussing the real-time, scattering, and asymptotic (product-state distribution) aspects of the dynamics. These experimental and theoretical results are compared with the extensive array of kinetic, crossed beam, and theoretical studies found in the literature for halogen radicalâhalogen molecule exchange reactions
Estimating within-household contact networks from egocentric data
Acute respiratory diseases are transmitted over networks of social contacts.
Large-scale simulation models are used to predict epidemic dynamics and
evaluate the impact of various interventions, but the contact behavior in these
models is based on simplistic and strong assumptions which are not informed by
survey data. These assumptions are also used for estimating transmission
measures such as the basic reproductive number and secondary attack rates.
Development of methodology to infer contact networks from survey data could
improve these models and estimation methods. We contribute to this area by
developing a model of within-household social contacts and using it to analyze
the Belgian POLYMOD data set, which contains detailed diaries of social
contacts in a 24-hour period. We model dependency in contact behavior through a
latent variable indicating which household members are at home. We estimate
age-specific probabilities of being at home and age-specific probabilities of
contact conditional on two members being at home. Our results differ from the
standard random mixing assumption. In addition, we find that the probability
that all members contact each other on a given day is fairly low: 0.49 for
households with two 0--5 year olds and two 19--35 year olds, and 0.36 for
households with two 12--18 year olds and two 36+ year olds. We find higher
contact rates in households with 2--3 members, helping explain the higher
influenza secondary attack rates found in households of this size.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS474 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Estimating within-school contact networks to understand influenza transmission
Many epidemic models approximate social contact behavior by assuming random
mixing within mixing groups (e.g., homes, schools and workplaces). The effect
of more realistic social network structure on estimates of epidemic parameters
is an open area of exploration. We develop a detailed statistical model to
estimate the social contact network within a high school using friendship
network data and a survey of contact behavior. Our contact network model
includes classroom structure, longer durations of contacts to friends than
nonfriends and more frequent contacts with friends, based on reports in the
contact survey. We performed simulation studies to explore which network
structures are relevant to influenza transmission. These studies yield two key
findings. First, we found that the friendship network structure important to
the transmission process can be adequately represented by a dyad-independent
exponential random graph model (ERGM). This means that individual-level sampled
data is sufficient to characterize the entire friendship network. Second, we
found that contact behavior was adequately represented by a static rather than
dynamic contact network.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS505 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Depletion of carriers and negative differential conductivity in an intrinsic graphene under a dc electric field
The heating of carriers in an intrinsic graphene under an abrupt switching
off a dc electric field is examined taking into account both the energy
relaxation via acoustic and optic phonons and the interband
generation-recombination processes. The later are caused by the interband
transitions due to optical phonon modes and thermal radiation. Description of
the temporal and steady-state responses, including the nonequilibrium
concentration and energy as well as the current-voltage characteristics, is
performed. At room temperature, a nearly-linear current-voltage characteristic
and a slowly-varied concentration take place for fields up to -- 20 kV/cm.
Since a predominant recombination of high-energy carriers due to optical phonon
emission at low temperatures, a depletion of concentration takes place below --
250 K. For lower temperatures the current tends to be saturated and a negative
differential conductivity appears below -- 170 K in the region of fields -- 10
V/cm.Comment: 8 pages, 10 figures, extended versio
Political and Media Discourses about Integrating Refugees in the UK
The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.This article addresses political and media discourses about integrating refugees in the UK in the context of the ârefugee crisisâ. A discursive psychological approach is presented as the best way to understand what talk about the concept is used to accomplish in these debates. A large corpus of political discussions (13 hours of debate featuring 146 politicians) and 960 newspaper articles from the UK were discourse analysed. The analysis identified five dilemmas about integration: Integration is positive and necessary, but challenging; Host communities are presented as welcoming, but there are limits to their capacity; Refugees are responsible for integration, but host communities need to provide support; Good refugees integrate, bad ones don't; Refugees are vulnerable and are skilled. All are used to warrant the inclusion or exclusion of refugees. The responsibility of western nations to support refugees is therefore contingent on the refugees behaving in specific ways
An Overview of the Kauffman Firm Survey: Results From the 2004-2007 Data
Based on surveys conducted over four years, provides an overview of trends among U.S. firms established in 2004 and the business and owner characteristics associated with survival and growth, including level of innovation, structure, and financing
An Overview of the Kauffman Firm Survey: Results From the 2004-2008 Data
Presents findings from longitudinal data on new businesses founded in 2004, including financing structure; products, services, and innovations; and characteristics of the owners. Examines indicators of growth and survival and effects of the recession
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