17,401 research outputs found
An approach for jointly modeling multivariate longitudinal measurements and discrete time-to-event data
In many medical studies, patients are followed longitudinally and interest is
on assessing the relationship between longitudinal measurements and time to an
event. Recently, various authors have proposed joint modeling approaches for
longitudinal and time-to-event data for a single longitudinal variable. These
joint modeling approaches become intractable with even a few longitudinal
variables. In this paper we propose a regression calibration approach for
jointly modeling multiple longitudinal measurements and discrete time-to-event
data. Ideally, a two-stage modeling approach could be applied in which the
multiple longitudinal measurements are modeled in the first stage and the
longitudinal model is related to the time-to-event data in the second stage.
Biased parameter estimation due to informative dropout makes this direct
two-stage modeling approach problematic. We propose a regression calibration
approach which appropriately accounts for informative dropout. We approximate
the conditional distribution of the multiple longitudinal measurements given
the event time by modeling all pairwise combinations of the longitudinal
measurements using a bivariate linear mixed model which conditions on the event
time. Complete data are then simulated based on estimates from these pairwise
conditional models, and regression calibration is used to estimate the
relationship between longitudinal data and time-to-event data using the
complete data. We show that this approach performs well in estimating the
relationship between multivariate longitudinal measurements and the
time-to-event data and in estimating the parameters of the multiple
longitudinal process subject to informative dropout. We illustrate this
methodology with simulations and with an analysis of primary biliary cirrhosis
(PBC) data.Comment: Published in at http://dx.doi.org/10.1214/10-AOAS339 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Qualitative properties of large buckled states of spherical shells
A system of 6th-order quasi-linear Ordinary Differential Equations is analyzed to show the global existence of axisymmetrically buckled states. A surprising nodal property is obtained which shows that everywhere along a branch of solutions that bifurcates from a simple eigenvalue of the linearized equation, the number of simultaneously vanishing points of both shear resultant and circumferential bending moment resultant remains invariant, provided that a certain auxiliary condition is satisfied
Alignment and orientation of an adsorbed dipole molecule
Half-cycle laser pulse is applied on an absorbed molecule to investigate its
alignment and orientation behavior. Crossover from field-free to hindered
rotation motion is observed by varying the angel of hindrance of potential
well. At small hindered angle, both alignment and orientation show
sinusoidal-like behavior because of the suppression of higher excited states.
However, mean alignment decreases monotonically as the hindered angle is
increased, while mean orientation displays a minimum point at certain hindered
angle. The reason is attributed to the symmetry of wavefunction and can be
explained well by analyzing the coefficients of eigenstates.Comment: 4 pages, 4 figures, to appear in Phys. Rev. B (2004
Dual Field Theories In (d-1)+1 Emergent Spacetimes From A Unifying Field Theory In d+2 Spacetime
According to Two-Time Physics, there is more to space-time than can be
garnered with the ordinary formulation of physics. Two-Time Physics has shown
that the Standard Model of Particles and Forces is successfully reproduced by a
two-time field theory in 4 space and 2 time dimensions projected as a
holographic image on an emergent spacetime in 3+1 dimensions. Among the
successes of this approach is the resolution of the strong CP problem of QCD as
an outcome of the restrictions imposed by the higher symmetry structures in 4+2
dimensions. In this paper we launch a program to construct the duals of the
Standard Model as other holographic images of the same 4+2 dimensional theory
on a variety of emergent spacetimes in 3+1 dimensions. These dual field
theories are obtained as a family of gauge choices in the master 4+2 field
theory. In the present paper we deal with some of the simpler gauge choices
which lead to interacting Klein-Gordon field theories for the conformal scalar
with a predicted SO(d,2) symmetry in a variety of interesting curved spacetimes
in (d-1)+1 dimensions. More challenging and more interesting gauge choices
(including some that relate to mass) which are left to future work are also
outlined. Through this approach we discover a new realm of previously
unexplored dualities and hidden symmetries that exist both in the macroscopic
and microscopic worlds, at the classical and quantum levels. Such phenomena
predicted by 2T-physics can in principle be confirmed both by theory and
experiment. 1T-physics can be used to analyze the predictions but in most
instances gives no clue that the predicted phenomena exist in the first place.
This point of view suggests a new paradigm for the construction of a
fundamental theory that is likely to impact on the quest for unification.Comment: LaTeX, 35 page
The Big Bang and Inflation United by an Analytic Solution
Exact analytic solutions for a class of scalar-tensor gravity theories with a
hyperbolic scalar potential are presented. Using an exact solution we have
successfully constructed a model of inflation that produces the spectral index,
the running of the spectral index and the amplitude of scalar perturbations
within the constraints given by the WMAP 7 years data. The model simultaneously
describes the Big Bang and inflation connected by a specific time delay between
them so that these two events are regarded as dependent on each other. In
solving the Fridemann equations, we have utilized an essential Weyl symmetry of
our theory in 3+1 dimensions which is a predicted remaining symmetry of
2T-physics field theory in 4+2 dimensions. This led to a new method of
obtaining analytic solutions in 1T field theory which could in principle be
used to solve more complicated theories with more scalar fields. Some
additional distinguishing properties of the solution includes the fact that
there are early periods of time when the slow roll approximation is not valid.
Furthermore, the inflaton does not decrease monotonically with time, rather it
oscillates around the potential minimum while settling down, unlike the slow
roll approximation. While the model we used for illustration purposes is
realistic in most respects, it lacks a mechanism for stopping inflation. The
technique of obtaining analytic solutions opens a new window for studying
inflation, and other applications, more precisely than using approximations.Comment: V2 improve computation with better agreement with WMAP 7 years data,
and also point out an exact solution for cyclic cosmolog
Steady-state entanglement in a double-well Bose-Einstein condensate through coupling to a superconducting resonator
We consider a two-component Bose-Einstein condensate in a double-well
potential, where the atoms are magnetically coupled to a single-mode of the
microwave field inside a superconducting resonator. We find that the system has
the different dark-state subspaces in the strong- and weak-tunneling regimes,
respectively. In the limit of weak tunnel coupling, steady-state entanglement
between the two spatially separated condensates can be generated by evolving to
a mixture of dark states via the dissipation of the photon field. We show that
the entanglement can be faithfully indicated by an entanglement witness.
Long-lived entangled states are useful for quantum information processing with
atom-chip devices.Comment: 9 pages, 7 figures, minor revisio
Empires of the Sinophone
This paper will consider how Sinophone literature from different parts of the world can serve as interventions to major theoretical and disciplinary issues in the humanities today in our new age of empires.postprin
Characteristic Length Scale of Electric Transport Properties of Genomes
A tight-binding model together with a novel statistical method are used to
investigate the relation between the sequence-dependent electric transport
properties and the sequences of protein-coding regions of complete genomes. A
correlation parameter is defined to analyze the relation. For some
particular propagation length , the transport behaviors of the coding
and non-coding sequences are very different and the correlation reaches its
maximal value . and \omax are characteristic values for
each species. The possible reason of the difference between the features of
transport properties in the coding and non-coding regions is the mechanism of
DNA damage repair processes together with the natural selection.Comment: 4 pages, 4 figure
Impact of Carbon Price Policies on U.S. Industry
This paper informs the discussion of carbon price policies by examining the potential for adverse impacts on domestic industries, with a focus on detailed sector-level analysis. The assumed policy scenario involves a unilateral economy-wide $10/ton CO2 charge without accompanying border tax adjustments or other complementary policies. Four modeling approaches are developed as a proxy for the different time horizons over which firms can pass through added costs, change input mix, adopt new technologies, and reallocate capital. Overall, we find that a readily identifiable set of industries experience particularly adverse impacts as measured by reduced output and that the relative burdens on different industries are remarkably consistent across the four time horizons. Output rebounds considerably over longer time horizons, and the adverse impacts on profits diminish even more rapidly in most cases. Over the short term employment losses mirror output declines, while gains in other industries fully offset the losses over the longer horizons. At the same time, leakage abroad is considerable in some sectors, particularly when reductions in exports are considered.carbon price, competitiveness, input-output analysis
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