254,573 research outputs found
Nonparametric tests of conditional treatment effects
We develop a general class of nonparametric tests for treatment effects conditional on covariates. We consider a wide spectrum of null and alternative hypotheses regarding conditional treatment effects, including (i) the null hypothesis of the conditional stochastic dominance between treatment and control groups; ii) the null hypothesis that the conditional average treatment effect is positive for each value of covariates; and (iii) the null hypothesis of no distributional (or average) treatment effect conditional on covariates against a one-sided (or two-sided) alternative hypothesis. The test statistics are based on L1-type functionals of uniformly consistent nonparametric kernel estimators of conditional expectations that characterize the null hypotheses. Using the Poissionization technique of Giné et al. (2003), we show that suitably studentized versions of our test statistics are asymptotically standard normal under the null hypotheses and also show that the proposed nonparametric tests are consistent against general fixed alternatives. Furthermore, it turns out that our tests have non-negligible powers against some local alternatives that are n−½ different from the null hypotheses, where n is the sample size. We provide a more powerful test for the case when the null hypothesis may be binding only on a strict subset of the support and also consider an extension to testing for quantile treatment effects. We illustrate the usefulness of our tests by applying them to data from a randomized, job training program (LaLonde, 1986) and by carrying out Monte Carlo experiments based on this dataset
An experimental study of the concatenated Reed-Solomon/Viterbi channel coding system performance and its impact on space communications
The need for efficient space communication at very low bit error probabilities to the specification and implementation of a concatenated coding system using an interleaved Reed-Solomon code as the outer code and a Viterbi-decoded convolutional code as the inner code. Experimental results of this channel coding system are presented under an emulated S-band uplink and X-band downlink two-way space communication channel, where both uplink and downlink have strong carrier power. This work was performed under the NASA End-to-End Data Systems program at JPL. Test results verify that at a bit error probability of 10 to the -6 power or less, this concatenated coding system does provide a coding gain of 2.5 dB or more over the Viterbi-decoded convolutional-only coding system. These tests also show that a desirable interleaving depth for the Reed-Solomon outer code is 8 or more. The impact of this "virtually" error-free space communication link on the transmission of images is discussed and examples of simulation results are given
Renormalization Group Technique Applied to the Pairing Interaction of the Quasi-One-Dimensional Superconductivity
A mechanism of the quasi-one-dimensional (q1d) superconductivity is
investigated by applying the renormalization group techniques to the pairing
interaction. With the obtained renormalized pairing interaction, the transition
temperature Tc and corresponding gap function are calculated by solving the
linearized gap equation. For reasonable sets of parameters, Tc of p-wave
triplet pairing is higher than that of d-wave singlet pairing due to the
one-dimensionality of interaction. These results can qualitatively explain the
superconducting properties of q1d organic conductor (TMTSF)2PF6 and the ladder
compound Sr2Ca12Cu24O41.Comment: 18 pages, 9 figures, submitted to J. Phys. Soc. Jp
New analytic results for electroweak baryon number violation
Real-time anomalous fermion number violation has been investigated for
massless chiral fermions in spherically symmetric SU(2) Yang-Mills gauge field
backgrounds which can be weakly dissipative or even nondissipative. Restricting
consideration to spherically symmetric fermion fields, a relation has been
found between the spectral flow of the Dirac Hamiltonian and two
characteristics of the background gauge field. This new result may be relevant
to electroweak baryon number violation in the early universe.Comment: 7 pages with jhep3.cls, based on a talk at the International
Europhysics Conference on High Energy Physics, Budapest, 200
Mean Field Theoretical Structure of He and Be Isotopes
The structures of He and Be even-even isotopes are investigated using an
axially symmetric Hartree-Fock approach with a Skyrme-IIIls mean field
potential. In these simple HF calculations, He and Be isotopes appear to be
prolate in their ground states and Be isotopes have oblate shape isomeric
states. It is also shown that there exists a level crossing when the nuclear
shape changes from the prolate state to the oblate state. The single neutron
levels of Be isotopes exhibit a neutron magic number 6 instead of 8 and show
that the level inversion between 1/2- and 1/2+ levels occurs only for a largely
deformed isotope. Protons are bound stronger in the isotope with more neutrons
while neutron levels are somewhat insensitive to the number of neutrons and
thus the nuclear size and also the neutron skin become larger as the neutron
number increases. In these simple calculations with Skyrme-IIIls interaction no
system with a clear indication of neutron halo was found among He and Be
isotopes. Instead of it we have found 8He+2n, 2n+8He+2n, and 16Be+2n like chain
structures with clusters of two correlated neutrons. It is also shown that 8He
and 14Be in their ground states are below the neutron drip line in which all
nucleons are bound with negative energy and that 16Be in its ground state is
beyond the neutron drip line with two neutrons in positive energy levels.Comment: CM energy correction, 1 figure and more discussions adde
AUTOTEM - Automated geometry meshing and heat conduction calculation
Temperature distribution for an arbitrary irregular body is calculated by AUTOTEM, which generates required input data automatically by computer. Temperature distribution is calculated for a two-dimensional plane section in /x,y/ coordinates or for an axisymmetric irregular body in /r,z/ coordinates
- …