Semiparametric theory and empirical processes in causal inference

In this paper we review important aspects of semiparametric theory and empirical processes that arise in causal inference problems. We begin with a brief introduction to the general problem of causal inference, and go on to discuss estimation and inference for causal effects under semiparametric models, which allow parts of the data-generating process to be unrestricted if they are not of particular interest (i.e., nuisance functions). These models are very useful in causal problems because the outcome process is often complex and difficult to model, and there may only be information available about the treatment process (at best). Semiparametric theory gives a framework for benchmarking efficiency and constructing estimators in such settings. In the second part of the paper we discuss empirical process theory, which provides powerful tools for understanding the asymptotic behavior of semiparametric estimators that depend on flexible nonparametric estimators of nuisance functions. These tools are crucial for incorporating machine learning and other modern methods into causal inference analyses. We conclude by examining related extensions and future directions for work in semiparametric causal inference

The universe formation by a space reduction cascade with random initial parameters

In this paper we discuss the creation of our universe using the idea of extra dimensions. The initial, multidimensional Lagrangian contains only metric tensor. We have found many sets of the numerical values of the Lagrangian parameters corresponding to the observed low-energy physics of our universe. Different initial parameters can lead to the same values of fundamental constants by the appropriate choice of a dimensional reduction cascade. This result diminishes the significance of the search for the 'unique' initial Lagrangian. We also have obtained a large number of low-energy vacua, which is known as a 'landscape' in the string theory.Comment: 17 pages, 1 figur

Heat conduction in 1D lattices with on-site potential

The process of heat conduction in one-dimensional lattice with on-site potential is studied by means of numerical simulation. Using discrete Frenkel-Kontorova, $\phi$--4 and sinh-Gordon we demonstrate that contrary to previously expressed opinions the sole anharmonicity of the on-site potential is insufficient to ensure the normal heat conductivity in these systems. The character of the heat conduction is determined by the spectrum of nonlinear excitations peculiar for every given model and therefore depends on the concrete potential shape and temperature of the lattice. The reason is that the peculiarities of the nonlinear excitations and their interactions prescribe the energy scattering mechanism in each model. For models sin-Gordon and $\phi$--4 phonons are scattered at thermalized lattice of topological solitons; for sinh-Gordon and $\phi$--4 - models the phonons are scattered at localized high-frequency breathers (in the case of $\phi$--4 the scattering mechanism switches with the growth of the temperature).Comment: 26 pages, 18 figure

Observation of Parity Violation in the Omega-minus -> Lambda + K-minus Decay

The alpha decay parameter in the process Omega-minus -> Lambda + K-minus has been measured from a sample of 4.50 million unpolarized Omega-minus decays recorded by the HyperCP (E871) experiment at Fermilab and found to be [1.78 +/- 0.19(stat) +/- 0.16(syst)]{\times}10^{-2}. This is the first unambiguous evidence for a nonzero alpha decay parameter, and hence parity violation, in the Omega-minus -> Lambda + K-minus decay.Comment: 10 pages, 7 figure

HyperCP: A high-rate spectrometer for the study of charged hyperon and kaon decays

The HyperCP experiment (Fermilab E871) was designed to search for rare phenomena in the decays of charged strange particles, in particular CP violation in $\Xi$ and $\Lambda$ hyperon decays with a sensitivity of $10^{-4}$. Intense charged secondary beams were produced by 800 GeV/c protons and momentum-selected by a magnetic channel. Decay products were detected in a large-acceptance, high-rate magnetic spectrometer using multiwire proportional chambers, trigger hodoscopes, a hadronic calorimeter, and a muon-detection system. Nearly identical acceptances and efficiencies for hyperons and antihyperons decaying within an evacuated volume were achieved by reversing the polarities of the channel and spectrometer magnets. A high-rate data-acquisition system enabled 231 billion events to be recorded in twelve months of data-taking.Comment: 107 pages, 45 Postscript figures, 14 tables, Elsevier LaTeX, submitted to Nucl. Instrum. Meth.

Aggressions, social cognitions, anger and sadness in bullies and victims

Background: The present study aimed to investigate children's social information processing (SIP) and emotions in the bullying situation, taking into account reactive and proactive aggression. More specifically, we investigated the way in which children interpret social information, which goals they select, how they evaluate their responses and which emotions they express in hypothetical situations. Method: The participants comprised 242 Dutch children (120 girls and 122 boys; mean age: 117.2 months), who were assigned by means of peer nominations (Salmivalli, Lagerspetz, et al., 1996) to one of the following roles: bully (n = 21), follower of the bully (n = 38), victim (n = 35), defender of the victim (n = 48), outsider (n = 52) and not involved (n = 32). Sixteen children (including 3 bully/victims) were not given any role. The reactive and proactive aggression scale (Dodge, & Coie, 1987) was filled out by teachers in order to test the association between these types of aggression and involvement in bullying. Children were presented with ambiguous scenarios and responded to questions about attribution of intent, goal selection and emotions (anger and sadness). In addition, two questionnaires were administered to children: one assessed perceived self-efficacy in performing aggression, inhibiting aggression and using verbal persuasion skills, and the other assessed expected outcomes from behaving aggressively or prosocially. Results: Results showed that while reactive aggression was common in bullies and victims, proactive aggression was only characteristic of bullies. Both bullies and victims, compared to the other children, scored higher on hostile interpretation, anger, retaliation and ease of aggression. Bullies and followers claimed that it was easy for them to use verbal persuasion, while victims turned out to be the saddest group. All children, irrespective of their role in the peer group, thought that aggressive as well as prosocial behavior was more likely to produce desired results from a friendly peer than from an aggressive one. Conclusions: Bullies and victims seem to be similar in reactive aggression, SIP, and in the expression of anger, but the motivations which lead to their behavior may be different, as well as the final outcomes of their acts. © Association for Child Psychology and Psychiatry, 2004

Specific Heat of Liquid Helium in Zero Gravity very near the Lambda Point

We report the details and revised analysis of an experiment to measure the specific heat of helium with subnanokelvin temperature resolution near the lambda point. The measurements were made at the vapor pressure spanning the region from 22 mK below the superfluid transition to 4 uK above. The experiment was performed in earth orbit to reduce the rounding of the transition caused by gravitationally induced pressure gradients on earth. Specific heat measurements were made deep in the asymptotic region to within 2 nK of the transition. No evidence of rounding was found to this resolution. The optimum value of the critical exponent describing the specific heat singularity was found to be a = -0.0127+ - 0.0003. This is bracketed by two recent estimates based on renormalization group techniques, but is slightly outside the range of the error of the most recent result. The ratio of the coefficients of the leading order singularity on the two sides of the transition is A+/A- =1.053+ - 0.002, which agrees well with a recent estimate. By combining the specific heat and superfluid density exponents a test of the Josephson scaling relation can be made. Excellent agreement is found based on high precision measurements of the superfluid density made elsewhere. These results represent the most precise tests of theoretical predictions for critical phenomena to date.Comment: 27 Pages, 20 Figure

Superconducting transition in Pb/Co nanocomposites: effect of Co volume fraction and external magnetic field

Pb films embedded with homogeneously distributed cobalt (Co) nanoparticles (mean size 4.5 nm) have been prepared. Previous transport investigations have shown that Co particles induce spontaneous vortices below the superconducting transition temperature (T$_{c}$) in zero external magnetic field. In this paper we study in detail the influence of the Co volume franction and an external magnetic field on the superconducting transition in such composites. The large difference in T$_c$-reduction between the as-prepared and annealed samples can be attributed to the different superconducting coherence lengths and the resulting different diameters of the spontaneous vortices in these samples.Comment: 4 pages, 5 figure

The uses of coherent structure (Dryden Lecture)

The concept of coherent structure in turbulent flow is a revolutionary idea which is being developed by evolutionary means. The main objective of this review is to list some solid achievements, showing what can be done by using the concept of coherent structure that cannot be done without it. The nature of structure is described in terms of some related concepts, including celerity, topology, and the phenomenon of coalescence and splitting of structure. The main emphasis is on the mixing layer, as the one flow whose structure is well enough understood so that technical applications are now being made in problems of mixing and chemistry. An attempt is made to identify some conceptual and experimental obstacles that stand in the way of progress in other technically important flows, particularly the turbulent boundary layer. A few comments are included about the role of structure in numerical simulations and in current work on manipulation and control of turbulent flow. Some recent developments are cited which suggest that the time is nearly right for corresponding advances to occur in turbulence modeling