Cross-validated bagged learning

Many applications aim to learn a high dimensional parameter of a data generating distribution based on a sample of independent and identically distributed observations. For example, the goal might be to estimate the conditional mean of an outcome given a list of input variables. In this prediction context, bootstrap aggregating (bagging) has been introduced as a method to reduce the variance of a given estimator at little cost to bias. Bagging involves applying an estimator to multiple bootstrap samples and averaging the result across bootstrap samples. In order to address the curse of dimensionality, a common practice has been to apply bagging to estimators which themselves use cross-validation, thereby using cross-validation within a bootstrap sample to select fine-tuning parameters trading off bias and variance of the bootstrap sample-specific candidate estimators. In this article we point out that in order to achieve the correct bias variance trade-off for the parameter of interest, one should apply the cross-validation selector externally to candidate bagged estimators indexed by these fine-tuning parameters. We use three simulations to compare the new cross-validated bagging method with bagging of cross-validated estimators and bagging of non-cross-validated estimators.     

Extraction of chloride acido complexes of triply charged metal cations in water–oxyethylated nonylphenol–salting-out agent systems

The characteristic features of extraction of chloride acido complexes of iron(III), thallium(III), indium, and gallium in water–oxyethylated nonylphenol (neonol AF-9-12)–salting-out agent systems are studied. The role of temperature, nature of the salting-out agent, and its salting-out ability is shown.     

Nonparametric estimation of past extropy under $$\alpha $$ -mixing dependence condition

Ricerche di Matematica - Di Crescenzo and Longobardi (J Appl Prob 39, 434–440, 2002), introduced the concept of past entropy for measuring uncertainty contained in past lifetime of random...     

Constraints onZ 1–Z 2 mixing from the decayZ 1→e− e + in the left-right symmetric model

We examine the decay ofZ ₁ in electrons with recent data from LEP. The partial width (Z ₁e^– e ⁺) is studied in the framework of a left-right symmetric model with standard electroweak corrections. Processes measured near the resonance has served to measure the neutral coupling constants very precisely, which is useful to set bounds on the parameters of the model. This partial decay occurs in the resonance zone. As a consequence the process is independent of the mass of the additionalZ ₂ heavy gauge boson which appears in this kind of models and so we have the mixing angle between the left and the right bosons as the only additional parameter. In this paper we take advantage of this fact to set a bound for : –9×10^–34×10^–3, which is in agreement with other constraints previously reported.     

Theoretical studies on the deacylation step of serine protease catalysis in the gas phase, in solution, and in elastase

The deacylation step of serine protease catalysis is studied using DFT and ab initio QM/MM calculations combined with MD/umbrella sampling calculations. Free energies of the entire reaction are calculated in the gas phase, in a continuum solvent, and in the enzyme elastase. The calculations show that a concerted mechanism in the gas phase is replaced by a stepwise mechanism when solvent effects or an acetate ion are added to the reference system, with the tetrahedral intermediate being a shallow minimum on the free energy surface. In the enzyme, the tetrahedral intermediate is a relatively stable species ( approximately 7 kcal/mol lower in energy than the transition state), mainly due to the electrostatic effects of the oxyanion hole and Asp102. It is formed in the first step of the reaction, as a result of a proton transfer from the nucleophilic water to His57 and of an attack of the remaining hydroxyl on the ester carbonyl. This is the rate-determining step of the reaction, which requires approximately 22 kcal/mol for activation, approximately 5 kcal/mol less than the reference reaction in water. In the second stage of the reaction, only small energy barriers are detected to facilitate the proton transfer from His57 to Ser195 and the breakdown of the tetrahedral intermediate. Those are attributed mainly to a movement of Ser195 and to a rotation of the His57 side chain. During the rotation, the imidazolium ion is stabilized by a strong H-bond with Asp102, and the C(epsilon)(1)-H...O H-bond with Ser214 is replaced by one with Thr213, suggesting that a "ring-flip mechanism" is not necessary as a driving force for the reaction. The movements of His57 and Ser195 are highly correlated with rearrangements of the binding site, suggesting that product release may be implicated in the deacylation process.     

Direct covalent grafting of conjugated molecules onto Si, GaAs, and Pd surfaces from aryldiazonium salts

Using aryldiazonium salts that are air-stable and easily synthesized, we describe here a one-step, room-temperature route to direct covalent bonds between pi-conjugated organic molecules on three material surfaces: Si, GaAs, and Pd. The Si can be in the form of single crystal Si including heavily doped p-type Si, intrinsic Si, heavily doped n-type Si, on Si(111) and Si(100), and on n-type polycrystalline Si. The formation of the aryl-metal or aryl-semiconductor bond attachments was confirmed by corroborating evidence from ellipsometry, reflectance FTIR, XPS, cyclic voltammetry, and AFM analyses of the surface-grafted monolayers. A data-encompassing explanation for the mechanism suggests a diazonium activation by reduction at the open circuit potential, with aryl radical secondary products bonding to the surface. The synthetic details are included for preparing the surface-grafted monolayers and the precursor diazonium salts. This spontaneous diazonium activation reaction offers an attractive route to highly passivating, robust monolayers and multilayers on many surfaces that allow for strong bonds between carbon and surface atoms with molecular species that are near perpendicular to the surface.     

Synthesis and Molecular Structures of Hydrotris(dimethylpyrazolyl)borate Complexes of the Lanthanides

The reaction of lanthanide triflates with 2 equiv of potassium hydrotris(dimethylpyrazolyl)borate (Tp(Me)()2) gives good yields of complexes of composition Ln(Tp(Me)()2)(2)OTf. For La (2), Ce (3), Pr (4), and Nd (5) the complexes are seven-coordinate in the solid state with the triflate group coordinated to the metal in unidentate fashion. Complex 5 crystallizes in the monoclinic space group P2(1)/c with a = 17.629(3) ?, b = 12.740(2) ?, c = 18.163(3) ?, beta = 107.35(1) degrees, V = 3893(1) ?(3), Z = 4, and R(w) = 0.0458. For the complexes of Y (1), Sm (6), Eu (7), Gd (8), Dy (9), Ho (10), and Yb (11), the smaller size of the metal ion leads to ejection of the triflate from the coordination sphere and the complexes are ionic in the solid state with a six-coordinate metal center. Complex 11 crystallizes in the monoclinic space group C2/m with a = 16.593(7) ?, b = 13.671(5) ?, c = 8.746(2) ?, beta = 91.66(3) degrees, V = 1983(1) ?(3), Z = 2, and R(w) = 0.0416. In solution, however, complex 6 adopts a seven-coordinate molecular structure with the triflate ion within the first coordination sphere.     

Synthesis and aldol reactivity of o- and C-enolate complexes of nickel

The often facile C-/O-tautomerization of transition metal enolates is severely hindered in the cyclic Ni complexes 1 and 2, allowing the study of their individual reactivities. At room temperature only the O-bound tautomer, 2, reacts with aldehydes, giving rise to the corresponding addition products.     

PERMEATION OF GAS THROUGH NEWTON BLACK FILMS AT DIFFERENT CHAIN LENGTH OF THESURFACTANT

The gas permeability coefficients K (cm/s) of Newton black foam films stabilized by four alkyltrimefhylammonium chloride homologues have been measured. The experimental results demonstrate well pronounced dependence: K decreases with increasing surfactant alkyl chain length. The temperature dependence of K has been studied as well. The experimental data are discussed on the basis of the nucleation theory of fluctuation formation of holes in the foam bilayers, assuming that the gas permeation occurs both through holes and through hole-free part of the film (background permeability). The mechanism of permeation through the hole-free film is discussed using the theories of monolayer permeability. The results are in favour of the energy-barrier theory.