The Loss Rank Principle for Model Selection

We introduce a new principle for model selection in regression and classification. Many regression models are controlled by some smoothness or flexibility or complexity parameter c, e.g. the number of neighbors to be averaged over in k nearest neighbor (kNN) regression or the polynomial degree in regression with polynomials. Let f_D^c be the (best) regressor of complexity c on data D. A more flexible regressor can fit more data D' well than a more rigid one. If something (here small loss) is easy to achieve it's typically worth less. We define the loss rank of f_D^c as the number of other (fictitious) data D' that are fitted better by f_D'^c than D is fitted by f_D^c. We suggest selecting the model complexity c that has minimal loss rank (LoRP). Unlike most penalized maximum likelihood variants (AIC,BIC,MDL), LoRP only depends on the regression function and loss function. It works without a stochastic noise model, and is directly applicable to any non-parametric regressor, like kNN. In this paper we formalize, discuss, and motivate LoRP, study it for specific regression problems, in particular linear ones, and compare it to other model selection schemes.Comment: 16 page

Noncontact atomic force microscopy II

Cataloged from PDF version of article.Background: Highly ordered three-dimensional colloidal crystals (supracrystals) comprised of 7.4 nm diameter Au nanocrystals (with a 5% size dispersion) have been imaged and analysed using a combination of scanning tunnelling microscopy and dynamic force microscopy. Results: By exploring the evolution of both the force and tunnel current with respect to tip-sample separation, we arrive at the surprising finding that single nanocrystal resolution is readily obtained in tunnelling microscopy images acquired more than 1 nm into the repulsive (i.e., positive force) regime of the probe-nanocrystal interaction potential. Constant height force microscopy has been used to map tip-sample interactions in this regime, revealing inhomogeneities which arise from the convolution of the tip structure with the ligand distribution at the nanocrystal surface. Conclusion: Our combined STM-AFM measurements show that the contrast mechanism underpinning high resolution imaging of nanoparticle supracrystals involves a form of nanoscale contact imaging, rather than the through-vacuum tunnelling which underpins traditional tunnelling microscopy and spectroscopy. © 2015 Sweetman et al; licensee Beilstein-Institut

Prevalence and Persistence of Pathogens in New York State Road-Kill Disposed of Through Composting: A Literature Review

Summary: Composting is being investigated by New York State Department of Transportation (NYSDOT) as a tool for managing road-killed animals in New York State, particularly white-tailed deer. As part of a project to evaluate the effectiveness of static pile composting to inactivate pathogens in road-killed carcasses, the Cornell Waste Management Institute conducted a literature review and consulted with experts to identify the pathogens that might be present and to assess their sensitivity to inactivation by heating.New York State Department of Transportatio

Perceived Red Tape and Precursors of Turnover: the Roles of Work Engagement and Career Adaptability

Drawing on job demands-resources theory, we propose that perceived red tape, as a hindrance job demand, triggers attitudinal and behavioral precursors of turnover in employees (turnover intentions and job search behaviors) by reducing their work engagement. In addition, we hypothesize that career adaptability, as a personal resource, buffers the detrimental effects of perceived red tape. In Study 1, three-wave data collected from employees (N = 202) working in Tanzanian public sector organizations supports the finding that work engagement mediates the effect of red tape on turnover intentions. Study 2 confirms this mediation, using data (N = 405) collected at three time points from a Chinese private organization, further verifying the mediating role of work engagement in the effect of red tape on job search behaviors. Supporting the moderating role of career adaptability, Study 2 also found that career adaptability attenuated the influence of red tape on work engagement and, subsequently, on turnover intentions and job search behaviors. Our article theoretically and empirically contributes to the understanding of how and when perceived red tape in organizations leads employees to consider leaving and prepare to leave

A Possible Hidden Population of Spherical Planetary Nebulae

We argue that relative to non-spherical planetary nebulae (PNs), spherical PNs are about an order of magnitude less likely to be detected, at distances of several kiloparsecs. Noting the structure similarity of halos around non-spherical PNs to that of observed spherical PNs, we assume that most unobserved spherical PNs are also similar in structure to the spherical halos around non-spherical PNs. The fraction of non-spherical PNs with detected spherical halos around them, taken from a recent study, leads us to the claim of a large (relative to that of non-spherical PNs) hidden population of spherical PNs in the visible band. Building a toy model for the luminosity evolution of PNs, we show that the claimed detection fraction of spherical PNs based on halos around non-spherical PNs, is compatible with observational sensitivities. We use this result to update earlier studies on the different PN shaping routes in the binary model. We estimate that ~30% of all PNs are spherical, namely, their progenitors did not interact with any binary companion. This fraction is to be compared with the ~3% fraction of observed spherical PNs among all observed PNs. From all PNs, ~15% owe their moderate elliptical shape to the interaction of their progenitors with planets, while \~55% of all PNs owe their elliptical or bipolar shapes to the interaction of their progenitors with stellar companions.Comment: AJ, in pres

Comet Machholz (C/2004 Q2): morphological structures in the inner coma and rotation parameters

Extensive observations of comet C/2004 Q2 (Machholz) were carried out between August 2004 and May 2005. The images obtained were used to investigate the comet's inner coma features at resolutions between 350 and 1500 km/pixel. A photometric analysis of the dust outflowing from the comet's nucleus and the study of the motion of the morphological structures in the inner coma indicated that the rotation period of the nucleus was most likely around 0.74 days. A thorough investigation of the inner coma morphology allowed us to observe two main active sources on the comet's nucleus, at a latitude of +85{\deg} \pm 5{\deg} and +45{\deg} \pm 5{\deg}, respectively. Further sources have been observed, but their activity ran out quite rapidly over time; the most relevant was at latcom. = 25{\deg} \pm 5{\deg}. Graphic simulations of the geometrical conditions of observation of the inner coma were compared with the images and used to determine a pole orientation at RA=95{\deg} \pm 5{\deg}, Dec=+35{\deg} \pm 5{\deg}. The comet's spin axis was lying nearly on the plane of the sky during the first decade of December 2004.Comment: 29 pages, 8 figures, 3 table

Exterior Differentials in Superspace and Poisson Brackets

It is shown that two definitions for an exterior differential in superspace, giving the same exterior calculus, yet lead to different results when applied to the Poisson bracket. A prescription for the transition with the help of these exterior differentials from the given Poisson bracket of definite Grassmann parity to another bracket is introduced. It is also indicated that the resulting bracket leads to generalization of the Schouten-Nijenhuis bracket for the cases of superspace and brackets of diverse Grassmann parities. It is shown that in the case of the Grassmann-odd exterior differential the resulting bracket is the bracket given on exterior forms. The above-mentioned transition with the use of the odd exterior differential applied to the linear even/odd Poisson brackets, that correspond to semi-simple Lie groups, results, respectively, in also linear odd/even brackets which are naturally connected with the Lie superalgebra. The latter contains the BRST and anti-BRST charges and can be used for calculation of the BRST operator cohomology.Comment: 12 pages, LATEX 2e, JHEP format. Correction of misprints. The titles for some references are adde