Evaluation Procedures for Forecasting with Spatiotemporal Data

The increasing use of sensor networks has led to an ever larger number of available spatiotemporal datasets. Forecasting applications using this type of data are frequently motivated by important domains such as environmental monitoring. Being able to properly assess the performance of different forecasting approaches is fundamental to achieve progress. However, traditional performance estimation procedures, such as cross-validation, face challenges due to the implicit dependence between observations in spatiotemporal datasets. In this paper, we empirically compare several variants of cross-validation (CV) and out-of-sample (OOS) performance estimation procedures, using both artificially generated and real-world spatiotemporal datasets. Our results show both CV and OOS reporting useful estimates, but they suggest that blocking data in space and/or in time may be useful in mitigating CV’s bias to underestimate error. Overall, our study shows the importance of considering data dependencies when estimating the performance of spatiotemporal forecasting models.

Logic of Representation and Information

<p>Classical reality is described in terms of objects and things and their mutual relationships. On the other hand, in the case of quantum reality, the collapse of the state in an interaction assigns a unique position to the observer. These two disparate views are based on different logics of representation. In this paper, we first summarize the early evolution of these ideas and then go beyond the implicit dependence of the quantum theory framework on the mathematical apparatus of calculus and vector spaces, by delving one layer deeper to an information-theoretic understanding of symbol representation. We examine some epistemic implications of the fact that, mathematically, <i>e</i>-symbol representation is optimal and 3 symbols are more efficient that 2 symbols, and this optimality leads to the idea that space itself is <i>e</i>-dimensional, and not 3-dimensional. We also discuss the principle of veiled nonlocality as a way to understand the split between the observer and the physical process. </p>

Logic of Representation and Information

<p>Classical reality is described in terms of objects and things and their mutual relationships. On the other hand, in the case of quantum reality, the collapse of the state in an interaction assigns a unique position to the observer. These two disparate views are based on different logics of representation. In this paper, we first summarize the early evolution of these ideas and then go beyond the implicit dependence of the quantum theory framework on the mathematical apparatus of calculus and vector spaces, by delving one layer deeper to an information-theoretic understanding of symbol representation. We examine some epistemic implications of the fact that, mathematically, <i>e</i>-symbol representation is optimal and 3 symbols are more efficient that 2 symbols, and this optimality leads to the idea that space itself is <i>e</i>-dimensional, and not 3-dimensional. We also discuss the principle of veiled nonlocality as a way to understand the split between the observer and the physical process. </p>

The renormalization group and the effective potential in the Wess–Zumino model

We consider the effective potential V in the massless Wess–Zumino model. By using the renormalization group equation, we show that the explicit and implicit dependence of V on the renormalization mass scale μ cancels. If V has an extremum at some non-vanishing value of the background field, then it follows that V is “flat”, independent of the background field. This is consistent with the general requirement that V be convex. The consequences for supersymmetric gauge theories are briefly considered.

von Kármán self-preservation hypothesis for magnetohydrodynamic turbulence and its consequences for universality

We argue that the hypothesis of preservation of shape of dimensionless second- and third-order correlations during decay of incompressible homogeneous magnetohydrodynamic (MHD) turbulence requires, in general, at least two independent similarity length scales. These are associated with the two Elsässer energies. The existence of similarity solutions for the decay of turbulence with varying cross-helicity implies that these length scales cannot remain in proportion, opening the possibility for a wide variety of decay behaviour, in contrast to the simpler classic hydrodynamics case. Although the evolution equations for the second-order correlations lack explicit dependence on either the mean magnetic field or the magnetic helicity, there is inherent implicit dependence on these (and other) quantities through the third-order correlations. The self-similar inertial range, a subclass of the general similarity case, inherits this complexity so that a single universal energy spectral law cannot be anticipated, even though the same pair of third-order laws holds for arbitrary cross-helicity and magnetic helicity. The straightforward notion of universality associated with Kolmogorov theory in hydrodynamics therefore requires careful generalization and reformulation in MHD.

Hackers and Cyber Terrorists

Many aspects of our modern society now have either a direct or implicit dependence upon information technology (IT). As such, a compromise of the availability or integrity in relation to these systems (which may encompass such diverse domains as banking, government, health care, and law enforcement) could have dramatic consequences from a societal perspective.

Hackers and Cyber Terrorists

Many aspects of our modern society now have either a direct or implicit dependence upon information technology (IT). As such, a compromise of the availability or integrity in relation to these systems (which may encompass such diverse domains as banking, government, health care, and law enforcement) could have dramatic consequences from a societal perspective.

The Additive Ep-Condition and the Critical Scuffing Limit for Rolling-Sliding

This paper introduces a new model for the scuffing load capacity in heavily loaded contacts, concerned specifically with the effects of EP-additive oils. The scuffing limit for the additive condition will be closely related to the initial additive-free case, using the calculation method of Blok, solely on a referential level. The process thermodynamics involved at a friction contact will be related to a phenomenological integral relation, containing the necessary internal coordinate to describe the implicit dependence of the friction coefficient with time. The experimental response of the friction contact depends on a relaxant friction coefficient due to the additive effect. The simple calculation method requires only three input parameters for the prediction of the scuffing limit, and these can be obtained from a few experimental scuffing tests. All the tribology of the present scuffing model can be considered to be contained in a simple linear relationship, with the sliding speed as the dominant variable. The calculation criterion has shown to have predictive capability which agrees well with experiments.