The time dimension of neural network models

This review attempts to provide an insightful perspective on the role of time within neural network models and the use of neural networks for problems involving time. The most commonly used neural network models are defined and explained giving mention to important technical issues but avoiding great detail. The relationship between recurrent and feedforward networks is emphasised, along with the distinctions in their practical and theoretical abilities. Some practical examples are discussed to illustrate the major issues concerning the application of neural networks to data with various types of temporal structure, and finally some highlights of current research on the more difficult types of problems are presented

Self-motility of an active particle induced by correlations in the surrounding solution

Current models of phoretic transport rely on molecular forces creating a "diffuse" particle-fluid interface. We investigate theoretically an alternative mechanism, in which a diffuse interface emerges solely due to a non-vanishing correlation length of the surrounding solution. This mechanism can drive self-motility of a chemically active particle. Numerical estimates indicate that the velocity can reach micrometers per second. The predicted phenomenology includes a bilinear dependence of the velocity on the activity and a possible double velocity reversal upon varying the correlation length.Comment: 6 pages, 2 figures, and 22 pages of supplemental material. To be published as Phys. Rev. Let

Feather growth rate and mass in nearctic passerines with variablemigratory behavior and molt pattern

Bird species vary greatly in the duration of their annual complete feather molt. However, such variation is not well documented in birds from many biogeographic areas, which restricts our understanding of the diversification of molt strategies. Recent research has revealed that molt duration can be estimated in passerines from ptilochronology-based measurements of the growth rate of their tail feathers. We used this approach to explore how molt duration varied in 98 Nearctic species that have different migratory strategies and molt patterns. As previously documented for Palearctic species, migration was associated with a shortening of molt duration among species that molted during summer on their breeding range. However, molts of winter-molting migratory species were as long as those of summer-molting sedentary species, which suggests that winter molt also allows Nearctic migrants to avoid the temporal constraints experienced during summer. Our results also suggest that migratory species that undergo a stopover molt within the Mexican monsoon region have the shortest molt duration among all Nearctic passerines. Interestingly, and contrary to expectations from a potential tradeoff between molt duration and feather quality, observed variation in feather growth rate was positively correlated with differences in tail feather mass, which may be caused by differences among groups in the availability of resources for molting. We encourage the use of similar approaches to study the variation in molt duration in other geographic areas where knowledge of the evolution of molt is limited.

Self-Motility of an Active Particle Induced by Correlations in the Surrounding Solution

Current models of phoretic transport rely on molecular forces creating a “diffuse” particle-fluid interface. We investigate theoretically an alternative mechanism, in which a diffuse interface emerges solely due to a nonvanishing correlation length of the surrounding solution. This mechanism can drive self-motility of a chemically active particle. Numerical estimates indicate that the velocity can reach micrometers per second. The predicted phenomenology includes a bilinear dependence of the velocity on the activity and a possible double velocity reversal upon varying the correlation length.Spanish Government through Grant No. FIS2017-87117-P (partially financed by FEDER funds

Formulation, Interpretation and Application of non-Commutative Quantum Mechanics

In analogy with conventional quantum mechanics, non-commutative quantum mechanics is formulated as a quantum system on the Hilbert space of Hilbert-Schmidt operators acting on non-commutative configuration space. It is argued that the standard quantum mechanical interpretation based on Positive Operator Valued Measures, provides a sufficient framework for the consistent interpretation of this quantum system. The implications of this formalism for rotational and time reversal symmetry are discussed. The formalism is applied to the free particle and harmonic oscillator in two dimensions and the physical signatures of non commutativity are identified.Comment: 11 page

A Quantitative Analysis of Flight Feather Replacement in the Moustached Tree Swift Hemiprocne mystacea, a Tropical Aerial Forager

The functional life span of feathers is always much less than the potential life span of birds, so feathers must be renewed regularly. But feather renewal entails important energetic, time and performance costs that must be integrated into the annual cycle. Across species the time required to replace flight feather increases disproportionately with body size, resulting in complex, multiple waves of feather replacement in the primaries of many large birds. We describe the rules of flight feather replacement for Hemiprocne mystacea, a small, 60g tree swift from the New Guinea region. This species breeds and molts in all months of the year, and flight feather molt occurs during breeding in some individuals. H. mystacea is one to be the smallest species for which stepwise replacement of the primaries and secondaries has been documented; yet, primary replacement is extremely slow in this aerial forager, requiring more than 300 days if molt is not interrupted. We used growth bands to show that primaries grow at an average rate of 2.86 mm/d. The 10 primaries are a single molt series, while the 11 secondaries and five rectrices are each broken into two molt series. In large birds stepwise replacement of the primaries serves to increase the rate of primary replacement while minimizing gaps in the wing. But stepwise replacement of the wing quills in H. mystacea proceeds so slowly that it may be a consequence of the ontogeny of stepwise molting, rather than an adaptation, because the average number of growing primaries is probably lower than 1.14 feathers per wing

Noncommutative quantum mechanics -- a perspective on structure and spatial extent

We explore the notion of spatial extent and structure, already alluded to in earlier literature, within the formulation of quantum mechanics on the noncommutative plane. Introducing the notion of average position and its measurement, we find two equivalent pictures: a constrained local description in position containing additional degrees of freedom, and an unconstrained nonlocal description in terms of the position without any other degrees of freedom. Both these descriptions have a corresponding classical theory which shows that the concept of extended, structured objects emerges quite naturally and unavoidably there. It is explicitly demonstrated that the conserved energy and angular momentum contain corrections to those of a point particle. We argue that these notions also extend naturally to the quantum level. The local description is found to be the most convenient as it manifestly displays additional information about structure of quantum states that is more subtly encoded in the nonlocal, unconstrained description. Subsequently we use this picture to discuss the free particle and harmonic oscillator as examples.Comment: 25 pages, no figure

Application of Finite-Time and Control Thermodynamics to Biological Processes at Multiple Scales

An overall synthesis of biology and non-equilibrium thermodynamics remains a challenge at the interface between the physical and life sciences. Herein, theorems from finite-time and control thermodynamics are applied to biological processes to indicate which biological strategies will succeed over different time scales. In general, living systems maximize power at the expense of efficiency during the early stages of their development while proceeding at slower rates to maximize efficiency over longer time scales. The exact combination of yield and power depends upon the constraints on the system, the degrees of freedom in question, and the time scales of the processes. It is emphasized that biological processes are not driven by entropy production but, rather, by <i>informed exergy flow</i>. The entropy production is the generalized friction that is minimized insofar as the constraints allow. Theorems concerning thermodynamic path length and entropy production show that there is a direct tradeoff between the efficiency of a process and the process rate. To quantify this tradeoff, the concepts of <i>compensated heat</i> and <i>waste heat</i> are introduced. Compensated heat is the exergy dissipated, which is necessary for a process to satisfy constraints. Conversely, waste heat is exergy that is dissipated as heat, but does not provide a compensatory increase in rate or other improvement. We hypothesize that it is waste heat that is minimized through natural selection. This can be seen in the strategies employed at several temporal and spatial scales, including organismal development, ecological succession, and long-term evolution. Better understanding the roles of compensated heat and waste heat in biological processes will provide novel insight into the underlying thermodynamic mechanisms involved in metabolism, ecology, and evolution

Can sexual selection drive female life histories? A comparative study on Galliform birds

Sexual selection is an important driver of many of the most spectacular morphological traits that we find in the animal kingdom (for example see Andersson, 1994). As such, sexual selection is most often emphasized as

Web-Based Geologic Maps, Databases, and HTML Pages for Marion County, Indiana

This poster was presented at the 2011 meeting of the Indiana Academy of Science, 126th Annual Academy Meeting, March 4-5, 2011, Indianapolis, Indiana.The Indiana Geological Survey (IGS) has created an internet map server for Marion County in central Indiana. The site provides detailed geologic information needed to address environmental issues, resource management issues, and land-use conflicts related to a growing population. Marion County is the location of Indianapolis, the state capital and largest city. The IGS anticipates that the Web site will be widely used by the general public, industry, and government entities concerned about the geology, groundwater, and other natural resources. The Marion County Web site links an Internet map server (IMS) and database to provide a portal to the IGS‘s enterprise geodatabases, which allow users to efficiently create, manage, update, and distribute maps and data. The IMS site retrieves maps of bedrock and surficial geology completed during earlier IGS mapping projects. Hydrogeology, infrastructure, and imagery map layers are also included. Database information includes lithologic information (iLITH) compiled from water-well records stored in the Indiana Department of Natural Resources, Division of Water archives and natural gamma-ray geophysical log data, stratigraphic test hole data, and petroleum well-record data from the IGS. Currently, the following products are being prepared: (1) illustrated Web pages discussing the surficial geology, bedrock geology, and bedrock topography; (2) illustrated Web pages discussing digital elevation model terrain, gamma-ray log, iLITH, and clay thickness data sets; (3) online glossary; and (4) metadata for the map layers. The development of the Web site is funded by the IGS and the Great Lakes Geologic Mapping Coalition.Great Lakes Geologic Mapping Coalitio