Functional observers for dynamical systems

In control theory, a state observer is an auxiliary dynamical system that mirrors the behaviour of a physical system, and it is driven by input and output measurements of the physical system in order to provide an estimate of internal states of the physical system. The primary consideration in the design of an observer is that the estimate of the states should be close to the actual value of the system states. On the other hand, the functional observation problem centers on the construction of an auxiliary dynamical system, known as the functional observer or functional reconstructor, driven by the available system inputs and outputs in order to estimate a linear function or functions of the system states. Obviously, a functional observer is a general form of the state observer because when the linear functions are chosen as the individual states of the system then the problem of functional observation reduces to the problem of state observation.

Hierarchical representation for spatial knowledge

One of the fundamental issues in building autonomous agents is to be able to sense, represent and react to the world. Some of the earlier work [Mor83, Elf90, AyF89] has aimed towards a reconstructionist approach, where a number of sensors are used to obtain input that is used to construct a model of the world that mirrors the real world. Sensing and sensor fusion was thus an important aspect of such work. Such approaches have had limited success, and some of the main problems were the issues of uncertainty arising from sensor error and errors that accumulated in metric, quantitative models. Recent research has therefore looked at different ways of examining the problems. Instead of attempting to get the most accurate and correct model of the world, these approaches look at qualitative models to represent the world, which maintain relative and significant aspects of the environment rather than all aspects of the world. The relevant aspects of the world that are retained are determined by the task at hand which in turn determines how to sense. That is, task directed or purposive sensing is used to build a qualitative model of the world, which though inaccurate and incomplete is sufficient to solve the problem at hand. This paper examines the issues of building up a hierarchical knowledge representation of the environment with limited sensor input that can be actively acquired by an agent capable of interacting with the environment. Different tasks require different aspects of the environment to be abstracted out. For example, low level tasks such as navigation require aspects of the environment that are related to layout and obstacle placement. For the agent to be able to reposition itself in an environment, significant features of spatial situations and their relative placement need to be kept. For the agent to reason about objects in space, for example to determine the position of one object relative to another, the representation needs to retain information on relative locations of start and finish of the objects, that is endpoints of objects on a grid. For the agent to be able to do high level planning, the agent may need only the relative position of the starting point and destination, and not the low level details of endpoints, visual clues and so on. This indicates that a hierarchical approach would be suitable, such that each level in the hierarchy is at a different level of abstraction, and thus suitable for a different task. At the lowest level, the representation contains low level details of agent's motion and visual clues to allow the agent to navigate and reposition itself. At the next level of abstraction the aspects of the representation allow the agent to perform spatial reasoning, and finally the highest level of abstraction in the representation can be used by the agent for high level planning.

Treatment response for acute depression is not associated with number of previous episodes: lack of evidence for a clinical staging model for major depressive disorder

Mental illness has been observed to follow a neuroprogressive course, commencing with prodrome, then onset, recurrence and finally chronic illness. In bipolar disorder and schizophrenia responsiveness to treatment mirrors these stages of illness progression, with greater response to treatment in the earlier stages of illness and greater treatment resistance in chronic late stage illness.

Using data from 5627 participants in 15 controlled trials of duloxetine, comparator arm (paroxetine, venlafaxine, escitalopram) or placebo for the treatment of an acute depressive episode, the relationship between treatment response and number of previous depressive episodes was determined. Data was dichotomised for comparisons between participants who had >3 previous episodes (n=1697) or ≤3 previous episodes (n=3930), and additionally for no previous episodes (n=1381) or at least one previous episode (n=4246). Analyses were conducted by study arm for each clinical trial, and results were then pooled.

There was no significant difference between treatment response and number of previous depressive episodes. This unexpected finding suggests that treatments to reduce symptoms of depression during acute illness do not lose efficacy for patients with a longer history of illness.

Laboratory studies on the coupled oscillations between an internal density interface and a shear layer

The results from experiments conducted in a 2m high flow compartment at large Reynolds numbers are reported in this paper. Flow entered the compartment through an opening at the base on one side of the compartment and exited from an opening at the bottom of the opposite wall of the compartment. A shear layer is formed at the boundary between the incoming flow and the ambient fluid in the compartment. The impingement of the shear layer on the opposite wall of the compartment gives rise to periodic vortex formation and highly organized oscillations in the shear layer. When a density interface is present inside the compartment, resonance conditions were set up when the oscillations of the internal standing waves were “locked in” with the shear layer oscillations. Under resonance conditions, internal standing waves with amplitudes of up to 0.1m were observed. The formation of the internal standing waves is linked to the shear layer oscillations. Resonance conditions result when the shear layer is oscillating close to the natural frequency of the stratified fluid system in the compartment. The results of this investigation are applicable for fresh water storage in floating bottom-opened tanks in the sea, where under resonance conditions, entrainment rates could be significantly increased.

A biocompatible ionic liquid as an antiwear additive for biodegradable lubricants

A biocompatible ionic liquid, tributyl(methyl)phosphonium diphenylphosphate, P1444DPP (IL1) was investigated as an antiwear additive and compared against Amine Phosphate (AP), one of the commonly used conventional antiwear additives in biodegradable lubricants. IL1 showed excellent antiwear performance, using a pin-on-disc tribometer, when blended in biodegradable base stocks. The steel balls after the test were analyzed using SEM-EDS techniques which confirmed the presence of phosphorous. The tribological properties under reciprocating conditions were also carried out using Optimol SRV oscillating friction and wear tester and the steel discs were observed under Atomic Force Microscopy (AFM), to show the buildup of tribofilm formed by IL1. The thickness of the lubricant film was confirmed by Elastohydrodynamic (EHD) Ultra Thin Film Measurement System. It was observed that IL1 has a better film forming ability than AP. © 2014 Elsevier Ltd.

Three-dimensional numerical simulation of blood flow in mouse aortic arch around atherosclerotic plaques

Atherosclerosis is a progressive disease, involving the build-up of lipid streaks in artery walls, leading to plaques. Understanding the development of atherosclerosis and plaque vulnerability is critically important since plaque rupture can result in heart attack or stroke. Plaques can be divided into two distinct types: those likely to rupture (vulnerable) or less likely to rupture (stable). In the last decade, researchers have been interested in studying the influence of the mechanical effects (blood shear stress, pressure forces and structural stress) on the plaque formation, progression and rupture processes but no general agreement has been found. The purpose of the present work is to include more realistic conditions for the numerical calculations of the blood flow by implementing real geometries with plaques in the numerical model. Hemodynamical parameters are studied in both diseased and healthy configurations. The healthy configuration is obtained by removing numerically the plaques from three dimensional geometries obtained by micro-computed tomography. A new hemodynamical parameter is also introduced to relate the location of plaques to the characteristics of the flow in the healthy configuration. © 2014 .

Debris

Debris captures a moment of collision between the natural and built environment. Digital simulations conjure a strange version of gravity within the frame. This technique creates a surreal unease, breaking our expectations of figure and ground in traditional landscape photography. This unease mirrors the new landscape of natural disaster zones; where sea has blended with land and the built environment has been forced back into chaos.

Nearshore-offshore-basin species diversity and body size variation patterns in Late Permian (Changhsingian) brachiopods

 B.V. Body size is a fundamental and defining character of an organism, and its variation in space and time is generally considered to be a function of its biology and interactions with its living environment. A great deal of body size related ecological and evolutionary research has been undertaken, mostly in relation to extant animals. Among the many body size-related hypotheses proposed and tested, the size-bathymetry relationship is probably the least studied. In this study, we compiled a global body size dataset of Changhsingian (Late Permian, ca. 254. Ma-252. Ma) brachiopod species from low-latitude areas (30°S-30°N) and analyzed their species diversity and body size distribution patterns in relation to the nearshore-offshore-basin bathymetric gradient. The dataset contained 1768 brachiopod specimens in 435 species referred to 159 genera and 9 orders, from 135 occurrences (localities) of 18 different palaeogeographic regions. Treating the whole of the Changhsingian Stage as a single time slice, we divided the nearshore-offshore-basin bathymetric gradient into three broad depth-related environments: nearshore, offshore and basinal environments, and compared how the species diversity and body size varied along this large-scale bathymetric gradient.Here, we report an array of complex patterns. First, we found a clear overall inverse correlation between species diversity and water depth along the nearshore-offshore-basin gradient, with most species concentrating in the nearshore environment. Second, when the median sizes of all low-latitude brachiopod species from the three environments were compared, we found that there was no significant size difference between the nearshore and offshore environments, suggesting that neither the wave base nor the hydrostatic pressure exerts a critical influence on the body size of brachiopods. On the other hand, the median sizes of brachiopods from the nearshore environment and, to a lesser extent, the offshore environment were found to be significantly larger than that of basinal brachiopods. This trend of significant size reduction in basinal brachiopods mirrors the relative low species diversity in the basinal environment, and neither can be easily explained by the tendency of decreasing food availability towards deeper sea environments. Rather, both trends are consistent with the hypothesis of an expanding Oxygen Minimum Zone (OMZ) in the bathyal (slope to deepsea) environments, where hypoxic to anoxic conditions are considered to have severely restricted the diversification of benthos and favored the relative proliferation of small-sized brachiopods. Finally, a significant difference was also found between eurybathic and stenobathic species in their body size response to the nearshore-offshore-basin gradient, in that eurybathic species (species found in all three environments) did not tend to change their body size significantly according to depth, whereas stenobathic forms (species restricted to a single environment) exhibit a decline in body size towards the basinal environment. This pattern is interpreted to suggest that bathymetrically more tolerant species are less sensitive to depth control with respect to their body size change dynamics, in contrast to stenobathic species which tend to grow larger in shallower water depths.