On second-order cone positive systems

Internal positivity offers a computationally cheap certificate for external (input-output) positivity of a linear time-invariant system. However, the drawback with this certificate lies in its realization dependency. Firstly, computing such a realization requires to find a polyhedral cone with a potentially high number of extremal generators that lifts the dimension of the state-space representation, significantly. Secondly, not all externally positive systems posses an internally positive realization. Thirdly, in many typical applications such as controller design, system identification and model order reduction, internal positivity is not preserved. To overcome these drawbacks, we present a tractable sufficient certificate of external positivity based on second-order cones. This certificate does not require any special state-space realization: if it succeeds with a possibly non-minimal realization, then it will do so with any minimal realization. While there exist systems where this certificate is also necessary, we also demonstrate how to construct systems, where both second-order and polyhedral cones as well as other certificates fail. Nonetheless, in contrast to other realization independent certificates, the present one appears to be favourable in terms of applicability and conservatism. Three applications are representatively discussed to underline its potential. We show how the certificate can be used to find externally positive approximations of nearly externally positive systems and demonstrated that this may help to reduce system identification errors. The same algorithm is used then to design state-feedback controllers that provide closed-loop external positivity, a common approach to avoid over- and undershooting of the step response. Lastly, we present modifications to generalized balanced truncation such that external positivity is preserved where our certificate applies

Adaptive cancelation of self-generated sensory signals in a whisking robot

Sensory signals are often caused by one's own active movements. This raises a problem of discriminating between self-generated sensory signals and signals generated by the external world. Such discrimination is of general importance for robotic systems, where operational robustness is dependent on the correct interpretation of sensory signals. Here, we investigate this problem in the context of a whiskered robot. The whisker sensory signal comprises two components: one due to contact with an object (externally generated) and another due to active movement of the whisker (self-generated). We propose a solution to this discrimination problem based on adaptive noise cancelation, where the robot learns to predict the sensory consequences of its own movements using an adaptive filter. The filter inputs (copy of motor commands) are transformed by Laguerre functions instead of the often-used tapped-delay line, which reduces model order and, therefore, computational complexity. Results from a contact-detection task demonstrate that false positives are significantly reduced using the proposed scheme

In search for the not-invented-here syndrome: The role of knowledge sources and firm success

The not-invented-here (NIH) syndrome refers to internal resistance in a company against externally developed knowledge. In this paper, we argue that the occurrence of the NIH syndrome depends on the source of external knowledge and the success of the firm that aims at adapting external knowledge. In line with social identity theory, we hypothesize that internal resistance is most likely to occur if knowledge is acquired from similar organizations. This hypothesis is supported by our finding that the NIH syndrome occurs when knowledge is acquired from competitors but not if knowledge is acquired from suppliers, customers or universities. Further, we show that successful companies are most likely to experience the NIH syndrome (if knowledge is acquired from competitors). This is in line with our hypothesis that firm success increases the extent to which employees identify themselves with their company resulting in stronger in-group favoritism and a superior tendency to reject externally generated knowledge. --Not-invented-here syndrome,external knowledge sources,firm success,social identity theory,organizational identity

Adsorption-like Collapse of Diblock Copolymers

A linear copolymer made of two reciprocally attracting N-monomer blocks collapses to a compact phase through a novel transition, whose exponents are determined with extensive MC simulations in two and three dimensions. In the former case, an identification with the statistical geometry of suitable percolation paths allows to predict that the number of contacts between the blocks grows like $N^{9/16}$. In the compact phase the blocks are mixed and, in two dimensions, also zipped, in such a way to form a spiral, double chain structure.Comment: 4 pages, 5 Postscript figure

The impact of the global financial crisis on industry growth

© 2014 The Authors. The Manchester School published by The University of Manchester and John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.This article has been made available through the Brunel Open Access Publishing Fund.This article investigates the real effects of the recent global financial crisis by using industry panel data across 82 countries. We find that industry growth indicators experienced a sharp drop following the crisis. However, a closer inspection indicates that an adverse effect is pronounced in industries that are more dependent on external finance, and also in those industries that rely on trade credit due to under-developed financial intermediation. It is also found that low- and lower-middle income countries tend to experience a lesser impact on growth. These findings provide new evidence of the negative externalities associated with credit-market friction

Vocation, motivation and approaches to learning: a comparative study

Purpose – The individual characteristics of students can have a strong influence on the success of the adopted innovations in terms of their transferability and sustainability. The purpose of this paper is to compare the motivations and approaches to learning on degrees with differing vocational components. Design/methodology/approach – Self-Determination Theory (SDT) and approaches to learning framework were used as theoretical background. Questionnaires were used to generate data. The sample was composed by 270 students enroled on differing degrees in term of motivation (accounting and nursing). Findings – The results reveal differences in the approaches to learning and motivation between nursing and accounting students. Nursing degree seem to attract more internally motivated students, presenting significantly higher scores in terms of deep approach and lower scores on surface approach. Significant relationships where found between motivation and approaches. Research limitations/implications – Data are obtained from students studying at a specific university in two degrees. Practical implications – The result suggest that different degrees could attract students with different motivations and approaches to learning. Educators must be aware of which type of students are being attracted to their classrooms, because the inconsistencies between the students’ motives and approaches, the way the contents are presented, the pedagogy and the assessment system could result in poorer learning and failure to transfer or sustain innovations. Originality/value – This paper adds to the very scarce literature linking motivation and approaches. The implications for curriculum design and delivery and specifically for assessment design are of interest for educators.Junta de Andalucía – FEDER (Proyectos de Excelencia: SEJ-02670