Impact of Approximation Error on the Decisions of LDPC Decoding

In this paper the impact of the approximation error on the decisions taken by LDPC decoders is studied. In particular, we analyze the mechanism, by means of which approximation error alters the decisions of a finite-word-length implementation of the decoding algorithm, with respect to the decisions taken by the infinite precision case, approximated here by double-precision floating-point. We focus on four popular algorithms for LDPC decoding, namely Log Sum-Product, Min-Sum, normalized Min-Sum and offset Min-Sum. A corresponding theoretical model is developed which derives an expression for the probability of altering the decision due to approximation. The model is applied to the above algorithms for the case of the first iteration as well as for higher numbers of iterations. Finally, experimental results prove the validity of the proposed model.     

An integrated semantic framework supporting universal accessibility to ICT

As we are moving rapidly to a digital economy, accessing and effectively using Information and Communication Technologies (ICT) in everyday life is widely recognized as an important requirement. However, the accessibility technologies that we have up to date are meeting the needs of only some, at a very high cost and, as a consequence, accessible ICT for all people still remains a major research and development goal. This work presents an integrated ontological framework for the semantic representation of terms and concepts (i.e., related to user needs and preferences (N&P) with respect to ICT use, as well as solutions, platforms and devices) that are required for addressing the universal accessibility in the scope of the Cloud4all project and the Global Public Inclusive Infrastructure (GPII). Cloud4all aims at advancing and building upon the concept of GPII through the development of the necessary tools and models for making ICT accessible for all by exploiting the cloud computing paradigm. The main goal of the proposed framework lays in the separation between generalized accessibility concepts, user interaction mechanisms and N&P with the particular details of different ICT artifacts. Thus, the framework aims at integrating concepts related with user N&P, as well as ICT solutions, platforms, devices and their customizable settings along with information concerning their vendors or implementers, in order to (a) offer the necessary expressiveness for defining/representing personal N&P across applications, platforms and devices, (b) link N&P with the conditions/context according to which these shall be applicable for (e.g., considering the user activity and the physical environment), (c) link interaction requirements (originated from user characteristics) with N&P and (d) support the Cloud4all matchmaking process through the mapping between N&P and application-specific settings based on semantic rules and automatic reasoning techniques.     

Calibrations scheduling with arbitrary lengths and activation length

Bender et al. (SPAA 2013) proposed a theoretical framework for testing in contexts where safety mistakes must be avoided. Testing in such a context is made by machines that need to be calibrated on a regular basis. Since calibrations have a non-negligible cost, it is important to study policies minimizing the total calibration cost while performing all the necessary tests. We focus on the single-machine setting, and we study the complexity status of different variants of the problem. First, we extend the model by considering that the jobs have arbitrary processing times, and we propose an optimal polynomial-time algorithm when the preemption of jobs is allowed. Then, we study the case where there are many types of calibrations with their corresponding lengths and costs. We prove that the problem becomes NP-hard for arbitrary processing times even when the preemption of the jobs is allowed. Finally, we focus on the case of unit processing time jobs, and we show that a more general problem, where the recalibration of the machine is not instantaneous, can be solved in polynomial time via dynamic programming.

     

The Granger-causality between income and educational inequality: a spatial cross-regressive VAR framework

This paper tests the causal processes between income and educational inequality within regions of the European Union, using a spatial cross-regressive VAR framework. The results show that there is a heterogeneous causality from income inequality to educational inequality and vice versa, and interregional income and educational externalities are relevant to this causality. This finding raises potentially interesting economic policy implications.     

Energy‐aware traffic allocation to optical lightpaths in multilayer core networks

The amount of traffic that is generated by users and high‐demanding services is expected to rise dramatically in the forthcoming years. This will unavoidably deteriorate the performance and increase the consumed energy of core networks, thus constraining the growth of Internet. To this effect, multilayer traffic engineering schemes in IP/multiprotocol label switching over dense wavelength division multiplexing networks have been proposed for achieving improved performance and increased energy savings by flexibly allocating traffic to optical lightpaths. In particular, the consumed energy in a router can be minimized if the lightpaths are established so as to traverse a router without electronic processing and conversion of their signal between optical and electrical layer. Accordingly, this paper aims at providing an energy‐aware solution to the problem of traffic allocation to optical lightpaths in multilayer core networks. The problem is first formulated and then a solution based on a heuristic algorithm, called energy‐aware traffic allocation to optical lightpaths (ETAL) is proposed. The efficiency and worthiness of ETAL is validated through numerous scenarios and simulations. The derived results indicate that the proposed algorithm is an efficient traffic engineering solution that exhibits better performance in terms of consumed energy (up to 44%), when compared to other similar traffic allocation schemes. Copyright © 2015 John Wiley & Sons, Ltd.     

Optimization of biogas production by co-digesting whey with diluted poultry manure

A series of laboratory experiments were performed in continuously stirred tank reactors at mesophilic conditions, fed semi-continuously with various mixtures of diluted poultry manure and whey. Co-digestion of whey with manure was proved to be possible without any need of chemical addition up to 50% participation of whey (by volume) to the daily feed mixture. Up to this point, specific biogas production (L/kg VS_in) remained roughly unchanged at the various whey fractions added in the feed mixture, mainly due to the lower chemical oxygen demand (COD) of whey compared to that of manure. At whey fractions above 50%, the reactor turned to be unstable, as shown by the considerable decrease in pH and biogas production. The experiments were scaled up to a continuously stirred pilot tank reactor, which had previously been acclimated to poultry manure digestion. Whey was gradually introduced in the feed, at increasing rates, replacing equivalent volumes of manure, in such a way, that total COD of the feed remained constant. For an hydraulic retention time of 18 days at 35 °C and organic loading rate of 4.9 g COD/L_R d, it was found that biogas production increased from 1.5 to 2.2 L/L_R d (almost 40%). This could be mainly attributed to the higher biodegradability of carbohydrates (main constituent of whey) compared to lipids (main constituent of manure) and to the correction (increase) of C:N ratio.     

Physical evaluation of a maize‐based extruded snack with curry powder

Response surface methodology was used to analyze the effect of screw speed (200–280 rpm), feed moisture (13.0–17.0%, wet basis), and curry powder (6.0–9.0%) on the bulk density, lateral expansion, and firmness of maize‐based extruded snack with curry powder. Regression equations describing the effect of each variable on the responses were obtained. Responses were most affected by changes in feed moisture followed by screw speed and curry powder (p < 0.05). Lateral expansion increased linearly as the amount of curry powder added was increased whereas a quadratic increase was obtained in lateral expansion with decreasing feed moisture. The firmness of samples was increased with an increase in feed moisture. The bulk density of samples was increased with increasing feed moisture and screw speeds. Radial expansion was found to be a better index to measure the physical properties of the extruded product indicated by a higher correlation coefficient.     

Design of product specifications and control policies in a single-stage production system

Screening (100%-inspection) is a common practice in quality engineering. Traditional screening procedures seek upper and lower specification limits for a quality characteristic associated with some product, such that the total quality cost per item is minimized. This practice ignores the effect of parts rejection on product lead times, inventory carrying costs, shortage costs, throughput, and, eventually, total profit rate of the system. In this paper, a single-stage production system is considered and two control policies arc determined jointly with the inspection plans. Numerical experiments indicate that such co-ordinated policies achieve a better performance than independently determined quality and production control policies     

Finite modeling of parabolic equations using Galerkin methods and inverse matrix approximations

In this paper we examine order reduction of parabolic systems using modal truncation. The parabolic distributed system is first approximated using the Galerkin method. The system matrices have a special structure that allows us to find the approximate spectrum of the parabolic system. To do this we compute approximate inverses of tridiagonal, diagonally dominant symmetric matrices. The approximation leads to algorithms of orderO(n), as opposed to traditional algorithms of orderO(n), wheren is the order of the system. Finally, an example is presented to illustrate the proposed algorithm.This research was supported by the National Science Foundation under contract NCR-9210408, by the Advanced Research Programs Agency under contract MDA-972-93-1-0032, and by the University of Hawaii Research Council Funds.     

Directed evolution on the cold adapted properties of TAB5 alkaline phosphatase

Psychrophilic alkaline phosphatase (AP) from the Antarctic strain TAB5 was subjected to directed evolution in order to identify the key residues steering the enzyme's cold-adapted activity and stability. A round of random mutagenesis and further recombination yielded three thermostable and six thermolabile variants of the TAB5 AP. All of the isolated variants were characterised by their residual activity after heat treatment, Michaelis-Menten kinetics, activation energy and microcalorimetric parameters of unfolding. In addition, they were modelled into the structure of the TAB5 AP. Mutations which affected the cold-adapted properties of the enzyme were all located close to the active site. The destabilised variants H135E and H135E/G149D had 2- and 3-fold higher kcat, respectively, than the wild-type enzyme. Wild-type AP has a complex heat-induced unfolding pattern while the mutated enzymes loose local unfolding transitions and have large shifts of the Tm values. Comparison of the wild-type and mutated TAB5 APs demonstrates that there is a delicate balance between the enzyme activity and stability and that it is possible to improve the activity and thermostability simultaneously as demonstrated in the case of the H135E/G149D variant compared to H135E.