Analysis of irregular three-dimensional packing problems in additive manufacturing: a new taxonomy and dataset

With most Additive Manufacturing (AM) technology variants, build processes take place inside an internal enclosed build container, referred to as a ‘build volume’. It has been demonstrated that the effectiveness with which this volume is filled with product geometries forms an important determinant of overall process efficiency in AM. For effective operations management, it is important to understand not only the problem faced, but also which methods have proved effective (or ineffective) for problems with these characteristics in the past. This research aims to facilitate this increased understanding. The build volume packing task can be formulated as a three-dimensional irregular packing (3DIP) problem, which is a combinatorial optimisation problem requiring the configuration of a set of arbitrary volumetric items. This paper reviews existing general cutting and packing taxonomies and provides a new specification which is more appropriate for classifying the problems encountered in AM. This comprises a clear-cut problem definition, a set of precise categorisation criteria for objectives and problem instances, and a simple notation. Furthermore, the paper establishes an improved terminology with terms that are familiar to, but not limited to, researchers and practitioners in the field of AM. Finally, this paper describes a new dataset to be used in the evaluation of existing and proposed computational solution methods for 3DIP problems encountered in AM and discusses the importance of this research for further underpinning work.     

Reliability assessment of fire safety systems in railway industry: a case study

Within the framework of railroad transportation systems, there are currently system rooms where critical systems such as signalization are available. For the system to achieve an uninterrupted mode of operation, it is crucial to mitigate risks or hazards against the rooms and to ensure an acceptable level of safety. This study handles the protection of a system room, owned by Istanbul Ula??m A.?. Edirnekap? branch, against an incident of fire as a safety-related system practice. Within this scope, the fire safety system has been handled as a safety-related system identified in IEC 61508. The safety integrity level required by the safety lifecycle for the relevant system has also been identified and safety functions that are required to be implemented have been put forth. Taking IEC 61508 as a reference for the functions, the required analyses have been performed through fault tree analysis. It has also been guaranteed that the relevant functions have met the required safety levels.     

The effect of experimental stress on sarcoplasmic reticulum Ca(2+) transport and meat quality in pig muscle

Stress before slaughter affects the meat quality of pigs and a disorder in the Ca(2+) transport of the sarcoplasmic reticulum (SR) results in inferior meat quality. The object of this work was to determine the impact of stress on SR Ca(2+) transport in pig muscle in animals with no mutation in the Ca(2+) release channel. At about 80 kg live weight, pigs were stressed either by running for 4 min (n=9) or by a 5 min application of a nose snare (n=7). Immediately before and after the application of the stress, as well as 4 h after the stress, biopsy samples of the longissimus muscle were taken and the Ca(2+) uptake of the homogenised muscle samples determined. The nose snare stress reduced the rate of Ca(2+) uptake by 9% (P=0.02) and running by 18% (P=0.06). Uptake in samples taken 4 h after the stress was at initial levels. The pigs were slaughtered at an average live weight of 109 kg. Half the pigs were stressed just before slaughter for 5 min by the use of a nose snare. Immediately after exsanguination longissimus muscle samples were taken, Ca(2+) uptake measured, and later standard meat quality parameters were determined. Although the stress reduced the Ca(2+) uptake rate (61.3 vs. 46.4 nM/min per mg protein for control and stressed pigs; P=0.04), the meat quality was not significantly affected.     

The Reaction-Bonded Aluminum Oxide (RBAO) Process: II, The Solid-State Oxidation of RBAO Compacts

The oxidation kinetics and the fraction of aluminum that is oxidized via solid–gas reaction in reaction-bonded aluminum oxide (RBAO) compacts are shown to be strongly dependent on the oxidation temperature and the characteristics (size and green density) of the RBAO compact. Based on the Biot number, the oxidation process of RBAO compacts is controlled by convective heat transfer. Low heat transfer from the surface of the compact results in too-rapid oxidation, thermal gradients, and core–shell oxidation of the compacts. Uniform oxidation of RBAO compacts is possible by oxidizing at low temperatures (400°–470°C), where slow surface reaction of the aluminum particles controls the oxidation of the compact. A grain model is presented to cover both linear and nonlinear oxidation regimes during the oxidation of a RBAO compact, and this model predicts the experimental results when surface reaction of the aluminum particles is the rate-controlling mechanism and oxidation of the compact occurs uniformly.     

Cell injury and meat quality of pig in the time period post mortem from two genotypes susceptible or resistant to malignant hyperthermia

 Muscles of pigs with mutated calcium release channels show increased metabolic activities, and ultimately inferior meat quality results. Different cellular changes in the time period post mortem (PM) are reported by investigating longissimus samples obtained immediately after death (0 h), 45 min PM, 4 h PM, and 22 h PM. The meat quality of such malignant hyperthermia susceptible (MHS) pigs was inferior to that of malignant hyperthermia resistant (MHR) pigs. Histological analysis of muscle fibres showed an enhanced rate and extent of the development of extracellular spaces in MHS muscle compared to MHR muscle in the time period PM. The permeability of crude sarcoplasmic reticulum (SR) to Ca²⁺ increased at a higher rate in MHS than in MHR muscle. Total muscle phospholipids contained a higher concentration of long chain n-3 fatty acids in MHS compared with MHR animals immediately after slaughter. The MHS homogenate lipids were more susceptible to stimulated peroxidation by Fe²⁺/ascorbate in samples obtained 45 min PM and 4 h PM, but there were no differences between the two genotypes for 0 h PM and 22 h PM samples, suggesting a retarded consumption of antioxidants in MHR compared to MHS muscle. The results suggest that in addition to the well-known denaturation of proteins, altered biochemical processes in muscle cells of stress-susceptible pigs cause injury to cell membranes as well as to SR membranes early in the time period PM. Received: 24 July 1998 / Revised version: 25 September 1998     

Therapeutic results with Cerebrolysin in the treatment of dementia

BACKGROUND: In the present study patients suffering from dementia were treated with an infusion therapy using the neurotrophic drug Cerebrolysin. The effectiveness of the therapy was examined under conditions of daily clinical practice. METHODS: 645 Patients were treated with 30 ml Cerebrolysin daily. The average period of treatment was 17.8 days. Prior to treatment patients were diagnosed according to DSM-III-R. In addition a differential diagnostic examination using the Hachinski Ischemic Score was performed. Clinical symptoms and the Clinical Global Impression (CGI) were determined before and after therapy. RESULTS: Cerebrolysin therapy led to a significant (p < 0.001) improvement in memory for 62% of the patients. 65% showed improvement in concentration, 50% in mood and fatigue, and 47% improved in vertigo. An improvement in the Clinical Global impression was observed in approximately 80% of the patients. The improvement of symptoms was significantly larger (p < 0.05) in younger, less afflicted patients than in the older, more seriously ill patients. The unusual good tolerance of Cerebrolysin was especially noteworthy. CONCLUSIONS: The present study confirms the results of earlier clinical studies with Cerebrolysin in the treatment of Alzheimer patients and patients with vascular dementia in which similar responder rates were observed. The significant dependence of therapeutic success on the length and severity of illness confirms that timely pharmacological intervention leads to best therapeutic results.     

Fair and efficient Transmission Control Protocol access in the IEEE 802.11 infrastructure basic service set

When the stations in an IEEE 802.11 infrastructure basic service set employ Transmission Control Protocol (TCP), this exacerbates per‐flow unfair access problem. We propose a novel analytical model to approximately calculate the maximum per‐flow TCP congestion window limit that prevents packet losses at the access point buffer and therefore provides fair TCP access both in the downlink and uplink. The proposed analysis is unique in considering the effects of varying number of uplink and downlink TCP flows, differing round trip times among TCP connections and the use of delayed TCP acknowledgment (ACK) mechanism. Motivated by the findings of this theoretical analysis and simulations, we design a link layer access control block to be employed only at the access point in order to resolve the unfair access problem. The proposed link layer access control block uses congestion control and ACK filtering approach by prioritizing the access of TCP data packets of downlink flows over TCP ACK packets of uplink flows. Via simulations, we show that the proposed algorithm can provide both short‐term and long‐term fair accesses while improving channel utilization and access delay. Copyright © 2013 John Wiley & Sons, Ltd.     

A high-temperature solar source of heat for a thermophotovoltaic generator: Theory and experiment

The selection of the geometrical parameters of a tungsten receiver-emitter for a solar thermophotovoltaic generator with a searchlight-type paraboloid mirror is substantiated theoretically. An experimental instrument equipped with an evacuated receiver of solar radiation is presented, and an experimental setup equipped with a concentration system tracking the Sun is described. It is confirmed that the calculated estimates that were obtained are correct, and it is demonstrated that the receiver can be heated to a temperature of 1900 K using a single-mirror concentrating system.     

Preslaughter handling of pigs and the effect on heart rate, meat quality, including tenderness, and sarcoplasmic reticulum Ca(2+) transport

It is known that stress applied to pigs can be of influence on meat quality combined with disturbed regulation of the intracellular Ca²⁺ concentration. However, the effect on meat tenderness is not sufficiently known.

In an experiment with pigs two kinds of stress (immobilisation by a nose snare (nose) and the use of an electrical goad (goad)) for 5 min just before slaughter were used and the results compared with minimum stress pigs (control). To quantify the level of stress, the heart rate during stress application was determined and it was found that the stress effect was highest in the goad pigs and surprisingly decreasing during the use of a nose snare. The meat quality did not differ between nose and control pigs, but was inferior in the goad group. Also, the goad stress significantly reduced the Ca²⁺ transport of the sarcoplasmic reticulum.

The principal hypothesis, that a disturbed Ca²⁺ transport will affect the tenderness by activating the calpain system, could not be verified. Tenderness did not differ between experimental groups using 24 h post-mortem samples, neither was there a difference in tenderness after storing the meat samples for 6 days.     

Effects of process variables on some quality properties of meatballs semi-cooked in a continuous type ohmic cooking system

Ohmic cooking of meatballs was conducted in a continuous type ohmic cooker using different voltage gradients (15, 20 and 25 V/cm) and holding times (0, 15 and 30 s). The color and textural properties and log reductions in total microbial count of the meatballs were assessed. The effects of process variables on these responses were evaluated by linear and quadratic mathematical models. Desirability function was used to determine the optimum ohmic pre-cooking condition by considering the criteria of minimizing hardness ratio, and maximizing chewiness ratio, resilience ratio, log reduction in microbial load, outside chroma ratio, inside chroma ratio and in range of springiness, gumminess and inside L ratios. The optimum ohmic pre-cooking condition was found to be a 15.26 V/cm voltage gradient with no holding time. It is concluded that application of the optimum condition in the related ohmic system offers potential for the production of high quality and safe semi-cooked meat products.