Threshold effects in the Teaching Space Allocation Problem with Splitting

Universities aim for good “Space Management” so as to use the teaching space efficiently. Part of this task is to assign rooms and time-slots to teaching activities with limited numbers and capacities of lecture theaters, seminar rooms, etc. It is also common that some teaching activities require splitting into multiple events. For example, lectures can be too large to fit in one room or good teaching practice requires that seminars/tutorials are taught in small groups. Then, space management involves decisions on splitting as well as the assignments to rooms and time-slots. These decisions must be made whilst satisfying the pedagogic requirements of the institution and constraints on space resources. The efficiency of such management can be measured by the “utilisation”: the percentage of available seat-hours actually used. In many institutions, the observed utilisation is unacceptably low, and this provides our underlying motivation: to study the factors that affect teaching space utilisation, with the goal of improving it. We give a brief introduction to our work in this area, and then introduce a specific model for splitting. We present experimental results that show threshold phenomena and associated easy-hard-easy patterns of computational difficulty. We discuss why such behaviour is of importance for space management.

Fatigue and biocompatibility properties of a poly(methyl methacrylate) bone cement with multi-walled carbon nanotubes

Composites of multi-walled carbon nanotubes (MWCNT) of varied functionality (unfunctionalised and carboxyl and amine functionalised) with polymethyl methacrylate (PMMA) were prepared for use as a bone cement. The MWCNT loadings ranged from 0.1 to 1.0 wt.%. The fatigue properties of these MWCNT–PMMA bone cements were characterised at MWCNT loading levels of 0.1 and 0.25 wt.% with the type and wt.% loading of MWCNT used having a strong influence on the number of cycles to failure. The morphology and degree of dispersion of the MWCNT in the PMMA matrix at different length scales were examined using field emission scanning electron microscopy. Improvements in the fatigue properties were attributed to the MWCNT arresting/retarding crack propagation through the cement through a bridging effect and hindering crack propagation. MWCNT agglomerates were evident within the cement microstructure and the degree of agglomeration was dependent on the level of loading and functionality of the MWCNT. The biocompatibility of the MWCNT–PMMA cements at MWCNT loading levels upto 1.0 wt.% was determined by means of established biological cell culture assays using MG-63 cells. Cell attachment after 4 h was determined using the crystal violet staining assay. Cell viability was determined over 7 days in vitro using the standard colorimetric MTT assay. Confocal scanning laser microscopy and SEM analysis was also used to assess cell morphology on the various substrates.

Fatigue Damage of Composite Structures Applying a Micromechanical Approach

Fatigue damage calculations of unidirectional polymer composites is presented applying micromechanics theory. An orthotropic micromechanical damage model is integrated with an isotropic fatigue evolution model to predict the micromechanical fatigue damage of the composite structure. The orthotropic micromechanical damage model is used to predict the orthotropic damage evolution within a single cycle. The isotropic fatigue model is used to predict the magnitude of fatigue damage accumulated as a function of the number of cycles. The advantage of using this approach is the cheap determination of model parameters since the orthotropic damage model parameters can be determined using available data from quasi-static loading tests. Decomposition of the state variables down to the constituent scale is accomplished by micromechanics theory. Phenomenological damage evolution models are then postulated for each constituent and for interphase among them. Comparison between model predictions and experimental data is presented.

Mechanical fatigue and spectrum analysis of small-satellite

Mechanical fatigue due to environmental loads and spectrum analysis due to launch loads of the primary structure of a low cost, low-earth orbit small satellite intended for earth observation missions are presented. The payload of the satellite under consideration is a precise optical unit to image the earth’s surface having a mass of 45 kg. 3-D Finite Element Model for the satellite structure is generated by applying substructure method. Modal analysis is required to determine natural frequencies of the satellite and define its mode shape. Then, ranking of mode shapes according to specific constraint is performed. Harmonic analysis at resonance frequencies with the highest ranking is done and cumulative fatigue damage analysis is performed. Spectrum analysis is performed for Small Sat structure to verify the satellite structure reliability under all dynamic random vibration loads applied during transportation and launch cases.

Thermal fatigue analysis of solar panel structure for micro-satellite applications

Thermal fatigue analysis based on 2D finite difference and 3D finite element methods is carried out to study the performance of solar panel structure during micro-satellite life time. Solar panel primary structure consists of honeycomb structure and composite laminates. The 2D finite difference (I-DEAS) model yields predictions of the temperature profile during one orbit. Then, 3D finite element analysis (ANSYS) is applied to predict thermal fatigue damage of solar panel structure. Meshing the whole structure with 2D multi-layer shell elements with sandwich option is not efficient, as it misses thermal response of the honeycomb structure. So we applied a mixed approach between 3D solid and 2D shell elements to model the solar panel structure without the sandwich option.

A micro-mechanics damage approach for fatigue of composite materials

A new model for fatigue damage evolution of polymer matrix composites (PMC) is presented. The model is based on a combination of an orthotropic damage model and an isotropic fatigue evolution model. The orthotropic damage model is used to predict the orthotropic damage evolution within a single cycle. The isotropic fatigue model is used to predict the magnitude of fatigue damage accumulated as a function of the number of cycles. This approach facilitates the determination of model parameters since the orthotropic damage model parameters can be determined from available data from quasi-static-loading tests. Then, limited amount of fatigue data is needed to adjust the fatigue evolution model. The combination of these two models provides a compromise between efficiency and accuracy. Decomposition of the state variables down to the constituent scale is accomplished by micro-mechanics. Phenomenological damage evolution models are then postulated for each constituent and for the micro-structural interaction among them. Model parameters are determined from available experimental data. Comparison between model predictions and additional experimental data is presented.

Thermal fatigue analysis of small-satellite structure

The small-satellite thermal subsystem main function is to control temperature ranges on equipments, and payload for the orbit specified. Structure subsystem has to ensure the satellite structure integrity. Structure integrity should meet two constraints; first constraint is accepted fatigue damage due to cyclic temperature, and second one is tolerable mounting accuracy at payload and Attitude Determination and Control Subsystem (ADCS) equipments’ seats. First, thermal analysis is executed by applying finitedifference method (IDEAS) and temperature profile for satellite components case is evaluated. Then, thermal fatigue analysis is performed applying finite-element analysis (ANSYS) to calculate the resultant damage due to on-orbit cyclic stresses, and structure deformations at the payload and ADCS equipments seats.

Fatigue in gynecological cancer patients during and after anticancer treatment

Research has indicated that individuals with gynecological cancer experience severe fatigue.

Cancer-related fatigue:A critical appraisal

This aim of this systematic review was to determine the prevalence and pattern of cancer-related fatigue (CRF), and identify factors associated with its development. Relevant literature was identified through an electronic database search using specified keywords. Included studies investigated CRF in adult cancer patients using a multidimensional fatigue measure. The methodological quality was assessed using six published standards. CRF is apparent both during and after anti-cancer therapy, however, the prevalence of CRF varied between studies. The variables associated with the development and persistence of CRF remain to be identified. Inconsistencies were evident in the pattern of CRF and its associated factors. This is likely to have arisen from the inherent difficulties in the measurement of a subjective sensation, further complicated by the myriad of outcome measures used. More methodologically sound research; assessing CRF from the commencement of therapy, considering all pertinent variables is needed.

Fatigue in gynaecological cancer patients:a pilot study

Fatigue is a frequent complaint of women with cancer. However, the incidence of fatigue has not been well studied, in particular gynaecological cancer, which despite its prevalence has received minimal investigation.