1,281 results for Conference paper

  • A simulation model for the dynamic allocation of network resources in a competitive wireless scenario

    Beltran, Fernando; Roggendorf, Matthias (2006)

    Conference paper
    The University of Auckland Library

    An open access copy of this article is available and complies with the copyright holder/publisher conditions. Next-generation wireless networks will enable the usage of different network technologies fully transparent to the user. Applications will be able to dynamically adapt to the conditions and technical constraints of the network. This vision requires a dynamic allocation of scarce network resources to different users. This paper presents simulation results from a model of admission control and dynamic resource allocation in wireless networks, in a two-provider, multiple-user scenario. The access allocation and connection procedure is implemented using an efficient (welfare maximizing) incentive mechanism for capacity allocation at both providers.

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  • Feedback model for an insect circadian clock

    Lewis, Robert D. (1988)

    Conference paper
    The University of Auckland Library

    An open access copy of this article is available and complies with the copyright holder/publisher conditions. Hemideina thoracica is a nocturnal orthopteran insect which exhibits clear circadian locomotor rhythmicity in constant conditions. Analysis of the free-running rhythms leads to the hypothesis that the underlying clock mechanism has two major interacting components, one responsible for the overt locomotor rhythm, and another whose output is not directly related to locomotor activity. A model comprising two linked populations of feedback oscillators accounts for much of the free-run liability seen in the real data.

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  • Statistical modeling of speech feature vector trajectories based on a piecewise continuous mean path

    Thomson, Mark M. (1995)

    Conference paper
    The University of Auckland Library

    An open access copy of this article is available and complies with the copyright holder/publisher conditions. One of the key tasks in speech recognition based on statistical methods is the calculation of the class conditional probability density. This paper presents a new statistical model of the trajectories of speech feature vectors. In this model each vector is assumed to correspond to a point on a mean path that consists of a number of concatenated straight line segments. The model characterizes both the deviation of the trajectory from the mean path and the deviation from the mean rate at which the vectors move through the vector space in a way that avoids the conditional independence assumption implicit in hidden Markov modeling. The model is formulated using a state space approach in which the state vector consists of only two elements. These represent the position on the mean path corresponding to the present observation vector and the rate at which points on the mean path are moving through the vector space. A method for estimating the parameters of the model using the Expectation Maximization algorithm is presented

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  • A preliminary study of the effect of surface coating on the initial deposition mechanisms of dairy fouling.

    Ramachandra, S. S.; Wiehe, S.; Hyland, M. M.; Bansal, B. (2005)

    Conference paper
    The University of Auckland Library

    An open access copy of this article is available and complies with the copyright holder/publisher conditions. Modification of heat transfer surfaces to minimize the effects of fouling in the dairy industry is investigated in the current study. Special attention is given to the initial deposition mechanisms, which are believed to determine the fouling and cleaning performance of the surfaces studied. Preliminary results have been obtained for stainless steel and titanium nitride (TiN) surfaces fouled for 3 minutes with whey protein and calcium phosphate. Scanning Electron Microscopy (SEM) images of air-dried, whey protein fouled samples showed both TiN and stainless steel surfaces were covered with a thin layer of deposit, following the topography of the heating surface. X-ray Photoelectron Spectroscopy (XPS) spectra for the TiN surfaces fouled with whey protein showed carbon and oxygen as the main components present. XPS analysis of the stainless steel surfaces is currently underway. Calcium phosphate fouling on stainless steel and TiN surfaces resulted in formation of a crystal matrix on some parts of the surface, while other parts appeared to have no deposition. X-ray microanalysis of these crystals yielded a Ca/P ratio of 1.4. X-ray Diffraction (XRD) analysis is being undertaken to better identify the phases formed. Also in consideration is SEM analysis under cryogenic conditions, and XPS analysis of freeze-dried samples to eliminate changes taking place during air-drying. Future experiments will involve fouling of diamond-like carbon (DLC) surfaces. It is expected that altering the fouling behavior and therefore deposit adhesion, may influence cleaning performance, which will be tested in cleaning runs. At a later stage, similar investigations will be performed using milk solutions to study the combined effect of proteins and minerals.

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  • Aropä and PeerWise: Supporting Student Contributed Pedagogy in Large Classes

    Hamer, John (2009)

    Conference paper
    The University of Auckland Library

    EDUCAUSE Australasia 2009, Perth Western Australia. 3‐6 May 2009 http://www.caudit.edu.au/educauseaustralasia09/. Aropä and PeerWise are two web-based tools that support collaborative learning in large, undergraduate classes. Aropä manages peer assessment activities, allowing students to take part in double-blind refereeing of their peers’ coursework. PeerWise is a data bank of multi-choice questions contributed, explained and discussed entirely by students. These systems leverage the latent intellectual capacity of a large class to provide new opportunities for learning. Using Aropä, each student might review three or four essays and receive a corresponding amount of feedback, all within a few days. The immediacy and diversity of the feedback is substantially greater than can be produced by a tutor. While the quality of the reviewing is typically variable, there are affective benefits in challenging students to distinguish between good and poor feedback. By eliminating the stamp of authority and introducing diverse, possibly conflicting feedback, students are required to exercise their critical judgement in deciding what information to accept and reject. Moreover, tutor marking can still be used, and can even be mixed in with the peer reviewing. PeerWise leverages the energy of a large class in a different way, building an annotated question bank that can contain thousands of multiple-choice questions. Each question is accompanied by an explanation written by the question author, overall quality and difficult ratings assigned by students who have answered the question, and possibly a forum in which misunderstandings and possible improvements are discussed. The question bank thus serves two complementary purposes: a creative medium in which students engage in deep learning and critical reflection; and a drill-and-test library for developing fluency with the course content. We have statistical evidence to show that active use of these tools strongly correlates with learning. Further, as a side-effect of channelling all interaction through a central database, a detailed record of student interaction is collected. This record allows instructors to monitor overall class performance and to assess individual students over time in modes that limit opportunities for plagiarism. With routine use, a rich picture of student performance is collected. We are currently at the point of building additional tools to further exploit the interaction data. These include reputation systems, whereby the quality of an individual’s comments and feedback is judged by the recipients, and recommender systems, in which participants are able to highlight instances of high quality work. Both of these ideas are present in popular online auction and shopping sites, but have not been widely adapted for educational use. The paper will describe the Aropä and PeerWise tools, discuss the education theory behind the ideas, present results from the ongoing research study into student learning and attitudes toward the tools, and elaborate some of our ideas for future development.

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  • Processing temporal aggregates in parallel

    Ye, Xinfeng; Keane, John A. (1997)

    Conference paper
    The University of Auckland Library

    An open access copy of this article is available and complies with the copyright holder/publisher conditions. Temporal databases maintain past, present and future data. TSQL2 is a query language designed for temporal databases. In TSQL2, the GROUP BY clause has the temporal grouping property. In temporal grouping, the time line of each attribute value is partitioned into several sections, and aggregate functions are computed for each time partition. This paper describes two approaches to parallelising an algorithm for computing temporal aggregates. The two approaches have been implemented on an SGI PowerChallenge SMP parallel system. The experimental results show that the performance of the two approaches depends on data skew ratio and the number of processors used in the computation

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  • Efficient frequency conversion in optical fibers with tailored birefringence

    Murdoch, S.G.; Rong, Z.; Leonhardt, R.; Harvey, J.D. (1998)

    Conference paper
    The University of Auckland Library

    An open access copy of this article is available and complies with the copyright holder/publisher conditions. Four wave mixing in optical fibers has long been recognised as important method of generating new optical frequencies. The process holds promise as a means of wavelength switching for optical communications, but the presence of a nonlinear term in the phase-matching condition normally prevents strong energy exchange between the waves. We present here a scheme for optimising the conversion efficiency. The four wave mixing process considered here is called polarisation modulation instability (PMI) where a strong pump wave on one axis of a birefringent fiber results in the growth of two equally detuned sidebands on the other axis. In the absence of any external seed the sidebands start to grow with a frequency shift f0 where the wavevector mismatch is zero. This mismatch is a function of the power of the pump and the fibre's birefringence, dispersion, and nonlinearity. Our analysis of the evolution of the power in the sidebands utilises three coupled mode equations which describe the interaction of a monochromatic pump, with a pair of sidebands polarised along the orthogonal fibre axis. In the absence of Raman gain, it is possible to solve these equations so that by varying the birefringence along the fibre, the sidebands with a frequency shift of f 0 are phase matched for the entire length of the fibre

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  • Quantum optics with large x(3) nonlinearities

    Walls, D.F.; Rebic, S.; Parkins, A.S.; Dunstan, M.; Collett, M.J. (1998)

    Conference paper
    The University of Auckland Library

    An open access copy of this article is available and complies with the copyright holder/publisher conditions. Summary form only given. For applications in quantum optics it is necessary that the quantum noise resulting from spontaneous emission by the atoms be small. The reduction of absorption in these systems effectively reduces the spontaneous emission. The use of quantum coherence effects to reduce quantum noise in atomic systems was first proposed by Dalton, Reid and Walls. An analysis of quantum noise in three level atoms interacting with 2 light fields by Gheri et al. demonstrated that a nonlinear phase shift could be imposed on the probe beam due to the signal. This particular configuration utilised a “ghost transition” where the population in one transition was nearly zero, thus the quantum noise due to spontaneous emission was negligible and the conditions for a good QND measurement were satisfied. This was verified in a recent experiment by Roch et al who using cold trapped atoms and the “ghost transition” scheme, obtained the best QND correlation scheme to date

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  • Data cache parameter measurements

    Li, Enyou; Thomborson, Clark (1998)

    Conference paper
    The University of Auckland Library

    An open access copy of this article is available and complies with the copyright holder/publisher conditions. We extend prior research by Saavedra and Smith on designing microbenchmarks to measure data cache parameters. Unlike Saavedra and Smith, we measure the parameters by characterizing read accesses separately from write accesses; and we do not assume that the address mapping function is a bit-selection. We can measure the cache capacity C, block size b, and associativity a; we can measure the cache-hit access time and penalty for read and write; we can determine whether a cache allocates on write; we can detect write-back and write-through policies. We present experimental results for two CPU/cache structures, a 200 MHz Pentium with MMX and a 180 MHz Pentium Pro

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  • Towards non-invasive electrical heart imaging

    Cheng, L.K.; Pullan, A.J. (1999)

    Conference paper
    The University of Auckland Library

    An open access copy of this article is available and complies with the copyright holder/publisher conditions. Before accurate, non-invasive, electrical images of the heart can be reconstructed several issues must be addressed. Geometric models must be created to match the subject, the appropriate resolution of the computational mesh must be determined and a continuous potential field must be generated from discretely sampled ECG signals. We investigate each of these issues with reference to a porcine model

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  • Skim milk fouling during ohmic heating.

    Bansal, B.; Chen, X. D.; Lin, S. X. Q. (2005)

    Conference paper
    The University of Auckland Library

    An open access copy of this article is available and complies with the copyright holder/publisher conditions. This study deals with the investigation of deposition from reconstituted skim milk solution in an ohmic heater. The heater was made of two concentric cylinders acting as two separate electrodes. The heating of the milk solution resulted in deposit formation on both electrodes. These deposits provided additional electrical resistance and the current passing through the milk solution dropped by up to 45% within 4 hours of operation. The applied voltage increased slightly during this time period. The deposit formation was reasonably uniform at any cross-section. Lowering the milk temperature at the inlet of the ohmic heater enhanced the rate of fouling. In contrast, increasing the milk solution flow rate by a factor of two was found to have almost no effect on the fouling rate. A mathematical model was developed to simulate the fouling process and investigate the effect of different parameters in detail.

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  • Dirty Work

    McMeel, Dermott; Coyne, Richard (2005)

    Conference paper
    The University of Auckland Library

    Conference Details: Proc. W1 18th British HCI Group Annual Conference 6-10 September – Designer, User, Meaning Maker: Rethinking Relationships for a More Creative HCI. pp. 26-29. Leeds: Leeds Metropolitan University. This research explores the potency of dirt as a category for understanding digital communications. Our eventual target domain is communication in the construction industry, which is characterised by contractual formalities on the one hand (working documents, specifications, forms), and informal communications on the other (onsite instructions, scribbles on paper). Electronic communications (such as email and message boards) represent hybrid formal-informal media in the increasingly litigious workplace. On the way to understanding the untidiness of the construction site, we analysed the use of formal and informal communications in group working by students in the design and construction of an interactive digital art installation. Our research so far draws on the interesting relationship between dirt, authority, and human-computer interaction.

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  • Modelling the pelvic floor for investigating difficulties during childbirth

    Li, XS; Kruger, JA; Chung, JH; Nash, MP; Nielsen, PMF (2008)

    Conference paper
    The University of Auckland Library

    Research has suggested that athletes involved in high-intensity sports for sustained periods have a higher probability of experiencing prolonged second stage of labour compared to non-athletes. The mechanism responsible for this complication is unknown but may depend on the relative size or tone of the pelvic floor muscles. Prolonged training can result in enlargement and stiffening of these muscles, providing increased resistance as the fetal head descends through the birth canal during a vaginal birth. On the other hand, recent studies have suggested an association between increased muscle bulk in athletes and higher distensibility. This project aims to use mathematical modelling to study the relationship between the size and tone of the pelvic floor muscles and the level of difficulty during childbirth. We obtained sets of magnetic resonance (MR) images of the pelvic floor region for a female athlete and a female non-athlete. Thirteen components of the pelvic floor were segmented and used to generate finite element (FE) models. The fetal head data was obtained by laser scanning a skull replica and a FE model was fitted to these data. We used contact mechanics to simulate the motion of the fetal head moving through the pelvic floor, constructed from the non-athlete data. A maximum stretch ratio of 3.2 was induced in the muscle at the left lateral attachment point to the pubis. We plan to further improve our modelling framework to include active muscle contraction and fetal head rotations in order to address the hypotheses that there is a correlation between the level of difficulty and the size or tone of the pelvic floor muscles.

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  • Reuse of Components in Formal Modeling and Verification of Distributed Control Systems

    Vyatkin, Valeriy; Hanish, Hans-Michael (2005)

    Conference paper
    The University of Auckland Library

    An open access copy of this article is available and complies with the copyright holder/publisher conditions. This paper describes formal modeling and verification of automation systems ftom the system engineering point of view. Reuse of model components is the key issue in order to bring the scientific modeling methodology into engineering practice. The reuse is achieved by the combination of modular modeling of automation systems with object-oriented description of models in UML style. This allows to benefit from advantages of both worlds: efficiently manage highly hierarchical complex models with UML tools and end up with efficiently executable models with distributed states that are compatible also with IEC61499 function block specifications. The approach is supported by the tool framework that is described in the contribution.

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  • Using CellML in Computational Models of Multiscale Physiology

    Nickerson, David; Hunter, Peter (2005)

    Conference paper
    The University of Auckland Library

    An open access copy of this article is available and complies with the copyright holder/publisher conditions. A computational modeling framework is presented which enables the integration of multiple physics and spatial scales in models of physiological systems. A novel aspect of the framework is the use of CellML to specify all model and simulation specific mathematical equations including cellular models and material constitutive relationships. Models of cardiac electromechanics at cellular, tissue, and organ spatial scales are used to illustrate the developed and implemented framework and other applications are discussed.

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  • Internet Applications for Computational Biology, the CMISS Web Browser Extension and and Use in Education

    Stevens, Carey; Blackett, Shane; LeGrice, Ian; Hunter, Peter (2005)

    Conference paper
    The University of Auckland Library

    An open access copy of this article is available and complies with the copyright holder/publisher conditions. The internet is becoming increasingly accessable and new technologies are enabling the delivery of more features to end users. It is therefore increasingly compelling to develop technology to facilitate the delivery of educational content and computational tools via the internet. Here we report on the internet enabling of the CMISS package as a web browser extension, and its use in a custom online teaching application for medical students.

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  • Providing reliable web services through active replication

    Ye, X. (2007)

    Conference paper
    The University of Auckland Library

    An open access copy of this article is available and complies with the copyright holder/publisher conditions. This paper presents a middleware that provides reliable web services using the active replication technique. The middleware uses a timestamp-based protocol to maintain the consistency of the replicas' states. Compared with the optimistic active replication protocol and group communication primitives, the protocol used in this paper reduces the replication overhead for a class of applications.

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  • Aging gracefully? Reviewing and enhancing Information Commons services at the University of Auckland

    Chidlow, Rachel; Mountifield, Hester (2010)

    Conference paper
    The University of Auckland Library

    Conference programme and links to all papers http://www.vala.org.au/vala2010/prog2010.htm The University Library’s Information Commons Group services and facilities have continued to thrive and improve student life and learning since the opening of the Kate Edger Information Commons in April 2003. The IC Group has a strong strategic focus on continuous improvement in areas of management, staff development, operations, space design, technology, resource development and client services. The IC Group collaborates with ITS in offering and improving electronic campus services for students. This paper outlines the “how” and “why” behind changes and improvements in the IC Group. The benefits to staff and students will also be demonstrated. This paper also briefly discusses the reengineering of the original service model to accommodate changes in learning, technology and student needs.

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  • Interaction of whey protein with modified stainless steel surfaces.

    Premathilaka, S. S.; Hyland, M. M.; Chen, Z. D.; Watkins, L. R.; Bansal, B. (2007)

    Conference paper
    The University of Auckland Library

    An open access copy of this article is available and complies with the copyright holder/publisher conditions. Modified stainless steel surfaces were fouled with whey protein solutions to study the deposition mechanisms and the effects of surface modification. Stainless steel samples were coated with diamond-like carbon (DLC) and titanium nitride (TiN). These surfaces are expected to present different surface chemistries to stainless steel in terms of their functional groups and hydrophobic or hydrophilic nature. Thus, it is expected that foulant-surface interactions will differ for the various fouled surfaces. The substrates were exposed to a flowing whey protein solution in a fouling rig designed to achieve laminar flow. X-ray Photoelectron Spectroscopy (XPS) was used to study the initial protein-surface interactions of samples fouled for 1 minute at 75°C. Ellipsometry was used to study the fouling and cleaning performance of samples fouled at 75°C and 85°C for up to 30 minutes followed by ultrasonic caustic cleaning of selected samples. XPS showed the presence of similar protein functional groups on all fouled surfaces. The bonding mechanisms during fouling of DLC is different to the stainless steel and TiN surfaces. The peptide link played a more active role at the deposit-surface interface for the non-polar DLC surface, while it was less significant for the two polar surfaces. Ellipsometry revealed that for the three surfaces, fouling increased in the order DLC<DLC. Furthermore, the nature of the surface influenced the structure of the deposit after the initial protein layer was formed. It was concluded that the surface chemistry can influence the deposition mechanisms in terms of the orientation of protein functional groups as well as the amount of fouling, the structure of the deposit and hence the deposit removal behaviour.

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  • Controlling Inrush Currents in Inductively Coupled Power Systems

    Boys, John T.; Chen, C.I.; Covic, Grant (2005)

    Conference paper
    The University of Auckland Library

    An open access copy of this article is available and complies with the copyright holder/publisher conditions. In an Inductively Coupled Power Transfer (ICPT) system, a multiplicity of (moving) loads take power from an elongated conductive loop (track) excited by a current in the range of 15-125A by magnetic induction at a VLF frequency of between 5-50kHz. In this application, the track performs the same function as a distribution line in a power system. However, frequency deviations cannot be tolerated in ICPT systems and therefore there are difficulties with inrush power surges as loads switch on. In severe cases, the inrush surge may compromise the security of the whole system. This paper proposes a solution to this problem using an ICPT pickup controller with input shaping where the poles that can cause an inrush are not excited. The paper is supported by theoretical analysis and experimental measurements and is applicable across a wide range of ICPT sizes and applications. The solution reduces the inrush effects to 10% of an uncontrolled system.

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