Hamilton Institute Seminars (HD / large)

Speaker:

Dr. I. Radusch

Abstract:

Future drivers and vehicles will benefit from upcoming integrated communication devices three-fold. Communication will increase safety and efficiency in traffic as well as making driving more enjoyable. Upcoming field operational tests will assess if available standards and implementations are ready for wide scale deployment. Additionally, simulation environments such as VSimRTI allow comprehensive pre-validation of novel vehicle functions utilizing vehicle-2-x communication.

Speaker:

Dr. J. Wenus

Abstract:

Microscopy of living cells is heavily employed in biomedicine to understand the mechanisms of disease progression and to develop novel pharmaceuticals. In particular, confocal microscopy which relies on laser-based excitation of fluorescent cellular biomarkers is frequently used for understanding molecular actions of therapeutic drugs to abnormal cells. However, prolonged exposure to highly energetic laser radiation often leads to light induced cell death before any spontaneous effects can occur --- an effect known as 'photo-toxicity'. To address this problem we have developed an automated live-cell imaging system 'ALISSA' which employs online image processing and analysis to automatically detect biological events and then trigger appropriate changes in the image acquisition settings. This way we minimize the photo-toxicity, obtain higher quality of the imaging data and minimize direct user involvement by introducing more automation to the whole experimental process. So far, ALISSA has been used in studies on cancer cells and neurons at the Royal College of Surgeons in Ireland and it is currently under development aimed towards applications in commercial high content screening systems.

This is a joint work between the RCSI, Dublin (H. Huber, H. Duessmann, J. Prehn) and the Hamilton Institute, NUI Maynooth (J. Wenus, P. Paul, D. Kalamatianos, P. Wellstead) with involvement from Siemens and Carl Zeiss MicroImaging.

We gratefully acknowledge financial support from the National Biophotonics and Imaging Platform Ireland (HEA PRTLI Cycle 4).

Speaker:

Dr. S. Dey

Abstract:

In this talk, we consider a wideband spectrum sharing system where a secondary user can share a number of orthogonal frequency bands each licensed to a distinct primary user. We address the problem of optimum secondary transmit power allocation for its ergodic capacity maximization subject to an average sum (across the bands) transmit power constraint and individual average interference constraints on the primary users. The major contribution of our work lies in considering quantized channel state information (CSI) (for the vector channel space consisting of all secondary-to-secondary and secondary-to-primary channels) at the secondary transmitter as opposed to the prevalent assumption of full CSI in most existing work.It is assumed that a band manager or a cognitive radio service provider has access to the full CSI information from the secondary and primary receivers and designs (offline) an optimal power codebook based on the statistical information(channel distributions) of the channels and feeds back the index of the codebook to the secondary transmitter for every channel realization in real-time, via a delay-free noiseless limited feedback channel. A modified Generalized Lloyds-type algorithm (GLA) is designed for deriving the optimal power codebook,which is proved to be globally convergent and empirically consistent. An approximate quantized power allocation (AQPA) algorithm is presented,that performs very close to its GLA based counterpart for large number of feedback bits and is significantly faster.We also present an extension of the modified GLA based quantized power codebook design algorithm for the case when the feedback channel is noisy. Numerical studies illustrate that with only 3-4 bits of feedback, the modified GLA based algorithms provide secondary ergodic capacity very close to that achieved by full CSI and with only as little as 4 bits of feedback, AQPA provides a comparable performance,thus making it an attractive choice for practical implementation.Various open problems and future research directions will also be discussed.

Speaker:

Dr. H. Touchette

Abstract:

The theory of large deviations, initiated by Cramer in the 1930s and later developed by Donsker and Varadhan in the 1970s, is an active field of probability theory that finds applications in many subjects, including statistics, finance, actuarial mathematics, engineering, and physics. Its use in physics dates back to the work of Ruelle, Lanford, and the late John Lewis, among others, who used concepts of large deviations in the 1970s and 1980s to study equilibrium systems and to put statistical mechanics on a rigorous footing.

I will give in this talk a survey of these applications, as well as more recent ones related to long-range equilibrium systems and nonequilibrium systems, at a level which assumes little knowledge of statistical mechanics or large deviations. As we cover these applications, we will see that large deviation theory and statistical mechanics share a common mathematical structure, which Lewis was well aware of, and which can be summarized by saying that an entropy function is to a physicist what a large deviation function (or rate function) is to a mathematician. Other connections of this sort will be discussed.

Speaker:

Dr. C. Bordenave

Abstract:

Consider N queues with non-homogeneous packet arrivals. The queues share a common communication channel. At the beginning of each timeslot, if queue i has a packet, it attempts to access the channel with probability p_i. This attempt is successful when no other queue attempts to access the channel. For arbitrary N, the stability region of such queuing system is a long standing open problem. However as the number of queues N goes to infinity, it is possible to compute the asymptotic stability region.

This is a joint work with David McDonald (Ottawa) and Alexandre Proutiere (Microsoft).

Speaker:

Prof. M. E. Valcher

Abstract:

Abstract: Positive switched systems typically arise to cope with two distinct modeling needs. On the one hand, switching among different models mathematically formalizes the fact that the system laws change under different operating conditions.On the other hand, the variables to be modeled may be quantities that have no meaning unless positive (temperatures, pressures,population levels, ...).

In this talk we consider the class of discrete-time positive switched systems, described, at each time t, by the first-order difference equation:

x(t+1) = A_{\sigma(t)} x(t),

where \sigma is a switching sequence, taking values in the finite set {1,2}, and for each index i, A_i is an n x n positive matrix. Assuming that both A_1 and A_2 are not Schur matrices, we focus on the stabilizability of the system, namely on the possibility of finding switching strategies that drive to zero the state evolution corresponding to every positive initial state x(0). To this end, we resort to state feedback switching laws, whose value at the time t depends on the value of some Lyapunov function in x(t).

We first explore quadratic positive definite functions, by extending a technique described by De Carlo et al.. Later, by taking advantage of the system positivity, we show that other classes of Lyapunov functions, such as linear copositive and quadratic copositive ones, may be used to design state-dependent stabilizing switching laws, and some of them may be designed under weaker conditions on the pair of matrices (A_1,A_2) with respect to those required for quadratic stabilizability.

Some comparisons between the performances of the switching strategies are given.

Speaker:

Prof. C. Seoighe

Abstract:

We describe a phylogenetic model of protein-coding sequence evolution that includes environmental variables. We apply it to a set of viral sequences from individuals with known human leukocyte antigen (HLA) genotype and include parameters to model selective pressures affecting mutations within immunogenic (epitope) regions that facilitate viral evasion of immune responses. We combine this evolutionary model with a hidden Markov model to identify regions of the HIV-1 genome that evolve under immune pressure in the presence of specific HLA class I alleles and may therefore represent potential T cell epitopes. This phylogenetic hidden Markov model (phylo-HMM) provides a probabilistic framework that can be combined with sequence or structural information to enhance epitope prediction.

Speaker:

Dr. C. Molina-París

Abstract:

T cells are specialised white blood cells that protect the body from infection and are also able to kill infected cells. T cells are characterised by the presence of a special receptor on their cell surface called T cell receptor (TCR). The specificity of the T cell, namely which pathogens it can recognise, is determined by the molecular structure of its TCR. T cells can be classified according to their TCRs. All T cells that have identical TCRs are said to belong to the same clonotype. There are two types of T cells: naive and memory. Naive T cells have not yet encountered pathogens and memory T cells have already encountered pathogen. In this talk, I will only consider the class of naive T cells. A diverse naive T cell pool is essential to protect against novel infections, as the immune system cannot predict which pathogens the organism will be exposed to during its life-time. A healthy adult human possesses approximately 10^(11) naive T cells, which belong to about 10^7-10^8 different clonotypes. The reliability of the immune response to pathogenic challenge depends critically on the size (how many cells) and diversity (how many different TCRs or clonotypes) of the naive T cell pool of the individual. Experimental evidence suggests that interactions between TCRs with self-peptides (self-peptide = a fragment of a household protein) displayed on the surface of specialised cells, called antigen presenting cells (APCs), are important in controlling naive T cell numbers. Naive T cells undergo one round of cell division after receiving a survival stimulus from these specialized APCs. Whether or not a particular naive T cell can receive a survival signal from an specialized APC depends both on the TCR it expresses and the array of self-peptides displayed on the surface of the APC. Competition amongst naive T cells for these interactions regulates the diversity of the naive T cell pool.

We have made use of a probabilistic (stochastic) model to describe this competition. In particular, we have modeled the time evolution of the number of T cells belonging to a particular clonotype. Our results indicate that competition maximizes TCR diversity by promoting the survival of T cell clonotypes that are most different from each other in terms of the self-peptides they are able to recognise.

Speaker:

Dr. R. Clement

Abstract:

Neural responses are often generated by the physical movement of an object or a limb. Each such set of responses corresponds a point on a smooth geometrical surface. To be able to manipulate such a representation the brain assigns coordinates to every point on the surface --- a procedure known as embedding.

In the first part of this talk the properties of the early visual system are exploited to produce a model of coordinate space based on features such as colour, orientation and movement. The feature model has the advantage over the geometric model that it is not restricted to 2 or 3-dimensional pictorial representations.

The neural mechanism is highly suited to embedding. In the second part of the talk the feature based coordinate space will be used to explore the neural embedding of the sensory stimuli encountered in binocular vision and in the movement of the eye.

In the final part of the talk the limitations on our ability to see objects arising from the neural embedding procedures will be outlined and in particular, what can be "seen" of the shape of surfaces embedded in more than three dimensions.

Speaker:

Dr. N. Pettit

Abstract:

As part of a wider improvement initiative across all parts of our value chain, Danfoss, in 2007, launched an initiative to significantly improve its product development processes. The goal was to make radical improvements on the dimensions of: value to customer, time to profit, unit cost and quality. In order to do this, we looked around to identify industry-wide accepted best practices to build on. When starting a similar program in production 4 years earlier, there were clear accepted practices that had proved themselves in multiple companies and industry sectors. These are centred on the manufacturing philosophy of Toyota and generally grouped under the term "lean production". These would often be merged with another set of practices termed "six sigma", that came out of Motorola and championed by GE.

In product development we found a different picture. Although many schools of thought have been adopted by industries, often trying to build on the back of lean production ideas (termed unsurprisingly "Lean product development"), these were found to be relatively immature in their application and narrow in what dimensions they improved when applied. Many proponents backed different tools and methods out of these schools as the "best" best practice, but non appeared to have a track record of significant impact on the multiple dimensions we needed, to justify their claims.

We undertook a significant exercise to look at the internal processes we wanted to improve. We then separated the tools and methods from the different schools of thought to identify which tools and methods were relevant to our processes and had a track record of success along at least one dimension. This led us to identify an underlying empirical set of principles that really seemed to drive true impact along all the dimensions we were looking for. Once we had these, we were able to go back and pick and choose a variety tools and methods from the different schools of thought, that embodied one or more of these principles --- stealing with pride. This gave us a set of tools that when used together would create the impact we were looking for. Finally we then created a system to adapt, improve and test these tools and methods before spreading them out, so that our people engaged in product development find them relevant, workable, and able to quickly deliver visible and significant improvement to their product development.

The talk will outline some of these principles and methods we have built up in this journey.