The construction of Chebyshev approximations in the complex plane

Imperial Users onl

Biases in Macroeconomic Forecasts: Irrationality or Asymmetric Loss?

Survey data on expectations frequently find evidence that forecasts are biased, rejecting the joint hypothesis of rational expectations and symmetric loss. While the literature has attempted to explain this bias through forecasters' strategic behavior, we propose a simpler explanation based on asymmetric loss. We establish that existing rationality tests are not robust to even small deviations from symmetry and hence have little ability to tell whether the forecaster is irrational or the loss function is asymmetric. We propose new and more general methods for testing forecast rationality jointly with flexible families of loss functions that embed quadratic loss as a special case. An empirical application to survey data on forecasts of nominal output growth shows strong evidence against rationality and symmetric loss. There is considerably weaker evidence against rationality once asymmetric loss is permittedrationality testing, forecasting, asymmetric loss

Designing a Clinically Viable Brain Computer Interface for the Control of Neuroprosthetics

Currently no brain computer interfaces exist that can control the individual fingers of a hand prosthesis and is suitable for permanent implantation in and individual with a single limb amputation. Within this thesis a design for a novel minimally invasive brain computer interface system is proposed that would be relatively low risk, allow for control of a prosthesis using existing cortical structures and be suitable for patients with loss of a single limb. The early stage development and proof of concept work has been done taking into account relevant regulatory requirements, so that a finalised version of the design would be suitable for regulatory certification. This novel design is found to be worth pursuing and may in turn open up new research opportunities

Development of a flexible modeling environment for evaluating subcortical auditory systems

Cochlear Synaptopathy (CS) is an emerging topic of hearing research that focuses on peripheral pathologies which leave pure-tone audiometric thresholds (PTA) unchanged but significantly impair threshold-independent hearing performance. Primary among the proposed mechanisms of CS is selective damage of low spontaneous rate (low SR) fibers of the auditory nerve (AN), yet no noninvasive quantitative measure of CS yet exists in humans. Recent work has established a relationship between Wave V latencies and a psychophysical measure of CS in humans, but current biophysical models do not fully account for the observed results. To begin to address the discrepancies between these experiments and biophysical models of hearing, a new comprehensive modeling tool was developed which allows parametric exploration of modeling space and direct comparison between major models of the auditory nerve and brainstem. More sophisticated models of the midbrain and brainstem were incorporated into the new modeling tool. Incorporating recent anatomical and electrophysiological results, which suggest a varying contribution of low-SR fibers for different audible frequencies, further addresses modeling efficacy

Understanding SCPHN students’ experience of practice educator led peer support groups

Specialist Community Public Health Nursing (SCPHN) students are expected to develop significant skills and competencies in practice whilst also achieving academic success. This workload can be very stressful for students particularly as their placements with Practice Educators can isolate them from other students, reducing the valuable support that peers can provide. Practice Educator led peer support groups were established in an attempt to ameliorate student stress and improve wellbeing by providing peer support whilst simultaneously delivering opportunities for learning and promoting preparedness for qualification. A service evaluation was subsequently conducted using focus group methodology to explore students’ experience of the peer support groups. This was to ascertain their effectiveness in supporting learning within practice placements and improving student wellbeing. Data analysis identified three key themes: ‘Peer support and Emotional nourishment’ and ‘Filling the Theory-Practice gap’, with a further theme focusing on ‘Group Organisation and Planning’ including ‘what would better look like?’. Findings indicated that the Support Groups were a valued and important element of SCHPN training for the student cohort involved in this service evaluation, engendering an improved sense of wellbeing and an enhanced educational experience

A Variational Approach to Particles in Lipid Membranes

A variety of models for the membrane-mediated interaction of particles in lipid membranes, mostly well-established in theoretical physics, is reviewed from a mathematical perspective. We provide mathematically consistent formulations in a variational framework, relate apparently different modelling approaches in terms of successive approximation, and investigate existence and uniqueness. Numerical computations illustrate that the new variational formulations are directly accessible to effective numerical methods

Some features of the upwelling off Oman

Hydrographic and ADCP data were collected in the coastal waters of Oman during the 1987 summer monsoon. The minimum surface temperatures, up to 5°C below ambient offshore values, were found close to the coast and in the vicinity of the Kuria Muria Islands. Strong surface gradients were observed near Ras al Hadd at the entrance to the Gulf of Oman where the geostrophic surface flow exceeded 1.0 m/s. The alongshore flux in the top 300 m of a region extending 100 km from the coast was estimated to be 10 × 106 m3/s. Evidence for an offshore filament of cool water was found in both current and temperature data

Heterogeneous Expectations and Tests of Efficiency in the Yen/Dollar Forward Foreign Exchange Rate Market

This paper examines the efficiency of the forward yen/dollar market using micro survey data. We first argue that the conventional tests of efficiency (unbiasedness) of the forward rate or of the survey forecasts do not correspond directly to the zero-profit condition. Instead, we use the survey data to calculate directly potential profits of individual forecasters based on a natural trading rule. We find that although the survey data are not the best predictor of future spot rate in terms of typical mean square forecast error criteria, the survey data can be used to obtain on average positive profits. However, these profits are small and highly variable. We also examine profits generated by a trading rule using regression forecasts, where forward premium is an explanatory variable. These profits are also small and highly variable.