Interpretation of the temperature dependence of equilibrium and rate constants

The objective of this review is to draw attention to potential pitfalls in attempts to glean mechanistic information from the magnitudes of standard enthalpies and entropies derived from the temperature dependence of equilibrium and rate constants for protein interactions. Problems arise because the minimalist model that suffices to describe the energy differences between initial and final states usually comprises a set of linked equilibria, each of which is characterized by its own energetics. For example, because the overall standard enthalpy is a composite of those individual values, a positive magnitude for AHO can still arise despite all reactions within the subset being characterized by negative enthalpy changes: designation of the reaction as being entropy driven is thus equivocal. An experimenter must always bear in mind the fact that any mechanistic interpretation of the magnitudes of thermodynamic parameters refers to the reaction model rather than the experimental system For the same reason there is little point in subjecting the temperature dependence of rate constants for protein interactions to transition-state analysis. If comparisons with reported values of standard enthalpy and entropy of activation are needed, they are readily calculated from the empirical Arrhenius parameters. Copyright (c) 2006 John Wiley & Sons, Ltd.

Variability in heart rate estimates from different pulse oximeters

Since its introduction, pulse oximetry has become a conventional clinical measure. Besides being arterial blood oxygen saturation (SpO2) measure, pulse oximeters can be used for other cardiovascular measurements, like heart rate (HR) estimations, derived from its photo plethysmographic (PPG) signals. The temporal coherence of the PPG signals and thereby HR estimates are heavily dependent on its minimal phase variability. A Masimo SET Rad-9TM, Novametrix Oxypleth and a custom designed PPG system were investigated for their relative phase variation. R-R intervals from electro-cardiogram (ECG) were recorded concurrently as reference. PPG signals obtained from the 3 systems were evaluated by comparing their respective beat-to-beat (B-B) intervals with the corresponding R-R estimates during a static test. For their relative B-B comparison to the ECG, Novametrix system differed 0.680.52% (p

Exchange rate exposure : do size and foreign operations matter?

Purpose – The purpose of this paper is to examine the effect of firm size and foreign operations on the exchange rate exposure of UK non-financial companies from January 1981 to December 2001. Design/methodology/approach – The impact of the unexpected changes in exchange rates on firms’ stock returns is examined. In addition, the movements in bilateral, equally weighted (EQW) and trade-weighted and exchange rate indices are considered. The sample is classified according to firm size and the extent of firms’ foreign operations. In addition, structural changes on the relationship between exchange rate changes and individual firms’ stock returns are examined over three sub-periods: before joining the exchange rate mechanism (pre-ERM), during joining the ERM (in-ERM), and after departure from the ERM (post-ERM). Findings – The findings indicate that a higher percentage of UK firms are exposed to contemporaneous exchange rate changes than those reported in previous studies. UK firms’ stock returns are more affected by changes in the EQW, and US$ European currency unit exchange rate, and respond less significantly to the basket of 20 countries’ currencies relative to the UK pound exchange rate. It is found that exchange rate exposure has a more significant impact on stock returns of the large firms compared with the small and medium-sized companies. The evidence is consistent across all specifications using different exchange rate. The results provide evidence that the proportion of significant foreign exchange rate exposure is higher for firms which generate a higher percentage of revenues from abroad. The sensitivities of firms’ stock returns to exchange rate fluctuations are most evident in the pre-ERM and post-ERM periods. Practical implications – This study provides important implications for public policymakers, financial managers and investors on how common stock returns of various sectors react to exchange rate fluctuations. Originality/value – The empirical evidence supports the view that UK firms’ stock returns are affected by foreign exchange rate exposure.

The exchange rate exposure of UK non-financial companies

Purpose – The purpose of this paper is to investigate the exchange rate exposure of UK nonfinancial companies from January 1981 to December 2001. Design/methodology/approach – The study employs different exchange rate measures and adopts an equally weighted exchange rate. The analyses are conducted at the firm level. All analyses are conducted by regressing the firm’s exchange rate exposure coefficients on its size, foreign activity variables and financial hedging proxies over the whole sample period. Findings – The findings show that a higher percentage of UK non-financial companies are exposed to exchange rate changes than those reported in previous studies. Generally, the results provide a stronger support for the suggested equally weighted rate as an economic variable, which affects firms’ stock returns. The results also show a high proportion of positive exposure coefficients among firms with significant exchange rate exposure, indicating a higher proportion of firms benefiting from an appreciation of the pound. Finally, the results also indicate evidence that firms’ foreign operations and hedging variables affect their sensitivity to exchange rate exposure. Practical implications – This study provides important implications for public policymakers who wish to understand links between policies that affect exchange rates and relative wealth effects. Originality/value – The empirical results of this study should help investors to examine how common stock returns react to exchange rate fluctuations when making financial decisions, and prove useful for financial managers when measuring exposure to foreign exchange rate changes.

The relative contributions of colour and luminance signals towards the visuomotor localisation of targets in human peripheral vision

We sought to determine the extent to which colour (and luminance) signals contribute towards the visuomotor localization of targets. To do so we exploited the movement-related illusory displacement a small stationary window undergoes when it has a continuously moving carrier grating behind it. We used drifting (1.0-4.2 Hz) red/green-modulated isoluminant gratings or yellow/black luminance-modulated gratings as carriers, each curtailed in space by a stationary, two-dimensional window. After each trial, the perceived location of the window was recorded with reference to an on-screen ruler (perceptual task) or the on-screen touch of a ballistic pointing movement made without visual feedback (visuomotor task). Our results showed that the perceptual displacement measures were similar for each stimulus type and weakly dependent on stimulus drift rate. However, while the visuomotor displacement measures were similar for each stimulus type at low drift rates (<4 Hz), they were significantly larger for luminance than colour stimuli at high drift rates (>4 Hz). We show that the latter cannot be attributed to differences in perceived speed between stimulus types. We assume, therefore, that our visuomotor localization judgements were more susceptible to the (carrier) motion of luminance patterns than colour patterns. We suggest that, far from being detrimental, this susceptibility may indicate the operation of mechanisms designed to counter the temporal asynchrony between perceptual experiences and the physical changes in the environment that give rise to them. We propose that perceptual localisation is equally supported by both colour and luminance signals but that visuomotor localisation is predominantly supported by luminance signals. We discuss the neural pathways that may be involved with visuomotor localization. © 2007 Springer-Verlag.

Effects of the rate of formant-frequency variation on the grouping of formants in speech perception

How speech is separated perceptually from other speech remains poorly understood. Recent research suggests that the ability of an extraneous formant to impair intelligibility depends on the modulation of its frequency, but not its amplitude, contour. This study further examined the effect of formant-frequency variation on intelligibility by manipulating the rate of formant-frequency change. Target sentences were synthetic three-formant (F1?+?F2?+?F3) analogues of natural utterances. Perceptual organization was probed by presenting stimuli dichotically (F1?+?F2C?+?F3C; F2?+?F3), where F2C?+?F3C constitute a competitor for F2 and F3 that listeners must reject to optimize recognition. Competitors were derived using formant-frequency contours extracted from extended passages spoken by the same talker and processed to alter the rate of formant-frequency variation, such that rate scale factors relative to the target sentences were 0, 0.25, 0.5, 1, 2, and 4 (0?=?constant frequencies). Competitor amplitude contours were either constant, or time-reversed and rate-adjusted in parallel with the frequency contour. Adding a competitor typically reduced intelligibility; this reduction increased with competitor rate until the rate was at least twice that of the target sentences. Similarity in the results for the two amplitude conditions confirmed that formant amplitude contours do not influence across-formant grouping. The findings indicate that competitor efficacy is not tuned to the rate of the target sentences; most probably, it depends primarily on the overall rate of frequency variation in the competitor formants. This suggests that, when segregating the speech of concurrent talkers, differences in speech rate may not be a significant cue for across-frequency grouping of formants.

Nonlinearity compensation in multi-rate 28 Gbaud WDM systems employing optical and digital techniques under diverse link configurations

Digital back-propagation (DBP) has recently been proposed for the comprehensive compensation of channel nonlinearities in optical communication systems. While DBP is attractive for its flexibility and performance, it poses significant challenges in terms of computational complexity. Alternatively, phase conjugation or spectral inversion has previously been employed to mitigate nonlinear fibre impairments. Though spectral inversion is relatively straightforward to implement in optical or electrical domain, it requires precise positioning and symmetrised link power profile in order to avail the full benefit. In this paper, we directly compare ideal and low-precision single-channel DBP with single-channel spectral-inversion both with and without symmetry correction via dispersive chirping. We demonstrate that for all the dispersion maps studied, spectral inversion approaches the performance of ideal DBP with 40 steps per span and exceeds the performance of electronic dispersion compensation by ~3.5 dB in Q-factor, enabling up to 96% reduction in complexity in terms of required DBP stages, relative to low precision one step per span based DBP. For maps where quasi-phase matching is a significant issue, spectral inversion significantly outperforms ideal DBP by ~3 dB.

Forecasting the UK/US exchange rate with divisia monetary models and neural networks

This paper compares the UK/US exchange rate forecasting performance of linear and nonlinear models based on monetary fundamentals, to a random walk (RW) model. Structural breaks are identified and taken into account. The exchange rate forecasting framework is also used for assessing the relative merits of the official Simple Sum and the weighted Divisia measures of money. Overall, there are four main findings. First, the majority of the models with fundamentals are able to beat the RW model in forecasting the UK/US exchange rate. Second, the most accurate forecasts of the UK/US exchange rate are obtained with a nonlinear model. Third, taking into account structural breaks reveals that the Divisia aggregate performs better than its Simple Sum counterpart. Finally, Divisia-based models provide more accurate forecasts than Simple Sum-based models provided they are constructed within a nonlinear framework.

Exchange rate exposure:do size and foreign operations matter?

Purpose – The purpose of this paper is to examine the effect of firm size and foreign operations on the exchange rate exposure of UK non-financial companies from January 1981 to December 2001. Design/methodology/approach – The impact of the unexpected changes in exchange rates on firms’ stock returns is examined. In addition, the movements in bilateral, equally weighted (EQW) and trade-weighted and exchange rate indices are considered. The sample is classified according to firm size and the extent of firms’ foreign operations. In addition, structural changes on the relationship between exchange rate changes and individual firms’ stock returns are examined over three sub-periods: before joining the exchange rate mechanism (pre-ERM), during joining the ERM (in-ERM), and after departure from the ERM (post-ERM). Findings – The findings indicate that a higher percentage of UK firms are exposed to contemporaneous exchange rate changes than those reported in previous studies. UK firms’ stock returns are more affected by changes in the EQW, and US$ European currency unit exchange rate, and respond less significantly to the basket of 20 countries’ currencies relative to the UK pound exchange rate. It is found that exchange rate exposure has a more significant impact on stock returns of the large firms compared with the small and medium-sized companies. The evidence is consistent across all specifications using different exchange rate. The results provide evidence that the proportion of significant foreign exchange rate exposure is higher for firms which generate a higher percentage of revenues from abroad. The sensitivities of firms’ stock returns to exchange rate fluctuations are most evident in the pre-ERM and post-ERM periods. Practical implications – This study provides important implications for public policymakers, financial managers and investors on how common stock returns of various sectors react to exchange rate fluctuations. Originality/value – The empirical evidence supports the view that UK firms’ stock returns are affected by foreign exchange rate exposure.

The exchange rate exposure of UK non-financial companies

Purpose – The purpose of this paper is to investigate the exchange rate exposure of UK nonfinancial companies from January 1981 to December 2001. Design/methodology/approach – The study employs different exchange rate measures and adopts an equally weighted exchange rate. The analyses are conducted at the firm level. All analyses are conducted by regressing the firm’s exchange rate exposure coefficients on its size, foreign activity variables and financial hedging proxies over the whole sample period. Findings – The findings show that a higher percentage of UK non-financial companies are exposed to exchange rate changes than those reported in previous studies. Generally, the results provide a stronger support for the suggested equally weighted rate as an economic variable, which affects firms’ stock returns. The results also show a high proportion of positive exposure coefficients among firms with significant exchange rate exposure, indicating a higher proportion of firms benefiting from an appreciation of the pound. Finally, the results also indicate evidence that firms’ foreign operations and hedging variables affect their sensitivity to exchange rate exposure. Practical implications – This study provides important implications for public policymakers who wish to understand links between policies that affect exchange rates and relative wealth effects. Originality/value – The empirical results of this study should help investors to examine how common stock returns react to exchange rate fluctuations when making financial decisions, and prove useful for financial managers when measuring exposure to foreign exchange rate changes.

Entropy Based Approach to Finding Interacting Genes Responsible for Complex Human Disease

2000 Mathematics Subject Classification: 62P10, 92D10, 92D30, 94A17, 62L10.

Early warnings of heart rate deterioration

Hospitals can experience difficulty in detecting and responding to early signs of patient deterioration leading to late intensive care referrals, excess mortality and morbidity, and increased hospital costs. Our study aims to explore potential indicators of physiological deterioration by the analysis of vital-signs. The dataset used comprises heart rate (HR) measurements from MIMIC II waveform database, taken from six patients admitted to the Intensive Care Unit (ICU) and diagnosed with severe sepsis. Different indicators were considered: 1) generic early warning indicators used in ecosystems analysis (autocorrelation at-1-lag (ACF1), standard deviation (SD), skewness, kurtosis and heteroskedasticity) and 2) entropy analysis (kernel entropy and multi scale entropy). Our preliminary findings suggest that when a critical transition is approaching, the equilibrium state changes what is visible in the ACF1 and SD values, but also by the analysis of the entropy. Entropy allows to characterize the complexity of the time series during the hospital stay and can be used as an indicator of regime shifts in a patient’s condition. One of the main problems is its dependency of the scale used. Our results demonstrate that different entropy scales should be used depending of the level of entropy verified.

Exchange rate overvaluation under hyperinflation: The case of Peru

This dissertation examines the behavior of the exchange rate under two different scenarios. The first one is characterized by, relatively, low inflation or a situation where prices adjust sluggishly. The second is a high inflation economy where prices respond very rapidly even to unanticipated shocks. In the first one, following a monetary expansion, the exchange rate overshoots, i.e. the nominal exchange rate depreciates at a faster pace than the price level. Under high levels of inflation, prices change faster than the exchange rate so the exchange rate undershoots its long run equilibrium value.^ The standard work in this area, Dornbusch (1976), explains the overshooting process in the context of perfect capital mobility and sluggish adjustment in the goods market. A monetary expansion will make the exchange rate increase beyond its long run equilibrium value. This dissertation expands on Dornbusch's model and provides an analysis of the exchange rate under conditions of currency substitution and price flexibility, characteristics of the Peruvian economy during the hyper inflation process that took place at the end of the 1980's. The results of the modified Dornbusch model reveal that, given a monetary expansion, the change in the price level will be larger than the change in the exchange rate if prices react more than proportionally to the monetary shock.^ We will expect this over-reaction in circumstances of high inflation when the velocity of money is increasing very rapidly. Increasing velocity of money, gives rise to a higher relative price variability which in turn contributes to the appearance of new financial (and also non-financial) instruments that report a higher return than the exchange rate, causing people to switch their demand for foreign exchange to this new assets. In the context of currency substitution, economic agents hoard and use foreign exchange as a store of value. The big decline in output originated by hyper inflation induces people to sell this hoarded money to finance current expenses, increasing the supply of foreign exchange in the market. Both, the decrease in demand and the increase in supply reduce the price of foreign exchange i.e. the real exchange rate. The findings mentioned above are tested using Peruvian data for the period January 1985-July 1990, the results of the econometric estimation confirm our findings in the theoretical model. ^

Essays on the determinants of private investment: The effects of relative price uncertainty and political instability

The objective of this study was to provide empirical evidence on the effects of relative price uncertainty and political instability on private investment. My effort is expressed in a single-equation model using macroeconomic and socio-political data from eight Latin American countries for the period 1970–1996. Relative price uncertainty is measured by the implied volatility of the exchange rate and political instability is measured by using indicators of social unrest and political violence. ^ I found that, after controlling for other variables, relative price uncertainty and political instability are negatively associated with private investment. Macroeconomic and political stability are key ingredients for the achievement of a strong investment response. This highlights the need to develop the state and build a civil society in which citizens can participate in decision-making and express consent without generating social turmoil. At the same time the government needs to implement structural policies along with relative price adjustments to eliminate excess volatility in price movements in order to provide a stable environment for investment. ^

Essays on exchange rate economics

Exchange rate economics has achieved substantial development in the past few decades. Despite extensive research, a large number of unresolved problems remain in the exchange rate debate. This dissertation studied three puzzling issues aiming to improve our understanding of exchange rate behavior. Chapter Two used advanced econometric techniques to model and forecast exchange rate dynamics. Chapter Three and Chapter Four studied issues related to exchange rates using the theory of New Open Economy Macroeconomics. ^ Chapter Two empirically examined the short-run forecastability of nominal exchange rates. It analyzed important empirical regularities in daily exchange rates. Through a series of hypothesis tests, a best-fitting fractionally integrated GARCH model with skewed student-t error distribution was identified. The forecasting performance of the model was compared with that of a random walk model. Results supported the contention that nominal exchange rates seem to be unpredictable over the short run in the sense that the best-fitting model cannot beat the random walk model in forecasting exchange rate movements. ^ Chapter Three assessed the ability of dynamic general-equilibrium sticky-price monetary models to generate volatile foreign exchange risk premia. It developed a tractable two-country model where agents face a cash-in-advance constraint and set prices to the local market; the exogenous money supply process exhibits time-varying volatility. The model yielded approximate closed form solutions for risk premia and real exchange rates. Numerical results provided quantitative evidence that volatile risk premia can endogenously arise in a new open economy macroeconomic model. Thus, the model had potential to rationalize the Uncovered Interest Parity Puzzle. ^ Chapter Four sought to resolve the consumption-real exchange rate anomaly, which refers to the inability of most international macro models to generate negative cross-correlations between real exchange rates and relative consumption across two countries as observed in the data. While maintaining the assumption of complete asset markets, this chapter introduced endogenously segmented asset markets into a dynamic sticky-price monetary model. Simulation results showed that such a model could replicate the stylized fact that real exchange rates tend to move in an opposite direction with respect to relative consumption. ^