The contribution of tropical cyclones to the atmospheric branch of Middle America's hydrological cycle using observed and reanalysis tracks

Middle America is affected by tropical cyclones (TCs) from the Eastern Pacific and the North Atlantic Oceans. We characterize the regional climatology (1998-2016) of the TC contributions to the atmospheric branch of the hydrological cycle, from May to December. TC contributions to rainfall are quantified using Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) product 3B42 and TC tracks derived from three sources: the International Best Track Archive for Climate Stewardship (IBTrACS), and an objective feature tracking method applied to the Japanese 55-year and ERA-Interim reanalyses. From July to October, TCs contribute 10-30% of rainfall over the west and east coast of Mexico and central Mexico, with the largest monthly contribution during September over the Baja California Peninsula (up to 90%). TCs are associated with 40-60% of daily extreme rainfall (above the 95th percentile) over the coasts of Mexico. IBTrACS and reanalyses agree on TC contributions over the Atlantic Ocean but disagree over the Eastern Pacific Ocean and continent; differences over the continent are mainly attributed to discrepancies in TC tracks in proximity to the coast and TC lifetime. Reanalysis estimates of TC moisture transports show that TCs are an important moisture source for the regional water budget. TC vertically integrated moisture flux (VIMF) convergence can turn regions of weak VIMF divergence by the mean circulation into regions of weak VIMF convergence. We discuss deficiencies in the observed and reanalysis TC tracks, which limit our ability to quantify robustly the contribution of TCs to the regional hydrological cycle

Electrical stimulation of the auditory nerve: the effect of electrode position on neural excitation

Publisher’s permission requested and denied.Histological studies have shown that the Melbourne/Cochlear electrode array lies along the outer wall of the scala tympani and is therefore some distance from the residual VIIIth nerve elements. In order to investigate the influence of electrode position on neural excitation we systematically varied the position of the electrode array within the cat scala tympani while recording electrically evoked auditory brainstem responses (EABRs). Using both normal hearing and long-term deafened animals, we observed significant reductions in EABR thresholds as the electrode array was moved from the outer wall towards the modiolus. Further threshold reductions were observed when the array was placed underneath the osseous spiral lamina (OSL) close to the peripheral dendrites. These changes were independent of the bipolar inter-electrode separation, and were observed over a wide range of cochlear pathologies varying from normal to a moderate spiral ganglion cell loss. Interestingly, the one animal exhibiting extensive neural loss showed no correlation between EABR threshold and electrode position. There was also a general decrease in the gradient of the EABR input-output function as the electrode array was moved closer to the neural elements. This was, however, only statistically significant when the electrode was positioned adjacent to the peripheral dendrites. Significant reductions in EABR threshold were also observed as the inter-electrode spacing of the bipolar electrodes was increased. The gradient of the EABR input-output function also increased with increasing inter-electrode spacing, although again, this was only significant when the electrode array was positioned close to the neural elements. The present results indicate that the optimum placement of a Melbourne/Cochlear electrode array is adjacent to the peripheral dendrites. However, such a site would be difficult to achieve in practice while minimizing insertion trauma. An array lying adjacent to the modiolus would be a safe alternative while ensuring a significant reduction in threshold compared with the existing site (outer wall). This placement should result in more localized neural excitation patterns, an increase in the number of bipolar electrodes available, together with an increase in their dynamic range. These changes may lead to further improvements in speech perception among cochlear implant patients

The influence of electrode geometry on the electrically evoked auditory brain stem response

The electrically-evoked auditory brainstem response (EABR) consists of a series of far-field potentials that reflect synchronous neural activity within the auditory brainstem in response to a transient electrical stimulus. The EABR appears relatively simply organized in terms of its amplitude and latency behaviour. The growth in amplitude of wave IV of the EABR, for example, reflects changes in the amplitude of the electrically-evoked VIII nerve compound action potential as a function of stimulus intensity. In addition, single unit population studies have shown a monotonic relationship between the growth in EABR amplitude and the number of nerve fibres being stimulated (Merzenich and White, 1977). The EABR can therefore, provide an insight into the response of the auditory nerve to electrical stimulation. We have used this technique to investigate the efficacy of electrical stimulation of the auditory nerve using a variety of stimulating electrode geometries

The effect of position of the scala tympani electrode array on auditory nerve excitation [Abstract]

This is an abstract of a paper from the Proceedings of the 51st Australian Physiological and Pharmacological Society, Brisbane, 17-20 April 1990, published by Australian Physiological and Pharmacological Society. This version is reproduced with the permission of publisher.Multiple-channel auditory prostheses provide both temporal and formant information to profoundly-totally deaf patients. This is achieved via direct electrical stimulation of selective regions of the residual auditory nerve using an electrode array located in the scala tympani. Histological evidence has shown that these electrode arrays lie along the outer wall of the scala tympani, some distance from the residual nerve elements. In the present study we systematically varied the position of the electrode array within the cat scala tympani in order to investigate the influence of electrode position on neural excitation. Such knowledge may contribute to the development of improved electrode arrays for auditory prostheses.17-20 Apri

Electrical stimulation of the auditory nerve: the influence of electrode position on neural excitation

Improved speech recognition among cochlear implant patients would appear to be dependent on a number of factors including improved speech processing strategies and an improvement in the effectiveness of electrically stimulating residual auditory nerve fibers (i.e. lower thresholds, wider dynamic ranges and more localized current spread). Previous human temporal bone studies have shown that free fit scala tympani electrode arrays generally lay along the outer wall of the scala tympani. Therefore, there is a relatively large distance between the electrode array and the residual neural elements within Rosenthal's canal. In the present study, we systematically varied the location of the electrode within the scala tympani to examine the influence of electrode position on neural excitation.10-15 September 198

Dimensions of the scala tympani in the human and cat with reference to cochlear implants

This is a publisher’s version of an article published in Annals of Otology, Rhinology & Laryngology published by Annals Publishing Company. This version is reproduced with permission from Annals Publishing Company. http://www.annals.com/The width, height, and cross-sectional area of the scala tympani in both the human and cat were measured to provide dimensional information relevant to the design of scala tympani electrode arrays. Both the height and width of the human scala tympani decrease rapidly within the first 1.5 mm from the round window. Thereafter, they exhibit a gradual reduction in their dimension with increasing distance from the round window. The cross-sectional area of the human scala tympani reflects the changes observed in both the height and width. In contrast, the cat scala tympani exhibits a rapid decrease in its dimensions over the first 6 to B mm from the round window. However, beyond this point the cat scala tympani also exhibits a more gradual decrease in its dimensions. Finally, the width of the scala tympani, in both human and cat, is consistently greater than the height

Temporal and spatial coding in auditory prostheses

Publisher’s permission requested and denied.By direct electrical stimulation of residual auditory nerve fibres, auditory prostheses by-pass the normal electro-mechanical transduction properties of the cochlea in patients who have few -if any -surviving inner or outer hair cells. These devices interface directly with the auditory nerve via stimulating electrodes placed within the scala tympani of the cochlea. While the great majority of profoundly-totally deaf patients using multiple-channel auditory prostheses receive considerable benefit from their device (Brown et al., 1987), a greater understanding of the basic response properties of the auditory nerve to electrical stimulation should result in the development of improved electrical stimulation regimes and electrode array designs. It is the purpose of this chapter to review these basic neural response properties