Acoustic scattering by benthic and planktonic shelled animals

Author Posting. © Acoustical Society of America, 2000. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 108 (2000): 535-550, doi:10.1121/1.429584.Acoustic backscattering measurements and associated scattering modeling were recently conducted on a type of benthic shelled animal that has a spiral form of shell (Littorina littorea). Benthic and planktonic shelled animals with this shape occur on the seafloor and in the water column, respectively, and can be a significant source of acoustic scattering in the ocean. Modeling of the scattering properties allows reverberation predictions to be made for sonar performance predictions as well as for detection and classification of animals for biological and ecological applications. The studies involved measurements over the frequency range 24 kHz to 1 MHz and all angles of orientation in as small as 1° increments. This substantial data set is quite revealing of the physics of the acoustic scattering by these complex shelled bodies and served as a basis for the modeling. Specifically, the resonance structure of the scattering was strongly dependent upon angle of orientation and could be traced to various types of rays (e.g., subsonic Lamb waves and rays entering the opercular opening). The data are analyzed in both the frequency and time domain (compressed pulse processing) so that dominant scattering mechanisms could be identified. Given the complexity of the animal body (irregular elastic shell with discontinuities), approximate scattering models are used with only the dominant scattering properties retained. Two models are applied to the data, both approximating the body as a deformed sphere: (1) an averaged form of the exact modal-series-based solution for the spherical shell, which is used to estimate the backscattering by a deformed shell averaged over all angles of orientation, and produces reasonably accurate predictions over all k1aesr (k1 is the acoustic wave number of the surrounding water and aesr is the equivalent spherical radius of the body), and (2) a ray-based formula which is used to estimate the scattering at fixed angle of orientation, but only for high k1aesr. The ray-based model is an extension of a model recently developed for the shelled zooplankton Limacina retroversa that has a shape similar to that of the Littorina littorea but swims through the water [Stanton et al., J. Acoust. Soc. Am. 103, 236–253 (1998b)]. Applications of remote detection and classification of the seafloor and water column in the presence of shelled animals are discussed.This work was supported by the U.S. Office of Naval Research Grant Nos. N00014-95-1- 0287 and N00014-96-1-0878, and the MIT/WHOI Joint Graduate Education Program

The College of Medicine in the Republic of Malawi: towards sustainable staff development

BACKGROUND: Malawi has a critical human resources problem particularly in the health sector. There is a severe shortage of doctors; there are only few medical specialists. The College of Medicine (COM) is the only medical school and was founded in 1991. For senior staff it heavily depends on expatriates. In 2004 the COM started its own postgraduate training programme (Master of Medicine) in the clinical specialties. METHODS: We explore to what extent a brain drain took place among the COM graduates by investigating their professional development and geographical distribution. Using current experience with the postgraduate programme, we estimate at what point all senior academic positions in the clinical departments could be filled by Malawians. We demonstrate the need for expatriate staff for its most senior academic positions in the interim period and how this can be phased out. Lastly we reflect on measures that may influence the retention of Malawian doctors. RESULTS: Since the start of the COM 254 students have graduated with an average of 17 students per year. Most (60%) are working in Malawi. Of those working abroad, 60% are in various postgraduate training programmes. In 2015, adequate numbers of Malawi senior academics should be available to fill most senior positions in the clinical departments, taking into account a 65% increase in staff to cope with increasing numbers of students. CONCLUSION: There seems to be no significant brain drain among graduates of the COM. The postgraduate programme is in place to train graduates to become senior academic staff. In the interim, the COM depends heavily upon expatriate input for its most senior academic positions. This will be necessary at least until 2015 when sufficient numbers of well trained and experienced Malawian specialists may be expected to be available. Improved pay structure and career development perspectives will be essential to consolidate the trend that most doctors will remain in the country

Structure of the Current Sheet in the 11 July 2017 Electron Diffusion Region Event.

The structure of the current sheet along the Magnetospheric Multiscale (MMS) orbit is examined during the 11 July 2017 Electron Diffusion Region (EDR) event. The location of MMS relative to the X-line is deduced and used to obtain the spatial changes in the electron parameters. The electron velocity gradient values are used to estimate the reconnection electric field sustained by nongyrotropic pressure. It is shown that the observations are consistent with theoretical expectations for an inner EDR in 2-D reconnection. That is, the magnetic field gradient scale, where the electric field due to electron nongyrotropic pressure dominates, is comparable to the gyroscale of the thermal electrons at the edge of the inner EDR. Our approximation of the MMS observations using a steady state, quasi-2-D, tailward retreating X-line was valid only for about 1.4 s. This suggests that the inner EDR is localized; that is, electron outflow jet braking takes place within an ion inertia scale from the X-line. The existence of multiple events or current sheet processes outside the EDR may play an important role in the geometry of reconnection in the near-Earth magnetotail

Airborne Visible/Infrared Imaging Spectrometer (AVIRIS): Recent improvements to the sensor

AVIRIS is a NASA-sponsored Earth-looking imaging spectrometer designed, built and operated by the Jet Propulsion Laboratory. Spectral, radiometric and geometric characteristics of the data acquired by AVIRIS are given in Table 1. AVIRIS has been operational since 1989, however in each year since 1989 major improvements have been completed in most of the subsystems of the sensor. As a consequence of these efforts, the capabilities of AVIRIS to acquire and deliver calibrated imaging spectrometer data of high quality have improved significantly over those in 1989. Improvements to AVIRIS prior to 1992 have been described previously (Porter et al., 1990, Chrien et al., 1991, & Chrien et al., 1992). In the following sections of this paper we describe recent and planned improvements to AVIRIS in the sensor task

Identification and implementation of potential energy efficiency programs in Indian Country: Working paper series--04-03

The strongest recommendation stemming from the Air Pollution Prevention forum of the Western Regional Air Partnership (WRAP) was for tribes to develop and implement energy plans. This paper provides a discussion of the benefits of any such plan and itemized a variety of components of any said plan. A brief discussion of the WRAP is presented is the framework of improving air quality. Based on the background of Jacobs (2000) and Smith (2000), the primary and secondary benefits of energy efficiency plans are then discussed. Then a series of specific recommendations are itemized. These include tribally sponsored programs, collaborative opportunities, and tribal leadership programs

Economic analysis of energy efficiency measures: Tribal case studies with The Confederated Salish and Kootenai Tribes of The Flathead Reservation, The Pascua Yaqui Tribe, and The Yurok Tribe: Working paper series--04-02

The best way to reduce air pollution from the production of electricity is not to produce it in the first place. This paper presents three cases studies explaining how energy efficiency programs can be beneficial to tribes from a purely cost-saving basis, The Yurok, Flathead and Pascua Yaqui Reservations graciously provided an opportunity to investigate energy efficiency for their tribes. In each case the consumption of electricity was reduced such that a positive net present value was present following an initial capital investment. In the case of the irrigation systems on the Flathead Reservation, the savings were substantial even though no explicit savings of water was accounted for. It is estimated that tribes can reduce electricity costs by 10-50% by following energy efficiency programs. Many programs can be very simple involving small upfront capital outlays, such as changing light bulbs or installing motion sensors. The Yurok case showed a return of 7.5% after simply changing bulbs and the Pasqua Yaqui case showed a possible return of 10-80%. Other tribes could make similar investments and realize similar benefits in addition to improved air quality. The strongest recommendation from the Air Pollution Prevention Forum to tribes was to develop an energy plan. These cases show that some fairly simple analysis can make a plan very beneficial

Recommendations for reducing energy consumption and improving air quality through energy efficiency in Indian Country: Working paper series--04-04

The strongest recommendation stemming from the Air Pollution Prevention forum of the Western Regional Air Partnership (WRAP) was for tribes to develop and implement energy plans. This paper provides a discussion of the benefits of any such plan and itemized a variety of components of any said plan. A brief discussion of the WRAP is presented is the framework of improving air quality. Based on the background of Jacobs (2000) and Smith (2000), the primary and secondary benefits of energy efficiency plans are then discussed. Then a series of specific recommendations are itemized. These include tribally sponsored programs, collaborative opportunities, and tribal leadership programs