Parameter mixing errors within a measuring volume with applications to incoherent scatter

The effect on parameter error estimates resulting from parameter variations within the measuring volume under consideration is studied in the framework of linear statistical inversion theory. It is shown that using estimates for the parameter averages is equivalent to having the theory corrected by the covariances of the variables coupled with the second derivatives of the theory function. If the parameter distributions were known exactly, this would only introduce a bias in the linear theory and hence a systematic error in the parameter centre point estimates. When the distributions are not known exactly, there is another source of error consisting of the uncertainties in the parameter variation estimates. This leads to new error bounds on the allowed parameter variability within the volume under consideration if some prescribed accuracy in the parameter average estimates is required. These considerations are applied to incoherent scatter (IS) radar measurements, where it is important to be able to estimate the effect of integrating both in space and time over a volume with varying parameters in order to obtain spectra or autocorrelation functions. Numerical examples are given in the case of the O⁺ content estimates in measurements with the EISCAT UHF radar, when for example the ion temperature varies over the integration ranges. The results obtained may be used in the design of experiments when high resolution composition measurements are required.     

A nonlinear maximum entropy method for spectral estimation applied to incoherent scatter radar measurements: application to synthetic incoherent scatter data

The EISCAT measurements are based on the autocorrelation function technique. An alternative approach is to derive the ionospheric parameters from an estimate of the power spectrum for the received radar signal. We have used a nonlinear maximum entropy method to deduce parameters from the power spectrum of a generated signal. A comparison has been made with parameters obtained by the ACF method. This preliminary study suggests that the spectrum method could become useful, especially for determining the position of peaks in the incoherent scatter spectrum.     

Observational technique and parameter estimation in plasma line spectrum observations of the ionosphere by chirped incoherent scatter radar

With the 430 MHz incoherent scatter radar facility at the Arecibo Observatory, the plasma line spectrum has been measured with a linearly frequency modulated or ‘chirped’ pulse. On reception the signal is demodulated (‘dechirped’). The paper describes the experimental set-up and the parameter estimation for day-time ionosphere observations. Using a non-linear least squares fit it is possible to determine the linear and quadratic coefficients of a locally parabolic plasma line frequency versus height profile. The strength of the plasma line and the point of tangency of the locally parabolic plasma line frequency profile can be determined very accurately. In measurements of the day-time ionosphere the plasma line was found to be enhanced by about 70 times over the thermal equilibrium level.     

Studies of the cusp and auroral zone with incoherent scatter radar: the scientific and technical case for a polar-cap radar

A combined scientific and technical case is presented for the establishment of a new incoherent scatter radar facility on the archipelago of Svalbard. The scientific case rests principally on the ability of such a system to contribute significantly to the elucidation of the chain of physical processes involved in solar wind-magnetosphere-ionosphere-thermosphere coupling, particularly those processes associated with the dayside cusp and auroral zone. These latter regions map magnetically to the vicinity of the dayside magnetopause, and the consequent prospect of conducting co-ordinated observations with the ESA Cluster spacecraft at high altitudes provides strong motivation for ensuring that the radar facility becomes operational no later than 1995. Important features of the Svalbard site include its relatively high geographic latitude, which allows cusp aurorae to be observed under winter solstice conditions, and its proximity to the existing EISCAT incoherent scatter system, with the possibility of joint operations. The latter possibility is not only important for studies of the structure and motion of the high-latitude ionosphere, but is also particularly significant for plasma-physics investigations, which form another major topic of study. It is possible that the facility will be able to contribute significantly to polar stratospheric-tropospheric circulation studies relevant to the ozone-depletion problem. To accomplish these objectives, a tristatic radar system, capable of making full velocity vector measurements, would be ideal. However, the realization of such a system on the islands of Svalbard would present formidable logistic difficulties and an adequate alternative would be a system with three co-located fully steerable parabolic antennae, which could be operated either independently or together, in any combination. This configuration lends itself to a construction scheme that would allow significant observations to be made at an early stage with a partial radar system. The proposed construction scheme could be implemented by 1995 and would have sufficient flexibility to incorporate possible enhancements to the radar system in the future.     

Comparison of incoherent scatter observations of electron density,and electron and ion temperature at Millstone Hill with the International Reference Ionosphere

Millstone Hill incoherent scatter (IS) observations of electron density (N_e, electron temperature (T_e) and ion temperature (T_i) are compared with the International Reference Ionosphere (IRI-86) for both noon and midnight, for summer, equinox and winter, at both solar maximum (1979–1980) and solar minimum (1985–1986). The largest difference inN_e is found in the topside, where values of N_e given by IRI-86 are generally larger than those obtained from IS measurements, by a factor which increases with increasing height, and which has a mean value near two at 600 km. Apart from the bottom of the profile, which is tied to the CIRA neutral temperature, the IRI-86 T_e model has no solar cycle variation. However, the IS measurements during the summer reveal larger T_e at solar maximum than at solar minimum. At other seasons higher T_e at solar maximum occurs only during the daytime at the greater heights. Nighttime T_e is shown by the IS radar to be generally larger in winter than in summer, an effect not included in the IRI. This is apparently due to photoelectron heating during winter from the sunlit ionosphere conjugate to Millstone Hill. The day-night difference in T_i given by IRI-86 above 600km is not as large in the IS measurements.     

EISCAT incoherent scatter radar observations and model studies of day to twilight variations in the D-region during the PCA event of August 1989

An intense solar proton event causing enhanced ionization in the ionospheric D-region occurred on 12 August 1989. The event was partially observed during three successive nights by the EISCAT UHF incoherent scatter radar at Ramfjordmoen near Tromsa, Norway. Ion production rates calculated from GOES-7 satellite measurements of proton flux and a detailed ion chemistry model of the D-region are used together with the radar data to deduce electron concentration, negative ion to electron concentration ratio, mean ion mass and neutral temperature in the height region from 70 to 90 km, at selected times which correspond to the maximum and minimum solar elevations occurring during the radar observations. The quantitative interpretation of EISCAT data as physical parameters is discussed. The obtained temperature values are compared with nearly simultaneous temperature measurements at Andøya based on lidar technique.     

Computation of whistler wave normals using a combined matched filtering and parameter estimation technique

A new method is presented for computing the wave normal directions of deterministic VLF signals that can be approximated by plane waves. The a priori information about the frequency-time behaviour of the signal is exploited by a matched filtering and subsequent parameter estimation technique. The method was developed basically to determine wave normal directions of whistlers from wave field components measured on-board. After an outline of the method, results obtained for simulated whistlers are presented that demonstrate the superiority of the new method over the cross-product and Means methods.     

A measure of pre-Q-ness with applications to archaeology

It is generally assumed that if down each column of a data matrix the quantities, or proportions, of the different types of artifacts in the provenances never fall and then rise again, the ordering of the provenances corresponding to that of the rows of the matrix is a serious candidate for their relative chronological ordering. In practice, of course, a data matrix is unlikely to give rise to such a perfect form even when it is known that there is a true relative chronological ordering of the provenances. Here we propose a measure of how far a data matrix fails to be perfect in this respect. As well as a discussion of the theoretical background, we offer some experimental results which lead us to hope that this measure is meaningful in certain situations. The approach adopted here stems from the earlier work by D. G. Kendall on Q-matrices.     

The limits of responsibility: a postcolonial politics of academic knowledge production

A range of recent debates in geography have considered responsibility and/or critical practice, including the connections between knowledge production, ethics and politics. Taking our cue from these debates, this paper explores the question and limits of responsibility in research across a global North–South divide. Emerging from reflections on our own research projects, we interrogate a central challenge of postcolonial knowledge production by examining two limits to, and constraints upon, responsible knowledge production across the global North–South: abstraction and representation, and learning. First, we argue that the forms of distancing that can inhere in abstraction risk sidestepping the concerns of 'the field' by decontextualising places/constituencies/ideas. This involves considering the representational economies at stake in negotiating slippages of distance or practices of learning. We argue in favour of creative and generative representations that might be produced through more participatory and uncertain practices. Second, we explore an ethical and indirect conception of learning as a basis for alternative modes of engagement with communities and researchers in research practice. In making this argument, we do not offer a kind of formula for responsibility in research nor do we argue simply for research to be more 'relevant'. Instead, and alert to our own positions of privilege, we seek to draw attention to these two limits to responsible praxis in the academic knowledge production process precisely because they can act as important registers for thinking through the politics of conducting research between different and sometimes co-constituting cultures of knowledge production.     

The pure effect of social preferences on regional location choices: The evolving dynamics of convergence to a steady state population distribution

This paper tracks the consequences of individuals’ desire to align their location with their social preferences. The social preference studied in the paper is distaste for relative deprivation, measured in a cardinal manner. Location is conceived as social space, with individuals choosing to relocate if, as a result, their relative deprivation will be reduced, holding their incomes constant. Conditions are provided under which the associated dynamics reaches a spatial steady state, the number of periods it takes to reach a steady state is specified, and light is shed on the robustness of the steady state outcome. By way of simulation it is shown that for large populations, a steady state of the relocation dynamics is almost always reached, typically in one period, and that cycles are more likely to occur when the populations’ income distributions are more equal.     

Automatic fitting of quasi-parabolic segments to ionospheric profiles with application to ground range estimation for single-station location

A method of automatically fitting a quasi-parabolic segment (QPS) model to measured profiles of electron concentration is described. The model consists of many smoothly joined quasi-parabolic segments. The base of the ionosphere is represented by a quasi-linear segment. This model has the advantage of possessing analytic solutions for ray quantities in a spherical ionosphere (neglecting the effect of the Earth's magnetic field). It is also able to represent measured vertical ionospheric profiles to within a few percent in electron concentration.The usefulness of the model is illustrated by an application to the single-station location (SSL) of a distant radio transmitter from angle-of-elevation measurements. The no magnetic field results can represent the ordinary mode and approximate results for the extraordinary mode can be obtained using a frequency scaling technique.     

The effect of culture on home-ownership

In this paper, we analyze the role of culture in determining whether, or not, an individual is a homeowner. We use data on first-generation immigrants who arrived in the United States under 6 years old. Following the epidemiological approach, any dissimilarity in the proportion of homeowners by country of origin may be interpreted as a consequence of cultural differences. Our estimates indicate that there is a positive and statistically significant relationship between the cultural proxy and the immigrants’ choice of home-ownership. Additionally, we present evidence of different mechanisms of transmission of culture, which reinforces our results on the cultural effect.     

Research,knowledge transfer,and innovation: The effect of Italian universities’ efficiency on local economic development 2006−2012

We test whether there is a link between the performance of universities, measured through a concept of efficiency, and the economic development of the regions in which they operate. Indicators of teaching, research, and third mission are considered as outputs. To handle endogeneity problems between the efficiency of universities and economic development, a system generalized method of moments and then an instrumental variable approach are used. Our findings reveal that the presence of efficient universities fosters local economic development. Knowledge spillovers occur to areas that are in close geographical proximity to efficient universities. Results are robust to different estimation strategies.     

The development and evolution of “cerebral thermometry”: Clinical applications of a nineteenth-century approach to cerebral localization and neurological diagnosis

ABSTRACT

Surface thermometers were developed in the latter half of the nineteenth century. In 1877, Broca, already famous for his contributions to the cerebral localization of nonfluent aphasia, presented his first clinical observations on cranial surface temperatures: In two cases, cranial surface temperatures were decreased over a middle cerebral artery infarction, and increased in surrounding areas, which Broca attributed to “compensatory hyperaemia.” As Broca made apparent in a later report in 1879, he had used a “thermometric crown,” an apparatus consisting of six to eight large-reservoir mercury thermometers strapped against the head. Following Broca’s report, American neurologists reported cases in which cranial surface temperatures were increased either locally over a superficial brain tumor or globally with a cerebral abscess. Despite promising anecdotal reports, contemporaries recognized that significant technical and practical problems limited its accuracy, reliability, and clinical utility. Advocates never demonstrated that this technology provided significant marginal benefit to the medical history and physical examination. The technique fell out of fashion before 1900, though some early advocates promoted it into the early twentieth century. It was ultimately replaced by more effective technologies for cerebral localization and neurological diagnosis.     

From 'industrial districts' to 'knowledge clusters': a model of knowledge dissemination and competitive advantage in industrial agglomerations

This paper integrates knowledge-based theories of the firm withgeograph-ical studies of industrial agglomeration to producea model that helps explain the competitive advantages enjoyedby proximate firms located in geographical clusters. We proposea hierarchy of specialized knowledge stocks at both firm andcluster levels and suggest that the comparative advantage conferredby knowledge resources at each level is protected, in part,by asymmetries in knowledge flows from level to level. The paperargues that codified component knowledge is more easily spreadthan firm-specific architectural knowledge. Nevertheless, overtime, agglomerations may develop a cluster-specific form ofarchitectural knowledge that facilitates the rapid disseminationof knowledge throughout the cluster by increasing the learningcapacity of proximate firms and thereby conferring cluster-specificcompetitive advantages.