3,675 research outputs found
Opportunities for ballistic missions to Halley's comet
Alternative strategies for ballistic missions to Halley's comet in 1985-86 are described. It is shown that a large science return would be acquired from a ballistic Halley intercept in spite of the high flyby speeds of almost 60 km/sec that are associated with this mission mode. The possibility of retargeting the cometary spacecraft to additional comets after the Halley intercept also exists. In one scenario two cometary spacecraft of identical design would be used to carry out four separate cometary encounters over a three-year period. One spacecraft would intercept Halley before its perihelion passage in December 1985 and then go on to comet Borrelly witn an encounter in January 1988. The other spacecraft would be targeted for a post-perihelion Halley intercept in March 1986 before proceeding towards an encounter with comet Tempel-2 in September 1988. The flyby speeds for the Borrelly and Tempel-2 intercepts are 21 and 13 km/sec, respectively
Halley's comet 1985-86: space exploration
A coordinated program to explore Halley's comet in 1985 to 86 is proposed. The program employs a variety of observational systems for remote observations and utilizes spacecraft encounters with the comet to obtain in-situ measurements. Included in the observational network are groundbased observatories, the Space Telescope, a Spacelab cometary observatory, small astronomical satellites, and experiments carried on airborne observatories and sounding rockets. It is assumed that a ballistic flythrough technique will be used to carry out the spacecraft encounters. The proposed strategy calls for the simultaneous launch of two spacecraft towards an intercept with Halley in March 1986. Following the Halley encounter one spacecraft is retargeted to intercept comet Borrelly in January 1988, while the other spacecraft proceeds to an encounter with comet Tempel 2 in September 1988
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Improving "bag-of-keypoints" image categorisation: Generative Models and PDF-Kernels
In this paper we propose two distinct enhancements to the basic
''bag-of-keypoints" image categorisation scheme proposed in [4]. In this
approach images are represented as a variable sized set of local image
features (keypoints). Thus, we require machine learning tools which
can operate on sets of vectors. In [4] this is achieved by representing
the set as a histogram over bins found by k-means. We show how this
approach can be improved and generalised using Gaussian Mixture Models
(GMMs). Alternatively, the set of keypoints can be represented directly
as a probability density function, over which a kernel can be de ned. This
approach is shown to give state of the art categorisation performance
Redefining the TRIPS Agreement to Accommodate en masse Compulsory Licensing of Vaccines & Other Pharmaceuticals for the Treatment of Covid-19
Two view learning: SVM-2K, theory and practice
Kernel methods make it relatively easy to define complex highdimensional
feature spaces. This raises the question of how we can
identify the relevant subspaces for a particular learning task. When two
views of the same phenomenon are available kernel Canonical Correlation
Analysis (KCCA) has been shown to be an effective preprocessing
step that can improve the performance of classification algorithms such
as the Support Vector Machine (SVM). This paper takes this observation
to its logical conclusion and proposes a method that combines this
two stage learning (KCCA followed by SVM) into a single optimisation
termed SVM-2K. We present both experimental and theoretical analysis
of the approach showing encouraging results and insights
Quantification of free and metal-complexed cyanide by tetrathionate derivatization
A sensitive and robust method for detection of free and metal-complexed cyanide in solutions is described. The method does not require a distillation step and is applicable for both low ionic strength and sea-water samples. The method is based on the reaction of cyanide with potassium tetrathionate followed by high-performance liquid chromatography (HPLC) separation and UV detection of formed thiocyanate. The detection limit of the method is 250 nmol L−1 cyanide (6.5 µg L−1 CN−) without a pre-concentration step. Storage for three days does not significantly change the results. The sum of free and weak metal-complexed cyanide can be measured by tetrathionate derivatization at a pH of 10. The sum of free, weak metal-complexed cyanide, iron(II) and iron(III)-complexed cyanides may be measured by tetrathionate derivatization at pH 4.4. Derivatization requires heating to 90°C for 20 min at pH = 10 and for 12 h at pH = 4.4. Weighted mean recoveries for free, iron(II), iron(III), nickel(II), silver(I), Cd(II) and Zn(II) complexed cyanide were in the range of 87 to 112% and weighted standard deviations were in the range of 1.7 to 10.0%. The method is not applicable for cyanide complexes of gold and cobalt. We illustrate an application of cyanide quantification using pore-waters from the Delaware Great Marsh
Addressing the social determinants of health: A case study from the Mitanin (Community Health Worker) programme in India
The Mitanin Programme, a government community health worker (CHW)
programme, was started in Chhattisgarh State of India in 2002. The CHWs
(Mitanins) have consistently adopted roles that go beyond health programme-
specific interventions to embrace community mobilization and action on local
priorities. The aim of this research was to document how and why the Mitanins
have been able to act on the social determinants of health, describing the
catalysts and processes involved and the enabling programmatic and organiza-
tional factors. A qualitative comparative case study of successful action by
Mitanin was conducted in two ‘blocks’, purposefully selected as positive
exemplars in two districts of Chhattisgarh. One case focused on malnutrition
and the other on gender-based violence. Data collection involved 17 in-depth
interviews and 10 group interviews with the full range of stakeholders in both
blocks, including community members and programme team. Thematic analysis
was done using a broad conceptual framework that was further refined. Action
on social determinants involved raising awareness on rights, mobilizing women’s
collectives, revitalizing local political structures and social action targeting both
the community and government service providers. Through these processes, the
Mitanins developed identities as agents of change and advocates for the
community, both with respect to local cultural and gender norms and in
ensuring accountability of service providers. The factors underpinning successful
action on social determinants were identified as the significance of the original
intent and vision of the programme, and how this was carried through into all
aspects of programme design, the role of the Mitanins and their identification
with village women, ongoing training and support, and the relative autonomy of
the programme. Although the results are not narrowly generalizable and do not
necessarily represent the situation of the Mitanin Programme as a whole, the
explanatory framework may provide general lessons for programmes in similar
contexts.Web of Scienc
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