1,475,332 research outputs found
Person Re-identification: Past, Present and Future
Person re-identification (re-ID) has become increasingly popular in the community due to its application and research significance. It aims at spotting a person of interest in other cameras. In the early days, hand-crafted algorithms and small-scale evaluation were predominantly reported. Recent years have witnessed the emergence of large-scale datasets and deep learning systems which make use of large data volumes. Considering different tasks, we classify most current re-ID methods into two classes, i.e., image-based and video-based; in both tasks, hand-crafted and deep learning systems will be reviewed. Moreover, two new re-ID tasks which are much closer to real-world applications are described and discussed, i.e., end-to-end re-ID and fast re-ID in very large galleries. This paper: 1) introduces the history of person re-ID and its relationship with image classification and instance retrieval; 2) surveys a broad selection of the hand-crafted systems and the large-scale methods in both image- and video-based re-ID; 3) describes critical future directions in end-to-end re-ID and fast retrieval in large galleries; and 4) finally briefs some important yet under-developed issues
Cryogenics for Superconductors: Refrigeration, Delivery, and Preservation of the Cold
Applications in superconductivity have become widespread, enabled by advancements in cryogenic engineering. In this paper, the history of cryogenic refrigeration, its delivery, its preservation and the important scientific and engineering advancements in these areas in the last 100 years will be reviewed, beginning with small laboratory dewars to very large scale systems. The key technological advancements in these areas that enabled the development of superconducting applications at temperatures from 4 to 77 K are identified. Included are advancements in the components used up to the present state-of-the-art in refrigeration systems design. Viewpoints as both an equipment supplier and the end-user with regard to the equipment design and operations will be presented. Some of the present and future challenges in these areas will be outlined. Most of the materials in this paper are a collection of the historical materials applicable to these areas of interest
Phylogenetic and phenotypic divergence of an insular radiation of birds
Evolutionary divergence of lineages is one of the key mechanisms underpinning large scale
patterns in biogeography and biodiversity. Island systems have been highly influential in shaping
theories of evolutionary diversification and here I use the insular Zosteropidae of the south west
Pacific to investigate the roles of ecology and biogeography in promoting evolutionary
divergence.
Initially I build a phylogenetic tree of the study group and use it to reveal the pattern of
colonisation and diversification. My results suggest a complex history of dispersal with the
observed pattern most likely a result of repeated bouts of colonisation and extinction. I then use
the new phylogeny to quantify the diversification rates of the Zosteropidae. I find a very high rate
of lineage divergence and suggest the most likely explanation relates to extensive niche
availability in the south west Pacific. I also find evidence for an overall slowdown in diversification
combined with repeated bursts of accelerated speciation, consistent with a model of taxon
cycles. I do not find evidence for sympatric speciation, however. Finally I combine morphological
and phylogenetic data to investigate the mode of evolution, evidence for character displacement
and influence of biogeography on trait evolution. I find little support for the traditional theory of
character displacement in sympatric species. I do, however, find some support for biogeographic
theories.
Taken together my results do not support traditional theories on the ecological and
biogeographical basis of divergence, even in those cases where Zosterops have been used as
exemplars. This appears to be because those theories assume rather simple patterns of
colonisation and a static ecological system. Instead, my results suggest that evolutionary
diversification is dominated by recurrent waves of colonisation and extinction, which, viewed at
any particular moment, tend to obscure any underlying ecological rules
Myths about Small Water Harvesting Systems
Not AvailableWe are writing in response to the
article by M Dinesh Kumar,
Ankit Patel, R Ravindranath,
O P Singh “Chasing a Mirage: Water
Harvesting and Artificial Recharge in
Naturally Water-Scarce Regions” (EPW,
30 August 2008).
The authors have argued that runoff
water harvesting does not offer any potential for groundwater recharge or for improving water supplies at the basin scale.
They have, thus, concluded that the investments made on this sector are a colossal waste of scarce resources and also
cause several negative social and environmental consequences. However, in the
conclusion they say, “The foregoing analysis does not suggest that water harvesting
and groundwater recharge systems do not
generate benefits”, thus indicating an iota
of doubt.
In the process of analysis, some of the
implicit underlying assumptions made by
authors include:
(1) Comparison of annual rainfall with
annual reference/potential evapotranspiration is the guiding principle/indicator
for runoff water harvesting.
(2) Water harvesting is essentially and
in all instances meant for groundwater
recharge.
(3) Runoff is the amount in excess of the
soil moisture storage and infiltration.
(4) Watershed programmes only have
problems of quality of implementation.
(5) Water harvesting systems are, by and
large, designed to capture the entire runoff and state government and central
developmental agencies alongwith nongovernmental organisations (NGOs) are
promoting the concept.
(6) The existing storage and diversion
capacities in river basins is close to utilisable flows.
(7) Water harvesting necessarily has to
be profit-oriented and in order to make
it happen it has to be utilised for high
value crops.
(8) Reliability of supplies from water harvesting systems is very poor in arid and
semi-arid regions of India, which are characterised by low mean annual rainfalls,
very few rainy days, high inter annual
variability in rainfall and rainy days and
high potential evapotranspiration.
(9) In order to call water harvesting systems profitable, the incremental benefits
by water harvesting systems have to be
beneficial at basin scale but not at the
local level.
In the light of these assumptions and
the consequent analysis branding water
harvesting systems as ineffective, we
would like to offer our comments.
India has a long history of water harvesting which has been neglected after the
creation of large storage structures and
popularisation of borewell technology.
However, the revival of the water harvesting systems by individuals, NGOs, and
developmental agencies, has led to their
importance being recognised particularly
in arid and semi-arid rainfed areas. Water
harvesting systems were started as part
of catchment area treatment in river
basin projects to act as complementary
storage structures and to reduce the silt
movement which otherwise would reach
the reservoir leading to siltation and
reduction in effective storage over a period
of time.Not Availabl
Large-Scale Absence of Sharks on Reefs in the Greater-Caribbean: A Footprint of Human Pressures
BACKGROUND: In recent decades, large pelagic and coastal shark populations have declined dramatically with increased fishing; however, the status of sharks in other systems such as coral reefs remains largely unassessed despite a long history of exploitation. Here we explore the contemporary distribution and sighting frequency of sharks on reefs in the greater-Caribbean and assess the possible role of human pressures on observed patterns. METHODOLOGY/PRINCIPAL FINDINGS: We analyzed 76,340 underwater surveys carried out by trained volunteer divers between 1993 and 2008. Surveys were grouped within one km2 cells, which allowed us to determine the contemporary geographical distribution and sighting frequency of sharks. Sighting frequency was calculated as the ratio of surveys with sharks to the total number of surveys in each cell. We compared sighting frequency to the number of people in the cell vicinity and used population viability analyses to assess the effects of exploitation on population trends. Sharks, with the exception of nurse sharks occurred mainly in areas with very low human population or strong fishing regulations and marine conservation. Population viability analysis suggests that exploitation alone could explain the large-scale absence; however, this pattern is likely to be exacerbated by additional anthropogenic stressors, such as pollution and habitat degradation, that also correlate with human population. CONCLUSIONS/SIGNIFICANCE: Human pressures in coastal zones have lead to the broad-scale absence of sharks on reefs in the greater-Caribbean. Preventing further loss of sharks requires urgent management measures to curb fishing mortality and to mitigate other anthropogenic stressors to protect sites where sharks still exist. The fact that sharks still occur in some densely populated areas where strong fishing regulations are in place indicates the possibility of success and encourages the implementation of conservation measures
Globular cluster luminosity function as distance indicator
Globular clusters are among the first objects used to establish the distance
scale of the Universe. In the 1970-ies it has been recognized that the
differential magnitude distribution of old globular clusters is very similar in
different galaxies presenting a peak at M_V ~ -7.5. This peak magnitude of the
so-called Globular Cluster Luminosity Function has been then established as a
secondary distance indicator. The intrinsic accuracy of the method has been
estimated to be of the order of ~0.2 mag, competitive with other distance
determination methods. Lately the study of the Globular Cluster Systems has
been used more as a tool for galaxy formation and evolution, and less so for
distance determinations. Nevertheless, the collection of homogeneous and large
datasets with the ACS on board HST presented new insights on the usefulness of
the Globular Cluster Luminosity Function as distance indicator. I discuss here
recent results based on observational and theoretical studies, which show that
this distance indicator depends on complex physics of the cluster formation and
dynamical evolution, and thus can have dependencies on Hubble type, environment
and dynamical history of the host galaxy. While the corrections are often
relatively small, they can amount to important systematic differences that make
the Globular Cluster Luminosity Function a less accurate distance indicator
with respect to some other standard candles.Comment: Accepted for publication in Astrophysics and Space Science. Review
paper based on the invited talk at the conference "The Fundamental Cosmic
Distance Scale: State of the Art and Gaia Perspective", Naples, May 2011. (13
pages, 8 figures
The Fifteenth Marcel Grossmann Meeting
The three volumes of the proceedings of MG15 give a broad view of all aspects of gravitational physics and astrophysics, from mathematical issues to recent observations and experiments. The scientific program of the meeting included 40 morning plenary talks over 6 days, 5 evening popular talks and nearly 100 parallel sessions on 71 topics spread over 4 afternoons. These proceedings are a representative sample of the very many oral and poster presentations made at the meeting.Part A contains plenary and review articles and the contributions from some parallel sessions, while Parts B and C consist of those from the remaining parallel sessions. The contents range from the mathematical foundations of classical and quantum gravitational theories including recent developments in string theory, to precision tests of general relativity including progress towards the detection of gravitational waves, and from supernova cosmology to relativistic astrophysics, including topics such as gamma ray bursts, black hole physics both in our galaxy and in active galactic nuclei in other galaxies, and neutron star, pulsar and white dwarf astrophysics. Parallel sessions touch on dark matter, neutrinos, X-ray sources, astrophysical black holes, neutron stars, white dwarfs, binary systems, radiative transfer, accretion disks, quasars, gamma ray bursts, supernovas, alternative gravitational theories, perturbations of collapsed objects, analog models, black hole thermodynamics, numerical relativity, gravitational lensing, large scale structure, observational cosmology, early universe models and cosmic microwave background anisotropies, inhomogeneous cosmology, inflation, global structure, singularities, chaos, Einstein-Maxwell systems, wormholes, exact solutions of Einstein's equations, gravitational waves, gravitational wave detectors and data analysis, precision gravitational measurements, quantum gravity and loop quantum gravity, quantum cosmology, strings and branes, self-gravitating systems, gamma ray astronomy, cosmic rays and the history of general relativity
- …