4,172 research outputs found
Refreshment by the case: Use of multimedia in case study assessment
This paper outlines a novel approach to developing, presenting and using a multimedia case study for the assessment of a large (circa 230 students) Operations Management module at undergraduate level on a Business Studies programme. Engagement, realism and handling complexity are important issues in Operations Management teaching, learning and assessment. It is argued that traditional text based case studies do not address these concerns sufficiently and consequently can encourage surface learning approaches. Consultancy and simulation are more likely to be effective on these issues with the greater focus on experiential learning. However the constraints of these techniques restrict use as assessment options, particularly for large undergraduate programmes. This paper offers tutors of Operations Management an alternative approach to facilitating experiential learning using a multimedia case. The action research reported here develops this multimedia approach, identifies the practical considerations and the potential for improved student learning outcomes. The findings indicate that this multimedia approach was engaging, realistic and challenging hence facilitated greater student interest, understanding and skills
A Precise Distance to IRAS 00420+5530 via H2O Maser Parallax with the VLBA
We have used the VLBA to measure the annual parallax of the H2O masers in the
star-forming region IRAS 00420+5530. This measurement yields a direct distance
estimate of 2.17 +/- 0.05 kpc (<3%), which disagrees substantially with the
standard kinematic distance estimate of ~4.6 kpc (according to the rotation
curve of Brand and Blitz 1993), as well as most of the broad range of distances
(1.7-7.7 kpc) used in various astrophysical analyses in the literature. The
3-dimensional space velocity of IRAS 00420+5530 at this new, more accurate
distance implies a substantial non-circular and anomalously slow Galactic
orbit, consistent with similar observations of W3(OH) (Xu et al., 2006;
Hachisuka et al. 2006), as well as line-of-sight velocity residuals in the
rotation curve analysis of Brand and Blitz (1993). The Perseus spiral arm of
the Galaxy is thus more than a factor of two closer than previously presumed,
and exhibits motions substantially at odds with axisymmetric models of the
rotating Galaxy.Comment: 33 pages, 12 figures; Accepted by ApJ (to appear March 2009
A best online algorithm for scheduling on two parallel batch machines
AbstractWe consider the online scheduling on two parallel batch machines with infinite batch size to minimize makespan, where jobs arrive over time. That is, all information of a job is not available until it is released. For this online scheduling problem, Nong et al. [Q.Q. Nong, T.C.E. Cheng, C.T. Ng, An improved online algorithm for scheduling on two unrestrictive parallel batch processing machines, Operations Research Letters, 36 (2008) 584–588] have provided an online algorithm with competitive ratio no greater than 2. We show that this bound is tight for the problem. Furthermore we give a new best possible online algorithm with a tighter structure
WUSL–SOD: Joint weakly supervised, unsupervised and supervised learning for salient object detection
Deep learning methods for salient object detection (SOD) have been studied actively and promisingly. However, it is still challenging for the studies with two aspects. The first one is a single type of label from the network to convey limit information, which leads to the poor generalization ability of the network. The second one is the difficulty to improve the accuracy and detect details of target. To address these challenges, we develop a novel approach via joint weakly supervised, unsupervised and supervised learning for SOD (WUSL–SOD), which differs from existing methods just based on ground-truth or other sparse labels. Specifically, to optimize the objective of the image, the unsupervised learning module (ULM) is designed to generate coarse saliency feature and suppress background noises via attention guiding mechanism. Then, we propose the weakly supervised learning module (WLM) based on scribbles for producing relatively accurate saliency feature. Note that this structure is used to enhance the details and remedy the deficiency of scribbles in WLM. For further refining information from the ULM and WLM, we propose a supervised learning module (SLM), which is not only applied to process and refine information from the ULM and WLM, but also enhance the image details and capture the entire target area. Furthermore, we also exchange information between the SLM and the WLM to obtain more accurate saliency maps. Extensive experiments on five datasets demonstrate that the proposed approach can effectively outperform the state-of-the-art approaches and achieve real-time.</p
On Convergence and Threshold Properties of Discrete Lotka-Volterra Population Protocols
In this work we focus on a natural class of population protocols whose
dynamics are modelled by the discrete version of Lotka-Volterra equations. In
such protocols, when an agent of type (species) interacts with an agent
of type (species) with as the initiator, then 's type becomes
with probability . In such an interaction, we think of as the
predator, as the prey, and the type of the prey is either converted to that
of the predator or stays as is. Such protocols capture the dynamics of some
opinion spreading models and generalize the well-known Rock-Paper-Scissors
discrete dynamics. We consider the pairwise interactions among agents that are
scheduled uniformly at random. We start by considering the convergence time and
show that any Lotka-Volterra-type protocol on an -agent population converges
to some absorbing state in time polynomial in , w.h.p., when any pair of
agents is allowed to interact. By contrast, when the interaction graph is a
star, even the Rock-Paper-Scissors protocol requires exponential time to
converge. We then study threshold effects exhibited by Lotka-Volterra-type
protocols with 3 and more species under interactions between any pair of
agents. We start by presenting a simple 4-type protocol in which the
probability difference of reaching the two possible absorbing states is
strongly amplified by the ratio of the initial populations of the two other
types, which are transient, but "control" convergence. We then prove that the
Rock-Paper-Scissors protocol reaches each of its three possible absorbing
states with almost equal probability, starting from any configuration
satisfying some sub-linear lower bound on the initial size of each species.
That is, Rock-Paper-Scissors is a realization of a "coin-flip consensus" in a
distributed system. Some of our techniques may be of independent value
5-Benzyl-2-phenyl-6,8-dihydro-5H-1,2,4-triazolo[3,4-c][1,4]oxazin-2-ium hexafluoridophosphate
The title compound, C18H18N3O+·PF6
−, is a chiral bicyclic 1,2,4-triazolium salt which contains four rings, viz. a triazolium, a morpholine and two phenyl rings. Analysis of bond lengths shows that the N—CH—N group in the triazolium ring conforms to a typical three-center/four-electron bond (also known as the Pimentel–Rundle three-center model). The structure is completed by a disordered PF6
− counter-ion [occupancies of F atoms 0.678 (8):0.322 (8)], which interacts with the main molecule through weak intermolecular P—F⋯π interactions
Karyotypic description of the stingless bee Oxytrigona cf. flaveola (Hymenoptera, Apidae, Meliponina) of a colony from Tangará da Serra, Mato Grosso State, Brazil
The aim was to broaden knowledge on the cytogenetics of the subtribe Meliponina, by furnishing cytogenetic data as a contribution to the characterization of bees from the genus Oxytrigona. Individuals of the species Oxytrigona cf. flaveola, members of a colony from Tangará da Serra, Mato Grosso State, Brazil, were studied. The chromosome number was 2n = 34, distributed among four chromosomal morphologies, with the karyotype formula 8m+8sm+16st+2t. Size heteromorphism in the first metacentric pair, subsequently confirmed by sequential staining with fluorochrome (DA/DAPI/CMA3 ), was apparent in all the examined individuals The nucleolar organizing regions (NORs) are possibly located in this metacentric chromosome pair. These data will contribute towards a better understanding of the genus Oxytrigona. Given that species in this group are threatened, the importance of their preservation and conservation can be shown in a sensible, concise fashion through studies such as this
Altruism can proliferate through group/kin selection despite high random gene flow
The ways in which natural selection can allow the proliferation of
cooperative behavior have long been seen as a central problem in evolutionary
biology. Most of the literature has focused on interactions between pairs of
individuals and on linear public goods games. This emphasis led to the
conclusion that even modest levels of migration would pose a serious problem to
the spread of altruism in group structured populations. Here we challenge this
conclusion, by analyzing evolution in a framework which allows for complex
group interactions and random migration among groups. We conclude that
contingent forms of strong altruism can spread when rare under realistic group
sizes and levels of migration. Our analysis combines group-centric and
gene-centric perspectives, allows for arbitrary strength of selection, and
leads to extensions of Hamilton's rule for the spread of altruistic alleles,
applicable under broad conditions.Comment: 5 pages, 2 figures. Supplementary material with 50 pages and 26
figure
Sociobiological Control of Plasmid copy number
Background:
All known mechanisms and genes responsible for the regulation of plasmid replication lie with the plasmid rather than the chromosome. It is possible therefore that there can be copy-up mutants. Copy-up mutants will have within host selective advantage. This would eventually result into instability of bacteria-plasmid association. In spite of this possibility low copy number plasmids appear to exist stably in host populations. We examined this paradox using a computer simulation model.

Model:
Our multilevel selection model assumes a wild type with tightly regulated replication to ensure low copy number. A mutant with slightly relaxed replication regulation can act as a “cheater” or “selfish” plasmid and can enjoy a greater within-host-fitness. However the host of a cheater plasmid has to pay a greater cost. As a result, in host level competition, host cell with low copy number plasmid has a greater fitness. Furthermore, another mutant that has lost the genes required for conjugation was introduced in the model. The non-conjugal mutant was assumed to undergo conjugal transfer in the presence of another conjugal plasmid in the host cell.

Results:
The simulatons showed that if the cost of carrying a plasmid was low, the copy-up mutant could drive the wild type to extinction or very low frequencies. Consequently, another mutant with a higher copy number could invade the first invader. This process could result into an increasing copy number. However above a certain copy number within-host selection was overcompensated by host level selection leading to a rock-paper-scissor (RPS) like situation. The RPS situation allowed the coexistence of high and low copy number plasmids. The non-conjugal “hypercheaters” could further arrest the copy numbers to a substantially lower level.

Conclusions:
These sociobiological interactions might explain the stability of copy numbers better than molecular mechanisms of replication regulation alone
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