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

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 $a$ of type (species) $i$ interacts with an agent $b$ of type (species) $j$ with $a$ as the initiator, then $b$'s type becomes $i$ with probability $P\_{ij}$. In such an interaction, we think of $a$ as the predator, $b$ 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 $n$-agent population converges to some absorbing state in time polynomial in $n$, 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:&#xd;&#xa;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.&#xd;&#xa;&#xd;&#xa;Model:&#xd;&#xa;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 &#x201c;cheater&#x201d; or &#x201c;selfish&#x201d; 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.&#xd;&#xa;&#xd;&#xa;Results:&#xd;&#xa;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 &#x201c;hypercheaters&#x201d; could further arrest the copy numbers to a substantially lower level.&#xd;&#xa;&#xd;&#xa;Conclusions:&#xd;&#xa;These sociobiological interactions might explain the stability of copy numbers better than molecular mechanisms of replication regulation alone

The effect of distance on reaction time in aiming movements

Target distance affects movement duration in aiming tasks but its effect on reaction time (RT) is poorly documented. RT is a function of both preparation and initiation. Experiment 1 pre-cued movement (allowing advanced preparation) and found no influence of distance on RT. Thus, target distance does not affect initiation time. Experiment 2 removed pre-cue information and found that preparing a movement of increased distance lengthens RT. Experiment 3 explored movements to targets of cued size at non-cued distances and found size altered peak speed and movement duration but RT was influenced by distance alone. Thus, amplitude influences preparation time (for reasons other than altered duration) but not initiation time. We hypothesise that the RT distance effect might be due to the increased number of possible trajectories associated with further targets: a hypothesis that can be tested in future experiments