264 research outputs found
A decomposition algorithm for robust lot sizing problem with remanufacturing option
In this paper, we propose a decomposition procedure for constructing robust optimal production plans for reverse inventory systems. Our method is motivated by the need of overcoming the excessive computational time requirements, as well as the inaccuracies caused by imprecise representations of problem parameters. The method is based on a min-max formulation that avoids the excessive conservatism of the dualization technique employed by Wei et al. (2011). We perform a computational study using our decomposition framework on several classes of computer generated test instances and we report our experience. Bienstock and Ă–zbay (2008) computed optimal base stock levels for the traditional lot sizing problem when the production cost is linear and we extend this work here by considering return inventories and setup costs for production. We use the approach of Bertsimas and Sim (2004) to model the uncertainties in the input
5. Forest Conservation
Expert assessors Rhett Harrison, Consultative Group on International Agricultural Research, Zambia Keith Kirby, University of Oxford, UK Gillian Petrokofsky, Biodiversity Institute Oxford, UK Rebecca K. Smith, University of Cambridge, UK William J. Sutherland, University of Cambridge, UK Tom Swinfield, Royal Society for the Protection of Birds, UK Scope of assessment: for the conservation of forest habitat (not specific species within forests), including tropical forests, temperate forests, w..
Measurement of the conductance of a hydrogen molecule
Recent years have shown steady progress in research towards molecular
electronics [1,2], where molecules have been investigated as switches [3-5],
diodes [6], and electronic mixers [7]. In much of the previous work a Scanning
Tunnelling Microscope was employed to address an individual molecule. As this
arrangement does not provide long-term stability, more recently
metal-molecule-metal links have been made using break junction devices [8-10].
However, it has been difficult to establish unambiguously that a single
molecule forms the contact [11]. Here, we show that a single H2 molecule can
form a stable bridge between Pt electrodes. In contrast to results for other
organic molecules, the bridge has a nearly perfect conductance of one quantum
unit, carried by a single channel. The H2-bridge provides a simple test system
and a fundamental step towards understanding transport properties of
single-molecule devices.Comment: 6 pages, 4 figure
Nonradial and nonpolytropic astrophysical outflows IX. Modeling T Tauri jets with a low mass-accretion rate
Context: A large sample of T Tauri stars exhibits optical jets, approximately
half of which rotate slowly, only at ten per cent of their breakup velocity.
The disk-locking mechanism has been shown to be inefficient to explain this
observational fact.
Aims: We show that low mass accreting T Tauri stars may have a strong stellar
jet component that can effectively brake the star to the observed rotation
speed.
Methods: By means of a nonlinear separation of the variables in the full set
of the MHD equations we construct semi- analytical solutions describing the
dynamics and topology of the stellar component of the jet that emerges from the
corona of the star.
Results: We analyze two typical solutions with the same mass loss rate but
different magnetic lever arms and jet radii. The first solution with a long
lever arm and a wide jet radius effectively brakes the star and can be applied
to the visible jets of T Tauri stars, such as RY Tau. The second solution with
a shorter lever arm and a very narrow jet radius may explain why similar stars,
either Weak line T Tauri Stars (WTTS) or Classical T Tauri Stars (CTTS) do not
all have visible jets. For instance, RY Tau itself seems to have different
phases that probably depend on the activity of the star.
Conclusions: First, stellar jets seem to be able to brake pre-main sequence
stars with a low mass accreting rate. Second, jets may be visible only part
time owing to changes in their boundary conditions. We also suggest a possible
scenario for explaining the dichotomy between CTTS and WTTS, which rotate
faster and do not have visible jets
KULIAH KERJA NYATA ALTERNATIF UNIVERSITAS AHMAD DAHLAN PERIODE ALTERNATIF 62 Divisi I.C.1 TAHUN AKADEMIK 2018/2019,Masjid Syakirin, Brontokusuman, Mergangsan, Yogyakarta
School dropout, problem behaviour and poor academic achievement : a longitudinal view of portuguese male offenders
This study examines school drop outs from the perspective of male adults
themselves through interviews with offenders currently serving sentences. Participants
were 10 Portuguese male inmates, between the ages of 19 and 46 years of age,
incarcerated in two prison facilities of the Azores. Qualitative and interpretative methods
were carried out using a semi-structured in-depth individual interview that was audiorecorded
and conducted on the basis of a list of topics. Interview transcripts and thematic
analysis were used in data treatment and analysis. The findings primarily indicate that
poor academic achievement and emotional and behavioural difficulties of participants
played a particular role in early school drop out. The trajectories these individuals
followed within the education system presented problem behaviour, learning disabilities,
and/or foster care interventions. While school drop out circumstances were apparently
various, analysis showed that they were underpinned by three distinct sets of conditions
generally not addressed by the education system. The analysis of the triggering factors
and the maintenance dynamics of school drop outs indicated three distinct types:
retention/absenteeism, life turning points and positive resolution. Implications for
secondary prevention and screening practices are discussed.FCT (SFRH/ BD/ 44245/ 2008)CIEC - unidade de investigação 317 da FC
Controlling Clusters of Colloidal Platelets:The Effects of Edge and Face Surface Chemistries on the Behaviour of Montmorillonite Suspensions
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