3,435 research outputs found
Resource allocation
This report discusses the problem of the allocation of resources: how should an organisation (such as MOD) invest bearing in mind the long term delay for the realization of investment strategies, and how might this apply in times of increasing budgetary constraints? After making certain simplifying assumptions, the Study Group constructed a prototype model based on the method of Optimal Control. This allows the decision maker to investigate the impact of particular investment strategies over a period of years, the impact being measured in terms of “quality” or “capability”. Interventions can be designed so that “quality” (Q) is maximized at a particular time, or so that the average quality over a given time interval is maximized. Both of these approaches are explored. This model shows reasonable behaviour when tested over a parameter set. It could be used as part of a systems approach to the defence budget as a whole, but the method itself is scalable to smaller (or larger) resourcing conundrums
Complex Networks from Simple Rewrite Systems
Complex networks are all around us, and they can be generated by simple
mechanisms. Understanding what kinds of networks can be produced by following
simple rules is therefore of great importance. We investigate this issue by
studying the dynamics of extremely simple systems where are `writer' moves
around a network, and modifies it in a way that depends upon the writer's
surroundings. Each vertex in the network has three edges incident upon it,
which are colored red, blue and green. This edge coloring is done to provide a
way for the writer to orient its movement. We explore the dynamics of a space
of 3888 of these `colored trinet automata' systems. We find a large variety of
behaviour, ranging from the very simple to the very complex. We also discover
simple rules that generate forms which are remarkably similar to a wide range
of natural objects. We study our systems using simulations (with appropriate
visualization techniques) and analyze selected rules mathematically. We arrive
at an empirical classification scheme which reveals a lot about the kinds of
dynamics and networks that can be generated by these systems
Linear Precoding in Cooperative MIMO Cellular Networks with Limited Coordination Clusters
In a cooperative multiple-antenna downlink cellular network, maximization of
a concave function of user rates is considered. A new linear precoding
technique called soft interference nulling (SIN) is proposed, which performs at
least as well as zero-forcing (ZF) beamforming. All base stations share channel
state information, but each user's message is only routed to those that
participate in the user's coordination cluster. SIN precoding is particularly
useful when clusters of limited sizes overlap in the network, in which case
traditional techniques such as dirty paper coding or ZF do not directly apply.
The SIN precoder is computed by solving a sequence of convex optimization
problems. SIN under partial network coordination can outperform ZF under full
network coordination at moderate SNRs. Under overlapping coordination clusters,
SIN precoding achieves considerably higher throughput compared to myopic ZF,
especially when the clusters are large.Comment: 13 pages, 5 figure
Assessment of total retinal blood flow using Doppler Fourier Domain Optical Coherence Tomography during systemic hypercapnia and hypocapnia.
The purpose of this study was to investigate changes in total retinal blood flow (RBF) using Doppler Fourier Domain Optical Coherence Tomography (Doppler FD-OCT) in response to the manipulation of systemic partial pressure of CO2 (PETCO2). Double circular Doppler blood flow scans were captured in nine healthy individuals (mean age ± standard deviation: 27.1 ± 4.1, six males) using the RTVue(™) FD-OCT (Optovue). PETCO2 was manipulated using a custom-designed computer-controlled gas blender (RespirAct(™)) connected to a sequential gas delivery rebreathing circuit. Doppler FD-OCT measurements were captured at baseline, during stages of hypercapnia (+5/+10/+15 mmHg PETCO2), return to baseline and during stages of hypocapnia (-5/-10/-15 mmHg PETCO2). Repeated measures analysis of variance (reANOVA) and Tukeys post hoc analysis were used to compare Doppler FD-OCT measurements between the various PETCO2 levels relative to baseline. The effect of PETCO2 on TRBF was also investigated using linear regression models. The average RBF significantly increased by 15% (P < 0.0001) with an increase in PETCO2 and decreased significantly by 10% with a decrease in PETCO2 (P = 0.001). Venous velocity significantly increased by 3.11% from baseline to extreme hypercapnia (P < 0.001) and reduced significantly by 2.01% at extreme hypocapnia (P = 0.012). No significant changes were found in the average venous area measurements under hypercapnia (P = 0.36) or hypocapnia (P = 0.40). Overall, increased and decreased PETCO2 values had a significant effect on RBF outcomes (P < 0.002). In healthy individuals, altered end-tidal CO2 levels significantly changed RBF as measured by Doppler FD-OCT
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