754 research outputs found
Biased Aspirations and Social Inequality at School: Evidence from French Teenagers
This paper provides empirical evidence on how aspirations are formed and affect individual behavior, decisions, and paths in the context of education. Using unique data on aspirations, academic performance and actual track assignment to high school of French ninth graders, we show that low-SES students have lower aspirations than their equally-achieving high-SES classmates, and that track assignments to high school the next year are even more unequal due to dysfunctional dynamics: first, both low aspirations and low SES are associated with slower academic progress over the year. Second, aspirations and parental SES play a role in track assignment independent of one’s academic performance. Our results suggest that, in France, an aspirational trap at school contributes to the poverty trap, leading to the perpetuation of social inequalities
Faster Goal-Oriented Shortest Path Search for Bulk and Incremental Detailed Routing
We develop new algorithmic techniques for VLSI detailed routing. First, we
improve the goal-oriented version of Dijkstra's algorithm to find shortest
paths in huge incomplete grid graphs with edge costs depending on the direction
and the layer, and possibly on rectangular regions. We devise estimates of the
distance to the targets that offer better trade-offs between running time and
quality than previously known methods, leading to an overall speed-up. Second,
we combine the advantages of the two classical detailed routing approaches -
global shortest path search and track assignment with local corrections - by
treating input wires (such as the output of track assignment) as reservations
that can be used at a discount by the respective net. We show how to implement
this new approach efficiently
The quality of school track assignment decisions by teachers
We study the quality of secondary school track assignment decisions in the
Netherlands, using a regression discontinuity design. In 6th grade, primary
school teachers assign each student to a secondary school track. If a student
scores above a track-specific cutoff on the standardized end-of-primary
education test, the teacher can upwardly revise this assignment. By comparing
students just left and right of these cutoffs, we find that between 50-90% of
the students are "trapped in track": these students are on the high track after
four years, only if they started on the high track in first year. The remaining
(minority of) students are "always low": they are always on the low track after
four years, independently of where they started. These proportions hold for
students near the cutoffs that shift from the low to the high track in first
year by scoring above the cutoff. Hence, for a majority of these students the
initial (unrevised) track assignment decision is too low. The results replicate
across most of the secondary school tracks, from the vocational to the academic
tracks, and stand out against an education system with a lot of upward and
downward track mobility
Research on Methods for Very Large Scale Integration Track Assignment Routing
Routing is a crucial stage in the physical design of Very Large Scale Integration (VLSI) circuits, comprising three phases: global routing, track assignment routing, and detailed routing. With the development of VLSI circuits, scholars have proposed various track assignment routing algorithms. However, improving the efficiency of track assignment routing and optimizing conflicting design rules have become bottlenecks in track assignment routing problems. This study addresses these bottlenecks by utilizing single-level horizontal and vertical Steiner trees to extract routability information of local wire nets, resolving the adaptation issue between global routing and detailed routing. The proposed algorithm enhances routability information by an average of 16.07% across ten benchmark circuits. Additionally, a Generative Neural Network model based on Conditional Variational Autoencoder (CVAE) is employed to improve the efficiency of track assignment routing, yielding significant simulation results. Furthermore, a negotiation-based tear-and-reassign approach is utilized to address track congestion issues, resulting in an average optimization of 26.03% in overlap cost, with a tradeoff of sacrificing 6.67% of wirelength on average
Delay Management Including Capacities of Stations
The question of delay management is whether passenger trains should wait for delayed feeder trains or should depart on time. Solutions to this problem strongly depend on the available capacity of the railway infrastructure. Although the limited capacity of the tracks has been considered in delay management models, the limited capacity of the stations has been neglected so far. In this paper, we develop a model for the delay management problem that includes the capacities of the stations. This model allows rescheduling the platform track assignment. Furthermore, we propose an iterative heuristic in which we first solve the delay management model with a fixed platform track assignment, and then improve this platform track assignment in each step. We show that the latter problem can be solved in polynomial time by describing it as a minimum cost flow model. Finally, we present an extension of the model that balances the delay of the passengers on one hand and the number of changes in the platform track assignment on the other. All models are evaluated on real-world instances from Netherlands Railways
Track Layouts of Graphs
A \emph{-track layout} of a graph consists of a (proper) vertex
-colouring of , a total order of each vertex colour class, and a
(non-proper) edge -colouring such that between each pair of colour classes
no two monochromatic edges cross. This structure has recently arisen in the
study of three-dimensional graph drawings. This paper presents the beginnings
of a theory of track layouts. First we determine the maximum number of edges in
a -track layout, and show how to colour the edges given fixed linear
orderings of the vertex colour classes. We then describe methods for the
manipulation of track layouts. For example, we show how to decrease the number
of edge colours in a track layout at the expense of increasing the number of
tracks, and vice versa. We then study the relationship between track layouts
and other models of graph layout, namely stack and queue layouts, and geometric
thickness. One of our principle results is that the queue-number and
track-number of a graph are tied, in the sense that one is bounded by a
function of the other. As corollaries we prove that acyclic chromatic number is
bounded by both queue-number and stack-number. Finally we consider track
layouts of planar graphs. While it is an open problem whether planar graphs
have bounded track-number, we prove bounds on the track-number of outerplanar
graphs, and give the best known lower bound on the track-number of planar
graphs.Comment: The paper is submitted for publication. Preliminary draft appeared as
Technical Report TR-2003-07, School of Computer Science, Carleton University,
Ottawa, Canad
Layout of Graphs with Bounded Tree-Width
A \emph{queue layout} of a graph consists of a total order of the vertices,
and a partition of the edges into \emph{queues}, such that no two edges in the
same queue are nested. The minimum number of queues in a queue layout of a
graph is its \emph{queue-number}. A \emph{three-dimensional (straight-line
grid) drawing} of a graph represents the vertices by points in
and the edges by non-crossing line-segments. This paper contributes three main
results:
(1) It is proved that the minimum volume of a certain type of
three-dimensional drawing of a graph is closely related to the queue-number
of . In particular, if is an -vertex member of a proper minor-closed
family of graphs (such as a planar graph), then has a drawing if and only if has O(1) queue-number.
(2) It is proved that queue-number is bounded by tree-width, thus resolving
an open problem due to Ganley and Heath (2001), and disproving a conjecture of
Pemmaraju (1992). This result provides renewed hope for the positive resolution
of a number of open problems in the theory of queue layouts.
(3) It is proved that graphs of bounded tree-width have three-dimensional
drawings with O(n) volume. This is the most general family of graphs known to
admit three-dimensional drawings with O(n) volume.
The proofs depend upon our results regarding \emph{track layouts} and
\emph{tree-partitions} of graphs, which may be of independent interest.Comment: This is a revised version of a journal paper submitted in October
2002. This paper incorporates the following conference papers: (1) Dujmovic',
Morin & Wood. Path-width and three-dimensional straight-line grid drawings of
graphs (GD'02), LNCS 2528:42-53, Springer, 2002. (2) Wood. Queue layouts,
tree-width, and three-dimensional graph drawing (FSTTCS'02), LNCS
2556:348--359, Springer, 2002. (3) Dujmovic' & Wood. Tree-partitions of
-trees with applications in graph layout (WG '03), LNCS 2880:205-217, 200
Layout optimization in ultra deep submicron VLSI design
As fabrication technology keeps advancing, many deep submicron (DSM) effects have become
increasingly evident and can no longer be ignored in Very Large Scale Integration
(VLSI) design. In this dissertation, we study several deep submicron problems (eg. coupling
capacitance, antenna effect and delay variation) and propose optimization techniques
to mitigate these DSM effects in the place-and-route stage of VLSI physical design.
The place-and-route stage of physical design can be further divided into several steps:
(1) Placement, (2) Global routing, (3) Layer assignment, (4) Track assignment, and (5) Detailed
routing. Among them, layer/track assignment assigns major trunks of wire segments
to specific layers/tracks in order to guide the underlying detailed router. In this dissertation,
we have proposed techniques to handle coupling capacitance at the layer/track assignment
stage, antenna effect at the layer assignment, and delay variation at the ECO (Engineering
Change Order) placement stage, respectively. More specifically, at layer assignment, we
have proposed an improved probabilistic model to quickly estimate the amount of coupling
capacitance for timing optimization. Antenna effects are also handled at layer assignment
through a linear-time tree partitioning algorithm. At the track assignment stage, timing is
further optimized using a graph based technique. In addition, we have proposed a novel
gate splitting methodology to reduce delay variation in the ECO placement considering
spatial correlations. Experimental results on benchmark circuits showed the effectiveness
of our approaches
On the Area of Hypercube Layouts
This paper precisely analyzes the wire density and required area in standard
layout styles for the hypercube. The most natural, regular layout of a
hypercube of N^2 nodes in the plane, in a N x N grid arrangement, uses
floor(2N/3)+1 horizontal wiring tracks for each row of nodes. (The number of
tracks per row can be reduced by 1 with a less regular design.) This paper also
gives a simple formula for the wire density at any cut position and a full
characterization of all places where the wire density is maximized (which does
not occur at the bisection).Comment: 8 pages, 4 figures, LaTe
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