Capítulo 2: Perspectivas sobre el conocimiento numérico en la niñez
2.1. EL CONOCIMIENTO NUMÉRICO: ENTRE LA CONSTRUCCIÓN LÓGICA GENERAL
2.1.1. L A CONSERVACIÓN DE CANTIDADES DISCRETAS COMO UMBRAL AL NÚMERO
3.1. Network and service description
We plan a transportation network to support nationwide trans-city overnight EDS, which is defined as key service in the service system182. Any order placed by the end of one business day (e.g. before 6:00 P.M.) should
be accomplished in the morning (e.g. before12:00 A.M.) of the next business day or next business day (e.g. before 6:00 P.M.). This service will be offered in target market defined by Company A, including most of the economically developed cities in China183
.
In this section, we describe in detail the network structure, parcelpaths and service on the target market.
3.1.1. Network structure
In order to provide a nationwide trans-city overnight EDS, we resort to a multimodal H/S network. We de- fine it with a fully interconnected/star shaped H/S structure for the strategic planning in this dissertation. Particularly, several cities in the potential hub set are chosen as hubs, while all the other cities belonging to the target market are allocated to one of these hubs subject to the maximum direct distance constraints. All the hubs also serve as gateways for the air network, which are fully interconnected by direct air service. The non-hub cities are connected to their “home” hubs by direct ground service184.
Single allocation criterion is adopted here under management and cost considerations. This decision is made by the management of Company A to maintain a non-overlapping organization structure and clear responsi- bility for subsidiaries. Furthermore, additional feeder links also increase fixed cost of the network.
Every hub is per se a demand node, which is also called in-hub demand node in this dissertation. Other de- mand nodes that are not chosen as hubs are also called normal demand nodes. Service area of a hub, i.e. all the cities allocated to it together with the hub itself, is defined as a hub region. Every normal demand node is equipped with a city station, in which all parcels from and to that city are consolidated and sorted (called local sorting). Every hub is equipped with a regional ground consolidation center, in which all parcels from or to that region are consolidated and sorted (called regional sorting). It also serves as a gateway of the air network for all the demands from or to other hub regions to make air-ground transshipment. Because it also consoli- dates and sorts parcels from and to that in-hub demand node, the city station and the regional consolidation center in the hub city is geographically coincident.
The network structure is illustrated in Fig.3-1. The dashed line encloses ground the tributary/feeder net- works, while the bold line encloses the air backbone network. Ground feeder links are represented by the fine dashed arrows and air backbone links are represented by the bold arrows.
182 See Tab.1-2 in Sec. 1.3.3.
183 See Sec.6.1.1.
184 As we have mentioned in Sec.2.2.5, hubs can be connected by air routes with stopovers if time permits. Moreover, several cities in one hub region can
be served by one truck route with several stopovers. However, routing problems are not included in this dissertation. The network is simplified with fully interconnected/star H/S structure.
Figure 3-1: Multimodal H/S network for the overnight EDS
3.1.2. Parcel paths
185The EDS begins from orders online or through service hotline from customers. A fleet of vans responds to the requests before the local cutoff time in the late afternoon and picks up the parcels from shippers and deliver to the city station. After twilight local sorting, parcels with destination in other cities are loaded on a truck and transported from the city station to the consolidation center in the hub city through highway. However, this feeder transportation to consolidation center can be saved for a hub city, since the city station and the consoli- dation center is identical so that the twilight local sorting is implemented in the consolidation center. That also means the cut-off time for an in-hub demand node can be later than other normal demand nodes in that hub region. After twilight regional sorting in the consolidation center, parcels with destination in other re-
185 We differentiate several related concepts in this dissertation. An “arc” or a “link” is a node-to-node direct connection by vehicles or aircraft. A “path”
is defined as a sequence of arcs used to deliver a parcel from its origin to its destination. A “route” is defined as a sequence of arcs traveled by the same vehicle. In this dissertation all the arcs, paths and routes are directed, i.e. in only one direction.
A B C D Region B Region D Region C Air Network
Hub/air gateway/regional ground consolidation center/in-hub demand node
Ground feeder link Air backbone link
Normal demand node/ city station Region A
gions are transported by direct flights to destination hubs. Parcels with destination in the same region are left in the consolidation center. Early in the morning of the next business day, after all trans-regional parcels ar- rive at their destination hub by air, both trans-regional and intra-regional parcels are sorted in the consolida- tion center according to their destinations, called sunrise regional sorting. A fleet of trucks is then dispatched from the regional consolidation center to every city station in that region. After the parcels arrive at their destination cities, city stations unload the parcels from trucks, conduct sunrise local sorting and reload them onto a fleet of vans for city distribution. Likewise, feeder transportation to city station is saved if the destina- tion city is that hub city. In this respect, after sunrise regional sorting parcels with destination in this hub city go directly into sunrise local sorting procedure.
Different nodes along a parcel path play different roles, which are described in Tab.3-1. Although hubs and in- hub demand nodes are geographically identical, they play different roles in the network. So we consider them as two different types of nodes in the network planning.
Nodes Roles in parcel
path Attributes
Hub
Origin Hub Cut-off time: the latest time that feeder trucks arrive at the hub, the earliest time that twilight regional sorting starts Destination Hub Set-up time: the latest time that aircraft arrive at the hub, the
earliest time that sunrise regional sorting starts
Demand node
Normal demand node
Origin city Cut-off time: the latest time that parcels arrive at city station, the earliest time that twilight local sorting starts
Destination city Set-up time: the latest time that feeder trucks arrive at city station, the earliest time that sunrise local sorting starts
In-hub demand node
Origin city
Cut-off time: the latest time that parcels arrive at regional con- solidation center, the earliest time that twilight local sorting starts (later than the cut-off time for normal demand node) Destination city
Set-up time: the latest time that sunrise regional sorting finish- es, the earliest time that sunrise local sorting starts (earlier than the set-up time for normal demand node)
Table 3-1: Nodes along parcel path and their attributes
In this regard, there are 4 different kinds of paths for trans-regional parcels, i.e. normal demand node to nor- mal demand node, normal demand node to in-hub demand node, in-hub demand node to normal demand node and in-hub demand node to in-hub demand node. Without the stretch of backbone air transportation, intra- regional parcel paths are quite similar to those for trans-regional. Or we can regard it as a degenerated hub arc in intra-regional parcel paths. Consequently, totally there are 8 different parcel paths, 4 for trans-regional parcels and 4 for intra-regional ones (see Fig.3-2). Fig.3-3 and Fig.3-4 illustrate in detail the parcel paths from a normal demand node to a normal demand node and from an in-hub demand node to an in-hub demand node, respectively.
Figure 3-2: Description of parcel paths Degenerated hub arc Normal demand node Normal demand node P ick up stretc h D eli ver y str et ch In-hub demand node In-hub demand node Hub arc
Figure 3-3: Parcel path from a normal demand node to a normal demand node Pick up from shipper Twilight local sorting Twilight regional sorting Feeder
transport transportFeeder
Air transport Sunrise local sorting Sunrise regional sorting Distribution to consignee
Activity
Waiting Origin city Origin city station Pick upfeeder route Origin hub
Backbone Hub Destination hub Delivery feeder route Destination city station Destination city Intercity
network Ground tributary network Air network
Intercity network Ground tributary network