6,136 research outputs found
Time Versus Cost Tradeoffs for Deterministic Rendezvous in Networks
Two mobile agents, starting from different nodes of a network at possibly
different times, have to meet at the same node. This problem is known as
. Agents move in synchronous rounds. Each agent has a
distinct integer label from the set . Two main efficiency
measures of rendezvous are its (the number of rounds until the
meeting) and its (the total number of edge traversals). We
investigate tradeoffs between these two measures. A natural benchmark for both
time and cost of rendezvous in a network is the number of edge traversals
needed for visiting all nodes of the network, called the exploration time.
Hence we express the time and cost of rendezvous as functions of an upper bound
on the time of exploration (where and a corresponding exploration
procedure are known to both agents) and of the size of the label space. We
present two natural rendezvous algorithms. Algorithm has cost
(and, in fact, a version of this algorithm for the model where the
agents start simultaneously has cost exactly ) and time . Algorithm
has both time and cost . Our main contributions are
lower bounds showing that, perhaps surprisingly, these two algorithms capture
the tradeoffs between time and cost of rendezvous almost tightly. We show that
any deterministic rendezvous algorithm of cost asymptotically (i.e., of
cost ) must have time . On the other hand, we show that any
deterministic rendezvous algorithm with time complexity must have
cost
Time vs. Information Tradeoffs for Leader Election in Anonymous Trees
The leader election task calls for all nodes of a network to agree on a
single node. If the nodes of the network are anonymous, the task of leader
election is formulated as follows: every node of the network must output a
simple path, coded as a sequence of port numbers, such that all these paths end
at a common node, the leader. In this paper, we study deterministic leader
election in anonymous trees.
Our aim is to establish tradeoffs between the allocated time and the
amount of information that has to be given to the nodes to
enable leader election in time in all trees for which leader election in
this time is at all possible. Following the framework of , this information (a single binary string) is provided to all
nodes at the start by an oracle knowing the entire tree. The length of this
string is called the . For an allocated time ,
we give upper and lower bounds on the minimum size of advice sufficient to
perform leader election in time .
We consider -node trees of diameter . While leader election
in time can be performed without any advice, for time we give
tight upper and lower bounds of . For time we give
tight upper and lower bounds of for even values of ,
and tight upper and lower bounds of for odd values of .
For the time interval for constant ,
we prove an upper bound of and a lower bound of
, the latter being valid whenever is odd or when
the time is at most . Finally, for time for any
constant (except for the case of very small diameters), we give
tight upper and lower bounds of
With Great Speed Come Small Buffers: Space-Bandwidth Tradeoffs for Routing
We consider the Adversarial Queuing Theory (AQT) model, where packet arrivals
are subject to a maximum average rate and burstiness
. In this model, we analyze the size of buffers required to avoid
overflows in the basic case of a path. Our main results characterize the space
required by the average rate and the number of distinct destinations: we show
that space suffice, where is the number of distinct
destinations and ; and we show that space is necessary. For directed trees, we describe an algorithm
whose buffer space requirement is at most where is the
maximum number of destinations on any root-leaf path
Impacts of Spatial Resolution and Viewing Angle on Remotely Sensed Estimates of Spartina alterniflora Aboveground Biomass
Coastal salt marshes sequester large quantities of “blue carbon” in plant biomass and sediments, and provide numerous other valuable ecosystem functions and services. However, these ecosystems are increasingly threatened by external stressors, including rising sea levels and a changing climate, which have resulted in large losses of tidal marsh habitat. Measuring plant biomass is critical for understanding how carbon storage may be affected as stressors continue to cause marsh losses, and for improving conservation and management efforts. A number of studies have quantified aboveground biomass (AGB) in salt marshes using remote sensing techniques, and with the development of high resolution sensors there is excellent potential to improve estimates over large scales. However, few studies have evaluated how variability in spatial resolution and viewing angle across platforms impacts AGB estimates, despite the large range of potential imaging systems available. Using 3 cm and 6 cm resolution nadir hyperspectral drone imagery, and 0.5-3 cm oblique imagery collected from a ground-based camera at three viewing angles from two different-aged barrier island salt marshes in Virginia, USA, I evaluated the accuracy of regression models predicting S. alterniflora AGB from vegetation indices across resolution and viewing angle. The overall best performing linear regression models were obtained using the 3 cm nadir drone imagery. However, the best 6 cm regression models demonstrated only minor losses in accuracy relative to 3 cm. AGB estimates from obliquely angled imagery were less accurate than either nadir resolution. The most accurate oblique models were obtained at the highest viewing angle, with performance decreasing as the viewing angle became shallower. These results suggest that not all platforms perform similarly within salt marsh ecosystems, and that both spatial resolution and viewing angle must be considered in choice of imaging systems
The Responses of Normal and Castrate Female Sparrows to Injections of Pregnant Mare Serum
During the winter months, ovaries and oviducts of the sparrows are greatly reduced. Injection of pregnant mare serum during this resting period stimulates the ovary to an activity which simulates that of the breeding season. Oviducts respond to the increased amounts of female hormone released by the ovary
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