Controlled mobility in stochastic and dynamic wireless networks

We consider the use of controlled mobility in wireless networks where messages arriving randomly in time and space are collected by mobile receivers (collectors). The collectors are responsible for receiving these messages via wireless transmission by dynamically adjusting their position in the network. Our goal is to utilize a combination of wireless transmission and controlled mobility to improve the throughput and delay performance in such networks. First, we consider a system with a single collector. We show that the necessary and sufficient stability condition for such a system is given by ρ<1 where ρ is the expected system load. We derive lower bounds for the expected message waiting time in the system and develop policies that are stable for all loads ρ<1 and have asymptotically optimal delay scaling. We show that the combination of mobility and wireless transmission results in a delay scaling of Θ([1 over 1−ρ]) with the system load ρ, in contrast to the Θ([1 over (1−ρ)[superscript 2]]) delay scaling in the corresponding system without wireless transmission, where the collector visits each message location. Next, we consider the system with multiple collectors. In the case where simultaneous transmissions to different collectors do not interfere with each other, we show that both the stability condition and the delay scaling extend from the single collector case. In the case where simultaneous transmissions to different collectors interfere with each other, we characterize the stability region of the system and show that a frame-based version of the well-known Max-Weight policy stabilizes the system asymptotically in the frame length.National Science Foundation (U.S.) (Grant CNS-0915988)United States. Army Research Office. Multidisciplinary University Research Initiative (Grant W911NF-08-1-0238

Distance decay 2.0-A global synthesis of taxonomic and functional turnover in ecological communities

Aim: Understanding the variation in community composition and species abundances (i.e., beta-diversity) is at the heart of community ecology. A common approach to examine beta-diversity is to evaluate directional variation in community composition by measuring the decay in the similarity among pairs of communities along spatial or environmental distance. We provide the first global synthesis of taxonomic and functional distance decay along spatial and environmental distance by analysing 148 datasets comprising different types of organisms and environments. Location: Global. Time period: 1990 to present. Major taxa studied: From diatoms to mammals. Method: We measured the strength of the decay using ranked Mantel tests (Mantel r) and the rate of distance decay as the slope of an exponential fit using generalized linear models. We used null models to test whether functional similarity decays faster or slower than expected given the taxonomic decay along the spatial and environmental distance. We also unveiled the factors driving the rate of decay across the datasets, including latitude, spatial extent, realm and organismal features. Results: Taxonomic distance decay was stronger than functional distance decay along both spatial and environmental distance. Functional distance decay was random given the taxonomic distance decay. The rate of taxonomic and functional spatial distance decay was fastest in the datasets from mid-latitudes. Overall, datasets covering larger spatial extents showed a lower rate of decay along spatial distance but a higher rate of decay along environmental distance. Marine ecosystems had the slowest rate of decay along environmental distances. Main conclusions: In general, taxonomic distance decay is a useful tool for biogeographical research because it reflects dispersal-related factors in addition to species responses to climatic and environmental variables. Moreover, functional distance decay might be a cost-effective option for investigating community changes in heterogeneous environments

Determination of cadmium in tobacco smoke by electrothermal atomic absorption spectroscopy with electrostatic precipitation of samples on the graphite tube atomizer

The determination of Cd in ambient air, associated with tobacco smoke, has been carried out by electrostatic precipitation of Cd directly in a graphite tube, which was subsequently used as an atomizer in electrothermal atomization atomic absorption spectroscopy (ET-AAS). It is shown that graphite tube permanently modified with Ir allows carrying out pyrolysis of collected samples at $1000^\circ$C, leading to minimization of the blank. The combination of electrostatic precipitation of Cd from ambient air into the graphite tube with high efficiency of Cd determination by ET-AAS allows to trace Cd in ambient air for 25 min after the smoking a cigarette. The limit of detection (LOD) of Cd determination was found to be 0.2 ng m$^{-3}$ The results of investigations confirm the danger of passive smoking due to the presence of Cd in smoking areas

Scope Dominance with Generalized Quantifiers

When two quantifiers Q1 and Q2 satisfy the scheme Q1x Q2y φ → Q2y Q1x φ, we say that Q1 is scopally dominant over Q2. This relation is central in analyzing and computing entailment relations between different readings of ambiguous sentences in natural language. This paper reviews the known results on scope dominance and mentions some open problems. 1 Basic definitions An arbitrary generalized quantifier of signature 〈n1,..., nk 〉 over a non-empty domain E is a relation f ⊆ ℘(E n1) ×... × ℘(E nk), where k ≥ 1, and ni ≥ 1 for all i ≤ k (e.g. Peters and Westerst˚ahl, 2006, p.65). In short, we say that f is a quantifier when it is of signature 〈1〉, a determiner (relation) when it is of signature 〈1, 1〉, and a dyadic quantifier when it is of signature 〈2〉. When R is a binary relation over some domain E (not necessarily E), we denote for every X, Y ∈ E: (1) a. RX = {Y ∈ E: R(X, Y)} b. R Y = {X ∈ E: R(X, Y)} In theories of natural language semantics, determiner relations are useful in describing the meaning of determiner expressions as in (2). (2) every: every = {〈A, B 〉 ⊆ E 2: A ⊆ B} some: some = {〈A, B 〉 ⊆ E 2: A ∩ B ̸ = ∅} more than half: mth = {〈A, B 〉 ⊆ E 2: |A ∩ B |&gt; |A ∩ B|} It is well-known (Peters and Westerst˚ahl, 2006, p.469) that meanings of natural language determiners – e.g. of the expression more than half – may be beyond what is expressible in first order logic. We assume that nouns denote sets A ⊆ E. Noun phrase meanings are then described as in (3) using a quantifier DA, where the noun denotation is the left 1 argument of the determiner relation D (cf. (1a)). (3) every student: every S = {B ⊆ E: S ⊆ B} some teacher: someT = {B ⊆ E: T ∩ B ̸ = ∅} more than half of the students: mthS = {B ⊆ E: |S ∩ B |&gt; |S ∩ B|} Truth values of simple sentences with intransitive verbs are derived as in (4), using the membership statement that the set denotation of the verb is in the quantifier denotation of the subject, or, equivalently, that the pair of sets denoted by the noun and the verb are in the determiner relation. (4) every student smiled: SM ∈ every S ⇔ 〈S, SM 〉 ∈ every ⇔ S ⊆ SM some teacher cried: C ∈ someT ⇔ 〈T, C 〉 ∈ some

Critical Level Policies in Lost Sales Inventory Systems with Different Demand Classes

International audienceWe consider a single-item lost sales inventory model with different classes of customers. Each customer class may have different lost sale penalty costs. We assume that the demands follow a Poisson process and we consider a single replenishment hypoexponential server. We give a Markov decision process associated with this optimal control problem and prove some structural properties of its dynamic programming operator. This allows us to show that the optimal policy is a critical level policy. We then discuss some possible extensions to other replenishment distributions and give some numerical results for the hyperexponential server case