Decentralization of Multiagent Policies by Learning What to Communicate

Effective communication is required for teams of robots to solve sophisticated collaborative tasks. In practice it is typical for both the encoding and semantics of communication to be manually defined by an expert; this is true regardless of whether the behaviors themselves are bespoke, optimization based, or learned. We present an agent architecture and training methodology using neural networks to learn task-oriented communication semantics based on the example of a communication-unaware expert policy. A perimeter defense game illustrates the system's ability to handle dynamically changing numbers of agents and its graceful degradation in performance as communication constraints are tightened or the expert's observability assumptions are broken.Comment: 7 page

Neural Network Memory Architectures for Autonomous Robot Navigation

This paper highlights the significance of including memory structures in neural networks when the latter are used to learn perception-action loops for autonomous robot navigation. Traditional navigation approaches rely on global maps of the environment to overcome cul-de-sacs and plan feasible motions. Yet, maintaining an accurate global map may be challenging in real-world settings. A possible way to mitigate this limitation is to use learning techniques that forgo hand-engineered map representations and infer appropriate control responses directly from sensed information. An important but unexplored aspect of such approaches is the effect of memory on their performance. This work is a first thorough study of memory structures for deep-neural-network-based robot navigation, and offers novel tools to train such networks from supervision and quantify their ability to generalize to unseen scenarios. We analyze the separation and generalization abilities of feedforward, long short-term memory, and differentiable neural computer networks. We introduce a new method to evaluate the generalization ability by estimating the VC-dimension of networks with a final linear readout layer. We validate that the VC estimates are good predictors of actual test performance. The reported method can be applied to deep learning problems beyond robotics

Changes in PM2.5 Peat Combustion Source Profiles with Atmospheric Aging in an Oxidation Flow Reactor

Smoke from laboratory chamber burning of peat fuels from Russia, Siberia, the USA (Alaska and Florida), and Malaysia representing boreal, temperate, subtropical, and tropical regions was sampled before and after passing through a potential-aerosol-mass oxidation flow reactor (PAM-OFR) to simulate intermediately aged (∼2 d) and well-aged (∼7 d) source profiles. Species abundances in PM2.5 between aged and fresh profiles varied by several orders of magnitude with two distinguishable clusters, centered around 0.1 % for reactive and ionic species and centered around 10 % for carbon. Organic carbon (OC) accounted for 58 %–85 % of PM2.5 mass in fresh profiles with low elemental carbon (EC) abundances (0.67 %–4.4 %). OC abundances decreased by 20 %–33 % for well-aged profiles, with reductions of 3 %–14 % for the volatile OC fractions (e.g., OC1 and OC2, thermally evolved at 140 and 280 ∘C). Ratios of organic matter (OM) to OC abundances increased by 12 %–19 % from intermediately aged to well-aged smoke. Ratios of ammonia (NH3) to PM2.5 decreased after intermediate aging. Well-aged NH+4 and NO−3 abundances increased to 7 %–8 % of PM2.5 mass, associated with decreases in NH3, low-temperature OC, and levoglucosan abundances for Siberia, Alaska, and Everglades (Florida) peats. Elevated levoglucosan was found for Russian peats, accounting for 35 %–39 % and 20 %–25 % of PM2.5 mass for fresh and aged profiles, respectively. The water-soluble organic carbon (WSOC) fractions of PM2.5 were over 2-fold higher in fresh Russian peat (37.0±2.7 %) than in Malaysian (14.6±0.9 %) peat. While Russian peat OC emissions were largely water-soluble, Malaysian peat emissions were mostly water-insoluble, with WSOC ∕ OC ratios of 0.59–0.71 and 0.18–0.40, respectively. This study shows significant differences between fresh and aged peat combustion profiles among the four biomes that can be used to establish speciated emission inventories for atmospheric modeling and receptor model source apportionment. A sufficient aging time (∼7 d) is needed to allow gas-to-particle partitioning of semi-volatilized species, gas-phase oxidation, and particle volatilization to achieve representative source profiles for regional-scale source apportionment

Complete Genome Sequence of Cyanobacterial Siphovirus KBS2A

Abstract We present the genome of a cyanosiphovirus (KBS2A) that infects a marine Synechococcus sp. (strain WH7803). Unique to this genome, relative to other sequenced cyanosiphoviruses, is the absence of elements associated with integration into the host chromosome, suggesting this virus may not be able to establish a lysogenic relationship. Go to: GENOME ANNOUNCEMENT As obligate parasites, viruses can regulate their host population dynamics but also influence the structure and productivity of microbial communities (1, 2). Synechococcus species are an abundant and ecologically important group of Cyanobacteria found in freshwater and marine ecosystems worldwide. Virus-cyanobacterium interactions may have important implications for global biogeochemical cycles. The most commonly isolated cyanophages are myoviruses and podoviruses (3, 4). Siphoviruses are a third group of viruses that infect cyanobacteria, but they have received less attention (5). The genomes of 5 cyanosiphoviruses have recently become available: that of P-SS2, a siphovirus infecting Prochlorococcus (MIT9313) (6), followed by the cyanosiphoviruses S-CBS1, S-CBS2, S-CBS3, and S-CBS4, isolated from the Chesapeake Bay Estuary, all infecting Synechococcus populations (5). Here, we present the complete genome of cyanosiphophage (KBS2A, originally named KBS-S-2A), a virus that infects Synechococcus sp. strain WH7803. The virus was isolated by plaque assay from the Chesapeake Bay by plating on Synechococcus sp. WH7803. Purified virus DNA was submitted to the Broad Institute as part of the Marine Phage Sequencing Project, where it was sequenced to ~30-fold coverage using 454 pyrosequencing. Translated open reading frames (ORFs) were compared with known protein sequences using the BLASTp program. ORF annotation was aided by the use of PSI-BLAST, HHpred, gene size, and domain conservation. The genome size of KBS2A is 40,658 bp. In total, 64 ORFs have been predicted in this genome; of these, 43 have homologues in databases, and among them, 33 have been assigned to a putative function. For most (88%) predicted ORFs with homologues, homology has been found with the other cyanosiphovirus genomes. We compared the genomic arrangements of the 6 sequenced cyanosiphoviruses using dot plot and global gene homology and found no common genomic organization, suggesting strong mosaicism in the cyanosiphoviruses. In cyanophages, cyanobacterium-related proteins can be found and are often associated with photosynthesis and transcriptional regulation (6). In previously sequenced cyanosiphovirus genomes (5, 6), numerous viral genes (6 to 40 per genome) possess homology with host genes. In the case of the KBS2A genome, only 3 ORFs (coding for RNA polymerase sigma factor RpoD, HNH endonuclease, and a putative DNA polymerase) show such homology, implying less exchange (and potentially interaction) with the host genome. The first annotated cyanosiphovirus genome (that of P-SS2) showed the presence of genes identified as encoding an integrase and excisionase, which are enzymes that allow for phage integration into the host’s genome (6). Moreover, the annotation of cyanosiphoviruses S-CBS1 and S-CBS3 led to the discovery of a prophage-like structure in two sequenced Synechococcus elongatus strains (5). In phage genomes, tRNA genes serve as indicators of potential phage integration by site-specific recombination (7, 8), although recent models have offered alternative suggestions for the role of these genes (9). Sequences of this nature can, however, be found in the P-SS2 and S-CBS4 genomes. No such features (tRNAs, integrases, etc.) were found in the genome of KBS2A, suggesting that this siphovirus might be an exclusively lytic phage rather than a temperate phage. Nucleotide sequence accession number. The complete sequence of the Synechococcus phage KBS2A genome can be accessed under the GenBank accession no. HQ634187. doi: 10.1128/genomeA.00472-1

Thermal Weapon Sight (TWS) AN/PAS-13 diffractive optics designed for producibility

The Thermal Weapon Sight (TWS) program is a manportable 3-5 micrometer forward-looking-infrared (FLIR) rifle sight. The manportable nature requires that the optics modules be lightweight, low cost and compact while maximizing performance. These objectives were met with diffractive optics. TWS promises to be the first FLIR sensor to incorporate kinoform surfaces in full scale production

Are there multiple kinds of episodic memory? An fMRI investigation comparing autobiographical and recognition memory tasks

What brain regions underlie retrieval from episodic memory? The bulk of research addressing this question with fMRI has relied upon recognition memory for materials encoded within the laboratory. Another, less dominant tradition has used autobiographical methods, whereby people recall events from their lifetime, often after being cued with words or pictures. The current study addresses how the neural substrates of successful memory retrieval differed as a function of the targeted memory when the experimental parameters were held constant in the two conditions (except for instructions). Human participants studied a set of scenes and then took two types of memory test while undergoing fMRI scanning. In one condition (the picture memory test), participants reported for each scene (32 studied, 64 nonstudied) whether it was recollected from the prior study episode. In a second condition (the life memory test), participants reported for each scene (32 studied, 64 nonstudied) whether it reminded them of a specific event from their preexperimental lifetime. An examination of successful retrieval (yes responses) for recently studied scenes for the two test types revealed pronounced differences; that is, autobiographical retrieval instantiated with the life memory test preferentially activated the default mode network, whereas hits in the picture memory test preferentially engaged the parietal memory network as well as portions of the frontoparietal control network. When experimental cueing parameters are held constant, the neural underpinnings of successful memory retrieval differ when remembering life events and recently learned events