On Polynomial Sized MDP Succinct Policies

Policies of Markov Decision Processes (MDPs) determine the next action to execute from the current state and, possibly, the history (the past states). When the number of states is large, succinct representations are often used to compactly represent both the MDPs and the policies in a reduced amount of space. In this paper, some problems related to the size of succinctly represented policies are analyzed. Namely, it is shown that some MDPs have policies that can only be represented in space super-polynomial in the size of the MDP, unless the polynomial hierarchy collapses. This fact motivates the study of the problem of deciding whether a given MDP has a policy of a given size and reward. Since some algorithms for MDPs work by finding a succinct representation of the value function, the problem of deciding the existence of a succinct representation of a value function of a given size and reward is also considered

Space Efficiency of Propositional Knowledge Representation Formalisms

We investigate the space efficiency of a Propositional Knowledge Representation (PKR) formalism. Intuitively, the space efficiency of a formalism F in representing a certain piece of knowledge A, is the size of the shortest formula of F that represents A. In this paper we assume that knowledge is either a set of propositional interpretations (models) or a set of propositional formulae (theorems). We provide a formal way of talking about the relative ability of PKR formalisms to compactly represent a set of models or a set of theorems. We introduce two new compactness measures, the corresponding classes, and show that the relative space efficiency of a PKR formalism in representing models/theorems is directly related to such classes. In particular, we consider formalisms for nonmonotonic reasoning, such as circumscription and default logic, as well as belief revision operators and the stable model semantics for logic programs with negation. One interesting result is that formalisms with the same time complexity do not necessarily belong to the same space efficiency class

A SAIL compatible three channel acoustic navigation interrogator

Ocean Acoustic Tomography data are significantly degraded if mooring motion is unknown. An autonomous instrument employing a solid state data logger designed to track and record mooring motion is described. Navigation is accomplished by simultaneously interrogating each of three bottom mounted transponders positioned in an equilateral triangle around the mooring's anchor at a range approximately equal to the depth of the tracked instrument. The three round-trip travel times thus obtained having a resolution of 125uS and a SNR dependent jitter of less than 1.5mS, define a unique instrument position and are recorded along with the time of day and day of year. The measurement period, the system clock and the program start time are set via a 20mA SAIL. Since the standby power requirement is negligible compared to the battery capacity, the instrument may be programmed months in advance of the deployment. System endurance varies with the measurement period, however, typical programs permit navigation for up to 21 months at 12 points per day. Upon recovery, the navigator data may be down-loaded via SAIL directly to the storage medium of a suitable computer.Funding was provided by the Office of Naval Research under Contract Nos. N00014-82-C-0152 and N00014-85-C-0379

Where Fail-Safe Default Logics Fail

Reiter's original definition of default logic allows for the application of a default that contradicts a previously applied one. We call failure this condition. The possibility of generating failures has been in the past considered as a semantical problem, and variants have been proposed to solve it. We show that it is instead a computational feature that is needed to encode some domains into default logic

Performance of a school hosted within a historical complex affected by the 2016 seismic sequence

Immediately after the August 24th, 2016, earthquake in Central Italy, universities have been asked to inspect schools and assess their usability, under the coordination of ReLUIS (Rete Laboratori Universitari Ingegneria Sismica = Earthquake Engineering University Laboratories Network). Later on, about one hundred schools deemed as unfit to use have been evaluated in order to establish if it was possible to repair them before September 2017 or if it was more appropriate to build a new school. Among investigated buildings there are not only those in the epicentral area, but also some located even 30-45 km from the epicentres of the main events. One of those is the music high school located in Teramo, Abruzzi region, housed within the former monastery of San Giovanni a Scorzone established in 1384. The seismic vulnerability of the building was investigated in 2014 according to the Italian Building Standard. Based on the documentation produced therein, observations made after the August event, and a new inspection carried out in December 2016, the building has been assessed according to the procedure proposed after the Emilia 2012 Earthquakes. Despite ground shaking not being very severe, due to high vulnerability, the performance was that of a damage level 2 (damage between significant and severe), with important distress to non-structural elements. Such performances call into question the suitability of housing critical functions in historical buildings that, however, can suffer an accelerated decay if left unused and, thus, unmaintained

WHOI SDSL data-link project—ethernet telemetry through sea cables

Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Atmospheric and Oceanic Technology 34 (2017): 269-275, doi:10.1175/JTECH-D-11-00196.1.A data telemetry technique for communicating over standard oceanographic sea cables that achieves a nearly 100-fold increase in bandwidth as compared to traditional systems has been recently developed and successfully used at sea on board two Research Vessel (R/V) Atlantis cruises with an 8.5-km, 0.322-in.-diameter three-conductor sea cable. The system uses commercially available modules to provide Ethernet connectivity through existing sea cables, linking serial and video underwater instrumentation to the shipboard user. The new method applies Synchronous Digital Subscriber Line (SDSL) communications technology to undersea applications, greatly increasing the opportunities to use scientific instrumentation from existing ships and sea cables at minimal cost and without modification.This development program has been supported, in part, through research grants from the National Science Foundation (OCE 0447395), the National Aeronautics and Space Administration’s ASTEP program (NNX09AB76G), and a WHOI Green and Hiam Innovative Technology Award.2017-07-2

On the Complexity of Case-Based Planning

We analyze the computational complexity of problems related to case-based planning: planning when a plan for a similar instance is known, and planning from a library of plans. We prove that planning from a single case has the same complexity than generative planning (i.e., planning "from scratch"); using an extended definition of cases, complexity is reduced if the domain stored in the case is similar to the one to search plans for. Planning from a library of cases is shown to have the same complexity. In both cases, the complexity of planning remains, in the worst case, PSPACE-complete

Tomato yield heterosis is triggered by a dosage sensitivity of the florigen pathway that fine-tunes shoot architecture

The superiority of hybrids has long been exploited in agriculture, and although many models explaining "heterosis" have been put forth, direct empirical support is limited. Particularly elusive have been cases of heterozygosity for single gene mutations causing heterosis under a genetic model known as overdominance. In tomato (Solanum lycopersicum), plants carrying mutations in SINGLE FLOWER TRUSS (SFT) encoding the flowering hormone florigen are severely delayed in flowering, become extremely large, and produce few flowers and fruits, but when heterozygous, yields are dramatically increased. Curiously, this overdominance is evident only in the background of "determinate" plants, in which the continuous production of side shoots and inflorescences gradually halts due to a defect in the flowering repressor SELF PRUNING (SP). How sp facilitates sft overdominance is unclear, but is thought to relate to the opposing functions these genes have on flowering time and shoot architecture. We show that sft mutant heterozygosity (sft/+) causes weak semi-dominant delays in flowering of both primary and side shoots. Using transcriptome sequencing of shoot meristems, we demonstrate that this delay begins before seedling meristems become reproductive, followed by delays in subsequent side shoot meristems that, in turn, postpone the arrest of shoot and inflorescence production. Reducing SFT levels in sp plants by artificial microRNAs recapitulates the dose-dependent modification of shoot and inflorescence production of sft/+ heterozygotes, confirming that fine-tuning levels of functional SFT transcripts provides a foundation for higher yields. Finally, we show that although flowering delays by florigen mutant heterozygosity are conserved in Arabidopsis, increased yield is not, likely because cyclical flowering is absent. We suggest sft heterozygosity triggers a yield improvement by optimizing plant architecture via its dosage response in the florigen pathway. Exploiting dosage sensitivity of florigen and its family members therefore provides a path to enhance productivity in other crops, but species-specific tuning will be required

Pseudozyma aphidis bloodstream infection in a patient with aggressive lymphoma and a history of intravenous drug use: Case report and review of the literature

Pseudozyma aphidis is an environmental fungus which causes opportunistic infections in immunocompromised patients. Here we report the case of a 54-year-old, intravenous drug user woman, newly diagnosed to have an aggressive lymphoma, who developed a bloodstream infection caused by P. aphidis treated successfully with amphotericin-B therapy. The precise identification was assessed by sequencing. We propose to consider intravenous drug use as a risk factor for invasive infections due to this environmental yeast