Higher-Dimensional Algebra III: n-Categories and the Algebra of Opetopes

We give a definition of weak n-categories based on the theory of operads. We work with operads having an arbitrary set S of types, or `S-operads', and given such an operad O, we denote its set of operations by elt(O). Then for any S-operad O there is an elt(O)-operad O+ whose algebras are S-operads over O. Letting I be the initial operad with a one-element set of types, and defining I(0) = I, I(i+1) = I(i)+, we call the operations of I(n-1) the `n-dimensional opetopes'. Opetopes form a category, and presheaves on this category are called `opetopic sets'. A weak n-category is defined as an opetopic set with certain properties, in a manner reminiscent of Street's simplicial approach to weak omega-categories. Similarly, starting from an arbitrary operad O instead of I, we define `n-coherent O-algebras', which are n times categorified analogs of algebras of O. Examples include `monoidal n-categories', `stable n-categories', `virtual n-functors' and `representable n-prestacks'. We also describe how n-coherent O-algebra objects may be defined in any (n+1)-coherent O-algebra.Comment: 59 pages LaTex, uses diagram.sty and auxdefs.sty macros, one encapsulated Postscript figure, also available as a compressed Postscript file at http://math.ucr.edu/home/baez/op.ps.Z or ftp://math.ucr.edu/pub/baez/op.ps.

Aspects of magnetic pulse compression and pulse sharpening

Imperial Users onl

ON KOFOID'S TRAIL: MARINE BIOLOGICAL LABORATORIES IN EUROPE AND THEIR LIFE HISTORIES

International audienceFrom early beginnings as centers of descriptive zoology, their focus shifted to physiology-development biology and oceanography. Today many marine stations have evolved into multi-disciplinary centers encompassing everything from genomics to remote sensing. However, other than the fun of a stroll down memory lane, re-tracing Kofoid's trail may help identify common traits of the survivors among the independents and this may be of some interest for those concerned with the future of marine institutions. Here then I conduct a short visit to three of the "independent" institutes described by Kofoid

Morphology and Ecology in Tintinnid Ciliates of the Marine Plankton: Correlates of Lorica Dimensions

International audienceTintinnid ciliates, characterized by the possession of a lorica into which the ciliate cell can contract, are a common component of the marine microzooplankton. Lorica architecture and size range widely and classically distinguishes species. Here relationships between ecological parameters and lorica dimensions (lorica oral diameter (LOD), lorica length (LL) and lorica volume (LV) are examined using data from literature reports. The relationships between lorica dimensions and reproductive potential, using maximum reported growth rates of natural populations (n = 52 species) are assessed. Susceptibility to copepod predation and lorica dimensions are considered based on reports of clearance rates of Acartia species feeding on tintinnid ciliates (n = 7 species). Diet and lorica dimension is analyzed using data on mean maximum food size contained in field-caught cells (n = 20 species), and preferred food size based on prey size associated with maximal reported clearance rates (n = 15 species). Overall, LOD is closely related to most of the ecological parameters. Maximum growth rate is related to LOD with smaller LODs corresponding to higher growth rates, in contrast to LL and LV. Maximum prey size is positively related to both LOD and LL but more tightly with LOD. Preferred prey size is positively related to LOD and LV but more tightly related to LOD. Clearance rates of Acartia species feeding on tintinnids are significantly related only to LOD with small LODs corresponding to lower copepod feeding rates. Relationships excluding data on species of Tintinnopsis, the species-rich genus which generally dominates coastal communities, are also examined and show similar trends. In tintinnids, LOD, known to be a conservative and relatively reliable species characteristic, appears related to a wide range of ecological characteristics

Active Markov Information-Theoretic Path Planning for Robotic Environmental Sensing

Recent research in multi-robot exploration and mapping has focused on sampling environmental fields, which are typically modeled using the Gaussian process (GP). Existing information-theoretic exploration strategies for learning GP-based environmental field maps adopt the non-Markovian problem structure and consequently scale poorly with the length of history of observations. Hence, it becomes computationally impractical to use these strategies for in situ, real-time active sampling. To ease this computational burden, this paper presents a Markov-based approach to efficient information-theoretic path planning for active sampling of GP-based fields. We analyze the time complexity of solving the Markov-based path planning problem, and demonstrate analytically that it scales better than that of deriving the non-Markovian strategies with increasing length of planning horizon. For a class of exploration tasks called the transect sampling task, we provide theoretical guarantees on the active sampling performance of our Markov-based policy, from which ideal environmental field conditions and sampling task settings can be established to limit its performance degradation due to violation of the Markov assumption. Empirical evaluation on real-world temperature and plankton density field data shows that our Markov-based policy can generally achieve active sampling performance comparable to that of the widely-used non-Markovian greedy policies under less favorable realistic field conditions and task settings while enjoying significant computational gain over them.Comment: 10th International Conference on Autonomous Agents and Multiagent Systems (AAMAS 2011), Extended version with proofs, 11 page

Cytomegalovirus Infection in Renal Transplant Recipients

Evidence of HCMV infection was assessed in a cohort of 47 renal allograft recipients followed prospectively for up to 1 year post transplantation. Serum was obtained from each patient and renal donor immediately pretransplant and tested for HCMV-specific antibody by standard or modified CFT and by Labsystems and NBL HCMV-IgG ELISA. Patients were classified as HCMV-seronegative if the antibody titre by CFT was less than 1:2. Whenever possible, a throat swab, urine and serum samples were taken from each individual immediately pretransplant and every 4 weeks thereafter. HCMV was isolated from specimens provided by 21 renal allograft recipients, 9 with primary HCMV infection and 12 with reinfection and/or reactivation. HCMV shedding usually continued intermittently throughout the first year post transplantation, isolates being obtained from multiple urine samples and/or throat swabs provided by 16 patients. In each renal allograft recipient, the HCMV isolation data was correlated with the timing of the fourfold or greater rise in HCMV CF antibody titre and/or a significant increase in HCMV-IgM and IgG measured by Labsystems indirect ELISA. There was considerable variation between individual patients in the timing and pattern of the humoral immune response. On or before the day of first HCMV isolation, 12 renal allograft recipients showed a fourfold or greater rise in HCMV CF antibody titre, 7 were positive for HCMV-IgM and 9 had evidence of a significant increase in the level of HCMV-IgG. These data show that serology alone is of limited value in the detection of active HCMV infection post renal transplantation. Taken overall, the CFT correlated best with HCMV isolation in transplant recipients with primary infection while a significant increase in HCMV-IgG correlated best with HCMV isolation in patients with reinfection and/or reactivation. Clinical findings were also correlated with HCMV isolation and/or serological data. The small number of renal transplant recipients in this study precluded statistical analysis. However, were more common in patients with primary HCMV infection. Furthermore, there was a close temporal correlation between the onset of symptoms and the HCMV-specific humoral response. Whenever possible, blood products used to transfuse the cohort of renal allograft recipients were also tested for HCMV CF antibody and the results correlated with the age of the blood donors at the time of donation. Blood donors aged between 20 and 29 years provided 61 blood packs of which 46 (75.4%) were HCMV-seronegative. There was no evidence to suggest that HCMV was transmitted via blood products. Four renal allograft recipients of a kidney from an HCMV-seronegative donor each received HCMV-seropositive blood products but none developed primary HCMV infection post-operatively. The HCMV serostatus was also available for 31 renal leucopenia, thrombocytopenia, acute rejection, chronic rejection, nephrectomy and pyrexial illness donors who provided kidneys for 37 renal allograft recipients. All 8 HCMV-seronegative recipients of a kidney from an HCMV-seropositive donor showed evidence of primary HCMV infection after the transplant operation. By contrast, none of the 9 HCMV-seronegative recipients of a kidney from an HCMV-seronegative donor developed HCMV infection throughout the period of study. These data provide further evidence that the donor kidney is the source of HCMV infection in renal transplant recipients. The ability to detect viral DNA by hybridot assay was also investigated. In preliminary experiments using partially double stranded M13 probes specific for HSV-1, the lower limit of sensitivity was in the ng range. Denaturing agarose gel electrophoresis showed radiolabelled M13 second strand synthesis to be incomplete. A BamHI subclone of the Hindlll E fragment (EHBI) of HCMV AD169 was cloned in the transcription plasmid pGEM2 and 32P-labelled cRNA synthesized. Optimal hybridization conditions were determined empirically. Four hundred and forty five urine specimens provided by 47 renal allograft recipients throughout the first year post transplantation were tested by RNA-DNA hybridization. When the results were correlated with HCMV isolation, the sensitivity and specificity of the hybridot assay was 25% and 67% respectively

Good Faith Purchase Study: True Owners and the Warehouse Lien

The commercial concept of good faith purchase has been an effective doctrine in the law of property and contract for facilitating changes necessary to a dynamic mercantile system. Today the concept finds itself under attack. Professor Gilmore, whose definitive review of the doctrine twenty-seven years ago has been required reading, now warns that the idea may have outlived its usefulness in some areas. He and others would, for example, restrict severely its application in the law of negotiable instruments. At its elementary level, the good faith purchase doctrine depends on the question of possession. That question, in turn, rests on the commercial value one accords possession and the way one perceives the commercial expectations that arise from it. Consistent, then, with the dissatisfaction that surrounds the doctrine of good faith purchase is the fact that we find controversy surrounding the role of possession in commercial law. The dissatisfaction and controversy, however, do not signal the demise of good faith purchase. The doctrine itself is a prerogative of the law for fashioning the stuff of the law\u27s correlative doctrine-security of property. That correlative precept teaches that no person may be deprived of property without consent and that a taker receives no greater interest than the transferor enjoyed. As commercial expectations change, the law must use good faith purchase differently, now invoking it, now staying it, and all with an eye to commercial reality. The debate we are witnessing over the roles of good faith purchase and of possession is indispensable to that process. This article reviews the doctrine of good faith purchase in a narrow and seldom considered context. The study is revealing in two ways. First, it demonstrates the nature of the doctrine itself as legislatures and courts utilize it to meet commercial exigencies. Second, the study attempts to explain the warehouse lien section of the Uniform Commercial (Code), a provision that harbors a number of technical problems