Dynamical tunneling in mushroom billiards

We study the fundamental question of dynamical tunneling in generic two-dimensional Hamiltonian systems by considering regular-to-chaotic tunneling rates. Experimentally, we use microwave spectra to investigate a mushroom billiard with adjustable foot height. Numerically, we obtain tunneling rates from high precision eigenvalues using the improved method of particular solutions. Analytically, a prediction is given by extending an approach using a fictitious integrable system to billiards. In contrast to previous approaches for billiards, we find agreement with experimental and numerical data without any free parameter.Comment: 4 pages, 4 figure

Predator hunting mode and host plant quality shape attack-abatement patterns of predation risk in an insect herbivore

Group formation reduces individual predation risk when the proportion of prey taken per predator encounter declines faster than the increase in group encounter rate (a ack-abatement). Despite a ack-abatement being an important component of group formation ecology, several key aspects have not been empirically studied, that is, interactions with the hunting mode of the predator and how these relationships are modi ed by local habitat quality. In 79 cage trials, we examined individual egg predation risk in di erent-sized egg clutches from the blue willow beetle Phratora vulgatissima for two predators with di erent hunting modes (consumption of full group [Orthotylus marginalis] vs. part group [Anthocoris nemorum]). Because these predators also take nutrients from plant sap, we could examine how the quality of alternative food sources (high- vs. low-quality host plant sap) in uenced a ack-abatement pa erns in the presence of di erent hunting strategies. For the O. marginalis predator, individual egg predation risk was largely independent of group size. For A. nemorum, egg predation risk clearly declined with increasing group size. However, approximately one-third of the grouping bene t was lost to an increase in group detectability. There were clear di erences in a ack-abatement pa erns between plants with high- vs. low-quality sap. When O. marginalis was the predator, there was no clear change in a ack-abatement in relation to host plant quality. However, for A. nemorum there was a clear reduction in overall predation risk and a stronger a ack-abatement pa ern with increasing group size when plant sap quality increased. This implies that the relative bene ts of prey grouping behavior for any species might show diurnal or seasonal changes as other aspects of resource/habitat quality change for the focal predator. Modulation of a ack-abatement by bo om-up e ects such as plant-based food resources is yet to be incorporated into general theory, despite the ubiquity of omnivorous predators and with omnivory being important for shaping food webs, ecosystem functions, and in biological control. Thus, ongoing re nement of a ack- abatement theory by focusing on bo om-up vs. top-down processes could have signi cant impacts on many important contemporary elds of study

Discovering the Elite Hypervolume by Leveraging Interspecies Correlation

Evolution has produced an astonishing diversity of species, each filling a different niche. Algorithms like MAP-Elites mimic this divergent evolutionary process to find a set of behaviorally diverse but high-performing solutions, called the elites. Our key insight is that species in nature often share a surprisingly large part of their genome, in spite of occupying very different niches; similarly, the elites are likely to be concentrated in a specific "elite hypervolume" whose shape is defined by their common features. In this paper, we first introduce the elite hypervolume concept and propose two metrics to characterize it: the genotypic spread and the genotypic similarity. We then introduce a new variation operator, called "directional variation", that exploits interspecies (or inter-elites) correlations to accelerate the MAP-Elites algorithm. We demonstrate the effectiveness of this operator in three problems (a toy function, a redundant robotic arm, and a hexapod robot).Comment: In GECCO 201

Wear Minimization for Cuckoo Hashing: How Not to Throw a Lot of Eggs into One Basket

We study wear-leveling techniques for cuckoo hashing, showing that it is possible to achieve a memory wear bound of $\log\log n+O(1)$ after the insertion of $n$ items into a table of size $Cn$ for a suitable constant $C$ using cuckoo hashing. Moreover, we study our cuckoo hashing method empirically, showing that it significantly improves on the memory wear performance for classic cuckoo hashing and linear probing in practice.Comment: 13 pages, 1 table, 7 figures; to appear at the 13th Symposium on Experimental Algorithms (SEA 2014

Open-Ended Evolutionary Robotics: an Information Theoretic Approach

This paper is concerned with designing self-driven fitness functions for Embedded Evolutionary Robotics. The proposed approach considers the entropy of the sensori-motor stream generated by the robot controller. This entropy is computed using unsupervised learning; its maximization, achieved by an on-board evolutionary algorithm, implements a "curiosity instinct", favouring controllers visiting many diverse sensori-motor states (sms). Further, the set of sms discovered by an individual can be transmitted to its offspring, making a cultural evolution mode possible. Cumulative entropy (computed from ancestors and current individual visits to the sms) defines another self-driven fitness; its optimization implements a "discovery instinct", as it favours controllers visiting new or rare sensori-motor states. Empirical results on the benchmark problems proposed by Lehman and Stanley (2008) comparatively demonstrate the merits of the approach

Human phosphodiesterase 4D7 (PDE4D7) expression is increased in TMPRSS2-ERG positive primary prostate cancer and independently adds to a reduced risk of post-surgical disease progression

background: There is an acute need to uncover biomarkers that reflect the molecular pathologies, underpinning prostate cancer progression and poor patient outcome. We have previously demonstrated that in prostate cancer cell lines PDE4D7 is downregulated in advanced cases of the disease. To investigate further the prognostic power of PDE4D7 expression during prostate cancer progression and assess how downregulation of this PDE isoform may affect disease outcome, we have examined PDE4D7 expression in physiologically relevant primary human samples. methods: About 1405 patient samples across 8 publically available qPCR, Affymetrix Exon 1.0 ST arrays and RNA sequencing data sets were screened for PDE4D7 expression. The TMPRSS2-ERG gene rearrangement status of patient samples was determined by transformation of the exon array and RNA seq expression data to robust z-scores followed by the application of a threshold >3 to define a positive TMPRSS2-ERG gene fusion event in a tumour sample. results: We demonstrate that PDE4D7 expression positively correlates with primary tumour development. We also show a positive association with the highly prostate cancer-specific gene rearrangement between TMPRSS2 and the ETS transcription factor family member ERG. In addition, we find that in primary TMPRSS2-ERG-positive tumours PDE4D7 expression is significantly positively correlated with low-grade disease and a reduced likelihood of progression after primary treatment. Conversely, PDE4D7 transcript levels become significantly decreased in castration resistant prostate cancer (CRPC). conclusions: We further characterise and add physiological relevance to PDE4D7 as a novel marker that is associated with the development and progression of prostate tumours. We propose that the assessment of PDE4D7 levels may provide a novel, independent predictor of post-surgical disease progression

Marine-derived C-14 calibration and activity record for the past 50,000 years updated from the Cariaco Basin

Author Posting. © Elsevier B.V., 2006. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Quaternary Science Reviews 25 (2006): 3216-3227, doi:10.1016/j.quascirev.2006.03.014.An expanded Cariaco Basin 14C chronology is tied to 230Th-dated Hulu Cave speleothem records in order to provide detailed marine-based 14C calibration for the past 50,000 years. The revised, high resolution Cariaco 14C calibration record agrees well with data from 230Th-dated fossil corals back to 33 ka, with continued agreement despite increased scatter back to 50 ka, suggesting that the record provides accurate calibration back to the limits of radiocarbon dating. The calibration data document highly elevated Δ14C during the Glacial period. Carbon cycle box model simulations show that the majority of observed Δ14C change can be explained by increased 14C production. However, from 45 to 15 ka, Δ14C remains anomalously high, indicating that the distribution of radiocarbon between surface and deep ocean reservoirs was different than it is today. Additional observations of the magnitude, spatial extent and timing of deep ocean Δ14C shifts are critical for a complete understanding of observed Glacial Δ14C variability

The neutron halo of 6^6He in a microscopic model

The two--neutron separation energy of $^6$He has been reproduced for the first time in a realistic parameter--free microscopic multicluster model comprising the $\alpha +n+n$ and $t+t$ clusterizations, with $\alpha$ cluster breathing excitations included. The contribution of the $t+t$ channel is substantial. A very thick (0.85 fm) neutron halo has been found in full agreement with the results of the latest phenomenological analysis.Comment: Submitted to Phys. Rev. C, 8 pages, Latex with Revtex, 2 figures (not included) available on request, 08-03-9

Model Calculations for the Two-Fragment Electro-Disintegration of 4^4He

Differential cross sections for the electro-disintegration process $e + {^4He} \longrightarrow {^3H}+ p + e'$ are calculated, using a model in which the final state interaction is included by means of a nucleon-nucleus (3+1) potential constructed via Marchenko inversion. The required bound-state wave functions are calculated within the integrodifferential equation approach (IDEA). In our model the important condition that the initial bound state and the final scattering state are orthogonal is fulfilled. The sensitivity of the cross section to the input $p{^3H}$ interaction in certain kinematical regions is investigated. The approach adopted could be useful in reactions involving few cluster systems where effective interactions are not well known and exact methods are presently unavailable. Although, our Plane-Wave Impulse Approximation results exhibit, similarly to other calculations, a dip in the five-fold differential cross-section around a missing momentum of $\sim 450 MeV/c$, it is argued that this is an artifact of the omission of re-scattering four-nucleon processes.Comment: 16 pages, 6 figures, accepted for publication by Phys.Rev.