Conformational Dynamics Guides Coherent Exciton Migration in Conjugated Polymer Materials: A First-Principles Quantum Dynamical Study

We report on high-dimensional quantum dynamical simulations of torsion-induced exciton migration in a single-chain oligothiophene segment comprising twenty repeat units, using a first-principles parametrized Frenkel J-aggregate Hamiltonian. Starting from an initial inter-ring torsional defect, these simulations provide evidence of an ultrafast two-time scale process at low temperatures, involving exciton-polaron formation within tens of femtoseconds, followed by torsional relaxation on a ~300 femtosecond time scale. The second step is the driving force for exciton migration, as initial conjugation breaks are removed by dynamical planarization. The quantum coherent nature of the elementary exciton migration step is consistent with experimental observations highlighting the correlated and vibrationally coherent nature of the dynamics on ultrafast time scales.Comment: 4 pages, 4 figure

Hartree-Fock Many-Body Perturbation Theory for Nuclear Ground-States

We investigate the order-by-order convergence behavior of many-body perturbation theory (MBPT) as a simple and efficient tool to approximate the ground-state energy of closed-shell nuclei. To address the convergence properties directly, we explore perturbative corrections up to 30th order and highlight the role of the partitioning for convergence. The use of a simple Hartree-Fock solution to construct the unperturbed basis leads to a convergent MBPT series for soft interactions, in contrast to, e.g., a harmonic oscillator basis. For larger model spaces and heavier nuclei, where a direct high-order MBPT calculation in not feasible, we perform third-order calculation and compare to advanced ab initio coupled-cluster calculations for the same interactions and model spaces. We demonstrate that third-order MBPT provides ground-state energies for nuclei up into tin isotopic chain that are in excellent agreement with the best available coupled-cluster results at a fraction of the computational cost.Comment: 6 pages, 5 figures, 1 tabl

Ab Initio Path to Heavy Nuclei

We present the first ab initio calculations of nuclear ground states up into the domain of heavy nuclei, spanning the range from 16-O to 132-Sn based on two- plus three-nucleon interactions derived within chiral effective field theory. We employ the similarity renormalization group for preparing the Hamiltonian and use coupled-cluster theory to solve the many-body problem for nuclei with closed sub-shells. Through an analysis of theoretical uncertainties resulting from various truncations in this framework, we identify and eliminate the technical hurdles that previously inhibited the step beyond medium-mass nuclei, allowing for reliable validations of nuclear Hamiltonians in the heavy regime. Following this path we show that chiral Hamiltonians qualitatively reproduce the systematics of nuclear ground-state energies up to the neutron-rich Sn isotopes.Comment: 5 pages, 5 figure

Understanding and Comparing Deep Neural Networks for Age and Gender Classification

Recently, deep neural networks have demonstrated excellent performances in recognizing the age and gender on human face images. However, these models were applied in a black-box manner with no information provided about which facial features are actually used for prediction and how these features depend on image preprocessing, model initialization and architecture choice. We present a study investigating these different effects. In detail, our work compares four popular neural network architectures, studies the effect of pretraining, evaluates the robustness of the considered alignment preprocessings via cross-method test set swapping and intuitively visualizes the model's prediction strategies in given preprocessing conditions using the recent Layer-wise Relevance Propagation (LRP) algorithm. Our evaluations on the challenging Adience benchmark show that suitable parameter initialization leads to a holistic perception of the input, compensating artefactual data representations. With a combination of simple preprocessing steps, we reach state of the art performance in gender recognition.Comment: 8 pages, 5 figures, 5 tables. Presented at ICCV 2017 Workshop: 7th IEEE International Workshop on Analysis and Modeling of Faces and Gesture

Xenobiotic monooxygenase activity and the response to inducers of cytochrome P-450 during embryonic and larval development in fish

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution August 1981Data demonstrating the presence and inducibility of the xenobiotic monooxygenase system in fish embryos and larvae are described. The ontogeny of benzo(a)pyrene monooxygenase (BPM) activity, and NADPH- and NADH-cytochrome c reductase activities, were followed in microsomes prepared from whole embryos of the estuarine killifish Fundulus heteroclitus. BPM activity was detectable as early as 4 days from fertilization, prior to the appearance of the liver rudiment, which indicates a substantial role for the extrahepatic tissues in xenobiotic metabolism in Fundulus embryos. At all stages assayed before hatching, BPM activity was uniformly low, but within 24 hours of hatching there was a 10-fold increase in specific activity. This increase was shown not to be age-dependent but required hatching, and was not an artifact of the presence of endogenous inhibitors in embryos. Both NADPH- and NADH-cytochrome c reductase activities were measurable at all stages assayed. The developmental patterns of these two reductases were distinct from each other and did not closely correlate with that of BPM activity. However, the functional involvement of the NADPH-cytochrome c reductase in monooxygenase activity was indicated by the inhibition of BPM activity by cytochrome c. The metabolism of benzo(a)pyrene by fractions prepared from whole Fundulus embryos and eleutheroembryos appears to be catalyzed by a typical cytochrome P-450 dependent monooxygenase. This activity is localized in the microsomal fraction, requires O2, NADPH and native enzyme, and is inhibited by CO. NADPH supports much higher activity than NADH. BPM activity was detectable in the livers of Fundulus eleutheroembryos, larvae and juveniles. The level of activity in Fundulus eleutheroembryo livers was about 1/4 the average adult activity. Specific activity rose continuously from the end of the embryonic period into the juvenile period when adult levels were approached. BPM activity was also measurable in the livers of brook trout (Salvelinus fontinalis) embryos and eleutheroembryos. The ontogenic pattern contrasted with that seen in Fundulus. At 6 and 1 days before hatching BPM specific activity in embryonic liver was close to the adult level. After hatching there was a 3-fold increase in activity, thus the livers of eleutheroembryos were considerably more active in metabolizing BP than those of adult brook trout. BPM activity was inducible in Fundulus embryos by both Aroclor 1254 and No.2 Fuel oii. Embryos were competent to respond to induction as early as 4 days from fertilization. In Fundulus eleutheroembryos, Aroclor 1254 induced BPM activity in both the liver and extrahepatic tissues. Aminopyrine N-demethylase activity was detectable in microsomes prepared from whole eleutheroembryos, but was not induced by Aroclor 1254. Neither NADPH- nor NADH-cytochrome c reductase activities were induced by Aroclor 1254 before hatching, but after hatching both activities were induced. A striking developmental change in the sensitivty of the induction response was observed in Fundulus. The tissue levels of PCBs necessary to produce a maximal induction of BPM activity were at least 5 times lower in post-hatching stages compared to prehatching stages. The relative insensitivity of the induction response prior to hatching may serve to protect embryos from damage from activated metabolites during organogenesis. Aroclor 1254 was also shown to induce BPM activity in brook trout embryonic liver. The data obtained with both Fundulus and brook trout indicate that levels of PCBs occurring in fish in contaminated environments are likely to induce the monooxygenase system during embryonic development. Metabolites of benzo( a) pyrene produced by microsomes prepared from adult Fundulus liver, and untreated and PCB exposed eleutheroembryos were analyzed by HPLC. Similar metabolite profiles were obtained in all cases, with a high proportion of benzo-ring dihydrodiols. The dihydrodiol peaks produced by e leutheroembryo microsomes were abolished by TCPO, indicating the presence of epoxide hydrolase. These results suggest that Fundulus embryos and eleutheroembryos can activate BP to the highly mutagenic trans-7, 8-dihydrodiol-9, 10-epoxides. Fish embryonic monooxygenase activity may play a role in pollutant-induced lesions, including teratogenic effects, by producing reactive and mutagenic metabolites during organodifferentiation.This work was supported by National Science Foundation grants OCE77-24517 and OCE80-18569

Ab Initio Calculations of Medium-Mass Nuclei with Explicit Chiral 3N Interactions

We present the first ab initio coupled-cluster calculations of medium-mass nuclei with explicit chiral three-nucleon (3N) interactions. Using a spherical formulation of coupled cluster with singles and doubles excitations including explicit 3N contributions, we study ground states of 16,24-O, 40,48-Ca and 56-Ni. We employ chiral NN plus 3N interactions softened through a similarity renormalization group (SRG) transformation at the three-body level. We investigate the impact of all truncations and quantify the resulting uncertainties---this includes the contributions from triples excitations, the truncation of the set of three-body matrix elements, and the omission of SRG-induced four-body interactions. Furthermore, we assess the quality of a normal-ordering approximation of the 3N interaction beyond light nuclei. Our study points towards the predictive power of chiral Hamiltonians in the medium-mass regime.Comment: 6 pages, 3 figures, 2 table