The dynamics of critical Kauffman networks under asynchronous stochastic update

We show that the mean number of attractors in a critical Boolean network under asynchronous stochastic update grows like a power law and that the mean size of the attractors increases as a stretched exponential with the system size. This is in strong contrast to the synchronous case, where the number of attractors grows faster than any power law.Comment: submitted to PR

Microwave Spectroscopy of a Cooper-Pair Transistor Coupled to a Lumped-Element Resonator

We have studied the microwave response of a single Cooper-pair transistor (CPT) coupled to a lumped-element microwave resonator. The resonance frequency of this circuit, $f_{r}$, was measured as a function of the charge $n_{g}$ induced on the CPT island by the gate electrode, and the phase difference across the CPT, $\phi_{B}$, which was controlled by the magnetic flux in the superconducting loop containing the CPT. The observed $f_{r}(n_{g},\phi_{B})$ dependences reflect the variations of the CPT Josephson inductance with $n_{g}$ and $\phi_{B}$ as well as the CPT excitation when the microwaves induce transitions between different quantum states of the CPT. The results are in excellent agreement with our simulations based on the numerical diagonalization of the circuit Hamiltonian. This agreement over the whole range of $n_{g}$ and $\phi_{B}$ is unexpected, because the relevant energies vary widely, from 0.1K to 3K. The observed strong dependence $f_{r}(n_{g},\phi_{B})$ near the resonance excitation of the CPT provides a tool for sensitive charge measurements.Comment: 10 pages, 6 figure

Microwave-Induced Dephasing in One-Dimensional Metal Wires

We report on the effect of monochromatic microwave (MW) radiation on the weak localization corrections to the conductivity of quasi-one-dimensional (1D) silver wires. Due to the improved electron cooling in the wires, the MW-induced dephasing was observed without a concomitant overheating of electrons over wide ranges of the MW power $P_{MW}$ and frequency $f$. The observed dependences of the conductivity and MW-induced dephasing rate on $P_{MW}$ and $f$ are in agreement with the theory by Altshuler, Aronov, and Khmelnitsky \cite{Alt81}. Our results suggest that in the low-temperature experiments with 1D wires, saturation of the temperature dependence of the dephasing time can be caused by an MW electromagnetic noise with a sub-pW power.Comment: 4 pages with 4 figures, paper revised, accepted by Phys Rev Let

Symptom severity of bipolar disorder during the menopausal transition

BACKGROUND: Little is known about the mood symptom experience of women with bipolar disorder during the menopausal transition (MT). Yet times of rapid hormonal decline, such as the postpartum, are associated with increased risk of severe mood episodes in bipolar disorder, and the MT is a time of increased risk for unipolar depression in women with or without a history of depression. METHODS: Enrollment included 56 women 40-60 years old diagnosed in the bipolar spectrum who were experiencing menopausal symptoms or were up to 5 years since their final menstrual period. Menopausal stages included early menopause, late menopause, or early postmenopause based on standardized criteria. Observational, prospective standardized mood symptom and reproductive hormone assessments were completed periodically. Concurrent menopausal symptoms as well as history of mood exacerbation during past reproductive events were assessed. RESULTS: Forty-four women were included in the main analysis. The average Montgomery-Asberg Depression Rating Scale (MADRS) score was 4.43 points higher in the late transition/early postmenopausal stage women (n = 29) compared to the early menopausal stage women (n = 15) (+/-SE 2.14; p = 0.039), corresponding to a roughly 10 % higher score (range 0-40) in the late/post stage across all study visits. Results were similar for the Young Mania Rating Scale (YMRS), where the average score was 2.54 points higher in the late/early postmenopausal stage women compared to the early menopausal stage women (+/-SE 1.15; p = 0.027), also roughly 10 % higher (range 0-26). Estradiol and follicle-stimulating hormone (FSH) absolute levels as well as between-visit change in levels were not notably associated with YMRS or MADRS during study observation. Total Greene Climacteric Symptom (menopausal symptom) score was significantly associated with MADRS but not YMRS. History of mood exacerbation premenstrually and/or postpartum was not significantly associated with YMRS or MADRS severity during the MT. CONCLUSIONS: These results support the theory that times of increased reproductive hormonal changes, such as the late MT and early postmenopause, here compared to early MT, are associated with greater mood symptom severity in bipolar spectrum women. Nonetheless, absolute or change in FSH and estradiol levels were not significantly associated with depression or mood elevation severity

Effect of microstructures on the electron-phonon interaction in the disordered metals Pd60_{60}Ag40_{40}

Using the weak-localization method, we have measured the electron-phonon scattering times $\tau_{ep}$ in Pd$_{60}$Ag$_{40}$ thick films prepared by DC- and RF-sputtering deposition techniques. In both series of samples, we find an anomalous $1/\tau_{ep} \propto T^2\ell$ temperature and disorder dependence, where $\ell$ is the electron elastic mean free path. This anomalous behavior cannot be explained in terms of the current concepts for the electron-phonon interaction in impure conductors. Our result also reveals that the strength of the electron-phonon coupling is much stronger in the DC than RF sputtered films, suggesting that the electron-phonon interaction not only is sensitive to the total level of disorder but also is sensitive to the microscopic quality of the disorder.Comment: accepted for publication in Phys. Rev.

Critical Kauffman networks under deterministic asynchronous update

We investigate the influence of a deterministic but non-synchronous update on Random Boolean Networks, with a focus on critical networks. Knowing that ``relevant components'' determine the number and length of attractors, we focus on such relevant components and calculate how the length and number of attractors on these components are modified by delays at one or more nodes. The main findings are that attractors decrease in number when there are more delays, and that periods may become very long when delays are not integer multiples of the basic update step.Comment: 8 pages, 3 figures, submitted to a journa

Learning about knowledge: A complex network approach

This article describes an approach to modeling knowledge acquisition in terms of walks along complex networks. Each subset of knowledge is represented as a node, and relations between such knowledge are expressed as edges. Two types of edges are considered, corresponding to free and conditional transitions. The latter case implies that a node can only be reached after visiting previously a set of nodes (the required conditions). The process of knowledge acquisition can then be simulated by considering the number of nodes visited as a single agent moves along the network, starting from its lowest layer. It is shown that hierarchical networks, i.e. networks composed of successive interconnected layers, arise naturally as a consequence of compositions of the prerequisite relationships between the nodes. In order to avoid deadlocks, i.e. unreachable nodes, the subnetwork in each layer is assumed to be a connected component. Several configurations of such hierarchical knowledge networks are simulated and the performance of the moving agent quantified in terms of the percentage of visited nodes after each movement. The Barab\'asi-Albert and random models are considered for the layer and interconnecting subnetworks. Although all subnetworks in each realization have the same number of nodes, several interconnectivities, defined by the average node degree of the interconnection networks, have been considered. Two visiting strategies are investigated: random choice among the existing edges and preferential choice to so far untracked edges. A series of interesting results are obtained, including the identification of a series of plateaux of knowledge stagnation in the case of the preferential movements strategy in presence of conditional edges.Comment: 18 pages, 19 figure