Informational drives for sensor evolution

© 2012 Massachusetts Institute of Technology Published under a Creative Commons Attribution 4.0 International (CC BY 4.0) licenseIt has been hypothesized that the evolution of sensors is a pivotal driver for the evolution of organisms, and especially, as a crucial part of the perception-action loop, a driver for cognitive development. The questions of why and how this is the case are important: what are the principles that push the evolution of sensorimotor systems? An interesting aspect of this problem is the co-option of sensors for functions other than those originally driving their development (e.g. the auditive sense of bats being employed as a 'visual' modality). Even more striking is the phenomenon found in nature of sensors being driven to the limits of precision, while starting from much simpler beginnings. While a large potential for diversification and exaptation is visible in the observed phenotypes, gaining a deeper understanding of why and how this can be achieved is a significant problem. In this present paper, we will introduce a formal and generic information-theoretic model for understanding potential drives of sensor evolution, both in terms of improving sensory ability and in terms of extending and/or shifting sensory function

Statistics of turbulent fluctuations in counter-rotating Taylor-Couette flows

The statistics of velocity fluctuations of turbulent Taylor-Couette flow are examined. The rotation rate of the inner and outer cylinder are varied while keeping the Taylor number fixed to $1.49 \times 10^{12}$ ($\mathcal{O}(\text{Re})=10^6$). The azimuthal velocity component of the flow is measured using laser Doppler anemometry (LDA). For each experiment $5\times10^6$ datapoints are acquired and carefully analysed. Using extended self-similarity (ESS) \cite{ben93b} the longitudinal structure function exponents are extracted, and are found to weakly depend on the ratio of the rotation rates. For the case where only the inner cylinder rotates the results are in good agreement with results measured by Lewis and Swinney \cite{lew99} using hot-film anemometry. The power spectra shows clear -5/3 scaling for the intermediate angular velocity ratios $-\omega_o/\omega_i \in \{0.6, 0.8, 1.0\}$, roughly -5/3 scaling for $-\omega_o/\omega_i \in \{0.2, 0.3, 0.4, 2.0\}$, and no clear scaling law can be found for $-\omega_0/\omega_i = 0$ (inner cylinder rotation only); the local scaling exponent of the spectra has a strong frequency dependence. We relate these observations to the shape of the probability density function of the azimuthal velocity and the presence of a neutral line

Matched wideband low-noise amplifiers for radio astronomy

Two packaged low noise amplifiers for the 0.3–4 GHz frequency range are described. The amplifiers can be operated at temperatures of 300–4 K and achieve noise temperatures in the 5 K range (<0.1 dB noise figure) at 15 K physical temperature. One amplifier utilizes commercially available, plastic-packaged SiGe transistors for first and second stages; the second amplifier is identical except it utilizes an experimental chip transistor as the first stage. Both amplifiers use resistive feedback to provide input reflection coefficient S11<−10 dB over a decade bandwidth with gain over 30 dB. The amplifiers can be used as rf amplifiers in very low noise radio astronomy systems or as i.f. amplifiers following superconducting mixers operating in the millimeter and submillimeter frequency range

Turbulence strength in ultimate Taylor-Couette turbulence

We provide experimental measurements for the effective scaling of the Taylor-Reynolds number within the bulk $\text{Re}_{\lambda,\text{bulk}}$, based on local flow quantities as a function of the driving strength (expressed as the Taylor number Ta), in the ultimate regime of Taylor-Couette flow. The data are obtained through flow velocity field measurements using Particle Image Velocimetry (PIV). We estimate the value of the local dissipation rate $\epsilon(r)$ using the scaling of the second order velocity structure functions in the longitudinal and transverse direction within the inertial range---without invoking Taylor's hypothesis. We find an effective scaling of $\epsilon_{\text{bulk}} /(\nu^{3}d^{-4})\sim \text{Ta}^{1.40}$, (corresponding to $\text{Nu}_{\omega,\text{bulk}} \sim \text{Ta}^{0.40}$ for the dimensionless local angular velocity transfer), which is nearly the same as for the global energy dissipation rate obtained from both torque measurements ($\text{Nu}_{\omega} \sim \text{Ta}^{0.40}$) and Direct Numerical Simulations ($\text{Nu}_{\omega} \sim \text{Ta}^{0.38}$). The resulting Kolmogorov length scale is then found to scale as $\eta_{\text{bulk}}/d \sim \text{Ta}^{-0.35}$ and the turbulence intensity as $I_{\theta,\text{bulk}} \sim \text{Ta}^{-0.061}$. With both the local dissipation rate and the local fluctuations available we finally find that the Taylor-Reynolds number effectively scales as Re$_{\lambda,\text{bulk}}\sim \text{Ta}^{0.18}$ in the present parameter regime of $4.0 \times 10^8 < \text{Ta} < 9.0 \times 10^{10}$.Comment: 15 pages, 8 figures, J. Fluid Mech. (In press

Interaction of Nucleosides and Related Compounds with Nucleic Acids as Indicated by the Change of Helix-Coil Transition Temperature

A series of compounds has been tested for effectiveness in lowering the melting temperature of poly A and of thymus DNA. The order of increasing activity was found to be: adonitol, methyl riboside (both negligible) < cyclohexanol < phenol, pyrimidine, uridine < cytidine, thymidine < purine, adenosine, inosine, deoxyguanosine < caffeine, coumarin, 2,6-dichloro-7-methylpurine. Urea was ineffective with poly A and only slightly effective with DNA. At a concentration of 0.3 M, purine lowered the Tm of DNA about 9°

The Detection of Defects in a Niobium Tri-layer Process

Niobium (Nb) LTS processes are emerging as the technology for future ultra high-speed systems especially in the digital domain. As the number of Josephson Junctions (JJ) per chip has recently increased to around 90000, the quality of the process has to be assured so as to realize these complex circuits. Until now, very little or no information is available in the literature on how to achieve this. In this paper we present an approach and results of a study conducted on an RSFQ process. Measurements and SEM inspection were carried out on sample chips and a list of possible defects has been identified and described in detail. We have also developed test-structures for detection of the top-ranking defects, which will be used for yield analysis and the determination of the probability distribution of faults in the process. A test chip has been designed, based on the results of this study, and certain types of defects were introduced in the design to study the behavior of faulty junctions and interconnections