A broadband microwave Corbino spectrometer at 3^3He temperatures and high magnetic fields

We present the technical details of a broadband microwave spectrometer for measuring the complex conductance of thin films covering the range from 50 MHz up to 16 GHz in the temperature range 300 mK to 6 K and at applied magnetic fields up to 8 Tesla. We measure the complex reflection from a sample terminating a coaxial transmission line and calibrate the signals with three standards with known reflection coefficients. Thermal isolation of the heat load from the inner conductor is accomplished by including a section of NbTi superconducting cable (transition temperature around 8 $-$ 9 K) and hermetic seal glass bead adapters. This enables us to stabilize the base temperature of the sample stage at 300 mK. However, the inclusion of this superconducting cable complicates the calibration procedure. We document the effects of the superconducting cable on our calibration procedure and the effects of applied magnetic fields and how we control the temperature with great repeatability for each measurement. We have successfully extracted reliable data in this frequency, temperature and field range for thin superconducting films and highly resistive graphene samples

Topology Architecture and Routing Algorithms of Octagon-Connected Torus Interconnection Network

Two important issues in the design of interconnection networks for massively parallel computers are scalability and small diameter. A new interconnection network topology, called octagon-connected torus (OCT), is proposed. The OCT network combines the small diameter of octagon topology and the scalability of torus topology. The OCT network has better properties, such as small diameter, regular, symmetry and the scalability. The nodes of the OCT network adopt the Johnson coding scheme which can make routing algorithms simple and efficient. Both unicasting and broadcasting routing algorithms are designed for the OCT network, and it is based on the Johnson coding scheme. A detailed analysis shows that the OCT network is a better interconnection network in the properties of topology and the performance of communication

Factors Affecting Ion Thruster’s Performance

In this project, we investigated how ion thrusters produce propulsion and how the design of ion thrusters affects the performance of the thruster. In the experiment, we build a high voltage power supply (0- 50 kV) and foil rings to produce ion wind. When considering the design of the thruster, we focus on three variables: the volume of the space, where ions are produced and the electric field intensity. Thus, to investigate the first variable we made foil rings with different radius and change the distance between the ring and positive cathode. To determine the propulsion produced we use a speed sensor to determine the magnitude of the wind produced

Combined effects of temperature, body size and food density on swimming behaviour and growth of juvenile brook trout (Salvelinus fontinalis)

This study is an attempt to quantify experimentally the body size allometry and thermal dependence of foraging rate (swimming velocity) in juvenile brook trout (Salvelinus fontinalis) under different food densities. The results of behavioural experiments on swimming velocity were used in conjunction with additional experimental data on maximum feeding rate and growth rate to carry out a theoretical analysis of the potential effects of changes in body size, temperature, and food density on growth, habitat use, and adult size. -- This study differs from previous studies of salmonid feeding in that the foraging movements of individual fish were tracked in real time through a computerized monitoring and control system that provided an accurate quantitative measure of the distance swum vs. time. The monitoring and control system automatically dispensed a food item each time an experimental fish had swum a prescribed distance. The distance swum per food item consumed, a measure of food density, could thus be held constant for any combination of temperature and body mass treatments, allowing for the investigation of the effects of temperature, body mass and food density on feeding behaviour under conditions close to those encountered in a natural foraging environment. -- The results of the foraging activity experiments show that the total distance swum, the proportion of time spent actively foraging, and swimming speed are all positively affected by both body mass and temperature, but not by food delivery schedule. The data are clearly not consistent with an optimal foraging model in which foraging velocity is predicted to decrease with increasing body mass and increase with increasing food density. -- The body mass allometric scaling factors for total distance swum (0.33-0.56), foraging time (0.21 -0.46), and swimming speed (0.10-0.12) at 5, 12, and 18 ﾟC are all markedly lower than the scalings for maximum feeding rate and both standard and active metabolic rates of fish. The allometric scalings for instantaneous and daily swimming costs, however, are close to the scalings for metabolic rates at all three temperatures, suggesting that swimming speeds are regulated by the instantaneous costs of swimming rather than its energy benefits. Because the rate of energy intake is directly proportional to the distance swum, the scaling for energy intake is expected to be well below that for energy requirements. -- In contrast to the situation for body mass, the values of the Van't Hoff thermal parameter for distance swum of experimental fish are close to those for sustained swimming speeds and the frequency of muscle contraction and tail beat of most fish, and also comparable to those for the standard and active metabolic rates of fish. This suggests that distance swum may respond to temperature changes in a way that parallels metabolic rate. If energy intake is a linear function of distance swum, then equivalent temperature scalings of distance swum and metabolic rate would mean that food intake should parallel temperature related changes in metabolic requirements. -- The growth rate data is consistent with previous studies and shows that there is a positive relationship between ration and the temperature for maximum growth at any body mass. Daily growth rate increases with increasing temperature at high ration level but decreases at low ration level. As a result, the temperature for maximum growth decreases as food density is decreased. -- The analyses of growth rate in actively foraging fish indicated that growth rate should increase with both body mass and temperature at high food densities, and decrease with both body mass and temperature at low food densities. At intermediate densities the situation was more complex as the effect of body mass and temperature on growth rate depended on food density, body size, and temperature. In the low food density simulation, Wmax, the body mass at which absolute growth rate is zero, is sensitive to both food density and temperature. Wmax is predicted to increase with increasing food density but decrease with increasing water temperature. -- The analyses of growth in actively foraging fish suggested that the temperature at which growth rate is maximized decreases with decreasing food density and increasing body mass. These results are consistent with previous studies of the effects of temperature on habitat use in fishes. It was not possible to draw any conclusions regarding the effect of temperature on adult size from the results presented in the thesis

Experimental and theoretical study of capillary force in adhesive contact between microspheres

This thesis describes investigations into the capillary forces between microparticles (ca. 200-1000 µm in diameter). Its original contributions to knowledge are the validations and developments of the existing theories both experimentally and theoretically. A novel technique for force-displacement measuring, in combination with an image acquisition system, has been developed to directly measure the capillary forces between two microparticles. The instrument is also cable of recording the side-view profile of the contacting process optically, which is necessary to correctly identify the geometric shape of the capillary, the pole-to-pole alignment, as well as the deformation behavior of these particles. The experiments cover samples with different mechanical properties, i.e. soft hydrogel and rigid polymer particles. The theoretical studies undertaken include both analytical and numerical analyses, which are developed for interpreting the experimental data. Classical contact mechanics theory such as Johnson-Kendall-Roberts (JKR) theory is used for the capillary formed spontaneously between two soft sponge-like hydrogel microparticles, while Kelvin equation and Young-Laplace equation are applied for the capillary formed between two PMMA microparticles due to liquid condensation. In general, the experimental data and the theoretical predictions show good agreement in both soft and rigid microparticles. For soft microparticles, the current research findings show that the work of adhesion is independent of the separation speed and, by contrast, Young’s modulus exhibits a linear increase with the separation speed. A viscoelastic model is used to further quantitatively characterize the deformation behavior of the soft hydrogel. It also demonstrates that the JKR theory reconciles with the generalized Hertz theory, which takes capillary force into account for soft microspheres in a relationship that the work of adhesion is equal to twice the surface tension of water. For rigid microparticles, both analytical and numerical models have been used to interpret the force-displacement curves measured during separation. The results demonstrate both the adhesion force and the capillary volume increase monotonically with the rise of the relative humidity. Also, subtle differences in the calculated capillary profile and adhesion forces between the analytical solution and the numerical simulation have been revealed. A surface roughness model is used to quantify the adhesion under the effect of relative humidity. These new findings are essential for developing techniques to quantitatively characterize the capillary force of colloids and granular materials and potentially to improve the material performance in their applications

Capillary force in adhesive contact between hydrogel microspheres

The paper reports an experimental study of the adhesive contact between liquid-bridged hydrogel microparticles. A novel nanomechanical tester has been developed to measure both the force-approach curves at sub-micro resolutions as well as the side-view images between two agarose spheres during pull-off. Meanwhile, the JKR theory has been extended to quantify the work of adhesion at the solid-liquid-vapor interface and Young’s modulus of the particles based on the measured parameters. Our research findings show the work of adhesion is independent of the separation speed and, by contrast, Young’s modulus exhibits a linear increase. Our study also demonstrates that JKR reconciles with the generalized Hertz theory, which takes capillary force into account for soft microspheres in a relationship that the work of adhesion is equal to twice the surface tension of water. These new findings are essential for developing techniques to quantitatively characterize capillary adhesion of soft particulate materials and potentially to improve the material performance in their applications

Improved Extreme Learning Machine and Its Application in Image Quality Assessment

Extreme learning machine (ELM) is a new class of single-hidden layer feedforward neural network (SLFN), which is simple in theory and fast in implementation. Zong et al. propose a weighted extreme learning machine for learning data with imbalanced class distribution, which maintains the advantages from original ELM. However, the current reported ELM and its improved version are only based on the empirical risk minimization principle, which may suffer from overfitting. To solve the overfitting troubles, in this paper, we incorporate the structural risk minimization principle into the (weighted) ELM, and propose a modified (weighted) extreme learning machine (M-ELM and M-WELM). Experimental results show that our proposed M-WELM outperforms the current reported extreme learning machine algorithm in image quality assessment

Hierarchical Pointer Net Parsing

Transition-based top-down parsing with pointer networks has achieved state-of-the-art results in multiple parsing tasks, while having a linear time complexity. However, the decoder of these parsers has a sequential structure, which does not yield the most appropriate inductive bias for deriving tree structures. In this paper, we propose hierarchical pointer network parsers, and apply them to dependency and sentence-level discourse parsing tasks. Our results on standard benchmark datasets demonstrate the effectiveness of our approach, outperforming existing methods and setting a new state-of-the-art.Comment: Accepted by EMNLP 201