Target-acquisition performance in undersampled infrared imagers: static imagery to motion video

In this research we show that the target-acquisition performance of an undersampled imager improves with sensor or target motion. We provide an experiment designed to evaluate the improvement in observer performance as a function of target motion rate in the video. We created the target motion by mounting a thermal imager on a precision two-axis gimbal and varying the sensor motion rate from 0.25 to 1 instantaneous field of view per frame. A midwave thermal imager was used to permit short integration times and remove the effects of motion blur. It is shown that the human visual system performs a superresolution reconstruction that mitigates some aliasing and provides a higher (than static imagery) effective resolution. This process appears to be relatively independent of motion velocity. The results suggest that the benefits of superresolution reconstruction techniques as applied to imaging systems with motion may be limited.     

Thermal-gradient-induced interaction energy ramp and actuation of relative axial motion in short-sleeved double-walled carbon nanotubes

We investigate the phenomenon of actuation of relative linear motion in double-walled carbon nanotubes (DWNTs) resulting from a temperature gradient. Molecular dynamics simulations of DWNTs with short outer tube reveal that the outer tube is driven towards the cold end of the long inner tube. It is also found that the terminal velocity of the sleeve roughly depends linearly on the applied thermal gradient. We calculate the inter-tube interaction energy surface which is revealed to have a gradient depending upon the applied thermal gradient. Consequently, it is proposed that the origin of the thermophoretic motion of the outer tube may be attributed partially to the existence of such an energy gradient. A simple analytical model is presented accounting for the gradient in energy profile as well as the effect of biased thermal noise. It is shown that the proposed model predicts the dynamical behaviour of the long-time performance reasonably well.     

Effect of Residual Stress on the Stability of Gold Thin Film Surfaces

The temporal evolution of the surface topography and x-ray diffractogram of gold thin films was obtained. We found by STM that the surface roughness decreased exponentially with time. X-ray analysis indicates that the microcrystals are strained i.e., the x-ray peaks shift with elapsed time towards the gold standard reflections. The rearrangement of the gold film is induced by surface strains that appear during film growth rather than by the thermal motion of atoms. A DC current was applied to the films to induce surface changes and to study electromigration phenomena. Results show that current effects accelerate film failure by surface diffusion produced by the growth of microcrystals at the expense of mechanically strained microcrystals.     

Effects of negative afterimages in visual illusions

We show that a broad class of visual illusions, including illusory motion, can be explained by the effects of negative afterimages. Two new illusions, illusory shading and illusory tilting, are devised on the basis of the proposed explanation. The general feature of these illusions is an alternation between a high-contrast (white or black) and a low-contrast (gray) local input signal, which can be caused either by eye motion over patterns of varied luminance or by a change in such patterns over time. A simple model of the local signal dynamics qualitatively reproduces the illusory effects by adding the negative afterimage to the original visual stimulus.     

A temperature and rate-dependent micromechanical model of molybdenum under neutron irradiation

In this paper we present a micromechanics-based model for neutron-irradiated single and polycrystalline BCC molybdenum which is capable of representing not only the effects of radiation hardening, yield drop and non-zero stress offset from the unirradiated stress-strain curves, but also the unique “radiation softening” effect observed in Mo at low to intermediate homologous temperatures (0.05 ? T/T_m ? 0.2) (Li et al., 2008) and low radiation doses. Specifically, a single smooth viscoplastic potential has been developed in which the critical resolved shear stress is decomposed into thermal and athermal components that overcome short range and long range barriers, respectively. The evolution of the athermal part is dependent on dislocation and defect densities, whereas the thermal part is modeled to be a function of temperature only. Impediment of dislocation motion due to defects results in hardening while defect annihilation due to dislocation motion accounts for yield drop and stress offset. Radiation softening is explained by invoking a critical temperature (T_c), with increase in radiation dose below which the thermal part of the flow stress undergoes a reduction due to increase in mobile point defects in the dislocation core area, whereas the athermal part increases. Beyond the critical temperature, however, thermal activation is sufficient for dislocation motion and the thermal component disappears. We argue that for low radiation doses, this critical temperature decreases with increase in radiation dose, resulting in a temperature range over which the flow stress actually drops below its value corresponding to the unirradiated condition. Polycrystalline response has been simulated based on a Taylor type homogenization scheme. The model is validated with experimental data for a range of temperatures and strain rates with increasing radiation dose.     

Effect of various thermal loadings on buckling and vibrational characteristics of nonlocal temperature-dependent functionally graded nanobeams

In this article, the thermal effects on buckling and free vibrational characteristics of functionally graded (FG) size-dependent nanobeams subjected to various types of thermal loading are investigated by presenting a Navier-type solution for the first time. Temperature-dependent material properties of FG nanobeams vary continuously along the thickness according to the power-law form. The small-scale effect is taken into consideration based on Eringen's nonlocal elasticity theory. The nonlocal equations of motion are derived through Hamilton's principle and they are solved applying an analytical solution. It is revealed that the proposed modeling can provide accurate frequency results of the FG nanobeams.     

Soret and Dufour effects on convective instabilities in binary nanofluids for absorption application

Thermodiffusion (Soret effect) and diffusionthermo (Dufour effect) effects on convective instabilities in nanofluids have been theoretically investigated. Thermodiffusion implies that mass diffusion is induced by thermal gradient, which is so-called the Soret effect. Diffusionthermo implies that heat transfer is induced by concentration gradient, which is so-called the Dufour effect. By using the linear stability theory under one-fluid model, a characteristic dimensionless parameter was newly obtained. From the instability analysis with given conditions, it is found that the convective motion in nanofluids sets in easily as the Soret and Dufour effects and the initial concentration of nanoparticles increase.     

Numerical modeling of startup and shutdown transients in reciprocating compressors

Several phenomena that affect energy consumption, noise level and reliability of compressors are associated with transient effects that occur during the compressor startup and shutdown. This paper presents a simulation methodology, experimentally validated, developed to analyze the compressor in such transients. Because the time scale associated with the compressor thermal behavior is much larger than that related to the mechanical physics, a thermal equilibrium condition has been considered herein for convenience. Results for valve displacement, piston motion, pressure in the compression chamber and resistive torques are provided to illustrate the application of the methodology and to assist an understanding of the physical aspects that affect the compressor performance throughout the startup and shutdown. It is observed that the dynamics of suction and discharge valves are greatly affected. Moreover, the model is employed to estimate the minimum voltage required for the compressor startup as a function of the equalized pressure and the auxiliary coil actuation time.     

Thermal stress relaxation in magnesium matrix composites controlled by dislocation breakaway

In metal matrix composites (MMCs) thermal stress relaxation can be achieved either by interface debonding, crack propagation or by dislocation motion. The present paper shows that in the case of magnesium matrix, interface thermal stresses are relaxed by dislocation motion. Moreover the results obtained by mechanical spectroscopy prove that this dislocation motion is controlled by a solid friction mechanism, which is not thermally activated. This point is very interesting for the development of MMCs, which exhibit a high damping capacity over a wide frequency range. Dislocation hysteretic motion in the magnesium matrix is evidenced by the dependence of the mechanical loss on the stress amplitude. The obtained relationship obeys perfectly to the Granato–Lücke model for dislocation breakaway.     

The effects of temperature, volume fraction and vibration time on the thermo-physical properties of a carbon nanotube suspension (carbon nanofluid)

In this investigation, nanofluids of carbon nanotubes are prepared and the thermal conductivity and volumetric heat capacity of these fluids are measured using a thin layer technique as a function of time of ultrasonication, temperature, and volume fraction. It has been observed that after using the ultrasonic disrupter, the size of agglomerated particles and number of primary particles in a particle cluster was significantly decreased and that the thermal conductivity increased with elapsed ultrasonication time. The clustering of carbon nanotubes was also confirmed microscopically. The strong dependence of the effective thermal conductivity on temperature and volume fraction of nanofluids was attributed to Brownian motion and the interparticle potential, which influences the particle motion. The effect of temperature will become much more evident with an increase in the volume fraction and the agglomeration of the nanoparticles, as observed experimentally. The data obtained from this work have been compared with those of other studies and also with mathematical models at present proven for suspensions. Using a 2.5% volumetric concentration of carbon nanotubes resulted in a 20% increase in the thermal conductivity of the base fluid (ethylene glycol).The volumetric heat capacity also showed a pronounced increase with respect to that of the pure base fluid.     

The use of magnetic nanoparticles in thermal therapy monitoring and screening: Localization and imaging (invited)

Magnetic nanoparticles have many diagnostic and therapeutic applications. A method termed magnetic spectroscopy of nanoparticle Brownian motion (MSB) was developed to interrogate in vivo the microscopic environment surrounding magnetic nanoparticles. We can monitor several effects that are important in thermal therapy and screening including temperature measurement and the bound state distribution. Here we report on simulations of nanoparticle localization. Measuring the spatial distribution of nanoparticles would allow us to identify ovarian cancer much earlier when it is still curable or monitor thermal therapies more accurately. We demonstrate that with well-designed equipment superior signal to noise ratio (SNR) can be achieved using only two harmonics rather than using all the harmonics containing signal. Alternatively, smaller magnetic field amplitudes can be used to achieve the same SNR. The SNR is improved using fewer harmonics because the noise is limited.     

Exact flow/heat solutions for the non-axisymmetric flow over a rotating disk

The present note is concerned with the exact non-axisymmetric solutions for the flow over a rotating disk. The governing non-axisymmetric flow equations of motion generate exact flow solutions from which analytic expressions for the vorticity, shear stresses, flow/thermal layer thicknesses and rate of heat transfer are obtained. The effects of Brinkman number, heat generation/absorption as well as thermal radiation on the temperature field can be better pursued from the extracted formulae.     

Hydrodynamic theory of fourth sound in clamped conditions

The hydrodynamic theory of fourth sound is developed in detail for the cases of a flat capillary and a porous superleak filled with superfluid helium whose normal fluid motion is completely clamped. The attenuation is calculated including rigorously all the thermal conduction effects in both the helium and the capillary walls. Also included in the case of the superleak are the Rayleigh scattering and the thermal effects of the resonator walls. Comparison of the superleak results with existing experiments leads to the conclusion that Q factors of fourth-sound resonators could be increased considerably.     

Thermal Kinetic Inductance Detectors for Ground-Based Millimeter-Wave Cosmology

We show measurements of thermal kinetic inductance detectors (TKIDs) intended for millimeter-wave cosmology in the 200–300 GHz atmospheric window. The TKID is a type of bolometer which uses the kinetic inductance of a superconducting resonator to measure the temperature of the thermally isolated bolometer island. We measure bolometer thermal conductance, time constant, and noise equivalent power. We also measure the quality factor of our resonators as the bath temperature varies to show they are limited by effects consistent with coupling to two-level systems.     

Visually Servoed 3-D Alignment of Multiple Objects with Subnanometer Precision

This paper presents a visual measurement technique and the associated visual servo control method that enable 3-D alignment of multiple objects with subnanometer precision. Such high precision is achieved through eliminating the bias error caused by spatial sampling in the in-plane motion estimation, using a highly sensitive measurement technique based on interference for the out-of-plane motion, and continuously compensating for time varying uncertainties induced by mechanical forces and thermal drifts. The developed measurement technique is integrated with a motion stage to experimentally demonstrate visually servoed 3-D alignment, in which two microcantilevers are aligned in the 3-D space with alignment errors below 1 nm (rms) in all axes. Nanostepping of 0.5 nm magnitude along the out-of-plane z-axis is also performed between the two microcantilevers to illustrate the super precision of the visually served 3-D alignment.     

Nonlinear convection with variable coefficient of thermal expansion

Summary The problem of nonlinear convection in a horizontal layer of fluid with variable coefficient of thermal expansion is considered. It is found that square cells transport always more heat than two-dimensional rolls and that rolls are always unstable. Variable coefficient of thermal expansion can strongly affect the critical Rayleigh number and the horizontal scale of the motion. Subcritical instabilities can exist which are associated with either hexagon pattern convection or square pattern convection. Particular forms of the coefficient thermal expansion are essential to determine the preferred flow patterns which could be of the forms of squares or hexagons with either upward of downward motion at the cells' centers.     

湿热状态下倾斜复合材料板混沌运动区域分析

在考虑湿热影响的基础上,利用Melnikov函数研究了倾斜复合材料矩形板的混沌运动,并讨论分析了倾斜角、湿度、温度、长宽比、板厚对复合材料矩形板发生混沌运动区域影响。     

Counterflow in rotating superfluid helium

We have observed a variety of effects involving thermal counterflow in rotating superfluid helium. In particular, the temperature and chemical potential gradients associated with the motion of vortex lines have been measured. The two-fluid equations for helium in rotation have been solved for channel flow in a channel of finite height and the results are compared with our data. Interesting effects associated with the onset of turbulence and with the onset of vortex line depinning are discussed.Supported by a grant from the National Science Foundation.     

Out-of-plane free vibration of functionally graded circular curved beams in thermal environment

A first known formulation for the out-of-plane free vibration analysis of functionally graded (FG) circular curved beams in thermal environment is presented. The formulation is based on the first order shear deformation theory (FSDT), which includes the effects of shear deformation and rotary inertia due to both torsional and flexural vibrations. The material properties are assumed to be temperature dependent and graded in the direction normal to the plane of the beam curvature. The equations of motion and the related boundary conditions, which include the effects of initial thermal stresses, are derived using the Hamilton’s principle. Differential quadrature method (DQM), as an efficient and accurate numerical method, is adopted to solve the thermoelastic equilibrium equations and the equations of motion. The formulations are validated by comparing the results, in the limit cases, with the available solutions in the literature for isotropic circular curved beams. In addition, for FG circular curved beams with soft simply supported edges, the results are compared with the obtained exact solutions. Then, the effects of temperature rise, boundary conditions, material and geometrical parameters on the natural frequencies are investigated.     

An investigation of surface energy input to gas during initiation of a nanosecond distributed surface discharge

The fraction of energy, directly introduced into gas during the initiation of a distributed pulsed surface discharge of the plasma sheet type, is analyzed using the results of investigation of the dynamics of resultant shock waves. Results are given of numerical calculation of development of flow within the model of thermal energy input. It is demonstrated that the experimentally obtained values of the velocity of motion of perturbations agree well with the calculation results assuming that 40 ± 10% of the energy of surface electric discharge of nanosecond duration changes to thermal energy in the stage of energy input, i.e., during the time which is much shorter than 1 μs.