Characterization of the Focal Cooling Necessary to Suppress Spontaneous Epileptiform Activity

It has been established that focal cooling to suppress epileptiform activity has become a real and viable option. However, the specific thermal parameters necessary to suppress epileptiform activity have only begun to be quantitatively defined. In 2002 it was reported that a 41 year-old man with medically intractable epilepsy undertook surgery to remove his tumor and resect adjacent epileptogenic tissue. Electrocorticography was performed before resection. Cold saline was impinged on the resulting interictal spike foci resulting in transient, complete cessation of spiking. We present a transient post-operative heat transfer analysis of the cold saline impingement on the surface of brain. An approximate temporal and spatial temperature distribution of the perfused human brain response to surface cooling was developed. The realistic extent of cooling below the brain surface due to impinging saline was quantified. The sensitivity of cooling penetration depth to (a) saline exit velocity from the syringe, and (b) syringe inside diameter, was evaluated. A parametric study was performed to characterize the effects of brain metabolism and blood perfusion on surface cooling. The required thermal parameters necessary to suppress epileptiform activity through focal cooling are here quantitatively approximated, i.e. heat flux removal and maximum and realistic cooling penetration depths. The relatively shallow penetration depth suggests that the spreading depolarization associated with epileptiform activity may be abolished through focal cooling without affecting the deeper neurons responsible for motor activity.

Performance of Dual Fuel Engine Running on Jojoba Oil as Pilot Fuel and CNG or LPG

The use of Jojoba Methyl Ester as a pilot fuel was investigated for almost the first time as a way to improve the performance of dual fuel engine running on natural gas or LPG at part load. The dual fuel engine used was Ricardo E6 variable compression diesel engine and it used either compressed natural gas (CNG) or liquefied petroleum gas (LPG) as the main fuel and Jojoba Methyl Ester as a pilot fuel. Diesel fuel was used as a reference fuel for the dual fuel engine results. During the experimental tests, the following have been measured: engine efficiency in terms of specific fuel consumption, brake power output, combustion noise in terms of maximum pressure rise rate and maximum pressure, exhaust emissions in terms of carbon monoxide and hydrocarbons, knocking limits in terms of maximum torque at onset of knocking, and cyclic data of 100 engine cycle in terms of maximum pressure and its pressure rise rate. The tests examined the following engine parameters: gaseous fuel type, engine speed and load, pilot fuel injection timing, pilot fuel mass and compression ratio. Results showed that using the Jojoba fuel with its improved properties has improved the dual fuel engine performance, reduced the combustion noise, extended knocking limits and reduced the cyclic variability of the combustion.

Numerical Investigation of Radiation Effects in Catalytic Combustion

In modeling catalytic combustion in a monolithic catalytic converter, it is generally assumed that the gas within the individual monolith channels does not interfere with thermal radiation. To date, no quantitative study has been undertaken to validate this assumption. Past studies for carbon monoxide combustion also appear to indicate that the emissivity of the washcoat has little effect on the thermal radiation field. In order to investigate these two issues, methane-air combustion on platinum is modeled inside a single channel of a monolith using a detailed surface reaction mechanism comprised of 24 reactions between 19 species. Radiation transport is modeled using the Discrete Ordinates Method and a gray formulation. Planck-mean absorption coefficients of the gases, calculated from the HITEMP and HITRAN databases, are used to investigate participating medium effects. All calculations were performed using the commercial CFD code, CFD-ACE+™, supplemented by user-subroutines for calculating the absorption coefficient of the gas mixture. Results show that the conversion percentages and temperature distributions are unaltered by the inclusion of participating medium radiation effects, verifying the commonly held belief, stated earlier. However, in strong contrast with carbon monoxide combustion, the emissivity of the washcoat was found to significantly affect flammability limits in the case of methane combustion—the flame being hotter and more stable for smaller values of emissivity.

A Quantitative Free Convection DNA Amplifier

The Polymerase Chain Reaction (PCR) has been used extensively to amplify targeted nucleic acids for many applications in molecular biology and, increasingly, in medical diagnostics. Outlined in this paper is a PCR device which takes account of the advantages offered by free convection. The design is, in it fundamental format a time-wise isothermal well-based thermocycler. A temperature gradient induced across the well causes convection forces to circulate the sample through the required temperatures necessary for amplification. Quantitative amplification is demonstrated with real time measurements of SYBR Green I fluorescence within the free convective DNA amplifier. Amplification of an 86-bp fragment of the pGEM®-T vector (Promega) is performed in a 25μl volume in eight minutes. A 10-fold dilution series and methods for calculating effective cycle times are presented. Also detailed within this paper are PIV and thermal imaging results of the free convection cavity. This device presents an opportunity for the development of a practical and inexpensive gene-expression measurement system.

New Frontiers of Micro and Nano-Scale Thermophysical Properties Sensing

The present keynote speech overviews new frontiers of sensing techniques for thermophysical properties in micro and nano-scale processes which are being developed at Keio. Especially, new optical sensing techniques to measure wide variety of thermophysical properties such as thermal diffusivity, thermal conductivity, viscosity, mass diffusion coefficient and surface tension of novel fluids and solids in micro and nano-scale are presented with an emphasis on their industrial applications. All of these new optical techniques have high spatial and temporal resolutions which have never been attained by other conventional measurement tools.

The Effect of Radiation and Turbulence on Heat Transport in Combustion in Porous Media

Combustion in inert porous media has been extensively investigated due to the many engineering applications and demand for developing high efficiency power production devices. The growing use of efficient radiant burners can be encountered in the power and process industries and, as such, proper mathematical models of flow, heat and mass transfer in porous media under combustion can benefit the development of such engineering equipment. This paper proposes a new mathematical model for computing temperature and flow variables inside a porous burner. A new concept called “double-decomposition” is used to represent all transported variables. A set of governing equations is presented and the numerical solution method proposed is discussed. Computations are carried out for a test case considering a simple one-energy equation model and one-step reaction rates. Simulations are presented comparing the inclusion of turbulence and radiation transfer in the model. It is shown that for high Re flows, inclusion of turbulence is as important as modeling radiation for obtaining reliable temperature distribution within the porous material.

Thermal Modeling and Luminosity Characterization of a Plasma Display Panel

Plasma Display Panels (PDPs) are a popular technology for large size television displays. Screen inefficiencies, which result in significant localized heat generation, necessitate the use of advanced thermal management materials to reduce both the peak temperatures and the spatial temperature variations across the screen. In the current study, infrared thermography was used to obtain thermal maps of a typical, 42", high-definition PDP screen for different illumination patterns and for several configurations of externally controlled heaters, simulating PDP heat generation. The results were used to validate a 3-dimensional numerical thermal model of the PDP which was then used to predict the beneficial effects of anisotropic graphite heat spreaders on the temperature distribution of the PDP. In addition, a color analyzer was used to determine the spatial and temporal variations in luminosity across the PDP when operated continuously for 1750 hours with different illumination patterns. The thermal model and experimental luminosity characteristics are used to evaluate the deleterious effects of temperature on PDP performance.

Optimal Porosity of Fibrous Battings for Thermal Insulation

The porosity of fibrous porous materials is an important factor to the thermal insulating performance of the material. This paper considers both the optimal porosity of uniform fibrous battings and the optimal distribution of the porosity of non-uniform fibrous battings for thermal insulation. The former was determined by an approximate analytical solution and a numerical simulation by using Finite Volume Method, and the latter was studied by applying Simulated Annealing Method. The study showed that the optimal porosity of uniform fibrous porous materials is very much dependent on fiber emissivity, and fiber radius, but little influenced by the temperature difference of the boundaries. For non-uniform fibrous materials, there can be an optimal distribution of porosity, which can be predicted by applying the Simulated Annealing Method.

Control of Flow Pattern and Solidification Interface Shape in an Induction Heated Czochralski Crystal Growth System

Optical crystals grown by Czochralski technique from a solute-rich melt usually suffer defects of melt inclusion or bubble core defects, which severely affect the optical, thermal and mechanical properties of the material. It is well known that the formation of melt inclusion or bubble core is highly related to species distribution in the growth system especially at the solidification interface and the shape of the growth interface. This paper has examined the flow pattern and solidification interface changes by changing the forced convection, e.g., crystal rotation and by changing the natural convection, e.g., inserting a horizontal disk plate. The relative effect of fluid-flow convection modes in the melt associated with crystal rotation rate is represented by a dimensionless parameter, Gr/Re2. Increasing the rotation rate will cause the solid-liquid interface change from the convex shape to concave. When the crystal rotation rate is relatively low and natural convection is strong, Gr/Re2 is large. In this case, the concentration of species pertinent to melt inclusion moves down along the axis of rotation. When the crystal rotation rate is increased, the value of Gr/Re2 decreases. The precipitated composition spreads over the growing interface may then be swiped away from the growth interface by increased crystal rotation. Melt inclusion-free crystals can thus be obtained. The relationship between Gr/Re2 and growth interface shape change is achieved by numerical simulations. The stagnant point location as a function of crystal rotation is also presented, which shows that the stagnant point moves outward by increasing Reynolds number and/or reducing Grashof number. From such understanding, the interface shape and melt inclusion position can then be controlled through control of Gr/Re2 in the growth system. Many times, it is, however, not practical in the experiments to use a high rotation rate for optical crystal growth since high rotation rate will introduce the striation defects. A new design to reduce natural convection is then proposed to improve the effect of crystal rotation and to control the solidification interface shape. Numerical simulations have been performed to demonstrate the possibility of the new design. Results show that such design is very effective and practical to control the melt inclusion and the solidification interface shape.

An Integral Model for Natural Convection From an Isothermal Right Circular Cone

An integral technique approximate model is developed in the current research to predict the convective heat transfer from a right circular cone. Much research has been done regarding stationary circular cones, but all of this prior research was achieved utilizing numerical techniques. As will be shown, the integral model predicts with almost the same precision as the former research. The advantage of the integral technique is its simplicity, culminating in a closed-form solution where the influence of individual system parameters and variables is directly observable. In addition, boundary layer thickness appreas explicitly in the analysis, which again tends to yield more insight at the expense of some accuracy.