Effect of the Exit Condition on the Performance of In-Tube Condensers

Data collected from the open literature plus some new, unpublished data show that the exit condition with in-tube condensation can change the flow regimes, introduce certain types of instabilities, and alter flooding velocities. All the possible orientations are considered: horizontal, vertical with vapor downflow, and vertical with vapor upflow (refluxing).     

MHD natural convection inside an inclined trapezoidal porous enclosure with internal heat generation or absorption subjected to isoflux heating

A steady laminar two‐dimensional magneto‐hydrodynamic natural convection flow in an inclined trapezoidal enclosure filled with a fluid‐saturated porous medium is investigated numerically using a finite difference method. The left and right vertical sidewalls of the trapezoidal enclosure are maintained at a cold temperature. The horizontal top wall is considered adiabatic while the bottom wall is subjected to isoflux heating. A volumetric internal heat generation or absorption is embedded inside the trapezoidal enclosure while an external magnetic field is applied on the left sidewall of the enclosure. In the current work, the following parametric ranges of the non‐dimensional groups are used: Hartmann number is varied as , Darcy number is taken as , 10^?4, and 8 × 10^?5, Rayleigh number is varied as , Prandtl number is considered constant at Pr = 0.7, the dimensionless internal heat generation or absorption parameter is varied as Δ = ?0.2, 0, 1, and 2.0, while the trapezoidal enclosure inclination angle is varied as . The results indicated a strong flow circulation occurs when the Darcy and the Rayleigh numbers are high. In addition, it is found that the Hartmann number, internal heat generation or absorption parameter and inclination angle have an important role on the flow and thermal characteristics. It is also found that when the enclosure inclination angle and Hartmann number increase the average Nusselt number along the hot bottom wall decreases. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21013     

Effects of diameter ratio of adiabatic circular cylinder and tilt angle on natural convection from a square open tilted cavity

A numerical analysis is carried out to study the performance of natural convection inside a square open tilted cavity filled with air. An adiabatic circular solid cylinder is placed at the center of the cavity and the sidewall in front of the breathing space is heated by a constant heat flux. The top and bottom walls are kept at the ambient constant temperature. Two‐dimensional forms of Navier–Stokes equations along with the energy equations are solved using the Galerkin finite element method. Results are obtained for a range of Grashof numbers from 10³ to 10⁶ at Pr = 0.71 while the tilt angle varies from 0 to 45° and the diameter ratio of the cylinder is considered to be 0.2, 0.3, and 0.4 with constant physical properties. The parametric studies for a wide range of cylinder diameter ratios and cavity tilt angles show significant features of the present problem in terms of stream functions and temperature profiles. The computational results indicate that the heat transfer coefficient is strongly influenced by the above governing parameters. It is also found that the average Nusselt number decreases when the diameter ratio increases. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.21001     

Convergence of fuzzy-pyramid algorithms

Pyramid linking is an important technique for segmenting images and has many applications in image processing and computer vision. The algorithm is closely related to the ISODATA clustering algorithm and shares some of its properties. This paper investigates this relationship and presents a proof of convergence for the pyramid linking algorithm. The convergence of the hard-pyramid linking algorithm has been shown in the past; however, there has been no proof of the convergence of fuzzy-pyramid linking algorithms. The proof of convergence is based on Zangwill's theorem, which describes the convergence of an iterative algorithm in terms of a descent function of the algorithm. We show the existence of such a descent function of the pyramid algorithm and, further, show that all the conditions of Zangwill's theorem are met; hence the algorithm converges.This research was supported by the U.S. Army Research Office under contract DAAL 03-91-G0050.     

Comparative evaluation of 3D vs. 2D modality for automatic detection of facial action units

Automatic detection of facial expressions attracts great attention due to its potential applications in human–computer interaction as well as in human facial behavior research. Most of the research has so far been performed in 2D. However, as the limitations of 2D data are understood, expression analysis research is being pursued in 3D face modality. 3D can capture true facial surface data and is less disturbed by illumination and head pose. At this junction we have conducted a comparative evaluation of 3D and 2D face modalities. We have investigated extensively 25 action units (AU) defined in the Facial Action Coding System. For fairness we map facial surface geometry into 2D and apply totally data-driven techniques in order to avoid biases due to design. We have demonstrated that overall 3D data performs better, especially for lower face AUs and that there is room for improvement by fusion of 2D and 3D modalities. Our study involves the determination of the best feature set from 2D and 3D modalities and of the most effective classifier, both from several alternatives. Our detailed analysis puts into evidence the merits and some shortcomings of 3D modality over 2D in classifying facial expressions from single images.     

Image processing on encoded video sequences

This paper presents a novel approach to processing encoded video sequences prior to complete decoding. Scene changes are easily detected using DCT coefficients in JPEG and MPEG encoded video sequences. In addition, by analyzing the DCT coefficients, regions of interest may be isolated prior to decompression, increasing the efficiency of any subsequent image processing steps, such as edge detection. The results are currently used in a video browser and are part of an ongoing research project in creating large video databases. The procedure is detailed with several examples presented and studied in depth.     

Impact of technology scaling on thermal behavior of leakage current in sub-quarter micron MOSFETs: perspective of low temperature current testing

The increase in the off-state current for sub-quarter micron CMOS technologies is making conventional I_DDQ testing ineffective. Since natural process variation together with low-V_TH devices can significantly increase the absolute leakage value and the variation, choosing a single threshold for I_DDQ testing is impractical. One of the potential solutions is the cooling of the chip during current testing. In this paper we analyze the impact of CMOS technology scaling on the thermal behavior of different leakage current mechanisms in n-MOSFETs and estimate the effectiveness of low temperature I_DDQ testing. We found that the conventional single threshold low temperature I_DDQ testing is not effective for sub-quarter micron CMOS technologies and propose the low temperature ΔI_DDQ test method. The difference between pass and fail current limits was estimated more than 200× for 0.13-μm CMOS technology.     

Leakage Current in Sub-Quarter Micron MOSFET: A Perspective on Stressed Delta I DDQ Testing

The effectiveness of single threshold I _DDQ measurement for defect detection is eroded owing to higher and more variable background leakage current in modern VLSIs. Delta I _DDQ is identified as one alternative for deep submicron current measurements. Often delta I _DDQ is coupled with voltage and thermal stress in order to accelerate the failure mechanisms. A major concern is the I _DDQ limit setting under normal and stressed conditions. In this article, we investigate the impact of voltage and thermal stress on the background leakage. We calculate I _DDQ limits for normal and stressed operating conditions of 0.18 m n-MOSFETs using a device simulator. Intrinsic leakage current components of transistor are analyzed and the impact of technology scaling on effectiveness of stressed I _DDQ testing is also investigated.     

A som study of DC-PBH laser catastrophic failures

OBIC and PL imaging modes of a SOM have been successfully applied to the failure analysis of catastrophically degraded DC-PBH lasers. High lateral resolution, variable in-depth penetration and selective excitation are the most interesting features. A degradation mechanism has been found due to the development of leakage paths in the confining junctions.     

Untersuchungen zum Schwefeltransport zwischen flüssigem kohlenstoffgesättigtem Eisen und basischen Schlacken während der Verschlackung sauerstoffaffiner Zusatzelemente,insbesondere des Siliziums

Gravimetrische Untersuchungen mit Hilfe einer Thermowaage zum Schwefeltransport zwischen siliziumhaltigen, kohlenstoffgesättigten Eisenschmelzen und CoO-Al₂O₃-Schlacken bei 1490 und 1550°C unter oxydierenden Bedingungen. Vergleich der Ergebnisse mit bereits vorliegenden volumetrischen Untersuchungen. Erörterung der Versuchsergebnisse mit Hilfe der Ionentheorie der Schlacke. Einfluß von Mangan, Silizium, Titan und Kohlenstoff auf den Anteil des Schwefeltransportes bei oxydierenden Bedingungen.