Modeling of Diffusion in Capillary Porous Materials During the Drying Process

This paper presents a model of heterogenous diffusion in capillary porous materials during the process of drying. The governing heat and mass transfer equations have been established using the liquid as well as vapor flow. Two models have been presented. Model 1 does not consider the heat conduction while the model 2 has been established by considering the conduction. The developed models and the numerical solutions of the resulting differential equations can take into account the moisture and temperature dependent thermophysical properties of the product. All equations have been established in spherical coordinates but the programme written for the purpose of calculations can be used for other geometries also. Numerical calculations have been performed for gas concrete and tiles using model 1, while model 2 has been used for gas concrete only because of the lack of data for thermophysical properties of the tile. For gas concrete it was seen that conduction has only marginal effect on the drying process and the numerical predictions of the drying process were reasonably accurate.     

Experimental investigations on solar chimney for room ventilation

Experimental investigations on a small size solar chimney show that the rate of ventilation increases with increase of the ratio between height of absorber and gap between glass and absorber. This finding is in agreement with results of the steady-state mathematical model developed for analysis of such systems. Nine different combination of absorber height and air gap have been investigated on the experimental set-up. Highest rate of ventilation induced with the help of solar energy was found to be 5.6 air change per hour in a room of 27 m³, at solar radiation 700 W/m² on vertical surface with the stack height-air gap ratio of 2.83 for a 1 m high chimney.     

Towed antennas for US submarine communications: a historical perspective

The evolution of the submarine and the development of radio communication are interrelated. From the earliest days, the effectiveness of a submarine as a war-fighting vessel was linked to its ability to receive orders via the then new medium of radio. This paper traces the earliest work that linked the two together - particularly from the viewpoint of the antenna as the ship's electronic "ears" - to the present, where work is being done to provide the "silent service" with the communications sensors needed to participate fully in the battle space of the future.     

COMAR [IEEE Committee on Man Radiation]

The author reports the activities of the IEEE Committee on Man and Radiation (COMAR). COMAR critically examines and interprets the literature on biological effects. Its findings are usually reported in the form of Technical Information Statements (TISs). While the Committee holds several regular meetings every year, most of the technical work is done offline, and discussed via e-mail. It should be pointed out that COMAR does not establish safety standards, but it has an interest in the standards activity within its scope     

Tripole to the rescue [antennas]

Whether it is the Palm VIIx handheld organizer or the VV Kyocera Smartphone, people love the freedom offered by the wireless connectivity of these gadgets. However, what the wireless service providers try to downplay is the low-speed Internet connection necessitated by the congested radio channels in the cellular/PCS bands. Several strategies are being tried to deal with this problem. The present paper discusses increasing the channel capacity in a scattering environment by using dual-polarized radio signals (Andrews et al. 2001). The extra capacity arises because there are six distinguishable electric and magnetic states of polarization at a given point, rather than two as is usually assumed. A set of three collocated orthogonal dipole antennas (“tripoles”) at both the transmitting and receiving sites can triple the data rate. Andrews et al. used this approach to transmit an image of a Joan Mire painting, sending the red, green, and blue components of the picture simultaneously via three electric polarization states. If three magnetic-dipole antennas were added to the system, three additional information channels would become available because, in a scattering environment, the three magnetic-field components would be uncorrelated with one another as well as with the electric-field components     

Using perturbation theory to compute the morphological similarity of diffusion tensors

Computing the morphological similarity of diffusion tensors (DTs) at neighboring voxels within a DT image, or at corresponding locations across different DT images, is a fundamental and ubiquitous operation in the postprocessing of DT images. The morphological similarity of DTs typically has been computed using either the principal directions (PDs) of DTs (i.e., the direction along which water molecules diffuse preferentially) or their tensor elements. Although comparing PDs allows the similarity of one morphological feature of DTs to be visualized directly in eigenspace, this method takes into account only a single eigenvector, and it is therefore sensitive to the presence of noise in the images that can introduce error intothe estimation of that vector. Although comparing tensor elements, rather than PDs, is comparatively more robust to the effects of noise, the individual elements of a given tensor do not directly reflect the diffusion properties of water molecules. We propose a measure for computing the morphological similarity of DTs that uses both their eigenvalues and eigenvectors, and that also accounts for the noise levels present in DT images. Our measure presupposes that DTs in a homogeneous region within or across DT images are random perturbations of one another in the presence of noise. The similarity values that are computed using our method are smooth (in the sense that small changes in eigenvalues and eigenvectors cause only small changes in similarity), and they are symmetric when differences in eigenvalues and eigenvectors are also symmetric. In addition, our method does not presuppose that the corresponding eigenvectors across two DTs have been identified accurately, an assumption that is problematic in the presence of noise. Because we compute the similarity between DTs using their eigenspace components, our similarity measure relates directly to both the magnitude and the direction of the diffusion of water molecules. The favorable performance characteristics of our measure offer the prospect of substantially improving additional postprocessing operations that are commonly performed on DTI datasets, such as image segmentation, fiber tracking, noise filtering, and spatial normalization.     

Doing double duty: power-line communications

In 2001, the German Minister of Economy passed several laws, allocating frequencies up to 30 MHz for the introduction of new technologies, such as power-line communications (PLC). The proposed PLC systems are designed to increase data to megabits per second, offering high speed Internet access. Interference to amateur radio operators and shortwave listeners is considered     

A 44 GHz monolithic semiconductor dipole antenna

Monolithic semiconductor antennas integrated with a diode detector have been fabricated using silicon-on-sapphire technology. The performance of these antennas is analyzed on the basis of earlier theoretical work on imperfectly conducting/resistive cylindrical dipoles. The measured radiation patterns of semiconductor antennas are compared with those of the corresponding printed metal dipoles.     

On a wing and a prayer [DARPA and MEMS]

Defense Advanced Research Projects Agency (DARPA) is offering funding for interdisciplinary research in the area of hybrid insect MEMS (microelectromechanical systems). DARPA aims to have MEMS intimately integrated into insects during their early stages of metamorphoses. In principle, this should lead to a more reliable bio-electromechanical interface to the insect, as compared with the earlier DARPA-funded attempts to glue the electronic module to an adult insect. DARPA's final demonstration goal is the delivery of an insect within five meters of a specific target located a hundred meters away using electronic remote control and/or GPS.     

Monolithic semiconductor antennas for millimeter wave Si and GaAs integrated circuit technologies

It has been reported that the radiation characteristics of semiconductor antennas can be controlled by modulating their conductivity during fabrication and/or operation. This paper describes novel physical layouts integrating these versatile antennas with other components used in the realization of millimeter wave systems. The monolithic integration is discussed for GaAs as well as Si IC technologies.