Wireless Internet access for mobile subscribers based on theGPRS/UMTS network

With the advent of IP technologies and the tremendous growth in data traffic, the wireless industry is evolving its core networks toward IP technology. Enabling wireless Internet access is one of the upcoming challenges for mobile radio network operators. The General Packet Radio Service is the packet-switched extension of GSM and was developed to facilitate access to IP-based services better than existing circuit-switched services provided by GSM. We illustrate how a visited mobile subscriber on a GPRS/UMTS network can access his/her home network via the gateway GPRS support node (GGSN). We also propose some implementation ideas on wireless Internet access for a remote mobile subscriber based on a GPRS/UMTS network     

Fire detection based on hidden Markov models

In this paper, a novel method of real-time fire detection based on HMMs is presented. First, we present an analysis of fire characteristics that provides evidence supporting the use of HMMs to detect fire; second, we propose an algorithm for detecting candidate fire pixels that entails the detection of moving pixels, fire-color inspection, and pixels clustering. The main contribution of this paper is the establishment and application of a hidden Markov fire model by combining the state transition between fire and non-fire with fire motion information to reduce data redundancy. The final decision is based on this model which includes training and application; the training provides parameters for the HMM application. The experimental results show that the method provides both a high detection rate and a low false alarm rate. Furthermore, real-time detection has been effectively realized via the learned parameters of the HMM, since the most time-consuming components such as HMM training are performed off-line.     

Key distribution for secure VSAT satellite communications

This paper presents modified Yacobi (1989) scheme that does not use the secret key provided by the key distribution center, but uses instead a random number generated by the user. This paper also presents the modified Diffie-Hellman (1976) and ID (identity) method which has directly mutual authentication between users and is able to defend the network from impostors. The proposed scheme based on the DH was applied to VSAT satellite communications and simulated on a PC using Montgomery (1993) algorithm and MD5 (Message Digest) for a feasible study of secure VSAT satellite communications     

Massless links with external forces and bushing effect for multibody dynamic analysis

When the contribution of lightweight components to the total energy of a system is small, the inertia effects are sometimes ignored by replacing them to massless links. For example, a revolute-spherical massless link generates two kinematic constraint equations between adjacent bodies and allows four relative degrees of freedom. In this paper, to implement a massless link systematically in a computer program using the velocity transformation technique, the velocity transformation matrix of massless links is derived and numerically implemented. The velocity transformation matrix for a revolute-spherical massless link and a revolute-universal massless link are appeared as a 6X4 matrix and a 6X3 matrix, respectively. A massless link model in a suspension composite joint transmitting external forces is also developed and the numerical efficiency of the proposed model is compared to a conventional multibody model. For a massless link transmitting external forces, forces acting on links are resolved and transmitted to the attached points with a quasi-static assumption. Numerical examples are presented to verify the formulation.     

Mechanism of Preventing Crystallization in Low-Firing Glass/Ceramic Composite Substrates

The formation of a crystal phase in the glass matrix of low-firing glass/ceramic composite substrates limits the efficiency of the ceramic substrate when it is used in circuit boards. In the present study, adding approximately 30 vol % or more of alumina to a borosilicate-glass/ceramic composite system as a ceramic filler caused the diffusion of aluminum ions from the alumina filler into the glass matrix and prevented the formation of a cristobalite crystal phase. The diffusion distance between the aluminum ions was ∼30 μm when the system was fired at 900°C for 10 min. Raman spectroscopic analysis proved that some of the aluminum ions had diffused into the glass matrix during firing, working as a network former in the glass matrix. Raman spectra near 460 and 1100 cm⁻¹ indicate the change of network structure in the borosilicate glass. These phenomena indicate that crystallization of the borosilicate glass was prevented in the alumina-filled borosilicate system.     

Lithium-assisted electrochemical welding in silicon nanowire battery electrodes

From in situ transmission electron microscopy (TEM) observations, we present direct evidence of lithium-assisted welding between physically contacted silicon nanowires (SiNWs) induced by electrochemical lithiation and delithiation. This electrochemical weld between two SiNWs demonstrates facile transport of lithium ions and electrons across the interface. From our in situ observations, we estimate the shear strength of the welded region after delithiation to be approximately 200 MPa, indicating that a strong bond is formed at the junction of two SiNWs. This welding phenomenon could help address the issue of capacity fade in nanostructured silicon battery electrodes, which is typically caused by fracture and detachment of active materials from the current collector. The process could provide for more robust battery performance either through self-healing of fractured components that remain in contact or through the formation of a multiconnected network architecture.     

Hybrid neural network bushing model for vehicle dynamics simulation

Although the linear model was widely used for the bushing model in vehicle suspension systems, it could not express the nonlinear characteristics of bushing in terms of the amplitude and the frequency. An artificial neural network model was suggested to consider the hysteretic responses of bushings. This model, however, often diverges due to the uncertainties of the neural network under the unexpected excitation inputs. In this paper, a hybrid neural network bushing model combining linear and neural network is suggested. A linear model was employed to represent linear stiffness and damping effects, and the artificial neural network algorithm was adopted to take into account the hysteretic responses. A rubber test was performed to capture bushing characteristics, where sine excitation with different frequencies and amplitudes is applied. Random test results were used to update the weighting factors of the neural network model. It is proven that the proposed model has more robust characteristics than a simple neural network model under step excitation input. A full car simulation was carried out to verify the proposed bushing models. It was shown that the hybrid model results are almost identical to the linear model under several maneuvers. This paper was recommended for publication in revised form by Associate Editor Hong Hee Yoo Dr. Wan-Suk Yoo was born in 1954, and received B.S. degree from Seoul National University (1976), and got M.S. degree from KAIST (1978) and Ph.D. from the University of Iowa (1985). He is currently a full professor at the Pusan National University in Korea, where he joined since 1978. His major area is vehicle dynamics and flexible multibody dynamics. He became an ASME Fellow (2004), and currently serving as an associate editor for the ASME, J. of computational and nonlinear dynamics. He is also serving a contributing editor for the multibody system dynamics journal. He is serving as ISC chair for the ACMD2008, and a member at IFToMM TC for multibody dynamics. He is currently a vicepresident of the KSME (Korean Society of Mechanical Engineers).     

Changes in the microstructure and hydrogen storage properties of Ti-Cr-V alloys by ball milling and heat treatment

Changes in the microstructure and hydrogen storage properties of Ti-Cr-V alloys were investigated after a combination of ball milling and heat treatment. Two different sets of balls and vials made of tungsten carbide (WC) and stainless steel (STS) were used for milling the samples. Ball milling using WC balls and vials induced WC contamination, and it caused compositional changes in the matrix during heat treatment. When STS balls and vials were used, meanwhile, no peak of the second phase caused by contamination was found in the X-ray diffraction (XRD) data. In the case of the sample that completed only the milling process, the crystallite size calculated from the XRD data, 20-30 nm, agreed well with the grain size obtained from transmission electron microscopy (TEM). On the other hand, for the sample that was heat treated after milling, the strain decreased from 0.74% to 0.18%, the crystallite size increased to 70-80 nm, and the grain size grew up to the level of hundreds of nanometers. The changes in microstructure induced by the ball milling and heat treatment influenced the hydrogen storage properties, such as plateau pressure, hysteresis, and phase transformation with hydrogen absorption. Thus, the relationship between the microstructure and hydrogen storage properties can be explained.