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     

Influence of Mn or Mn plus Fe on the hydrogen storage properties of the Ti-Cr-V alloy

To increase the hydrogen storage capacity and the plateau pressure of the Ti_0.32Cr_0.43V_0.25 alloy, a fraction of the Cr was replaced with Mn or a combination of Mn and Fe. When Mn was used alone, the effective hydrogen storage capacity increased to about 2.5 wt% though the plateau pressure showed no significant change. When Fe was added with Mn, however, both the effective hydrogen storage capacity and the plateau pressure increased. The BCC (body centered cubic) lattice parameter of the alloy decreased linearly with the Fe content, but it was not affected by Mn alone. The effective hydrogen storage capacity of the Ti_0.32Cr_0.32V_0.25Fe_0.03Mn_0.08 alloy was about 2.5 wt%, higher than 2.35 wt% in the original alloy. The estimated usable hydrogen stored in the Ti_0.32Cr_0.32V_0.25Fe_0.03Mn_0.08 alloy was 2.71 wt% in the temperature and pressure range of 293–353 K and 5–0.002 MPa, respectively.     

Analysis of a planar 3 degree-of-freedom adjustable compliance mechanism

In this work, a planar three degree-of-freedom parallel mechanism as another type of assembly device which utilizes joint compliances is proposed. In order to generate the desired operational compliance characteristics at RCC point, these joint compliances can be adjusted either by properly replacing the joint compliances or by actively controlling stiffness at joints. The operational compliance matrix for this mechanism is obtained explicitly by symbolic manipulation, and its operational compliance characteristics are examined. It is found that the RCC point exists at the center of the workspace when the mechanism maintains symmetric configurations. Compliance characteristics and its sensitivity of this mechanism are analyzed with respect to the magnitude of the diagonal compliance components and two different matrix norms by measuring compliance sensitivity. It is expected that the analysis results provide the designer with a helpful information to determine a set of optimal parameters of this RCC mechanism.     

Effect of succinic anhydride as an electrolyte additive on electrochemical characteristics of silicon thin-film electrode

The effect of an electrolyte additive, succinic anhydride (SA), on the electrochemical performances of a silicon thin-film electrode, which is prepared by radio-frequency magnetron sputtering, is investigated. The introduction of SA into a liquid electrolyte consisting of ethylene carbonate/diethyl carbonate/1 M LiPF₆ significantly enhances the capacity retention and coulombic efficiency of the electrode. This improvement in the electrochemical performance of the electrode is attributed to modification of the solid/electrolyte interphase (SEI) layer by the introduction of SA. The differences in the characteristic properties of SEI layers, with or without SA, are explained by analysis with scanning electron microscopy, electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy.     

Effect of electric fields on the stabilization of premixed laminar bunsen flames at low AC frequency: Bi-ionic wind effect

The stabilization characteristics of laminar premixed bunsen flames have been investigated experimentally by applying AC electric fields at low frequency below 60 Hz together with DC in the single electrode configuration. The blowoff velocity has been measured for varying AC voltage and frequency. A transition frequency between low and high frequency regimes has been identified near 40–50 Hz, where AC electric fields have minimal effect on flame stabilization. In the low frequency regime, the blowoff velocity decreased linearly with AC voltage such that the flames became less stable. This was consistent with the DC result, implying the influence of the ionic wind effect. The variation of blowoff velocity with AC frequency showed a non-monotonic behavior in that the velocity decreased and then increased, exhibiting minimum blowoff velocity near 6–8 Hz. Based on the molecular kinetic theory, the developing degree of ionic wind was derived. By considering the ionic wind effects arising from both positive and negative ions in a flame zone, the bi-ionic wind effect successfully explained the non-monotonic behavior of blowoff velocity with AC frequency in the low frequency regime.     

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.     

Räumliche Ausbreitung von Feinstbindemittelsuspensionen im Lockergestein

Spatial propagation of ultra‐fine binder suspensions in loose rock. During the injection of ultra‐fine binder suspensions depth filtration mechanisms result in an enrichment of the binder particles in the vicinity of the injection point and a concomitant depletion of binder in the margins of the injected body. The consequence is a reduction in the predicted reach of the injection. This effect is accompanied by increased permeabilities and reduced strengths at the margins of the injected body. The effects of depth filtration mechanisms on the propagation of ultra‐fine binder suspensions in loose rock zones is investigated in a series of large scale injection tests generating suggestions for the execution of injection operations with ultra‐fine binder suspensions.     

Fracture behavior of crumb rubber‐filled elastomers

The fracture behavior of a crumb rubber‐filled elastomer was observed in optical micrographs. It was found that the failure started from the surface of the unfilled samples. The failure, however, started from a cavity around a crumb in the crumb‐filled samples. This paper suggests that the failure mechanism in the crumb‐filled elastomers (NR, NBR) was based on the microscopic observation of highly strained samples. This paper also considers the failure behavior of two‐component systems: NR/NBR, SBR/NR, and NR/SBR. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3137–3144, 1999