Performance analysis and overflowed traffic characterization in multiservice hierarchical wireless networks

A cellular hierarchical network with heterogeneous traffic is considered, where calls with shorter (longer) average call-holding time are assigned to the associated lower (upper) layer. The main contribution of this paper is that an efficient and reasonably accurate analytical method is proposed to calculate performance measures of interest, i.e., new call-blocking probability and forced termination probability for conversational services, new call-blocking probability, forced termination probability, and the average number of assigned time slots for streaming services. In particular, a simple two-state MMPP/sup (1,2,...,K)/, that takes into account not only the dependence among overflowed calls of the same class but also the correlation among overflowed calls of different classes, is used to approximate overflowed traffic to reduce computational complexity and improve accuracy. The methods with the multiclass overflowed traffic being approximated as independent Poisson processes and interrupted Poisson processes are also conducted for comparison. Importantly, it is shown via simulation results that the proposed model generates more accurate results than those obtained with the other two approximation methods. Last but not least, the effect of nonuniform traffic density on performance measures is studied via simulation. It is shown that the nonuniform traffic density may have a significant impact on the performance.     

An innovative channel management strategy for highly reliable handoff in cellular networks

In this paper, we have resolved the problem of forced call termination that occurs when mobile traffic is concentrated on a hot‐spot cell in cellular networks. Enhanced Channel Management Scheme (ECMS) is an innovative way to increase the flexibility of channel usage over non‐uniform traffic distribution. ECMS exploits mobile hosts initiated or active in overlapping areas between cells. The scheme consists of three phases to monitor the status of channels on each base station and to make a channel reservation using the availability list maintained for the candidate‐MH selection. When the traffic load in a cell is intolerably high, ECMS invokes the load‐balancing procedure to distribute its traffic to adjacent cells. The reserved channels are used to support the safe and fast handoff. From the simulation, we observed that ECMS outperformed other compatible channel assignment schemes such as directed handoff schemes in blocking probability and channel utilization. Copyright © 2002 John Wiley & Sons, Ltd.     

Thermal comfort study of young Chinese people in Hong Kong

The purpose of this study is to investigate the thermal comfort of college-age Chinese subjects and obtain the optimum thermal conditions for buildings. 134 college-age Chinese subjects wearing 0.6 clo standard clothing were exposed under sedentary activity for 3 h to several different thermal conditions. The neutral temperature of young Hong Kong Chinese was found to be 24.9°C. This is not significantly different from previous studies with Danish and American subjects. Using the probit technique for analysing subjective responses of thermal sensation the neutral zone was found to be between 22.2 and 25.2°C.     

Purification and crystallization of complexes modeling the active state of the fragile histidine triad protein

Fragile histidine triad protein (Fhit) is a diadenosine triphosphate (ApppA) hydrolase encoded at the human chromosome 3 fragile site which is frequently disrupted in tumors. Reintroduction of FHIT coding sequences to cancer cell lines with FHIT deletions suppressed the ability of these cell lines to form tumors in nude mice even when the reintroduced FHIT gene had been mutated to allow ApppA binding but not hydrolysis. Because this suggested that the tumor suppressor activity of Fhit protein depends on substrate-dependent signaling rather than ApppA catabolism, we prepared two crystalline forms of Fhit protein that are expected to model its biologically active, substrate-bound state. Wild-type and the His96Asn forms of Fhit were overexpressed in Escherichia coli, purified to homogeneity and crystallized in the presence and absence of ApppA and an ApppA analog. Single crystals obtained by vapor diffusion against ammonium sulfate diffracted X-rays to beyond 2.75 A resolution. High quality native synchrotron X-ray data were collected for an orthorhombic and a hexagonal crystal form.      

Catalytic fluorination of HCFC-133a (1,1,1-trifluoro-2-chloroethane)

Catalytic fluorination of HCFC-133a was performed over metal oxide catalysts. Chromium oxide showed the best catalytic activity among several metal oxides tested. An increase in the crystallinity with decreased surface area resulted in a decrease of catalytic activity for the fluorination reaction. Active phase of chromia is Cr-O-F-OH having a proper ratio of O/F and a high hydroxyl content. The hydroxyl content on the catalyst is strongly dependent on support material. The selectivity to HFC-134a is independent of the O/F ratio on the Cr surface.     

Sodium ramping in hemodialysis: a study of beneficial and adverse effects

Sodium ramping has been introduced as a technique to decrease side effects occurring during hemodialysis. We studied sodium ramping in 414 dialysis sessions in 23 patients by randomizing 2-week blocks of dialysis to either steady dialysate sodium of 140 mEq/L, linear sodium ramping during dialysis from 155 mEq/L to 140 mEq/ L, or stepwise ramping (sodium of 155 mEq/L for 3 hours and 140 mEq/L for 1 hour). We studied the number and severity of hypotensive and hypertensive episodes. A hypotensive episode was defined as an abrupt decline of systolic blood pressure of more than 50 mm Hg, a decrease in blood pressure accompanied by symptoms requiring intervention, or systolic blood pressure of less than 90 mm Hg even without symptoms. A hypertensive episode was defined as a sudden increase in systolic blood pressure of over 30 mm Hg. We also recorded other side effects (headache, cramps, nausea, vomiting, dizziness, thirst, fatigue, weight gain, and blood pressure) during, immediately after, and between dialysis sessions. There was no major difference between the two ramping protocols, but compared with standard dialysis, both decreased total number of side effects from 4.0 to 3.0 (P = 0.057); the number of hypotensive episodes decreased from 1.3 to 0.7 (P = 0.036). The lowest blood pressure was 114/66 mm Hg during control and 123/69 mm Hg during ramping (P < 0.0001). The frequency of cramps during dialysis decreased from 0.9 to 0.5 (P = 0.006). There was no difference in headache, nausea, or vomiting. The number of hypertensive episodes increased from 0.045 to 0.086 during ramping (P = 0.125). Of 23 patients, only five (22%) had a marked decrease in symptoms; two of the three most symptomatic patients showed no significant improvement. Between dialysis sessions, patients complained of more fatigue and thirst (P < 0.0001 and P = 0.0028, respectively), and interdialytic weight gain following ramping was 5.1% of body weight compared with 4.4% without ramping (P < 0.0001). Blood pressure also increased following ramping, from 143/79 mm Hg to 152/81 mm Hg (P = 0.001). Ramping can decrease the overall number of side effects, but increases interdialytic symptoms, weight gain, and hypertension. In most instances, it simply changes the time the side effects occur. Only 22% of patients have significant benefit. These patients can be identified only through trial and error, as no model of these patients can be created.     

Grey relational analysis coupled with principal component analysis for optimization design of the cutting parameters in high-speed end milling

This paper investigates optimization design of the cutting parameters for rough cutting processes in high-speed end milling on SKD61 tool steel. The major characteristics indexes for performance selected to evaluate the processes are tool life and metal removal rate, and the corresponding cutting parameters are milling type, spindle speed, feed per tooth, radial depth of cut, and axial depth of cut. In this study, the process is intrinsically with multiple performance indexes so that grey relational analysis that uses grey relational grade as performance index is specially adopted to determine the optimal combination of cutting parameters. Moreover, the principal component analysis is applied to evaluate the weighting values corresponding to various performance characteristics so that their relative importance can be properly and objectively described. The results of confirmation experiments reveal that grey relational analysis coupled with principal component analysis can effectively acquire the optimal combination of cutting parameters. Hence, this confirms that the proposed approach in this study can be an useful tool to improve the cutting performance of rough cutting processes in high-speed end milling process.