Dependence of Lower Molding Temperature Limit and Molding Time on Molding Mechanism in Dental Thermoforming

Effectiveness and safety of a sports mouthguard depend on its thickness and material, and the thermoforming process affects these. The purpose of this study was to clarify the effects of differences in molding mechanisms on the lower molding temperature limit and molding time in dental thermoforming. Ethylene vinyl acetate resin mouthguard sheet and two thermoforming machines;vacuum blower molding machine and vacuum ejector/pressure molding machine were used. The molding pressures for suction molding were −0.018 MPa for vacuum blower molding and −0.090 MPa for vacuum ejector molding, and for pressure molding was set to 0.090 MPa or 0.450 MPa. Based on the manufacturer’s standard molding temperature of 95˚C, the molding temperature was lowered in 2.5˚C increments to determine the lower molding temperature limit at which no molding defects occurred. In order to investigate the difference in molding time depending on the molding mechanism, the duration of molding pressure was adjusted in each molding machine, and the molding time required to obtain a sample without molding defects was measured. The molding time of each molding machine were compared using one-way analysis of variance. The lower molding temperature limit was 90.0˚C for the vacuum blower machine, 77.5˚C for the vacuum ejector machine, 77.5˚C for the pressure molding machine at 0.090 MPa, and 67.5˚C for the pressure molding machine at 0.45 MPa. The lower molding temperature limit was higher for lower absolute values of molding pressure. The molding time was shorter for pressure molding than for suction molding. Significant differences were observed between all conditions except between the pressure molding machine at 0.090 MPa and 0.45 MPa (P < 0.01). A comparison of the differences in lower molding temperature limit and molding time due to molding mechanisms in dental thermoforming revealed that the lower molding temperature limit depends on the molding pressure and that the molding time is longer for suction molding than for pressure molding.

Criteria of limiting temperature and parametric analysis of the large deflection behavior for fully restrained steel beams in fire

This paper mainly involve 3 parts:1) To apply the minimum principle of acceleration in dynamics of elastic-plastic continua at finite deformation to the statics problems,a computing model is presented for the restrained steel beams exposed to the fire.In this model,both effects of large deflection and thermal expansion deformation are taken into account,and the constitutive equations with the temperature effects are used.Then a dynamic finite difference(DFD) method is presented by using the dis-crete technique,which can be used in simulating the response of the steel beams at elevated temperature,and the large deflec-tion behavior and catenary action effects of the beams can be adequately expressed.The primary numerical results show that the method is valid and credible.Compared with other methods,this technique is very simple,and it can also be further devel-oped to simulate the behavior of steel beams subjected to the coupling loading of explosion and fire when both effects of strain rate and inertia are considered.2) By using this DFD method,detailed parametric analysis are presented so as to check the consistency of response results for several different formulas of thermal expansion deformation and retention factors of steel at elevated temperature,the influence of these parameters on the critical temperature is examined.3) Based on the analysis for the curves of temperature-generalized yield function comprised by the axial force and bending moment,both criteria to determine the limiting temperature(or failure temperature) of large deflection steel beams are presented more explicitly,that is,both lim-iting temperatures can be determined by if the catenary force begins to appear or arrives at the maximum value,respectively.It is shown by numerical results that both limiting temperatures are close to the both critical temperatures which are correspond-ing to the maximum deflections equal to span/20 and span/10,respectively.This conclusion may be helpful to make rational fire resisting design for the steel beams.

COEXISTENCE OF PRIMARY USERS AND SECONDARY USERS UNDER INTERFERENCE TEMPERATURE AND SINR LIMIT

Spectrum sharing offers the opportunity for promising efficiency gains, and it will be a valuable tool in the era of future radios.To address this issue, we develop a multi-user cognitive radio sharing network based on opportunistic spectrum access and propose a new spectrum sharing strategy.The objective of our interest is to obtain the number of secondary users who can coexist peacefully with primary users to improve the utility of licensed spectrum, at the same time maximize the total goodput under the interference temperature and SINR constraints.Through analysis and simulation, the new strategy of spectrum sharing does improve the goodput performance as well as guarantee the Quality of Service(QoS) of primary and secondary users.

A new protocol for concurrently allocating licensed spectrum to underlay cognitive users

Cognitive radio technology makes efficient use of the valuable radio frequency spectrum in a non-interfering manner to solve the problem of spectrum scarcity. This paper aims to design a scheme for the concurrent use of licensed frequencies by Underlay Cognitive Users （UCUs）. We develop a new receiver-initiated Medium Access Control （MAC） protocol to facilitate the selections of alternative reliable carrier frequencies. A circuit is designed to establish reliable carrier selections based on the Received Signal Strength Indicator （RSSI） at the receiving end. Based on both packet-level simulations and various performance parameters, a comparison is carried out among conventional techniques, including the Multiple Access with Collision Avoidance （MACA） and MACA by invitation（MACA-BI） techniques, and our scheme. The simulated results demonstrate that when conventional techniques are used, the system overhead time increases from 0.5 s on the first attempt to 16.5 s on the sixth attempt. In the proposed scheme under the same failure condition, overhead time varies from 0.5 s to 2 s. This improvement is due to the complete elimination of the exponential waiting time that occurs during failed transmissions. An average efficiency of 60% is achieved with our scheme while only 43% and 34% average efficiencies are achieved with the MACA and MACA-BI techniques, respectively. The throughput performance of our scheme on the fourth attempt is 7 Mbps, whereas for the MACA and MACA-BI protocols, it is 1.9 Mbps and 2.2 Mbps respectively.

Design and Range of Application of Slot Bushings with Volumetric Orifice Fields

A design of a slot bushing with a volumetric field has been developed, which allows to produce continuous fibers from melts with difficult processing characteristics in order to produce fibers with better operating characteristics. The operability of the design was confirmed when solving two problems of special technological complexity. 1. 400 and 800 orifice bushings for production of continuous fibers from the basalt melt have been developed and recommended for manufacture. 2. The process of production of continuous fibers from standard glass using 2400 orifice bushing with perforated plates instead of orifice tips without air cooling, has been realized for the first time.

Variational principle and zero temperature limits of asymptotically （sub）-additive projection pressure

Let {Si}li=l be an iterated function system （IFS） on Rd with an attractor K. Let （S,cr） denote the one-sided full shift over the finite alphabet {1,2,...,l}, and let π：∑ -K be the coding map. Given an asymptotically （sub）-additive sequence of continuous functions{Si}n≥1, we define the asymptotically additive projection pressure Pπ and show the variational principle for Pπunder certain affine IFS. We also obtain variational principle for the asymptotically sub-additive projection pressure if the IFS satisfies asymptotically weak separation condition （AWSC）. Furthermore, when the IFS satisfies AWSC, we investigate the zero temperature limits of the asymptotically sub-additive projection pressure Pπ（β） with positive parameter β.

Study on fire extinguishing performance of ultrafine water mist in a cup burner

Two simplified models for predicting minimum extinguishing concentration(MEC) of ultrafine water mist(UFM)(<10 m) were developed based on limiting oxygen concentration(LOC) and combustion limit temperature(CLT),respectively.Experiment was conducted using a modified cup burner which can reduce the surface adsorption of UFM.Two typical liquid fuels,n-heptane and ethanol,were used in the experiment.Tests using the same scenario were repeated 20 times or 10 times according to the variance of extinguishing time.The average and the standard deviations of extinguishing time were used to evaluate the fire extinguishing performance of UFM.Experimental results agree well with the model based on LOC,and disagree with the model based on CLT.The disagreements were explained by analyzing flow behavior of UFM.It was concluded that the primary mechanism of fire extinguishment with UFM was oxygen dilution.