This paper proposes a soft-start method with the features of a small on-chip capacitor and start stability for dc-dc converters. During the soft-start process, a slowly and linearly ramped-up voltage reference is generated based on the principle of the small on-chip capacitor charged by an oscillatorcontrolled pulse current to replace the normal reference. Meanwhile, the switching frequency is also reduced so that the inductor current has more time to decay and massive inrush current can be avoided. However, in this way, the system may be unstable in that the bandwidth could not keep less than 1/7 of the reduced switching frequency. In this paper, an error amplifier (EA) with gain-degeneration is proposed to solve this problem. When the switching frequency is reduced, the gain of the EA is also reduced and the bandwidth becomes narrower accordingly. A dc-dc converter using the proposed soft-start method has been implemented with a 0.5-µm CMOS process. Experimental results show that a soft-start period of 600 µs is achieved with an onchip capacitor of 15 pF. Furthermore, both the output voltage and inductor current rise smoothly without oscillation and overshoot during the startup process.
This article presents a computational study on contact characteristics of contact pressure and resultant deformation between an N95 filtering facepiece respirator and a newly developed digital headform. The geometry of the headform model is obtained based on computed tomography scanning of a volunteer. The segmentation and reconstruction of the headform model is performed by Mimics v16.0 (Materialise, Leuven, Belgium), which is a medical image processing software. The respirator model is obtained by scanning the surface of a 3M 8210 N95 respirator using a 3D digitizer and then the model is transformed by Geomagic Studio v12.0 (3D system, Rock Hill, SC), a reverse engineering software. The headform model contains a soft tissue layer, a skull layer, and a separate nose. The respirator model contains two layers (an inner face sealing layer and an outer layer) and a nose clip. Both the headform and respirator are modeled as solid elements and are deformable. The commercial software, LS-DYNA (LSTC, Livermore, CA), is used to simulate the contact between the respirator and headform. Contact pressures and resultant deformation of the headform are investigated. Effects of respirator stiffness on contact characteristics are also studied. A Matlab (MathWorks, Natick, MA) program is developed to calculate local gaps between the headform and respirator in the stable wearing state.
To evaluate the effect of restorative materials on stress distribution of endodontically treated teeth, the 3D models of an endodontically treated mandibular fi rst molar, restoration, and cement layer were created. Three different materials (composite resin, ceramage and ceramic) were studied and two loading conditions (vertical and oblique load) were simulated. Mohr-Coulomb failure criterion of enamel, dentine, endocrown and cement were evaluated separately. It is indicated that under both loading conditions, the highest values of Mohr-Coulomb failure criterion were observed in Ceramage-restored group for remaining tooth structure while in ceramic-restored group for the restoration. Compared to composite resin and Ceramage, ceramic endocrown transferred less stress, namely was more protective to the tooth structure.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.