[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

The boundary layer equations for plane, incompressible, and steady flow are 

$$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$

Boundary Layer Theory

Mechanical properties of ultrathin membranes consisting of one layer, two overlapped layers, and three overlapped layers of graphene oxide platelets were investigated by atomic force microscopy (AFM) imaging in contact mode. In order to evaluate both the elastic modulus and prestress of thin membranes, the AFM measurement was combined with the finite element method (FEM) in a new approach for evaluating the mechanics of ultrathin membranes. Monolayer graphene oxide was found to have a lower effective Young’s modulus (207.6 ± 23.4 GPa when a thickness of 0.7 nm is used) as compared to the value reported for “pristine” graphene. The prestress (39.7−76.8 MPa) of the graphene oxide membranes obtained by solution-based deposition was found to be 1 order of magnitude lower than that obtained by others for mechanically cleaved graphene. The novel AFM imaging and FEM-based mapping methods presented here are of general utility for obtaining the elastic modulus and prestress of thin membranes.

/pdf/mechanical-properties-of-monolayer-graphene-oxide-1rrlwy9yyp.pdf

Mechanical Properties of Monolayer Graphene Oxide

This book attempts to achieve a difficult goal: to teach statistics to the novice so as to impart a liking and understanding of statistics. The book is geared toward a medical audience, since most examples are from the medical literature. The structure of the book consists of the following elements in each chapter: a small number of statistical rules of thumb, followed by a nontechnical explanation, a demonstration of how to work through the mechanics of doing the statistical test in question, a summary, and sample problems to be solved by the reader. (The answers, with explanations, are provided in an appendix.) Although a variety of univariate statistics are included, certain topics that are important in medical research are not. For example, there is little or no discussion of multiple regression, life-table techniques, or pooling of studies. These omissions, especially of multiple regression, are unfortunate. The Primer was derived from

Primer of Biostatistics

A type of strain sensor with high tolerable strain based on a ZnO nanowires/polystyrene nanofibers hybrid structure on a polydimethylsiloxane film is reported. The novel strain sensor can measure and withstand high strain and demonstrates good performance on rapid human-motion measurements. In addition, the device could be driven by solar cells. The results indicate that the device has potential applications as an outdoor sensor system.

http://www.nanoscience.gatech.edu/paper/2011/11_AM_09.pdf

High-Strain Sensors Based on ZnO Nanowire/Polystyrene Hybridized Flexible Films

Statement of problem The external contour of an implant and the magnitude of occlusal loading can have significant effects on the load transfer characteristics and may result in different bone failure rates for different implant systems. Purpose The goal of this study was to investigate the effects of external geometry and occlusal load magnitude on bone failure modes for 5 commercially available dental implant systems. Material and methods Five different implant systems; Ankylos, Astra, Bicon, ITI, and Nobel Biocare, comparable in size, but different in thread profile and crest module shapes, were compared using the finite element method. Type II bone quality was approximated and complete osseous integration was assumed. Occlusal loads of varying magnitudes (0 to 2000 N) were applied on the abutments supporting single tooth restorations at 11.3 degrees from the vertical axis with a 1-mm offset. Total overloaded bone area, where tensile and compressive normal stresses fell outside of the recommended limits of 100 and 170 MPa, respectively, was investigated for different load levels. Results For moderate levels of occlusal loads up to 300 N, the compact bone was not overloaded by any of the implant systems. At the extreme end of the occlusal load range (1000 N or more) the overloading characteristics of implants may be dependent on geometric shape. Conclusion In general, overloading occurs near the superior region of compact bone, in compression, and it is primarily caused by the normal and lateral components of the occlusal load. At the region of intersection of compact and trabecular bone, overloading occurs in tension due to the vertical component of the occlusal load. For excessive forces greater than 1000 N, the overloaded areas of the bone varied considerably among 5 different implants systems evaluated.

/pdf/evaluation-of-load-transfer-characteristics-of-five-1e33j7xlkk.pdf

Evaluation of load transfer characteristics of five different implants in compact bone at different load levels by finite elements analysis

Mechanics of the tapered interference fit in dental implants.

Mechanics of the taper integrated screwed-in (TIS) abutments used in dental implants

http://www1.coe.neu.edu/~smuftu/Papers/Paper-JBiomech-2008-Chou-Jagodnik-Muftu.pdf

Predictions of bone remodeling around dental implant systems

Statement of problem Strain levels in periimplant bone are affected by implant dimensions, bone quality, and implant insertion depth, resulting in different bone maintenance characteristics. Purpose The purpose of this study was to evaluate the biomechanical response of the jaw bone to a wide-diameter, short (WDS) implant, and a narrow-diameter, long (NDL) implant for various simulated clinical scenarios. Material and methods The finite element method was used to evaluate periimplant bone strain distribution for 5 × 6-mm (WDS) and 3.5 × 10.7-mm (NDL) implants. A 3-dimensional segment of the mandible was constructed from a computerized tomography image of the premolar region. Occlusal force was simulated by applying a 100-N oblique load on the abutment. Bone strain distributions for 5 different implant insertion depths and 2 different levels of alveolar bone quality were evaluated. Results For an NDL implant, approximately 60% to 80% of the bone volume surrounding the implant was subjected to 200-1000 μstrain (μɛ), and 15% to 35% was subjected to 1000-3000 μɛ, regardless of the alveolar bone quality. For a WDS implant, the bone volume subjected to 1000-3000 μɛ increased, and the bone volume subjected to 200-1000 μɛ decreased in lower quality alveolar bone. For both implant types, bone volume experiencing strain levels less than 200 μɛ, and/or greater than 3000 μɛ, was predicted to be relatively small. Conclusions In general, the thread design promoted relatively high strain around the thread tips, and the bone inside grooves was less strained. A more even and higher strain distribution in the periimplant bone was generated by the WDS implant as compared to the NDL implant. Regardless of the implant dimensions and simulated clinical scenarios, the development of high strain in the alveolar region was inevitable. Strain levels in periimplant bone were reduced as the insertion depth of the implant was increased.

Combined effects of implant insertion depth and alveolar bone quality on periimplant bone strain induced by a wide-diameter, short implant and a narrow-diameter, long implant

Sinan Müftü

Papers

Evaluation of load transfer characteristics of five different implants in compact bone at different load levels by finite elements analysis

Mechanics of the tapered interference fit in dental implants.

Mechanics of the taper integrated screwed-in (TIS) abutments used in dental implants

Predictions of bone remodeling around dental implant systems

Combined effects of implant insertion depth and alveolar bone quality on periimplant bone strain induced by a wide-diameter, short implant and a narrow-diameter, long implant