1
|
Rana B, Cho SS, Hong IP. Passive Type Reconfigurable Intelligent Surface: Measurement of Radiation Patterns. Micromachines (Basel) 2023; 14:818. [PMID: 37421051 DOI: 10.3390/mi14040818] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2023] [Revised: 03/16/2023] [Accepted: 04/03/2023] [Indexed: 07/09/2023]
Abstract
The demand for unprecedented data and ubiquitous wireless connections have led to the adoption of new types of transmitters and receivers. Additionally, different new types of devices and technologies need to be proposed for such demand. Reconfigurable intelligent surface (RIS) is going to play a very significant role in the upcoming beyond-5G/6G communications. It is envisioned that not only the RIS will be deployed to assist and create a smart wireless environment for the upcoming communications, but also the receiver and transmitter can be fabricated using RIS to make a smart and intelligent transmitter and receiver. Thus, the latency of upcoming communications can be reduced very significantly using RIS, which is a very important factor. Artificial intelligence assists communications and shall be adopted widely for the next generation networks. In this paper, radiation pattern measurement results of our previously published RIS have been provided. This work is the extension work of our previously proposed RIS. The polarization-independent passive type of RIS working in the sub-6 GHz frequency band using low-cost FR4-substrate was designed. Each unit cell with dimensions of 42 mm × 42 mm had a single-layer substrate backed by a copper plate. A 10 × 10-unit cell array was fabricated to check the performance of the RIS. Such types of unit cells and RIS were designed to set up initial measurement facilities in our laboratory for any kinds of RIS measurements.
Collapse
Affiliation(s)
- Biswarup Rana
- Smart Natural Space Research Centre, Kongju National University, Cheonan 31080, Republic of Korea
| | - Sung-Sil Cho
- Department of Smart Information Technology Engineering, Kongju National University, Cheonan 31080, Republic of Korea
| | - Ic-Pyo Hong
- Department of Smart Information Technology Engineering, Kongju National University, Cheonan 31080, Republic of Korea
| |
Collapse
|
2
|
Syuy A, Shtarev D, Lembikov A, Gurin M, Kevorkyants R, Tselikov G, Arsenin A, Volkov V. Effective Method for the Determination of the Unit Cell Parameters of New MXenes. Materials (Basel) 2022; 15:8798. [PMID: 36556603 PMCID: PMC9783200 DOI: 10.3390/ma15248798] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/12/2022] [Revised: 12/07/2022] [Accepted: 12/07/2022] [Indexed: 06/17/2023]
Abstract
MXenes are of great practical interest. While the physical properties of such a well-known MAX phase as Ti3AlC2 and the Ti3C2 MXene that is based on it have been widely studied, it is extremely important to study the properties of new four-component MAX-phases and the MXenes based on them. To do this, first, it is necessary to characterize the obtained materials. In this work, the Ti3-xNbxC2 MXene was characterized. Since the material is fairly new, there are no crystallographic data for such systems in the international databases. We proposed a method for the determination of the main unit cell parameters of the new Ti3-xNbxC2 MXene, which was based on a combination of the DFT method, TEM studies, and an X-ray diffraction analysis.
Collapse
Affiliation(s)
- Alexander Syuy
- Institute of High Technologies and Advanced Materials, Far Eastern Federal University, 690922 Vladivostok, Russia
- Center for Photonics and 2D Materials, Moscow Institute of Physics and Technology, 141701 Dolgoprudny, Russia
| | - Dmitry Shtarev
- Institute of High Technologies and Advanced Materials, Far Eastern Federal University, 690922 Vladivostok, Russia
| | - Alexey Lembikov
- Institute of High Technologies and Advanced Materials, Far Eastern Federal University, 690922 Vladivostok, Russia
| | - Mikhail Gurin
- Institute of High Technologies and Advanced Materials, Far Eastern Federal University, 690922 Vladivostok, Russia
| | - Ruslan Kevorkyants
- Hong Kong Quantum AI Lab Ltd., Hong Kong Science and Technology Parks Corporation, Hong Kong, China
| | - Gleb Tselikov
- Center for Photonics and 2D Materials, Moscow Institute of Physics and Technology, 141701 Dolgoprudny, Russia
| | - Aleksey Arsenin
- Center for Photonics and 2D Materials, Moscow Institute of Physics and Technology, 141701 Dolgoprudny, Russia
| | - Valentyn Volkov
- Center for Photonics and 2D Materials, Moscow Institute of Physics and Technology, 141701 Dolgoprudny, Russia
| |
Collapse
|
3
|
Majid A, Younes TM, Jabeen A, Batool H, Alkhedher M, ElDin SM. Predictions on Structural and Electronic Properties to Synthesize Bismuth-Carbon Compounds in Different Periodicities. Materials (Basel) 2022; 15:8150. [PMID: 36431634 PMCID: PMC9696474 DOI: 10.3390/ma15228150] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/24/2022] [Revised: 11/09/2022] [Accepted: 11/10/2022] [Indexed: 06/16/2023]
Abstract
This work was carried out to explore the compounds of bismuth with carbon using density functional theory (DFT)-based computations. The structures of the compounds BiC, BiC2, BiC3, Bi2C3, BiC5, and Bi2C5 were predicted at a generalized gradient approximation (GGA-PBE) level of theory. The calculations were carried out on the structures in unit cell and supercell geometries in slab and bulk periodicities. The structural and electronic properties of the mentioned compounds were investigated in detail. The calculations of the structures revealed lattice constants of the compounds for cubic unit cell as 212.2 pm for BiC, 176.9 pm for BiC2, 240.5 pm for BiC3, 232.4 pm for Bi2C3, and 354.5 pm for Bi2C5. The compounds BiC, BiC2, BiC3, BiC5, and Bi2C5 were found to be metallic, whereas Bi2C3 exhibited semiconducting character with a band gap of 0.305 eV. This work provides an initial framework for preparing new 2D materials from BixCy.
Collapse
Affiliation(s)
- Abdul Majid
- Department of Physics, University of Gujrat, Gujrat 50700, Pakistan
| | - Tariq M. Younes
- Department of Mechatronics Engineering, Faculty of Engineering Technology, Al Balqa Applied University, Amman 1705, Jordan
| | - Alia Jabeen
- Department of Physics, University of Gujrat, Gujrat 50700, Pakistan
| | - Hira Batool
- Department of Physics, University of Gujrat, Gujrat 50700, Pakistan
| | - Mohammad Alkhedher
- Mechanical and Industrial Engineering Department, Abu Dhabi University, Abu Dhabi 111188, United Arab Emirates
| | - Sayed M. ElDin
- Center of Research, Faculty of Engineering & Technology, Future University in Egypt, New Cairo 11835, Egypt
| |
Collapse
|
4
|
Rana B, Cho SS, Hong IP. Parameters and Measurement Techniques of Reconfigurable Intelligent Surfaces. Micromachines (Basel) 2022; 13:1841. [PMID: 36363862 PMCID: PMC9697697 DOI: 10.3390/mi13111841] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Revised: 10/20/2022] [Accepted: 10/25/2022] [Indexed: 06/16/2023]
Abstract
Reconfigurable intelligent surface (RIS)-aided wireless communications systems are one the promising wireless communication system where the wave can be guided by the RIS. It is envisioned that beyond-5G/6G communication will have a low-cost, high spectral efficiency, high energy efficiency, and smart wireless environment. In this paper, initially, different measurement techniques of the RIS have been discussed, which are available in the literature. Then, a new type of RIS has been proposed. Finally, a different parameter measurement technique for our proposed RIS has been presented. A low-cost FR4 substrate with a height of 1.6 mm was considered to design the RIS in the sub-6 GHz frequency band. Another important thing is that our proposed IRS is a single-layer substrate backed by a copper plate. The area of each unit cell was 42 mm × 42 mm. The RIS was designed to operate at the central frequency of the 3.5 GHz frequency band. The novelty of the proposed RIS is that it is a polarization-independent structure. Thus, polarization-related losses can be overcome using this structure. A 10×10-unit cell array was designed to check the radiation performance. The magnitude of the reflection coefficients was measured in our laboratory for the proposed configuration.
Collapse
Affiliation(s)
- Biswarup Rana
- Smart Natural Space Research Centre, Kongju National University, Cheonan 31080, Korea
| | - Sung-Sil Cho
- Department of Smart Information Technology Engineering, Kongju National University, Cheonan 31080, Korea
| | - Ic-Pyo Hong
- Department of Smart Information Technology Engineering, Kongju National University, Cheonan 31080, Korea
| |
Collapse
|
5
|
Li N, Zhang Y, Tang Q, Wang H, He D, Yao Y, Fan Y. Porous interbody fusion cage design via topology optimization and biomechanical performance analysis. Comput Methods Biomech Biomed Engin 2022; 26:650-659. [PMID: 35652627 DOI: 10.1080/10255842.2022.2081505] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
The porous interbody fusion cage could provide space and stable mechanical conditions for postoperative intervertebral bone ingrowth. It is considered to be an important implant in anterior cervical discectomy and internal fixation. In this study, two types of unit cells were designed using topology optimization method and introduced to the interbody fusion cage to improve the biomechanical performances of the cage. Topology optimization under two typically loading conditions was first conducted to obtain two unit cells (O-unit cell and D-unit cell) with the same volume fraction. Porous structures were developed by stacking the obtained unit cells in space, respectively. Then, porous interbody fusion cages were obtained by the Boolean intersection between the global structural layout and the porous structures. Finite element models of cervical spine were created that C5-C6 segment was fused by the designed porous cages. The range of motion (ROM) of the cervical spine, the maximum stress on the cage and the bone graft, and the stress and displacement distributions of the cage were analyzed. The results showed the ROMs of C5-C6 segment in D-unit cell and O-unit cell models were range from 0.14° to 0.25° under different loading conditions; the cage composed of the D-unit cells had a more uniform stress distribution, smaller displacement on cage, a more reasonable internal stress transfer mode (transmission along struts of the unit cell), and higher stress on the internal bone graft (0.617 MPa). In conclusion, the optimized porous cage is a promising candidate for fusion surgery, which would avoid the cage subsidence, and promote the fusion of adjacent endplates.
Collapse
Affiliation(s)
- Nan Li
- Department of Spine Surgery, Beijing Jishuitan Hospital, The Fourth Clinical Medical College of Peking University, Beijing, China
| | - Yang Zhang
- Key Laboratory of Biomechanics and Mechanobiology (Beihang University), Ministry of Education, Beijing Advanced Innovation Center for Biomedical Engineering, School of Biological Science and Medical Engineering, Beihang University, Beijing, China
| | - Qiaohong Tang
- Key Laboratory of Biomechanics and Mechanobiology (Beihang University), Ministry of Education, Beijing Advanced Innovation Center for Biomedical Engineering, School of Biological Science and Medical Engineering, Beihang University, Beijing, China
| | - Hongkun Wang
- Key Laboratory of Biomechanics and Mechanobiology (Beihang University), Ministry of Education, Beijing Advanced Innovation Center for Biomedical Engineering, School of Biological Science and Medical Engineering, Beihang University, Beijing, China
| | - Da He
- Department of Spine Surgery, Beijing Jishuitan Hospital, The Fourth Clinical Medical College of Peking University, Beijing, China
| | - Yan Yao
- Key Laboratory of Biomechanics and Mechanobiology (Beihang University), Ministry of Education, Beijing Advanced Innovation Center for Biomedical Engineering, School of Engineering Medicine, Beihang University, Beijing, China
| | - Yubo Fan
- Key Laboratory of Biomechanics and Mechanobiology (Beihang University), Ministry of Education, Beijing Advanced Innovation Center for Biomedical Engineering, School of Biological Science and Medical Engineering, Beihang University, Beijing, China.,Key Laboratory of Biomechanics and Mechanobiology (Beihang University), Ministry of Education, Beijing Advanced Innovation Center for Biomedical Engineering, School of Engineering Medicine, Beihang University, Beijing, China
| |
Collapse
|
6
|
Li Y, Ni W, Duan P, Zhang S, Wang J. Experimental Study and Mechanism Analysis of Preparation of α-Calcium Sulfate Hemihydrate from FGD Gypsum with Dynamic Method. Materials (Basel) 2022; 15:ma15093382. [PMID: 35591716 PMCID: PMC9104283 DOI: 10.3390/ma15093382] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/23/2022] [Revised: 05/03/2022] [Accepted: 05/06/2022] [Indexed: 02/04/2023]
Abstract
Flue-gas desulphurization (FGD) gypsum is a highly prevalent industrial by-product worldwide, which can be an excellent alternative to natural gypsum due to its high content of CaSO4·2H2O. The preparation of α-calcium sulfate hemihydrate is a high-value pathway for the efficient use of FGD gypsum. Here, a dynamic method, or an improved autoclaved process, was used to produce α-calcium sulfate hemihydrate from FGD gypsum. In this process, the attachment water of the mixture of FGD gypsum and crystal modifiers was approximately 18%, and the pH value was approximately 6.0. The mixture did not need to be pressed into bricks or made into slurry, and it was directly sent into the autoclave reactor for reaction. It was successfully applied to the practical production and application of FGD gypsum, citric acid gypsum and phosphogypsum. In this work, the compositions and morphology of the product at different stages of the reaction were examined and compared. In particular, single-crystal diffraction was used to produce the crystal structure of CaSO4·0.5H2O, and the results were as follows: a = 13.550(3); b = 13.855(3); c = 12.658(3); β = 117.79(3)°; space group C2. The preferential growth along the c-axis and the interaction mechanism between the carboxylate groups and the crystal were discussed throughout the analysis of the crystal structure.
Collapse
Affiliation(s)
- Ying Li
- School of Civil and Resource Engineering, University of Science and Technology Beijing, No. 30 Xueyuan Road, Haidian District, Beijing 100083, China; (W.N.); (S.Z.); (J.W.)
- Correspondence:
| | - Wen Ni
- School of Civil and Resource Engineering, University of Science and Technology Beijing, No. 30 Xueyuan Road, Haidian District, Beijing 100083, China; (W.N.); (S.Z.); (J.W.)
| | - Pengxuan Duan
- School of Materials Science and Engineering, Guilin University of Technology, Jian’gan Road 12#, Guilin 541004, China;
| | - Siqi Zhang
- School of Civil and Resource Engineering, University of Science and Technology Beijing, No. 30 Xueyuan Road, Haidian District, Beijing 100083, China; (W.N.); (S.Z.); (J.W.)
| | - Jiajia Wang
- School of Civil and Resource Engineering, University of Science and Technology Beijing, No. 30 Xueyuan Road, Haidian District, Beijing 100083, China; (W.N.); (S.Z.); (J.W.)
| |
Collapse
|
7
|
Lu G, Gubbin CR, Nolen JR, Folland TG, Diaz-Granados K, Kravchenko II, Spencer JA, Tadjer MJ, Glembocki OJ, De Liberato S, Caldwell JD. Collective Phonon-Polaritonic Modes in Silicon Carbide Subarrays. ACS Nano 2022; 16:963-973. [PMID: 34957830 DOI: 10.1021/acsnano.1c08557] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Localized surface phonon polaritons (LSPhPs) can be implemented to engineer light-matter interactions through nanoscale patterning for a range of midinfrared application spaces. However, the polar material systems studied to date have mainly focused on simple designs featuring a single element in the periodic unit cell. Increasing the complexity of the unit cell can serve to modify the resonant near-fields and intra- and inter-unit-cell coupling as well as to dictate spectral tuning in the far-field. In this work, we exploit more complicated unit-cell structures to realize LSPhP modes with additional degrees of design freedom, which are largely unexplored. Collectively excited LSPhP modes with distinctly symmetric and antisymmetric near-fields are supported in these subarray designs, which are based on nanopillars that are scaled by the number of subarray elements to ensure a constant unit-cell size. Moreover, we observe an anomalous mode-matching of the collective symmetric mode in our fabricated subarrays that is robust to changing numbers of pillars within the subarrays as well as to defects intentionally introduced in the form of missing pillars. This work therefore illustrates the hierarchical design of tailored LSPhP resonances and modal near-field profiles simultaneously for a variety of IR applications such as surface-enhanced spectroscopies and biochemical sensing.
Collapse
Affiliation(s)
- Guanyu Lu
- Department of Mechanical Engineering, Vanderbilt University, Nashville, Tennessee 37212, United States
| | - Christopher R Gubbin
- School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, United Kingdom
| | - J Ryan Nolen
- Interdisciplinary Materials Science, Vanderbilt University, Nashville, Tennessee 37212, United States
| | - Thomas G Folland
- School of Physics and Astronomy, The University of Iowa, Iowa City, Iowa 52242, United States
| | - Katja Diaz-Granados
- Interdisciplinary Materials Science, Vanderbilt University, Nashville, Tennessee 37212, United States
| | - Ivan I Kravchenko
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, United States
| | - Joseph A Spencer
- US Naval Research Laboratory, Washington, D.C. 20375, United States
| | - Marko J Tadjer
- US Naval Research Laboratory, Washington, D.C. 20375, United States
| | - Orest J Glembocki
- Department of Mechanical Engineering, Vanderbilt University, Nashville, Tennessee 37212, United States
| | - Simone De Liberato
- School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, United Kingdom
| | - Joshua D Caldwell
- Department of Mechanical Engineering, Vanderbilt University, Nashville, Tennessee 37212, United States
| |
Collapse
|
8
|
Park KM, Min KS, Roh YS. Design Optimization of Lattice Structures under Compression: Study of Unit Cell Types and Cell Arrangements. Materials (Basel) 2021; 15:97. [PMID: 35009238 PMCID: PMC8746100 DOI: 10.3390/ma15010097] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2021] [Revised: 12/21/2021] [Accepted: 12/22/2021] [Indexed: 06/01/2023]
Abstract
Additive manufacturing enables innovative structural design for industrial applications, which allows the fabrication of lattice structures with enhanced mechanical properties, including a high strength-to-relative-density ratio. However, to commercialize lattice structures, it is necessary to define the designability of lattice geometries and characterize the associated mechanical responses, including the compressive strength. The objective of this study was to provide an optimized design process for lattice structures and develop a lattice structure characterization database that can be used to differentiate unit cell topologies and guide the unit cell selection for compression-dominated structures. Linear static finite element analysis (FEA), nonlinear FEA, and experimental tests were performed on 11 types of unit cell-based lattice structures with dimensions of 20 mm × 20 mm × 20 mm. Consequently, under the same relative density conditions, simple cubic, octahedron, truncated cube, and truncated octahedron-based lattice structures with a 3 × 3 × 3 array pattern showed the best axial compressive strength properties. Correlations among the unit cell types, lattice structure topologies, relative densities, unit cell array patterns, and mechanical properties were identified, indicating their influence in describing and predicting the behaviors of lattice structures.
Collapse
Affiliation(s)
- Kwang-Min Park
- Construction Technology Research Centre, Construction Division, Korea Conformity Laboratories, Seoul 08503, Korea;
| | - Kyung-Sung Min
- Construction Technology Research Centre, Construction Division, Korea Conformity Laboratories, Seoul 08503, Korea;
| | - Young-Sook Roh
- Architectural Engineering Program, Department of Architectural Engineering, Seoul National University of Science and Technology, Seoul 01811, Korea;
| |
Collapse
|
9
|
Shi HL, Li ZA. UnitCell Tools, a package to determine unit-cell parameters from a single electron diffraction pattern. IUCrJ 2021; 8:805-813. [PMID: 34584741 PMCID: PMC8420764 DOI: 10.1107/s2052252521007867] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Accepted: 08/02/2021] [Indexed: 05/26/2023]
Abstract
Electron diffraction techniques in transmission electron microscopy (TEM) have been successfully employed for determining the unit-cell parameters of crystal phases, albeit they exhibit a limited accuracy compared with X-ray or neutron diffraction, and they often involve a tedious measurement procedure. Here, a new package for determining unit-cell parameters from a single electron diffraction pattern has been developed. The essence of the package is to reconstruct a 3D reciprocal primitive cell from a single electron diffraction pattern containing both zero-order Laue zone and high-order Laue zone reflections. Subsequently, the primitive cell can be reduced to the Niggli cell which, in turn, can be converted into the unit cell. Using both simulated and experimental patterns, we detail the working procedure and address some effects of experimental conditions (diffraction distortions, misorientation of the zone axis and the use of high-index zone axis) on the robustness and accuracy of the software developed. The feasibility of unit-cell determination of the TiO2 nanorod using this package is also demonstrated. Should the parallel-beam, nano-beam and convergent-beam modes of the TEM be used flexibly, the software can determine unit-cell parameters of unknown-structure crystallites (typically >50 nm).
Collapse
Affiliation(s)
- Hong-Long Shi
- School of Science, Minzu University, 27 Zhong guancun South Avenue, Haidian District, Beijing 100081, People’s Republic of China
| | - Zi-An Li
- Institute of Physics, The Chinese Academy of Sciences, No. 8, 3rd South Street, Zhongguancun, Haidian District, Beijing 100190, People’s Republic of China
| |
Collapse
|
10
|
Kim H, Lee S. Electrical Heating Performance of Graphene/PLA-Based Various Types of Auxetic Patterns and Its Composite Cotton Fabric Manufactured by CFDM 3D Printer. Polymers (Basel) 2021; 13:polym13122010. [PMID: 34205431 PMCID: PMC8234701 DOI: 10.3390/polym13122010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2021] [Revised: 06/07/2021] [Accepted: 06/17/2021] [Indexed: 11/16/2022] Open
Abstract
To evaluate the electrical heating performance by auxetic pattern, re-entrant honeycomb (RE), chiral truss (CT), honeycomb (HN), and truss (TR), using graphene/PLA (Polylactic acid) filament, were manufactured by CFDM (conveyor fused deposition modelling) 3D printer. In addition, HN and TR, which was indicated to have an excellent electrical heating property, were selected to verify the feasibility of applying fabric heating elements. The result of morphology was that the number of struts constituting the unit cell and the connected points were TR < HN < CT < RE. It was also influenced by the surface resistivity and electrical heating performance. RE, which has the highest number of struts constituting the unit cell and the relative density, had the highest value of surface resistivity, and the lowest value was found in the opposite TR. In the electrical heating performance of samples, the heat distribution of RE was limited even when the applied voltage was increased. However, HN and TR were diffused throughout the sample. In addition, the surface temperature of RE, CT, HN, and TR was about 72.4 °C, 83.1 °C, 94.9 °C, and 85.9, respectively as applied at 30 V. When the HN and TR were printed on cotton fabric, the surface resistivity of HN/cotton and TR/cotton was about 103 Ω/sq, which showed conductive material. The results of electrical heating properties indicated that the heat distribution of HN/cotton showed only in the region where power was supplied, but the TR/cotton was gradually expanded and presented stable electric heating properties. When 30 V was applied, the surface temperature of both samples showed more than 80 °C, and the shape was maintained stably due to the high thermal conductivity of the cotton fabric. Therefore, this study ensured that HN and TR show excellent electrical heating performance among four types of auxetic patterns with continuity.
Collapse
Affiliation(s)
- Hyelim Kim
- Research Institute of Convergence Design, Dong-A University, Busan 49315, Korea;
| | - Sunhee Lee
- Department of Fashion Design, Dong-A University, Busan 49315, Korea
- Correspondence: ; Tel.: +82-51-200-7329
| |
Collapse
|
11
|
Mostafa KG, Momesso GA, Li X, Nobes DS, Qureshi AJ. Dual Graded Lattice Structures: Generation Framework and Mechanical Properties Characterization. Polymers (Basel) 2021; 13:polym13091528. [PMID: 34068753 PMCID: PMC8126252 DOI: 10.3390/polym13091528] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Revised: 04/19/2021] [Accepted: 04/20/2021] [Indexed: 11/16/2022] Open
Abstract
Additive manufacturing (AM) enables the production of complex structured parts with tailored properties. Instead of manufacturing parts as fully solid, they can be infilled with lattice structures to optimize mechanical, thermal, and other functional properties. A lattice structure is formed by the repetition of a particular unit cell based on a defined pattern. The unit cell's geometry, relative density, and size dictate the lattice structure's properties. Where certain domains of the part require denser infill compared to other domains, the functionally graded lattice structure allows for further part optimization. This manuscript consists of two main sections. In the first section, we discussed the dual graded lattice structure (DGLS) generation framework. This framework can grade both the size and the relative density or porosity of standard and custom unit cells simultaneously as a function of the structure spatial coordinates. Popular benchmark parts from different fields were used to test the framework's efficiency against different unit cell types and grading equations. In the second part, we investigated the effect of lattice structure dual grading on mechanical properties. It was found that combining both relative density and size grading fine-tunes the compressive strength, modulus of elasticity, absorbed energy, and fracture behavior of the lattice structure.
Collapse
Affiliation(s)
- Khaled G. Mostafa
- Additive Design and Manufacturing Systems (ADaMS) Lab, Department of Mechanical Engineering, University of Alberta, Edmonton, AB T6G 1H9, Canada; (K.G.M.); (X.L.)
| | | | - Xiuhui Li
- Additive Design and Manufacturing Systems (ADaMS) Lab, Department of Mechanical Engineering, University of Alberta, Edmonton, AB T6G 1H9, Canada; (K.G.M.); (X.L.)
| | - David S. Nobes
- Department of Mechanical Engineering, University of Alberta, Edmonton, AB T6G 1H9, Canada;
| | - Ahmed J. Qureshi
- Additive Design and Manufacturing Systems (ADaMS) Lab, Department of Mechanical Engineering, University of Alberta, Edmonton, AB T6G 1H9, Canada; (K.G.M.); (X.L.)
- Correspondence: ; Tel.: +1-(780)-492-3609
| |
Collapse
|
12
|
Nazir A, Arshad AB, Hsu CP, Jeng JY. Effect of Fillets on Mechanical Properties of Lattice Structures Fabricated Using Multi-Jet Fusion Technology. Materials (Basel) 2021; 14:ma14092194. [PMID: 33923348 PMCID: PMC8123134 DOI: 10.3390/ma14092194] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/08/2021] [Revised: 04/21/2021] [Accepted: 04/22/2021] [Indexed: 11/21/2022]
Abstract
Cellular structures with tailored topologies can be fabricated using additive manufacturing (AM) processes to obtain the desired global and local mechanical properties, such as stiffness and energy absorption. Lattice structures usually fail from the sharp edges owing to the high stress concentration and residual stress. Therefore, it is crucial to analyze the failure mechanism of lattice structures to improve the mechanical properties. In this study, several lattice topologies with fillets were designed, and the effects of the fillets on the stiffness, energy absorption, energy return, and energy loss of an open-cell lattice structure were investigated at a constant relative density. A recently developed high-speed AM multi-jet fusion technology was employed to fabricate lattice samples with two different unit cell sizes. Nonlinear simulations using ANSYS software were performed to investigate the mechanical properties of the samples. Experimental compression and loading–unloading tests were conducted to validate the simulation results. The results showed that the stiffness and energy absorption of the lattice structures can be improved significantly by the addition of fillets and/or vertical struts, which also influence other properties such as the failure mechanism and compliance. By adding the fillets, the failure location can be shifted from the sharp edges or joints to other regions of the lattice structure, as observed by comparing the failure mechanisms of type B and C structures with that of the type A structure (without fillets). The results of this study suggest that AM software designers should consider filleted corners when developing algorithms for generating various types of lattice structures automatically. Additionally, it was found that the accumulation of unsintered powder in the sharp corners of lattice geometries can also be minimized by the addition of fillets to convert the sharp corners to curved edges.
Collapse
Affiliation(s)
- Aamer Nazir
- Department of Mechanical Engineering, National Taiwan University of Science and Technology, 43 Keelung Road, Section 4, Taipei 10607, Taiwan; (A.N.); (A.-B.A.)
- High Speed 3D Printing Research Center, National Taiwan University of Science and Technology, No. 43, Section 4, Keelung Road, Taipei 10607, Taiwan;
| | - Ahmad-Bin Arshad
- Department of Mechanical Engineering, National Taiwan University of Science and Technology, 43 Keelung Road, Section 4, Taipei 10607, Taiwan; (A.N.); (A.-B.A.)
- High Speed 3D Printing Research Center, National Taiwan University of Science and Technology, No. 43, Section 4, Keelung Road, Taipei 10607, Taiwan;
| | - Chi-Pin Hsu
- High Speed 3D Printing Research Center, National Taiwan University of Science and Technology, No. 43, Section 4, Keelung Road, Taipei 10607, Taiwan;
- Graduate Institute of Biomedical Engineering, National Taiwan University of Science and Technology, No. 43, Section 4, Keelung Road, Taipei 10607, Taiwan
| | - Jeng-Ywan Jeng
- Department of Mechanical Engineering, National Taiwan University of Science and Technology, 43 Keelung Road, Section 4, Taipei 10607, Taiwan; (A.N.); (A.-B.A.)
- High Speed 3D Printing Research Center, National Taiwan University of Science and Technology, No. 43, Section 4, Keelung Road, Taipei 10607, Taiwan;
- President Office, Lunghwa University of Science and Technology, No.300, Sec.1, Wanshou Rd. Guishan District, Taoyuan City 333326, Taiwan
- Correspondence:
| |
Collapse
|
13
|
Schönfeld D, Chalissery D, Wenz F, Specht M, Eberl C, Pretsch T. Actuating Shape Memory Polymer for Thermoresponsive Soft Robotic Gripper and Programmable Materials. Molecules 2021; 26:522. [PMID: 33498348 PMCID: PMC7864034 DOI: 10.3390/molecules26030522] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2020] [Revised: 01/08/2021] [Accepted: 01/18/2021] [Indexed: 11/16/2022] Open
Abstract
For soft robotics and programmable metamaterials, novel approaches are required enabling the design of highly integrated thermoresponsive actuating systems. In the concept presented here, the necessary functional component was obtained by polymer syntheses. First, poly(1,10-decylene adipate) diol (PDA) with a number average molecular weight M n of 3290 g·mol-1 was synthesized from 1,10-decanediol and adipic acid. Afterward, the PDA was brought to reaction with 4,4'-diphenylmethane diisocyanate and 1,4-butanediol. The resulting polyester urethane (PEU) was processed to the filament, and samples were additively manufactured by fused-filament fabrication. After thermomechanical treatment, the PEU reliably actuated under stress-free conditions by expanding on cooling and shrinking on heating with a maximum thermoreversible strain of 16.1%. Actuation stabilized at 12.2%, as verified in a measurement comprising 100 heating-cooling cycles. By adding an actuator element to a gripper system, a hen's egg could be picked up, safely transported and deposited. Finally, one actuator element each was built into two types of unit cells for programmable materials, thus enabling the design of temperature-dependent behavior. The approaches are expected to open up new opportunities, e.g., in the fields of soft robotics and shape morphing.
Collapse
Affiliation(s)
- Dennis Schönfeld
- Fraunhofer Institute for Applied Polymer Research IAP, Geiselbergstr. 69, 14476 Potsdam, Germany; (D.S.); (D.C.)
| | - Dilip Chalissery
- Fraunhofer Institute for Applied Polymer Research IAP, Geiselbergstr. 69, 14476 Potsdam, Germany; (D.S.); (D.C.)
| | - Franziska Wenz
- Fraunhofer Institute for Mechanics of Materials IWM, Wöhlerstr. 11, 79108 Freiburg, Germany; (F.W.); (M.S.); (C.E.)
- Department of Microsystems Engineering IMTEK, University of Freiburg, Georges-Koehler-Allee 078, 79110 Freiburg, Germany
| | - Marius Specht
- Fraunhofer Institute for Mechanics of Materials IWM, Wöhlerstr. 11, 79108 Freiburg, Germany; (F.W.); (M.S.); (C.E.)
- Department of Microsystems Engineering IMTEK, University of Freiburg, Georges-Koehler-Allee 078, 79110 Freiburg, Germany
| | - Chris Eberl
- Fraunhofer Institute for Mechanics of Materials IWM, Wöhlerstr. 11, 79108 Freiburg, Germany; (F.W.); (M.S.); (C.E.)
- Department of Microsystems Engineering IMTEK, University of Freiburg, Georges-Koehler-Allee 078, 79110 Freiburg, Germany
| | - Thorsten Pretsch
- Fraunhofer Institute for Applied Polymer Research IAP, Geiselbergstr. 69, 14476 Potsdam, Germany; (D.S.); (D.C.)
| |
Collapse
|
14
|
Martinez-Marquez D, Delmar Y, Sun S, Stewart RA. Exploring Macroporosity of Additively Manufactured Titanium Metamaterials for Bone Regeneration with Quality by Design: A Systematic Literature Review. Materials (Basel) 2020; 13:E4794. [PMID: 33121025 PMCID: PMC7662257 DOI: 10.3390/ma13214794] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/23/2020] [Revised: 10/21/2020] [Accepted: 10/23/2020] [Indexed: 12/14/2022]
Abstract
Additive manufacturing facilitates the design of porous metal implants with detailed internal architecture. A rationally designed porous structure can provide to biocompatible titanium alloys biomimetic mechanical and biological properties for bone regeneration. However, increased porosity results in decreased material strength. The porosity and pore sizes that are ideal for porous implants are still controversial in the literature, complicating the justification of a design decision. Recently, metallic porous biomaterials have been proposed for load-bearing applications beyond surface coatings. This recent science lacks standards, but the Quality by Design (QbD) system can assist the design process in a systematic way. This study used the QbD system to explore the Quality Target Product Profile and Ideal Quality Attributes of additively manufactured titanium porous scaffolds for bone regeneration with a biomimetic approach. For this purpose, a total of 807 experimental results extracted from 50 different studies were benchmarked against proposed target values based on bone properties, governmental regulations, and scientific research relevant to bone implants. The scaffold properties such as unit cell geometry, pore size, porosity, compressive strength, and fatigue strength were studied. The results of this study may help future research to effectively direct the design process under the QbD system.
Collapse
Affiliation(s)
| | | | | | - Rodney A. Stewart
- School of Engineering and Built Environment, Griffith University, Gold Coast, QLD 4222, Australia; (D.M.-M.); (Y.D.); (S.S.)
| |
Collapse
|
15
|
Dauter Z, Jaskolski M. Multiplicity-weighted Euler's formula for symmetrically arranged space-filling polyhedra. Acta Crystallogr A Found Adv 2020; 76:580-583. [PMID: 32869755 PMCID: PMC7459769 DOI: 10.1107/s2053273320007093] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Accepted: 05/26/2020] [Indexed: 11/23/2022]
Abstract
For many tested cases of identical space-filling polyhedra, such as the space-group-specific asymmetric units or Dirichlet domains, the numbers of their faces (Fn), edges (En) and vertices (Vn), in each case normalized by division by the multiplicity of their (potentially special) symmetry position, fulfill a modified Euler’s formula Fn − En + Vn = 1. The famous Euler’s rule for three-dimensional polyhedra, F − E + V = 2 (F, E and V are the numbers of faces, edges and vertices, respectively), when extended to many tested cases of space-filling polyhedra such as the asymmetric unit (ASU), takes the form Fn − En + Vn = 1, where Fn, En and Vn enumerate the corresponding elements, normalized by their multiplicity, i.e. by the number of times they are repeated by the space-group symmetry. This modified formula holds for the ASUs of all 230 space groups and 17 two-dimensional planar groups as specified in the International Tables for Crystallography, and for a number of tested Dirichlet domains, suggesting that it may have a general character. The modification of the formula stems from the fact that in a symmetrical space-filling arrangement the polyhedra (such as the ASU) have incomplete bounding elements (faces, edges, vertices), since they are shared (in various degrees) with the space-filling neighbors.
Collapse
Affiliation(s)
- Zbigniew Dauter
- Macromolecular Crystallography Laboratory, National Cancer Institute, Argonne, IL 60439, USA
| | - Mariusz Jaskolski
- Department of Crystallography, Faculty of Chemistry, A. Mickiewicz University and Center for Biocrystallographic Research, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland
| |
Collapse
|
16
|
Geng Y, Jiang J, Lin F, Shao H, Zhang C, Chen N. Study of Compaction Properties and Permeability Prediction of Multilayered Quadriaxial Non-Crimp Fabric in Liquid Composite Molding Process. Polymers (Basel) 2020; 12:E1525. [PMID: 32660048 DOI: 10.3390/polym12071525] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Revised: 07/05/2020] [Accepted: 07/08/2020] [Indexed: 11/29/2022] Open
Abstract
A systematic experimental study was performed to detect the compaction and permeability properties of multilayered biaxial and quadriaxial preforms under vacuum pressure. Compression response on ply level showed that the degree of nesting between quadriaxial NCF was more pronounced and the nesting deformation mechanism was affected by the interaction with stitch yarns. Owing to the meso-channels in the fibrous structure and the nesting between layers, the in-plane permeability of quadriaxial NCF did not follow an inverse proportion relationship with the fiber volume fraction. To predict the in-plane permeability of multilayered quadriaxial NCFs, unit cell models at a high level of geometrical details were built, including local variations in yarn cross-sections and the nesting deformation between layers. Numerical methods were implemented, and the prediction results were in very good agreement with the experimental data. Besides, the major contributing parameters to the enhancement of the in-plane permeabilities were identified by investigating the correlation between permeability and structural parameters of quadriaxial NCF. The modeling methodology and the principles established can be applied to the design of the quadriaxial NCF fabrics, where the permeability enhancement was evidenced.
Collapse
|
17
|
D'Mello RJ, Waas AM. Influence of Unit Cell Size and Fiber Packing on the Transverse Tensile Response of Fiber Reinforced Composites. Materials (Basel) 2019; 12:E2565. [PMID: 31408944 DOI: 10.3390/ma12162565] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/17/2019] [Revised: 08/05/2019] [Accepted: 08/07/2019] [Indexed: 12/05/2022]
Abstract
Representative volume elements (RVEs) are commonly used to compute the effective elastic properties of solid media having repeating microstructure, such as fiber reinforced composites. However, for softening materials, an RVE could be problematic due to localization of deformation. Here, we address the effects of unit cell size and fiber packing on the transverse tensile response of fiber reinforced composites in the context of integrated computational materials engineering (ICME). Finite element computations for unit cells at the microscale are performed for different sizes of unit cells with random fiber packing that preserve a fixed fiber volume fraction—these unit cells are loaded in the transverse direction under tension. Salient features of the response are analyzed to understand the effects of fiber packing and unit cell size on the details of crack path, overall strength and also the shape of the stress-strain response before failure. Provision for damage accumulation/cracking in the matrix is made possible via the Bazant-Oh crack band model. The results suggest that the choice of unit cell size is more sensitive to strength and less sensitive to stiffness, when these properties are used as homogenized inputs to macro-scale models. Unit cells of smaller size exhibit higher strength and this strength converges to a plateau as the size of the unit cell increases. In this sense, since stiffness has also converged to a plateau with an increase in unit cell size, the converged unit cell size may be thought of as an RVE. Results in support of these insights are presented in this paper.
Collapse
|
18
|
Dauter Z, Wlodawer A. Crystallographically correct but confusing presentation of structural models deposited in the Protein Data Bank. Acta Crystallogr D Struct Biol 2018; 74:939-945. [PMID: 30198902 PMCID: PMC6130463 DOI: 10.1107/s2059798318009828] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2018] [Accepted: 07/09/2018] [Indexed: 11/10/2022] Open
Abstract
The Protein Data Bank (PDB) constitutes a collection of the available atomic models of macromolecules and their complexes obtained by various methods used in structural biology, but chiefly by crystallography. It is an indispensable resource for all branches of science that deal with the structures of biologically active molecules, such as structural biology, bioinformatics, the design of novel drugs etc. Since not all users of the PDB are familiar with the methods of crystallography, it is important to present the results of crystallographic analyses in a form that is easy to interpret by nonspecialists. It is advisable during the submission of structures to the PDB to pay attention to the optimal placement of molecules within the crystal unit cell, to the correct representation of oligomeric assemblies and to the proper selection of the space-group symmetry. Examples of significant departures from these principles illustrate the potential for the misinterpretation of such suboptimally presented crystal structures.
Collapse
Affiliation(s)
- Zbigniew Dauter
- Synchrotron Radiation Research Section, Macromolecular Crystallography Laboratory, NCI, Argonne National Laboratory, Argonne, IL 60439, USA
| | - Alexander Wlodawer
- Protein Structure Section, Macromolecular Crystallography Laboratory, National Cancer Institute, Frederick, MD 21702, USA
| |
Collapse
|
19
|
Abstract
The developments in crystallography, since it was first covered in Science Progress in 1917, following the formulation of the Bragg equation, are described. The advances in instrumentation and data analysis, coupled with the application of computational methods to data analysis, have enabled the solution of molecular structures from the simplest binary systems to the most complex of biological structures. These developments are shown to have had major impacts in the development of chemical bonding theory and in offering an increasing understanding of enzyme-substrate interactions. The advent of synchrotron radiation sources has opened a new chapter in this multi-disciplinary field of science.
Collapse
Affiliation(s)
- Terence J. Kemp
- Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK
| | | |
Collapse
|
20
|
Liu YJ, Song G, Yin HM. Boundary effect on the elastic field of a semi-infinite solid containing inhomogeneities. Proc Math Phys Eng Sci 2015; 471:20150174. [PMID: 26345084 DOI: 10.1098/rspa.2015.0174] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Accepted: 05/14/2015] [Indexed: 11/12/2022] Open
Abstract
The boundary effect of one inhomogeneity embedded in a semi-infinite solid at different depths has firstly been investigated using the fundamental solution for Mindlin's problem. Expanding the eigenstrain in a polynomial form and using the Eshelby's equivalent inclusion method, one can calculate the eigenstrain and thus obtain the elastic field. When the inhomogeneity is far from the boundary, the solution recovers Eshelby's solution. The method has been extended to a many-particle system in a semi-infinite solid, which is first demonstrated by the cases of two spheres. The comparison of the asymptotic form solution with the finite-element results shows the accuracy and capability of this method. The solution has been used to illustrate the boundary effects on its effective material behaviour of a semi-infinite simple cubic lattice particulate composite. The local field of a semi-infinite composite has been calculated at different volume fractions. A representative unit cell has been taken with different depths to the surface. The average stress and strain of the unit cell have been calculated under uniform loading conditions of normal or shear force on the surface, respectively. The effective elastic moduli of the unit cell not only depend on the material proportion, but also on its distance to the surface. The present model can be extended to other types of particle distribution and ellipsoidal particles.
Collapse
Affiliation(s)
- Y J Liu
- Department of Civil Engineering and Engineering Mechanics , Columbia University , 610 Seeley W. Mudd 500 West 120th Street, New York, NY 10027, USA
| | - G Song
- Department of Civil Engineering and Engineering Mechanics , Columbia University , 610 Seeley W. Mudd 500 West 120th Street, New York, NY 10027, USA
| | - H M Yin
- Department of Civil Engineering and Engineering Mechanics , Columbia University , 610 Seeley W. Mudd 500 West 120th Street, New York, NY 10027, USA
| |
Collapse
|
21
|
Abstract
Tetracalcium phosphate, Ca4O(PO4)2, has a monoclinic modification with the parameters a= 11.99, b = 9.48, and c = 6.97 A, α = 90.8°, z = 4, and space group P21 or P21/m. From a comparison with the work of Trömel and Zaminer, it is concluded that this salt has monoclinic and orthorhombic modifications with the most probable space groups being P21 and P21221, respectively. The results support the view that tetracalcium phosphate has a layer-type structural relationship to hydroxyapatite, Ca5(OH)(PO4)3. This would account, in part, for variations in the compositions of apatitic materials in which the ratio Ca/P is greater than 10/6, and it suggests that tetracalcium phosphate may be present in the mineral of tooth and bone.
Collapse
Affiliation(s)
- Walter E Brown
- Research Associate, American Dental Association, National Bureau of Standards, Washington, D.C. 20234
| | - Earl F Epstein
- National Institute of Dental Research, National Institutes of Health, Bethesda, Md. (present address. Department of Chemistry, University of Wisconsin, Madison, Wis.)
| |
Collapse
|