523 research outputs found
Machine learning for crystal identification and discovery
As computers get faster, researchers -- not hardware or algorithms -- become
the bottleneck in scientific discovery. Computational study of colloidal
self-assembly is one area that is keenly affected: even after computers
generate massive amounts of raw data, performing an exhaustive search to
determine what (if any) ordered structures occur in a large parameter space of
many simulations can be excruciating. We demonstrate how machine learning can
be applied to discover interesting areas of parameter space in colloidal self
assembly. We create numerical fingerprints -- inspired by bond orientational
order diagrams -- of structures found in self-assembly studies and use these
descriptors to both find interesting regions in a phase diagram and identify
characteristic local environments in simulations in an automated manner for
simple and complex crystal structures. Utilizing these methods allows analysis
methods to keep up with the data generation ability of modern high-throughput
computing environments.Comment: Fixed typo, added missing acknowledgment, added supplementary
informatio
Model Pembelajaran Asam Basa Berbasis Scs (Science Process Skills) Melalui Kegiatan Laboratorium Sebagai Wahana Pendidikan Sains Siswa Mts
Tujuan penelitian ini adalah untuk memperkenal- kan dan mengetahui efektivitas Model Pembelajaran SCS ( Science Process Skills ) melalui kegiatan Laboratorium Sebagai Wahana Pendidikan Sains yang cocok bagi siswa MTs agar meningkatkan: penguasaan konsep kimia, ke- mampuan berpikir kreatif, dan keterampilan sains siswa. Metode yang digunakan adalah metode penelitian kelas, dan difokuskan pada pokok bahasan asam basa. Penelitian ini dilakukan di salah satu MTs Negeri di kota Semarang dengan subyek sebanyak 40 siswa kelas III. Instrumen yang digunakan dalam penelitian ini meliputi model pembelaja- ran, soal-soal tes, pedoman wawancara, pedoman obser- vasi dan angket, sedang LKS digunakan pada saat kegiatan laboratorium. Dalam model pembelajaran dikembangkan empat jenis konsep yaitu konsep kongkret, konsep yang menyatakan sifat, konsep yang melibatkan penggambaran simbol, dan konsep berdasarkan prinsip. Model pembela- jaran ini dapat meningkatkan pemahaman konsep pada setiap kelompok kemampuan siswa, mengembangkan ke- mampuan berpikir kreatif dengan hasil tertinggi pada as- pek membangun konsep di atas pengetahuan yang telah ada pada diri siswa dan terendah pada aspek memilih hal- hal yang mungkin tidak relevan, serta keterampilan sains mengatasi kurangnya waktu pembelajaran, bagian-bagian pembelajaran tertentu dapat dilaksanakan di luar jam ke- las
A Broadband Superabsorber at Optical Frequencies: Design and Demonstration
Metasurface based super absorbers exhibit near unity absorbance. While the
absorption peak can be tuned by the geometry/size of the sub-wavelength
resonator, broadband absorption can be obtained by placing multiple resonators
of various size or shapes in a unit cell. Metal dispersion hinders high
performance broadband absorption at optical frequencies and careful designing
is essential to achieve good structures. We propose a novel analytical
framework for designing a broadband super absorber which is much faster than
the time consuming full wave simulations that are employed so far. Analytical
expressions are derived for the wavelength dependency of the design parameters,
which are then used in the optimization of broadband absorption. Numerical
simulations report an average polarization-independent absorption of ~97 in the
450 to 950 nm spectral region with a near unity absorption (99.36) in the 500
to 850 nm region. Experimentally, we demonstrate an average absorption over 98
in the 450 to 950 nm spectral region at 20 degree incident angle The designed
super absorber is polarization insensitive and has a weak launch angle
dependency. The proposed framework simplifies the design process and provides a
quicker optimal solution for high performance broadband super absorbers
Crystalline Assemblies and Densest Packings of a Family of Truncated Tetrahedra and the Role of Directional Entropic Forces
Polyhedra and their arrangements have intrigued humankind since the ancient
Greeks and are today important motifs in condensed matter, with application to
many classes of liquids and solids. Yet, little is known about the
thermodynamically stable phases of polyhedrally-shaped building blocks, such as
faceted nanoparticles and colloids. Although hard particles are known to
organize due to entropy alone, and some unusual phases are reported in the
literature, the role of entropic forces in connection with polyhedral shape is
not well understood. Here, we study thermodynamic self-assembly of a family of
truncated tetrahedra and report several atomic crystal isostructures, including
diamond, {\beta}-tin, and high- pressure lithium, as the polyhedron shape
varies from tetrahedral to octahedral. We compare our findings with the densest
packings of the truncated tetrahedron family obtained by numerical compression
and report a new space filling polyhedron, which has been overlooked in
previous searches. Interestingly, the self-assembled structures differ from the
densest packings. We show that the self-assembled crystal structures can be
understood as a tendency for polyhedra to maximize face-to-face alignment,
which can be generalized as directional entropic forces.Comment: Article + supplementary information. 23 pages, 10 figures, 2 table
Fabrication of polyhedral particles from spherical colloids and their self-assembly into rotator phases
Particle shape is a critical parameter that plays an important role in
self-assembly, for example, in designing targeted complex structures with
desired properties. In the last decades an unprecedented range of monodisperse
nanoparticle systems with control over the shape of the particles have become
available. In contrast, the choice of micron-sized colloidal building blocks of
particles with flat facets, i.e., particles with polygonal shapes, is
significantly more limited. This can be attributed to the fact that, contrary
to nanoparticles, the larger colloids are significantly harder to synthesize as
single crystals. Herein, we demonstrate that the simplest building block, such
as the micron-sized polymeric spherical colloidal particle, is already enough
to fabricate particles with regularly placed flat facets, including completely
polygonal shapes with sharp edges. As an illustration that the yields are high
enough for further self-assembly studies we demonstrate the formation of 3D
rotator phases of fluorescently labelled, micron-sized and charged rhombic
dodecahedron particles. Our method for fabricating polyhedral particles opens a
new avenue for designing new materials.Comment: 5 pages, published in Angewandte Chemie International Editio
A Directional Entropic Force Approach to Assemble Anisotropic Nanoparticles into Superlattices
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102048/1/13980_ftp.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/102048/2/anie_201306009_sm_miscellaneous_information.pd
Heterogeneous Catalysis through Microcontact Printing
Here, we investigate four different chemical pathways (Scheme 1a–d) relevant to the Cu-catalyzed azide–alkyne cycloaddition (CuAAC) reaction.[13] Three of those pathways lead to surfaces functionalized with organic molecules.[5, 11, 14] At the outset, our practical goal was to identify surface-functionalization protocols that are capable of attaining 1) spatial selectivity, 2) high surface coverage, and 3) rapid reaction kinetics. Our ultimate goal is to achieve a fundamental understanding of how different reaction pathways influence the chemical outcome as it applies to the organic functionalization of surfaces
First Synthesis of Continuous Mesoporous Copper Films with Uniformly Sized Pores by Electrochemical Soft Templating
Although mesoporous metals have been synthesized by electrochemical methods, the possible compositions have been limited to noble metals (e.g., palladium, platinum, gold) and their alloys. Herein we describe the first fabrication of continuously mesoporous Cu films using polymeric micelles as soft templates to control the growth of Cu under sophisticated electrochemical conditions. Uniformly sized mesopores are evenly distributed over the entire film, and the pore walls are composed of highly crystalized Cu. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei
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