7,781 research outputs found
Reduced Order Models for Profiled Steel Diaphragm Panels
The objective of this paper is to provide progress on development and validation of reduced order models for the in plane strength and stiffness of profiled steel panels appropriate for use in structural models of an entire building. Profiled steel panels, i.e, metal deck, often serve as a key distribution element in building lateral force resisting systems. Acting largely as an in-plane shear diaphragm, metal deck as employed in walls, roofs, and floors plays a key role in creating and driving three-dimensional building response. As structural modeling evolves from two-dimensional frameworks to fully three-dimensional buildings, accurate and computationally efficient models of profiled steel panels are needed. Three-dimensional building response is increasingly required by ever-evolving structural standards, particularly in seismic design, and structural efficiency demands that the benefits of three-dimensional response be leveraged in design. Equivalent orthotropic plate models provide a potential reduced order model for profiled steel panels that is investigated in this paper. A recent proposal for the rigidities in such a model are assessed against shell finite element models of profiled steel panels. In addition, the impact of discrete connections and discrete panels, as occurs in an actual roof system, are assessed when applying these reduced order models. Extension of equivalent orthotropic plate models to elastic buckling and strength, in addition to stiffness, both represent work in progress, but initial results are provided. Examples show that equivalent orthotropic plate models must be used with care to yield useful results. This effort is an initial step in developing efficient whole building models that accurately incorporate the behavior of profiled steel panels as diaphragms
Enantiomerically pure β-phenylalanine analogues from α–β-phenylalanine mixtures in a single reactive extraction step
An efficient and selective method for the extraction of α-amino acids in preference over their β-isomers using PdCl2(PPh3)2 was discovered, which enables the separation of product mixtures obtained in the enantioselective enzymatic formation of β-amino acids.
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Thermally stimulated relaxation and behaviors of oxygen vacancies in SrTiO<inf>3</inf> single crystals with (100), (110) and (111) orientations
Abstract
The strontium titanate (SrTiO3) single crystals with different orientations of (100), (110) and (111) were investigated using thermally stimulated depolarization current (TSDC) measurements, which has been proved to be an effective strategy to fundamentally study the relationship between relaxation phenomena and defect chemistry in dielectrics. The origins of different relaxations in SrTiO3 crystals were identified and the activation energy of oxygen vacancies was estimated from TSDC measurements. It was further found that oxygen-treated SrTiO3 crystals exhibit different relaxation behaviors. Noticeable changes of thermal relaxation associated with oxygen vacancies have taken place in relation to the crystalline anisotropy. The SrTiO3 (110) samples display higher concentration and activation energy of oxygen vacancies. First-principles calculations were carried out on SrTiO3 (110) crystals to study the effect of oxygen vacancy on different surface microstructure. From the resulting minimum formation energy of 0.63 eV, it demonstrates that the oxygen vacancies tend to form on the TiO-terminated surfaces. Considering the band structure, oxygen vacancies near the surface contribute to the transition of crystal from insulator to metallic characteristic.</jats:p
Incorporation of μ3-CO3 into an MnIII/MnIV Mn12 cluster: {[(cyclam)MnIV(μ-O)2MnIII(H2O)(μ-OH)]6(μ3-CO3)2}Cl8·24H2O
The centrosymmetric title cluster, hexaaquadi-μ3-carbonato-hexacyclamhexa-μ2-hydroxido-dodeca-μ2-oxido-hexamanganese(IV)hexamanganese(III) octachloride tetracosahydrate, [Mn12(CO3)2O12(OH)6(C10H24N4)6(H2O)6]Cl8·24H2O, has two μ3-CO3 groups that not only bridge octahedrally coordinated MnIII ions but also act as acceptors to two different kinds of hydrogen bonds. The carbonate anion is planar within experimental error and has an average C—O distance of 1.294 (4) Å. The crystal packing is stabilized by O—H⋯Cl, O—H⋯O, N—H⋯Cl and N—H⋯O hydrogen bonds. Two of the four independent chloride ions are disordered over five positions, and eight of the 12 independent water molecules are disordered over 21 positions
A comparison of the local spiral structure from Gaia DR2 and VLBI maser parallaxes
Context. The Gaia mission has released the second data set (Gaia DR2), which
contains parallaxes and proper motions for a large number of massive, young
stars. Aims. We investigate the spiral structure in the solar neighborhood
revealed by Gaia DR2 and compare it with that depicted by VLBI maser
parallaxes. Methods. We examined three samples with different constraints on
parallax uncertainty and distance errors and stellar spectral types: (1) all OB
stars with parallax errors of less than 10%; (2) only O-type stars with 0.1 mas
errors imposed and with parallax distance errors of less than 0.2 kpc; and (3)
only O-type stars with 0.05 mas errors imposed and with parallax distance
errors of less than 0.3 kpc. Results. In spite of the significant distance
uncertainties for stars in DR2 beyond 1.4 kpc, the spiral structure in the
solar neighborhood demonstrated by Gaia agrees well with that illustrated by
VLBI maser results. The O-type stars available from DR2 extend the spiral arm
models determined from VLBI maser parallaxes into the fourth Galactic quadrant,
and suggest the existence of a new spur between the Local and Sagittarius arms.Comment: 4 pages, 3 figures, 1 table, accepted for publication in A&
Systematics of g factors of 2_1^+ states in even-even nuclei from Gd to Pt: A microscopic description by the projected shell model
The systematics of g factor of first excited 2^+ state vs neutron number N is
studied by the projected shell model. The study covers the even-even nuclei of
all isotopic chains from Gd to Pt. g factors are calculated by using the
many-body wavefunctions that reproduces well the energy levels and B(E2)'s of
the ground-state bands. For Gd to W isotopes the characteristic feature of the
g factor data along an isotopic chain is described by the present model.
Deficiency of the model in the g factor description for the heavier Os and Pt
isotopes is discussed.Comment: 9 pages, 5 figure
GAP: From sound design to practical implementation in clinical trials for traditional chinese medicine
The past few years have witnessed encouraging progress in improving the methodological quality of clinical research of traditional Chinese medicine (TCM). This improvement has contributed to wider academic acceptance of the findings of TCM clinical studies, which were previously deemed dubious. As a proof of this statement, one clinical study testing the effects of a Chinese patent drug Qili Qiangxin Capsules on chronic heart failure has just published a research article on the Journal of the American College of Cardiology, a medical journal of international prestige. However, a sound and scientific design does not always see to its practicality in the conduct of the study, and in fact we observed a widening gap between the two elements. In this special issue, we called for papers discussing efforts to bridge the gap between scientific design and practical implementation of clinical research with TCM
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