Non-optimized Geometry Research Articles

Designing the 3D-microbattery geometry using the level-set method

Strategies for automatic design of power-optimized 3D-microbattery geometries are here investigated by utilization of the level-set method with structure topology optimization. The methodology is extended from solid mechanics to electrochemical systems, where battery operation is simulated using the Nernst–Planck equation. The calculations are carried out for the 3D-“trench” geometry with LiCoO2 and LiC6 as electrodes, separated with a LiPF6·PEO20 polyethylene oxide polymer electrolyte. With the goal to achieve a maximum uniform electrochemical activity over the electrode surface area, an optimized electrode design is produced by coating the current collectors non-uniformly with active material. This is shown to be an effect of the 3D design of the cell. Evaluation of the resulting optimized cell by simulations of the discharge process demonstrates uniform electrode material utilization and almost uniform current density distribution over the entire electrode–electrolyte interface. Comparisons between optimized and non-optimized geometries showed that the geometry optimization increased the cell performance up to 2.25 times. This effect is mainly achieved by minimizing the internal energy losses caused by non-uniformities in the ionic transport in the battery.

Inferring stress from faulting: From early concepts to inverse methods

We review the evolution of concepts on and methods of estimating the state of stress from fault movements. Theories of failure in isotropic materials suggested a simple geometrical construction of optimal principal stress directions from a fault plane and its associated slip. These optimal directions align shear stress and slip directions and maximize the difference between shear stress and frictional resistance on the fault plane. Optimal stress directions for calcite twinning are obtained by a similar construction, with the difference that they maximize shear stress. Force representation of seismic sources independently introduced pressure, P, and tension, T, axes at positions that also maximize shear stress on both nodal planes.Frictional slip theory and the constraint that slip and shear stress directions be parallel allowed to address reactivation of pre-existing faults. This suggested that stress could also be inverted from reactivated fault and slip data or earthquake focal mechanisms. Early methods relied on geometrical constructions as a substitute for calculations, whereas later methods relied on software as these calculations became tractable with the help of computers. Similar methods were developed for the inversion of stress from crystal twin gliding with non-optimal geometry, with a different criterion that relies on a threshold of the component of shear stress along the gliding line.Even though these methods seek a common stress tensor compatible with fault and slip data, their main use is to separate polyphase data into homogeneous subsets and help deciphering complex tectonic histories. Fault and slip data can also be analyzed to constrain the strain rather than the stress tensor. In most cases this involves a summation and yields an average strain for the considered rock volume. Stress inversion thus appears better suited for differentiating heterogeneous data whereas strain analysis appears better suited for homogenizing them.

Osteoarthritis susceptibility genes influence the association between hip morphology and osteoarthritis

The identified osteoarthritis (OA) susceptibility genes are mainly active in skeletal development and could thus affect joint geometry. Because nonoptimal joint geometry is a risk factor for the development of OA, we investigated if and how the path that leads from nonoptimal joint geometry to OA of the hip is influenced by these genes. The shape of the hips of subjects in the Genetics, Osteoarthritis and Progression Study, consisting of sibling pairs with symptomatic OA at multiple joint locations, was quantified by applying a statistical shape model to radiographs. Shape aspects (modes) were correlated to OA characteristics. We then tested for the association of shape modes with OA susceptibility single-nucleotide polymorphisms (SNPs) of GDF5, FRZB, and DIO2. Four of 23 shape modes (mode 1, mode 17, mode 18, and mode 21) were strongly associated with OA characteristics. We observed a significant interaction between carrier status of DIO2 rs12885300 and hip OA characteristics for mode 1 (P = 0.005). This indicates that this specific aspect of hip shape correlates with OA characteristics only in carriers of the susceptibility allele. Our results suggest that it is more likely that the rs12885300 SNP of DIO2 increases the vulnerability of cartilage to nonoptimal bone shapes rather than directly influencing the formation of these shapes.

Shear velocity structure of the Northland Peninsula, New Zealand, inferred from ambient noise correlations

Ambient noise correlation has been successfully applied in several cases to regions with dense seismic networks whose geometries are well suited to tomographic imaging. The utility of ambient noise correlation‐based methods of seismic imaging where either network or noise field characteristics are less ideal has yet to be fully demonstrated. In this study, we focus on the Northland Peninsula of New Zealand using data from five seismographs deployed in a linear pattern parallel to the direction from which most of the ambient noise arrives. Shear wave velocity profiles computed from Rayleigh and Love wave dispersion curves using the Neighborhood Algorithm are in good agreement with the results of a previous active source refraction experiment and a teleseismic receiver function and surface wave analysis. In particular, we compute a path‐averaged Moho depth of ∼28 km along a ∼250 km profile. The use of both Rayleigh and Love wave measurements enables us to estimate the degree of radial anisotropy in the crust, yielding values of 2–15%. These results demonstrate that ambient noise correlation methods provide useful geophysical constraints on lithospheric structure even for nonoptimal network geometries and noise field characteristics.

The importance of the effective intermediate principal stress ( σ′ 2) to fault slip patterns

In normal faulting regimes, the magnitudes and orientations of the maximum and minimum principal compressive stresses may be known with some confidence. However, the magnitude of the intermediate principal compressive stress is generally much more difficult to constrain and is often not considered to be an important factor. In this paper, we show that the slip characteristics of faults and fractures with complex or nonoptimal geometry are highly sensitive to variation or uncertainty in the ambient effective intermediate principal stress ( σ′ 2). Optimally oriented faults and fractures may be less sensitive to such variations or uncertainties. Slip tendency ( T s) analysis provides a basis for quantifying the effects of uncertainty in the magnitudes and orientations of all principal stresses and in any stress regime, thereby focusing efforts on the most important components of the system. We also show, for a normal faulting stress regime, that the proportion of potential surfaces experiencing high slip tendency (e.g., T s ≥ 0.6) decreases from a maximum of about 38% where σ′ 2 = σ′ 3, to a minimum of approximately 14% where σ′ 2 is halfway between σ′ 3 and σ′ 1, and increases to another high of approximately 29% where σ′ 2 = σ′ 1. This analysis illustrates the influence of the magnitude of σ′ 2 on rock mass strength, an observation previously documented by experimental rock deformation studies. Because of the link between fault and fracture slip characteristics and transmissivity in critically stressed rock, this analysis can provide new insights into stress-controlled fault transmissivity.

Optimization of the design of superconducting inhomogeneous nanowires

We study the optimization of the superconducting properties of inhomogeneous nanowires.The main goal of this research is to find an optimized geometry that allows one tomaximize the desired property of superconductors, such as the maximum value of thelocal superconducting gap or total condensation energy. We consider the axiallysymmetric design of multilayered nanowires with the possibility of adjusting andchanging the layer thickness. We use numerical solution of the Bogoliubov–de Gennesequations to obtain the local superconducting gap for different arrangements ofinhomogeneous structures. The values of the optimized properties can be up to300% greater than for a non-optimized geometry. The optimized configuration of multilayersstrongly depends on the desired property one wants to optimize and on the number oflayers in the nanowire.

One quarter million (500×500)pixel arrays of silicon microcavity plasma devices: Luminous efficacy above 6lumens∕watt with Ne/50% Xe mixtures and a green phosphor

Arrays comprising 250 000 Si microcavity plasma devices, each with an emitting aperture of 50×50μm2 and tapered sidewalls (inverted pyramid cavity), have been fabricated in 100-mm (4″) diam. wafers and operated in the rare gases and Ar∕N2 mixtures with sinusoidal ac or bipolar dc excitation. Having an overall active area of 25cm2 and a 25% filling factor, these 500×500 arrays exhibit the pixel-to-pixel emission uniformity characteristics of arrays at least a factor of 6 smaller, and yet are efficient in generating vacuum ultraviolet (VUV) radiation. Luminous efficacies above 6lm∕W and luminance values approaching 2000cd∕m2 are measured when a 500×500 array, operating with a Ne/50% Xe gas mixture, illuminates a 20-μm-thick film of a commercial green phosphor (Mn:Zn2SiO4). Despite the nonoptimal transmission geometry of the array-phosphor structure, the efficacy and luminance produced by the VUV-driven phosphor for a Ne/50% Xe mixture and a total pressure of 800Torr are measured to be 7.2±0.6lm∕Watt and 525±75cd∕m2, respectively, for a 20-kHz sinusoidal ac voltage of ∼284V rms. Maximizing the luminous efficacy–luminance product lowers the optimal pressure of Ne/50% Xe mixtures to roughly 1atm. The magnitude of the radiant output generated by these arrays, in addition to the rapid rise in emitting efficiency with increased Xe content in Ne/10%–50% Xe mixtures, suggest that this microplasma array structure will be of value for both microdisplay and biomedical applications.

Experimental validation of CFD mass transfer simulations in flat channels with non-woven net spacers

The objective of the present paper is to validate experimentally the mass transfer simulations presented in a previous paper by the same authors [J. Membr. Sci. 208 (2002) 289]. In the present study, mass transfer coefficients were obtained by the limiting current method. The results from CFD simulations were successfully validated by experiments. The experiments confirm that the geometric parameters of spacers have a considerable influence on mass transfer at a given cross-flow power consumption. Comparison of the experiments with different non-woven spacers shows that there is an optimal spacer geometry, which agrees with those of the optimal spacer obtained by CFD simulations. The experiments also indicate that the woven and non-woven spacers perform equally well. Since all commercial net spacers investigated in this study had non-optimal spacer geometries, they showed lower mass transfer coefficients at a given cross-flow power consumption than the optimal spacer.

Theory, simulation and measurement of chemical mass shifts in RF quadrupole ion traps

A comprehensive description of chemical mass shifts in the RF quadrupole ion trap (Paul trap) is given and their origin is explained. Extending a previously proposed model, it is shown that chemical mass shifts are a result of an ejection delay caused by field imperfections in RF ion traps with non-optimized geometry, in particular, field imperfections resulting from holes in the end-cap electrodes, and of compound-dependent modifications of this ejection delay by collisions of the ions with the buffer gas. Elastic collisions change peak shapes and peak widths, but give rise to only very small chemical mass shifts. Inelastic collisions, which result in dissociation, can lead to large chemical mass shifts. The field imperfections present in real ion traps are examined, and differences in the ion ejection behavior and in the chemical mass shifts occurring in boundary ejection and resonance ejection scans are investigated. The dependence of the shifts on the trap geometry, on the buffer gas pressure, on the RF amplitude scan rate, on ion mass, and on ion chemical structure, are explained. The proposed model for chemical mass shifts is validated through experimental measurements and quantitative simulations using the ion trap simulation program ITSIM. It is shown that peak shapes in mass spectra can be reproduced or predicted by simulations, for ion traps with a variety of geometries and operating conditions. Very good agreement between simulations and experiments is found, provided experimental and simulated geometries differ slightly in the end-cap separation, indicating that additional previously neglected field imperfections may be present in common RF ion traps.

Direction interval retrieval with thresholded nudging: a method for improving the accuracy of QuikSCAT winds

The SeaWinds scatterometer was developed by NASA JPL, Pasadena, CA, to measure the speed and direction of ocean surface winds. It was then launched onboard the QuikSCAT spacecraft. The accuracy of the majority of the swath and the size of the swath are such that the SeaWinds on QuikSCAT Mission (QSCAT) meets its science requirements despite shortcomings at certain cross-track positions. Nonetheless, it is desirable to modify the baseline processing in order to improve the quality of the less accurate portions of the swath, in particular near the far swath and nadir. Two disparate problems have been identified for these regions. At far swath, ambiguity removal skill is degraded due to the absence of inner beam measurements, limited azimuth diversity and boundary effects. Near nadir, due to nonoptimal measurement geometry, (measurement azimuths approximately 180/spl deg/ apart) there is a marked decrease in directional accuracy even when ambiguity removal works correctly. Two algorithms have been developed: direction interval retrieval (DIR) to address the nadir performance issue and thresholded nudging (TN) to improve ambiguity removal at far swath. The authors illustrate the impact of the two techniques by exhibiting prelaunch simulation results and postlaunch statistical performance metrics with respect to ECMWF wind fields and buoy data.

Optimization of travelling wave ultrasonic motors using a three-dimensional analysis of the contact mechanism at the stator–rotor interface

The present paper investigates optimization rules and new design methodologies dealing with the contact mechanics in rotative travelling wave ultrasonic motors (TWUM). The proposed approaches focus on the design of the rotor, including the friction layer that is usually deposited onto its lower surface, while the stator is supposed to be preliminary designed. Contact aspects such as the transmission of mechanical power as well as the wear mechanism of the friction layer are investigated, according to the analysis of the stator–rotor contact mechanics in both hoop and radial directions. Considering a classical wear criterion in a preliminary step, a contact ratio, that allows the mechanical power to be optimized, is pointed out in the hoop direction. In a further step, the contact conditions in the radial direction are improved through the elastic fitting of the stator and rotor radial deflexions, therefore allowing the material's wear to be decreased. Some experimental tests, that have been recently performed, give a comparison of wear marks, which occur onto optimal and non-optimal rotor geometries. A first mechanism synthesis is finally proposed in such a way to allow the mechanical architecture of the rotor (including the friction layer) to be automatically designed according to a given set of mechanical constraints.

Fabrication of CVD Diamond Optics with Antireflective Surface Structures

Polycrystalline CVD diamond is an excellent material for advanced optical applications, especially in the IR spectral range. However, one drawback of diamond is the significant reflection loss of 29%, caused by its high refraction index n = 2.4. We fabricated subwavelength, “moth-eye” antireflective structured (ARS) surfaces (two-dimensional array of pyramids) by filling with CVD diamond the inverted pyramids etched in a Si substrate, followed by the substrate removal to obtain the patterned diamond replica. An increase in IR transmission up to T = 80% was observed at wavelengths λ > 10 μm for the ARS surfaces compared to T = 71% for flat surfaces even at the non-optimized geometry of the surface relief. A further increase in transmission could be achieved by combining ARS and a single layer AR coating of amorphous carbon.

Cell geometry optimisation of 4H–SiC power UMOSFETs by electrothermal simulation

Technology computer aided design (TCAD) models for electrothermal simulation of 4H–SiC UMOSFET devices are used to show that: (1) temperature gradients along the highly resistive channels of UMOSFET devices are not significant and (2) neglecting electrothermal effects during cell design simulations can lead to a nonoptimal cell geometry, resulting in up to 45% degradation in device on-state resistance.

Effects of non-optimal acquisition geometry in myocardial perfusion imaging using Ectomography

Ectomography is a limited view angle method, which has been implemented by rotating a slant hole collimator in front of a stationary gamma camera detector. The system is mobile and can be used for acute perfusion studies. To achieve high image quality in myocardial perfusion imaging, the detector should be positioned perpendicular to the long axis of the left ventricle. The aim of this study is to investigate the effects of (1) misalignment of the detector head with respect to the left ventricle, (2) truncation of the myocardial projection images and (3) external activity. Phantom studies were performed with 5 different slant hole collimators. A heart phantom, containing two defects, was placed in a thorax phantom. Studies with different degree of misalignment were performed using a mobile tomographic gamma camera. Studies with external activity present, and truncation of the apex were also performed. Results show that moderate misalignment causes little influence on size and position of the defect in the reconstructed sections, neither does presence of external activity. Effects of apical truncation do not propagate into nontruncated regions. In conclusion, positioning of a mobile system based on Ectomography does not have to be perfect, allowing rapid positioning in acute situations.

Modulating carbon monoxide binding affinity and kinetics in myoglobin: the roles of the distal histidine and the heme pocket docking site

Myoglobin has long served as a model system for understanding the relations between protein structure, dynamics, and function. Its ability to discriminate between toxic CO and vital O2, two small ligands that are almost equivalent in size and dipole moment, has attracted much attention. To understand discrimination and reversible ligand-binding in Mb, both the bound state and the "docked" state that leads to binding need to be studied. We have reported previously the nearly linear Fe–C–O geometry of bound CO and the nearly orthogonal geometry of docked CO [Lim et al. (1995), Science 269 : 962]. With the exception of X-ray structures, a preponderance of evidence points to a nearly linear Fe–C–O geometry and calls into question the proposal that the highly conserved distal histidine forces CO to bind in a nonoptimal geometry. The differences between the bound CO structures determined using IR and X-ray methods might arise from a water molecule hydrogen bonded to the distal histidine in some of the unit cells. Discrimination by Mb is manifested not only thermodynamically but also kinetically. Time-resolved CO rebinding studies that compare Mb with microperoxidase suggest that the heme pocket docking site in Mb exerts steric control of the ligand rebinding rate, slowing the rate of CO binding by a factor of more than 104.

Conformation-dependent dipoles of liquid crystal molecules and fragments from first principles

We determine accurate molecular dipole moments for mesogenic fragments and liquid crystal molecules from quantum mechanical computer simulations adapted from large-scale electronic structure calculations on periodic solids. We employ density functional theory and use ab initio pseudopotentials for the interaction between valence electrons and ions and the generalized gradient approximation to account for the many-body effects of exchange and correlation. Periodic boundary conditions are enforced so that the molecular electronic wave function can be expanded in terms of a plane wave basis set. We test our method on several small molecules and then apply it to determine the direction, position and dipole moment magnitude for 4-4' pentyl-cyanobiphenyl (5CB) (and related fragments), phenyl benzoate, and 2-2'difluorobiphenyl. For the latter compound, we parametrize a torsional potential for rotation about the dihedral bond. We perform full structural optimization, and find that the torsional barrier heights for fully relaxed molecular structures are substantially reduced relative to nonoptimized geometries. We then demonstrate the influence of conformation and temperature on the molecular dipole moment. We also find that simple vector addition of dipole moments of fragments provides a good estimate of the total dipole moment of the complete molecule. We compare our results to experiment and to conventional quantum chemistry methods where data is available.

Vertical Si p-MOS transistor selectively grown by low pressure chemical vapour deposition

Low pressure chemical vapour deposition was used to define the channel length of vertical Si p-MOS transistors. Comparing to a conventional lateral transistor, the vertical structure is expected to enhance the packing density. The growth technique permits an easy reduction of the channel length without complex technological preparation steps. Besides, it allows a selective deposition in which facet growth occurs, which in turn leads to a thinner channel length compared to the distance between the two pn-junctions in the volume area. Therefore, the facet growth leads to a shift of the punch-through effect to higher voltages. Device characteristics of a non-optimized transistor geometry, on which the gate oxide is prepared after the epitaxial growth, with a channel length of approximately 250 nm and a gate oxide thickness of 12 nm, show a transconductance of 70 mS mm −1, an ideal sub-threshold behaviour of 100 mV dec −1, an off-current below 10 −12 A μm −2 and a breakthrough voltage | V D|>4 V. Devices with a preparation of the gate oxide before epitaxial growth have also been studied. These devices show a transconductance of 25 mS mm −1 for a gate oxide thickness of 40 nm.

Structural basis for the specific interaction of lysine-containing proline-rich peptides with the N-terminal SH3 domain of c-Crk.

Proline-rich segments in the guanine nucleotide exchange factor C3G bind much more strongly to the N-terminal Src homology 3 domain (SH3-N) of the proto-oncogene product c-Crk than to other SH3 domains. The presence of a lysine instead of an arginine in the peptides derived from C3G appears to be crucial for this specificity towards c-Crk. In order to understand the chemical basis of this specificity we have determined the crystal structure of Crk SH3-N in complex with a high affinity peptide from C3G (PPPALPPKKR, Kd approximately 2 microM) at 1.5 A resolution. The peptide adopts a polyproline type II helix that binds, as dictated by electrostatic complementarity, in reversed orientation relative to the orientation seen in the earliest structures of SH3-peptide complexes. A lysine in the C3G peptide is tightly coordinated by three acidic residues in the SH3 domain. In contrast, the co-crystal structure of c-Crk SH3-N and a peptide containing an arginine at the equivalent position (determined at 1.9 A resolution) reveals non-optimal geometry for the arginine and increased disorder. The c-Crk SH3 domain engages in an unusual lysine-specific interaction that is rarely seen in protein structures, and which appears to be a key determinant of its unique ability to bind the C3G peptides with high affinity.

Synthesis, configuration, and activity of isomeric 2-phenyl-2-(N-piperidinyl)bicyclo[3.1.0]hexanes at phencyclidine and sigma binding sites.

The novel semirigid derivatives (+)-cis-1-[2-phenyl-2-bicyclo[3.1.0]hexyl]piperidine [(+)-8], its enantiomer (-)-8, and (+-)-trans-1-[2-phenyl-2-bicyclo[3.1.0]hexyl]piperidine [(+/-)-9] were synthesized as probes to investigate the mode of interaction of phencyclidine (PCP) with its binding site on the N-methyl-D-aspartate receptor complex. Each target compound was obtained in five steps starting from cyclopent-2-enone. (+)- and (-)-8 were obtained in greater than 98% optical purity through three recrystallizations from ethanol of the (S)-(+)- and (R)-(-)-mandelate salts of intermediate (+-)-cis-2-phenyl-2-bicyclo[3.1.0]hexylamine ([(+/-)-16]. Crystallization of the (R)-(-)-mandelate salt afforded (1R,2R,5S)-(-)-16, whereas the (S)-(+)-mandelate salt afforded (1S,2S,5R)-(+)-16; the absolute configuration was determined by single-crystal X-ray analysis of (-)-16.(R)-(-)-mandelate. Single-crystal X-ray analysis of (+/-)-9-picrate confirmed its trans configuration and provided conformational data. (+)- and (-)-8 and (+/-)-9 were examined for their ability to interact with PCP and sigma binding sites in vitro using [3H]TCP and [3H]pentazocine as radioligands. The binding was compared with that of PCP and contrasted with the rigid symmetrical phencyclidine derivatives cis- and trans-1-[3-phenyl-3-bicyclo[3.1.0]hexyl]piperidines (6 and 7). The results of the study indicated that the conformations of PCP represented by 6-9 are not optimal for potent interaction at either of these sites. Affinities ranged from 582 nM [(+/-)-9] to 29,000 nM [(+)-8] at PCP binding sites and from 1130 nM [(-)-8] to 16,300 nM (7) at sigma sites. In this assay, PCP exhibited affinities of 64.5 nM at PCP and 1090 nM at sigma sites. Qualitative correlation between the sigma and PCP binding data suggests some similarities between these binding sites. An axial phenyl and equatorial piperidine ring with the nitrogen lone pair of electrons antiperiplanar to the phenyl ring has been postulated as the receptor-active conformation of PCP-like ligands at the PCP binding site. Comparison of the binding data of 7-9 with that of the previously described methylcyclohexyl-PCP derivatives allowed its rationalization in terms of this model. It is likely that the lowered affinity in this bicyclo[3.1.0]hexane series is a consequence of nonoptimal geometry (pseudoequatorial phenyl or pseudoboat) for binding as opposed to the presence of steric bulk which proved deleterious in the methylcyclohexyl-PCP derivatives.

Sterically congested polycyclic aromatic hydrocarbons with nonoptimal geometries. 4,5-Didehydroacenaphthene as a precursor for the synthesis of 7,14-diphenyl-8,9-(1',8'-naphthenylene)acephenanthrene

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSterically congested polycyclic aromatic hydrocarbons with nonoptimal geometries. 4,5-Didehydroacenaphthene as a precursor for the synthesis of 7,14-diphenyl-8,9-(1',8'-naphthenylene)acephenanthreneBenjamin F. Plummer, Steven R. Russell, W. Gregory Reese, William H. Watson, and Mariusz KrawiecCite this: J. Org. Chem. 1991, 56, 10, 3219–3223Publication Date (Print):May 1, 1991Publication History Published online1 May 2002Published inissue 1 May 1991https://doi.org/10.1021/jo00010a010RIGHTS & PERMISSIONSArticle Views242Altmetric-Citations18LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts