Equivalent Core Research Articles

High resolution measurements of carbon monoxide along a late Holocene Greenland ice core: evidence for in situ production

Abstract. We present high-resolution measurements of carbon monoxide (CO) concentrations from a shallow ice core of the North Greenland Eemian Ice Drilling project (NEEM-2011-S1). An optical-feedback cavity-enhanced absorption spectrometer (OF-CEAS) coupled to a continuous melter system performed continuous, online analysis during a four-week measurement campaign. This analytical setup generated stable measurements of CO concentrations with an external precision of 7.8 ppbv (1σ), based on repeated analyses of equivalent ice core sections. However, this first application of this measurement technique suffered from a poorly constrained procedural blank of 48 ± 25 ppbv and poor accuracy because an absolute calibration was not possible. The NEEM-2011-S1 CO record spans 1800 yr and the long-term trends within the most recent section of this record (i.e., post 1700 AD) resemble the existing discrete CO measurements from the Eurocore ice core. However, the CO concentration is highly variable (75–1327 ppbv range) throughout the ice core with high frequency (annual scale), high amplitude spikes characterizing the record. These CO signals are too abrupt and rapid to reflect atmospheric variability and their prevalence largely prevents interpretation of the record in terms of atmospheric CO variation. The abrupt CO spikes are likely the result of in situ production occurring within the ice itself, although the unlikely possibility of CO production driven by non-photolytic, fast kinetic processes within the continuous melter system cannot be excluded. We observe that 68% of the CO spikes are observed in ice layers enriched with pyrogenic aerosols. Such aerosols, originating from boreal biomass burning emissions, contain organic compounds, which may be oxidized or photodissociated to produce CO within the ice. However, the NEEM-2011-S1 record displays an increase of ~0.05 ppbv yr−1 in baseline CO level prior to 1700 AD (129 m depth) and the concentration remains elevated, even for ice layers depleted in dissolved organic carbon (DOC). Thus, the processes driving the likely in situ production of CO within the NEEM ice may involve multiple, complex chemical pathways not all related to past fire history and require further investigation.

A comparative theoretical study on core-hole excitation spectra of azafullerene and its derivatives

The core-hole excitation spectra-near-edge x-ray absorption spectroscopy (NEXAFS), x-ray emission spectroscopy (XES), and x-ray photoelectron spectroscopy (XPS) shake-up satellites have been simulated at the level of density functional theory for the azafullerene C59N and its derivatives (C59N)(+), C59HN, (C59N)2, and C59N-C60, in which the XPS shake-up satellites were simulated using our developed equivalent core hole Kohn-Sham (ECH-KS) density functional theory approach [B. Gao, Z. Wu, and Y. Luo, J. Chem. Phys. 128, 234704 (2008)] which aims for the study of XPS shake-up satellites of large-scale molecules. Our calculated spectra are generally in good agreement with available experimental results that validates the use of the ECH-KS method in the present work. The nitrogen K-edge NEXAFS, XES, and XPS shake-up satellites spectra in general can be used as fingerprints to distinguish the azafullerene C59N and its different derivatives. Meanwhile, different carbon K-edge spectra could also provide detailed information of (local) electronic structures of different molecules. In particular, a peak (at around 284.5 eV) in the carbon K-edge NEXAFS spectrum of the heterodimer C59N-C60 is confirmed to be related to the electron transfer from the C59N part to the C60 part in this charge-transfer complex.

Evaluation of a pump method for unbiased sampling of stream hyporheos

The applicability of a pump method for field surveys of hyporheos was investigated for taxon-specific collection bias by comparing a pump method with a core method in a shore area of the lower reach of Kizu River in Japan. A sampling bias index for the first 10 l of pump samples compared with 10 l hyporheic water (equivalent) core samples showed that the pump method underestimated the abundance of most taxa, except for the heliozoan Centrohelida. Animals were classified into three groups based on body size and sampling bias index; animals with small bodies and high sampling bias indices generally had flatness indices near 1.0. The animals were also classified into three groups based on patterns of reduction in serial fraction values in consecutive pumpings. Although Crustacea tended to be overrepresented in the pump samples, relative densities among them were comparable to those in the core samples, except for harpacticoid copepods. Animals with an intermediate reduction pattern had a similar relative abundance in the 50-l pump and 1,000-cm3 core samples, except for Crustacea and Centrohelida. The results suggest that by using an adequate taxon-dependent volume of water, the pump method is useful for examining the community composition of hyporheic fauna.

Simulation and Analysis for Current Transformers with DC Bias and Remnant Flux

The transfer characteristics of current transformers (CT) change due to DC bias, which directly impacts the accuracy of measurement and power metering. Based on equivalent circuit models and core magnetizing characteristic, qualitatively analysis current transformer saturation increase errors of CT. Transfer errors under DC bias and remnant flux are also obtained based on J-A model of CT in PSCAD/EMTDC and full-wave Fourier algorithm to show that the ratio error and phase displacement increase with the DC bias. Based on FFT spectrum analysis to identify remnant flux and DC bias provides scientific basis for error compensation of CT.

A layerwise/solid-element method of the linear static and free vibration analysis for the composite sandwich plates

In the traditional analysis schemes of the composite sandwich structures the core is firstly simplified as an equivalent anisotropic material and then modeled by the plates and shells theories. Its main disadvantage is that the equivalent core will result in large equivalent error especially in the key area and the thick core will further reduce the analysis accuracy of the plates and shells theories. Therefore, a layerwise/solid-element method (LW/SE) is proposed in this paper, in which the layerwise theory is used to model the behavior of the composite laminated facesheets while the eight-noded solid element is employed to discretize the core. Three models, the full model, the local model and the equivalent model, are presented to model the core. Several numerical examples are investigated and the static analysis and free vibration analysis of the composite sandwich plates are tested. The results of proposed method are in good agreement with those of 3D finite element model. A detailed comparative study is conducted to investigate the performance of three modeling schemes for static analysis and free vibration analysis problems.

Amdahl's law in the era of process variation

In this paper we propose to extend Amdahl's law for modelling multicores with process variation using simple mathematical techniques. We consider three major families of multicore processors - symmetric, asymmetric, and dynamic. We consider a conservative operating mode for setting the target frequency plain, and a more optimised method opt. Subsequently, we propose three separate corollaries to the standard Amdahl's law to model the performance of different multicore configurations with different modes of operation. We observe that most of the major trends published in prior work or the ones that we observe through Monte Carlo simulations can be explained by a simple hypothetical concept called an equivalent core. The crux of our approach is to look at a set of equivalent cores with no variation that have the same performance as the target system. It is much simpler and much more intuitive to reason in terms of equivalent cores. Along with being an effective analytical tool, it can be used to speed up a lot of heuristics, and can be exposed to higher level software for advanced scheduling decisions. Lastly, we validate our models with experiments on a real system, and the maximum error is limited to 8%.

Compression strength of stitched foam-core sandwich composites with impact induced damage

Compression-after-impact responses of sandwich structures composed of stitched foam core and woven face sheets have been investigated experimentally and numerically. In the impact experiment, the force-time curves are recorded and analyzed to study the impact response of stitched foam core sandwich structures. In the compression-after-impact test, the damage mechanism of stitched sandwich structures during compression loading is revealed. The compression cracks start from the impact-induced damage location and propagate perpendicular to the compression direction. The final failure of the structure is controlled by the crush of the woven skin in the upper panel. For the relatively densely stitched foam sandwich, more fiber resin columns embed in the stitched samples decrease the impact-induced damage in upper panel when subject to impact load and increase the stiffness and strength of the foam in the compression direction during the compression-after-impact test, causing an increase in compression strength of relatively densely stitched sandwich. The relationship of compression-after-impact strength with stitching density appears linear when the impact energy is small, since there is no perforation or penetration. In numerical simulation, multi-scale approach has been developed on evaluating the compression-after-impact strength of sandwich structures. The classical theory of homogenization is adapted and used by treating the foam strengthened by the glass fiber resin column as orthotropic equivalent core material whose elastic properties depended on each component and their volume participation. Then, a nonlinear finite element model using this approach is proposed. Good agreements between finite element model and experiment are found.

Theory of operation for differential ion mobility spectrometry without alpha

Using the Langevin equation for ion motion in the presence of a variable electric field, and expressing the collision frequency in a manner that conforms to scattering a polyatomic ion with an equivalent hard-sphere core, a relationship is derived for the compensation and dispersion fields in a differential ion mobility spectrometer (DIMS). For a conservative collision (no clustering or ion-neutral dissociation or rearrangement interactions), the compensation field depends on both even and odd powers of the dispersion field, and the relationship between both fields is independent of pressure when the fields are divided by the drift gas density. Because the first and most important approximation for the compensation field is proportional to the square of ion mobility under zero field conditions, the compensation field increases with the temperature of the drift gas, but the functional form for the temperature dependence involves higher order terms and requires additional knowledge of the temperature dependence for the collision cross section. Duty cycle curves for long-chain secondary ketones compare favorably to experiments using an asymmetric rectangular waveform for excitation.

Scattering loss in optical waveguide with trapezoidal cross section

To get the scattering loss of the trapezoidal core waveguide, a new analysis model is presented based on the perturbation equivalent method and modified effective-index method. Firstly, the trapezoidal core waveguide is successfully equivalent to the rectangular one with both restricting the same optical field energy by adopting the perturbation method. Then, the equivalent rectangular core waveguide is decomposed into two slab waveguides by employing the modified effective-index method. The trapezoidal core waveguide scattering theory model is established based on the slab waveguide scattering theory. With the sidewalls surface roughness in the range from 0 to 100 nm in the single model trapezodial core waveguide, optical simulation shows excellent agreement with the results from the scattering loss model presented. The relationship between the dimension and side-wall roughness with the scattering loss can be determined in the trapezoidal core waveguide by the scattering loss model.

New Model for Shear Failure of RC Beam-Column Interior Joints with Different Depth Beams

On the basis of the experiment of 12 abnormal joints with different depth beams, failure process, seismic capacity and construction measure of this kind of joints are analyzed. Shear strength and failure model of joints with equivalent core height are analyzed by using mathematical model based on quadruple flexural resistance. The model satisfies equilibrium equations relating magnitude of external forces such as column shear, beam shear and axial force in column, to the magnitude of stress resultants. The results show that the model can reasonably explain the reasons for joints failure, have explicit mathematical model and good agreement between experimental results and calculated results of this model is achieved.

The Compact Levitated Dipole Configuration for Plasma Confinement

A new magnetic configuration for magnetic confinement of fusion plasmas is proposed. This configuration is closely related to the levitated dipole configuration, and shares the same mechanism for plasma stability. The difference between the two configurations rests in the use of shaping coils to alter the far field region of the dipole field, resulting in greatly reduced total reactor volume given equivalent plasma parameters and core volume. In this paper we will discuss the magnetic geometry of the compact levitated dipole configurations and employ stability theory in the low beta limit to predict its properties.

Shear Behavior of Interior Joints with Different Depth Beams in RC Frame Structures

Six specimens of interior joints with different depth beams were tested under reversed cyclic loading. The failure characteristics and shear force versus shear angle skeleton curves of interior joints are analyzed. Based on the experimental study, an analytical model for equivalent joint core of abnormal joint under the combined action of axial load and shear is established, and the shear stress versus shear angle curves of equivalent joint core of tested specimens was calculated by using modified compression field theory (MCFT).Test results indicated that the first crack appeared in the minor core (determined by the low beam and the top column), and the final failure appeared in the large core (determined by the high beam and the bottom column). The critical crack load was quite nearly with the ultimate load of abnormal joints, and seismic behavior of beam-column joint sub-assemblage was poorer than that of ordinary joints. Good agreement between experimental results and prediction results is achieved.

X-ray absorption spectra of graphene from first-principles simulations

Near edge x-ray absorption fine-structure spectra of graphenes are calculated using hybrid density-functional theory with the equivalent core hole approximation, aiming to resolve the ongoing debat ...

Orientation of Si phthalocyanine investigated by X‐ray absorption spectroscopy and molecular orbital calculation

AbstractWe have investigated the orientation effect of silicon phthalocyanine dichloride evaporated on the highly oriented pyrolytic graphite (HOPG) surfaces using linearly polarized synchrotron radiation. Polarization angular dependences of Si 1s and Cl 1s near‐edge X‐ray absorption fine structure (NEXAFS) spectra were observed and compared with theoretical calculations based on equivalent core (Z + 1) approximation using the Hartree‐Fock molecular orbital method. The calculated properties are in agreement with the experimental spectra in symmetry, intensity and energy position. The intensities for the lowest energy peaks observed at both Si and Cl edges are enhanced when X‐ray electric field vector (E) is perpendicular to the surface. We assigned these peaks to out‐of‐plane transition into σz*(SiCl) final state orbital. We concluded that phthalocyanine plane is oriented parallel to the surface. Copyright © 2010 John Wiley & Sons, Ltd.

Bending Loss Evaluations of Holey Fibers Having a Core Consisting of an Elliptical-Hole Lattice by Various Approaches

In general, an accurate evaluation of the bending loss of an optical fiber with an arbitrary refractive index profile is a cumbersome task, especially for holey fibers (HFs). In this paper, various approaches are applied and compared for the bending loss evaluations of single-polarization elliptical-hole core circular-hole HFs (EC-CHFs), which are circular-hole HFs having a core with an elliptical-hole lattice structure. Our simulation results show that when bending loss formulas for weakly guiding circular fibers are applied to a HF by regarding it as an approximate circular fiber having an equivalent step-index (SI) profile, the definition of the core region is the most crucial issue. Moreover, we also show that the results obtained by the approximate approach based on the bending loss formulas for the equivalent SI circular fiber are in good agreement with direct approaches with numerical simulations for the real EC-CHF structure, if the equivalent core radius is suitably defined for the real cross section.

Model for three-phase induction motors with stator core faults

A new dynamic model for an induction motor (IM) in abc machine variables is proposed in this work. This model is able to represent asymmetrical stator core faults (SCF) by modelling them as the variation of the equivalent core loss resistance per phase. One model in qd0 variables and another one in sequence components are deduced and used as tools to analyse and simulate SCF. It is demonstrated that there is a good correlation between SCF severity and the magnitude of the IM stator negative sequence current, impedance and power. The comparison of simulation and experimental results suggests the validity of the theoretical proposal.

Steel Hexagonal Honeycomb Core Equivalent Elastic Moduli for Bridge Deck Sandwich Panels

Glass fiber-reinforced polymer (GFRP) materials possess inherently high strength-to-weight ratios, but their effective elastic moduli are low relative to civil engineering (CE) construction materials. While elastic modulus may be comparable to that of some CE materials, the lower shear modulus adversely affects stiffness. As a result, serviceability issues are what govern GFRP deck design in the CE bridge industry. An innovative solution to increase the stiffness of a commercial GFRP reinforced-sinusoidal honeycomb sandwich panel was proposed; this solution would completely replace the GFRP honeycomb core with a hexagonal honeycomb core constructed from commercial steel roof decking. The purpose of this study was to perform small-scale tests to characterize the steel hexagonal honeycomb core equivalent elastic moduli in an effort to simplify the modeling of the core. The steel core equivalent moduli experimental results were compared with theoretical hexagonal honeycomb elastic modulus equations from the literature, demonstrating the applicability of the theoretical equations to the steel honeycomb core. Core equivalent elastic modulus equations were then proposed to model and characterize the steel hexagonal honeycomb as applicable to sandwich panel design. The equivalent honeycomb core will enable an efficient sandwich panel stiffness design technique, both for structural analysis methods (i.e., hand calculations) and finite-element analysis procedures.

Impact of Die-to-Die and Within-Die Parameter Variations on the Clock Frequency and Throughput of Multi-Core Processors

A statistical performance simulator is developed to explore the impact of parameter variations on the maximum clock frequency (FMAX) and throughput distributions of multi-core processors in a future 22 nm technology. The simulator captures the effects of die-to-die (D2D) and within-die (WID) transistor and interconnect parameter variations on critical path delays in a die. A key component of the simulator is an analytical multi-core processor throughput model, which enables computationally efficient and accurate throughput calculations, as compared with cycle-accurate performance simulators, for single-threaded and highly parallel multi-threaded (MT) workloads. Based on microarchitecture designs from previous microprocessors, three multi-core processors with either small, medium, or large cores are projected for the 22 nm technology generation to investigate a range of design options. These three multi-core processors are optimized for maximum throughput within a constant die area. A traditional single-core processor is also scaled to the 22 nm technology to provide a baseline comparison. <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">The salient contributions from this paper are: 1) product-level variation analysis for multi-core processors must focus on throughput, rather than just FMAX, and 2) multi-core processors are more variation tolerant than single-core processors due to the larger impact of memory latency and bandwidth on throughput.</i> To elucidate these two points, statistical simulations indicate that multi-core and single-core processors with an equivalent total core area have similar FMAX distributions (mean degradation of 9% and standard deviation of 5%) for MT applications. In contrast to single-core processors, memory latency and bandwidth constraints significantly limit the throughput dependency on FMAX in multi-core processors, thus reducing the throughput mean degradation and standard deviation by ~50% for the small and medium core designs and by ~30% for the large core design. This improvement in the throughput distribution indicates that multi-core processors could significantly reduce the product design and process development complexities due to parameter variations as compared to single-core processors, enabling faster time to market for high-performance microprocessor products.

Homogenization of the core layer in stitched sandwich structures

After highlighting the improvement of the mechanical performances involved by transverse reinforcement implementation in previous several studies, the mechanical behavior of stitched sandwich structures is analytically approached in this paper. The final purpose of this work is a modeling of the elastic performances of these structures. To predict the in-plane behavior, the classical theory of sandwiches is adapted and used by treating the foam core strengthened by stitches as a homogenized volume. This approach leads to the creation of an orthotropic equivalent core material. Its elastic properties depend on each component and their volume participation. The comparison between simulated and experimental values is quite good. The main interest of the multi-scale approach concerns a predictive tool. Indeed, it becomes realistic to obtain the elastic properties of stitched sandwich according to the geometrical parameters of the stitches and the mechanical properties of the components.

Distinct site- and state-selective dissociation of methyl-trifluoroacetate observed in core-electron excitation at the oxygen K-edge region

Distinct site- and state-selective dissociation following the O1s core-excitation has been found in the gaseous molecules of methyl trifluoroacetate (MTFA). The site- and state-selective dissociation was examined by measuring the branching ratios of dominant CH3+ and CHO+ fragments. The branching ratios from MTFA showed that site-selective dissociation takes place via the excitation from the different atomic sites to the same π*CO resonance state, (O1sCO-1π*CO) and (O1sOMe-1π*CO). A pronounced O1sOMe site-selectivity was identified by a significant increment of CHO+ formation at the (O1sOMe→π*CO) band. The site-selectivity was also justified by an equivalent core approximation using the density functional theory calculation. State-selective dissociation was identified among the (O1sOMe-1π*CO), (O1sOMe-1σ*O-Me) and (O1sOMe-1σ*C-OMe) transitions originated from the same OMe core. State-selective production of CH3+ could be found at the (O1sOMe→σ*O-Me) band, whereas state-selective formation of CHO+ was observed at the (O1sOMe→π*CO) and (O1sOMe→σ*C-OMe) bands.