First-order Comparison Research Articles

Frozen no more, a case study of Arctic permafrost impacts of oil and gas withdrawal

Approximately 8100 km2 of Alaska are leased to the oil and gas industry for exploration and extraction. According to industry estimates, subsurface expansion from these leases could cover up to 130.2 km2 per pad. As industrial oil extraction activities increase across the thawing Alaskan permafrost, impacts on the permafrost environment will include rapid thaw, increased hydrological flux, and the release of climate warming greenhouse gases. Here, we use remote sensing and field observations to provide a first-order comparison of the direct impacts to the permafrost tundra from oil well pads, and the long-term consequences of a legacy oil pads on the warming North Slope of Alaska. We find that oil well pads on the permafrost accelerate permafrost degradation and persist despite remediation.

A Reevaluation of Cryolava Flow Evolution: Assumptions, Physical Properties, and Conceptualization.

Cryovolcanism has been invoked to explain numerous features observed on icy bodies. Many of these features show similar morphologies to volcanic features observed on Earth suggesting similar physics involved in their formation. Cryovolcanism lies at the intersection of volcanology and hydrology but as such, no one model from either discipline satisfactorily represents cryolava flow emplacement. We produced a new model for cryolava flow evolution that draws from both disciplines to track the physical, chemical, and thermal states of a hypothetical H2O-NaCl flow on a Europa-like body as it evolves away from the vent. This model is currently restricted to compositions on the water-rich side of this chemical system and only predicts emplacement up to the turbulent to laminar transition. Modeling the laminar regime and a broader compositional space will be dealt with separately. Concentrations between 5 and 23wt% (H2O-NaCl eutectic) and initial flow thicknesses of 0.1, 1, 10, and 100m were set as initial conditions. Model results suggest that flow may reach 40-60vol% solids before transitioning to laminar flow. The thermal budget for these flows is dominated by the heat loss from vaporization in the low-pressure environment. This model produces length to thickness aspect ratios, for the given compositions, that are broadly consistent with candidate cryovolcanic features on Ceres and Titan. These first-order comparisons are not ideal and suggest the need for future modeling of cryovolcanic features in at least two dimensions.

Two-stage procedure in a first-order autoregressive process and comparison with a purely sequential procedure

A two-stage procedure in a first-order autoregressive model is considered that investigates the point and the interval estimation of parameters based on the least squares estimator. The two-stage procedure is shown to be as effective as the best fixed-sample-size procedure. In this regard, the significant properties of the procedure, such as asymptotic risk efficiency, asymptotic efficiency, and asymptotic consistency, are established. A Monte Carlo simulation study is conducted to compare the performance of the two-stage procedure and the purely sequential procedure. Finally, real-time series data are considered to illustrate the applicability of the two-stage procedure.

A Compact, Reconfigurable, Multi-UWB Radar for Snow Thickness Evaluation and Altimetry: Development and Field Trials

We developed a portable ultra-wideband radar system capable of reconfigurable operation in multiple frequency bands (separate or simultaneous) spanning from microwaves through millimeter waves. The instrument provides a compact solution for fine-resolution measurements of elevation changes and superficial snow/firn thickness from low-altitude, mid-sized airborne platforms. In this article, we provide an overview of the radar system design and its performance during laboratory testing. We demonstrate its application in aerial surveys of snow layer thickness at S/C bands, dual-band airborne altimetry at Ku-/Ka-bands, and present first-order comparisons with coincident airborne lidar data.

Fast and Accurate Core Analysis by the Full-Immersion Pressure-Pulse Decay: Part 2—Practice and Demonstration

Summary This study continues the work of presenting a novel approach for making petrophysical assessments of tight core samples. This method, the full-immersion pressure-pulse decay (Hannon 2019), involves applying a rapid increase in pressure in a chamber surrounding the entire outer surface area of a cylindrical sample, shutting the system in, and monitoring the pressure decay in the chamber as it reaches a new equilibrium. A precursor article covered the numerical simulator designed to model flow through the sample, demonstrating its performance and accuracy in addition to providing a first-order comparison between the speed and shape of the pressure-decay responses of the full-immersion method with those of other similar transient methods. This study covers the parameter-estimation procedure and experimental verification through a proof-of-concept laboratory investigation. The investigations provided here demonstrate that under appropriate, achievable experimental conditions, the pressure data can be analyzed in such a way that returns an estimate of the porosity and apparent permeabilities both parallel and perpendicular to bedding from a single test performed on a single cylindrical sample. After determining these experimental conditions (the uniqueness window), this report outlines a data-inversion strategy to estimate the petrophysical properties (porosity, horizontal permeability, and vertical permeability) from each test. This strategy is put to the test through comparisons with measurements performed by a commercial core laboratory. A common set of samples recovered from an outcrop of a tight-gas sandstone formation were investigated using the full-immersion method, and their results are compared with those from conventional steady-state measurement procedures performed by the commercial laboratory. Comparisons between petrophysical characterizations of these samples, which had permeabilities between 25 nd and 2.3 μd, demonstrated close agreement in most cases. However, whereas steady-state measurements performed at the professional laboratory required 4 to 5 hours of testing time per measurement of a single permeability, similar assessments using the full-immersion technique, requiring approximately 5 to 10 minutes to complete, returned estimates of the horizontal and vertical permeability simultaneously. Additional analyses are provided to determine principal reasons of discrepancies in instances where agreement was not as strong. Based on lessons learned from these experiences, the report closes with suggestions on areas of improvement in the experimental approach. Once complete, these developments should propel this technology to fill a critical need to determine petrophysical properties (porosity and permeability) of tight rocks in a time-efficient manner and in a way that does not compromise their accuracy.

Next-generation, affordable SO2 abatement for coal-fired power generation - A comparison of limestone-based wet flue gas desulphurization and Sulfacid® technologies for Medupi power station

SYNOPSIS Coal is used to generate more than three-quarters of South Africa's electricity, while numerous coal-fired boilers are employed for steam generation in industrial processes. However, coal-fired power generation is responsible for the release of the largest quantities of SO2 emissions to the atmosphere and leads to detrimental health and welfare effects in communities in the proximity of coal-fired plants. The classical industrial SO2 abatement solution for the coal-fired power generation industry is wet flue gas desulphurization, which uses a limestone adsorbent and produces a gypsum by-product (WFGD L/G). In South Africa, due to the poor quality of the limestone the gypsum product is unsaleable and is co-disposed with coal ash. In comparison, the Sulfacid® process technology converts SO2 contained in industrial flue gas into saleable sulphuric acid using a catalytic process requiring only water and air. This process does not require limestone. The scale of the latest commercial applications of the Sulfacid® SO2 abatement technology in the chemical, fertilizer, and copper mining industries demonstrates the potential and readiness of this technology to be employed in the coal-fired electricity and steam production sectors. This paper provides a first-order direct comparison between the techno-economic aspects of the WFGD (L/G) and Sulfacid® technologies using the requirements specified for the 6 x 800 MWe Eskom coal-fired Medupi power station. The results indicate that affordable flue gas desulphurization technology exists that could be adopted by the South African industry to reduce SO2 emissions to legislative limits and beyond. Keywords: SO2 abatement, coal-fired power, and heat generation, sulphuric acid, wet fluidized gas desulphurization, Sulfacid®, waste-to-chemicals.

Towards 3D modelling of convection in planetesimals and meteorite parent bodies

ABSTRACT Observations of asteroid belt members, investigations of meteorites and thermal evolution models converge on the paradigm of the ubiquity of melting processes in the planetesimals of the early Solar system. At least partial melting of planetesimals that fulfilled size and accretion time requirements to surpass the solidus temperatures of metal and silicates led to the weakening of the rock due to the interstitial melt. A decrease of the viscosity relative to melt-free material facilitates solid-state convection on partially molten bodies. Additional melting can produce liquid-like layers with suspended particles, i.e. magma oceans. Thermal evolution models indicate that partially molten layers can occur in the interior of undifferentiated bodies and in silicate mantles of differentiated ones. They can exist before a magma ocean forms or after it solidifies and above a whole-mantle magma ocean or below a shallow magma ocean. Thus, convection is likely. Attempts to model and to quantify the effects of convection in planetesimals remain rare. This study discusses the possibility of solid-state convection in partially molten planetesimals, presents a first-order comparison of a 3D mantle convection model with a conduction model taking a Vesta-sized body as an example and illustrates the importance of convection for meteorite parent bodies.

VS30 and Spectral Response from Collocated Shallow, Active-, and Passive-Source VS Data at 27 Sites in Puerto Rico

Shear-wave velocity (VS) and time-averaged shear-wavevelocity to 30 m depth (VS30) are the key parameters used in seismic site response modeling and earth- quake engineering design. Where VS data are limited, available data are often used to develop and refine map-based proxy models of VS30 for predicting ground-motion intensities. In this paper, we present shallow VS data from 27 sites in Puerto Rico. These data were acquired using a multimethod acquisition approach consisting of noninvasive, collocated, active-source body-wave (refraction/reflection), active- source surface wave at nine sites, and passive-source surface-wave refraction micro- tremor (ReMi) techniques. VS-versus-depth models are constructed and used to calculate spectral response plots for each site. Factors affecting method reliability are analyzed with respect to site-specific differences in bedrock VS and spectral response. At many but not all sites, body- and surface-wave methods generally determine similar depths to bedrock, and it is the difference in bedrock VS that influences site ampli- fication. The predicted resonant frequencies for the majority of the sites are observed to be within a relatively narrow bandwidth of 1-3.5 Hz. For a first-order comparison of peak frequency position, predictive spectral response plots from eight sites are plot- ted along with seismograph instrument spectra derived from the time series of the 16 May 2010 Puerto Rico earthquake. We show how a multimethod acquisition approach using collocated arrays compliments and corroborates VS results, thus adding confi- dence that reliable site characterization information has been obtained.

The Large Sample Performance of a Maximum Likelihood Method for OFDM Carrier Frequency Offset Estimation

This paper is concerned with the performance analysis of a blind method for carrier frequency offset (CFO) estimation in OFDM systems. The method generates a maximum likelihood CFO estimate when message-carrying symbols and channel are assumed nonrandom. It has been observed in simulation that, when a large number of OFDM blocks are in use under noisy scenarios, the performance of the method does not achieve the corresponding Cramer-Rao lower bound (CRB) and is lower bounded by another (larger) CRB when symbols are assumed random. This phenomenon is caused by the inconsistency of nonrandom symbol estimates and is further verified by using first-order perturbation analysis and comparison with the two CRBs.

Crossbar NoCs Are Scalable Beyond 100 Nodes

We describe the design and layout of a radix-128 crossbar in 90 nm CMOS. The data path is 32 bits wide and runs at 750 MHz using a three-stage pipeline, while fitting in a silicon area as small as 6.6 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> by filling it at the 90% level. The control path occupies 7 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> next to the data path by filling it at 35% level, and reconfigures the data path once every three clock cycles. Next, we arrange 128 1 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> “user tiles” around the crossbar, forming a 150 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> die, and we connect all tiles to the crossbar via global links running on top of the tiles. Including the overhead of repeaters and flip flops on global links, the area cost of the crossbar is 11% of the die. Thus, we prove that crossbar networks-on-chips (NoCs) are small enough for radices exceeding by far the few tens of ports, that were believed to be the practical limit up to now, and reaching above 100 ports. We also attempt a first-order comparison between our crossbar and a model of a popular mesh NoC, and we find that our crossbar NoC increases performance when traffic is global and stressed, at the cost of worse performance when traffic is local and benign. Finally, we present an experimental cost analysis showing that crossbar area practically grows as <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</i> ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> ), as all wiring of the crossbar fits over its standard cells, while crossbar delay grows as O( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> √ <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">W</i> ) , as wire length increases with the perimeter of the crossbar.

Carboniferous high-pressure metamorphism of Ordovician protoliths in the Argentera Massif (Italy), Southern European Variscan belt

The age of high-pressure metamorphism is crucial to identify a suitable tectonic model for the vast Variscan orogeny. Banded H P granulites from the Gesso-Stura Terrain in the Argentera Massif, Italy, have been recently described (Ferrando et al., 2008) relicts of high-pressure metamorphism in the western part of the Variscan orogen. Bulk rock chemistry of representative lithologies reveals intermediate silica contents and calc-alkaline affinity of the various cumulate layers. Enrichment in incompatible elements denotes a significant crustal component in line with intrusion during Ordovician rifting. Magmatic zircon cores from a Pl-rich layer yield scattered ages indicating a minimum protolith age of 486 ± 7 Ma. Carboniferous zircons (340.7 ± 4.2 and 336.3 ± 4.1 Ma) are found in a Pl-rich and a Pl-poor layer, respectively. Their zoning, chemical composition (low Th/U, flat HREE pattern and Ti-in-zircon temperature) and deformation indicate that they formed during the high-pressure event before decompression and mylonitisation. The proposed age for high-pressure metamorphism in the Argentera Massif proves that subduction preceded anatexis by less than 20 Ma. The new data allow a first-order comparison with the Bohemian Massif, which is located at the eastern termination of the Variscan orogen. Similarities in evolution at either end of the orogen support a Himalayan-type tectonic model for the entire European Variscides.

Adding Environmental Gas Physics to the Semianalytic Method for Galaxy Formation: Gravitational Heating

Motivated by hydrodynamical simulations, we present results of an attempt to include more detailed gas physics within semianalytic models (SAMs) of galaxy formation, focusing on the role played by environmental effects. The main difference from previous SAMs is that we include heating of the intracluster medium (ICM) by the net surplus of gravitational potential energy released from gas that has been stripped from infalling satellites. Gravitational heating appears to be an efficient heating source able to prevent cooling in environments corresponding to dark matter halos more massive than M* at any given redshift because of the continued growth by mergers. The energy release by gravitational heating can match that by AGN feedback in massive galaxies and can exceed it in the most massive ones. However, there is a fundamental difference in the way the two processes operate. Gravitational heating becomes important at late times, when the peak activity of AGNs is already over, and it is very mass dependent. This mass dependency and time behavior gives the right trend to recover downsizing in the star formation rate of massive galaxies. We present a number of first-order comparisons of our model to well-established observations of galaxy properties, which can be summarized as follows. The cosmic star formation rate is reproduced well. In addition, the star formation episode of our model galaxies is a strong function of mass. Massive galaxies with M* > 1011 M☉ make most of their stars at look-back times of roughly 11 Gyr and show very low amounts of residual star formation at late times due to suppression by environmental effects. Furthermore, the luminosity function and color bimodality of the galaxy population are reproduced well.

Binary black hole coalescence in semianalytic puncture evolution

Binary black hole coalescence is treated semianalytically by a novel approach. Our prescription employs the conservative Skeleton Hamiltonian that describes orbiting Brill-Lindquist wormholes (termed punctures in numerical relativity) within a waveless truncation to the Einstein field equations [G. Faye, P. Jaranowski, and G. Sch\"afer, Phys. Rev. D 69, 124029 (2004)]. We incorporate, in a transparent Hamiltonian way and in Burke-Thorne gauge structure, the effects of gravitational radiation reaction into the above Skeleton dynamics with the help of 3.5PN accurate angular momentum flux for compact binaries in quasicircular orbits to obtain a semianalytic puncture evolution to model merging black hole binaries. With the help of the TaylorT4 approximant at 3.5PN order, we perform a first-order comparison between gravitational-wave phase evolutions in numerical relativity and our approach for equal-mass binary black holes. This comparison reveals that a modified Skeletonian reactive dynamics that employs flexible parameters will be required to prevent the dephasing between our scheme and numerical relativity, similar to what is pursued in the effective one-body approach. A rough estimate for the gravitational waveform associated with the binary black hole coalescence in our approach is also provided.

Inspiral, merger, and ring-down of equal-mass black-hole binaries

We investigate the dynamics and gravitational-wave (GW) emission in the binary merger of equal-mass black holes as obtained from numerical relativity simulations. The simulations were performed with an evolution code based on generalized harmonic coordinates developed by Pretorius, and used quasiequilibrium initial-data sets constructed by Cook and Pfeiffer. Results from the evolution of three sets of initial data are explored in detail, corresponding to different initial separations of the black holes, and exhibit between 2-8 GW cycles before coalescence. We find that to a good approximation the inspiral phase of the evolution is quasicircular, followed by a 'blurred, quasicircular plunge' lasting for about 1-1.5 GW cycles. After this plunge the GW frequency decouples from the orbital frequency, and we define this time to be the start of the merger phase. Roughly 10-15 M separates the time between the beginning of the merger phase and when we are able to extract quasinormal ring-down modes from gravitational waves emitted by the newly formed black hole. This suggests that the merger lasts for a correspondingly short amount of time, approximately 0.5-0.75 of a full GW cycle. We present first-order comparisons between analytical models of the various stages of the merger and the numericalmore » results--more detailed and accurate comparisons will need to await numerical simulations with higher accuracy, better control of systemic errors (including coordinate artifacts), and initial configurations where the binaries are further separated. During the inspiral, we find that if the orbital phase is well modeled, the leading order Newtonian quadrupole formula is able to match both the amplitude and phase of the numerical GW quite accurately until close to the point of merger. We provide comparisons between the numerical results and analytical predictions based on the adiabatic post-Newtonian (PN) and nonadiabatic resummed-PN models (effective-one-body and Pade models). For all models considered, 3PN and 3.5PN orders match the inspiral numerical data the best. From the ring-down portion of the GW, we extract the fundamental quasinormal mode and several of the overtones. Finally, we estimate the optimal signal-to-noise ratio (SNR) for typical binaries detectable by GW experiments. We find that, when the merger and ring-down phases are included, binaries with total mass larger than 40M{sub {center_dot}} (sources for ground-based detectors) are brought in band and can be detected with signal-to-noise up to {approx_equal}15 at 100 Mpc, whereas for binaries with total mass larger than 2x10{sup 6}M{sub {center_dot}} (sources for space-based detectors) the SNR can be {approx_equal}10{sup 4} at 1 Gpc.« less

International railway comparisons

This technical note presents data on international railway comparisons. It is intended as a general introduction to some of the main themes and problems of international comparisons. The authors provide a selection of time series data for a set of countries and an extensive collection of reference sources on international rail statistics. Interesting general conclusions on first-order comparisons are highlighted. Key economics-based references for those wishing to study the subject in depth are provided at the end.

On the theoretical comparison of low-bias steady-state estimators

The time-average estimator is typically biased in the context of steady-state simulation, and its bias is of order 1/ t , where t represents simulated time. Several “low-bias” estimators have been developed that have a lower order bias, and, to first-order, the same variance of the time-average. We argue that this kind of first-order comparison is insufficient, and that a second-order asymptotic expansion of the mean square error (MSE) of the estimators is needed. We provide such an expansion for the time-average estimator in both the Markov and regenerative settings. Additionally, we provide a full bias expansion and a second-order MSE expansion for the Meketon--Heidelberger low-bias estimator, and show that its MSE can be asymptotically higher or lower than that of the time-average depending on the problem. The situation is different in the context of parallel steady-state simulation, where a reduction in bias that leaves the first-order variance unaffected is arguably an improvement in performance.

Non-linear mixture models for cross-sectional financial log returns

High-frequency financial log returns are known to exhibit sharp departures from the usual normality assumption. This article carries out an in-depth evaluation of the effectiveness of multidimensional non-linear mixed models that arise from considering a scale mixture-based approach to modeling non-normal log returns over a cross-sectional period of time. Simulation-based first-order and second-order comparison measures that compare the non-linear mixed model with the linear model show strong preference in favour of the non-linear mixed models. The methodology is illustrated through a thorough analysis of quarterly intra-day log returns from CISCO, DELL, COKE, and S&P500 for the years 1998–2000.

First-Order Performance Prediction of Cache Memory with Wafer-Level3D Integration

The advantages of 3D design can be exploited by reducing the memory access time. In this article, the authors use a simulator based on analytical models to build an optimal processor-memory configuration for two designs: a graphics processor and a microprocessor. One emerging alternative approach to relieving these interconnect constraints is the use of wafer-level 3D integration, which provides a high density of high-performance, low-parasitic vertical interconnects. A wafer-level 3D design is partitionable into multiple chips connected by short vertical vias. This arrangement reduces the length of many global interconnects without introducing any logic complexity. Wafer-level 3D integration also reduces the required number of repeaters, thereby improving the area efficiency and reducing the power consumed within the interconnect network. With micron-size interwafer vias, wafer-level 3D integration allows a large memory bandwidth with little wafer area consumption. We have developed a software program that allows a first-order comparison of cache designs in 2D and 3D IC technologies. We present a first-order estimate of the performance improvements achieved by 3D implementation of cache memory, with emphasis on large caches in deep-submicron technologies.

Holographic data storage: optimized scheduling using the nonlocal polymerization-driven diffusion model

The choice of an exposure schedule that maximizes the uniformity and capacity of a holographic recording medium is of critical importance in ensuring the optimum performance of any potential holographic data storage scheme. We propose a methodology to identify an optimum exposure schedule for photopolymer materials governed by the nonlocal polymerization-driven diffusion model. Using this model, the relationship between the material properties (nonlocality and nonlinearity), the recording conditions and the schedule are clarified. In this way, we provide a first-order comparison of the behavior of particular classes of photopolymer materials for use as holographic storage media. We demonstrate, using the nonlocal polymerization-driven diffusion model, that the exposure schedule is independent of the number of gratings to be recorded and that the optimum schedule may necessitate leaving unpolymerized monomer at the end of the recording process.

Test of a ridge–plume interaction model using oceanic crustal structure around Iceland

Segmentation of oceanic crust by fracture zones is controlled both by asthenosphere temperature and by spreading geometry at the time of crustal formation. South of Iceland, young crust adjacent to the Reykjanes Ridge and old crust adjacent to the continental margins is smooth and unsegmented, while intermediate age crust is segmented. The older part of the boundary between segmented and unsegmented crust is coincident with magnetic chron 17 (end Middle Eocene time) and was principally controlled by a coeval change in spreading obliquity of 30°. The younger part of the boundary has moved outwards from Iceland by 500 km between Late Eocene time and the present. The shape of this diachronous part of the boundary is principally controlled by asthenosphere temperature and probably records the position of a critical asthenosphere isotherm in the head of the Iceland Plume. The planform geometry of the diachronous boundary is well matched by a scaling law which predicts the spread of hot plume material along the ridge (or ‘waist width’) if the Iceland Plume is assumed fixed relative to other Indo-Atlantic hotspots. This match suggests that the apparent increase in the size of the Iceland Plume head since Late Eocene time can be explained by westward migration of the Reykjanes Ridge relative to the centre of a plume of constant flux on timescales over 8 Myr. Comparison of observed and predicted waist widths provides a constraint on plume volume flux and allows a direct first-order comparison between Iceland and Hawaiian Plume fluxes.