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Irregular access patterns are a major problem for today's optimizing compilers. In this paper, a novel approach will be presented that enables transformations that were designed for regular loop structures to be applied to linked ...
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Irregular access patterns are a major problem for today's optimizing compilers. In this paper, a novel approach will be presented that enables transformations that were designed for regular loop structures to be applied to linked list data structures. This is achieved by linearizing access to a linked list, after which further data restructuring can be performed. Two subsequent optimization paths will be considered: annihilation and sublimation, which are driven by the occurring regular and irregular access patterns in the applications. These intermediate codes are amenable to traditional compiler optimizations targeting regular loops. In the case of sublimation, a run-time step is involved which takes the access pattern into account and thus generates a data instance specific optimized code. Both approaches are applied to a sparse matrix multiplication algorithm and an iterative solver: preconditioned conjugate gradient. The resulting transformed code is evaluated using the major compilers for the x86 platform, GCC and the Intel C compiler.
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Diffuse nutrient loss from agriculture is degrading surface and groundwater quality throughout Europe, leaving water bodies at risk of not reaching targets set by the Water Framework Directive (WFD). Mitigation methods to reduce d...
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Diffuse nutrient loss from agriculture is degrading surface and groundwater quality throughout Europe, leaving water bodies at risk of not reaching targets set by the Water Framework Directive (WFD). Mitigation methods to reduce diffuse agricultural nutrient loss need to be implemented where water bodies have been identified as at risk of not reaching good status by 2015. Though the effectiveness of individual mitigation methods has usually been assessed in controlled experiments, it is necessary to quantify impact under a wider range of environmental and agricultural conditions and at the catchment scale to ensure that action taken now will be sufficient to meet WFD targets. Due to catchment buffering and long transit times (＞ 50 years), it is unlikely that responses to intervention will be observed by 2015 in many water bodies. In this review, we compare the attributes and usefulness of different approaches (direct measurement, nutrient budgeting, risk assessment and modelling) to assess the efficacy of actions to mitigate sources and transport of nitrogen (N) and phosphorus (P) from agricultural land to water. Modelling and 'measured changes in farm activity' through budgeting avoid the time lags associated with direct measurement and enable rapid evaluations of different options before implementation. Budgeting approaches using on-farm data also provide a simpler, more communicable means of assessment but currently fail to consider the timing and transport aspects of mitigation and assume a direct causal relationship between potential and actual nutrient loss. Risk assessment and modelling applications are potentially more comprehensive and able to better reflect choice of mitigation at a range of scales, but assessments demand increased availability of data, and there is a large degree of uncertainty associated with their spatial and temporal dimensions which is difficult to validate adequately. The failings of individual approaches suggest that these assessment methods should be integrated to maximise their potential usefulness and positive attributes. This will enable nutrient inputs to be utilised most efficiently at broad scales and site specific actions to reduce nutrient transport and delivery can be targeted most cost-effectively at smaller scales. Such an integrated approach will also more effectively engage and involve the farmer in what must be an iterative process.
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Heat flow patterns in the presence of natural convection have been analyzed with Bejan's heatlines concept. Momentum and energy transfer are characterized by streamfunctions and heatfunctions, respectively such that streamfunction...
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Heat flow patterns in the presence of natural convection have been analyzed with Bejan's heatlines concept. Momentum and energy transfer are characterized by streamfunctions and heatfunctions, respectively such that streamfunctions and heatfunctions satisfy the dimensionless forms of momentum and energy balance equations, respectively. Finite element method has been used to solve the velocity and thermal fields and the method has also been found robust to obtain the streamfunction and heatfunction accurately. The unique solution of heatfunctions for situations in differential heating is a strong function of Dirichlet boundary condition which has been obtained from average Nusselt numbers for hot or cold regimes. The physical significance of heatlines have been demonstrated for a comprehensive understanding of energy distribution and optimal thermal management via analyzing three cases. Case 1 involves the uniform and non-uniform heating of bottom wall with cooled side walls. The studies illustrate that the heat flow primarily occurs from the central regime of the bottom wall to a very small regime of the top portion of side walls. A large portion of central regime of cold side walls do not receive significant amount of heat. In order to maximize the thermal energy distribution, the distributed heating at the middle portions of the bottom and side walls have been considered in case 2 and heatlines clearly depict the distributions of heat from the hot walls to the large regimes of the cold wall. Further case 3 illustrates the enhanced heat flows in presence of heated bottom and left side walls. Heatline is found as an effective numerical tool to visualize energy distribution in order to establish a suitable heating strategy.
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Time-resolved optical spectroscopy has been used to measure the shock pressure steadiness, emissivity, and temperature of liquid deuterium shocked to 22-90 GPa. The shock was produced using magnetically accelerated flyer plate imp...
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Time-resolved optical spectroscopy has been used to measure the shock pressure steadiness, emissivity, and temperature of liquid deuterium shocked to 22-90 GPa. The shock was produced using magnetically accelerated flyer plate impact, and spectra were acquired with a suite of four fiber-optic-coupled spectrometers with streak camera detectors. The shock pressure changes by an average of -1.2% over the 10-30 ns cell transit time, determined from the relative changes in the shock front self-emission with time. The shock front reflectivity was measured from 5140 A and 5320 A laser light reflected from the D_2 shock. The emissivity inferred from the reflectivity measurements was in reasonably good agreement with quantum molecular dynamics simulation predictions. The spectral radiance wavelength dependence was found to agree well (average normalized χ~2=1.6) with a Planckian multiplied by the emissivity. The shock front temperature was determined from the emissivity and the wavelength-dependent shock self-emission. Thirty-seven temperature measurements spanning the 22-90 GPa range were accumulated. The large number of temperature measurements enables a comparison of the scatter in the data with expectations for a Gaussian distribution. This facilitates determination of uncertainties that incorporate both apparatus contributions and otherwise unquantified systematic effects that cause self-emission variations from one experiment to another. Agreement between temperatures determined from the absolute spectral radiance and from the relative shape of the spectrum further substantiates the absence of systematic biases. The weighted mean temperature uncertainties were as low as ±3-4%, enabling the discrimination between competing models for the D_2 equation of state (EOS). The temperature results agree well with models that predict a maximum compression of ～4.4. Softer models that predict approximately sixfold compression are inconsistent with the data to a very high statistical confidence level. Previous analysis [D. Saumon and T. Guillot, Astrophys. J. 609, 1170 (2004)] of Jupiter's internal structure has shown that the core mass is restricted to be less than approximately three times the mass of the Earth, if EOS models consistent with these temperature measurements are employed.
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We review how a magnetic-resonance force microscope (MRFM) can be applied to perform ferromagnetic resonance spectroscopy of individual submicron-size samples. We restrict our attention to a thorough study of the spin-wave eigenmo...
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We review how a magnetic-resonance force microscope (MRFM) can be applied to perform ferromagnetic resonance spectroscopy of individual submicron-size samples. We restrict our attention to a thorough study of the spin-wave eigenmodes excited in Permalloy (Py) disks patterned out of the same 43.3-nm-thin film. The disks have a diameter of either 1.0 or 0.5 μm and are quasisaturated by a perpendicularly applied magnetic field. It is shown that quantitative spectroscopic information can be extracted from the MRFM measurements. In particular, the data are extensively compared with complementary approximate models of the dynamical susceptibility: (ⅰ) a two-dimensional analytical model, which assumes a homogeneous magnetization dynamics along the thickness, and ⅱ) a full three-dimensional micromagnetic simulation, which assumes a homogeneous magnetization dynamics below a characteristic length scale c and approximates the cylindrical sample volume by a discretized representation with regular cubic mesh of lateral size c=3.9 nm. In our analysis, the distortions due to a breaking of the axial symmetry are taken into account; both models incorporating the possibility of a small misalignment between the applied field and the normal of the disks.
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The effect of β-iron intermetallics and porosity on the tensile properties in cast Al-Si-Cu and Al-Si-Mg alloys were investigated for this research study, using experimental and industrial 319.2 alloys, and industrial A356.2 allo...
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The effect of β-iron intermetallics and porosity on the tensile properties in cast Al-Si-Cu and Al-Si-Mg alloys were investigated for this research study, using experimental and industrial 319.2 alloys, and industrial A356.2 alloys. The results showed that the alloy ductility and ultimate tensile strength (UTS) were subject to deterioration as a result of an increase in the size of P-iron intermetallics, most noticeable up to P-iron intermetallic lengths of ～100 μm in 319.2 alloys, or ～70 μm in A356.2 alloys. An increase in the size of the porosity was also deleterious to alloy ductility and UTS. Although tensile properties are interpreted by means of UTS vs. log elongation plots in the present study, the properties for all sample conditions were best interpreted by means of log UTS vs. log elongation plots, where the properties increased linearly between conditions of low cooling rate-high Fe and high cooling rate-low Fe. The results are explained in terms of the β-Al_5FeSi platelet size and porosity values obtained.
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The objective of this research was to develop a community carbon footprint model that could be used to assess the size and major components of a community's carbon dioxide (CO_2) emissions. The town of Biggar aims to become Scotla...
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The objective of this research was to develop a community carbon footprint model that could be used to assess the size and major components of a community's carbon dioxide (CO_2) emissions. The town of Biggar aims to become Scotland's first carbon neutral town. As expected for this rural community, car transport accounted for nearly half of the CO_2 emissions, with natural gas and electricity consumption resulting in a further 24% and 12% of total emissions, respectively, and air travel being the last major component at 10% of emissions. An assessment was also made of the wind and solar resources of the town. One large wind turbine would provide the town's electricity, while three to four turbines would be needed to offset all CO_2 emissions. In contrast, offsetting by tree planting would require in the region of 2,000 ha of trees.
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We analyzed 151 organohalogen chemicals (OHCs) in whole blood and subcutaneous fat of 57 polar bears sampled along the Alaskan Beaufort Sea coast in spring, 2003. All major organochlorine pesticides, PCBs, PBDEs and their congener...
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We analyzed 151 organohalogen chemicals (OHCs) in whole blood and subcutaneous fat of 57 polar bears sampled along the Alaskan Beaufort Sea coast in spring, 2003. All major organochlorine pesticides, PCBs, PBDEs and their congeners were assessed. Concentrations of most OHCs continue to be lower among Southern Beaufort Sea polar bears than reported for other populations. Additionally, toxaphenes and related compounds were assessed in adipose tissue, and 8 perflourinated compounds (PFCs) were examined in blood. Perfluorooctane sulfonate (PFOS) concentrations exceeded those of any other contaminant measured in blood. SChlordane concentrations were higher in females, and both EPCBs and EChlordane concentrations in adipose tissue decreased significantly with age. The rank order of OHC mean concentrations; ΣPCB ＞ Σ10PCB ＞ PCB153 ＞ ΣChlordane> Oxychlordane ＞ PCB180 ＞ ΣHCH ＞ β-HCH＞ ΣDDT ＞ p,p-DDE ＞ ΣPBDE ＞ HCB ＞ Toxaphene was similar for compounds above detection limits in both fat and blood. Although correlation between OHC concentrations in blood and adipose tissue was examined, the predictability of concentrations in one matrix for the other was limited.
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The Pribilof Islands form a unique ecosystem. An anti-cyclonic oceanic flow exists around the islands. Nutrients are introduced into this circulation from two sources: (1) the flow along the 100-m isobath with intrusions of nutrie...
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The Pribilof Islands form a unique ecosystem. An anti-cyclonic oceanic flow exists around the islands. Nutrients are introduced into this circulation from two sources: (1) the flow along the 100-m isobath with intrusions of nutrient-rich water in Pribilof Canyon, and (2) the westward transport and vertical mixing of middle-shelf water, which contains nutrient-rich bottom water. Enhanced tidal mixing around the Pribilofs introduces this deeper, nutrient-rich water into the euphotic zone and thus supports prolonged production around the islands. Further, the middle-shelf water that is advected into the region causes the upper 50 m of the water column around the islands to freshen throughout the summer. This enhances the frontal structure and strengthens the baroclinic flow along the 100-m isobath. The strengthening of the frontal structure can moderate ecosystem productivity by limiting the intrusion of slope water rich in nutrients and oceanic copepods.
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Measurements of nutrients, primary (~(14)C) productivity and new (nitrate) productivity collected in the southeastern Bering Sea in July and August 2004 together with measurements from July 1981 are used to characterize the region...
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Measurements of nutrients, primary (~(14)C) productivity and new (nitrate) productivity collected in the southeastern Bering Sea in July and August 2004 together with measurements from July 1981 are used to characterize the regional production system during summer and to analyze the major physical and nutrient factors controlling biological patterns. The patterns of surface productivity suggested by the two different summers were remarkably similar in the regions of data overlap and agree with recent compilations of summer conditions from remotely sensed data. Summer was characterized by low production in the middle and outer shelf associated with surface mixed layers that were stabilized by heat. Elevated productivity was restricted to regions associated with the surface expression of thermohaline fronts, as well as to tidally mixed regions adjacent to and between the Pribilof Islands. Based on Chl a and productivity measurements, the biological impact of the shelf-break front of the southeastern Bering Sea extends at least as far inshore as the Pribilof Islands. The existence of elevated summer productivity associated with a recently identified shelf-partition front between the Pribilof domain and the middle shelf domain east of St. Paul Island was confirmed, and its thermohaline nature resulting from cumulative intrusions of slope-derived water is described. Yearly estimates of new and primary productivity compiled for the various biophysical regimes range from > 1800 mmol N m~(-2) yr~(-1) and > 170 g C m~(-2) yr~(-1) at the shelf-break front to less than 700 mmol N m~(-2) yr~(-1) and 100 g C m~(-2) yr~(-1) in oceanic and coastal waters. We hypothesize that trace metals, rather than macronutrients or grazing, likely restrict the seaward extent of elevated production at the shelf-break front. Iron may be supplied to the front by isopycnal mixing from deeper shelf waters that were in contact with sediments. By extending elevated production throughout the summer, the thermohaline and tidal fronts enhance the coupling of primary production to epipelagic food webs for the large populations of fish, birds and mammals in the region. Changes in the intensity or location of these frontal systems may impact populations that forage in them from the nearby Pribilof Islands.
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