Search

The Martian bow shock position is known to be correlated with solar extreme ultraviolet irradiance. Since this parameter is also correlated with the evolution of the solar cycle, it is expected that the Martian bow shock position should also vary over such a period. However, previous reports on this topic have often proved contradictory. Using 13 years of observations of the Martian bow shock by the Mars Express mission over the period 2004 to 2017, we report that the Martian bow shock position does vary over the solar cycle. Over this period, our analysis shows the bow shock position to increase on average by 7% between the solar minimum and maximum phases of solar cycle 23–24, which could be even larger for more extreme previous solar cycles. We show that both annual and solar cycle variations play major roles in the location of the bow shock at Mars.

The Super Dual Auroral Radar Network (SuperDARN) is a network of High Frequency (HF) radars located in the high- and mid-latitude regions of both hemispheres that is operated under international cooperation. The network was originally designed for monitoring the dynamics of the ionosphere and upper atmosphere in the high-latitude regions. However, over the last approximately 15 years SuperDARN has expanded into the mid-latitude regions. With radar coverage that now extends continuously from auroral to sub-auroral and mid-latitudes a wide variety of new scientific findings have been obtained. In this paper, the background of mid-latitude SuperDARN is presented at first. Then the accomplishments made with mid-latitude SuperDARN radars are reviewed in five specified scientific and technical areas: convection, ionospheric irregularities, HF propagation analysis, ion-neutral interactions and magnetohydrodynamic (MHD) waves. Finally, the present status of mid-latitude SuperDARN is updated and directions for future research are discussed.

The statistics of unusually high rates of change in the horizontal component of the geomagnetic field (dB/dt) are a useful indicator of the likelihood of damaging geomagnetically induced currents (GIC) in ground-based infrastructure such as electricity networks. Using extreme value theory (Coles, 2001) we present a global model of the probability of extreme |dB/dt| based on several decades of measurements from 125 magnetometers worldwide, with time cadences (dt) ranging from 1 to 60 minutes. The occurrence rate of peaks in |dB/dt| above the 99.97th percentile is a function of magnetic latitude, magnetic local time, month, sunspot number, solar wind and interplanetary magnetic field conditions, and the direction of the field fluctuation. This information may be used to improve the extreme value model. The patterns of occurrence are presented and compared with previously studied distributions of Sudden Commencements, Pc5 ULF waves, and auroral substorm onsets, giving insight into the relative importance of these drivers in GIC modelling. Reference: S. Coles, An introduction to Statistical Modeling of Extreme Values, Springer-Verlag London ltd, 2001.

The orientation of field-aligned current sheets (FACs) can be inferred from dual-spacecraft correlations of the FAC signatures between two Swarm spacecraft (A and C), using the maximum correlations obtained from sliding data segments. Statistical analysis of both the correlations and the inferred orientations shows clear trends in magnetic local time (MLT) which reveal behaviour of both large and small scale currents. The maximum correlation coefficients show distinct behaviour in terms of either the time shift, or the shift in longitude between Swarm A and C for various filtering levels. The low-latitude FACs show the strongest correlations for a broad range of MLT centred on dawn and dusk, with a higher correlation coefficient on the dusk-side and lower correlations near noon and midnight. The current sheet orientations are shown to broadly follow the mean shape of the auroral boundary for the lower latitudes corresponding to Region 2 FACs and that these are most well-ordered on the dusk side. Together with these correlation trends, individual events have also been sampled by higher altitude spacecraft in conjunction with Swarm (mapping both to region 1 and 2), showing that two different domains of FACs are apparent: small-scale (some tens of km) which are time variable and large-scale (>100 km) which are rather stationary. We investigate further how these FAC regimes are dependent on geomagnetic activity, focusing on high activity events. The trends found here for different activities are compared to effects seen in the ground magnetometer signals (dH/dt).

The Super Dual Auroral Radar Network (SuperDARN) is a network of High Frequency (HF) radars located in the high- and mid-latitude regions of both hemispheres that is operated under international cooperation. The network was originally designed for monitoring the dynamics of the ionosphere and upper atmosphere in the high-latitude regions. However, over the last approximately 15 years SuperDARN has expanded into the mid-latitude regions. With radar coverage that now extends continuously from auroral to sub-auroral and mid-latitudes a wide variety of new scientific findings have been obtained. In this paper, the background of mid-latitude SuperDARN is presented at first. Then the accomplishments made with mid-latitude SuperDARN radars are reviewed in five specified scientific and technical areas: convection, ionospheric irregularities, HF propagation analysis, ion-neutral interactions and magnetohydrodynamic (MHD) waves. Finally, the present status of mid-latitude SuperDARN is updated and directions for future research are discussed.

The statistics of unusually high rates of change in the horizontal component of the geomagnetic field (dB/dt) are a useful indicator of the likelihood of damaging geomagnetically induced currents (GIC) in ground-based infrastructure such as electricity networks. Using extreme value theory (Coles, 2001) we present a global model of the probability of extreme |dB/dt| based on several decades of measurements from 125 magnetometers worldwide, with time cadences (dt) ranging from 1 to 60 minutes. The occurrence rate of peaks in |dB/dt| above the 99.97th percentile is a function of magnetic latitude, magnetic local time, month, sunspot number, solar wind and interplanetary magnetic field conditions, and the direction of the field fluctuation. This information may be used to improve the extreme value model. The patterns of occurrence are presented and compared with previously studied distributions of Sudden Commencements, Pc5 ULF waves, and auroral substorm onsets, giving insight into the relative importance of these drivers in GIC modelling. Reference: S. Coles, An introduction to Statistical Modeling of Extreme Values, Springer-Verlag London ltd, 2001.

The orientation of field-aligned current sheets (FACs) can be inferred from dual-spacecraft correlations of the FAC signatures between two Swarm spacecraft (A and C), using the maximum correlations obtained from sliding data segments. Statistical analysis of both the correlations and the inferred orientations shows clear trends in magnetic local time (MLT) which reveal behaviour of both large and small scale currents. The maximum correlation coefficients show distinct behaviour in terms of either the time shift, or the shift in longitude between Swarm A and C for various filtering levels. The low-latitude FACs show the strongest correlations for a broad range of MLT centred on dawn and dusk, with a higher correlation coefficient on the dusk-side and lower correlations near noon and midnight. The current sheet orientations are shown to broadly follow the mean shape of the auroral boundary for the lower latitudes corresponding to Region 2 FACs and that these are most well-ordered on the dusk side. Together with these correlation trends, individual events have also been sampled by higher altitude spacecraft in conjunction with Swarm (mapping both to region 1 and 2), showing that two different domains of FACs are apparent: small-scale (some tens of km) which are time variable and large-scale (>100 km) which are rather stationary. We investigate further how these FAC regimes are dependent on geomagnetic activity, focusing on high activity events. The trends found here for different activities are compared to effects seen in the ground magnetometer signals (dH/dt).

Nonhorizontal localized electron density structures associated with regions of near‐radial crustal magnetic fields are routinely detected via radar oblique echoes on the dayside of Mars with the ionospheric sounding mode of the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) radar onboard Mars Express. Previous studies mostly investigated these structures at a fixed plasma frequency and assumed that the larger apparent altitude of the structures compared to the normal surrounding ionosphere implied that they are bulges. However, the signal is subjected to dispersion when it propagates through the plasma, so interpretations based on the apparent altitude should be treated with caution. We go further by investigating the frequency dependence (i.e., the altitude dependence) of the shape of 48 density structure events, using time series of MARSIS electron density profiles corrected for signal dispersion. Four possible simplest shapes are detected in these time series, which can give oblique echoes: bulges, dips, downhill slopes, and uphill slopes. The altitude differences between the density structures and their edges are, in absolute value, larger at low frequency (high altitude) than at high frequency (low altitude), going from a few tens of kilometers to a few kilometers as frequency increases. Bulges dominate in numbers in most of the frequency range. Finally, the geographical extension of the density structures covers a wide range of crustal magnetic fields orientations, with near‐vertical fields toward their center and near‐horizontal fields toward their edges, as expected. Transport processes are suggested to be a key driver for these density structures.

The AuroraWatch UK aurora alert service uses a network of magnetometers from across the United Kingdom to measure the disturbance in the Earth's magnetic field caused by the aurora borealis (northern lights). The service has been measuring disturbances in the Earth's magnetic field from the UK and issuing auroral visibility alerts to its subscribers, since September 2000. These alerts have four levels, corresponding to the magnitude of disturbance measured, which indicate from where in the UK an auroral display might be seen. In the following, we describe the AuroraWatch UK system in detail and reprocess the historical magnetometer data using the current alert algorithm to compile an activity database. This data set is composed of over 150,000h (99.94% data availability) of magnetic disturbance measurements, including nearly 9,000h of enhanced geomagnetic activity. Plain Language Summary Witnessing the aurora borealis, more commonly known as the northern lights, is a much desired event, often featuring in people's "bucket lists." Although rarer than in more arctic regions, such as Scandinavia, Iceland, and Canada, the northern lights are seen from the UK too. To help with this aurora-hunting endeavor, the AuroraWatch UK service sends alerts to its followers when UK aurora sightings may be possible. The service has been running for 17 years and has over 100,000 subscribers. We have recorded over 150,000 h of magnetic field measurements including nearly 9,000 h where geomagnetic activity was large enough for an aurora to potentially be seen from at least some parts of the UK.

Nonhorizontal localized electron density structures associated with regions of near‐radial crustal magnetic fields are routinely detected via radar oblique echoes on the dayside of Mars with the ionospheric sounding mode of the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) radar onboard Mars Express. Previous studies mostly investigated these structures at a fixed plasma frequency and assumed that the larger apparent altitude of the structures compared to the normal surrounding ionosphere implied that they are bulges. However, the signal is subjected to dispersion when it propagates through the plasma, so interpretations based on the apparent altitude should be treated with caution. We go further by investigating the frequency dependence (i.e., the altitude dependence) of the shape of 48 density structure events, using time series of MARSIS electron density profiles corrected for signal dispersion. Four possible simplest shapes are detected in these time series, which can give oblique echoes: bulges, dips, downhill slopes, and uphill slopes. The altitude differences between the density structures and their edges are, in absolute value, larger at low frequency (high altitude) than at high frequency (low altitude), going from a few tens of kilometers to a few kilometers as frequency increases. Bulges dominate in numbers in most of the frequency range. Finally, the geographical extension of the density structures covers a wide range of crustal magnetic fields orientations, with near‐vertical fields toward their center and near‐horizontal fields toward their edges, as expected. Transport processes are suggested to be a key driver for these density structures.

The AuroraWatch UK aurora alert service uses a network of magnetometers from across the United Kingdom to measure the disturbance in the Earth's magnetic field caused by the aurora borealis (northern lights). The service has been measuring disturbances in the Earth's magnetic field from the UK and issuing auroral visibility alerts to its subscribers, since September 2000. These alerts have four levels, corresponding to the magnitude of disturbance measured, which indicate from where in the UK an auroral display might be seen. In the following, we describe the AuroraWatch UK system in detail and reprocess the historical magnetometer data using the current alert algorithm to compile an activity database. This data set is composed of over 150,000h (99.94% data availability) of magnetic disturbance measurements, including nearly 9,000h of enhanced geomagnetic activity. Plain Language Summary Witnessing the aurora borealis, more commonly known as the northern lights, is a much desired event, often featuring in people's "bucket lists." Although rarer than in more arctic regions, such as Scandinavia, Iceland, and Canada, the northern lights are seen from the UK too. To help with this aurora-hunting endeavor, the AuroraWatch UK service sends alerts to its followers when UK aurora sightings may be possible. The service has been running for 17 years and has over 100,000 subscribers. We have recorded over 150,000 h of magnetic field measurements including nearly 9,000 h where geomagnetic activity was large enough for an aurora to potentially be seen from at least some parts of the UK.

Total ionospheric Joule heating variations have been studied with special focus on the effect of ionospheric neutral winds. Electric field data from the Super Dual Auroral Radar Network (SuperDARN) have been combined with models for the neutral wind, ionospheric Pedersen conductivity and magnetic field to calculate two Joule heating components; the convection heating and wind correction terms. Due to the motion of a dusk-side neutral wind cell, semi-diurnal variations in the wind correction are shown to reduce heating at some universal times, whilst enhancing it at others. This means that the wind correction propagates into the total Joule heating, transforming the usual diurnal trend due to day-night conductivity changes into a semi-diurnal double peak, which becomes increasingly prominent at higher levels of geomagnetic activity. We show that there are significant contributions from the wind correction term across all seasons and activity levels which act to consistently modify Joule heating from that deduced using ion convection alone.

We present SuperDARN radar observations of ionospheric convection during substorms. Substorms were grouped according to their onset latitude, onset magnetic local time, and the prevailing sense of IMF BY. The radar observations were then sorted according to substorm group and average convection patterns produced. Here, we discuss the patterns corresponding to substorms with onsets occurring in the 65∘−67∘ onset latitude range, at either early (20 − 22h) or late (01 − 03h) magnetic local times, during intervals of either dominant positive or negative IMF BY. We show that the morphology of the convection patterns differs from that predicted by existing empirical models, with the location of the nightside convection throat being largely consistent with the location of substorm onset. The expected IMF BY-induced dawn-dusk convection asymmetry can be enhanced on the nightside when the substorm onset occurs at a fortuitous location, but can equally be removed or even reversed from this expected state. Thus the nightside convection asymmetries are seemingly unrelated to the instantaneous sense of IMF BY.

We describe a method of producing high-resolution models of the Earth’s combined external and induced magnetic field (EIMF) using the method of Empirical Orthogonal Functions (EOFs) applied to the SuperMAG archive of ground-based magnetometer data. EOFs partition the variance of a system into independent modes, allowing us to extract the spatiotemporal patterns of greatest dynamical importance without applying the a priori assumptions of other methods (such as spherical harmonic analysis, parameterised averaging, or multi-variate regression). We develop an approach based on that of Beckers and Rixen [2003] and use the EOF modes to infill missing data in a self-consistent manner. Applying our method to a north polar case study spanning February 2001 (chosen for its proximity to solar maximum and good data coverage), we demonstrate that 41.7% and 9.4% of variance is explained by the leading two modes, respectively describing the temporal variations of the Disturbance Polar types 2 and 1 (DP2 and DP1) patterns. A further 14.1% of variance is explained by four modes that describe separate aspects of the motion of the DP1 and DP2 systems. Thus, collectively over 65% of variance is described by the leading 6 modes and is attributable to DP1 and DP2. This attribution is based on inspection of the spatial morphology of the modes, and analysis of the temporal variation of the mode amplitudes with respect to solar wind measures and substorm occurrence. This study is primarily a demonstration of the technique and a prelude to a model spanning the full solar cycle.

We present SuperDARN radar observations of ionospheric convection during substorms. Substorms were grouped according to their onset latitude, onset magnetic local time, and the prevailing sense of IMF BY. The radar observations were then sorted according to substorm group and average convection patterns produced. Here, we discuss the patterns corresponding to substorms with onsets occurring in the 65∘−67∘ onset latitude range, at either early (20 − 22h) or late (01 − 03h) magnetic local times, during intervals of either dominant positive or negative IMF BY. We show that the morphology of the convection patterns differs from that predicted by existing empirical models, with the location of the nightside convection throat being largely consistent with the location of substorm onset. The expected IMF BY-induced dawn-dusk convection asymmetry can be enhanced on the nightside when the substorm onset occurs at a fortuitous location, but can equally be removed or even reversed from this expected state. Thus the nightside convection asymmetries are seemingly unrelated to the instantaneous sense of IMF BY.

Total ionospheric Joule heating variations have been studied with special focus on the effect of ionospheric neutral winds. Electric field data from the Super Dual Auroral Radar Network (SuperDARN) have been combined with models for the neutral wind, ionospheric Pedersen conductivity and magnetic field to calculate two Joule heating components; the convection heating and wind correction terms. Due to the motion of a dusk-side neutral wind cell, semi-diurnal variations in the wind correction are shown to reduce heating at some universal times, whilst enhancing it at others. This means that the wind correction propagates into the total Joule heating, transforming the usual diurnal trend due to day-night conductivity changes into a semi-diurnal double peak, which becomes increasingly prominent at higher levels of geomagnetic activity. We show that there are significant contributions from the wind correction term across all seasons and activity levels which act to consistently modify Joule heating from that deduced using ion convection alone.

We describe a method of producing high-resolution models of the Earth’s combined external and induced magnetic field (EIMF) using the method of Empirical Orthogonal Functions (EOFs) applied to the SuperMAG archive of ground-based magnetometer data. EOFs partition the variance of a system into independent modes, allowing us to extract the spatiotemporal patterns of greatest dynamical importance without applying the a priori assumptions of other methods (such as spherical harmonic analysis, parameterised averaging, or multi-variate regression). We develop an approach based on that of Beckers and Rixen [2003] and use the EOF modes to infill missing data in a self-consistent manner. Applying our method to a north polar case study spanning February 2001 (chosen for its proximity to solar maximum and good data coverage), we demonstrate that 41.7% and 9.4% of variance is explained by the leading two modes, respectively describing the temporal variations of the Disturbance Polar types 2 and 1 (DP2 and DP1) patterns. A further 14.1% of variance is explained by four modes that describe separate aspects of the motion of the DP1 and DP2 systems. Thus, collectively over 65% of variance is described by the leading 6 modes and is attributable to DP1 and DP2. This attribution is based on inspection of the spatial morphology of the modes, and analysis of the temporal variation of the mode amplitudes with respect to solar wind measures and substorm occurrence. This study is primarily a demonstration of the technique and a prelude to a model spanning the full solar cycle.

As known from previous studies on the solar quiet (Sq) variation of the geomagnetic field, the strength and pattern of ionospheric dynamo currents change significantly from day to day. The present study investigates the relative importance of two sources that contribute to the day-to-day variability of the ionospheric currents at middle and low latitudes. One is high-latitude electric fields that are caused by magnetospheric convection, and the other is atmospheric waves from the lower atmosphere. Global ionospheric current systems, commonly known as Sq current systems, are simulated using the National Center for Atmospheric Research thermosphere-ionosphere-mesosphere-electrodynamics general circulation model. Simulations are run for 1–30 April 2010 with a constant solar energy input but with various combinations of high-latitude forcing and lower atmospheric forcing. The model well reproduces geomagnetic perturbations on the ground, when both forcings are taken into account. The contribution of high-latitude forcing to the total Sq current intensity (Jtotal) is generally smaller than the contribution of wave forcing from below 30 km, except during active periods (Kp≥4), when Jtotal is enhanced due to the leakage of high-latitude electric fields to lower latitudes. It is found that the penetration electric field drives ionospheric currents at middle and low latitudes not only on the dayside but also on the nightside, which has an appreciable effect on the Dst index. It is also found that quiet time day-to-day variability in Jtotal is dominated by symmetric-mode migrating diurnal and semidiurnal tidal winds at 45–60° latitude at ∼110 km.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Architecture, 1987., Includes bibliographical references (leaves 92-94)., This thesis proposes a new tool for the designer that acts as an Intelligent adjunct In the design process. Architects express abstract concepts in physical concrete realities. The tools of the trade act as a medium through which to express these concepts; pencil. paper. models. Yet these tools do not allow for any intelligent discourse. While translating an abstract Idea into a physical object. a designer must keep track of complex associations between various elements within a design. As an idea becomes further developed. the associations between elements become more difficult to manage. On occasion matrices are employed to maintain a consistent relational system. yet complexity often forces design concepts to get distorted or lost. This thesis provides one solution; a method for to the management of this barrage of associative information. while still providing a stimulating design environment. With the proposed tool. a designer can use numerous media simultaneously; for our purposes digital video and an object-oriented graphics editor. The video environment acts as an analysis tool for exploring existing archetypes. In search of inherent themes. The graphics editor is a tool for synthesizing objects. creating a whole from a series of parts discovered in the video environment. The key to this tool is its ability to retain knowledge while acting as an intelligent adjunct in the design process. The designer operates with objects. These objects "know" what their behavior Is. and how to perform certain operations. Other attributes and relationships can also be attached to objects. or classes of objects. Compilation of both environments Is possible. due to a central knowledge base that maintains all the information from all objects. This single knowledge base allows objects In one environment to be shared by the other. creating an interactive environment between two Independent media. computers and video. and eliminating the bold line that separates the two., by Janet Elizabeth Gardner., M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Architecture, 1987., Includes bibliographical references (leaves 92-94)., This thesis proposes a new tool for the designer that acts as an Intelligent adjunct In the design process. Architects express abstract concepts in physical concrete realities. The tools of the trade act as a medium through which to express these concepts; pencil. paper. models. Yet these tools do not allow for any intelligent discourse. While translating an abstract Idea into a physical object. a designer must keep track of complex associations between various elements within a design. As an idea becomes further developed. the associations between elements become more difficult to manage. On occasion matrices are employed to maintain a consistent relational system. yet complexity often forces design concepts to get distorted or lost. This thesis provides one solution; a method for to the management of this barrage of associative information. while still providing a stimulating design environment. With the proposed tool. a designer can use numerous media simultaneously; for our purposes digital video and an object-oriented graphics editor. The video environment acts as an analysis tool for exploring existing archetypes. In search of inherent themes. The graphics editor is a tool for synthesizing objects. creating a whole from a series of parts discovered in the video environment. The key to this tool is its ability to retain knowledge while acting as an intelligent adjunct in the design process. The designer operates with objects. These objects "know" what their behavior Is. and how to perform certain operations. Other attributes and relationships can also be attached to objects. or classes of objects. Compilation of both environments Is possible. due to a central knowledge base that maintains all the information from all objects. This single knowledge base allows objects In one environment to be shared by the other. creating an interactive environment between two Independent media. computers and video. and eliminating the bold line that separates the two., by Janet Elizabeth Gardner., M.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Architecture, 1987., Includes bibliographical references (leaves 92-94)., This thesis proposes a new tool for the designer that acts as an Intelligent adjunct In the design process. Architects express abstract concepts in physical concrete realities. The tools of the trade act as a medium through which to express these concepts; pencil. paper. models. Yet these tools do not allow for any intelligent discourse. While translating an abstract Idea into a physical object. a designer must keep track of complex associations between various elements within a design. As an idea becomes further developed. the associations between elements become more difficult to manage. On occasion matrices are employed to maintain a consistent relational system. yet complexity often forces design concepts to get distorted or lost. This thesis provides one solution; a method for to the management of this barrage of associative information. while still providing a stimulating design environment. With the proposed tool. a designer can use numerous media simultaneously; for our purposes digital video and an object-oriented graphics editor. The video environment acts as an analysis tool for exploring existing archetypes. In search of inherent themes. The graphics editor is a tool for synthesizing objects. creating a whole from a series of parts discovered in the video environment. The key to this tool is its ability to retain knowledge while acting as an intelligent adjunct in the design process. The designer operates with objects. These objects "know" what their behavior Is. and how to perform certain operations. Other attributes and relationships can also be attached to objects. or classes of objects. Compilation of both environments Is possible. due to a central knowledge base that maintains all the information from all objects. This single knowledge base allows objects In one environment to be shared by the other. creating an interactive environment between two Independent media. computers and video. and eliminating the bold line that separates the two., by Janet Elizabeth Gardner., M.S.

An experimental analysis of a plastic model four -cell swept back wing is presented. The model is cantilevered with a massive root rib oriented 60° with the spars. Three other ribs are located perpendicular to the spars. The results were compared with results previously obtained from tests performed on an aluminum alloy model of the same structure. Spanwise stresses and deflections compared very well. Considerable error was observed in chordwise stresses and shear stresses due to lack of joint duplication at the root rib and a difference in Poisson's Ratio between the two materials., http://archive.org/details/experimentalanal1094512148, Lieutenant, United States Navy

Prior work has shown that the global earliest-deadline-first (GEDF) scheduling algorithm ensures bounded deadline tardiness on multiprocessors with no utilization loss; therefore, GEDF may be a good candidate scheduling algorithm for soft real-time workloads. However, such workloads are often implemented assuming an average-case provisioning, and in prior tardiness-bound derivations for GEDF, worst-case execution costs are assumed. As worst-case costs can be orders of magnitude higher than average-case costs, using a worst-case provisioning may result in significant wasted processing capacity. In this paper, prior tardiness-bound derivations for GEDF are generalized so that execution times are probabilistic, and a bound on expected (mean) tardiness is derived. It is shown that, as long as the total expected utilization is strictly less than the number of available processors, the expected tardiness of every task is bounded under GEDF. The result also implies that any quantile of the tardiness distribution is also bounded. The uploaded paper is from the upcoming RTAS. I would like to hear suggestions about how to ease the assumption of independent execution times in this analysis.