Adapting Critical Chain Project Management to Army Engineer Construction Projects

For decades, Army Engineers have utilized the systems of the Critical Path Method (CPM) and multi-level Gantt chart planning system for its construction projects. While these methods are well accepted, they are not without their flaws. Research and literature in project management has given weight to several viable alternative options to planning projects. One such option, Critical Chain Project Management (CCPM), was developed to address the flaws of CPM by offering a holistic approach to project management based on strict resource control and the use of time buffers. This method attempts to eliminate multitasking and procrastination that can plague efficiency and offer managers more flexibly on tasks that otherwise had no leeway. CCPM may give project managers more flexibility and control while at the same time shortening the overall length of a project, saving time and money. The purpose of this thesis was to address the time saving and resource management benefits of utilizing CCPM over CPM and analyze the viability of those benefits being applied to U.S. Army Corps of Engineers construction project planning. Through the use of surveys of Army Engineer project supervisors, several key factors that cause delays because of CPM were identified and rated. The validity of CCPM based solutions to the same issues were also assessed by Army project supervisors in the survey. Analysis of the survey results indicated that CCPM may offer solutions to major issues that Army project supervisors face

JOINT STIFFNESS IN OLD AND YOUNG RUNNERS DURING SHOD AND BAREFOOT RUNNING

The purpose of this study was to investigate the relationship between ankle and knee joint stiffness in barefoot and shod running. Fifteen old and 15 young individuals served as participants in this study. Joint kinematics and kinetics were collected while the participants ran overground in two running conditions: barefoot and shod. A quasi-joint stiffness was calculated using the quotient of the change in moment divided by the change in angle for the ankle and knee joints. A two-way ANOVA was conducted to asses ankle and knee joint stiffnesses. There were no interactions and no main effects for the knee joint stiffness. For the ankle joint, there was only a significant difference between conditions. These results indicate that in barefoot running, it is necessary to have a more compliant ankle to maintain the heel from touching the ground

Which is the primary factor influencing running stride parameters: age or lower limb strength?

Much still remains unknown about the impact of age, and age-related changes in muscle function, on gait parameters. The aim of this study was to examine the impact of strength on running gait parameters across the adult lifespan. We tested the hypothesis that a greater amount of the variance in peak hip, knee and ankle sagittal plane moments would be explained by peak isometric joint torques as compared to age. Twenty-four healthy adults, ages 20-66 years, completed 5 trials on an overground 20-meter runway at a standardized velocity of 3.5 ms-1 (± 5%). Participants performed maximal isometric plantar flexion and knee extension for three contractions lasting three seconds each. Linear regression analysis between strength, age, and moments were performed. At the ankle, age alone explained 14.4% of the variance in the peak ankle joint moment. There was not a significant increase in the variance explained when strength was added to the model. At the knee, neither age nor strength explained a significant portion of the variance in peak knee moments. However, together age and strength explained 27.9% of the variance in the peak knee moment. No significant associations were found between the hip moments and either knee and ankle strength. These results suggest that other age-related physiological changes may drive changes in gait mechanics more so than maximal torque production. A more dynamic measure of muscle function, such as power or isokinetic torque at varying speeds may have greater predictive value for gait performance

AGE RELATED CHANGES IN LOWER EXTREMITY COORDINATION PATTERNS IN FEMALE RUNNERS

The aim of this study was to compare the coordination patterns of the lower extremity joints in older and younger females during running. The results of this study show that the older runners have maintained similar movement and coordination patterns to younger runners as a result of years of running experience. The results in this study could provide researchers and clinicians the information necessary to develop shoe wear and orthotic devices to reduce the risk of injury in specific populations

Jellyfish galaxies with the IllustrisTNG simulations -- Citizen-science results towards large distances, low-mass hosts, and high redshifts

We present the ``Cosmological Jellyfish'' project - a citizen-science classification program to identify jellyfish galaxies within the IllustrisTNG cosmological simulations. Jellyfish (JF) are satellite galaxies that exhibit long trailing gas features -- `tails' -- extending from their stellar body. Their distinctive morphology arises due to ram-pressure stripping (RPS) as they move through the background gaseous medium. Using the TNG50 and TNG100 simulations, we construct a sample of $\sim 80,000$ satellite galaxies spanning an unprecedented range of stellar masses, $10^{8.3-12.3}\,\mathrm{M_\odot}$, and host masses of $M_\mathrm{200,c}=10^{10.4-14.6}\,\mathrm{M_\odot}$ back to $z=2$ \citep[extending the work of][]{yun_jellyfish_2019}. Based on this sample, $\sim 90,000$ galaxy images were presented to volunteers in a citizen-science project on the Zooniverse platform who were asked to determine if each galaxy image resembles a jellyfish. Based on volunteer votes, each galaxy was assigned a score determining if it is a JF or not. This paper describes the project, the inspected satellite sample, the methodology, and the classification process that resulted in a dataset of $5,307$ visually-identified jellyfish galaxies. We find that JF galaxies are common in nearly all group- and cluster-sized systems, with the JF fraction increasing with host mass and decreasing with satellite stellar mass. We highlight JF galaxies in three relatively unexplored regimes: low-mass hosts of $M_\mathrm{200,c}\sim10^{11.5-13}\,\mathrm{M_\odot}$, radial positions within hosts exceeding the virial radius $R_\mathrm{200,c}$, and at high redshift up to $z=2$. The full dataset of our jellyfish scores is publicly available and can be used to select and study JF galaxies in the IllustrisTNG simulations.Comment: submitted to MNRAS ; See additional jellyfish companion papers today on astro-ph: Rohr et al. and Goeller et al.; Jellyfish image gallery: https://www.tng-project.org/explore/gallery/zinger23

Jellyfish galaxies with the IllustrisTNG simulations -- No enhanced population-wide star formation according to TNG50

Due to ram-pressure stripping, jellyfish galaxies are thought to lose large amounts, if not all, of their interstellar medium. Nevertheless, some, but not all, observations suggest that jellyfish galaxies exhibit enhanced star formation compared to control samples, even in their ram pressure-stripped tails. We use the TNG50 cosmological gravity+magnetohydrodynamical simulation, with an average spatial resolution of 50-200 pc in the star-forming regions of galaxies, to quantify the star formation activity and rates (SFRs) of more than 700 jellyfish galaxies at $z=0-1$ with stellar masses $10^{8.3-11}\,\mathrm{M}_\odot$ in hosts with mass $10^{11.5-14.3}\,\mathrm{M}_\odot$. We extract their global SFRs, the SFRs within their main stellar body vs. within the tails, and we follow the evolution of the star formation along their individual evolutionary tracks. We compare the findings for jellyfish galaxies to those of diversely-constructed control samples, including against satellite and field galaxies with matched redshift, stellar mass, gas fraction and host halo mass. According to TNG50, star formation and ram-pressure stripping can indeed occur simultaneously within any given galaxy, and frequently do so. Moreover, star formation can also take place within the ram pressure-stripped tails, even though the latter is typically subdominant. However, TNG50 does not predict elevated population-wide SFRs in jellyfish compared to analog satellite galaxies with the same stellar mass or gas fraction. Simulated jellyfish galaxies do undergo bursts of elevated star formation along their history but, at least according to TNG50, these do not translate into a population-wide enhancement at any given epoch.Comment: 20 pages, 10 figures, 1 table, submitted to MNRAS. See additional jellyfish companion papers today on astro-ph: Zinger et al. and Rohr et a

The hot circumgalactic media of massive cluster satellites in the TNG-Cluster simulation: existence and detectability

The most massive galaxy clusters in the Universe host tens to hundreds of massive satellite galaxies, but it is unclear if these satellites are able to retain their own gaseous atmospheres. We analyze the evolution of $\sim90,000$ satellites of stellar mass $\sim10^{9-12.5}\,M_\odot$ around 352 galaxy clusters of mass $M_{\rm vir}\sim10^{14.3-15.4}\,M_\odot$ at $z=0$ from the new TNG-Cluster suite of cosmological magneto-hydrodynamical galaxy cluster simulations. The number of satellites per host increases with host mass, and the mass--richness relation broadly agrees with observations. A halo of mass $M_{\rm 200c}\sim10^{14.5}\,(10^{15})\,M_\odot$ hosts $\sim100\,(300)$ satellites today. Only a minority of satellites retain some gas, and this fraction increases with stellar mass. Lower mass satellites $\sim10^{9-10}\,M_\odot$ are more likely to retain part of their cold interstellar medium, consistent with ram pressure preferentially removing hot extended gas first. At higher stellar masses $\sim10^{10.5-12.5}\,M_\odot$ the fraction of gas-rich satellites increases to unity, and nearly all satellites retain a sizeable portion of their hot, spatially-extended circumgalactic medium (CGM), despite the ejective activity of their supermassive black holes. According to TNG-Cluster, the CGM of these gaseous satellites can be seen in soft X-ray emission (0.5-2.0 keV) that is $\gtrsim10$ times brighter than the local background. This X-ray surface brightness excess around satellites extends to $\sim30-100$ kpc, and is strongest for galaxies with higher stellar masses and larger host-centric distances. Approximately 10 per cent of the soft X-ray emission in cluster outskirts $\sim0.75-1.5R_{\rm 200c}$ originates from satellites. The CGM of member galaxies reflects the dynamics of cluster-satellite interactions and contributes to the observationally-inferred properties of the intracluster medium.Comment: Submitted to A&A, comments welcome. See companion papers by Nelson et al., Lehle et al., Truong et al., Lee et al., and Ayromlou et al., and see the TNG-Cluster website at www.tng-project.org/cluster

The heart of galaxy clusters: demographics and physical properties of cool-core and non-cool-core halos in the TNG-Cluster simulation

We analyze the physical properties of the gaseous intracluster medium (ICM) at the center of massive galaxy clusters with TNG-Cluster, a new cosmological magnetohydrodynamical simulation. Our sample contains 352 simulated clusters spanning a halo mass range of $10^{14} < {\rm M}_{\rm 500c} / M_\odot < 2 \times 10^{15}$ at $z=0$. We focus on the proposed classification of clusters into cool-core (CC) and non-cool-core (NCC) populations, the $z=0$ distribution of cluster central ICM properties, and the redshift evolution of the CC cluster population. We analyze resolved structure and radial profiles of entropy, temperature, electron number density, and pressure. To distinguish between CC and NCC clusters, we consider several criteria: central cooling time, central entropy, central density, X-ray concentration parameter, and density profile slope. According to TNG-Cluster and with no a-priori cluster selection, the distributions of these properties are unimodal, whereby CCs and NCCs represent the two extremes. Across the entire TNG-Cluster sample at $z=0$ and based on central cooling time, the strong CC fraction is $f_{\rm SCC} = 24\%$, compared to $f_{\rm WCC} = 60\%$ and $f_{\rm NCC} = 16\%$ for weak and non-cool-cores, respectively. However, the fraction of CCs depends strongly on both halo mass and redshift, although the magnitude and even direction of the trends vary with definition. The abundant statistics of simulated high-mass clusters in TNG-Cluster enables us to match observational samples and make a comparison with data. The CC fractions from $z=0$ to $z=2$ are in broad agreement with observations, as are radial profiles of thermodynamical quantities, globally as well as split for CC versus NCC halos. TNG-Cluster can therefore be used as a laboratory to study the evolution and transformations of cluster cores due to mergers, AGN feedback, and other physical processes.Comment: Submitted to A&A, comments welcome. See the TNG-Cluster website at www.tng-project.org/cluster/ for more detail

Jellyfish galaxies with the IllustrisTNG simulations – No enhanced population-wide star formation according to TNG50

Due to ram-pressure stripping, jellyfish galaxies are thought to lose large amounts, if not all, of their interstellar medium. Nevertheless, some, but not all, observations suggest that jellyfish galaxies exhibit enhanced star formation compared to control samples, even in their ram pressure-stripped tails. We use the TNG50 cosmological gravity+magnetohydrodynamical simulation, with an average spatial resolution of 50-200 pc in the star-forming regions of galaxies, to quantify the star formation activity and rates (SFRs) of more than 700 jellyfish galaxies at z = 0 − 1 with stellar masses 108.3 − 10.8 M⊙ in hosts with mass 1010.5 − 14.3 M⊙. We extract their global SFRs, the SFRs within their main stellar body vs. within the tails, and we follow the evolution of the star formation along their individual evolutionary tracks. We compare the findings for jellyfish galaxies to those of diversely-constructed control samples, including against satellite and field galaxies with matched redshift, stellar mass, gas fraction and host halo mass. According to TNG50, star formation and ram-pressure stripping can indeed occur simultaneously within any given galaxy, and frequently do so. Moreover, star formation can also take place within the ram pressure-stripped tails, even though the latter is typically subdominant. However, TNG50 does not predict elevated population-wide SFRs in jellyfish compared to analogue satellite galaxies with the same stellar mass or gas fraction. Simulated jellyfish galaxies do undergo bursts of elevated star formation along their history but, at least according to TNG50, these do not translate into a population-wide enhancement at any given epoch

Jellyfish galaxies with the IllustrisTNG simulations -- When, where, and for how long does ram pressure stripping of cold gas occur?

Jellyfish galaxies are the prototypical examples of satellite galaxies undergoing strong ram pressure stripping (RPS). We analyze the evolution of 535 unique, first-infalling jellyfish galaxies from the TNG50 cosmological hydrodynamical galaxy simulation. These have been visually inspected to be undergoing RPS sometime in the past 5 billion years (since $z=0.5$), have satellite stellar masses $M_{\star}^{\rm sat}\sim10^{8-10.5}{\rm M}_\odot$, and live in hosts with $M_{\rm 200c}\sim10^{12-14.3}{\rm M}_\odot$ at $z=0$. We quantify the cold gas $(\leq10^{4.5}$K) removal using the tracer particles, confirming that for these jellyfish, RPS is the dominant driver of cold gas loss after infall. Half of these jellyfish are completely devoid of cold gas by $z=0$, and these galaxies have earlier infall times and smaller satellite-to-host mass ratios than those that still have some gas today. RPS can act on jellyfish galaxies over long timescales of $\approx1.5-8$Gyr. Jellyfish in more massive hosts are impacted by RPS for a shorter time span and, at a fixed host halo mass, jellyfish with lower stellar masses at $z=0$ have shorter RPS time spans. While RPS may act for long periods of time, the peak RPS period -- where at least 50% of the total RPS occurs -- begins within $\approx1$Gyr of infall and lasts $\lesssim2$Gyr. During this period, the jellyfish are at host-centric distances between $\sim0.2-2R_{\rm 200c}$, illustrating that much of RPS occurs at large distances from the host galaxy. Jellyfish continue forming stars until they have lost $\approx98$% of their cold gas. For groups and clusters in TNG50 $(M_{\rm 200c}\sim10^{13-14.3}{\rm M}_\odot)$, jellyfish galaxies deposit more cold gas ($\sim10^{11-12}{\rm M}_\odot$) into halos than exist in them at $z=0$, demonstrating that jellyfish, and in general satellite galaxies, are a significant source of cold gas accretion.Comment: 20 pages, 11 figures + 3 appendices with 4 figures. Submitted to MNRAS. Key figures are 2, 8, 9, 11. See additional jellyfish companion papers today on astro-ph: Zinger+ and Goeller+. All data used in this publication, including the Cosmological Jellyfish Project results, are publicaly availabl