Lattice Monte Carlo calculations for unitary fermions in a finite box

We perform lattice Monte Carlo simulations for up to 66 unitary fermions in a finite box using a highly improved lattice action for nonrelativistic spin 1/2 fermions. We obtain a value of $0.366^{+0.016}_{-0.011}$ for the Bertsch parameter, defined as the energy of the unitary Fermi gas measured in units of the free gas energy in the thermodynamic limit. In addition, for up to four unitary fermions, we compute the spectrum of the lattice theory by exact diagonalization of the transfer matrix projected onto irreducible representations of the octahedral group for small to moderate size lattices, providing an independent check of our few-body simulation results. We compare our exact numerical and simulation results for the spectrum to benchmark studies of other research groups, as well as perform an extended analysis of our lattice action improvement scheme, including an analysis of the errors associated with higher partial waves and finite temporal discretization.Comment: Significant revisions from previous version. Included data at a larger volume and performed an infinite volume extrapolation of the Bertsch parameter. Published versio

Clustering in mixing flows

We calculate the Lyapunov exponents for particles suspended in a random three-dimensional flow, concentrating on the limit where the viscous damping rate is small compared to the inverse correlation time. In this limit Lyapunov exponents are obtained as a power series in epsilon, a dimensionless measure of the particle inertia. Although the perturbation generates an asymptotic series, we obtain accurate results from a Pade-Borel summation. Our results prove that particles suspended in an incompressible random mixing flow can show pronounced clustering when the Stokes number is large and we characterise two distinct clustering effects which occur in that limit.Comment: 5 pages, 1 figur

Combining Different Motivation and Cognitive Supports in Undergraduate Biology in Different Contexts: Lessons Learned

Researchers acknowledge that students’ learning and achievement requires both effective cognition and the motivation to apply it. In addition, both cognition and motivation are multidimensional, each involving different processes that may be less or more salient in different contexts. However, most basic research and intervention studies focus on either cognition OR motivation, and commonly only target a single process. We designed an intervention to investigate the role of different combinations of cognitive and motivational supports in first-year undergraduate introductory biology courses. We sought an online delivery approach with minimal burden on the instructor that can accompany any such course. Building on prior research, we selected four types of cognitive supports and three types of motivational supports. Cognitive supports: Priming Prior Knowledge, Demonstrating Worked Examples, Instructing Study Strategies and Scaffolding Organization of Lectures. Motivational supports: Self-Efficacy Promoting Feedback, Value Enhancement Through Relevance Writing, and Perceived Cost Alleviation Through Persuasion. The intervention study was designed to test the effects of different combinations of these cognition and motivation supports. Initial development began in 2015-2016 with post-iterative experiments in 2017. Overall, there were 3,092 undergraduate student participants, tested in 10 studies at 3 universities over 4 years. Students were randomly assigned to either a no-treatment control condition or one of 17 combinations of cognition and motivation intervention modules delivered via the Internet, each over the course of a semester. A meta-analysis of the overall effect of all interventions on grades across the 10 studies was positive (g = .30), with significant moderation of fidelity (i.e., students’ access; g = .24) and research phase (stronger effect in later administrations; g = .26). Moreover, certain combinations had little effect across administrations (e.g., any combination with Priming Prior Knowledge). However, the development and testing process also pointed to contextual and situational factors that influenced the effect of mostly effective interventions. For example, in one institution, Scaffolding Organization of Lectures through thematically segmenting lecture videos had the unintended consequence of students stopping lecture attendance. Or, in one institution but not in others, students “crammed” on the supports, which undermined the effect and required modifying the intervention in order to regulate timely access in that institution. Additionally, for yet to be explored reasons, successful combinations of modules were more effective in certain administrations in some institutions than in others. Finally, in certain administrations, there were unanticipated direct effects of motivational modules on cognitive biological reasoning, and cognitive modules on motivational beliefs The current study demonstrated that, when aggregated across context, time, and participants, a “hands-off” administration of a combination of certain cognitive and motivational supports can meaningfully improve undergraduate students’ motivation, biological reasoning, and course grades, with a stronger effect than a cognitive or motivation intervention alone. In addition, however, the findings point to important contextual as well as potentially unpredictable factors as moderating the effect of such interventions. “Evidence-based practice” might need to be considered a “first-step” in a systematic design process of catering any intervention to the particular educational context

How Instructors Can Enhance Biology Students\u27 Motivation, Learning, and Grades Through Brief Relevance Writing and Worked-Example Interventions

The high failure rate of students in gateway science, technology, engineering, and mathematics (STEM) courses has been a persistent problem for biology programs nationwide. Common wisdom contends that addressing this problem requires major curricular overhauls. While desirable, such large systematic changes are often expensive or impractical. We propose an alternative approach: supplementing the regular instruction with brief online modules targeting specific cognitive (learning) and motivational mechanisms. We conducted an intervention study to test the effects of different combinations of cognitive and motivational modules on undergraduate introductory biology students\u27 learning, motivation, achievement, and intentions to remain in science. Introductory biology students at three research universities were randomly assigned to a no-treatment control condition or one of several combinations of cognition motivation modules. In this article, we describe the modules that are easiest for instructors to integrate with existing course content: worked examples (demonstrations of biology problem solving) and relevance writing (brief open-ended writing assignments about connections of biology concepts to one\u27s life). Increased student engagement in these modules led to higher motivation, biology reasoning, and course grades. These findings support the effectiveness of delivering brief online supplemental modules on students\u27 success in introductory biology courses. This easily implemented intervention can utilize online tools such as Blackboard, Canvas, or Moodle and provides an option when major changes to course instruction are not practical

An Exhumed Late Paleozoic Canyon in the Rocky Mountains

Landscapes are thought to be youthful, particularly those of active orogenic belts. Unaweep Canyon in the Colorado Rocky Mountains, a large gorge drained by two opposite‐flowing creeks, is an exception. Its origin has long been enigmatic, but new data indicate that it is an exhumed late Paleozoic landform. Its survival within a region of profound late Paleozoic orogenesis demands a reassessment of tectonic models for the Ancestral Rocky Mountains, and its form and genesis have significant implications for understanding late Paleozoic equatorial climate. This discovery highlights the utility of paleogeomorphology as a tectonic and climatic indicator

Pursuing the Half Empty Question : Biology Undergraduates\u27 Differential Engagement in a Brief Relevance Writing Intervention

Whereas relevance-writing interventions have shown effects on students’ achievement, a persistent finding is that interventions benefit students with low, but not high, outcome expectancies—a phenomenon that Schwartz et al. (2016) termed the half empty question. In the current mixed-methods study, we investigated the role of undergraduate students’ patterns of engagement in a relevance-writing intervention and their relations to biology course achievement. Ninety-six students who were administered four relevance writing assignments were found to manifest two patterns: Students who completed at least 50% of the intervention in a timely manner outperformed those who completed less-then-50% or completed it late, regardless of their pre-intervention motivation. A closer look into individual students’ patterns showed diverse perceptions about the relevance-writing tasks

Direct and Simultaneous Observation of Ultrafast Electron and Hole Dynamics in Germanium

Understanding excited carrier dynamics in semiconductors is crucial for the development of photovoltaics and efficient photonic devices. However, overlapping spectral features in optical/NIR pump-probe spectroscopy often render assignments of separate electron and hole carrier dynamics ambiguous. Here, ultrafast electron and hole dynamics in germanium nanocrystalline thin films are directly and simultaneously observed by attosecond transient absorption spectroscopy (ATAS) in the extreme ultraviolet at the germanium M_{4,5}-edge (~30 eV). We decompose the ATAS spectra into contributions of electronic state blocking and photo-induced band shifts at a carrier density of 8*10^{20}cm^{-3}. Separate electron and hole relaxation times are observed as a function of hot carrier energies. A first order electron and hole decay of ~1 ps suggests a Shockley-Read-Hall recombination mechanism. The simultaneous observation of electrons and holes with ATAS paves the way for investigating few to sub-femtosecond dynamics of both holes and electrons in complex semiconductor materials and across junctions.Comment: Includes Supplementary Informatio

Factors contributing to the temperature beneath plaster or fiberglass cast material

<p>Abstract</p> <p>Background</p> <p>Most cast materials mature and harden via an exothermic reaction. Although rare, thermal injuries secondary to casting can occur. The purpose of this study was to evaluate factors that contribute to the elevated temperature beneath a cast and, more specifically, evaluate the differences of modern casting materials including fiberglass and prefabricated splints.</p> <p>Methods</p> <p>The temperature beneath various types (plaster, fiberglass, and fiberglass splints), brands, and thickness of cast material were measured after they were applied over thermometer which was on the surface of a single diameter and thickness PVC tube. A single layer of cotton stockinette with variable layers and types of cast padding were placed prior to application of the cast. Serial temperature measurements were made as the cast matured and reached peak temperature. Time to peak, duration of peak, and peak temperature were noted. Additional tests included varying the dip water temperature and assessing external insulating factors. Ambient temperature, ambient humidity and dip water freshness were controlled.</p> <p>Results</p> <p>Outcomes revealed that material type, cast thickness, and dip water temperature played key roles regarding the temperature beneath the cast. Faster setting plasters achieved peak temperature quicker and at a higher level than slower setting plasters. Thicker fiberglass and plaster casts led to greater peak temperature levels. Likewise increasing dip-water temperature led to elevated temperatures. The thickness and type of cast padding had less of an effect for all materials. With a definition of thermal injury risk of skin injury being greater than 49 degrees Celsius, we found that thick casts of extra fast setting plaster consistently approached dangerous levels (greater than 49 degrees for an extended period). Indeed a cast of extra-fast setting plaster, 20 layers thick, placed on a pillow during maturation maintained temperatures over 50 degrees of Celsius for over 20 minutes.</p> <p>Conclusion</p> <p>Clinicians should be cautious when applying thick casts with warm dip water. Fast setting plasters have increased risk of thermal injury while brand does not appear to play a significant role. Prefabricated fiberglass splints appear to be safer than circumferential casts. The greatest risk of thermal injury occurs when thick casts are allowed to mature while resting on pillow.</p

The Statistics of Supersonic Isothermal Turbulence

We present results of large-scale three-dimensional simulations of supersonic Euler turbulence with the piecewise parabolic method and multiple grid resolutions up to 2048^3 points. Our numerical experiments describe non-magnetized driven turbulent flows with an isothermal equation of state and an rms Mach number of 6. We discuss numerical resolution issues and demonstrate convergence, in a statistical sense, of the inertial range dynamics in simulations on grids larger than 512^3 points. The simulations allowed us to measure the absolute velocity scaling exponents for the first time. The inertial range velocity scaling in this strongly compressible regime deviates substantially from the incompressible Kolmogorov laws. The slope of the velocity power spectrum, for instance, is -1.95 compared to -5/3 in the incompressible case. The exponent of the third-order velocity structure function is 1.28, while in incompressible turbulence it is known to be unity. We propose a natural extension of Kolmogorov's phenomenology that takes into account compressibility by mixing the velocity and density statistics and preserves the Kolmogorov scaling of the power spectrum and structure functions of the density-weighted velocity v=\rho^{1/3}u. The low-order statistics of v appear to be invariant with respect to changes in the Mach number. For instance, at Mach 6 the slope of the power spectrum of v is -1.69, and the exponent of the third-order structure function of v is unity. We also directly measure the mass dimension of the "fractal" density distribution in the inertial subrange, D_m = 2.4, which is similar to the observed fractal dimension of molecular clouds and agrees well with the cascade phenomenology.Comment: 15 pages, 19 figures, ApJ v665, n2, 200