Efficient cruising for swimming and flying animals is dictated by fluid drag

Many swimming and flying animals are observed to cruise in a narrow range of Strouhal numbers, where the Strouhal number ${St = 2fA/U}$ is a dimensionless parameter that relates stroke frequency $f$, amplitude $A$, and forward speed $U$. Dolphins, sharks, bony fish, birds, bats, and insects typically cruise in the range $0.2 < St < 0.4$, which coincides with the Strouhal number range for maximum efficiency as found by experiments on heaving and pitching airfoils. It has therefore been postulated that natural selection has tuned animals to use this range of Strouhal numbers because it confers high efficiency, but the reason why this is so is still unclear. Here, by using simple scaling arguments, we argue that the Strouhal number for peak efficiency is largely determined by fluid drag on the fins and wings.Comment: 10 page

Scaling the propulsive performance of heaving and pitching foils

Scaling laws for the propulsive performance of rigid foils undergoing oscillatory heaving and pitching motions are presented. Water tunnel experiments on a nominally two-dimensional flow validate the scaling laws, with the scaled data for thrust, power, and efficiency all showing excellent collapse. The analysis indicates that the behaviour of the foils depends on both Strouhal number and reduced frequency, but for motions where the viscous drag is small the thrust closely follows a linear dependence on reduced frequency. The scaling laws are also shown to be consistent with biological data on swimming aquatic animals.Comment: 11 page

Forces and energetics of intermittent swimming

Experiments are reported on intermittent swimming motions. Water tunnel experiments on a nominally two-dimensional pitching foil show that the mean thrust and power scale linearly with the duty cycle, from a value of 0.2 all the way up to continuous motions, indicating that individual bursts of activity in intermittent motions are independent of each other. This conclusion is corroborated by PIV flow visualizations, which show that the main vortical structures in the wake do not change with duty cycle. The experimental data also demonstrate that intermittent motions are generally energetically advantageous over continuous motions. When metabolic energy losses are taken into account, this conclusion is maintained for metabolic power fractions less than 1.Comment: 9 page

Automating Microfluidics: Reconfigurable Virtual Channels for Cell and Droplet Transport

The emerging field of digital microfluidics promises to solve many shortcomings of traditional continuous-flow fluidics. This technology has a few incarnations, including EWOD (eletrowetting on dielectric) and DEP (dielectrophoresis) chips. Both consist of large arrays of electrical pixels which move droplets and cells. They actuate fluids actively, have error feedback, are programmable, perform operations in parallel, and do not rely on external pumps. For these reasons we foresee the increased use of digital microfluidics in the near future. We also foresee a gradual shift away from purpose-built microfluidic devices, towards multi-purpose platforms with specific applications encoded in software. To this extent we present here a new paradigm of encoding and automating microfluidic operations using video files. We use this technology to create several configurations of virtual microfluidic channels and to play film clips using living cells on a DEP chip.Engineering and Applied SciencesPhysic

On instabilities in neural network-based physics simulators

When neural networks are trained from data to simulate the dynamics of physical systems, they encounter a persistent challenge: the long-time dynamics they produce are often unphysical or unstable. We analyze the origin of such instabilities when learning linear dynamical systems, focusing on the training dynamics. We make several analytical findings which empirical observations suggest extend to nonlinear dynamical systems. First, the rate of convergence of the training dynamics is uneven and depends on the distribution of energy in the data. As a special case, the dynamics in directions where the data have no energy cannot be learned. Second, in the unlearnable directions, the dynamics produced by the neural network depend on the weight initialization, and common weight initialization schemes can produce unstable dynamics. Third, injecting synthetic noise into the data during training adds damping to the training dynamics and can stabilize the learned simulator, though doing so undesirably biases the learned dynamics. For each contributor to instability, we suggest mitigative strategies. We also highlight important differences between learning discrete-time and continuous-time dynamics, and discuss extensions to nonlinear systems.Comment: 15 page

Pengaruh Inovasi Produk terhadap Peningkatan Daya Saing UMKM Kuliner di Kota Pangkalpinang

MSMEs are a sector that plays a vital role in driving the wheels of the economy, both at the national and regional levels. MSMEs are considered capable of absorbing a large number of workers, increasing community income, and actively contributing to reducing economic disparities. The aim of this study is to understand the influence of product innovation on the competitiveness of culinary MSMEs in Pangkalpinang City. This study focuses on quantitative research using data collection methods through the distribution of questionnaires. The sample in this study was determined using the Slovin formula with a total of 100 respondents, employing a non-probability sampling method with an accidental sampling technique. The collected data were analyzed using simple linear regression with the independent variable being product innovation and the dependent variable being the competitiveness of MSMEs. Based on the results of data analysis, it can be concluded that product innovation has a positive and significant effect on enhancing the competitiveness of culinary MSMEs in Pangkalpinang City

A Post-Pierce Program: Using IDR to Improve the Los Angeles Fire Department\u27s Current Complaint and Disciplinary Procedure

Having an alternative to litigation is important for employees and employers in all organizations and corporations. One such option is through internal dispute resolution (IDR) mechanisms. IDR mechanisms are alternative processes used instead of litigation to solve a dispute in its early stages. When organizations and corporations do not have an established set of mechanisms in place or the employees are unaware of the procedure, lawsuits result. The Los Angeles Fire Department (LAFD) is one such organization that does not have a strong, established IDR procedure in place. This paper analyzes the LAFD\u27s current complaint and disciplinary procedure and how the flaws in this procedure have created million-dollar taxpayer-funded settlements