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1. The dynamic effect of mechanical losses of transmissions on the equation of motion of legged robots

   https://doi.org/10.1109/ICRA48506.2021.9561739  

   Sim, Youngwoo; Ramos, Joao (January 2021, 2021 IEEE International Conference on Robotics and Automation (ICRA))

   Industrial manipulators do not collapse under their own weight when powered off due to the friction in their joints. Although these mechanism are effective for stiff position control of pick-and-place, they are inappropriate for legged robots that must rapidly regulate compliant interactions with the environment. However, no metric exists to quantify the robot’s performance degradation due to mechanical losses in the actuators and transmissions. This paper provides a fundamental formulation that uses the mechanical efficiency of transmissions to quantify the effect of power losses in the mechanical transmissions on the dynamics of a whole robotic system. We quantitatively demonstrate the intuitive fact that the apparent inertia of the robots increase in the presence of joint friction. We also show that robots that employ high gear ratio and low efficiency transmissions can statically sustain more substantial external loads. We expect that the framework presented here will provide the fundamental tools for designing the next generation of legged robots that can effectively interact with the world. 

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2. The dynamic effect of mechanical losses of transmissions on the equation of motion of legged robots

   Sim, Youngwoo; Ramos, Joao (January 2021, IEEE International Conference on Robotics and Automation)

   null (Ed.)

   Industrial manipulators do not collapse under their own weight when powered off due to the friction in their joints. Although these mechanism are effective for stiff position control of pick-and-place, they are inappropriate for legged robots that must rapidly regulate compliant interactions with the environment. However, no metric exists to quantify the robot’s performance degradation due to mechanical losses in the actuators and transmissions. This paper provides a fundamental formulation that uses the mechanical efficiency of transmissions to quantify the effect of power losses in the mechanical transmissions on the dynamics of a whole robotic system. We quantitatively demonstrate the intuitive fact that the apparent inertia of the robots increase in the presence of joint friction. We also show that robots that employ high gear ratio and low efficiency transmissions can statically sustain more substantial external loads. We expect that the framework presented here will provide the fundamental tools for designing the next generation of legged robots that can effectively interact with the world. 

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3. Extensions of two constructions of Ahmad

   https://doi.org/10.3233/COM-210380  

   Goh, Jun Le; Lempp, Steffen; Ng, Keng Meng; Soskova, Mariya I. (December 2022, Computability)

   Brattka, Vasco; Greenberg, Noam; Kalimullin, Iskander; Soskova, Mariya (Ed.)

   In her 1990 thesis, Ahmad showed that there is a so-called “Ahmad pair”, i.e., there are incomparable Σ 2 0 -enumeration degrees  a 0 and  a 1 such that every enumeration degree x < a 0 is ⩽ a 1 . At the same time, she also showed that there is no “symmetric Ahmad pair”, i.e., there are no incomparable Σ 2 0 -enumeration degrees  a 0 and  a 1 such that every enumeration degree x 0 < a 0 is ⩽ a 1 and such that every enumeration degree x 1 < a 1 is ⩽ a 0 . In this paper, we first present a direct proof of Ahmad’s second result. We then show that her first result cannot be extended to an “Ahmad triple”, i.e., there are no Σ 2 0 -enumeration degrees  a 0 , a 1 and  a 2 such that both ( a 0 , a 1 ) and ( a 1 , a 2 ) are an Ahmad pair. On the other hand, there is a “weak Ahmad triple”, i.e., there are pairwise incomparable Σ 2 0 -enumeration degrees  a 0 , a 1 and  a 2 such that every enumeration degree x < a 0 is also ⩽ a 1 or ⩽ a 2 ; however neither ( a 0 , a 1 ) nor ( a 0 , a 2 ) is an Ahmad pair. 

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4. Characterization of inpaint residuals in interferometric measurements of the epoch of reionization

   https://doi.org/10.1093/mnras/stad441  

   Pagano, Michael; Liu, Jing; Liu, Adrian; Kern, Nicholas S; Ewall-Wice, Aaron; Bull, Philip; Pascua, Robert; Ravanbakhsh, Siamak; Abdurashidova, Zara; Adams, Tyrone; et al (February 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT To mitigate the effects of Radio Frequency Interference (RFI) on the data analysis pipelines of 21 cm interferometric instruments, numerous inpaint techniques have been developed. In this paper, we examine the qualitative and quantitative errors introduced into the visibilities and power spectrum due to inpainting. We perform our analysis on simulated data as well as real data from the Hydrogen Epoch of Reionization Array (HERA) Phase 1 upper limits. We also introduce a convolutional neural network that is capable of inpainting RFI corrupted data. We train our network on simulated data and show that our network is capable of inpainting real data without requiring to be retrained. We find that techniques that incorporate high wavenumbers in delay space in their modelling are best suited for inpainting over narrowband RFI. We show that with our fiducial parameters discrete prolate spheroidal sequences (dpss) and clean provide the best performance for intermittent RFI while Gaussian progress regression (gpr) and least squares spectral analysis (lssa) provide the best performance for larger RFI gaps. However, we caution that these qualitative conclusions are sensitive to the chosen hyperparameters of each inpainting technique. We show that all inpainting techniques reliably reproduce foreground dominated modes in the power spectrum. Since the inpainting techniques should not be capable of reproducing noise realizations, we find that the largest errors occur in the noise dominated delay modes. We show that as the noise level of the data comes down, clean and dpss are most capable of reproducing the fine frequency structure in the visibilities. 

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5. Hybridization kinetics of out-of-equilibrium mixtures of short RNA oligonucleotides

   https://doi.org/10.1093/nar/gkac784  

   Todisco, Marco; Szostak, Jack W. (September 2022, Nucleic Acids Research)

   Abstract Hybridization and strand displacement kinetics determine the evolution of the base paired configurations of mixtures of oligonucleotides over time. Although much attention has been focused on the thermodynamics of DNA and RNA base pairing in the scientific literature, much less work has been done on the time dependence of interactions involving multiple strands, especially in RNA. Here we provide a study of oligoribonucleotide interaction kinetics and show that it is possible to calculate the association, dissociation and strand displacement rates displayed by short oligonucleotides (5nt–12nt) that exhibit no expected secondary structure as simple functions of oligonucleotide length, CG content, ΔG of hybridization and ΔG of toehold binding. We then show that the resultant calculated kinetic parameters are consistent with the experimentally observed time dependent changes in concentrations of the different species present in mixtures of multiple competing RNA strands. We show that by changing the mixture composition, it is possible to create and tune kinetic traps that extend by orders of magnitude the typical sub-second hybridization timescale of two complementary oligonucleotides. We suggest that the slow equilibration of complex oligonucleotide mixtures may have facilitated the nonenzymatic replication of RNA during the origin of life. 

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