206 research outputs found
Electric Machine with Boosted Inductance to Stabilize Current Control
High-powered motors typically have very low resistance and inductance (R and L) in their windings. This makes the pulse-width modulated (PWM) control of the current very difficult, especially when the bus voltage (V) is high. These R and L values are dictated by the motor size, torque (Kt), and back-emf (Kb) constants. These constants are in turn set by the voltage and the actuation torque-speed requirements. This problem is often addressed by placing inductive chokes within the controller. This approach is undesirable in that space is taken and heat is added to the controller. By keeping the same motor frame, reducing the wire size, and placing a correspondingly larger number of turns in each slot, the resistance, inductance, torque constant, and back-emf constant are all increased. The increased inductance aids the current control but ruins the Kt and Kb selections. If, however, a fraction of the turns is moved from their "correct slot" to an "incorrect slot," the increased R and L values are retained, but the Kt and Kb values are restored to the desired values. This approach assumes that increased resistance is acceptable to a degree. In effect, the heat allocated to the added inductance has been moved from the controller to the motor body, which in some cases is preferred
Adaptation and robustness in a chemotaxis network
Adaptation is a behavior of biological systems in which a sustained change in input signal leads to a transient output response that returns to the pre--âstimulated output level. Cells use adaptation to maintain sensitivity to the changes in their environment and to remain in homeostasis while the input signal is perturbed. Signaling networks in both prokaryotic and eukaryotic cells demonstrate adaptation, which is a common feature of chemotaxis, a signal transduction process that enables cells to sense chemical gradients in their extracellular environment and to adjust their movement in response. In the case of Escherichia coli, the bacteria swim in random directions in the absence of a chemical gradient, but will move toward or away from the chemical when a gradient exists. In this study, we use computational methods to study adaptation in the chemotaxis network of Escherichia coli. Based on the well--âcharacterized two--âstate model of Barkai and Leibler (Nature 1997), we numerically analyze the chemotactic network with ordinary differential equations and measure the adaptation time and precision of the response to a change in ligand concentration. The adaptation time is the time that the signal takes to reach steady--âstate after a perturbation in input, and precision measures the difference between output and input levels. We find that the network exhibits a sensitive response and precise adaptation to the input stimulus. We also analyze the robustness of the network by randomly varying the kinetic parameters and characterizing the change in behavior. The adaptation demonstrates robustness: although the adaption time varies over a wide range, the precision is nearly perfect regardless of the values of the parameters. This shows that adaptation in this network depends more strongly on the topology of the network than on the values of kinetic parameters
Training Neural Networks with Universal Adiabatic Quantum Computing
The training of neural networks (NNs) is a computationally intensive task
requiring significant time and resources. This paper presents a novel approach
to NN training using Adiabatic Quantum Computing (AQC), a paradigm that
leverages the principles of adiabatic evolution to solve optimisation problems.
We propose a universal AQC method that can be implemented on gate quantum
computers, allowing for a broad range of Hamiltonians and thus enabling the
training of expressive neural networks. We apply this approach to various
neural networks with continuous, discrete, and binary weights. Our results
indicate that AQC can very efficiently find the global minimum of the loss
function, offering a promising alternative to classical training methods.Comment: 14 page
One-loop Yukawas on Intersecting Branes
We calculate Yukawa interactions at one-loop on intersecting D6 branes. We
demonstrate the non-renormalization theorem in supersymmetric configurations,
and show how Yukawa beta functions may be extracted. In addition to the usual
logarithmic running, we find the power-law dependence on the infra-red cut-off
associated with Kaluza-Klein modes. Our results may also be used to evaluate
coupling renormalization in non-supersymmetric cases.Comment: 48 pages, 9 figures; minor corrections, JHEP styl
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Green-Emissive Zn2+ Complex Supported by a Macrocyclic Schiff-Base/Calix[4]arene-Ligand: Crystallographic and Spectroscopic Characterization
The macrocyclic calix[4]arene ligand H2L comprises two non-fluorescent 2,6-bis-(iminomethyl)phenolate chromophores, which show a chelation-enhanced fluorescence enhancement upon Zn2+ ion complexation. Macrocyclic [ZnL] complexes aggregate in the absence of external coligands via intermolecular ZnâN bonds to give dimeric [ZnL]2 structures comprising two five-coordinated Zn2+ ions. The absorption and emission wavelengths are bathochromically shifted upon going from the liquid (λmax,abs (CH2Cl2)=404â
nm, λmax,em (CH2Cl2)=484â
nm) to the solid state (λmax,abs=424 nm (4â
wt%, BaSO4 pellet), λmax,em=524â
nm (neat solid)). Insights into the electronic nature of the UV-vis transitions were obtained with time-dependent density functional theory (TD-DFT) calculations for a truncated model complex
Cosmic Inflation and Genetic Algorithms
Large classes of standard single-field slow-roll inflationary models consistentwith the required number of e-folds, the current bounds on the spectral indexof scalar perturbations, the tensor-to-scalar ratio, and the scale of inflation canbe efficiently constructed using genetic algorithms. The setup is modular andcan be easily adapted to include further phenomenological constraints. Asemi-comprehensive search for sextic polynomial potentials results inâŒ(300,000) viable models for inflation. The analysis of this dataset revealsa preference for models with a tensor-to-scalar ratio in the range0.0001â€râ€0.0004. We also consider potentials that involve cosine andexponential terms. In the last part we explore more complex methods ofsearch relying on reinforcement learning and genetic programming. Whilereinforcement learning proves more difficult to use in this context, the geneticprogramming approach has the potential to uncover a multitude of viableinflationary models with new functional forms
A Basic Robotic Excavator (the Glenn Digger): Description, Design, and Initial Operation
This paper describes the design, commercial part selections, fabrication, assembly, installation, and initial operation of a two degree of freedom robotic excavator. Colloquially referred to as "the NASA Glenn Digger," it was designed specifically to be mounted onto, and to operate with, the then newly developed Centaur 2 robotic mobility base. The excavator, when mounted to Centaur 2, is designed to scoop loose regolith from the terrain, raise its loaded bucket up and dump the load into a hopper of at least a 1-m-height. The hopper represents the input to a machine that would process the raw material, such as to produce oxygen from lunar regolith as would be required for long-term lunar habitation. This equipment debuted at the annual Research and Technology Studies ("Desert RATS", Ref. 1) event held north of Flagstaff, Arizona, in September of 2010, when the Digger was successfully joined to Centaur 2 and the shoveling articulation was demonstrated. During 2011, the hardware was modified for added strength, strain gauges were added to measure loads, and the controls were improved in preparation for the 2011 Desert RATS event, where additional "field operations" experience was gained
Decoding Nature with Nature's Tools: Heterotic Line Bundle Models of Particle Physics with Genetic Algorithms and Quantum Annealing
The string theory landscape may include a multitude of ultraviolet embeddings of the Standard Model, but identifying these has proven difficult due to the enormous number of available string compactifications. Genetic Algorithms (GAs) represent a powerful class of discrete optimisation techniques that can efficiently deal with the immensity of the string landscape, especially when enhanced with input from quantum annealers. In this letter, we focus on geometric compactifications of the E 8 Ă E 8 heterotic string theory compactified on smooth CalabiâYau threefolds with Abelian bundles. We make use of analytic formulae for bundleâvalued cohomology to impose the entire range of spectrum requirements, something that has not been possible so far. For manifolds with a relatively low number of KĂ€hler parameters, we compare the GA search results with results from previous systematic scans, showing that GAs can find nearly all the viable solutions while visiting only a tiny fraction of the solution space. Moreover, we carry out GA searches on manifolds with a larger numbers of KĂ€hler parameters where systematic searches are not feasible
Ball Screw Actuator Including an Axial Soft Stop
An actuator includes an actuator housing, a ball screw, and an axial soft stop assembly. The ball screw extends through the actuator housing and has a first end and a second end. The ball screw is coupled to receive a drive force and is configured, upon receipt of the drive force, to selectively move in a retract direction and an extend direction. The axial soft stop assembly is disposed within the actuator housing. The axial soft stop assembly is configured to be selectively engaged by the ball screw and, upon being engaged thereby, to translate, with compliance, a predetermined distance in the extend direction, and to prevent further movement of the ball screw upon translating the predetermined distance
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Dinuclear lanthanide complexes supported by a hybrid salicylaldiminato/calix[4]arene-ligand: Synthesis, structure, and magnetic and luminescence properties of (HNEt3)[Ln2(HL)(L)] (Ln = SmIII, EuIII, GdIII, TbIII)
The synthesis, structures, and properties of a new calix[4]arene ligand with an appended salicylaldimine unit (H4L = 25-[2-((2-methylphenol)imino)ethoxy]-26,27,28-trihydroxy-calix[4]arene) and four lanthanide complexes (HNEt3)[Ln2(HL)(L)] (Ln = SmIII (4), EuIII (5), GdIII (6), and TbIII (7)) are reported. X-ray crystallographic analysis (for 4 and 6) reveals an isostructural series of dimeric complexes with a triply-bridged NO3Ln(ÎŒ-O)2(OHâŻO)LnO3N core and two seven coordinated lanthanide ions. According to UV-vis spectrometric titrations in MeCN and ESI-MS the dimeric nature is maintained in solution. The apparent stability constants range between logK = 5.8 and 6.3. The appended salicylaldimines sensitize EuIII and TbIII emission (λexc 311 nm) in the solid state or immersed in a polycarbonate glass at 77 K (for 5, 7) and at 295 K (for 7). © The Royal Society of Chemistry 2019
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