M. A. Johnson
A5079185421- Atomic and Molecular Physics
- Hydraulic and Pneumatic Systems
- Particle accelerators and beam dynamics
- Cavitation Phenomena in Pumps
- Adaptive Control of Nonlinear Systems
- Muon and positron interactions and applications
- Magnetic confinement fusion research
- Iterative Learning Control Systems
- Particle Accelerators and Free-Electron Lasers
- Scientific Research and Discoveries
- Quantum, superfluid, helium dynamics
- Dark Matter and Cosmic Phenomena
- Quantum Mechanics and Applications
- Vehicle Noise and Vibration Control
- Advanced Frequency and Time Standards
- Advanced Control Systems Optimization
- Fault Detection and Control Systems
- Cold Atom Physics and Bose-Einstein Condensates
- Plasma Diagnostics and Applications
- Nuclear physics research studies
- Flow Measurement and Analysis
- Ultrasound and Cavitation Phenomena
- Spacecraft and Cryogenic Technologies
- Planetary Science and Exploration
- Elasticity and Wave Propagation
Cockcroft Institute
2016-2024
Sci-Tech Daresbury
2016-2024
University of Manchester
2003-2024
Daresbury Laboratory
2022-2024
Northwestern University
2011-2022
Michigan Technological University
2007-2016
University of Strathclyde
2000-2003
U.S. Air Force Institute of Technology
1991-2002
Wright-Patterson Air Force Base
2002
University of Auckland
1991-1992
Einstein's general theory of relativity from 19151 remains the most successful description gravitation. From 1919 solar eclipse2 to observation gravitational waves3, has passed many crucial experimental tests. However, evolving concepts dark matter and energy illustrate that there is much be learned about gravitating content universe. Singularities in lack a quantum gravity suggest our picture incomplete. It thus prudent explore exotic physical systems. Antimatter was unknown Einstein 1915....
We report a new, high-precision measurement of the proton elastic form factor ratio μpGE/GM for four-momentum transfer squared Q2=0.3–0.7(GeV/c)2. The was performed at Jefferson Lab (JLab) in Hall A using recoil polarimetry. With total uncertainty approximately 1%, new data clearly show that deviation from unity observed previous polarization measurements high Q2 continues down to lowest value this measurement. updated global fit includes results yields an electric (magnetic) roughly 2%...
The spectrum of the hydrogen atom has played a central part in fundamental physics over past 200 years. Historical examples its importance include wavelength measurements absorption lines solar by Fraunhofer, identification transition Balmer, Lyman and others, empirical description allowed wavelengths Rydberg, quantum model Bohr, capability electrodynamics to precisely predict frequencies, modern 1S-2S Hänsch precision few parts 1015. Recent technological advances have us focus on...
In 1928, Dirac published an equation 1 that combined quantum mechanics and special relativity. Negative-energy solutions to this equation, rather than being unphysical as initially thought, represented a class of hitherto unobserved unimagined particles-antimatter. The existence particles antimatter was confirmed with the discovery positron 2 (or anti-electron) by Anderson in 1932, but it is still unknown why matter, antimatter, survived after Big Bang. As result, experimental studies...
The observation of hyperfine structure in atomic hydrogen by Rabi and co-workers the measurement zero-field ground-state splitting at level seven parts 1013 are important achievements mid-twentieth-century physics. work that led to these also provided first evidence for anomalous magnetic moment electron, inspired Schwinger's relativistic theory quantum electrodynamics gave rise maser, which is a critical component modern navigation, geo-positioning very-long-baseline interferometry systems....
Abstract The photon—the quantum excitation of the electromagnetic field—is massless but carries momentum. A photon can therefore exert a force on an object upon collision 1 . Slowing translational motion atoms and ions by application such 2,3 , known as laser cooling, was first demonstrated 40 years ago 4,5 It revolutionized atomic physics over following decades 6–8 it is now workhorse in many fields, including studies degenerate gases, information, clocks tests fundamental physics. However,...
Abstract Antihydrogen, a positron bound to an antiproton, is the simplest anti-atom. Its structure and properties are expected mirror those of hydrogen atom. Prospects for precision comparisons two, as tests fundamental symmetries, driving vibrant programme research. In this regard, limiting factor in most experiments availability large numbers cold ground state antihydrogen atoms. Here, we describe how improved synthesis process results maximum rate 10.5 ± 0.6 atoms trapped detected per...
In 1906, Theodore Lyman discovered his eponymous series of transitions in the extreme-ultraviolet region atomic hydrogen spectrum1,2. The patterns spectrum helped to establish emerging theory quantum mechanics, which we now know governs world at scale. Since then, studies involving Lyman-α line-the 1S-2P transition a wavelength 121.6 nanometres-have played an important part physics and astronomy, as one most fundamental Universe. For example, this has long been used by astronomers studying...
The positron, the antiparticle of electron, predicted by Dirac in 1931 and discovered Anderson 1933, plays a key role many scientific everyday endeavours. Notably, positron is constituent antihydrogen, only long-lived neutral antimatter bound state that can currently be synthesized at low energy, presenting prominent system for testing fundamental symmetries with high precision. Here, we report on use laser cooled Be
Antiprotons created by laser ionization of antihydrogen are observed to rapidly escape the ALPHA trap. Further, positron plasmas heat more quickly after trap is illuminated light for several hours. These phenomena can be caused patch potentials—variations in electrical potential along metal surfaces. A simple model effects potentials explains particle loss, and an experimental technique using trapped electrons developed measuring electric field produced potentials. The validated controlled...
We describe a novel technique, based on image compression and machine learning, for transverse phase space tomography in two degrees of freedom an accelerator beamline. The technique has been used the CLARA test facility at Daresbury Laboratory: results from learning method are compared with those conventional algorithm (algebraic reconstruction) applied to same data. use allows reconstruction 4D distribution beam be carried out much more rapidly than using algorithms also enables reduce...
A concept is proposed for utilizing artificial neural networks to enhance the high-speed tracking accuracy of robotic manipulators. Tracking a function controller's ability compensate disturbances produced by dynamical interactions between links. model-based control algorithm uses nominal model those reduce disturbances. The problem how provide accurate dynamics information controller in presence payload uncertainty and modeling error. Neural network estimation series recognize variation...
The simultaneous control of the density and particle number non-neutral plasmas confined in Penning-Malmberg traps is demonstrated. Control achieved by setting plasma's applying a rotating electric field while simultaneously fixing its axial potential via evaporative cooling. This novel method particularly useful for stabilizing positron plasmas, as procedures used to collect positrons from radioactive sources typically yield with variable densities numbers; it also simplifies optimization...
A form of adaptive model-based control is proposed and experimentally evaluated. An neural network controller (AMBNNC) uses multilayer perceptron artificial networks to estimate the payload during high-speed manipulator motion. The adapts feedforward compensator unmodeled system dynamics variation. nets are trained through repetitive training on trajectory tracking error data. AMBNNC was evaluated third link a PUMA-560 manipulator. Tracking performance for wide range conditions compared...
The objective of this investigation was to develop a dimensionless model for predicting the onset cavitation in torque converters applicable general converter designs. Dimensional analysis applied test results from matrix that ranged populations comprised strict geometric similitude those with more relaxed similarities onto inclusion all tested. Stator thresholds at stall operating condition were experimentally determined dynamometer cell using nearfield acoustical measurements. Cavitation...
Magnetically trapped antihydrogen atoms can be cooled by expanding the volume of trap in which they are confined. We report a proof-of-principle experiment antiatoms deliberately released from expanded and static traps. Antiatoms escape at an average depth <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mn>0.08</a:mn><a:mo>±</a:mo><a:mn>0.01</a:mn><a:mspace width="0.28em"/><a:mi mathvariant="normal">K</a:mi></a:mrow></a:math> (statistical errors only) while depths <d:math...
The classical ship roll control PID design method is based on a single performance criterion. This paper extends this to nonlinear constrained optimisation, which includes all the controller and stability criteria. classic first introduced before going discuss set of specifications. It then shown how these specifications are incorporated into optimised design. optimal applied controllers for three separate ships, present particular problems method. Conclusions drawn from results obtained.
Dimensional analysis has been applied to automotive torque converters understand the response of performance changes in torque, size, working fluid, or operating temperature. The objective this investigation was develop a suitable dimensional for estimating effect exact geometric scaling particular converter design on onset cavitation. Torque thresholds cavitation were determined experimentally with dynamometer test cell at stall condition using nearfield acoustical measurements....
The ALPHA Collaboration, based at the CERN Antiproton Decelerator, has recently implemented a novel beamline for low energy (≲100 eV) positron and antiproton transport between cylindrical Penning traps that have strong axial magnetic fields. Here, we describe how combination of semianalytical numerical calculations was used to optimize layout design this beamline. Using experimental measurements taken during initial commissioning instrument, evaluate its performance validate models...