Light Speed Grand Challenge RF Thrust Meeting: Mission Scale Simulations.
Abstract not provided.
Welliver, Marc↗
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ON THE PROPER USE OF THE REDUCED SPEED OF LIGHT APPROXIMATION
I show that the reduced speed of light (RSL) approximation, when used properly (i.e., as originally designed—only for local sources but not for the cosmic background), remains a highly accurate numerical method for modeling cosmic reionization. Simulated ionization and star formation histories from the “Cosmic Reionization on Computers” project are insensitive to the adopted value of the RSL for as long as that value does not fall below about 10% of the true speed of light. A recent claim of the failure of the RSL approximation in the Illustris reionization model appears to be due to the effective speed of light being reduced in the equation for the cosmic background too and hence illustrates the importance of maintaining the correct speed of light in modeling the cosmic background.
79 ASTRONOMY AND ASTROPHYSICS↗
Study of the one-way speed of light anisotropy with particle beams
Concepts of high precision studies of the one-way speed of light anisotropy are discussed. The high energy particle beam allows measurement of a one-way speed of light anisotropy (SOLA) via analysis of the beam momentum variation with sidereal phase without the use of synchronized clocks. High precision beam position monitors could provide accurate monitoring of the beam orbit and determination of the particle beam momentum with relative accuracy on the level of 10^-10, which corresponds to a limit on SOLA of 10^-18 with existing storage rings. A few additional versions of the experiment are also presented.
Wojtsekhowski, Bogdan B.↗
Photon (Non)Conservation in the Reduced Speed of Light Approximation and How to (Almost) Fix It
The "Reduced Speed of Light" (RSL) approximation is commonly used to speed up radiative transfer calculations in cosmological simulations. However, it has been shown previously that the RSL approximation leads to photon non-conservation when the radiation field is rapidly evolving in time. I show that these missing photons can be counted exactly for some numerical schemes. Adding them back into a simulation, however, is a much harder task. I show one example of such a scheme, which achieves sub-percent accuracy on simple tests. Unfortunately, the scheme performs much worse on semi-realistic simulations of cosmic reionization, leading to a faster overlap and significant errors in the point-wise comparison of the RSL radiation field with the reference simulation that maintains the full speed of light for the radiative transfer.
Gnedin, Nickolay Y. [Fermilab; Chicago U., KICP; C↗
Measuring the speed of light with ultra-compact radio quasars
In this paper, based on a 2.29 GHz VLBI all-sky survey of 613 milliarcsecond ultra-compact radio sources with 0.0035< z <3.787, we describe a method of identifying the sub-sample which can serve as individual standard rulers in cosmology. If the linear size of the compact structure is assumed to depend on source luminosity and redshift as l {sub m} = l L {sup β} (1+ z ) {sup n} , only intermediate-luminosity quasars (10{sup 27} W/Hz< L < 10{sup 28} W/Hz) show negligible dependence (| n |≅ 10{sup −3}, |β|≅ 10{sup −4}), and thus represent a population of such rulers with fixed characteristic length l =11.42 pc. With a sample of 120 such sources covering the redshift range 00.46< z <2.8, we confirm the existence of dark energy in the Universe with high significance under the assumption of a flat universe, and obtain stringent constraints on both the matter density Ω {sub m} =0.323{sup +0.245}{sub −0.145} and the Hubble constant H {sub 0}=66.30{sup +7.00}{sub −8.50} km sec{sup −1} Mpc{sup −1}. Finally, with the angular diameter distances D {sub A} measured for quasars extending to high redshifts (0 z ∼ 3.), we reconstruct the D {sub A} ( z ) function using the technique of Gaussian processes. This allows us to identify the redshift corresponding to the maximum of the D {sub A} ( z ) function: 0 z {sub m} =1.7 and the corresponding angular diameter distance D {sub A} ( z {sub m} )=1719.01±43.46 Mpc. Similar reconstruction of the expansion rate function H ( z ) based on the data from cosmic chronometers and BAO gives us H ( z {sub m} )=176.77±6.11 km sec{sup −1} Mpc{sup −1}. These measurements are used to estimate the speed of light: c =3.039(±0.180)× 10{sup 5} km/s. This is the first measurement of the speed of light in a cosmological setting referring to the distant past.
79 ASTRONOMY AND ASTROPHYSICS↗
Audi e-tron Green Light Optimized Speed Advisory On-Road Data
To aid researchers in studying the capabilities and benefits of vehicle-to-infrastructure communication, Argonne National Laboratory collected a robust set of on-road driving data of the Audi Green Light Optimized Speed Advisory (GLOSA) system implemented in the e-tron battery electric vehicle. This dataset includes 33 tests, each roughly 27 miles in length and roughly 45 to 75 minutes in duration. The team selected Kane County Highway Route 34 from Main Street in Batavia, Illinois to Middlecreek Lane in St. Charles, Illinois as the route do to its high density of GLOSA-active lights and the most opportunities to observe the system per hour of test time. The data include parameters from the following sources: GLOSA system driving the dash indicators, multiple powertrain parameters including real-time battery power/energy consumption, GPS, front radar gap, and rear radar gap. 
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
Speed-of-light pulses in a massless nonlinear Dirac equation
Here, in this work, we explore a massless nonlinear Dirac equation, i.e., a nonlinear Weyl equation. We study the dynamics of its pulse solutions and find that a localized one-hump initial condition splits into a localized two-hump pulse, while an associated phase structure emerges in suitable components of the spinor field. For times larger than a transient time t s this pulse moves with the speed of light, effectively featuring linear wave dynamics and maintaining its shape (both in two and three dimensions). We show that for the considered nonlinearity, this pulse represents an exact solution of the nonlinear equation. Finally, we briefly comment on the generalization of the results to a broader class of nonlinearities.
97 MATHEMATICS AND COMPUTING↗
Digital Modeling on Large Kernel Metamaterial Neural Network
Deep neural networks (DNNs) utilized recently are physically deployed with computational units (e.g., CPUs and GPUs). Such a design might lead to a heavy computational burden, significant latency, and intensive power consumption, which are critical limitations in applications such as Internet of Things (IoT), edge computing, and usage of drones. Recent advances in optical computational units (e.g., metamaterial) have shed light on energy-free and light-speed neural networks. However, the digital design of the metamaterial neural network (MNN) is fundamentally limited by its physical limitations, such as precision, noise, and bandwidth during fabrication. Moreover, the unique advantages of MNN’s (e.g., light-speed computation) are not fully explored via standard 3×3 convolution kernels. In this paper, we propose a novel large kernel metamaterial neural network (LMNN) that maximizes the digital capacity of the state-of-the-art (SOTA) MNN with model re-parametrization and network compression, while also considering the optical limitation explicitly. The new digital learning scheme can maximize the learning capacity of MNN while modeling the physical restrictions of meta-optics. With the proposed LMNN, the computation cost of the convolutional front-end can be offloaded to fabricated optical hardware. The experimental results on two publicly available datasets demonstrate that the optimized hybrid design improved classification accuracy while reducing computational latency. In conclusion, the development of the proposed LMNN is a promising step towards the ultimate goal of energy-free and light-speed AI.
97 MATHEMATICS AND COMPUTING↗
Speed-of-light pulses in the massless nonlinear Dirac equation with a potential
In this work, we consider the massless nonlinear Dirac (NLD) equation in 1 + 1 dimension with scalar-scalar self-interaction g 2 2 ( Ψ ¯ Ψ ) 2 in the presence of three external electromagnetic real potentials V ( x ) , a potential barrier, a constant potential, and a potential well. By solving numerically the NLD equation, we find different scenarios depending on initial conditions, namely, propagation of the initial pulse along one direction, splitting of the initial pulse into two pulses traveling in opposite directions, and focusing of two initial pulses followed by a splitting. For all considered cases, the final waves travel with the speed of light and are solutions of the massless linear Dirac equation. During these processes the charge and the energy are conserved, whereas the momentum is conserved when the solutions possess specific symmetries. For the case of the constant potential, we derive exact analytical solutions of the massless NLD equation that are also solutions of the massless linearized Dirac equation. Decay or growth of the initial pulse is also predicted from the evolution of the charge for the case of a non-zero imaginary part of the potential.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Piezoelectrically actuated silicon-nitride-based high-speed spatial light modulator
Advancements in light modulator technology have been driving discoveries and progress across various fields. The problem of large-scale coherent optical control of atomic quantum systems—including cold atoms, ions, and solid-state color centers—presents among the most stringent requirements. This motivates a new generation of high-speed large-scale modulator technology operating in the visible to near-infrared wavelength range. We introduce a scalable modulator technology based on piezoelectrically actuated silicon nitride resonant waveguide gratings fabricated on 200 mm diameter silicon wafers with CMOS-compatible processes. We present a proof-of-concept device with 4 × 4 individually addressable 50 μ m × 50 μ m pixels or channels, each containing a resonant waveguide grating with a ~ 780 nm design wavelength, supporting > 100 MHz modulation speeds, and a spectral response with > 20 dB extinction.
integrated optics↗
Molecular Materials with Short Radiative Lifetime for High-Speed Light-Emitting Devices
Not Available
Zhao, Yingbo (ORCID:0000000262897015)↗
Bright electroluminescence in ambient conditions from WSe 2 p-n diodes using pulsed injection
Transition metal dichalcogenide (TMDC) monolayers are promising materials for next-generation nanoscale optoelectronics, including high-speed light sources and detectors. However, most past reports on TMDC light-emitting diodes are limited to operation in high vacuum, while most applications require operation under ambient conditions. Here, we study the time-resolved electroluminescence of monolayer WSe 2 p-n junctions under ambient conditions and identify the decay in current over time as the main issue preventing stable device operation. We show that pulsed voltage bias overcomes this issue and results in bright electroluminescence under ambient conditions. This is achieved in a simple single-gate structure, without the use of dual gates, heterostructures, or doping methods. Internal quantum efficiency of electroluminescence reaches ~1%, close to the photoluminescence quantum efficiency, indicating efficient exciton formation with injected carriers. Emission intensity is stable over hours of device operation. Finally, our device exhibits ~15 ns rise and fall times, the fastest direct modulation speed reported for TMDC light-emitting diodes.
2D materials↗
Effect of vertical canopy architecture on transpiration, thermoregulation and carbon assimilation
Quantifying the impact of natural and anthropogenic disturbances such as deforestation, forest fires and vegetation thinning among others on net ecosystem—atmosphere exchanges of carbon dioxide, water vapor and heat—is an important aspect in the context of modeling global carbon, water and energy cycles. The absence of canopy architectural variation in horizontal and vertical directions is a major source of uncertainty in current climate models attempting to address these issues. This work demonstrates the importance of considering the vertical distribution of foliage density by coupling a leaf level plant biophysics model with analytical solutions of wind flow and light attenuation in a horizontally homogeneous canopy. It is demonstrated that plant physiological response in terms of carbon assimilation, transpiration and canopy surface temperature can be widely different for two canopies with the same leaf area index (LAI) but different leaf area density distributions, under several conditions of wind speed, light availability, soil moisture availability and atmospheric evaporative demand.
54 ENVIRONMENTAL SCIENCES↗
Vacuum laser acceleration of super-ponderomotive electrons using relativistic transparency injection
Abstract Intense lasers can accelerate electrons to very high energy over a short distance. Such compact accelerators have several potential applications including fast ignition, high energy physics, and radiography. Among the various schemes of laser-based electron acceleration, vacuum laser acceleration has the merits of super-high acceleration gradient and great simplicity. Yet its realization has been difficult because injecting free electrons into the fast-oscillating laser field is not trivial. Here we demonstrate free-electron injection and subsequent vacuum laser acceleration of electrons up to 20 MeV using the relativistic transparency effect. When a high-contrast intense laser drives a thin solid foil, electrons from the dense opaque plasma are first accelerated to near-light speed by the standing laser wave in front of the solid foil and subsequently injected into the transmitted laser field as the opaque plasma becomes relativistically transparent. It is possible to further optimize the electron injection/acceleration by manipulating the laser polarization, incident angle, and temporal pulse shaping. Our result also sheds light on the fundamental relativistic transparency process, crucial for producing secondary particle and light sources.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Optical emission from a kilonova following a gravitational-wave-detected neutron-star merger
The merger of two neutron stars has been predicted to produce an optical–infrared transient (lasting a few days) known as a ‘kilonova’, powered by the radioactive decay of neutron-rich species synthesized in the merger. Evidence that short γ-ray bursts also arise from neutron-star mergers has been accumulating. In models of such mergers, a small amount of mass (10 -4 –10 -2 solar masses) with a low electron fraction is ejected at high velocities (0.1–0.3 times light speed) or carried out by winds from an accretion disk formed around the newly merged object. This mass is expected to undergo rapid neutron capture (r-process) nucleosynthesis, leading to the formation of radioactive elements that release energy as they decay, powering an electromagnetic transient. A large uncertainty in the composition of the newly synthesized material leads to various expected colours, durations and luminosities for such transients. Observational evidence for kilonovae has so far been inconclusive because it was based on cases of moderate excess emission detected in the afterglows of γ-ray bursts. Here we report optical to near-infrared observations of a transient coincident with the detection of the gravitational-wave signature of a binary neutron-star merger and with a low-luminosity short-duration γ-ray burst. Our observations, taken roughly every eight hours over a few days following the gravitational-wave trigger, reveal an initial blue excess, with fast optical fading and reddening. Using numerical models, we conclude that our data are broadly consistent with a light curve powered by a few hundredths of a solar mass of low-opacity material corresponding to lanthanide-poor (a fraction of 10 -4.5 by mass) ejecta.
Arcavi, Iair↗
Giant Modal Gain Coefficients in Colloidal II–VI Nanoplatelets
Modal gain coefficient is a key figure of merit for a laser material. Previously, net modal gain coefficients larger than a few thousand cm –1 were achieved in II–VI and III–V semiconductor gain media, but this required operation at cryogenic temperatures. In this work, using pump-fluence-dependent variable-stripe-length measurements, we show that colloidal CdSe nanoplatelets enable giant modal gain coefficients at room temperature up to 6600 cm –1 under pulsed optical excitation. Furthermore, we show that exceptional gain performance is common to the family of CdSe nanoplatelets, as shown by examining samples having different vertical thicknesses and lateral areas. Altogether, colloidal II–VI nanoplatelets with superior optical gain properties are promising for a broad range of applications, including high-speed light amplification and loss compensation in plasmonic photonic circuits.
42 ENGINEERING↗
Ghost particles and Project Poltergeist: Long-ago Lab physicists studied science that haunted them
A neutrino is a tiny, almost massless particle that travels at near light speeds. They were first formed in the early universe and are continually being produced in the nuclear reactions of stars, like the sun, and nuclear reactions on earth. The existence of these “ghost particles” was incredibly difficult to detect, but doing so has helped scientists better understand fundamental principles in physics. Los Alamos Manhattan Project scientist Frederick Reines, along with his colleague Clyde Cowan, is credited with the experimental discovery of the nearly massless elementary particle after his team definitively proved the neutrino’s existence in 1956. Reines received the Nobel Prize in Physics in 1995.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Ghost particles and Project Poltergeist: Long-ago Lab physicists studied science that haunted them
A neutrino is a tiny, almost massless particle that travels at near light speeds. They were first formed in the early universe and are continually being produced in the nuclear reactions of stars, like the sun, and nuclear reactions on earth. The existence of these “ghost particles” was incredibly difficult to detect, but doing so has helped scientists better understand fundamental principles in physics. Los Alamos Manhattan Project scientist Frederick Reines, along with his colleague Clyde Cowan, is credited with the experimental discovery of the nearly massless elementary particle after his team definitively proved the neutrino’s existence in 1956. Reines received the Nobel Prize in Physics in 1995.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗