Abstract. Wavelet transform has recently been developed to the level of sophistication suitable for application to signal processing in magnetospheric research. We explore this new technique in decomposing signals in the time-frequency domain by first conducting continuous wavelet transform on a test signal to show its ability to resolve multiple-frequency components embedded within white noise of half the amplitude as the signal. We then use this tool to examine the large-amplitude magnetic fluctuations observed during a current disruption event.The results show the current disruption to be a multiscale phenomenon, encompassing low-as well as high-frequency components. The lowest-frequency component appears to behave quite independently from the higher-frequency components. The analysis shows for the first time that in current disruption the high-frequency components constitute a broadband excitation with a nonstationary nature, i.e., some oscillations appear to cascade from high to low frequency as time progresses.

Online controlled experiments (OCEs), also known as A/B tests, have become ubiquitous in evaluating the impact of changes made to software products and services. While the concept of online controlled experiments is simple, there are many practical challenges in running OCEs at scale. To understand the top practical challenges in running OCEs at scale and encourage further academic and industrial exploration, representatives with experience in large-scale experimentation from thirteen different organizations (Airbnb, Amazon, Booking.com, Facebook, Google, LinkedIn, Lyft, Microsoft, Netflix, Twitter, Uber, Yandex, and Stanford University) were invited to the first Practical Online Controlled Experiments Summit. All thirteen organizations sent representatives. Together these organizations have tested more than one hundred thousand experiment treatments last year. Thirty-four experts from these organizations participated in the summit in Sunnyvale, CA, USA on December 13-14, 2018. While there are papers from individual organizations on some of the challenges and pitfalls in running OCEs at scale, this is the first paper to provide the top challenges faced across the industry for running OCEs at scale and some common solutions.

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We investigate properties of the states of a Hermitian spin-+ field in a Robertson-Walker spacetime constructed by an energy-minimization requirement. It is shown that the singularity structure A of the commutator function ( [ @ ( x ) , 9 ( x 1 ) ] )for these states is such that current renormalization theory yields an infinite value for the renormalized expectation value of the trace of the stress tensor.

Recent theoretical models and preliminary observations indicate that super small striations (SSS) in the plasma density with scale size of 10 cm can be excited by F region HF heating at frequencies close to multiples of the electron gyrofrequency. We present here new experimental results using the High Frequency Active Auroral Research Program ionospheric heater at a frequency close to the fourth electron gyroharmonic with simultaneous GPS, Stimulated Electromagnetic Emission, ionosonde, and occasional Incoherent Radar Scattering diagnostics. Differential phase measurements of GPS signals through the heated region indicated the presence of SSS with extremely high amplitude (δn/n = 0.2-0.3) at scale size comparable to the electron gyroradius. The highest amplitude of GPS scintillations coincide with the highest level of the Broad Upshifted Maximum (BUM) and occurred when the HF frequency is slightly above the fourth harmonic of the electron cyclotron frequency. Frequency sweeps indicate that the scintillation amplitude exhibits hysteresis similar to that observed for the BUM amplitude when the HF frequency is cycled about the fourth harmonic of the cyclotron frequency. The results favor a four wave parametric process as the physical mechanism of the SSS. Additional experiments allowed the determination of the excitation and decay rates of the SSS.