Contributors:Lörch, Niels, Amitai, Ehud, Nunnenkamp, Andreas, Bruder, Christoph
We study the synchronization of a Van der Pol self-oscillator with Kerr anharmonicity to an external drive. We demonstrate that the anharmonic, discrete energy spectrum of the quantum oscillator leads to multiple resonances in both phase locking and frequency entrainment not present in the corresponding classical system. Strong driving close to these resonances leads to nonclassical steady-state Wigner distributions. Experimental realizations of these genuine quantum signatures can be implemented with current technology.
Contributors:Lüders, Klaus, Pohl, Robert Otto, Beuermann, Gustav, Samwer, Konrad
Contributors:Xin, Zhang, Jie, Shao, Wenwei, An, Tiantian, Yang, Malekian, Reza
This is a supplement to file K4BSE 34.124 -84.203 5 MHz.csv submitted last week, just after the frequency measurement period. I'd wondered about some jumps in frequency error I saw in my earlier submission (see xlxs file attached of the original frequency measurement run), so in this test I measured frequency error in exactly the same way, except that I was measuring a 10 MHz signal from a rubidium stabilized frequency source. The receiver was still stabilized by a GPSDO. I see some similar-magnitude frequency jumps here (note change in vertical scale). Also some frequency drifts is seen between some of the jumps, consistent with frequency drift in the test data submitted previously. I presume the jumps are due to the frequency calibration jumps in the K3's local oscillator. As best I can tell, the frequency of the K3 in the locked mode is determined by measurement of the frequency of an external 10 MHz oscillator, which is then used to calculate a correction to the tuned frequency of the radio. The jumps of a fraction of a Hz are consistent with the stated frequency accuracy of the radio when locked to a good reference (eg., the GPSDO used).
Contributors:Siow, Matthew, Couzin, Iain
Army ants (Eciton burchellii) have been studied for nearly a century, but
observable patterns in their traffic organization have not yet been explored,
despite the fact that this organization contributes greatly to their optimal foraging.
Using pheromones and tactile cues to transmit information from ant to ant, they
coordinate their movements in order to optimize traffic and create a collective
behavior that increases the overall efficiency of the colony. Garnier et al. (2013)
discovered that E. burchellii traffic possesses regular, periodic oscillations that
allow it to gain maximum stability. In this paper, we explored these traffic
oscillations at trail junctions to determine how army ants optimize their network of
foraging trails. After conducting research at La Selva Biological Station in Costa
Rica, we found that the mean oscillationfrequencies and periods of army ant
traffic are uniform and unrelated to traffic direction. Despite this overarching
uniformity, each zone of a trail junction possesses a different oscillationfrequency
compared to the other two zones of the same junction. Lastly, oscillationfrequency
increases as traffic becomes more unidirectional. By displaying differential
oscillatory behavior at trail junctions, army ants spontaneously adapt to their
constantly changing environment in order to optimize traffic dynamics. Finally, we
propose ideas for future research that have the potential to delve deeper into the
study of trail junctions.
Festival of Frequency Measurement 5MHz 1 October 2019 at location Sunnyvale, CA by Tom Minnis WB6HYD
Start time UTC: 23:15:09 Sept 30, 2019, End time: 0:40:10 Oct 2, 2019
Receiver: FLEX-6400 with external GPS disciplined 10MHz oscillator, FURUNO GF8802
Antenna: AV680 multi-band vertical
Analysis tool: fldigi ver 4.1.08
I was not able to get fldigi to log the RF frequency correctly so I created the RF corrected column by adding the Freq Error to 5MHz. The computer was running Windows 8.1 and the internal time of day clock is updated every hour using NTP
Contributors:U. Ramesh Babu, V. Vijay Kumar Reddy, S. Tara Kalyani
Contributors:Abbott, Joshua L., Straube, Arthur V., Aarts, Dirk G. A. L., Dullens, Roel P. A.
A colloidal particle is driven across a temporally oscillating one-dimensional optical potential energy landscape and its particle motion is analysed. Different modes of dynamic mode locking are observed and are confirmed with the use of phase portraits. The effect of the oscillationfrequency on the mode locked step width is addressed and the results are discussed in light of a high-frequency theory and compared to simulations. Furthermore, the influence of the coupling between the particle and the optical landscape on mode locking is probed by increasing the maximum depth of the optical landscape. Stronger coupling is seen to increase the width of mode locked steps. Finally, transport across the temporally oscillating landscape is studied by measuring the effective diffusion coefficient of a mobile particle, which is seen to be highly sensitive to the driving velocity and mode locking.
Contributors:Francesco R. Ruggeri
Contributors:Deng, Jian, Caulfield, Colm-cille
Using two-dimensional direct numerical simulations, we investigate the flow in a fluid of kinematic viscosity ν and density ρ around elliptical foils of density ρ_s with major axis c and minor axis b for three different aspect ratios: AR = b/c = 1 (a circle); AR = 0.5; and AR = 0.1. The vertical location of these foils y_s(t) = A sin(2πf₀t) oscillates with amplitude A and frequency f₀ in two distinct ways: ‘pure’ oscillation, where the foils are constrained to remain in place; and ‘flying’ oscillation, where horizontal motion is allowed. We simulate the flow for a range of the two appropriate control parameters, the nondimensional amplitude or Keulegan-Carpenter number KC = 2πA/c and the nondimensional frequency or Stokes number β = f₀c²/ν. We observe three distinct patterns of asymmetry, labelled ‘S-type’ for synchronous asymmetry, ‘QP_H-type’ and ‘QP_L-type’ for quasi-periodic asymmetry at sufficiently high and sufficiently low (i.e. AR = 0.1) aspect ratios respectively. These patterns are separated at the critical locus in KC − β space by a ‘freezing point’ where the two incommensurate frequencies of the QP-type flows combine, and we show that this freezing point tends to occur at smaller values of KC as AR decreases. We find for the smallest aspect ratio case (AR = 0.1) that the transition to asymmetry, for all values of KC, occurs for a critical value of an ‘amplitude’ Stokes number βA = β(KC)² = 4π² f0A²/ν ≃ 3. The QP_L-type asymmetry for AR = 0.1 is qualitatively different in physical and mathematical structure from the QP_H-type asymmetry at higher aspect ratio. The flow at the two ends of the ellipse become essentially decoupled from each other for the QP_L -type asymmetry, the two frequencies in the horizontal force signature being close to the primary frequency, rather than twice the primary frequency as in the QP_H-type asymmetry. Furthermore, the associated coefficients arising from a Floquet stability analysis close to the critical threshold are profoundly different for low aspect ratio foils. Freedom to move slightly suppresses the transition to S-type asymmetry, and for certain parameters, if a purely oscillating foil subject to S-type asymmetry is released to move, flow symmetry is rapidly recovered due to the negative feedback of small horizontal foil motion. Conversely, for the ‘higher’ aspect ratios, the transition to QP_H-type asymmetry is encouraged when the foil is allowed to move, with strong positive feedback occurring between the shed vortices from successive oscillation cycles. For AR = 0.1, freedom to move significantly encourages the onset of asymmetry, but the newly observed ‘primary’ QP_L-type asymmetry found for pure oscillation no longer occurs when the foil flies, with S-type asymmetry leading ultimately to locomotion at a constant speed occurring all along the transition boundary for all values of KC and β.