Function Of Pump Frequency Research Articles

The behavior of electron density and temperature during ionospheric heating near the fifth electron gyrofrequency

AbstractThe experimental phenomena involving the changes in electron temperature and electron density as a function of pump frequency during an ionospheric heating campaign at European Incoherent Scatter near Tromsø, Norway, are reported. When the pump frequency is slightly above the fifth electron gyrofrequency, the UHF radar observation shows some apparent enhancements over a wide altitude range in radar echo, ion line, and electron density respectively, which are apparently altitude independent and consistent temporally with the upshifting and spread of plasma line around the reflection altitude. However, they do not, in fact, correspond to true increase in electron density. Based on some existing theories, some discussions are presented to try to explain the above enhancements and the upshifting and spread of plasma line. Even so, the mechanism remains to be determined. In addition, the observation also shows some enhancements in electron temperature as a function of pump frequency around the reflection altitude of the pump, which are dependent on the behavior of dispersion of the upper hybrid wave near the fifth electron gyrofrequency.

Results of Ionospheric Heating Experiments Involving an Enhancement in Electron Density in the High Latitude Ionosphere**supported by National Natural Science Foundation of China (No. 40831062)

Observations are presented of the phenomenon of the enhancement in electron density and temperature that is caused by a powerful pump wave at a frequency near the fifth gyrofrequency. The observations show that the apparent enhancement in electron density extending over a wide altitude range and the enhancement in electron temperature around the reflection altitude occur as a function of pump frequency. Additionally, the plasma line spectra show unusual behavior as a function of pump frequency. In conclusion, the upper hybrid wave resonance excited by the pump wave plays a dominating role and leads to the enhancement in electron temperature at the upper hybrid altitude. The phenomenon of apparent enhancement in electron density does not correspond to the true enhancement in electron density, this may be due to some mechanism that preferentially involves the plasma transport process and leads to the strong backscatter of radar wave along the magnetic line, which remains to be determined.

Spin current pumping in helical Luttinger liquids

We study the DC spin current induced into an unbiased quantum spin Hall system through a two-point contacts setup with time dependent electron tunneling amplitudes. By means of two external gates, it is possible to drive a current with spin-preserving and spin-flipping contributions showing peculiar oscillations as a function of pumping frequency, electron-electron interaction and temperature. From its interference patterns as a function of the Fabry-Perot and Aharonov-Bohm phases, it is possible to extract information about the helical nature of the edge states and the intensity of the electron-electron interaction.

Modeling and optimization of colloidal micro-pumps

Manipulating micro-particles is very important in microfluidic applications, such as biomedical flows and self-assembled structures. Here, flows generated by the forced motion of colloidal micro-particles in a microchannel are investigated. The force coupling method combined with the spectral/hp element method is used to numerically simulate the dynamics of the flow, while a penalty method is used to determine the required forces on the particles. The pumping motion is investigated for two specific systems: a peristaltic micro-pump and a gear micro-pump. We verify the accuracy of the simulations and then for each system, we investigate the net flow rate as a function of pump frequency and channel dimension, and present optimization results. The results for the net flow rate are comparable to and within the range of the experimental data.

Quantum pump for spin and charge transport in a Luttinger liquid.

We study two different parametric pumps--one for pumping spin currents, the other for charge currents--in interacting quantum wires. We find that, as a function of pumping frequency, the spin or charge pumped per cycle has a nonuniversal crossover--depending on pumping details--between two universal fixed point values of 0 and twice the electronic spin or charge quantum number. The direction of flow between these two fixed points depends on whether the interactions are repulsive or attractive, while the quantization itself is a signature of interactions.

Vibrational energy redistribution in polyatomic liquids: 3D infrared–Raman spectroscopy

Vibrational energy relaxation (VER) in polyatomic liquids and solutions can be studied in unprecedented detail using ultrafast incoherent anti-Stokes Raman spectroscopy to monitor the decay of a parent vibration generated with a tunable mid-IR pump pulse, and the appearance of daughter excitations at lower frequencies. A 2D vibrational spectroscopy technique results from fixing the mid-IR pump pulse and obtaining a time series of anti-Stokes Raman spectra. A 3D technique results from obtaining 2D spectra as a function of pump frequency. This 3D technique is presently the most powerful method available for studying VER in condensed phases. It provides information on VER mechanisms and pathways, liquid-state structural relaxation resulting in spectral diffusion, excitation transfer among sites with different local structures, strong correlations between vibrations as a result of Fermi resonance, and extremely weak anharmonic interactions resulting in VER via multistep vibrational cascades. The technique is illustrated by recent results obtained with ambient temperature associated liquids water (and deuterated water) and methanol, and by new measurements of strong correlations between CH stretching and bending and OH stretching and bending vibrations in methanol.