Sub-Terahertz Monochromatic Transduction with Semiconductor Acoustic Nanodevices

We demonstrate semiconductor superlattices or nanocavities as narrow band acoustic transducers in the sub-terahertz range. Using picosecond ultrasonics experiments in the transmission geometry with pump and probe incident on opposite sides of the thick substrate, phonon generation and detection processes are fully decoupled. Generating with the semiconductor device and probing on the metal, we show that both superlattices and nanocavities generate spectrally narrow wavepackets of coherent phonons with frequencies in the vicinity of the zone center and time durations in the nanosecond range, qualitatively different from picosecond broadband pulses usually involved in picosecond acoustics with metal generators. Generating in the metal and probing on the nanoacoustic device, we furthermore evidence that both nanostructured semiconductor devices may be used as very sensitive and spectrally selective detectors

Aerospace lubrication technology transfer to industrial applications

Difficulties encountered in entering industrial markets with an aerospace lubrication and coating technology are discussed along with the technical, financial, and managerial solutions that evolved

Sound velocity and absorption measurements under high pressure using picosecond ultrasonics in diamond anvil cell. Application to the stability study of AlPdMn

We report an innovative high pressure method combining the diamond anvil cell device with the technique of picosecond ultrasonics. Such an approach allows to accurately measure sound velocity and attenuation of solids and liquids under pressure of tens of GPa, overcoming all the drawbacks of traditional techniques. The power of this new experimental technique is demonstrated in studies of lattice dynamics, stability domain and relaxation process in a metallic sample, a perfect single-grain AlPdMn quasicrystal, and rare gas, neon and argon. Application to the study of defect-induced lattice stability in AlPdMn up to 30 GPa is proposed. The present work has potential for application in areas ranging from fundamental problems in physics of solid and liquid state, which in turn could be beneficial for various other scientific fields as Earth and planetary science or material research

Effect of picosecond strain pulses on thin layers of the ferromagnetic semiconductor (Ga,Mn)(As,P)

The effect of picosecond acoustic strain pulses (ps-ASP) on a thin layer of (Ga,Mn)As co-doped with phosphorus was probed using magneto-optical Kerr effect (MOKE). A transient MOKE signal followed by low amplitude oscillations was evidenced, with a strong dependence on applied magnetic field, temperature and ps-ASP amplitude. Careful interferometric measurement of the layer's thickness variation induced by the ps-ASP allowed us to model very accurately the resulting signal, and interpret it as the strain modulated reflectivity (differing for $\sigma_{\pm}$ probe polarizations), independently from dynamic magnetization effects.Comment: 6 pages, 5 figure

Partial frequencies and Chladni’s law in church bells

The rim partials of a church bell (those with an antinode at the soundbow) generate the strike pitch or perceived note of the bell. The spacing in frequency of the higher rim partials has an important effect on the tonal quality of the bell. Investigations into the partial frequencies of 2752 bells, both bronze and steel, of a wide variety of dates, founders and sizes, show a simple and unexpected relationship between the frequencies of the rim partials. This relationship explains why attempts to tune the higher rim partials independently have failed. A modified version of Chladni’s law provides insight into the musical relationship of the partials, and predicts the partials of individual bells well, but fails to give a simple model of the spacing between the partials seen in bells with different profiles

The molecular and dusty composition of Betelgeuse's inner circumstellar environment

The study of the atmosphere of red supergiant stars in general and of Betelgeuse (alpha Orionis) in particular is of prime importance to understand dust formation and how mass is lost to the interstellar medium in evolved massive stars. A molecular shell, the MOLsphere (Tsuji, 2000a), in the atmosphere of Betelgeuse has been proposed to account for the near- and mid-infrared spectroscopic observations of Betelgeuse. The goal is to further test this hypothesis and to identify some of the molecules in this MOLsphere. We report on measurements taken with the mid-infrared two-telescope beam combiner of the VLTI, MIDI, operated between 7.5 and 13.5 $\mu$m. The data are compared to a simple geometric model of a photosphere surrounded by a warm absorbing and emitting shell. Physical characteristics of the shell are derived: size, temperature and optical depth. The chemical constituents are determined with an analysis consistent with available infrared spectra and interferometric data. We are able to account for the measured optical depth of the shell in the N band, the ISO-SWS spectrum and K and L band interferometric data with a shell whose inner and outer radii are given by the above range and with the following species: H2O, SiO and Al2O3. These results confirm the MOLsphere model. We bring evidence for more constituents and for the presence of species participating in the formation of dust grains in the atmosphere of the star, i.e. well below the distance at which the dust shell is detected. We believe these results bring key elements to the understanding of mass loss in Betelgeuse and red supergiants in general and bring support to the dust-driven scenario.Comment: 11 pages, 10 figures, accepted for publication in A&

Competing interactions in artificial spin chains

The low-energy magnetic configurations of artificial frustrated spin chains are investigated using magnetic force microscopy and micromagnetic simulations. Contrary to most studies on two-dimensional artificial spin systems where frustration arises from the lattice geometry, here magnetic frustration originates from competing interactions between neighboring spins. By tuning continuously the strength and sign of these interactions, we show that different magnetic phases can be stabilized. Comparison between our experimental findings and predictions from the one-dimensional Anisotropic Next-Nearest-Neighbor Ising (ANNNI) model reveals that artificial frustrated spin chains have a richer phase diagram than initially expected. Besides the observation of several magnetic orders and the potential extension of this work to highly-degenerated artificial spin chains, our results suggest that the micromagnetic nature of the individual magnetic elements allows observation of metastable spin configurations.Comment: 5 pages, 4 figure

In the wake of Terra Nullius?

Terra nullius is the principle of a violence that inheres in every origin. And, in its wake, there is no law, no text, no culture, free ofthat violence. The origin is no accident. Terra nullius is not an historical error. Our conceptual legacy is the unsettled and unsettling history of this violence. It demands critical... thinking. Or else... we are condemned to repeat this origin again and again

Droplets move over viscoelastic substrates by surfing a ridge

Liquid drops on soft solids generate strong deformations below the contact line, resulting from a balance of capillary and elastic forces. The movement of these drops may cause strong, potentially singular dissipation in the soft solid. Here we show that a drop on a soft substrate moves by surfing a ridge: the initially flat solid surface is deformed into a sharp ridge whose orientation angle depends on the contact line velocity. We measure this angle for water on a silicone gel and develop a theory based on the substrate rheology. We quantitatively recover the dynamic contact angle and provide a mechanism for stick-slip motion when a drop is forced strongly: the contact line depins and slides down the wetting ridge, forming a new one after a transient. We anticipate that our theory will have implications in problems such as self-organization of cell tissues or the design of capillarity-based microrheometers.Comment: 9 pages, 5 figure