Friedemann Freund

Bio: Friedemann Freund is an academic researcher from Ames Research Center. The author has contributed to research in topics: Charge carrier & Electric current. The author has an hindex of 31, co-authored 97 publications receiving 3293 citations. Previous affiliations of Friedemann Freund include Arizona State University & Search for extraterrestrial intelligence.

Electric currents streaming out of stressed igneous rocks - A step towards understanding pre-earthquake low frequency EM emissions

Abstract: Transient electric currents that flow in the Earth’s crust are necessary to account for many non-seismic pre-earthquake signals, in particular for low frequency electromagnetic (EM) emissions. We show that, when we apply stresses to one end of a block of igneous rocks, two currents flow out of the stressed rock volume. One current is carried by electrons and it flows out through a Cu electrode directly attached to the stressed rock volume. The other current is carried by p-holes, i.e., defect electrons on the oxygen anion sublattice, and it flows out through at least 1 m of unstressed rock to meet the electrons that arrive through the outer electric circuit. The two outflow currents are part of a battery current. They are coupled via their respective electric fields and fluctuate. Applying the insight gained from these laboratory experiments to the field, where large volume of rocks must be subjected to ever increasing stress, leads us to suggest transient, fluctuating currents of considerable magnitude that would build up in the Earth’s crust prior to major earthquakes. � 2006 Elsevier Ltd. All rights reserved.

Time-resolved study of charge generation and propagation in igneous rocks

Abstract: Electrical resistivity changes, ground potentials, electromagnetic (EM), and luminous signals preceding or accompanying earthquakes have been reported many times, in addition to ground uplift and tilt and other parameters. However, no concept exists that would tie these diverse phenomena together into a physically coherent model. Using low-to medium-velocity impacts to measure electrical signals with microsecond time resolution, it is observed that when gabbro and diorite cores are impacted at relatively low velocities, ≈ 100 m/s, highly mobile charge carriers are generated in a small volume near the impact point. They spread through the rocks, causing electric potentials exceeding +400 mV, EM, and light emission. As the charge cloud spreads, the rock becomes momentarily conductive. When a granite block is impacted at higher velocity, ≈ 1.5 km/s, the propagation of the P and S waves is registered through the transient piezoelectric response of quartz. After the sound waves have passed, the surface of the granite block becomes positively charged, suggesting the same charge carriers as observed during the low-velocity impact experiments, expanding from within the bulk. During the next 2–3 ms the surface potential oscillates, indicating pulses of electrons injected from ground and contact electrodes. The observations are consistent with positive holes, e.g., defect electrons in the O2- sublattice, traveling via the O 2p-dominated valence band of the silicate minerals. The positive holes propagate as charge clouds rather than as classical EM waves. Before activation, they lay dormant in form of electrically inactive positive hole pairs, PHP, chemically equivalent to peroxy links, O3X/OO//XO3 with X = Si4+, Al3+, etc. PHPs are introduced into the minerals by way of hydroxyl, O3X-OH, which all nominally anhydrous minerals incorporate when crystallizing in H2O-laden environments. The fact that positive holes can be activated by low-energy impacts, and their attendant sound waves, suggests that they can also be activated in the crust by microfractures during the dilatancy phase. Depending on where in the stressed rock volume the charge carriers are activated, they will form rapidly moving or fluctuating charge clouds that can account for earthquake-related electrical signals and EM emission. Wherever such charge clouds intersect the surface, high fields are expected, causing electric discharges and earthquake lights.

Endogenous production, exogenous delivery and impact-shock synthesis of organic molecules: an inventory for the origins of life

Abstract: The contribution of organic-rich comets, carbonaceous asteroids, and interplanetary dust particles and of impact shock-synthesized organics in the atmosphere to the origin of life on earth is studied and quantitatively compared with the principal non-heavy-bombardment sources of prebiotic organics. The results suggest that heavy bombardment before 3.5 Gyr ago either produced or delivered quantities of organics comparable to those produced by other energy sources.

Organic Molecules in the Interstellar Medium, Comets, and Meteorites: A Voyage from Dark Clouds to the Early Earth

Abstract: ▪ Abstract Our understanding of the evolution of organic molecules, and their voyage from molecular clouds to the early solar system and Earth, has changed dramatically. Incorporating recent observ...

A voyage from dark clouds to the early Earth

Abstract: Stellar nucleosynthesis of heavy elements, followed by their subsequent release into the interstellar medium, enables the formation of stable carbon compounds in both gas and solid phases. Spectroscopic astronomical observations provide evidence that the same chemical pathways are widespread both in the Milky Way and in external galaxies. The physical and chemical conditions—including density, temperature, ultraviolet radiation and energetic particle flux—determine reaction pathways and the complexity of organic molecules in different space environments. Most of the organic carbon in space is in the form of poorly-defined macromolecular networks. Furthermore, it is also unknown how interstellar material evolves during the collapse of molecular clouds to form stars and planets. Meteorites provide important constraints for the formation of our Solar System and the origin of life. Organic carbon, though only a trace element in these extraterrestrial rock fragments, can be investigated in great detail with sensitive laboratory methods. Such studies have revealed that many molecules which are essential in terrestrial biochemistry are present in meteorites. To understand if those compounds necessarily had any implications for the origin of life on Earth is the objective of several current and future space missions. However, to address questions such as how simple organic molecules assembled into complex structures like membranes and cells, requires interdisciplinary collaborations involving various scientific disciplines. Introduction Life in the Universe is the consequence of the increasing complexity of chemical pathways which led to stable carbon compounds assembling into cells and higher organisms.

Influence of water on plastic deformation of olivine aggregates 2. Dislocation creep regime

Abstract: Triaxial compressive creep experiments have been conducted over a range of hydrous conditions to investigate the effect of water fugacity on the creep behavior of olivine aggregates in the dislocation creep regime. Samples synthesized from powders of San Carlos olivine were deformed at confining pressures of 100 to 450 MPa and temperatures between 1473 and 1573 K. Water was supplied by the dehydration of talc. Water fugacities of ∼80 to ∼520 MPa were obtained by varying the confining pressure under water-saturated conditions with the oxygen fugacity buffered at Ni/NiO. Sancles were deformed at differential stresses of ∼20 to 230 MPa. The transition from diffusion creep to dislocation creep occurs near 100 MPa for both the hydrous case and the anhydrous case. Under hydrous conditions creep experiments yield a stress exponent of n ≈ 3 and an activation energy of Q ≈ 470 kJ/mol. The creep rate of olivine is enhanced significantly with the presence of water. At a water fugacity of ∼300 MPa, samples crept ∼5–6 times faster than those deformed under anhydrous conditions at similar differential stresses and temperatures. Within the range of water fugacity investigated, the strain rate is proportional to water fugacity to the 0.69 to 1.25 power, assuming values for the activation volume of 0 to 38×10−6 m3/mol, respectively. We argue that water influences creep rate primarily through its effect on the concentrations of intrinsic point defects and hence on ionic diffusion and dislocation climb. With increasing water fugacity the charge neutrality condition changes from [FeMe•] = 2[VMe″] to [FeMe•] = [HMe′]. For the latter charge neutrality condition the concentration of silicon interstitials is proportional to fH2O1, suggesting that under hydrous conditions dislocation climb is rate limited by diffusion of Si occurring by an interstitial mechanism. Our experimentally determined constitutive equation permits extrapolation from laboratory to mantle conditions in order to assess the rheological behavior of regions of the upper mantle with different water contents, such as beneath a mid-ocean ridge and in the mantle wedge above a subducting slab.