Interpreting motion and force for narrow-band intermodulation atomic force microscopy

Intermodulation atomic force microscopy (ImAFM) is a mode of dynamic atomic force microscopy that probes the nonlinear tip-surface force by measurement of the mixing of multiple tones in a frequency comb. A high $Q$ cantilever resonance and a suitable drive comb will result in tip motion described by a narrow-band frequency comb. We show by a separation of time scales, that such motion is equivalent to rapid oscillations at the cantilever resonance with a slow amplitude and phase or frequency modulation. With this time domain perspective we analyze single oscillation cycles in ImAFM to extract the Fourier components of the tip-surface force that are in-phase with tip motion ($F_I$) and quadrature to the motion ($F_Q$). Traditionally, these force components have been considered as a function of the static probe height only. Here we show that $F_I$ and $F_Q$ actually depend on both static probe height and oscillation amplitude. We demonstrate on simulated data how to reconstruct the amplitude dependence of $F_I$ and $F_Q$ from a single ImAFM measurement. Furthermore, we introduce ImAFM approach measurements with which we reconstruct the full amplitude and probe height dependence of the force components $F_I$ and $F_Q$, providing deeper insight into the tip-surface interaction. We demonstrate the capabilities of ImAFM approach measurements on a polystyrene polymer surface.Comment: 12 pages, 7 figure

Phase imaging with intermodulation atomic force microscopy

Intermodulation atomic force microscopy (IMAFM) is a dynamic mode of atomic force microscopy (AFM) with two-tone excitation. The oscillating AFM cantilever in close proximity to a surface experiences the nonlinear tip-sample force which mixes the drive tones and generates new frequency components in the cantilever response known as intermodulation products (IMPs). We present a procedure for extracting the phase at each IMP and demonstrate phase images made by recording this phase while scanning. Amplitude and phase images at intermodulation frequencies exhibit enhanced topographic and material contrast.Comment: 6 pages, 6 page

Osteosynthese distaler Radiusfrakturen mit der AO/ASIF Titan-Pi-Platte

Zusammenfassung: Die AO/ASIF Titan-Pi-Platte wurde entwickelt, um eine optimale Versorgung distaler, intraartikulärer und instabiler Radiusfrakturen zu gewährleisten. Dies soll durch eine optimale Anpassung an die Anatomie sowie durch Winkelstabilität und flachem Design erfolgen. Ziel der vorliegenden retrospektiven Fallkontrollstudie war es, die objektiven und subjektiven Resultate anhand einer konsekutiven Reihe von 61Patienten mindestens 12Monate (12-29Monate) postoperativ mittels Befragung, klinischer Untersuchung und konventioneller radiologischer Bildgebung zu erheben. Nach Klassifikation der AO handelte es sich um 3A2-, 23A3-, 1B1-, 12C1- und 22C2-Frakturen. Die Resultate zeigen insgesamt ein gutes bis sehr gutes Resultat bezüglich des subjektiven Befindens. Die Messungen des Bewegungsumfangs ergaben durchschnittlich über 80% im Vergleich zur Gegenseite. Die klinische Prüfung der Extensorensehnen ergab keine Rupturen und 18% Irritationen. Das Kollektiv mit Osteosynthesematerialentfernung zeigte einen signifikant größeren Bewegungsumfang der Extension und Ulnarabduktion, eine höhere Kraft sowie nur 3,8% Sehnenirritationen. Mit der Pi-Platte lassen sich gute subjektive und objektive Resultate erreichen. Aufgrund der signifikant besseren Beweglichkeit und höheren Kraft sowie der geringeren Rate an Sehnenirritationen nach Entfernung der Platte sollte die Indikation zur Osteosynthesematerialentfernung großzügig gestellt werde

Solid-State Excitation Laser for Laser-Ultrasonics

The inspection speed of laser-ultrasonics compared with conventional ultrasonic testing is limited by the pulse repetition rate of the excitation laser. The maximum pulse repetition rate reported up to now for CO2-lasers, which are presently used for nearly all systems, is in the range of 400 Hz. In this paper a new approach based on a diode-pumped solid-state laser is discussed, which is currently being developed. This new excitation laser is designed for a repetition rate of 1 kHz and will operate at a mid-IR wavelength of 3.3 m. The higher repeti-tion rate enables a higher inspection speed, whereas the mid-IR wavelength anticipates a better coupling efficiency. The total power for pumping the laser crystals is transported via flexible optical fibres to the compact laser head, thus allowing operation on a robot arm. The laser head consists of a master oscillator feeding several lines of power amplifiers and in-cludes nonlinear optical wavelength conversion by an optical parametric process. It is char-acterized by a modular construction which provides optimal conditions for operation at high average power as well as for easy maintenance. These features will enable building reliable, long-lived, rugged, smart laser ultrasonic systems in futur

Spectral properties and geology of bright and dark material on dwarf planet Ceres

Variations and spatial distributions of bright and dark material on dwarf planet Ceres play a key role in understanding the processes that have led to its present surface composition. We define limits for bright and dark material in order to distinguish them consistently, based on the reflectance of the average surface using Dawn Framing Camera data. A systematic classification of four types of bright material is presented based on their spectral properties, composition, spatial distribution, and association with specific geomorphological features. We found obvious correlations of reflectance with spectral shape (slopes) and age; however, this is not unique throughout the bright spots. Although impact features show generally more extreme reflectance variations, several areas can only be understood in terms of inhomogeneous distribution of composition as inferred from Dawn Visible and Infrared Spectrometer data. Additional material with anomalous composition and spectral properties are rare. The identification of the composition and origin of the dark, particularly the darkest material, remains to be explored. The spectral properties and the morphology of the dark sites suggest an endogenic origin, but it is not clear whether they are more or less primitive surficial exposures or excavated subsurface but localized material. The reflectance, spectral properties, inferred composition, and geologic context collectively suggest that the bright and dark material tends to gradually change toward the average surface over time. This could be because of multiple processes, i.e., impact gardening/space weathering, and lateral mixing, including thermal and aqueous alteration, accompanied by changes in composition and physical properties such as grain size, surface temperature, and porosity (compaction).Comment: Meteoritics and Planetary Science; Dawn at Ceres special issu