The spinning Astrid-2 satellite used for modeling the Earth's mainmagnetic field

The Swedish micro-satellite Astrid-2 was successfully launched into a near polar orbit in December 1998. Despite the fact that the primary science mission was auroral research, the magnetic instrument was designed to accomplish high-resolution and high-precision vector field magnetic measurements, and therefore mapping of the Earth's magnetic field was possible. The spacecraft spins about a highly stable axis in space. This fact and the globally distributed data make the magnetic measurements well suited for the estimate of a magnetic field model at the spacecraft altitude (about 1000 km). This paper describes the initial analysis of the Astrid-2 magnetic data. As a result of the study of a single day (February 7, 1999), magnetically fairly quiet, it was possible to in-flight adjust the calibration of the magnetometer and find a magnetic field model fitting the scalar component of the measurements to better than 5 nT_rms for latitudes equatorward of 50°. Several methods for field modeling are discussed in this paper under the assumption that the direction of the spin axis in inertial space is nearly constant, and this assumption is corroborated by the observations. The approximate inertial orientation of the magnetometer could then be determined simultaneously with the instrument intrinsic calibration and the estimate of main field model coefficients     

Coefficient sensitivity of state-space digital filters derivedusing balanced model truncation

The issue of coefficient sensitivity in digital filters derived using the technique of balanced model truncation is investigated. It is known that balanced systems have minimal sensitivity and we present some simulation results which show that subsequent truncation generates only a negligible deviation from this minimum. This is a desirable situation when designing reduced-order state-space digital filters     

Controlled ultrasound tissue erosion: the role of dynamic interaction between insonation and microbubble activity

Previous studies showed that ultrasound can mechanically remove tissue in a localized, controlled manner. Moreover, enhanced acoustic backscatter is highly correlated with the erosion process. "Initiation" and "extinction" of this highly backscattering environment were studied in this paper. The relationship between initiation and erosion, variability of initiation and extinction, and effects of pulse intensity and gas saturation on time to initiation (initiation delay time) were investigated. A 788-kHz single-element transducer was used. Multiple pulses at a 3-cycle pulse duration and a 20-kHz pulse repetition frequency were applied. I(SPPA) values between 1000 and 9000 W/cm2 and gas saturation ranges of 24%-28%, 39%-49%, and 77%-81% were tested. Results show the following: (1) without initiation, erosion was never observed; (2) initiation and extinction of the highly backscattering environment were stochastic in nature and dependent on acoustic parameters; (3) initiation delay times were shorter with higher intensity and higher gas saturation (e.g., the mean initiation delay time was 66.9 s at I(SPPA) of 4000 W/cm2 and 3.6 ms at I(SPPA) of 9000 W/cm2); and (4) once initiated by high-intensity pulses, the highly backscattering environment and erosion can be sustained using a significantly lower intensity than that required to initiate the process.     

Large‐Scale Fabrication of MoS2 Ribbons and Their Light‐Induced Electronic/Thermal Properties: Dichotomies in the Structural and Defect Engineering

Controlled design and patterning of layered transition metal dichalcogenides (TMDs) into specific dimensions and geometries hold great potential for next‐generation micro/nanoscale electronic applications. Herein, the large‐scale fabrication of MoS₂ ribbons with widths ranging from micro‐ to nanoscale is reported. Their unique electric and thermal properties introduced by the shape change and defect creation are also demonstrated, with particular focus on the performance associated with light–matter interactions. The theoretical calculation indicates significantly increased absorption and scattering efficiency of the MoS₂ ribbons with decreasing width. As a result, enhanced photocarrier generation ability is detected on their phototransistors with defect‐modulated light‐response behavior. The light‐induced thermal transport properties of the MoS₂ ribbons are further studied. A decreased thermal conductivity is observed on narrower ribbons, attributed to the defects created during fabrication. It is also found that the effect of phonon scattering at ribbon edges on their thermal conductivity is insignificant, and the thermal transport has no obvious dependence on the ribbon direction at such width scale. This study evaluates the prospects for designing and fabricating TMD semiconductors with specific geometries for future optoelectronic applications.