Biomedical subjects

G Busse

Publications and source records attributed to G Busse.

At least 19 recordsLinked to original sources

PubMed2004

Nonlinear acoustic approach to material characterisation of polymers and composites in tensile tests.

The paper reports on experimental study of elastic nonlinearity of polymers and glass fibre-reinforced (GFR-) composites in a wide range of tensile stress applied (up to a fracture limit). Focused slanted transmission mode (FSTM) of air-coupled ultrasound is adapted for remote generation and detection of flexural waves in the samples of plastics. Local noncontact measurements of flexural wave velocity as a function of static strain are used to calculate the second-order nonlinearity parameters beta2 and study their behaviour through a loading cycle. Molecular untangling and crazing phenomena are identified, respectively, with maxima of positive and negative beta2 in thermoplastics. In composites, mechanics of fibre-matrix interaction is considered for brittle and plastic fractures. Hysteresis in velocity variation during loading-unloading cycle is used as an indicator of residual defect accumulation.

Journal Article↗

PubMed2004

Nonlinear modulation technique for NDE with air-coupled ultrasound.

The present study is aimed at expanding flexibility and application area of nonlinear acoustic modulation (NAM-) technique by combining the benefits of noncontact ultrasound excitation (remote locating and imaging of defects) with sensitivity of nonlinear methods in a new air-coupled NAM-version. A pair of focused air-coupled transducers was used to generate and receive (high-frequency) longitudinal or flexural waves in plate-like samples. Low-frequency (LF-) vibrations were excited with a shaker or a loudspeaker. Temporal and spectral analysis of the output signal revealed an extremely efficient nonlinear amplitude modulation and multiple frequency side-bands for sound transmission and flexural wave propagation through cracked defects. On the contrary, a negligible modulation was observed for large and medium scale inclusions and material inhomogeneities (linear defects). A new subharmonic mode of the NAM was observed at high excitation levels. It was also shown for the first time that nonlinear vibrations of cracks resulted in radiation of a very high-order harmonics (well above 100) of the driving excitation in air that enabled imaging of cracks remotely by registration their highly nonlinear "acoustic emission" with air-coupled transducers.

Journal Article↗

PubMed2003

First investigations of the kinetics of the topochemical reaction of p-formyl-trans-cinnamic acid by time-resolved X-ray diffraction.

Under UV irradiation p-formyl-trans-cinnamic acid (p-FCA) crystals in the beta-phase dimerise irreversibly to solid 4,4'-diformyl-beta-truxinic acid. The experimental conditions were chosen in such a way (non-aqueous environment and room temperature) that the product formed is amorphous. The kinetics of this bimolecular reaction, which has not yet been characterised, was investigated by picosecond time-resolved X-ray diffraction. From the experimental results a mechanism for this topochemical reaction is proposed including two observed time constants, one less than 100 ps and another of several seconds. The feasibility of investigating this class of substances by time-resolved X-ray diffraction from third generation synchrotron sources and future free-electron lasers is discussed.

Cinnamates↗

PubMed2002

Air-coupled ultrasound inspection of various materials.

Conventional ultrasound inspection, a standard non-destructive testing method, uses a coupling medium (e.g. water) because of impedance mismatch. This liquid contact is a drawback because it prevents inspection of many materials. There is a need, then, for air-coupled ultrasound testing, which is now feasible because of low impedance focused narrow band transducers and sensitive electronics, both of which improve the signal-to-noise ratio. We present results obtained on fibre-reinforced plastics, water sensitive materials (e.g. reinforced ceramics), and "shape adaptive" structures to reveal delaminations, impacts, and growth of internal defects. Actuators embedded in "adaptive" structures are used as transmitters while the receiver records the signals. Thus it is possible to image defect areas and non-linear behaviour of potential defects.

Journal Article↗

PubMed2002

CAN: an example of nonclassical acoustic nonlinearity in solids.

A new class of nonlinear acoustic phenomena has been observed for acoustic wave interaction with simulated and realistic nonbonded contact interfaces (cracked defects) in solids. "Nonclassical" effects are due to substantially asymmetric stiffness characteristics of the interface for normal stress that results in specific contact acoustic nonlinearity (CAN). The asymmetry in the contact restoring forces causes the stiffness parametric modulation and instability of oscillations, which results in acoustic wave fractional subharmonic generation. The CAN subharmonics and higher harmonics reveal threshold dynamic behaviour, evident hysteresis, and instability effects.

Journal Article↗

PubMed2002

Acoustic non-linearity for defect selective imaging.

Non-linear acoustic effects are of increasing interest in close-to-application research in which mostly ultrasonic frequencies above 1 MHz are used. If the excitation frequency is reduced, one can use high power excitation performed locally by a piezoceramic stack actuator that provides much higher vibration amplitudes. The combination of this excitation with a scanning laser interferometer provides a system for rapidly imaging non-linearities and thereby selectively detecting defects in most kinds of materials. This contribution presents various experimental results showing the potential of this new technique.

Journal Article↗

PubMed1997

[The patient with respiratory problems].

Despite improvements in operative and anesthesiological techniques, respiratory problems in surgical patients have been minimized but not eliminated. In addition to risks which are typical for the individual patient, the perioperative respiratory morbidity is affected by anesthesiological manipulations as well as the operation and the nature of the operation (elective versus emergency). In this paper, after describing anesthesia-associated disturbances of the respiratory situation together with worsening due to the disease in patients with COLD, techniques and methods for therapy, prophylaxis, and prognostic assessment are delineated. Two examples are given for patients with respiratory problems (abdomino-thoracic esophageal resection as a example of local trauma in patients with numerous preoperative risk factors and acute necrotizing pancreatitis to describe the sequelae of a toxic process). The essence of our discussion is that, prognostically, preoperative diagnosis is of reduced value. Only a synopsis of clinical findings together with spirometry and blood gas analysis appears to be relevant. Early mobilization in conjunction with excellent postoperative pain therapy is of utmost importance, which is equivalent to the almost routine placement of a patient controllable epidural analgesia technique. These concepts have shown in the two patient groups described that respiratory morbidity may be reduced significantly. Cooperation between surgeons and anesthesiologists, which is characterized by complete and mutually high competence on both sides, is essential for successfully managing patients at increased respiratory risk.

Anesthesia, Epidural↗

PubMed1997