Viscoelastic properties of f-actin, microtubules, f-actin/alpha-actinin, and f-actin/hexokinase determined in microliter volumes with a novel nondestructive method.
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A nondestructive method to determine viscoelastic properties of gels and fluids involves an oscillating glass fiber serving as a sensor for the viscosity of the surrounding fluid. Extremely small displacements (typically 1-100 nm) are caused by the glass rod oscillating at its resonance frequency. These displacements are analyzed using a phase-sensitive acoustic microscope. Alterations of the elastic modulus of a fluid or gel change the propagation speed of a longitudinal acoustic wave. The system allows to study quantities as small as 10 microliters with temporal resolution >1 Hz. For 2-100 microM f-actin gels a final viscosity of 1.3-9.4 mPa s and a final elastic modulus of 2.229-2.254 GPa (corresponding to 1493-1501 m/s sound velocity) have been determined. For 10- to 100-microM microtubule gels (native, without stabilization by taxol), a final viscosity of 1.5-124 mPa s and a final elastic modulus of 2.288-2. 547 GPa (approximately 1513-1596 m/s) have been determined. During polymerization the sound velocity in low-concentration actin solutions increased up to +1.3 m/s (approximately 1.69 kPa) and decreased up to -7 m/s (approximately 49 kPa) at high actin concentrations. On polymerization of tubulin a concentration-dependent decrease of sound velocity was observed, too (+48 to -12 m/s approximately 2.3-0.1 MPa, for 10- to 100-microM tubulin). This decrease was interpreted by a nematic phase transition of the actin filaments and microtubules with increasing concentration. 2 mM ATP (when compared to 0.2 mM ATP) increased polymerization rate, final viscosity and elastic modulus of f-actin (17 microM). The actin-binding glycolytic enzyme hexokinase also accelerated the polymerization rate and final viscosity but elastic modulus (2.26 GPa) was less than for f-actin polymerized in presence of 0.2 mM ATP (2.28 GPa). (+info)
What is distinct about infants' "colic" cries?
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AIMS: To investigate (1) whether colic cries are acoustically distinct from pre-feed "hunger" cries; (2) the role of the acoustic properties of these cries versus their other properties in accounting for parents' concerns about colic. DESIGN: From a community sample, infants were selected who met Wessel colic criteria for amounts of crying and whose mothers identified colic bouts. Using acoustic analyses, the most intense segments of nine colic bouts were compared with matched segments from pre-feed cries presumed to reflect hunger. RESULTS: The colic cries did not have a higher pitch or proportion of dysphonation than the pre-feed cries. They did contain more frequent shorter utterances, but these resembled normal cries investigated in other studies. There is no evidence that colic cries have distinct acoustic features that are reproducible across samples and studies, which identify a discrete clinical condition, and which are identified accurately by parents. CONCLUSIONS: The most reliable finding is that colic cries convey diffuse acoustic and audible information that a baby is highly aroused or distressed. Non-acoustic features, including the prolonged, hard to soothe, and unexplained nature of the cries may be specific to colic cries and more important for parents. These properties might reflect temperament-like dispositions. (+info)
Voice-controlled robotic arm in laparoscopic surgery.
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AIM: To report on our experience with a voice-directed robotic arm for scope management in different procedures for "solo-surgery" and in complex laparoscopic operations. METHODS: A chip card with orders for the robotic arm is individually manufactured for every user. A surgeon gives order through a microphone and the optic field is thus under direct command of the surgeon. RESULTS: We analyzed 200 cases of laparoscopic procedures (gallbladder, stomach, colon, and hernia repair) done with the robotic arm. In each procedure the robotic arm worked precisely; voice understanding was exact and functioned flawlessly. A hundred "solo-surgery" operations were performed by a single surgeon. Another 96 complex videoscopic procedures were performed by a surgeon and one assistant. In comparison to other surgical procedures, operative time was not prolonged, and the number of used ports remained unchanged. CONCLUSION: Using the robotic arm in some procedures abolishes the need for assist ance. Further benefit accrued by the use of robotic assistance includes greater stability of view, less inadvertent smearing of the lens, and the absence of fatigue. The robotic arm can be used successfully in every operating theater by all surgeons using laparoscopy. (+info)
Cochlear function: hearing in the fast lane.
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The cochlea amplifies sound over a wide range of frequencies. Outer hair cells have been thought to play a mechanical part in this amplification, but it has been unclear whether they act rapidly enough. Recent work suggests that outer hair cells can indeed work at frequencies that cover the auditory range. (+info)
Advances in photoacoustic noninvasive glucose testing.
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We report here on in vitro and in vivo experiments that are intended to explore the feasibility of photoacoustic spectroscopy as a tool for the noninvasive measurement of blood glucose. The in vivo results from oral glucose tests on eight subjects showed good correlation with clinical measurements but indicated that physiological factors and person-to-person variability are important. In vitro measurements showed that the sensitivity of the glucose measurement is unaffected by the presence of common blood analytes but that there can be substantial shifts in baseline values. The results indicate the need for spectroscopic data to develop algorithms for the detection of glucose in the presence of other analytes. (+info)
Mosquito hearing: sound-induced antennal vibrations in male and female Aedes aegypti.
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Male mosquitoes are attracted by the flight sounds of conspecific females. In males only, the antennal flagellum bears a large number of long hairs and is therefore said to be plumose. As early as 1855, it was proposed that this remarkable antennal anatomy served as a sound-receiving structure. In the present study, the sound-induced vibrations of the antennal flagellum in male and female Aedes aegypti were compared, and the functional significance of the flagellar hairs for audition was examined. In both males and females, the antennae are resonantly tuned mechanical systems that move as simple forced damped harmonic oscillators when acoustically stimulated. The best frequency of the female antenna is around 230 Hz; that of the male is around 380 Hz, which corresponds approximately to the fundamental frequency of female flight sounds. The antennal hairs of males are resonantly tuned to frequencies between approximately 2600 and 3100 Hz and are therefore stiffly coupled to, and move together with, the flagellar shaft when stimulated at biologically relevant frequencies around 380 Hz. Because of this stiff coupling, forces acting on the hairs can be transmitted to the shaft and thus to the auditory sensory organ at the base of the flagellum, a process that is proposed to improve acoustic sensitivity. Indeed, the mechanical sensitivity of the male antenna not only exceeds the sensitivity of the female antenna but also those of all other arthropod movement receivers studied so far. (+info)
Experience-dependent modification of ultrasound auditory processing in a cricket escape response.
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The ultrasound acoustic startle response (ASR) of crickets (Teleogryllus oceanicus) is a defense against echolocating bats. The ASR to a test pulse can be habituated by a train of ultrasound prepulses. We found that this conditioning paradigm modified both the gain and the lateral direction of the startle response. Habituation reduced the slope of the intensity/response relationship but did not alter stimulus threshold, so habituation extended the dynamic range of the ASR to higher stimulus intensities. Prepulses from the side (90 degrees or 270 degrees azimuth) had a priming effect upon the lateral direction of the ASR, increasing the likelihood that test pulses from the front (between -22 degrees and +22 degrees ) would evoke responses towards the same side as prepulse-induced responses. The plasticity revealed by these experiments could alter the efficacy of the ASR as an escape response and might indicate experience-dependent modification of auditory perception. We also examined stimulus control of habituation by prepulse intensity or direction. Only suprathreshold prepulses induced habituation. Prepulses from one side habituated the responses to test pulses from either the ipsilateral or contralateral side, but habituation was strongest for the prepulse-ipsilateral side. We suggest that habituation of the ASR occurs in the brain, after the point in the pathway where the threshold is mediated, and that directional priming results from a second process of plasticity distinct from that underlying habituation. These inferences bring us a step closer to identifying the neural substrates of plasticity in the ASR pathway. (+info)
Vocal tract length and acoustics of vocalization in the domestic dog (Canis familiaris).
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The physical nature of the vocal tract results in the production of formants during vocalisation. In some animals (including humans), receivers can derive information (such as body size) about sender characteristics on the basis of formant characteristics. Domestication and selective breeding have resulted in a high variability in head size and shape in the dog (Canis familiaris), suggesting that there might be large differences in the vocal tract length, which could cause formant behaviour to affect interbreed communication. Lateral radiographs were made of dogs from several breeds ranging in size from a Yorkshire terrier (2.5 kg) to a German shepherd (50 kg) and were used to measure vocal tract length. In addition, we recorded an acoustic signal (growling) from some dogs. Significant correlations were found between vocal tract length, body mass and formant dispersion, suggesting that formant dispersion can deliver information about the body size of the vocalizer. Because of the low correlation between vocal tract length and the first formant, we predict a non-uniform vocal tract shape. (+info)