Direct visualization of particle attachment to a pendant drop.

An experimental investigation is carried out into the attachment of a single particle to a liquid drop. High-speed videography is used to directly visualize the so-called 'snap-in' effect which occurs rapidly over sub-millisecond timescales. Using high-magnification, the evolution of the contact line around the particle is tracked and dynamic features such as the contact angle, wetted radius and force are extracted from these images to help build a fundamental understanding of the process. By examining the wetted length in terms of an arc angle, ϕ, it is shown that the early wetting stage is an inertial-dominated process and best described by a power law relation, i.e. ϕ ∼ (t/τ)α, where τ is an inertial timescale. For the subsequent lift-off stage, the initial particle displacement is matched with that predicted using a simple balance between particle weight and capillary force with reasonable agreement. The lift-off force is shown to be on the order of 1-100 µN, whilst the force of impacting droplets is known to be on the order of 10-1000 mN. This explains the ease in which liquid marbles are formed during impact experiments.

Noise interference with echo delay discrimination in bat biosonar.

Echolocating big brown bats (Eptesicus fuscus) were trained in a two-choice task to discriminate differences in the delay of electronic echoes at 1.7 ms delay (30 cm simulated range). Difference thresholds (∼45 µs) were comparable to previously published results. At selected above-threshold differences (116 and 232 µs delay), performance was measured in the presence of wideband random noise at increasing amplitudes in 10-dB steps to determine the noise level that prevented discrimination. Performance eventually failed, but the bats increased the amplitude and duration of their broadcasts to compensate for increasing noise, which allowed performance to persist at noise levels about 25 dB higher than without compensation. In the 232-µs delay discrimination condition, echo signal-to-noise ratio (2E/N0) was 8-10 dB at the noise level that depressed performance to chance. Predicted echo-delay accuracy using big brown bat signals follows the Cramér-Rao bound for signal-to-noise ratios above 15 dB, but worsens below 15 dB due to side-peak ambiguity. At 2E/N0 = 7-10 dB, predicted Cramér-Rao delay accuracy would be about 1 µs; considering side-peak ambiguity it would be about 200-300 µs. The bats' 232 µs performance reflects the intrusion of side-peak ambiguity into delay accuracy at low signal-to-noise ratios.

Perception of echo phase information in bat sonar.

Echolocating bats (Eptesicus fuscus) can detect changes as small as 500 nanoseconds in the arrival time of sonar echoes when these changes appear as jitter or alternations in arrival time from one echo to the next. The psychophysical function relating the bat's performance to the magnitude of the jitter corresponds to the half-wave rectified cross-correlation function between the emitted sonar signals and the echoes. The bat perceives the phase or period structure of the sounds, which cover the 25- to 100-kilohertz frequency range, as these are represented in the auditory system after peripheral transformation. The acoustic image of a sonar target is apparently derived from time-domain or periodicity information processing by the nervous system.

Echolocation in bats: signal processing of echoes for target range.

Echolocating bats Eptesicus fuscus and Phyllostomus hastatus can discriminate between the nearer and farther of two targets. Their errors in discrimination are predicted accurately by the autocorrelation functions of their sonar cries. These bats behave as though they have an ideal sonar system which cross correlates the transmitted cry with the returning echo to extract targetrange information.

Echolocation in bats: the external ear and perception of the vertical positions of targets.

Echolocating bats (Eptesicus fuscus) can perceive changes of as little as 3 degrees of arc in the vertical angles separating pairs of horizontal rods. This acuity depends upon modification of sounds entering the external ear canal by the structures of the external ear. Deflection of the tragus degrades the acuity of vertical-angle perception from 3 degrees to about 12 degrees to 14 degrees. The pinna-tragus structure produces a strong secondary echo of sounds entering the external ear canal, and the delay of this echo after the time when the sound directly enters the ear canal apparently encodes the vertical direction of a sound source.

Echo detection and target-ranging neurons in the auditory system of the bat Eptesicus fuscus.

Some of the neurons in the nucleus intercollicularis and auditory cortex of the echolocating bat Eptesicus fuscus respond selectively to sonar echoes occurring with specific echo delays or pulse-echo intervals. They do not respond for a wide range of other types of sounds or for sonar echoes at longer or shorter pulse-echo intervals; they may, therefore, be specialized for detection and ranging of sonar targets.

Sonar tracking of horizontally moving targets by the big brown bat Eptesicus fuscus.

When following a moving target, echolocating bats (Eptesicus fuscus) keep their heads aimed at the target's position. This tracking behavior seems not to involve predicting the target's trajectory, but is achieved by the bat's pointing its head at the target's last known position. The bat obtains frequent position updates by emitting sonar signals at a high rate. After the lag between head and target positions and the nonunity tracking gain were corrected for, bats' tracking accuracy in the horizontal plane was +/- 1.6 degree.

Periodical cicada: sound production and hearing.

The two main species intermingled in a brood of the 17-year cicada (Magicicada) have distinctive sound-making patterns and correspondingly different hearing abilities. Thus, they are acoustically isolated for mating purposes. Their simultaneous emergence and community "singing" has the important advantage of repelling predators.

Echolocation and pursuit of prey by bats.

Echolocating bats use different information-gathering strategies for hunting prey in open, uncluttered environments, in relatively open environments with some obstacles, and in densely cluttered environments. These situations differ in the extent to which individual targets such as flying insects can be detected as isolated objects or must be separated perceptually from backgrounds. Echolocating bats also differ in whether they use high-resolution, multidimensional images of targets or concentrate specifically on one particular target dimension, such as movement, to detect prey.

Target structure and echo spectral discrimination by echolocating bats.

Echolocating bats can use sonar to discriminate among targets which reflect echoes differing in spectral distribution of energy but not in overall intensity. They can detect differences smaller than 1 millimeter in fine target structure. Bats may be capable of classifying targets from echo spectral signatures and might thus be able to distinguish among flying insect prey by sonar.

Irradiated lithium formate and amino acids.

Radiation-induced free radicals in solids show a microwave saturation effect when studied by electron spin resonance. A comparison is made between such effects in lithium formate and amino acids. The relative effectiveness of neutrons against high-energy photons is also considered.

Localization of a growth suppressor activity in MCF7 breast cancer cells to chromosome 17q24-q25.

Chromosome 17 is one of the most frequently altered chromosomes in malignant breast cancer. At least four genes implicated in breast cancer reside on chromosome 17 (p53, 17p13; Her-2/neu/ERBB2, 17q12; BRCA1, 17q21; and nm23, 17q22). In addition, allelic imbalance has been described for at least five regions of chromosome 17. We have previously shown that the introduction of a normal human chromosome 17 into the breast cancer cell line MCF7 by microcell mediated chromosome transfer (MMCT) results in the in vitro growth arrest of these cells within 8 weeks, suggesting the presence of a growth suppressor on chromosome 17. Additionally, we have shown that the tumor suppressor gene p53 is not responsible for this phenotype, as it is wild type in MCF7 cells, and overexpression has no effect on either the in vitro or in vivo growth of these cells. We have further localized this growth suppressor gene to 17q24-q25 by transfer of chromosome 17 hybrids containing defined deletions. Whereas transfer of hybrids that contained an intact 17q (delta43/A9 and delta26/A9) resulted in growth arrest, two hybrids with overlapping deletions at 17q24-q25, had no effect on growth of MCF7 cells. Molecular analyses revealed that 50/70 (71%) of the resulting delta2/MCF7 or delta624/MCF7 MMCT clones retained an intact introduced chromosome 17. In contrast, only 8/34 (24%) of delta43/MCF7 revertants (deleted for 17p13.1-pter) which escaped growth arrest showed no breakage of the introduced chromosome 17. We did not observe a preferential loss of an intragenic BRCA1 marker in the MMCT hybrids, excluding BRCA1 as the gene responsible for this growth arrest phenotype. These data therefore implicate a new growth suppressor gene involved in breast cancer that is localized to chromosome 17q24-q25.

Cell migration in the rat embryonic neocortex.

Three-dimensional reconstructions of the normal rat embryonic (E) neocortex on days E15, E17, E19, and E21, using Skandha (software designed by J. Prothero, University of Washington, Seattle), show that the neocortical ventricular zone shrinks rapidly in the medial direction during cortical morphogenesis. [3H]thymidine autoradiography indicates that the shrinkage of the ventricular zone occurs before neurons in lateral and ventrolateral parts of layers IV-II are generated. Consequently, most of these neurons originate 400-1000 microns medial to their settling sites in the cortical plate. Embryos killed at daily intervals up to E21 after a single injection of [3H]thymidine on either E17 or E18 revealed the presence of a prominent migratory path, the lateral cortical stream, used by neurons migrating to the lateral and ventrolateral cortical plate; neurons migrating to the dorsal cortical plate follow a direct radial path. Arrival times of neurons in the cortical plate depend on the migratory path and are proportional to the overall distance travelled. Neurons that migrate only radially arrive in the dorsal cortical plate in two days (shortest route). Neurons that migrate laterally arrive in the lateral cortical plate in 3 days (longer route) and in the ventrolateral cortical plate in 4 days (longest route). [3H]thymidine autoradiography also shows that cells generated in the neocortical ventricular zone migrate in the lateral cortical stream for 5 or more days and accumulate in a reservoir. Cells leave the reservoir to enter the piriform cortex and destinations (as yet undetermined) in the basal telencephalon. The lateral cortical stream is found wherever the neocortical primordium surrounds the basal ganglia and is absent behind the basal ganglia. A computer analysis of nuclear orientation in anterior and posterior parts of the intermediate zone in the dorsal neocortex between days E17 and E22 shows that horizontally oriented nuclei are more common anteriorly where many cells are migrating laterally than posteriorly where most cells are migrating radially.

Syndrome of short stature, widow's peak, ptosis, posteriorly angulated ears, and joint problems: exclusion of the Aarskog (FGD1) gene as a candidate gene.

A syndrome encompassing postnatal onset of short stature, widow's peak, ptosis, posteriorly angulated ears, and limitation of forearm supination is reported in a boy and his mother. The boy has not yet experienced dislocation of patella or other joint anomaly except for limitation of supination of the forearms. On the other hand, the mother has a milder limitation of supination only on the left arm and is devoid of ptosis. Their condition is reminiscent of that described in the family reported by Kapur et al. [1989: Am. J. Med. Genet. 33: 357-363.], which showed an X-linked dominant mode of inheritance. DNA study on our family using an intragenic polymorphism of the Aarskog syndrome (FGD1) gene and four other adjacent markers convincingly excludes the possibility that their condition could be caused by a mutation of the FGD1 gene. Our family and the family reported by Kapur et al. may suggest segregation of a novel X-linked dominant condition.

A view of the world through the bat's ear: the formation of acoustic images in echolocation.

Echolocating bats perceive objects as acoustic images derived from echoes of the ultrasonic sounds they emit. They can detect, track, identify, and intercept flying insects using sonar. Many species, such as the big brown bat, Eptesicus fuscus, emit frequency-modulated sonar sounds and perceive the distance to targets, or target range, from the delay of echoes. For Eptesicus, a point-target's image has a sharpness along the range axis that is determined by the acuity of echo-delay perception, which is about 10 ns under favorable conditions. The image as a whole has a fine range structure that corresponds to the cross-correlation function between emissions and echoes. A complex target- which has reflecting points, called "glints", located at slightly different distances and reflects echoes containing overlapping components with slightly different delays--is perceived in terms of its range profile. The separation of the glints along the range dimension is encoded by the shape of the echo spectrum created by interference between overlapping echo components. However, Eptesicus transforms the echo spectrum back into an estimate of the original delay separation of echo components. The bat thus converts spectral cues into elements of an image expressed in terms of range. The absolute range of the nearest glint is encoded by the arrival time of the earliest echo component, and the spectrally encoded range separation of additional glints is referred to this time-encoded reference range for the image as a whole. Each individual glint is represented by a cross-correlation function for its own echo component, the nearest of which is computed directly from arrival-time measurements while further ones are computed by transformation of the echo spectrum. The bat then sums the cross-correlation functions for multiple glints to form the entire image of the complex target. Range and shape are two distinct features of targets that are separately encoded by the bat's auditory system, but the bat perceives unitary images that require fusion of these features to create a synthetic psychological dimension of range. The bat's use of cross-correlation-like images reveals neural computations that achieve fusion of stimulus features and offers an example of high-level operations involved in the formation of perceptual "wholes".

Analysis of the dose-response relationships following the irradiation of amino acids.

A comparison is made between results recently reported on the induction of free radicals in irradiated alanine and studies previously published on irradiated amino acids. It is shown that there is good qualitative agreement between the old and the new measurements although several quantitative inconsistencies are noted. A query is raised as to whether the new data can truly be interpreted in terms of the theory of track structure when some of the effects observed are not fully taken into account.

Track studies in water vapor using a low-pressure cloud chamber. I. Macroscopic measurements.

Techniques have been developed to operate a low-pressure cloud chamber with pure water vapor. Photographs have been obtained of the tracks arising in this medium from the passage of ionizing radiation. The sources used were low-energy X rays, 242Cm alpha particles, and low-energy protons. Track lengths of the electrons were similar to those found previously in tissue-equivalent gas. W values of 35.6 +/- 0.4 and 32.6 +/- 0.6 eV per ion pair for carbon and aluminum X rays also compare closely with those in tissue-equivalent gas, but are somewhat higher than the predictions of Monte Carlo calculations. Differential w values were obtained: for alpha particles of energy 5.3 MeV the value was 33.0 +/- 3.0 eV per ion pair; for protons of energy 390, 230, and 85 keV the values were 30.6 +/- 1.9, 31.9 +/- 2.0, and 33.6 +/- 3.4 eV per ion pair. The energy losses of protons in water vapor were measured in a second (dummy) chamber used for energy calibration. Results support Janni's values of stopping power for protons in the energy range 40-480 keV.

Track studies in water vapor using a low-pressure cloud chamber. II. Microdosimetric measurements.

A low-pressure cloud chamber has been adapted to operate with pure water vapor. Photographs were obtained of tracks arising from the passage of ionizing radiation. The sources used were low-energy X rays, 242Cm alpha particles, and low-energy protons. Distributions of lineal energy, radial distances around an ion track, and interdroplet distances were measured and compared with the predictions of Monte Carlo calculations. After allowing for diffusion and the limitations of the geometry of the system, the measured and calculated distributions were found to be in good agreement.

Survival and yields of chromosome aberrations in hamster and human lung cells irradiated by alpha particles.

The effects of alpha-particle irradiation on hamster and human lung cells have been studied. In both cases two end points were taken, cell death and the induction of chromosome aberrations. The hamster cells were common stock V79 cells; the human ones were freshly derived from fetal material. For both types of cells, the survival curves could be described by straight lines in the conventional exponential plot, with values of D(o) of 0.78 and 0.37 Gy for the hamster and human cells, respectively. The rate of induction of chromosome aberrations could also be described by straight lines with slopes of 0.30 and 0.62 aberration per cell per gray. Thus, for this second end point also, it appears that human cells are twice as sensitive to the effects of alpha-particle irradiation as hamster cells.

Experimental calculations of droplet diffusion in a low-pressure cloud chamber.

A low-pressure cloud chamber was used for several years to display the tracks created by the passage of ionizing particles through vapors of interest. The spatial distributions of the ions that were formed were of special interest, but the accuracy with which these distributions could be determined was reduced by the presence of diffusion. This meant that the droplets, when photographed, had moved significantly away from the point of creation of the parent ion. In the present investigation photographs obtained by previous workers have been analyzed in an attempt to quantify the extent to which the droplets had diffused. The results suggest that the diffusion, when converted to standard density (1000 kg/m3), was independent of the pressure inside the cloud chamber and the mixture used. It could be represented by a one-dimensional root-mean-square diffusion distance whose value was calculated to be 2.42 +/- 0.04 nm. Values for the diffusion of thermalized electrons (< approximately 4 eV) before capture to form negative ions were also calculated. They appeared to lie in the range 3.5-5.0 nm, and were again independent of the pressure and nature of the mixture. The magnitude of the diffusion was large enough to mask any measurable prediffusion structure for a distance in the region of 10 nm radially around the track path of the alpha-particle and proton tracks analyzed.