No description available.

No description available.

<p> Taking inspiration from nature has promoted the production of man made pores, analogous to protein channels, providing a platform in unraveling the mechanism for nanoscale transportation. This gives insight to applications such as drug delivery, cancer detection and bio-electronics. Therefore, to gain more insight, hydrogels of different structural stiffnesses were translocated through pores with 800 <i>nm</i> and 500 <i>nm</i> diameters. The stiffness of the hydrogels were classified into 3 categories of 2%, 5% and 10% crosslink percentage, 2% being the least rigid and 10% the most. The characterization of each set of particles were classified by their resistive pulse, charge intake, average translocation time and effective particle size. It was determined that the characterization of each resistive pulse is defined by the inner structure of each pore&rsquo;s imperfections. Now by focusing on each individual pore, we could see slight variations between each set of hydrogels as they translocate the unique pore. What we obtained was the translocation times for more compressible hydrogels being faster than for more rigid ones. The charge intake gave insight into the particle size, with larger charge intake into the pore referring to larger particles and smaller intake for smaller one. This made clear the notion that bigger diameter hydrogels with same crosslink percentages will translocate at a slower rate than smaller hydrogels. The other piece of data obtained was the average effective diameter for all 3 hydrogel sets at given voltages. Both 500 <i>nm</i> and 800 <i>nm</i> pores coincided in the order of effective particle size translocated, from smallest to greatest starting at 10%, 2%, and 5%, respectively. This indicates that even though the 2% crosslink is the most compressible hydrogel, it did not translocate the biggest particles. Instead the 5% crosslink hydrogels translocated the bigger sizes, meaning that the 2 extremes are not ideal for bigger particle translocation. The 10% is obviously too rigid to allow big hydrogels than the other 2 sets, but the 2% indicates that some phenomena exists that tells us a compressibility to an extreme won&rsquo;t produce bigger sized translocations. The latter phenomena is still not fully understood, but because both sized pores gave the same effect and follow the same trend, it indicates the probability of this being true pretty high and with good certainty. We&rsquo;ve now characterized these translocations and understand that by classifying the effects of our parameters, the properties of any given translocated object can be deciphered. This leads to the ultimate goal of using these techniques to develop applications for bio technology.</p>

No description available.

No description available.

No description available.

This thesis addresses the problem of how a listener groups together acoustic components which have arisen from the same environmental event, a phenomenon known as auditory scene analysis. A computational model of auditory scene analysis is presented, which is able to separate speech from a variety of interfering noises. The model consists of four processing stages. Firstly, the auditory periphery is simulated by a bank of bandpass filters and a model of inner hair cell function. In the second stage, physiologically-inspired models of higher auditory organization - aiditory maps - are used to provide a rich representational basis for scene analysis. Periodicities in the acoustic input are coded by an ant ocorrelation map and a crosscorrelation map. Information about spectral continuity is extracted by a frequency transition map. The times at which acoustic components start and stop are identified by an onset map and an offset map. In the third 8tage of processing, information from the periodicity and frequency transition maps is used to characterize the auditory scene as a collection of symbolic auditory objects. Finally, a search strategy identifies objects that have similar properties and groups them together. Specifically, objects are likely to form a group if they have a similar periodicity, onset time or offset time. The model has been evaluated in two ways, using the task of segregating voiced speech from a number of interfering sounds such as random noise, "cocktail party" noise and other speech. Firstly, a waveform can be resynthesized for each group in the auditory scene, so that segregation performance can be assessed by informal listening tests. The resynthesized speech is highly intelligible and fairly natural. Secondly, the linear nature of the resynthesis process allows the signal-to-noise ratio (SNR) to be compared before and after segregation. An improvement in SNR is obtained after segregation for each type of interfering noise. Additionally, the performance of the model is significantly better than that of a conventional frame-based autocorrelation segregation strategy.

No description available.

A gamma camera system is described. This takes the following form. A conventional collimator-crystal system is set up to produce scintillation images corresponding to the pattern of radioactivity in a patient or phantom. Thereafter these faint points of light are imaged by a lens of high light-gathering power onto the photocathode of an image intensifier. This amplifies the light intensity by a factor of approximately 10. 6, \when they are photographed bya conventional camera. An important feature of the equipment is a system which switches the image intensifier on only when a wanted signal appears in the crystal: other spurious signals, e.g. background radiation, scattered gamma-rays from the patient, thermal electrons in the image Intensifier, are to a large extent rejected by this system. An important feature of it is the method of gathering spare light from the crystal by photomultiplier tubes placed round the periphery. Light guide designs to do this are described, with experimental results, and the appropriate calculations discussed. The design of the electronics equipment is examined, and its limitations, as these affect the sensitivity of the equipment, computed. In all of the above, the statistics of the process are discussed in detail and the effect on the basic sensitivity, quantum mottle, and degraded gamma-rays are computed. The effect of non-uniformity across the crystal on the pulse-height-analysis is measured, and its effect on the final design indicated. A very important loss of contrast was discovered in the form of scatter of light in the optics of the system, mainly in the crystal and its attendant light-guide/encapsulation. This was investigated thoroughly and possible cures discussed: it was felt that a gating system to differentiate between scattered light and wanted signal could be devised, using a G.C.T.V. system. This however imposed severe restrictions in that a greater fraction of the crystal's light was required to fall on the image intensifier cathode; calculations indicated that this was not possible with existing components - the main limitation being the image intensifier diameter. Calculations are carried out to indicate the specification of components necessary to overcome these limitations, and also to match the sensitivity of the Anger camera. The modulation transfer function of the crystal is calculated from the experimental results, using a programmable calculator. Simulated optical and X-ray experiments on moving the collimator (to eliminate possible structure) are described, and a proposed method of doing this requiring much less complicated equipment than was previously thought necessary, is described. Finally a detailed specification/design of a feasible clinical instrument is delineated, making use of the results of the experiments carried out with equipment actually built.

The power output of a medical ultrasonic transducer is usually determined by measuring the radiation force exerted by the ultrasonic beam on an absorbing or reflecting target. The theory of the radiation force is somewhat involved and strictly applies only to a continuous ultrasonic beam, but the method is commonly used to determine the (time-averaged) powers of both continuous and short-pulsed beams. An ultrasound calorimeter was developed so that the validity of the radiation force method might be tested by making comparative measurements of ultrasonic power in water. In the thesis, the physical origin of the radiation force exerted on absorbing and reflecting targets is explained. The force exerted by a pulsed ultrasonic beam is discussed briefly, and the significance of real deviations from the model upon which the theory is based are considered. In addition, the mean sound pressure in the ultrasonic beam is discussed. The development of the calorimeter is described. The calorimeter was of the continuous-flow type and used castor oil to absorb the ultrasonic beam. Its accuracy was thoroughly assessed and ranged from ± 7.2% at 1.5 MHz to ± 24% at 6 MHz; it could detect a minimum power of 0.1 mW. Radiation force measurements of ultrasonic power were made with an accuracy of typically ± 5% using one absorbing and two reflecting targets suspended from an analytical balance. Calorimetric and radiation force measurements of the powers of both continuous and short-pulsed ultrasonic beams were found to be in good agreement. It is concluded that the generally-accepted relationship between the radiation force and ultrasonic beam power is correct and that, as widely assumed, the (time-averaged) force exerted by a pulsed beam is equal to the force exerted by a continuous beam of the same time-averaged power.