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The nanoscale patterns produced by bombardment of the (100) surface of silicon with a 2 keV Kr ion beam are investigated both experimentally and theoretically. In our experiments, we find that the patterns observed at high ion fluences depend sensitively on the angle of incidence Θ. For Θ values between 74° and 85°, we observe five decidedly different kinds of morphologies, including triangular nanostructures traversed by parallel-mode ripples, long parallel ridges decorated by short-wavelength ripples, and a remarkable mesh-like morphology. In contrast, only parallel-mode ripples are present for low ion fluences except for Θ = 85°. Our simulations show that triangular nanostructures that closely resemble those in our experiments emerge if a linearly dispersive term and a conserved Kuramoto–Sivashinsky nonlinearity are appended to the usual equation of motion. We find ridges traversed by ripples, on the other hand, in simulations of the Harrison–Pearson–Bradley equation (Harrison et al 2017 Phys. Rev. E 96 032804). For Θ = 85°, the solid surface is apparently stable and simulations of an anisotropic Edwards–Wilkinson equation yield surfaces similar to those seen in our experiments. Explaining the other two kinds of patterns we find in our experiments remains a challenge for future theoretical work.

Ion bombardment (IB) is a promising nanofabrication technique for producing nanoripples. A critical issue that restricts the application of IB is the limited quality of IB-induced nanoripples. Photoresist (PR) and antireflection coating (ARC) are of technological relevance for lithographic exposure processes. Moreover, to improve the quality of IB-induced self-organized nanoripples, in this study, a PR/ARC bilayer was bombarded at an incidence angle of 50°. The surface normalized defect density and power spectral density, obtained via scanning atomic force microscopy, indicate the superiority of the PR/ARC bilayer nanoripples over those of single PR or ARC layers. The growth mechanism of the improved nanoripples, deciphered via the temporal evolution of the morphology, involves the following processes: (i) formation of a well-grown IB-induced nanoripple prepattern on the PR, (ii) transfer of nanoripples from the PR to the ARC, forming an initial ARC nanoripple morphology for subsequent IB, and (iii) conversion of the initial nonuniform ARC nanoripples into uniform nanoripples. In this unique method, the angle of ion-incidence should be chosen so that ripples form on both PR and ARC films. Overall, this method facilitates nanoripple improvement, including prepattern fabrication for guiding nanoripple growth and sustainable nanoripple development via a single IB. Thus, the unique method presented in this study can aid in advancing academic research and also has potential applications in the field of IB-induced nanoripples.

A large number of neurophysiological studies have detailed the functional changes in taste sensation that accompany development, primarily in the sheep and rat. Single fiber studies in sheep have demonstrated other unique aspects of developing salt taste responses. In neurophysiological experiments, the receptive field size, or number of fungiform papillae innervated by one single chorda tympani nerve fiber, was determined in fetuses, perinatal animals, and lambs by electrically stimulating single papillae. Consideration of neurophysiological data on the normal development of taste function shows that there are marked maturational changes in responses to sodium chloride. There have been numerous anatomical studies of developing taste buds and in such species as sheep and humans, in which taste buds develop prenatally, it has been suggested that taste buds are functional before birth. The development of receptive fields of single peripheral and central neurons has been investigated and factors influencing development of the taste system are beginning to be studied.

As a result of increasing control of environmental pollution in Hong Kong, the practice of discharging untreated service-reservoir wash water to the nearest watercourse is no longer permitted. This paper describes the results of field tests on alternative methods of treating the effluents produced from cleaning fresh-water and sea-water service reservoirs in Hong Kong, including trials of alternative cleaning procedures using high-pressure jetting which were designed to (a) upgrade the cleaning efficiency and (b) reduce the resulting pollution load. The results of effluent treatment, based on pilot-plant trials incorporating various combinations of filtration and centrifugation, are presented. The option which was selected for full-scale implementation, based on a mobile centrifugation and microfiltration unit, using a membrane developed in China specifically for the water industry, is described.

The transformation from the C49 to the C54 phase in TiSi2 thin films has been studied for more than a decade because of its importance to the semiconductor industry. In previous work we identified three dominant C54 orientations in TiSi2 thin films on Si(001) substrates using x-ray pole figure analysis. In the current study the evolution of the three prominent C54 texture components was further examined using synchrotron based time-resolved in situ x-ray diffraction. The kinetics results show significant differences in the nucleation and growth kinetics of the individual orientations. Simulations suggest that this could be explained by an inhomogeneous nucleation of different texture components in the thin film, but not by simple differences in nucleation and/or growth rates. Classical Johnson–Mehl–Avrami–Kolmogorov (JMAK) analysis of nucleation and growth was applied to model the C49–C54 phase transformation kinetics for each C54 orientation. These results showed a systematic decrease of the Avrami expon...

We study the time evolution of a perturbation to the edge of an otherwise straight, current-carrying, single-crystal metal line. If the applied current exceeds a critical value, the perturbation grows to become a slit-shaped void that spans the wire, and that leads to electrical failure. The slits in our simulations are remarkably similar to those observed in experiments, and in some respects resemble viscous fingers in a Hele-Shaw cell.

We introduce a dynamic fuse model for the damage done to a current-carrying polycrystalline metal film by electromigration. For all initial densities of defects p, the mean failure time 〈${\mathit{T}}_{\mathit{f}}$〉 is, to an excellent approximation, proportional to the average length of the shortest path across the film in a certain metric. 〈${\mathit{T}}_{\mathit{f}}$〉 tends to zero as (${\mathit{p}}_{\mathit{c}}$-p${)}^{4/3}$ as the percolation threshold p=${\mathit{p}}_{\mathit{c}}$ is approached.

We perform Monte Carlo simulations of the pouring of hard ellipsoids into a three-dimensional container. Both oblate and prolate ellipsoids of revolution are examined. Oblate ellipsoids pack so that their symmetry (semi-minor) axes are preferentially aligned with the direction of gravity, and their orientational alignment increases with increasing aspect ratio. Conversely, for prolate ellipsoids, the symmetry (semi-major) axes tend to lie within the plane perpendicular to gravity. The ellipsoids form novel packings that we call "oriented glasses". No translational order is present: the packings are amorphous, but still exhibit long-range orientational order. In addition, the density of the packings is not a monotone function of the aspect ratio, and exhibits a global maximum for slightly elongated particles.

1. Previous work from this laboratory has shown that rostral nucleus tractus solitarii (rNTS) neurons can be separated into four different classes on the basis of responses to a current injection paradigm consisting of membrane hyperpolarization immediately followed by a depolarizing pulse. These classes have been termed Group I, II, III, and IV neurons. The regular repetitive firing discharge pattern of Group I cells is changed into an irregular spike train by membrane hyperpolarization. Hyperpolarization of Group II neurons delays the firing discharge induced by depolarization. Hyperpolarization had the least effect on the discharge pattern of Group III neurons. The discharge pattern of Group IV neurons consisted of a short burst of spikes. We used whole-cell recordings and pharmacological channel blockers in an in vitro brain stem slice preparation to determine the ionic basis for the repetitive firing properties of rNTS neurons. 2. Application of 4-aminopyridine (4-AP, 1 mM) decreased input resistance and increased action potential duration in all groups of neurons. However, the discharge pattern of Group I, III, and IV neurons was either unaltered or slightly modified by 4-AP. In contrast the delay in firing of Group II cells induced by hyperpolarization was strongly reduced and in some cases completely suppressed by application of 4-AP. This suggests that a 4-AP-sensitive conductance primarily underlies the firing pattern of Group II cells. 3. Voltage-clamp recordings revealed that the delay in Group II neurons is due to a transient outward potassium current that is partially inactivated around the resting membrane potential. Hyperpolarization removed this inactivation, causing a delay in the firing of the cell. The potassium current was blocked by 4-AP. A similar current was occasionally seen in neurons of the other groups. On the basis of its voltage and pharmacological dependence this current was presumed to be an A-current (IKA). 4. Blockade of calcium currents by a low-calcium (0.5 mM) saline containing 2 mM Co2+ depressed the excitability of rNTS cells. For Group II neurons the delay in firing activity was increased. In the other groups the repetitive firing pattern was suppressed. In addition the amplitude of the afterhyperpolarization occurring after a short train of action potentials was substantially reduced. This indicates that calcium currents (ICa) and calcium-activated potassium currents (IKCa) contribute to the repetitive firing properties of rNTS neurons. 5. In about half of Group I, III, and IV neurons an additional property was found.(ABSTRACT TRUNCATED AT 400 WORDS)

Abshnct. We introduce a dynamic fuse model for the damage done m a metal thin film by electromigration, and study the growth of a single crack that is perpendicular to the direction of the ambient current. As the cradr length 2r grows large, the velocity of the crack tips v scales as u(x) -.xu. We argue that the value of the exponent OL is exactly 2. This result is in excellent agreement with our numerical work. There is currently much interest in random media that are changed irreversibly by an applied field. These so-called ‘breakdown problems’ play an important role in non-equilibrium statistical physics and materials science. ‘Bum out’ of random fuse networks 11-51, dielectric breakdown [2,5-121, the onset of superconductivity in granular superconductors [13-171, and the fracture of brittle materials [18-251 have all been studied using breakdown models. Most of the progress on breakdown models has come from Monte Carlo simulations. However, in an important series of papers, Duxbury and co-workers developed a ‘Lifshitztype’ theoq~ for the breakdown voltage of a two-dimensional random fuse network in the lit in which the insulating bonds are initially dilute [24 The first step in constructing this theory was to determine the breakdown voltage of a line defect (or ‘crack‘) oriented perpendicularly io the direction of the ambient current. The breakdown models mentioned so far are quasi-static, since failure occurs instantaneously when the applied voltage (or stress) is sufficiently large. The first mly kinetic breakdown model was introduced by Sornette and Vanneste 126,271. Their model describes the failure of fuse networks that burn out due to Joule heating. In their model, the temperature T of a fuse with resistance R carrying current I obeys the equation

The authors study generalized diffusion-limited aggregation with a lifetime tau , a model introduced by Miyazima et al (1988). Their Monte Carlo simulations for tau =1 and for tau =2 indicate that the asymptotic behaviour is most likely to be identical for all finite values of tau . Their estimate for the exponent v characterizing the asymptotic regime is in strong disagreement with that found by Miyazima et al.

The authors perform Monte Carlo simulations of the pouring of elliptical particles into a two-dimensional box under the influence of a uniform gravitational field. Ellipses with sufficiently large aspect ratios form novel packings that they call nematic glasses. The granules in these packings are ordered orientationally, and yet the packings are amorphous. A heuristic explanation of the formation of this state is presented.

%e introduce a growing self-avoiding walk in three dimensions (3D) that can terminate only by returning to its point of origin. This "tricolor walk" depends on two parameters, p and q, and is a direct generalization of the smart kinetic walk to 3D. Our walk is closely related to percolation with three colors (black, white, and gray): the tricolor walk directly constructs a loop formed by the con8uence of a black, a white, and a gray cluster. The parameters p and q are the fraction of sites colored black and white, respectively. %e present numerical and analytical evidence that for p =q = —, ', the fractal dimension of the tricolor walk is exactly 2. For p=q & —, ', the walks undergo a percolation transition at p =-0.2915. Our Monte Carlo simulations strongly suggest that this transition is not in the same universality class as the usual percolation transition in 3D. The mean length of the Snite walks y is divergent throughout an extended region of the parameter space.

The authors introduce a growing self-avoiding walk in three dimensions (3D) that can terminate only by returning to its point of origin. This symmetric tricolour walk (STW) is a direct generalization of the smart kinetic walk to 3D, and yet is readily simulated. Their Monte Carlo simulations strongly suggest that the fractal dimension of the STW is exactly 2. This conclusion is supported by a mapping of the STW onto a self-attracting self-avoiding walk at its collapse transition.

The regions where the three colors meet (the «tricords»)'are studied in percolation with three colors in three dimensions (3D). The tricords undergo a percolation transition as the proportions of the three colors are varied. Our Monte Carlo simulations indicate that this transition is not in the same universality class as the usual percolation transition in 3D

The critical properties of the perimeters (or 'hulls') of antipercolation clusters are studied in two dimensions by Monte Carlo simulations on the triangular lattice. Two different types of hulls are constructed with the help of two kinetic walk algorithms. For the standard hull, the authors very accurately determine the size distribution exponent tau '=2.14250.0003, as well as the fractal dimension dfS=1.7500.001. The corresponding exponents for regular percolation hulls (15/7 and 7/4 respectively) are within the error bars of their results for antipercolation. For the reduced hull, they obtain the estimate dfR=1.3340.004 for the fractal dimension, a result which is again close to that found for regular percolation.

We present the results of a Monte Carlo study of the surfaces (or "hulls" ) of percolation clusters in three dimensions. The hulls were generated directly by a growing self-avoiding surface, called the smart kinetic surface, which is a generalization of the smart kinetic walk from two dimensions to three. We find that the fractal dimension of the hull at the percolation threshold is D'=2. 548+0.014. Two other hull critical exponents were measured directly' we obtained ~'=2. 19+0.01 and y'=1. 77+0.02. These results are in accord with scaling laws which relate the hull exponents, and with a heuristic argument which suggests that the bulk and hull critical exponents are equal. The properties of percolation hulls determine the scaling behavior of transport, adsorption, and catalytic processes taking place at the surface of sintered metal powders.

A percolation model, which the authors call bond percolation on antipercolation clusters, is introduced for venereal epidemics in a heterosexual population. A spin model which is equivalent to this model is found and solved in the Bethe cluster approximation. They obtain the static critical exponents beta =1 and gamma =1 using this approximation, and these are the same as the mean-field exponents for regular percolation. The approximate phase diagram for arbitrary coordination number z is also constructed. Finally, the probability that an infected individual belongs to an infected group with s individuals is obtained analytically in the limit z to infinity .

We introduce a dynamic fuse model for the damage done to a current-carrying polycrystalline metal thin film by electromigration. We determine the exact scaling behavior of the crack tip velocity for a single crack oriented perpendicularly to the direction of the ambient current. A Lifshitz-type theory works well only when the initial density of defects (p) is small. For all p, the mean failure time is to an excellent approximation proportional to the average length of the shortest path across the film in a certain metric. This conclusion is supported by our simulations and by analytical work based on a variational formulation of our problem. Using the shortest-path approximation, we show that the mean failure time tends to zero as (${\mathit{p}}_{\mathit{c}}$-p${)}^{4/3}$ as the percolation threshold p=${\mathit{p}}_{\mathit{c}}$ is approached. We also use the shortest-path approximation to account for experimental results on the lifetime of long polycrystalline metal wires of varying lengths and widths.

1. To better understand sensory information processing in pontine neurons that receive afferent fiber terminations from oral cavity and upper airway receptors, we investigated the response characteristics of single neurons to stimulation of the oral cavity and epiglottis with different stimulus modalities. These response characteristics were then compared with previously recorded response properties of neurons located in other brain stem regions that receive oral cavity and upper airway sensory inputs. 2. Receptive field sizes of pontine neurons were mapped, and responses to mechanical, thermal, and chemical stimuli were determined. A total of 47 neurons were isolated and most neurons were located near the dorsomedial border of the rostral trigeminal subnucleus oralis and caudal principal trigeminal nucleus. The likelihood that a particular stimulus modality would elicit a response was somewhat dependent on a neuron's location. Neurons that responded to chemical stimuli were always located outside the trigeminal nucleus, whereas neurons that responded exclusively to mechanical or thermal stimuli were more frequently located in the trigeminal nucleus. Receptive fields were mapped for 45 of the 47 neurons. Forty-three of the neurons had a single ipsilateral receptive field and > 80% of the receptive fields were > 100 mm2. The majority of neurons responded to only one of the three stimulus modalities. The remaining neurons were multimodal and the combination of stimulus modalities most frequently observed was mechanical and chemical. 3. Mechanical stimuli were the most effective of the three stimulus modalities, eliciting responses in > 65% of the neurons. Neurons that responded to mechanical stimuli were generally rapidly adapting and a moving stimulus was more effective than a punctate stimulus. Mechanosensitive neurons that also responded to chemical stimuli exhibited larger mean response frequencies than mechanosensitive neurons that did not respond to chemical stimuli. Chemical stimuli elicited responses in about half the neurons. A greater percentage of neurons with receptive fields on the epiglottis than neurons with oral cavity receptive fields responded to chemical stimuli. The effectiveness of a chemical stimulus was dependent on a neuron's receptive field. NH4Cl was the most effective stimulus for neurons with receptive fields located in the oral cavity, whereas KCl was more effective for neurons with receptive fields on the epiglottis. Thermal stimuli were relatively ineffective whatever the location of a neuron's receptive field. The majority of neurons showed an increase in response frequency to cooling the receptive field and in all thermosensitive neurons the response was restricted to the dynamic phase of thermal stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

We present the results of a Monte Carlo study of the surfaces (or ``hulls'') of percolation clusters in three dimensions. The hulls were generated using a novel growing self-avoiding surface. Our results strongly suggest that the surface and bulk of the infinite cluster have the same fractal dimension at the percolation threshold, and that the other bulk and hull critical exponents are identical as well. These conclusions are supported by heuristic scaling arguments.

Two growing self-avoiding surfaces are introduced as possible models of rapidly polymerising polymer membranes. Monte Carlo simulations indicate that diffusion-limited self-avoiding surfaces have fractal dimension D=2.35+or-0.05, and so are in a different universality class than diffusion-limited aggregates. In contrast, Eden self-avoiding surfaces (1961) appear to be compact, just as the clusters are in the usual Eden model. Both growing surfaces have different fractal dimensions than previously considered models of self-avoiding surfaces in equilibrium.

The crossover between invasion percolation (IP) and the Eden model is studied in one-dimensional. Although the mean run length diverges in IP, it converges in the Eden model and for a broad class of perturbations to IP. In addition, IP has anomalous fluctuation effects which are absent in the Eden model. By studying a specific family of models which interpolate between the IP ( alpha =0) and Eden ( alpha =1/2) limits, we show that the behaviour of the variance crosses over to that found in the Eden model for any alpha >0.

We study the effect of quantum fluctuations of the phase on the low-temperature behavior of two models of Josephson junction chains with Coulomb interactions taken into account. The first model, which represents a chain of junctions close to a ground plane, is the Hamiltonian version of the two-dimensional XY model in one space and one time dimension. We demonstrate explicitly how the Nelson-Kosterlitz jump manifests itself in the conduction properties of this system at a critical value of the superconducting grain capacitance. In the second model, the charging energy for a single junction in the chain is just the parallel-plate capacitor energy Q/sup 2//8C, where Q is the charge difference across the junction and C is its capacitance. We show that for any nonzero charging energy (i.e., C

The indefinitely growing self-avoiding walk is solved exactly on a regular fractal, the Sierpinski gasket. The fractal dimension D=In 5/In 2-1 differs from the value of D for the equilibrium self-avoiding walk on this fractal.

The connectivity constant omega for Hamiltonian walks on Dhar's 4-simplex (1978) is found using an exact set of recursion relations. The result omega =1.399710 . . . differs from the value of omega for Hamiltonian walks on the square lattice. As a consequence, omega must depend on other lattice characteristics besides the coordination number and the fractal dimension. The first correction to the leading-order asymptotic behaviour is also obtained.

The two components of thyroid plasma membranes known to interact with thyrotropin, i.e., a glycoprotein with specific thyrotropin binding activity and the gangliosides of the thyroid membranes, are shown to segregate differently when membranes are solubilized with lithium diiodosalicylate. Individually examined, the interaction of each component with thyrotropin exhibits a different sensitivity to salts. The data suggest that the thyrotropin receptor on the thyroid membrane is a complex which is composed of both glycoprotein and ganglioside components and that its properties are derived from each component.

Extracellular responses from neurons in the nucleus of the solitary tract (NST) were studied in rats aged 5 days to adulthood during chemical stimulation of the tongue with monochloride salts, citric and hydrochloric acids, sucrose, sodium saccharin, and quinine hydrochloride. Multiunit taste responses were recorded in rats at 5-7 days of age and single-unit responses were recorded from 111 neurons in four other age groups of 14-20 days, 25-35 days, 50-60 days, and adult. NST neurons in rats aged 5-7 days consistently responded to relatively high concentrations (0.5 M) of NH4Cl and KCl and to citric and hydrochloric acid. However, they often did not respond to 0.5 M NaCl or to 0.1 M NH4Cl. Single NST neurons in rats aged 14 days and older characteristically responded to all 0.1 and 0.5 M salts and to both acids. At least 75% of neurons also responded to sucrose and sodium saccharin, and 46% responded to all of these stimuli and quinine hydrochloride. After 14 days, no developmental changes occurred in the number of stimuli to which neurons responded. There were substantial developmental alterations in the response magnitudes to some chemical stimuli. Average response frequencies increased after 35 days of age for 0.1 and 0.5 M NaCl, LiCl, KCl, and for sucrose and sodium saccharin. Response frequencies for NH4Cl, citric and hydrochloric acid, and quinine hydrochloride, however, did not change throughout development. The proportion of single NST neurons that responded maximally to specific monochloride salts did not change during development. Most single neurons in all age groups responded equally well to NH4Cl, NaCl, and LiCl. No NST neuron responded maximally to KCl. There were also no developmental differences in response latencies in rats aged 14 days and older. Response frequencies of second-order NST neurons generally reflect changes in responses from the primary afferent, chorda tympani fibers, throughout development; however, the increases in salt response frequencies from NST neurons occur comparatively later in development. Furthermore, at all ages, the taste responses to monochloride salts include higher response frequencies and a general loss in response specificity in NST compared to chorda tympani neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

In a recent letter Lyklema and Evertsz (see ibid., vol.19, p.895-900 (1986)) found a value of nu for the eta =1 Laplacian random walk which differs from the value the authors obtained for the diffusion-limited self-avoiding walk (DLSAW). They show that this results from different boundary conditions at the ends of these chains and not from a failing in our Monte Carlo studies of the DLSAW.

The authors present an exact bond-to-site transformation for diffusion-limited aggregation. The equivalence maps a class of partial adhesion problems on arbitrary lattices to absolute adhesion problems on transformed lattices. Examples are given for diffusion in the presence and absence of an external field. The correspondence relates two conjectured aspects of universality in the scaling behaviour, namely the irrelevance of lattice structure and adhesion probability.

The murine Leydig tumor cell line 1 (MLTC-1) contains gonadotropin receptors (GR) that are coupled to adenylate cyclase through the stimulatory guanine nucleotide binding protein (G/sub s/). The binding of human choriogonadotropin (hGC) causes MLTC-1 cells to accumulate cAMP. With time, the ability of MLTC-1 cells to respond to hCG is attenuated by a process called desensitization. The hydrodynamic properties of GR from control and desensitized MLTC-1 cells were studied. Sucrose density gradient sedimentation in H/sub 2/O and D/sub 2/O and gel filtration chromatography were used to estimate the Stokes radius (a), partial specific volume (v/sub c/), sedimentation coefficient (s/sub 20,w/), and molecular weight (M/sub r/) of the detergent-solubilized hormone-receptor complex (hCG-GR). (/sup 125/I)hCG was bound to MLTC-1 cells under conditions that allow (37/sup 0/C) or prevent (0/sup 0/C) desensitization, and hCG-GR was solubilized in Triton X-100. In the absence of desensitization, control hCG-GR had a M/sub r/ of 213,000, whereas desensitized hCG-GR had a M/sub r/ of 158,000. Deglycosylated hCG (DG-HCG) is an antagonist that binds to GR with high affinity but fails to stimulate adenylate cyclase or cause desensitization. (/sup 125/I)DG-hCG was bound to MLTC-1 cells and DG-hCG-GR solubilized in Triton X-100. The hydrodynamic properties of DG-hCG-GR weremore » the same as that for control hCG-GR. There was no evidence for the association of adenylate cyclase or G/sub s/ with GR in Triton X-100 solubilized preparations. When hCG was cross-linked to GR and solubilized with sodium dodecyl sulfate (SDS), the M/sub r/ was found to be 116,000, which was similar to that determined by SDS-polyacrylamide gel electrophoresis and less than that of the Triton X-100 solubilized control hCG-GR.« less

We study directed diffusion-limited aggregation on the Bethe lattice. An exact nonlinear recursion relation for the probability distribution of the density on finite lattices is constructed. The aggregates in a problem on the infinite lattice display marginal scaling behavior: They are compact up to a logarithmic correction. A mapping between models with perfect and partial adhesion on contact is given as a simple example of university.

To quantify the development of upper airway chemoreceptors, epiglottal taste buds were counted in cat fetuses, kittens and adults. Taste buds with structural characteristics similar to those in the adult were observed in all fetuses close to term and in kittens from birth. During the first postnatal week a mean of 76 taste buds was present on the kitten epiglottis and by adulthood 800 were observed. The number of taste buds increased as a logarithmic function of both age and weight, but the correlation with weight is better than that with age. The presence of epiglottal taste buds from very early developmental stages suggests that these receptors may mediate the reflex apnoea and swallowing that occur in response to chemical stimulation of the larynx in newborns.

• The pathologic changes in a rare case of mucopolysaccharidosis (MPS) type IIIB or Sanfilippo's syndrome B (absence of α- N -acetylglucosaminidase) are presented, along with the biochemical findings. Comparisons were made with other reported cases of MPS III subtypes and related storage disorders in terms of clinical, light microscopic, electron microscopic, and chemical findings, and a correlation of the ultrastructural changes made with the severe neurological dysfunction noted in this disorder. At present, MPS III subtypes cannot be separated from one another by morphological means because the same expression and distribution of lesions may be encountered among differing subtypes.

Epiglottal taste buds of the sheep increase in number during development, and continue to increase until the epiglottis has reached its adult size. However, since the increase in taste bud numbers is paralleled by increase in the surface area of the epiglottis, the density of taste buds decreases progressively in the fetus and newborn. After birth the density remains relatively constant. From examination of the morphological stages of epiglottal taste bud development, we conclude that taste buds are originally produced by de novo formation, but that further increase in numbers is effected by division of existing, developing taste buds. Because of the large number of taste buds, and the maintenance of their density on the epiglottis, it is concluded that they have an important functional role in upper airway protective reflexes.