Zeta functions that hear the shape of a Riemann surface

To a compact hyperbolic Riemann surface, we associate a finitely summable spectral triple whose underlying topological space is the limit set of a corresponding Schottky group, and whose “Riemannian” aspect (Hilbert space and Dirac operator) encode the boundary action through its Patterson–Sullivan measure. We prove that the ergodic rigidity theorem for this boundary action implies that the zeta functions of the spectral triple suffice to characterize the (anti-)complex isomorphism class of the corresponding Riemann surface. Thus, you can hear the complex analytic shape of a Riemann surface, by listening to a suitable spectral triple.     

How we hear what is not there: a neural mechanism for the missing fundamental illusion

How the brain estimates the pitch of a complex sound remains unsolved. Complex sounds are composed of more than one tone. When two tones occur together, a third lower pitched tone is often heard. This is referred to as the "missing fundamental illusion" because the perceived pitch is a frequency (fundamental) for which there is no actual source vibration. This phenomenon exemplifies a larger variety of problems related to how pitch is extracted from complex tones, music and speech, and thus has been extensively used to test theories of pitch perception. A noisy nonlinear process is presented here as a candidate neural mechanism to explain the majority of reported phenomenology and provide specific quantitative predictions. The two basic premises of this model are as follows: (I) The individual tones composing the complex tones add linearly producing peaks of constructive interference whose amplitude is always insufficient to fire the neuron (II): The spike threshold is reached only with noise, which naturally selects the maximum constructive interferences. The spacing of these maxima, and consequently the spikes, occurs at a rate identical to the perceived pitch for the complex tone. Comparison with psychophysical and physiological data reveals a remarkable quantitative agreement not dependent on adjustable parameters. In addition, results from numerical simulations across different models are consistent, suggesting relevance to other sensory modalities.     

Auditory perception is not special: we see the world, we feel the world, we hear the world

The literature on "contrast" provides no evidence that durational contrast should occur in the speech and nonsence signals used in research cited by Diehl et al. [J. Acoust. Soc. Am. 89, 2905-2909 (1991)]. Moreover, there is evidence that, in comparable signals, it does not occur. Accordingly, their own account of the collection of findings on rate normalization is not viable. Their comments on my research do not imperil my interpretation of it or challenge my criticism that classification judgments of acoustically analogous speech and nonsense signals do not permit interpretation, by themselves, in terms of underlying auditory-system mechanisms. Their arguments that in auditory perception, uniquely, we hear proximal stimulation, not its physical causal sources, is implausible. Their theoretical perspective generally, I argue, is unrealistic.     

Averaged electrical parameters of forest vegetation and the height of forest cover

A device and a method for measuring the electrical parameters (resistivity ρ and permittivity ?) of forest vegetation are described. The measuring method and the data processing technique are detailed for a forest area the resistivity and permittivity of which measured in the ranges of long and very long waves are ρ = 37 ± 12 kΩ m and ? = 1.6 · 0.3, respectively. It is found that coordinate measurements in forest vegetation with a single-frequency GPS receiver always involve a one-sided systematic drift, since the permittivity is other than unity. This circumstance makes it possible to develop a way of determining the average height of forest cover. For example, the average height of trees is roughly equal to 21 m in the given forest area.     

Can one hear the shape of an electrode? I. Numerical study of the active zone in Laplacian transfer

The concept of active zone in the Laplacian transport to and across irregular interfaces is rigorously introduced. It applies to arbitrary geometries and uses the coarse-graining method proposed by Sapoval to compute the flux across an irregular interface from its geometry without solving the general Laplace problem. Such transport play a dominant role in electrochemistry, heterogeneous catalysis and physiological diffusion processes. In the field of electrochemistry, the method permits one to predict the impedance of an electrode of arbitrary geometry for any value of the frequency. It shows that, for systems with aspect ratios of the order of a few times unity or less, impedance spectroscopy yields in principle a reliable approximate measure of the length of the chord corresponding to a perimeter length inversely proportional to the interface capacitance and frequency. For these cases, impedance spectroscopy can determine the shape of an electrode to the extent that the knowledge of the average chord length as a function of the perimeter determines the shape. For systems of arbitrary geometry, it is shown that impedance spectroscopy permits a measure of the size of the active zone. These results can be transposed to several problems related to Laplacian transfer, such as etching of irregular solids and catalysis in the Eley-Rideal regime. Received 3 November 1998 and Received in final form 8 December 1998     

Effects of pulsing of a target tone on the ability to hear it out in different types of complex sounds

Judgments of whether a sinusoidal probe is higher or lower in frequency than the closest partial ("target") in a multi-partial complex are improved when the target is pulsed on and off. These experiments explored the contribution of reduction in perceptual confusion and recovery from adaptation to this effect. In experiment 1, all partials except the target were replaced by noise to reduce perceptual confusion. Performance was much better than when the background was composed of multiple partials. When the level of the target was reduced to avoid ceiling effects, no effect of pulsing the target occurred. In experiment 2, the target and background partials were irregularly and independently amplitude modulated. This gave a large effect of pulsing the target, suggesting that if recovery from adaptation contributes to the effect, amplitude fluctuations do not prevent this. In experiment 3, the background was composed of multiple steady partials, but the target was irregularly amplitude modulated. This gave better performance than when the target was unmodulated and a moderate effect of pulsing the target. It is argued that when the target and background are steady tones, pulsing the target may result both in reduction of perceptual confusion and recovery from adaptation.     

Solitons in the one-dimensional forest fire model

Fires in the one-dimensional Bak-Chen-Tang forest fire model propagate as solitons, resembling shocks in Burgers turbulence. The branching of solitons, creating new fires, is balanced by the pairwise annihilation of oppositely moving solitons. Two distinct, diverging length scales appear in the limit where the growth rate of trees, p, vanishes. The width of the solitons, w, diverges as a power law, 1/p, while the average distance between solitons diverges much faster as d approximately exp(pi2/12p).     

Searching for the earliest galaxies in the 21cm forest

We use a model developed by Xu,Ferrara,and Chen(Mon Not Roy Astron Soc,submitted) to compute the 21 cm line absorption signatures imprinted by star-forming dwarf galaxies(DGs) and starless minihalos(MHs). The method,based on a statistical comparison of the equivalent width(W ν ) distribution and flux correlation function,allows us to derive a simple selection criteria for candidate DGs at very high(z ≤ 8) redshift. We find that ≈18% of the total number of DGs along a line of sight to a target radio source(GRB or quasar) can be identified by the condition W ν0; these objects correspond to the high-mass tail of the DG distribution at high redshift,and are embedded in large HII regions. The criterion W ν0.37 kHz instead selects ≈11% of MHs. Selected candidate DGs could later be re-observed in the near-IR by the JWST with high efficiency,thus providing a direct probe of the most likely reionization sources.     

Solute friction and forest interaction

Solute friction is known to prevail in crystals where a solution of point defects results in a diffuse resistance to dislocation motion. This property is often used to strengthen materials. In this paper we show that it also affects dislocation–dislocation interactions. Dislocation dynamics simulations are used to investigate and quantify this property. The solute friction results in a shielding of elastic interactions leading to a significant decrease of the intrinsic strengths of junction and annihilation reactions. Simulations in static and dynamic conditions show that the interaction stability decreases with the friction stress. A model is proposed to account for the modification of the interaction coefficient predicted by massive simulations in latent hardening conditions. Results suggest that the observed softening is mainly due to the decrease of the line tension of dislocations involved in the dislocation–dislocation interactions.     

From dislocation junctions to forest hardening

The mechanisms of dislocation intersection and strain hardening in fcc crystals are examined with emphasis on the process of junction formation and destruction. Large-scale 3D simulations of dislocation dynamics were performed yielding access for the first time to statistically averaged quantities. These simulations provide a parameter-free estimate of the dislocation microstructure strength and of its scaling law. It is shown that forest hardening is dominated by short-range elastic processes and is insensitive to the detail of the dislocation core structure.     

Some results of experimental investigations of the combustion of forest materials

Results of long-term experimental investigations of the combustion of forest combustible materials are presented. For performing the investigations, a test bench had been developed and built which was completed with instruments for optical and thermal imaging. The higher measurement accuracy has made it possible to obtain some new data and to refine the previously known ones. The predictions of numerical simulations of ground forest fires are discussed.     

Detection of small forest fires by lidar

The possibility of detecting small forest fires with the help of a simple and cheap lidar operating at 0.532-μm wavelength up to distances of about 6.5 km is demonstrated. The values of the signal-to-noise ratio (SNR) achieved in the experiments are consistent with theoretical estimations obtained by computational modeling of the lidar detection process, including simulation of the smoke-plume shape and of the laser beam–plume interaction. This model was used to assess the potential of the lidar technique for fire surveillance in large forest areas. In particular, the upper limiting range for effective detection (SNR>5) of small localized fires in dry- and clear-weather conditions is estimated at 7–15 km depending on operation mode, burning rate, and observation geometry. Received: 29 August 2001 / Published online: 29 November 2001     

Dynamics of forest fire under rotational constraint

A rotationally constrained forest fire model is studied on square and triangular lattices of size 400×400. The critical probabilityp _c for onset of fire propagation is determined. The scaling relationsMt ^d _r, R_gt^v andMR _g ^d _f are analysed at fire propagation probabilityp=p _c whereM is the number of burnt trees,R _g the radius of gyration andd _f the fractal dimension of the cluster of burnt trees at timet. Numerical estimates ofd _t, v andd _f have been obtained.     

A radar backscatter model for forest stands

A Monte Carlo method for calculating the radar backscatter cross-sections from a forest stand is presented in this study. The model for the forest stand consists of two layers: the top layer contains a mixture of randomly orientated dielectric circular disks or small needles representing the leaves of the deciduous trees or coniferous trees respectively, as well as cylindrical-shaped scatterers, representing the branches of the foliage, while the bottom layer consists of randomly distributed vertical cylinders modelling the tree trunks. The phase matrices of the disks and needles are formulated using the generalized Rayleigh-Gans approximation whereas those of the branches and tree trunks are obtained from the infinite-cylinder approximation. The ground is modelled as a Kirchhoff rough surface based on the stationary-phase approximation. The relative contributions from the tree trunks, branches and trunks, leaves and trunks, and the entire forest stand are studied separately. It is found that leaves seem to dominate at higher frequencies while branches at lower frequencies. Effects of various physical and geometrical parameters such as dielectric constants, volume fractions, sizes and orientation distributions of the scatterers in a forested canopy are also studied. Finally, the results from the model are compared with the measured angular distributions of the radar backscattering cross-sections from some field measurements reported in the literature.     

Attitudes of Children With Dysphonia

SUMMARY: Because voice disorders in childhood may have a negative impact on communicative effectiveness, social development, and self-esteem, the objective was to determine the impact of voice disorders on lives of children from the perspective of chronically dysphonic children and their parents. This study consisted of focused interviews with chronically dysphonic children and their caregivers. Focused interviews were conducted with 10 children in each of the following age groups: Toddler (2-4 years old), Young Child (5-7 years old), School-Aged Child (8-12 years old), and Adolescent (13-18 years old). Interview questions were formulated to elicit attitudes in the following conceptual domains: emotional, social/functional, and physical. Interviews were transcribed and subjected to systematic qualitative analyses that identified common themes within each age group for each conceptual domain. For Toddlers, interviews relied heavily on parents and the biggest concerns were found in the physical and functional domains. Young Children expressed that their biggest issues related to voice were physical ("run out of air," "sometimes voice does not work"). Ninety percent of Young Children were repeatedly asked to use a quieter voice. Emotional factors and physical factors were prominent in the interviews of School-Aged Children and Adolescents. Children and Adolescents often felt that their dysphonic voice received undue attention and also limited their participation in important events. Anger, sadness, and frustration were also expressed. Chronic dysphonia negatively affects the lives of children. This work will serve as the basis for development of a valid, reliable, and age-appropriate measure of voice-related quality of life in children.     

儿童发育性髋关节脱位的磁共振形态学定量

发育性髋关节脱位（developmental dysplasia of the hip,DDH）作为一类常见的、严重威胁儿童健康成长的髋关节疾病会严重影响到儿童的肢体发育和生活质量,其早诊断、早治疗非常重要.磁共振成像（magnetic resonance imaging,MRI）技术可提供丰富的有关髋关节发育情况的形态学信息.目前,基于磁共振图像的DDH临床诊断主要凭借医生的肉眼观测,对医生要求甚高,而且无法定量判断DDH病情.本文提出了一种针对儿童DDH磁共振图像的形态学定量评估方法,通过对DDH病理改变密切相关的形态学参数的自动测定,完成形态学参数的定量评估,为临床提供辅助的量化参考.该方法包括磁共振图像预处理、股骨及盆骨分割、髋关节三维模型重建,以及结合了厚度搜索、三维霍夫变换和最小二乘拟合等算法实现的中心边缘角（center-edge angle,CEA）、髋臼角（acetabular index,AI）和股骨颈前倾角（femoral neck anteversion,FNA）等重要指标的自动测量.儿童DDH形态学定量评估方法的建立对儿童DDH的筛查、诊断和确诊患儿手术方案的制定,以及术后的动态随访,都具有重要参考价值.