High-speed three-dimensional shape measurement using GOBO projection

A projector which uses a rotating slide structure to project aperiodic sinusoidal fringe patterns at high frame rates and with high radiant flux is introduced. It is used in an optical three-dimensional (3D) sensor based on coded-light projection, thus allowing the analysis of fast processes. Measurements of an inflating airbag, a rope skipper, and a soccer ball kick at a 3D frame rate of more than 1300 independent point clouds per second are presented.     

Optical three-dimensional shape analysis of metallic nanoparticles after laser-induced deformation

The 3D shape of Ag nanoparticles in glass irradiated by fs laser pulses is investigated by optical spectroscopy. It is shown that in general spheroids are produced with their symmetry axis oriented along the direction of the linear laser polarization. Depending on the actual irradiation conditions, oblate or prolate spheroids are obtained. The halo of small Ag clusters and Ag ions around the reshaped particles causes a redshift of the surface plasmon resonances via refractive index increase.     

Cross-sectional tongue shape during the production of vowels

This study used ultrasound imaging to examine the cross-sectional shape of the tongue during the production of the ten English vowels ( see text ) in two consonant contexts--/p/ and /s/--and at two scan angles--anterior and posterior. Results were compared with models of sagittal tongue shape. A newly built transducer holder and head restraint maintained the ultrasound transducer in a fixed position inferior to the mandible at a chosen location and angle. The transducer was free to move only in a superior/inferior direction, and demonstrated reliable tracking of the jaw. Since the tongue is anisotrophic along its length, anterior and posterior scan angles were examined to identify differences in tongue shape. Similarly, the coarticulatory effects of the sibilant /s/ versus the bilabial /p/ were examined, to assess variability of intrinsic tongue shape for the vowels. Results showed that the subject's midsagittal tongue grooving was almost universal for the vowels. Posterior grooves were deeper than anterior grooves. In /s/ context, posterior tongue grooves were shallower than in /p/ context. Anteriorly, /s/ context caused deeper grooves for low vowels. Cross-sectional tongue shape varied with tongue position similarly to sagittal tongue shape.     

A three-dimensional model of tongue movement based on ultrasound and x-ray microbeam data

Point-tracking techniques provide timing information about structural movements of the tongue. Imaging techniques provide information about cross-sectional and pharyngeal tongue shape and movement. This study joined these techniques in a single subject. Five pellets on the tongue surface were tracked using x-ray microbeam, and the midsagittal and coronal planes of the tongue were imaged using real-time ultrasound. The speech materials were the consonants [s] and [l] and the vowels [i], [a], and [o] combined in VCVCe utterances. Analyses concentrated on the difference in tongue movements related to the two consonants. A model of tongue movement was developed, in which critical features of consonant shape and position dominated the tongue opening movement. In this model, the tongue is divided into subdivisions termed "functional segments" in both the sagittal and coronal planes. Movements of the functional segments created observable opening movement patterns.     

The three-dimensional shape of the bow shock

Summary The radial distance to the bow shock obtained in earlier studies is first reviewed. Recently, HEOS 2 data have provided an extensive exploration of the bow shock location away from the ecliptic plane. These shock crossings have been used to find with a least-squares technique a conic surface that best describes the shock. The limitation of HEOS 2 observations is discussed in relation to both usual and unusual locations fo the bow shock. It seems clear from ≈2000 shock crossings which have been examined that, when the interplanetary magnetic field has a southward component, the shock is closer to the Earth, by 1R _E, than when it has a northward component.

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Riassunto In questo lavoro dapprima si commentano studi precedenti della distanza radiale dalla Terra dell'onda d'urto stazionaria nel piano dell'eclittica. Poi, facendo uso dei dati che HEOS 2 ha fornito, esplorando per la prima volta vaste regioni dello spazio fuori dall'eclittica, si descrive lo studio fatto: con una tecnica dei minimi quadrati, abbiamo studiato la superficie quadrica che meglio descrive l'onda d'urto. Si discutono le limitazioni delle osservazioni di HEOS 2 in relazione sia alle posizioni più probabili sia in relazione alle posizioni meno probabili. Sembra chiaro, dalle 2000 posizioni dell'onda d'urto che sono state esaminate, che quandro il campo magnetico interplanetario ha una componente diretta a sud dell'eclittica, l'onda d'urto è più vicina alla terra di 1R _E, rispetto ai casi con una componente diretta a nord dell'eclittica.

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Резюме Сначала анализируется радиальное расстояние до ударной волны сжатия, полученное в предыдущих исследованиях. Недавние данные с HEOS 2 дали обширную информацию о местоположении ударных волны сжатия относителыно плоскости эклиптики. Эти данные о пересечениях ударных волн используются для нахождения, с помошью техники наименьших квадратов, конической поверхности, которая наилучшим образом описывает ударную волну. Обсуждаются ограничения наблюдении на HEOS 2, связанные с обычными и необычными локализациями ударной волны сжатия. По-видимому, из ≈2000 пересечений ударных волн, которые были исследованы, в тех случаях, когда межпланетное магнитное поле имеет компоненту, направленную к югу, то ударная волна ближе к Земле на 1R _E, чем, когда межпланетное поле имеет компоненту, направленную на север.

     

Variational optimization of the 2DM: approaching three-index accuracy using extended cluster constraints

The reduced density matrix is variationally optimized for the two-dimensional Hubbard model. Exploiting all symmetries present in the system, we have been able to study 6 × 6 lattices at various fillings and different values for the on-site repulsion, using the highly accurate but computationally expensive three-index conditions. To reduce the computational cost we study the performance of imposing the three-index constraints on local clusters of 2 × 2 and 3 × 3 sites. We subsequently derive new constraints which extend these cluster constraints to incorporate the open-system nature of a cluster on a larger lattice. The feasibility of implementing these new constraints is demonstrated by performing a proof-of-principle calculation on the 6 × 6 lattice. It is shown that a large portion of the three-index result can be recovered using these extended cluster constraints, at a fraction of the computational cost.     

Analysis of mode shapes of a rigidly backed cylindrical foam using three-dimensional finite element acoustical analysis

In this study, the three-dimensional finite element frequency domain acoustical analysis is used to determine the modal shapes of cylindrical foam with a rigid backing and subjected to a unit normal incidence impulsive sound pressure loading while placed in the impedance tube. The acoustic results predicted for the foam are validated by data from the two-microphone acoustic measurements, and good agreement between the measured and predicted acoustic results is observed. The mode shapes of the incident face of the foam at a low frequency, resonant and anti-resonant frequencies as well as the frequency that occurring the peak loss modulus are illustrated. It is found that the modal behaviors of the cylindrical foam are dominated by the fluid, although the acoustic properties of the cylindrical foam are also influenced by the circumferential edge constraints and the modal movements of the solid skeleton.     

A contribution to simulating a three-dimensional larynx model using the finite element method

A three-dimensional model is presented to simulate the larynx during vocalization. The finite element method is used to calculate the airflow velocity and pressure along the larynx as well as tissue displacement. It is assumed that the larynx tissue is transversely isotropic and divided into three tissues: cover, ligament, and body. A contact-impact algorithm is incorporated to deal with the physics of the collision between both true vocal folds. The results show that the simulated larynx can reproduce the vertical and horizontal phase difference in the tissue movements and that the false vocal folds affect the pressure distribution over the larynx surfaces. The effects of exciting the larynx with different pressure drops are also investigated.     

Wood species identification using improved active shape model

In this paper, we propose a robust wood species identification scheme by using color wood surface images. First, a novel wood image acquirement system is devised, and the wood color image is converted into a V₁V₂I color-base image. Second, the corresponding grey histograms for V₁ and V₂ are established. Third, an improved active shape model is used to fulfill the curve deformation of the histogram curve of the standard specimen. This active shape model will then converge to the histogram curve of the test specimen. Finally, wood recognition is performed by comparing the initial and final active shape models with the histogram curve of the test specimen. We have experimentally proved that this scheme improves the mean recognition accuracy to approximately 90% for 5 wood species and that it can also be applied to the Gaussian noisy images. Moreover, the recognition accuracy can be further improved by combining this scheme with the texture feature recognition.     

Automatic analysis of three-dimensional displacement field using ESPI

Electronic speckle pattern interferometry (ESPI) has been used to study the in-plane and out-of-plane displacements of the object. In order to improve the accuracy, a Fourier filtration algorithm has been used to remove the speckle noise and get the holographic-quality ESPI fringe pattern. The processing steps of this method are described in detail in this paper. In addition, a phase shifter, which is easily used with simplified structure and high stability, is also presented. It can be applied to various coherent arrangements in experiments to obtain phase shifted fringe patterns. Experiments of determining the 3D displacement field of a circular fixed plate with a uniform load have been carried out using these methods. The results presented in this paper indicate that the accuracy of this method is satisfactory.     

A full-wave three-dimensional analysis of open dielectric waveguides and periodic structures using an equivalent network model

An accurate fully vectorial wave analysis to calculate the propagation characteristics and field distribution of open dielectric waveguides and optical integrated circuits is presented. Based on the periodic repetition concept and using an equivalent network model, a method to analyze wave propagation in these guides is developed, which is able to take the simultaneous presence of mixed polarizations into account. Compared with conventional approaches like mode matching as well as with other numerical methods, the presented three-dimensional (3D) method shows individual advantages like accuracy, simplicity, and numerical efficiency. To show both validity and usefulness of this approach, some fundamental structures are investigated and the obtained numerical results are presented.     

Prediction of backscatter coefficient in trabecular bones using a numerical model of three-dimensional microstructure

A model of ultrasonic backscattering for cancellous bone saturated by water is proposed. This model assumes that scattering is caused by the solid trabeculae and describes the cancellous bone as a weak scattering medium. The backscatter coefficient is related to the spatial Fourier transform of bone microarchitecture and to the density and compressibility fluctuations between the solid trabeculae and the saturating fluid. The computations of the model make use of three-dimensional numerical images of bone microarchitecture, obtained by tomographic reconstructions with a 10 microm spatial resolution. With this model, the predictions of the frequency dependence and of the magnitude of the backscatter coefficient are reasonably accurate. The theoretical predictions are compared to experimental data obtained on 19 specimens. An accuracy error of approximately 1 dB was found (difference between the averaged experimental values and theoretical predictions). One limit of the model may come from inaccurate values of trabecular bone characteristics needed for the computations (density and longitudinal velocity), which are yet to be precisely determined for human trabecular bone. However, the model is only slightly sensitive to variations of bone material properties. It was found that an accuracy error of 2.2 dB at maximum resulted from inaccurate a priori values of bone material properties. A computation of the elastic mean free path in the medium suggests that multiple scattering plays a minor role in the working frequency bandwidth (0.4-1.2 MHz). It follows from these results that a weak scattering medium model may be appropriate to describe scattering from trabecular bone.     

Star-triangle relation for a three-dimensional model

The solvablesl(n)-chiral Potts model can be interpreted as a three-dimensional lattice model with local interactions. To within a minor modification of the boundary conditions it is an Ising-type model on the body-centered cubic lattice with two- and three-spin interactions. The corresponding local Boltzmann weights obey a number of simple relations, including a restricted star-triangle relation, which is a modified version of the well-known star-triangle relation appearing in two-dimensional models. We show that these relations lead to remarkable symmetry properties of the Boltzmann weight function of an elementary cube of the lattice, related to the spatial symmetry group of the cubic lattice. These symmetry properties allow one to prove the commutativity of the row-to-row transfer matrices, bypassing the tetrahedron relation. The partition function per site for the infinite lattice is calculated exactly.On leave of absence from the Institute for High Energy Physics, Protvino, Moscow Region, 142284, Russia.     

Critical behavior of a three-dimensional dimer model

The phase transition behavior of a dimer model on a three-dimensional lattice is studied. This model is of biological interest because of its relevance to the lipid bilayer main phase transition. The model has the same kind of inactive low-temperature behavior as the exactly solvable Kasteleyn dimer model on a two-dimensional honeycomb lattice. Because of low-temperature inactivity, determination of the lowest-lying excited states allows one to locate the critical temperature. In this paper the second-lowest-lying excited states are studied and exact asymptotic results are obtained in the limit of large lattices. These results together with a finite-size scaling ansatz suggest a logarithmic divergence of the specific heat aboveT _c for the three-dimensional model. Use of the same ansatz recovers the exact divergence (α=1/2) for the two-dimensional model.     

Critical properties of a three-dimensional p-spin model

In this paper we study the critical properties of a finite dimensional generalization of the p-spin model. We find evidence that in dimension three, contrary to its mean field limit, the glass transition is associated to a diverging susceptibility (and correlation length). Received 13 May 1998     

Diffraction of electromagnetic waves in a three-dimensional magnetodielectric body of arbitrary shape

A numerical method of solving the problem of the diffraction of electromagnetic waves by a three-dimensional magnetodielectric body of arbitrary shape in the resonance frequency region is proposed. The method is applied in the form of a FORTRAN software package for calculating the components of the diffraction field of bodies with different electrodynamic and geometrical parameters. The directivity parameters of some bodies of complex shape are given.V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 87–91, June, 1995.     

A novel three-dimensional shape measurement method based on a look-up table

Fringe projection profilometry is widely used for three-dimensional shape measurement. In an oblique-angle projection, the fringe cycle is broadened on the reference plane. Phase errors are mainly caused by the nonlinear gamma of the projector and fringe cycle broadening. This study describes a phase error compensation method to eliminate these phase errors. A look-up table that stores phase errors is constructed for phase error compensation. Based on it, a new height equation is proposed. The experimental results show that the proposed method can compensate for the phase errors of the fringe projection profilometry, thereby improving the measurement accuracy significantly.