Axis Points Research Articles

CT evaluation of cervical pedicle in a Chinese population for surgical application of transpedicular screw placement

The lower cervical pedicle size differs between the Chinese and the non-Chinese population. Knowledge of pedicle dimensions and surface landmarks is crucial for the safe placement of screws, but few quantitative data concerning the lower cervical pedicle using CT scan and multiplanar reformations (MPR) in a Chinese population exist. The aim of this study was to evaluate lower cervical pedicle (C3-C7) dimensions in a Chinese population by computed axial tomography for surgical application. The dimensions of the pedicles (C3-C7) were determined in 60 patients from CT images of cervical spinal lesions. Measurements of pedicle height, width, pedicle axis length, effective length, and two angles of the pedicles, the distances from the projection point of the pedicle axis to the lateral edge of the lateral mass and to the inferior edge of the superior facet were measured. The smallest outer pedicle width was found at C3 among the female and C4 among the male. This measurement was significantly different between male and female patients in the outer pedicle width (P < 0.05; independent samples t test) at C3 and C4. The mean values of the outer pedicle width ranged from 5.4 to 6.7 mm in males, and 4.4 to 6.3 mm in females. The projection point of the pedicle axis in the lateral-superior area of the cervical lateral mass was the most important. There were significant correlations (P < 0.01; Kendall's W test) between the vertebral level and both pedicle angles (PTA and PSA). The smallest pedicle transverse angle was at C7 in males and females. The cervical spinal cord or vertebral artery may be at risk of injury if the angulation of the screw insert is over-medial or over-lateral in the transverse plane. Therefore, preoperative CT evaluation of pedicle transverse angle is very important. Considering the amount of variation among individuals, our data on CT measurements of pedicle in a Chinese population in conjunction with evaluation of the results of preoperative CT may enhance the safety of transpedicular screw fixation in the lower cervical spine.

Computation of medial axis and offset curves of curved boundaries in planar domain

In this paper, we begin our research from the generating theory of the medial axis. The normal equidistant mapping relationships between two boundaries and its medial axis have been proposed based on the moving Frenet frames and Cesaro’s approach of the differential geometry. Two pairs of adjoint curves have been formed and the geometrical model of the medial axis transform of the planar domains with curved boundaries has been established. The relations of position mapping, scale transform and differential invariants between the curved boundaries and the medial axis have been investigated. Based on this model, a tracing algorithm for the computation of the medial axis has been generated. In order to get the accurate medial axis and branch points, a Two_Tangent_Points_Circle algorithm and a Three_Tangent_Points_Circle algorithm have been generated, which use the results of the tracing algorithm as the initial values to make the iterative process effective. These algorithms can be used for the computation of the medial axis effectively and accurately. Based on the medial axis transform and the envelope theory, the trimmed offset curves of curved boundaries have been investigated. Several numerical examples are given at the end of the paper.

Integral representation of the n-th derivative in de Branges-Rovnyak spaces and the norm convergence of its reproducing kernel

In this paper, we give an integral representation for the boundary values of derivatives of functions of the de Branges–Rovnyak spaces ℋ(b), where b is in the unit ball of H ∞ (ℂ + ). In particular, we generalize a result of Ahern–Clark obtained for functions of the model spaces K b , where b is an inner function. Using hypergeometric series, we obtain a nontrivial formula of combinatorics for sums of binomial coefficients. Then we apply this formula to show the norm convergence of reproducing kernel k ω,n b of evaluation of the n-th derivative of elements of ℋ(b) at the point ω as it tends radially to a point of the real axis.

Condensed surfaces of magnetic neutron stars, thermal surface emission, and particle acceleration above pulsar polar caps

For sufficiently strong magnetic fields and/or low temperatures, the neutron star surface may be in a condensed state with little gas or plasma above it. Such surface condensation can significantly affect the thermal emission from isolated neutron stars, and may lead to the formation of a charge-depleted acceleration zone ("vacuum gap") in the magnetosphere above the stellar polar cap. Using the latest results on the cohesive property of magnetic condensed matter, we quantitatively determine the conditions for surface condensation and vacuum gap formation in magnetic neutron stars. We find that condensation can occur if the thermal energy kT of the neutron star surface is less than about 8% of its cohesive energy Q_s, and that a vacuum gap can form if the neutron star's rotation axis and magnetic moment point in opposite directions and kT is less than about 4% of Q_s. Thus, vacuum gap accelerators may exist for some neutron stars. Motivated by this result, we also study the physics of pair cascades in the vacuum gap model for photon emission by accelerating electrons and positrons due to both curvature radiation and resonant/nonresonant inverse Compton scattering. Our calculations of the condition of cascade-induced vacuum breakdown and the related pulsar death line/boundary generalize previous works to the superstrong field regime. We find that inverse Compton scatterings do not produce a sufficient number of high energy photons in the gap and thus do not lead to pair cascades for most neutron star parameters. We discuss the implications of our results for the recent observations of neutron star thermal radiation as well as for the detection/non-detection of radio emission from high-B pulsars and magnetars.

Minimal symmetric Darlington synthesis

We consider the symmetric Darlington synthesis of a p x p rational symmetric Schur function S with the constraint that the extension is of size 2p x 2p. Under the assumption that S is strictly contractive in at least one point of the imaginary axis, we determine the minimal McMillan degree of the extension. In particular, we show that it is generically given by the number of zeros of odd multiplicity of I-SS*. A constructive characterization of all such extensions is provided in terms of a symmetric realization of S and of the outer spectral factor of I-SS*. The authors's motivation for the problem stems from Surface Acoustic Wave filters where physical constraints on the electro-acoustic scattering matrix naturally raise this mathematical issue.

반응표면법을 이용한 5축 임펠러 정삭 가공의 최적화

An impeller is a important part of turbo-machinery. It has a set of twisted surfaces because it consists of many blades. Five-axis machining is required to produce a impeller because of interference between tool and workpiece. It can obtain good surface integrity and high productivity. This paper proposes finish cutting method for machining impeller with 5-axis machining center and optimization of cutting condition by response surface method. Firstly, cutting methods are selected by consideration of operation characteristics. Secondly, response factors are determined as cutting time and cutting error for prediction of productivity. Experiments are projected by central composite design with axis point. Thirdly, regression linear models are estimated as single surface in the leading edge and as dual surface in the hub surface cutting. Finally, cutting conditions are optimized.

An algorithm for determination of the disbalance of a rotor with electromagnetic bearings

An algorithm for identification of the disbalance of a nonuniform flexible rotor on electromagnetic bearings is presented. The algorithm is based on the solution of the inverse problem of the rotor dynamics using data on the motion of the rotor axis points and the electromagnetic forces controlling the rotor motion. The algorithm operation is illustrated using as an example a computer model of a nonuniform flexible vertical rotor with a nonlinear system for the control of the electromagnetic support of the rotor.

Androgen receptors in a cichlid fish, Astatotilapia burtoni: Structure, localization, and expression levels

Androgens are an important output of the hypothalamic-pituitary-gonadal (HPG) axis that controls reproduction in all vertebrates. In male teleosts two androgens, testosterone and 11-ketotestosterone, control sexual differentiation and development in juveniles and reproductive behavior in adults. Androgenic signals provide feedback at many levels of the HPG axis, including the hypothalamic neurons that synthesize and release gonadotropin-releasing hormone 1 (GnRH1), but the precise cellular site of androgen action in the brain is not known. Here we describe two androgen receptor subtypes, ARalpha and ARbeta, in the cichlid Astatotilapia burtoni and show that these subtypes are differentially located throughout the adult brain in nuclei known to function in the control of reproduction. ARalpha was expressed in the ventral part of the ventral telencephalon, the preoptic area (POA) of the hypothalamus and the ventral hypothalamus, whereas ARbeta was more widely expressed in the dorsal and ventral telencephalon, the POA, and the ventral and dorsal hypothalamus. We provide the first evidence in any vertebrate that the GnRH1-releasing neurons, which serve as the central control point of the HPG axis, express both subtypes of AR. Using quantitative real-time PCR, we show that A. burtoni AR subtypes have different expression levels in adult tissue, with ARalpha showing significantly higher expression than ARbeta in the pituitary, and ARbeta expressed at a higher level than ARalpha in the anterior and middle brain. These data provide important insight into the role of androgens in regulating the vertebrate reproductive axis.

Hemispherical Power Asymmetry in the Third-Year Wilkinson Microwave Anisotropy Probe Sky Maps

We consider the issue of hemispherical power asymmetry in the third-year WMAP data, adopting a previously introduced modulation framework. Computing both frequentist probabilities and Bayesian evidences, we find that the model consisting of an isotropic CMB sky modulated by a dipole field gives a substantially better fit to the observations than the purely isotropic model, even when accounting for the larger prior volume. For the ILC map, the Bayesian log-evidence difference is ~1.8 in favor of the modulated model, and the raw improvement in maximum log likelihood is 6.1. The best-fit modulation dipole axis points toward (l, b) = (225°, -27°), and the modulation amplitude is 0.114, in excellent agreement with the results from the first-year analyses. The frequentist probability of obtaining such a high modulation amplitude in an isotropic universe is ~1%. These results are not sensitive to data set or sky cut. Thus, the statistical evidence for a power asymmetry anomaly is both substantial and robust, although not decisive, for the currently available data. Increased sky coverage through better foreground handling and full-sky and high-sensitivity polarization maps may shed further light on this issue.

Generating subdivision surfaces from profile curves

The construction of freeform models has always been a challenging task. A popular approach is to edit a primitive object such that its projections conform to a set of given planar curves. This process is tedious and relies very much on the skill and experience of the designer in editing 3D shapes. This paper describes an intuitive approach for the modeling of freeform objects based on planar profile curves. A freeform surface defined by a set of orthogonal planar curves is created by blending a corresponding set of sweep surfaces. Each of the sweep surfaces is obtained by sweeping a planar curve about a computed axis. A Catmull–Clark subdivision surface interpolating a set of data points on the object surface is then constructed. Since the curve points lying on the computed axis of the sweep will become extraordinary vertices of the subdivision surface, a mesh refinement process is applied to adjust the mesh topology of the surface around the axis points. In order to maintain characteristic features of the surface defined with the planar curves, sharp features on the surface are located and are retained in the mesh refinement process. This provides an intuitive approach for constructing freeform objects with regular mesh topology using planar profile curves.

The orientation of galaxy dark matter haloes around cosmic voids

Using the Millennium N-body Simulation we explore how the shape and angular momentum of galaxy dark matter haloes surrounding the largest cosmological voids are oriented. We find that the major and intermediate axes of the haloes tend to lie parallel to the surface of the voids, whereas the minor axis points preferentially in the radial direction. We have quantified the strength of these alignments at different radial distances from the void centres. The effect of these orientations is still detected at distances as large as 2.2 Rvoid from the void centre. Taking a subsample of haloes expected to contain disc-dominated galaxies at their centres we detect, at the 99.9 per cent confidence level, a signal that the angular momentum of those haloes tends to lie parallel to the surface of the voids. Contrary to the alignments of the inertia axes, this signal is only detected in shells at the void surface (1 < R < 1.07 Rvoid) and disappears at larger distances. This signal, together with the similar alignment observed using real spiral galaxies, strongly supports the prediction of the Tidal Torque theory that both dark matter haloes and baryonic matter have acquired, conjointly, their angular momentum before the moment of turnaround.

Sequential Unfolding of Individual Helices of Bacterioopsin Observed in Molecular Dynamics Simulations of Extraction from the Purple Membrane

Multiple molecular dynamics simulations of bacterioopsin pulling from its C-terminus show that its α-helices unfold individually. In the first metastable state observed in the simulations, helix G is unfolded at its C-terminal segment while the rest of helix G (residues 200–216) is folded and opposes resistance because of a salt-bridge network consisting of Asp-212 and Lys-216 on helix G and Arg-82 and Asp-85 on helix C. Helix G unfolds inside the bundle because the external force is applied to its C-terminal end in a direction perpendicular to the surface of the membrane. Inversely, helix F has to flip by 180° to exit from the membrane because the applied force and the helical N-C axis point in opposite directions. At the highest peak of the force, which cannot be interpreted in single-molecule force spectroscopy experiments, helix F has a pronounced kink at Pro-186. Mutation of Pro-186 and/or the charged side chains mentioned above, which are involved in very favorable electrostatic interactions in the low-dielectric region of the membrane, are expected to reduce the highest peak of the force. Helices E and D unfold in a similar way to helices G and F, respectively. Hence, the force-distance profile and sequence of events during forced unfolding of bacterioopsin are influenced by the up-and-down topology of the seven-helix bundle. The sequential extraction of individual helices from the membrane suggests that the spontaneous (un)folding of bacterioopsin proceeds through metastable bundles of fewer than seven helices. The metastable states observed in the simulations provide atomic level evidence that corroborates the interpretation of very recent force spectroscopy experiments of bacteriorhodopsin refolding.

Isomorphism between the solution spaces of a discrete convolution equation and a convolution equation on the space of entire functions

In this paper, we solve the problem of reconstructing an arbitrary solution of a homogeneous convolution equation from its values at integer points of the real axis.

Road tracking in aerial images based on human–computer interaction and Bayesian filtering

A typical way to update map road layers is to compare recent aerial images with existing map data, detect new roads and add them as cartographic entities to the road layer. This method cannot be fully automated because computer vision algorithms are still not sufficiently robust and reliable. More importantly, maps require final checking by a human due to the legal implications of errors. In this paper we introduce a road tracking system based on human–computer interactions (HCI) and Bayesian filtering. Bayesian filters, specifically, extended Kalman filters and particle filters, are used in conjunction with human inputs to estimate road axis points and update the tracking algorithms. Experimental results show that this approach is efficient and reliable and that it produces substantial savings over the traditional manual map revision approach. The main contribution of the paper is to propose a general and practical system that optimizes the performance of road tracking when both human and computer resources are involved.

A method to extract morphological traits of plant organs from 3D point clouds as a database for an architectural plant model

Combining process-based and three-dimensional (3D) structural models for specific crops to functional–structural plant models (FSPMs) enable ecophysiologists to investigate the interaction of single plants or plant stands with their biotic and abiotic environment in a unique way. The present study was part of a collaborative research program on the development of a FSPM for the sample plant ( Hordeum vulgare L.). The emphasis of this paper is put on two main aspects. First, improved generic and flexible functions are formulated for modeling the shape of leaves and stems of graminaceous plants as organ-related triangulated surfaces, where the parameters may be directly interpreted in terms of morphological traits. The proposed functions constitute the structural model, which is amplified by topological information to a so-called architectural model. Second, we suggest a new approach to parameterize these functions based on 3D point cloud data obtained by digitization of entire plants. Since no automated technique is available to process 3D point clouds in a way appropriate for parameterization of the architectural model, the required algorithms are developed and implemented in Matlab ®. Our approach comprises the following steps. First, the measured set of points is partitioned into subsets representing each organ. Each subset is then divided further to represent organ segments. Next, the centroid of each partial point cloud representing an organ segment is computed. The sequence of these centroid points describes the organ axis. By means of the architectural model for leaves and stems, triangulated surfaces are assembled from the computed organ axis points and from user-defined initial values for the various parameters in the model (e.g. maximum leaf width). Finally, the parameters in the functions describing leaf and stem surfaces are estimated by fitting computed triangulated surfaces into the related point cloud using least squares optimization. Hence, the proposed method allows the use of 3D point clouds obtained with modern 3D digitizing techniques for the parameterization of an organ-based architectural model.

Hypothalamic–pituitary–adrenal axis activity in adults who were prenatally exposed to the Dutch famine

The hypothalamic-pituitary-adrenal (HPA) axis has been proposed to be susceptible to fetal programming, the process by which an adverse fetal environment elicits permanent physiological and metabolic alterations predisposing to disease in later life. It is hypothesized that fetal exposure to poor circumstances alters the set point of the HPA axis, leading to increased HPA axis activity and subsequent increased cortisol concentrations. In this study, we tested the hypothesis that prenatal exposure to famine during different periods of gestation is associated with increased activity of the HPA axis. We assessed plasma cortisol concentrations after a dexamethasone suppression and an ACTH1-24 -stimulation test in a group of 98 men and women randomly sampled from the Dutch famine birth cohort. Cohort members were born as term singletons around the 1944-1945 Dutch famine. Cortisol profiles after dexamethasone suppression and ACTH1-24 stimulation were similar for participants exposed to famine during late, mid- or early gestation (P = 0.78). Cortisol concentrations after dexamethasone suppression test did not differ between those exposed and those unexposed to famine in utero (mean difference -2% (95% confidence interval (CI) -27 to 23)). Neither peak cortisol concentration (20 nmol/l (95% CI -27 to 66)), cortisol increment (-5 nmol/l (95% CI -56 to 47)) or cortisol area under the curve post-ACTH1-24 injection (4% (95% CI -4 to 12)) differed between exposed and unexposed participants. Prenatal famine exposure does not seem to affect HPA axis activity at adult age, at least not at the adrenal level. This does not exclude altered HPA axis activity at the levels of the hippocampus and hypothalamus.

Utilisation de la phase stationnaire pour localiser la provenance du bruit sur l'axe d'une structure élastique à symétrie de révolution

Consider the problem numbered (1) in the text. Along the axis, the pressure may be expressed as a combination of axisymmetric modes only. For high wave numbers, the method of stationary phase may be used to show that the pressure on the axis comes only from the vicinities of a few parallels. Generally, only the parallel constituting the points nearest to this axis point is to be considered. For low circumferential mode numbers (especially n = 0 ), the curvature greatly influences the wavelength of the modes of the structure in vacuo: thus, the method of stationary phase can be applied, for most aeronautical airborne structures, even from the first axisymmetric mode and not only above the coincidence frequency. Using an expression established earlier, we can give an expression for the pressure on the axis of an axisymmetric enclosure. To cite this article: D. Brenot, C. R. Mecanique 334 (2006).

Monte Carlo dose calculations for a 6-MV photon beam in a thorax phantom

In this study we evaluated the accuracy of the Monte Carlo (MC) and effective path length (EPL) methods for dose calculations in the inhomogeneous thorax phantom. The Philips SL 75/5 linear accelerator head was modeled using the MCNP4C Monte Carlo code. An anatomic inhomogeneous thorax phantom was irradiated with a 6-MV photon beam, and the doses along points of the central axis of the beam were measured by a small ionization chamber. The central axis relative dose was calculated by the MCNP4C code and the EPL method in a conventional treatment planning system. The results of calculations and measurements were compared. For all measured points on the thorax phantom the results of the MC method were in agreement with the actual measurement (local difference was less than 2%). For the EPL method, the amount of error was dependent on the field size and the point location in the phantom. The maximum error was +19.5 and +26.8 for field sizes of 10 x 10 and 5 x 5 cm2 for lateral irradiation. Our study showed large, unacceptable errors for EPL calculations in the lung for both field sizes. The accuracy of the MC method was better than the recommended value of 3%. Thus, application of this method is strongly recommended for lung dose calculations, especially for small field sizes.

The Subtalar Joint Axis Locator

A new clinical device, the subtalar joint axis locator, was created to track the three-dimensional location of the subtalar joint axis during weightbearing movements of the foot. The assumption was that if the anterior exit point of the subtalar joint axis is stationary relative to the dorsal aspect of the talar neck, then, by performing radiographs of the feet with the subtalar joint axis locator in place on the foot, the ability of the locator to track rotations and translations of the talar neck and thus the subtalar joint axis in space could be approximated. In this preliminary study of two adults, the subtalar joint axis locator accurately tracked the talar neck position during weightbearing rotational motions of the subtalar joint. The device was also used in a series of subjects to determine its dynamic capabilities. It is possible, then, that the subtalar joint axis locator can reliably track the spatial location of the subtalar joint axis during weightbearing movements of the foot.

Determination of root canal curvatures before and after canal preparation (part II): A method based on numeric calculus

The aim of this paper is to present a new method based on numeric calculus to provide data on any type of root canal curvature at any point of the long axis of the canal. Twenty severely curved, simulated root canals were prepared with rotary FlexMaster and Profile instruments in the crown-down technique and manually in the step-back technique. The inner and outer curvatures were registered in a system of coordinates before and after preparation in increments of 0.5 mm. Using an equalising function, the curvatures were first represented in graphic and algebraic form. The maximum and the mean curvature as well as the length of the arc from the apical foramen to the point of maximum curvature were determined mathematically. An increase in maximum curvature was registered for all four shaping systems investigated. The radius of the inner curvature decreased by 0.5-1.2 mm in the manual systems as a result of the preparation. The Profile system displayed the smallest changes in radius (-0.9 mm) even with the outer curvature, and manual preparation with stainless steel files the most pronounced change (-1.8 mm). The point of maximum curvature at the inner curvature was displaced by 1.6 mm to the apical foramen through manual preparation with Ni-Ti files. At the outer curvature, the maximum displacement (1.8 mm) recorded was also the result of preparation with Ni-Ti hand files, while a displacement of only 0.3 mm to the apical foramen was recorded with the other systems. The method offers a means of determining curvatures precisely without random specification of reference points. The method is also capable of registering only minor changes in curvature in the two-dimensional long axis of the canal.