Geometric Regions Research Articles

STABILITY OF VORTEX PHASES IN FERROELECTRIC EASY-PLANE NANO-CYLINDERS

ABSTRACT Bounded charges induced by the polarization gradient in finite-size ferroelectrics are known to produce the unfavorable depolarization electric field that suppresses the uniform ferroelectric state. To reduce the depolarization energy the non-uniform vortex (toroidal) state is formed inside ferroelectric nano-particles, nano-disks, and nano-rods. Based on self-consistent solution of Ginzburg-Landau equations coupled with electrostatic equations, we study the multivortex toroidal states appearing in the nanometric easy-plane ferroelectric cylinder. The geometrical textures, critical temperatures and stability regions for these states are calculated.

Theoretical studies on the carcinogenicity of polycyclic aromatic hydrocarbons

The distinct molecular regions of a set of 28 polycyclic aromatic hydrocarbons (PAHs) showing varying degrees of carcinogenic activity (CA) have been analyzed on the basis of their calculated molecular electrostatic potential (MESP) at B3LYP/6-31+G(d,p) level of theory. The MESP, being a property directly related to electron density, clearly distinguishes the electron dense centers in the molecule into K, L, M, and newly defined N regions. Further, a quantitative structure activity relationship (QSAR) model of carcinogenicity is developed using the volume of MESP lobes at the named regions for a set of 17 carcinogenic molecules with experimentally known CA index. The QSAR equation suggested that all the geometrical regions are significant in determining the carcinogenic property of PAHs. The model clearly showed that K and M regions have activating carcinogenic effect whereas L and N regions have deactivating carcinogenic effect. The CA showed considerable enhancement when any three distinct regions are present in a PAH. On the other hand, all the PAH systems with only one type of region are inactive irrespective of whether the region is activating or deactivating. Similarly, molecules showing the presence of two types of regions are either inactive or weakly active. The essential features of both the "K, L region" and the "bay region" theories of carcinogenesis are well evident in the new QSAR model, as the former theory works on the basis of activating K and deactivating L regions whereas the latter theory is related with the activating M region.

Analyses of the role of grain boundaries in mesoscale dynamic fracture resistance of SiC–Si 3N 4 intergranular nanocomposites

Silicon carbide (SiC)–silicon nitride (Si 3N 4) nanocomposites with SiC dispersions as well as Si 3N 4 matrix of mesoscale dimensions (∼1 μm) are considered to have exceptional strength attributed to interactions of SiC dispersions with Si 3N 4 grain boundaries (GBs). However, an account of GBs on the strength of these nanocomposites is not available. In order to analyze this issue, cohesive finite element method (CFEM) based mesoscale dynamic fracture analyses of SiC–Si 3N 4 nanocomposites with an explicit account of length scales associated with Si 3N 4 GBs, SiC particles, and Si 3N 4 grains are performed. Analyses indicate that primary mechanism of fracture in the nanocomposite microstructures is intergranular Si 3N 4 matrix cracking. GBs are responsible for crack deflection and accordingly damage is limited to a smaller geometric region in microstructures with GBs. On an average, a microstructure with GBs present is stronger than the corresponding microstructure with GBs removed. However, in cases where the second phase SiC particles are in the wake of microcracks the microstructure without GB becomes stronger against fracture in comparison to the corresponding one with GBs owing to the crack bridging effect caused by the second phase SiC particles.

Increasing the speed of DOSXYZnrc Monte Carlo simulations through the introduction of nonvoxelated geometries

This article presents a method for increasing the speed of DOSXYZnrc Monte Carlo simulations through the introduction of nonvoxelated geometries defined in any coordinate system. Nonvoxelated geometries are used to isolate regions of uniform density and composition from the scoring grid. Particle transport within these geometric regions is not restricted by the boundary constraints of the scoring grid. This allows for larger particle steps, which in turn reduces the calculation time. A water tank phantom, water-lung interface phantom, cylindrical calibration phantom, and CT phantom were each used to test the application of the nonvoxelated approach. Each phantom was simulated using both the original DOSXYZnrc code and the new nonvoxelated code. The equivalence between the original and nonvoxelated simulations were quantified using a chi2 analysis. To within the statistical uncertainty, the voxelated and nonvoxelated simulations were found to give nearly identical results, regardless of boundary crossing algorithm. The speed increase was found to be a function of both voxel dimension and field size. Using nonvoxelated geometries and the EXACT boundary crossing algorithm, the speed increase was as high as 9.0, 5.1, 5.7, and 1.3 times faster for the water tank, water-lung interface, cylindrical calibration, and CT phantoms, respectively. If the PRESTA-I boundary crossing algorithm was used, the calculation speed increase was up to 6.0, 2.7, 3.3, and 1.2 times faster. These results clearly show that the nonvoxelated technique greatly increases simulation speed without any loss in dose accuracy.

ANALYSIS OF HIGH FREQUENCY PLANE WAVE SCATTERING FROM A DOUBLE NEGATIVE CYLINDER VIA THE MODIFIED WATSON TRANSFORMATION AND DEBYE EXPANSION

The modified Watson transform is applied to the Mie series expression of the electromagnetic field scattered by a high frequency plane wave incident on an infinitely long double negative cylinder. The Debye expansion is applied to the Mie series coefficients to obtain a physical insight into the scattering mechanisms and achieve an efficient approach for the computation of the scattered field. The first two terms of the Debye series are computed using the residue series in the geometrical shadow regions and using the steepest descent method in the geometrically lit regions. It is observed that the results obtained from the series and from the modified Watson transform are in good agreement. The angular boundaries for the geometrically lit and the geometrical shadow regions of the double negative cylinder corresponding to the first two terms of the Debye series are determined. These are compared with the corresponding angular boundaries for a double positive cylinder. It is observed that the spatial extent of the geometrical shadow of the double negative cylinder corresponding to the second term of the Debye series is very small compared to that of the double positive cylinder due to the negative refraction in the double negative cylinder when the magnitude of the refractive index n is greater than √ 2.

Improvement in the Low Frequency Performance of Geometric Transition Radar Absorbers Using Square Loop Impedance Layers

A technique is described for improving the low frequency performance of geometric transition (GT) radar absorbers based on lossy foam pyramids. The technique makes use of the fact that at high frequencies, only the geometric transition region of the absorber is utilized whereas at low frequencies, the whole absorber thickness interacts with the incident wave. Hence the low frequency performance may be improved, without compromising that at high frequencies, by electrically loading the absorber base layer using one or more frequency selective surfaces (FSS) whose elements are typically in the form of single or nested loops. Other advantages of this technique include minimal increases in weight and manufacturing costs. The paper includes comparative predictions of unmodified and loaded GT absorber reflectivity at both normal and oblique incidence and discusses the effect on absorber performance of tolerance variations in the dimensions and location of the loading FSS elements. Finally, free-space reflectivity measurements on unmodified and loaded commercial absorber blocks are made over the frequency range 1-10 GHz and these confirm the validity of the technique.

Gastrointestinal Disease in Simian Immunodeficiency Virus-Infected Rhesus Macaques Is Characterized by Proinflammatory Dysregulation of the Interleukin-6-Janus Kinase/Signal Transducer and Activator of Transcription3 Pathway

Gastrointestinal disease and inflammation are common sequelae of human and simian immunodeficiency virus (SIV) infection. Nevertheless, the molecular mechanisms that lead to gastrointestinal dysfunction remain unclear. We investigated regulation of the interleukin (IL)-6-JAK-STAT3 pathway in jejunum and colon, collected at necropsy, from 10 SIV-infected macaques with diarrhea (group 1), 10 non-SIV-infected macaques with diarrhea (group 2), and 7 control uninfected macaques (group 3). All group 1 and 2 macaques had chronic diarrhea, wasting, and colitis, but group 1 animals had more frequent and severe lesions in the jejunum. A significant increase in IL-6 and SOCS-3 gene expression along with constitutive STAT3 activation was observed in the colon of all group 1 and 2 macaques and in the jejunum of only group 1 macaques compared to controls. Further, in colon, histopathology severity scores correlated significantly with IL-6 (groups 1 and 2) and SOCS-3 (group 2) gene expression. In jejunum, a similar correlation was observed only in group 1 animals. Phosphorylated STAT3 (p-STAT3) was localized to lymphocytes (CD3+) and macrophages (CD68+), with fewer CD3+ lymphocytes expressing p-STAT3 in group 1 macaques. Despite high SOCS-3 expression, STAT3 remained constitutively active, providing a possible explanation for persistent intestinal inflammation and immune activation that may favor viral replication and disease pro-gression.

ECO-System: Embracing the Change in Placement

In a realistic design flow, circuit and system optimizations must interact with physical aspects of the design. For example, improvements in timing and power may require the replacement of large modules with variants that have different power/delay tradeoff, shape, and connectivity. New logic may be added late in the design flow, which is subject to interconnect optimization. To support such flexibility in design flows, we develop a robust system in performing Engineering Change Orders (ECOs). In contrast with the existing stand-alone tools that offer poor interfaces to the design flow and cannot handle a full range of modern very large scale integration layouts, our ECO-system reliably handles fixed objects and movable macros in instances with widely varying amounts of whitespace. It detects geometric regions and sections of the netlist that require modification and applies an adequate amount of change in each case. Given a reasonable initial placement, it applies minimal changes but is capable of replacing large regions to handle pathological cases. The ECO-system can be used in the range from high-level synthesis to physical synthesis and detail placement.

Simple and rigorous analytical expression of the propagating field behind an axicon illuminated by an azimuthally polarized beam

A simple and rigorous analytical expression of the propagating field behind an axicon illuminated by an azimuthally polarized beam has been deduced by use of the vector interference theory. This analytical expression can easily be used to calculate accurately the propagation field distribution of azimuthally polarized beams throughout the whole space behind an axicon with any size base angle, not just restricted inside the geometric focal region as does the Fresnel diffraction integral. The numerical results show that the pattern of the beam produced by the azimuthally polarized Gaussian beam that passes through an axicon is a multiring, almost-equal-intensity, and propagation-invariant interference beam in the geometric focal region. The number of bright rings increases with the propagation distance, reaching its maximum at half of the geometric focal length and then decreasing. The intensity of bright rings gradually decreases with the propagation distance in the geometric focal region. However, in the far-field (noninterference) region, only one single-ring pattern is produced and the dark spot size expands rapidly with propagation distance.

An efficient framework for photon Monte Carlo treatment planning**This work was presented in part at the First European Workshop on Monte Carlo Treatment Planning (EWG-MCTP) held in Gent, Belgium from 22 to 25 October 2006.

Currently photon Monte Carlo treatment planning (MCTP) for a patient stored in the patient database of a treatment planning system (TPS) can usually only be performed using a cumbersome multi-step procedure where many user interactions are needed. This means automation is needed for usage in clinical routine. In addition, because of the long computing time in MCTP, optimization of the MC calculations is essential. For these purposes a new graphical user interface (GUI)-based photon MC environment has been developed resulting in a very flexible framework. By this means appropriate MC transport methods are assigned to different geometric regions by still benefiting from the features included in the TPS. In order to provide a flexible MC environment, the MC particle transport has been divided into different parts: the source, beam modifiers and the patient. The source part includes the phase-space source, source models and full MC transport through the treatment head. The beam modifier part consists of one module for each beam modifier. To simulate the radiation transport through each individual beam modifier, one out of three full MC transport codes can be selected independently. Additionally, for each beam modifier a simple or an exact geometry can be chosen. Thereby, different complexity levels of radiation transport are applied during the simulation. For the patient dose calculation, two different MC codes are available. A special plug-in in Eclipse providing all necessary information by means of Dicom streams was used to start the developed MC GUI. The implementation of this framework separates the MC transport from the geometry and the modules pass the particles in memory; hence, no files are used as the interface. The implementation is realized for 6 and 15 MV beams of a Varian Clinac 2300 C/D. Several applications demonstrate the usefulness of the framework. Apart from applications dealing with the beam modifiers, two patient cases are shown. Thereby, comparisons are performed between MC calculated dose distributions and those calculated by a pencil beam or the AAA algorithm. Interfacing this flexible and efficient MC environment with Eclipse allows a widespread use for all kinds of investigations from timing and benchmarking studies to clinical patient studies. Additionally, it is possible to add modules keeping the system highly flexible and efficient.

Spatial correlation properties of focused partially coherent vortex beams

The spatial correlation properties in the geometrical focal region of a converging, partially coherent vortex wave field are analyzed. Expressions are derived for a pair of points on the axis of symmetry and for a pair of points in the focal plane. It is found that the longitudinal and transverse coherence lengths in the focal region change with the variation of the topological charge and the normalized coherence length of the vortex field. In addition, the degree of coherence is shown to possess phase singularities.

Efficient photon treatment planning by the use of Swiss Monte Carlo Plan

Currently photon Monte Carlo treatment planning (MCTP) for a patient stored in the patient database of a treatment planning system (TPS) usually can only be performed using a cumbersome multi-step procedure where many user interactions are needed. Automation is needed for usage in clinical routine. In addition, because of the long computing time in MCTP, optimization of the MC calculations is essential. For these purposes a new GUI-based photon MC environment has been developed resulting in a very flexible framework, namely the Swiss Monte Carlo Plan (SMCP). Appropriate MC transport methods are assigned to different geometric regions by still benefiting from the features included in the TPS. In order to provide a flexible MC environment the MC particle transport has been divided into different parts: source, beam modifiers, and patient. The source part includes: Phase space-source, source models, and full MC transport through the treatment head. The beam modifier part consists of one module for each beam modifier. To simulate the radiation transport through each individual beam modifier, one out of three full MC transport codes can be selected independently. Additionally, for each beam modifier a simple or an exact geometry can be chosen. Thereby, different complexity levels of radiation transport are applied during the simulation. For the patient dose calculation two different MC codes are available. A special plug-in in Eclipse providing all necessary information by means of Dicom streams was used to start the developed MC GUI. The implementation of this framework separates the MC transport from the geometry and the modules pass the particles in memory, hence no files are used as interface. The implementation is realized for 6 and 15 MV beams of a Varian Clinac 2300 C/D. Several applications demonstrate the usefulness of the framework. Apart from applications dealing with the beam modifiers, three patient cases are shown. Thereby, comparisons between MC calculated dose distributions and those calculated by a pencil beam or the AAA algorithm. Interfacing this flexible and efficient MC environment with Eclipse allows a widespread use for all kinds of investigations from timing and benchmarking studies to clinical patient studies. Additionally, it is possible to add modules keeping the system highly flexible and efficient.

Young's Diagnostics of Phase Singularities into Polychromatic Light Fields

Two original approaches for the diagnostics of phase singularities (such as optical vortices, screw dislocations of a wave front) based on the Young-Rubinowicz mOdel of diffraction phenomena are represented. Both techniques are implemented without using a separate reference wave, as in common interference techniques. That is why they are very convenient for analysis of spatially coherent polychromatic fields. The first technique is based on the use of an opaque strip as the diffraction device. Bending Young's interference fringes produced by the edge diffraction waves from two rims of the strip within the geometrical shadow region reflect helicity of a wave front, so that the direction and magnitude of bending correspond directly to the sign and the modulus of topological charge of the optical vortex, respectively. This technique is practicable for diagnostics of isolated polychromatic vortices, such as rainbow Laguerre-Gaussian mode, where the condition of mutual spectral purity is satisfied. Another technique is based on the use of knife-edge diffraction. The edge of an opaque screen serves as the source of a reference wave, which interferes with the tested field within the directly illuminated region. One observes typical interference forklets near the geometrical shadow boundary, which detect optical vortices. This technique is more applicable to diagnostics of phase singularities in polychromatic speckle fields due to the condition of mutual spectral purity is satisfied automatically.

THE LAYERED NET SURFACE PROBLEMS IN DISCRETE GEOMETRY AND MEDICAL IMAGE SEGMENTATION

Efficient detection of multiple inter-related surfaces representing the boundaries of objects of interest in d-D images (d >/= 3) is important and remains challenging in many medical image analysis applications. In this paper, we study several layered net surface (LNS) problems captured by an interesting type of geometric graphs called ordered multi-column graphs in the d-D discrete space (d >/= 3 is any constant integer). The LNS problems model the simultaneous detection of multiple mutually related surfaces in three or higher dimensional medical images. Although we prove that the d-D LNS problem (d >/= 3) on a general ordered multi-column graph is NP-hard, the (special) ordered multi-column graphs that model medical image segmentation have the self-closure structures and thus admit polynomial time exact algorithms for solving the LNS problems. Our techniques also solve the related net surface volume (NSV) problems of computing well-shaped geometric regions of an optimal total volume in a d-D weighted voxel grid. The NSV problems find applications in medical image segmentation and data mining. Our techniques yield the first polynomial time exact algorithms for several high dimensional medical image segmentation problems. Experiments and comparisons based on real medical data showed that our LNS algorithms and software are computationally efficient and produce highly accurate and consistent segmentation results.

Total gluon shadowing due to fluctuation effects

We show a new physical phenomenon expected for the ratio R pA of the unintegrated gluon distribution of a nucleus over the unintegrated gluon distribution of a proton scaled up by the atomic factor A 1 / 3 in the fluctuation-dominated (diffusive scaling) region at high energy. We calculate the dependence of R pA on the atomic number A, the rapidity Y and the transverse gluon momentum k ⊥ . We find that R pA exhibits an increasing gluon shadowing with growing rapidity, approaching 1 / A 1 / 3 at asymptotic rapidities which means total gluon shadowing, due to the effect of gluon number fluctuations or pomeron loops. The increase of R pA with rising gluon momentum decreases as the rapidity grows. In contrast, in the geometric scaling region where the effect of fluctuations is negligible, the ratio R pA shows only partial gluon shadowing in the fixed-coupling case, basically independent on the rapidity and the gluon momentum.

Isomorphism and Possible Invariance of Error Cells Under Spherocylindrical Transposition

The purpose of this article is to investigate the invariance and isomorphism of error cells with cylinder power measured positively and negatively in the cylinder-sphere plane. Cells with cylinder power measured positively and negatively are mapped to symmetric power space to see whether isomorphism and the invariance are conserved under the mapping and spherocylindrical transposition. Principal powers of refraction are measured and are rounded off to multiples of 0.25 D and 1 degrees or 5 degrees , say, for the principal meridians. Geometric regions in the cylinder-sphere plane with positive and negative cylinder represent uncertainty surrounding the powers and are respectively transformed to a plane containing the axis of scalar powers in symmetric power space. Cells from principal powers become error cells surrounding readings of cylinder and sphere as well as error regions about astigmatic powers. These are presented in the plane for scalar powers and semipowers of positive and negative cylinders. In symmetric power space, planes containing the axis of scalar powers are distinguished from one another by the cylinder axis of the lens power. Although error cells in clinical measure are not invariant under spherocylindrical transposition, cells represented in positive cylinder form have the same shape as cells for which the power is expressed in negative cylinder form. Error cells in symmetric power space about powers in negative cylinders can be rotated about the axis of scalar powers to coincide perfectly with cells about powers in positive cylinder form for near spherical and astigmatic powers. The error regions in symmetric power space do not depend on the spherocylindrical form in which the original measurements are made and their isomorphism is conserved in the mapping.

Surface waves on a semitoroidal water ring

We study the dynamics of surface waves on a semitoroidal ring of water that is excited by vertical vibration. We create this specific fluid volume by patterning a glass plate with a hydrophobic coating, which confines the fluid to a precise geometric region. To excite the system, the supporting plate is vibrated up and down, thus accelerating and decelerating the fluid ring along its toroidal axis. When the driving acceleration is sufficiently high, the surface develops a standing wave, and at yet larger accelerations, a traveling wave emerges. We also explore frequency dependencies and other geometric shapes of confinement.

Concepts and Preliminary Data Toward the Realization of Image-guided Liver Surgery

Image-guided surgery provides navigational assistance to the surgeon by displaying the surgical probe position on a set of preoperative tomograms in real time. In this study, the feasibility of implementing image-guided surgery concepts into liver surgery was examined during eight hepatic resection procedures. Preoperative tomographic image data were acquired and processed. Accompanying intraoperative data on liver shape and position were obtained through optically tracked probes and laser range scanning technology. The preoperative and intraoperative representations of the liver surface were aligned using the iterative closest point surface matching algorithm. Surface registrations resulted in mean residual errors from 2 to 6 mm, with errors of target surface regions being below a stated goal of 1 cm. Issues affecting registration accuracy include liver motion due to respiration, the quality of the intraoperative surface data, and intraoperative organ deformation. Respiratory motion was quantified during the procedures as cyclical, primarily along the cranial–caudal direction. The resulting registrations were more robust and accurate when using laser range scanning to rapidly acquire thousands of points on the liver surface and when capturing unique geometric regions on the liver surface, such as the inferior edge. Finally, finite element models recovered much of the observed intraoperative deformation, further decreasing errors in the registration. Image-guided liver surgery has shown the potential to provide surgeons with important navigation aids that could increase the accuracy of targeting lesions and the number of patients eligible for surgical resection.

On the Geometrical Characteristic of Wireless Ad-Hoc Networks and its Application in Network Performance Analysis

A wireless ad-hoc network can be roughly considered as one consisting of a collection of mobile nodes distributed in a finite region, which adopts a non-centralized and self-organized structure. In such networks, messages are transmitted, received and forwarded in a finite geometrical region. In addition, the transmission of messages is highly dependent on the locations of the mobile nodes. As a result, the geometrical relationships between the nodes, and especially the distance between them are of fundamental importance. In this paper, we propose a space decomposition method to analyze the probability distribution of the distance between nodes in an ad-hoc network. In particular, we derive two theoretical expressions for the probability distribution of the distance between nodes under the assumption that the nodes are independently and uniformly distributed in either a rectangular region or hexagonal region. Further results on the node degree distribution and max-flow capacity of the network are then presented based upon these expressions

Structural Analysis of ITER Lower In-Vessel-Viewing Port

A finite element model of the International Thermonuclear Experimental Reactor (ITER) in-vessel viewing port was developed by the ANSYS code in order to evaluate the stress level of this structure. The thermal, elastic and modal analyses were made in succession based on the loads designated by the ITER International team. The designed loads include electromagnetic loads, seismic loads, pressure, temperature and gravity. The preliminary results of the finite element analysis (FEA) show that the stress intensity exceeded the allowable stress and the maximum stress was concentrated in the geometric discontinuous region of the shroud stub extension (SSE). Therefore, the SSE has been modified recently. For the modified structure, we found that the stresses do not exceed the allowable value for all load combinations. In addition the modal analysis results show that the natural frequencies of the IVV port structure are located in the typical diapason of seismic excitation.