Portal Plane Research Articles

Attractive Interactions between Heteroallenes and the Cucurbituril Portal.

In this paper, we report on the noteworthy attractive interaction between organic azides and the portal carbonyls of cucurbiturils. Five homologous bis-α,ω-azidoethylammonium alkanes were prepared, where the number of methylene groups between the ammonium groups ranges from 4 to 8. Their interactions with cucurbit[6]uril were studied by NMR spectroscopy, IR spectroscopy, X-ray crystallography, and computational methods. Remarkably, while the distance between the portal plane and most atoms at the guest end groups increases progressively with the molecular size, the β-nitrogen atoms maintain a constant distance from the portal plane in all homologues, pointing at a strong attractive interaction between the azide group and the portal. Both crystallography and NMR support a specific electrostatic interaction between the carbonyl and the azide β-nitrogen, which stabilizes the canonical resonance form with positive charge on the β-nitrogen and negative charge on the γ-nitrogen. Quantum computational analyses strongly support electrostatics, in the form of orthogonal dipole-dipole interaction, as the main driver for this attraction. The alternative mechanism of n → π* orbital delocalization does not seem to play a significant role in this interaction. The computational studies also indicate that the interaction is not limited to azides, but generalizes to other isoelectronic heteroallene functions, such as isocyanate and isothiocyanate. This essentially unexploited attractive interaction could be more broadly utilized as a tool not only in relation to cucurbituril chemistry, but also for the design of novel supramolecular architectures.

Multi-stage approach for structural damage detection problem using basis pursuit and particle swarm optimization

In order to solve structural damage detection problem, a multi-stage method using particle swarm optimization is presented. First, a new spars recovery method, named Basis Pursuit (BP), is utilized to preliminarily identify structural damage locations. The BP method solves a system of equations which relates the damage parameters to the structural modal responses using the sensitivity matrix. Then, the results of this stage are subsequently enhanced to the exact damage locations and extents using the PSO search engine. Finally, the search space is reduced by elimination of some low damage variables using micro search (MS) operator embedded in the PSO algorithm. To overcome the noise present in structural responses, a method known as Basis Pursuit De-Noising (BPDN) is also used. The efficiency of the proposed method is investigated by three numerical examples: a cantilever beam, a plane truss and a portal plane frame. The frequency response is used to detect damage in the examples. The simulation results demonstrate the accuracy and efficiency of the proposed method in detecting multiple damage cases and exhibit its robustness regarding noise and its advantages compared to other reported solution algorithms.

基于空间圆拟合的地铁盾构洞门检测方法

地下铁道盾构施工中需要对始发、接收洞门的位置和姿态进行检测，以确保盾构施工不至于偏离设计线路。洞门位置通过洞门中心坐标来表达；洞门姿态通过洞门所在平面与水平面和设计线路夹角来表达。这些都不能直接观测，需要通过洞门圈的测量，拟合洞门圈所在空间圆来计算得到。本文以天津某地铁工程为例，介绍了基于空间圆拟合的地铁盾构洞门检测方法，及其数据处理过程。It is necessary to detect the position and posture of originating and receiving portal during subway shield construction, in order to ensure that the shield construction will not deviate from the design line. Portal position is expressed by the coordinates of the center of the portal, while portal posture is expressed by the angle between portal plane and horizontal plane, and the angle between portal plane and design line. These data cannot be directly observed, but they can be indirectly observed by calculating the measuring portal circle. Taking Tianjin subway project as an example, this paper introduces the data processing of subway shield tunnel portal detection based on spatial circle fitting.

Transverse hepatectomy: a 14-years experience.

Transverse hepatectomy, removal of hepatic segments IVB, V, VI, (III) in continuity with the gallbladder through the transverse portal plane, was first introduced by Paul Sugarbaker in 1990. In 1995 the first transverse hepatectomy in Hungary was carried out by our workgroup. This article summarizes our experience with transverse hepatectomies during the period from 1995 to 2008. During this time 72 trisegmentectomies were performed 22 out of these operations were transverse hepatectomies. The average resection time for transverse hepatectomy was 1 hour and 20 minutes, there was an average 0.8 unit blood transfusion requirement per patient, the average exclusion time was 20.6 minutes, the average time spent in hospital postoperatively was 10.1 days and there were 2 perioperative deaths due to sepsis and hemorrhagic shock. In our experience transverse hepatectomy proved to be a bloodless, relatively easy procedure, which enables safe removal of the antero-lateral segments. This new type of major hepatic resection is very useful in metastasis surgery and has minimal associated morbidity and mortality.

Experimental method to obtain scattering contribution in portal dose images

A method for evaluating scattered dose contribution in portal images acquired under clinical conditions (phantom-device distance of 30 cm) is presented. This method is based on radiographic film and ionisation chamber measurements and is valid for homogenecus polystyrene phantoms and square fields of different size. The portal imaging device consisted of a radiographic film placed between slabs of polystyrene under full build-up conditions (1.5 cm for 6 MV beam and 3 cm for 18 MV and 1 cm of polystyrene backscatter material. First the primary dose image in the portal plane P(i,j) is obtained using a projection algorithm, then the scattered dose image S(i,j) is found by subtracting the primary dose image in the portal plane P(i,j) from the total dose image acqu red in the portal plane T(i,j). The ratio S(i,j)/T between the scattered dose distribution and the dose value measured on the bearn axis in the portal plane was found to be uniform within the radiation field for all the geometrical configuration of phantoms and fields studied. Under these conditions the mean value of the scatter fraction S/T evaluated within a ROI centred on the bearn axis accurately describes the scatter fraction distribution S(i,j)/T within the whole radiation field. S/T ranges from 7.4% to 31.1% in the 6 MV beam and from 8.9% to 30.8% in the 18 MV beam. Finally an analytical method to evaluate the ratio S/T has been developed from the experimental results. It comprises phantom, accelerator head and portal imaging device contributions and depends on field size and phantom thickness.

On Saturation Control of a Non-Ideal Vibrating Portal Frame Foundation Type Shear-Building

In this paper, we examine the nonlinear control method based on the saturation phenomenon and of systems coupled with quadratic nonlinear ties applied to a shear-building portal plane frame foundation that supports an unbalanced direct current with limited power supply (non-ideal system). We analyze the equations of motion by using the method of averaging and numerical simulation. The interaction of the non-ideal structure with the saturation controller may lead to the occurrence of interesting phenomena during the forward passage through the several resonance states of the systems. Special attention is focused on passage through resonance when the non-ideal excitation frequency is near the portal frame natural frequency and when the non-ideal system frequency is approximately twice the controller frequency (two-to-one internal resonance).

On non-ideal and non-linear portal frame dynamics analysis using bogoliubov averaging method

We apply the Bogoliubov Averaging Method to the study of the vibrations of an elastic foundation, forced by a Non-ideal energy source. The considered model consists of a portal plane frame with quadratic nonlinearities, with internal resonance 1:2, supporting a direct current motor with limited power. The non-ideal excitation is in primary resonance in the order of one-half with the second mode frequency. The results of the averaging method, plotted in time evolution curve and phase diagrams are compared to those obtained by numerically integrating of the original differential equations. The presence of the saturation phenomenon is verified by analytical procedures.

Monte Carlo simulation of a dynamic MLC: Implementation and applications

PurposeStudy of behavior and influence of a multileaf collimator (MLC) on dose calculation, verification, and portal energy spectra in the case of intensity-modulated fields obtained with a step-and-shoot or a dynamic technique. MethodsThe 80-leaf MLC for the Varian Clinac 2300 C/D was implemented in a previously developed Monte Carlo (MC) based multiple source model (MSM) for a 6 MV photon beam. Using this model and the MC program GEANT, dose distributions, energy fluence maps and energy spectra at different portal planes were calculated for three different MLC applications. ResultsThe comparison of MC-calculated dose distributions in the phantom and portal plane, with those measured with films showed an agreement within 3 % and 1.5 mm for all cases studied. The deviations mainly occur in the extremes of the intensity modulation. The MC method allows to investigate, among other aspects, dose components, energy fluence maps, tongue-and-groove effects and energy spectra at portal planes. ConclusionThe MSM together with the implementation of the MLC is appropriate for a number of investigations in intensity-modulated radiation therapy (IMRT).

Portal dosimetry using x-ray film: an experimental and computational study.

To evaluate the accuracy and precision of relative portal dosimetry using x-ray film, we compared the radiation doses measured by x-ray film and by an ion chamber at various portal planes that were 0 to 50 cm behind an 18 cm thick phantom. In addition, we calculated photon spectra at the measurement planes by using the Monte Carlo particle transport technique. The experiments showed that the film usually measured relative doses to within 5% of the measurements by the ion chamber and that the errors were associated with the changes in the spectra of photon energy fluence at portal planes. The relative magnitude of low-energy fluence in the photon fluence spectrum and its variance across the portal plane caused the film response to differ from the ion-chamber response especially with lead screen on top of film in the film cassette. Relative film dosimetry may be improved to accuracy of better than 2% by using solid water or other tissue equivalent cassettes.

Calculation of portal dose using the convolution/superposition method.

The convolution/superposition method was used to predict the dose throughout an extended volume, which includes a phantom and a portal imaging device. From the calculated dose volume, the dose delivered in the portal image plane was extracted and compared to a portal dose image. This comparison aids in verifying the beam configuration or patient setup after delivery of the radiation. The phantoms used to test the accuracy of this method include a solid water cube, a Nuclear Associates CT phantom, and an Alderson Rando thorax phantom. The dose distribution in the image plane was measured with film and an electronic portal imaging device in each case. The calculated portal dose images were within 4% of the measured images for most voxels in the central portion of the field for all of the extended volumes. The convolution/superposition method also enables the determination of the scatter and primary dose contributions using the particular dose deposition kernels for each contribution. The ratio of primary dose to total dose was used to extract the primary dose from the detected portal image, which enhances the megavoltage portal images by removing scatter blurring. By also predicting the primary energy fluence, we can find the ratio of computed primary energy fluence to total dose. Multiplying this ratio by the measured dose image estimates the relative primary energy fluence at the portal imager. The image of primary energy fluence possesses higher contrast and may be used for further quantitative image processing and dose modeling.