Cross Field Research Articles

SU-E-T-541: Dose Calculation Algorithm for External Neutron Radiotherapy Based on Pencil Beam Method.

To evaluate the availability and performance of pencil beam algorithm for fast neutrons radiotherapy dose calculations and to achieve improvements in universality, speed and inhomogeneities corrections. Pencil beam (PB) method uses integration of dose kernel cross field size to estimate dose distribution. In order to calculate dose kernels we used general purpose Monte-Carlo (MC) code MCNP. The same program was used also for PB benchmarking. Multi-group approach used for kernels calculation virtually allows calculation for arbitrary spectrum. Nevertheless we took four common spectra to investigate accuracy and to establish according corrections. Several approaches for inhomogeneities corrections have been investigated. The output of MC calculations is discrete kernel data, which does not allow fast calculations. To overcome this limitation we investigated different dose kernels approximations and integrations. PB dose kernel library was established. Comparison of PB calculation with reference algorithm shows adequate precision for arbitrary neutron spectra with inhomogeneities correction, while calculations are fast enough for optimization tasks. Secondary photon dose distributions comparison give worse still promising results. Researches of this paper show benefits and limitations of PB method for neutron teletherapy treatment planning. Calculations made during research allow saying that results of PB method are generally acceptable. Still additional data are needed to evaluate our results, probably voxel phantom MC calculations and/or beam data measurements.

The Application of Chaotic Encryption Model in the Network Identity Authentication

This paper analyzes a sort of color still image algorithm based on the Logistic map sorting, and verifies the confidentiality. Further, this algorithm will be applied to the authentication module in network identity authentication system. A new, safe and effective certification system is realized based on the network identity card, and the authority authentication is provided for users requiring identity identification on the network. Nowadays, cryptography and network security is a hot topic for communication and computer industry. Currently, encryption technique in the information security mainly contains conventional private key encryption system and public key encryption system, the former has low computation overhead, but its encryption strength is not high; the latter, although has high encryption strength, its computation cost is huge. Therefore, it has profound theoretical significance and wide application prospects to research a sort of information encryption algorithms and information security software system with security, good confidentiality and high calculation speed. Chaos phenomenon is a determinacy process which is similar to random, and often appears in nonlinear dynamical system, this process is neither periodic nor convergent, and is sensitively dependent on initial value [1-3]. These basic features of chaotic system can just meet the basic requirements of secret communication and cryptology. The researches of Secret communication, information encryption and information hiding technology are based on chaos theory, and have become one of popular and frontier topics developed by the cross fields of international nonlinear science and information science. Also it is an international, high-tech researched new field, cryptography based on chaos theory has recently become very popular science [2]. In our paper, chaotic model images encryption technology is applied to Network identity authentication system to prevent rampant e-commerce fraud.

Numerical investigation of the influence of large turbulence scales on the parallel and perpendicular transport of cosmic rays

In recent analytical investigations it has been demonstrated that the turbulence behavior at large scales has a very strong influence on the perpendicular diffusion coefficient of charged particles. In the present paper we use computer simulations to investigate numerically cross field transport and particle propagation along the mean magnetic field for different turbulence models at large scales. Our results are compared with quasilinear theory and nonlinear diffusion theories. We show that for different forms of the turbulence spectrum at large scales, the perpendicular mean free paths obtained numerically are in agreement with recent predictions made by analytical theory. It is also shown that the parallel diffusion coefficient contains always a strong nonlinear contribution which is, however, independent of the assumed spectrum at large scales.

Insistent Dryland Narratives: Portraits of Knowledge about Human-Environmental Interactions in Sahelian Environment Policy Documents

The drylands in the West African Sahel region have, since the catastrophic drought event in the 1970s, been a focal point of interest in the cross field between environmental research, knowledge systems and policy intervention strategies. Major international institutions, agencies and conventions have played an important role in shaping national planning efforts aimed at reducing environmental degradation in tropical drylands and at limiting their vulnerability to external stressors such as economic globalization, climate variation, and demographic pressure. The paper summarizes how significant, internationally initiated policy documents, such as National Environmental Action Plans (from the 1980s), National Adaptation Plan of Action (from the 2000s), or the Great Green Wall Initiative (signed in 2010), refer to and explain the state, complexity, and change processes in the human-environmental systems that they aim at guiding towards sustainability. It specifically looks at characterizations of land use changes and their relation to multiple driving forces. The paper asks if apparent discrepancies between contemporary scientific advancements and dominant narratives in policy documents can, in part, be interpreted as persistence of environmental myths caused by the repetition of the keywords, which turns theories into blueprints for action.

Generating Quad Mesh of 3D Articulated Shape for Sculpting Modeling

In this paper, we propose a novel quad remeshing algorithm for articulated shapes. Different from existing methods that are essentially based on local analysis to align with local geometric features, our method focuses on the global structure and generates quad mesh with edge flow aligning with the skeleton. To achieve this, we firstly extract the skeleton from 3D shape. It captures the global structure of the shape and decomposes the shape into feature parts. We detect tube-like parts and build sweeping surface on them. For joint part connecting tube-like parts, we generate a smooth cross field interpolating the directions from its adjacent tube-like parts. Using this cross field, we generate the quad mesh of joint part. It smoothly connects adjacent sweep surfaces. The mesh models generated in our system greatly benefit the sculpting operators for sculpting modeling and skeleton-based animation.

Simple quad domains for field aligned mesh parametrization

We present a method for the global parametrization of meshes that preserves alignment to a cross field in input while obtaining a parametric domain made of few coarse axis-aligned rectangular patches, which form an abstract base complex without T-junctions. The method is based on the topological simplification of the cross field in input, followed by global smoothing.

A stray bullet in the brain

In 2003, after the second Gulf War, the authors were medical doctors at the humanitarian Mission of the Red Cross Field Hospital in Baghdad, Iraq. Our experience in the fi eld indicated that civilians were at a high risk for injuries caused by stray bullets. Whilst we were attending an out-patient activity, we saw a 10-year old boy with a deep lesion of the skin in the left frontal-parietal area of his head caused by a stray bullet 2 months earlier. The bullet had entered the upper parietal portion of the skull (fi gures A, B). Clinical and neurological examination showed no defi cit of power, cognition, sense of touch, or speech. Blood test results were unremarkable. The scalp A stray bullet in the brain

Unusual resonances in nanoplasmonic structures due to nonlocal response

We study the nonlocal response of a confined electron gas within the hydrodynamical Drude model. We address the question whether plasmonic nanostructures exhibit nonlocal resonances that have no counterpart in the local-response Drude model. Avoiding the usual quasi-static approximation, we find that such resonances do indeed occur, but only above the plasma frequency. Thus the recently found nonlocal resonances at optical frequencies for very small structures, obtained within quasi-static approximation, are unphysical. As a specific example we consider nanosized metallic cylinders, for which extinction cross sections and field distributions can be calculated analytically.

Kinetic Alfven wave instability in a Lorentzian dusty plasma: Non-resonant particle approach

Analysis of the electromagnetic streaming instability is carried out which is related to the cross field drift of kappa distributed ions. The linear dispersion relation for electromagnetic wave using Vlasov-fluid equations in a dusty plasma is derived. Modified two stream instability (MTSI) in a dusty plasma has been discussed in the limit ωpd2/c2k⊥2≪1. Numerical calculations of the growth rate of instability have been carried out. Growth rates of kinetic Alfvén instability are found to be small as compared to MTSI. Maximum growth rates for both instabilities occur in oblique directions for V0≥VA. It is shown that the presence of both the charged dust particles and perpendicular ion beam sensibly modify the dispersion relation of low-frequency electromagnetic wave. The dispersion characteristics are found to be insensible to the superthermal character of the ion distribution function. Applications to different intersteller regions are discussed.

Software compensation of Eddy current fields in multislice high order dynamic shimming

Dynamic B 0 shimming (DS) can produce better field homogeneity than static global shimming by dynamically updating slicewise shim values in a multislice acquisition. The performance of DS however is limited by eddy current fields produced by the switching of 2nd and 3rd order unshielded shims. In this work, we present a novel method of eddy field compensation (EFC) applied to higher order shim induced eddy current fields in multislice DS. This method does not require shim shielding, extra hardware for eddy current compensation or subject specific prescanning. The interactions between shim harmonics are modeled assuming steady state of the medium and long time constant, cross and self term eddy fields in a DS experiment and ‘correction factors’ characterizing the entire set of shim interactions are derived. The correction factors for a given time between shim switches are shown to be invariable with object scanned, shim switching pattern and actual shim values, allowing for their generalized prospective use. Phantom and human head, 2nd and 3rd order DS experiments performed without any hardware eddy current compensation using the technique show large reductions in field gradients and offsets leading to significant improvements in image quality. This method holds promise as an alternative to expensive hardware based eddy current compensation required in 2nd and 3rd order DS.

Sedative and anxiolytic effects of the methanolic extract of <i>Leea indica</i> (Burm. f.) Merr. leaf

The sedative and anxiolytic potential of Leea indica (Burm. f.) Merr., a Bangladeshi tribal medicinal plant was studied for the first time. The crude methanol extract of L. indica leaves was evaluated for its central nervous system (CNS) depressant effect using rodent behavioral models, such as hole cross, open field and thiopental sodium induced sleeping time tests for its sedative properties and an elevated plus-maze (EPM) test for its anxiolytic potential, respectively. The methanol extract of L. indica at doses of 200 mg/kg, p.o. and 400 mg/kg, p.o., displayed a dose dependent suppression of motor activity, exploratory behavior (in hole cross and open field tests) and prolongation of thiopental induced sleeping time in mice; the highest CNS depressant effect was shown at a dose of 400 mg/kg, p.o. In the EPM test, both dose of methanol extract significantly (p < 0.01) increased exploration to and time spent by the treated mice in EPM open arms in a dose dependent manner. These results provide in vivo evidence that leaves of L. indica in general have significant sedative and anxiolytic effects. However, these results may rationalize the scientific basis for use of this plant in traditional medicine for treatment of anxiety and related disorders.

From plasmonic nanoantennas to split-ring resonators: tuning scattering strength

Evolution of the absorption and scattering cross sections, quality-factor (Q-factor), and field enhancement of three-dimensional retardation-based plasmonic resonators being transformed from straight gold nanorod antennas to split-ring resonators by bending is considered. The optical resonances are confirmed to be of plasmonic origin and are specifically shown to be related to the formation of standing waves of short-range surface plasmon polaritons supported by straight and bent nanorods. We verify that by bending nanoantennas it is possible to reduce and ultimately, in the split-ring resonator limit, practically eliminate their scattering at the fundamental resonance, resulting in a substantial increase in the corresponding Q-factors. The decrease in scattering by bending is connected with the attenuation of the electric-dipole response in favor of a magnetic-dipole one, leading to Q-factors exceeding the quasi-static limit by a factor of &#x223c;1.7. Simultaneously, the structures exhibit local field enhancements of &gt;50.

Symposium 7: Contributing to a Learning Methodology for Web 2.0 Learning

This paper contributes to the development of a methodology for designing Web 2.0 mediated learning based on a PBL approach. It does so by identifying tensions in the cross field between learning and Web 2.0. To establish an overview we begin by defining the intersections between learning and Web 2.0. In relation to this, and with reference to (Ryberg, Glud, Buus, &amp; Georgsen, 2010), we argue that a problem-based approach to learning fits well with the characteristics of Web 2.0 activities. Moreover, we argue that the connection between Web 2.0 and learning gives rise to an overarching tension between who controls the networked learning environment and processes: the teacher or the learner? We propose a conceptual model where this tension can be understood as expressible across at least four dimensions: the learning process, the motivation, the infrastructure, and resources/content. Also we identify a number of crucial questions that need to be considered in relation to each of these dimensions when designing for web 2.0 mediated learning. These questions and tensions are what we explore in this paper as they contribute to the development of a learning methodology and some mediating design artefacts, which we further discuss in (Buus, Georgsen, Ryberg, Glud, &amp; Davidsen, 2010). The intention of the conceptual model and questions is to prompt practitioners to discuss and critically reflect on their course designs during the planning and design phase. Furthermore, we discuss some additional mediating design artefacts, which we are developing to support practitioners’ design of Web 2.0 oriented learning. These are descriptions of existing practices and activities which will be uploaded in the wiki-based social community Methopedia.

Two sources of cross-field error in racetrack fluxgate

This contribution covers cross-field response of fluxgate sensors with a flat, single-sheet race-track core, which to our knowledge has not been studied yet. In the case of race-track shape, it was commonly believed that the error is automatically lower than for the ringcore due to the shape anisotropy. Instead we observed that the exact geometry of the race track (i.e., ratio between the longitudinal and upright section) and the position of the coils start to play a significant role, not only the core homogeneity—there is no more symmetry as in the case of a ring core. We found the cross-field response dependent on defining the perpendicular angle, either to the sensor’s core axis or to the axis of the feedback coil; these two axes were misaligned by up to 1°. When arranging the cross field to be perpendicular to the feedback coil axis, we were able to verify results previously published in literature: we obtained 60 nT response for 50 μT cross-field.

Evidence‐based medicine meets evidence‐based design: An interdisciplinary study of acoustics and sleep disruption as a context for improving teamwork.

Hospital noise‐induced sleep arousal probability curves were derived by exposing laboratory monitored sleeping human subjects to 14 common stimuli selected and scaled from a recorded inpatient hospital sound‐scape. The research process in this recently published successful project, which informed the 2010 Guidelines for the Construction of Health Care Facilities, serves as a context for discussion of the promise and pitfalls of interdisciplinary teamwork, bringing together evidence‐based medicine and evidence‐based design, to solve real world problems. Revealing normally unspoken professional assumptions, work ethics, record keeping requirements, and conflict of interest concerns, this program seeks to make cross field boundary breaking collaboration easier and more successful and to improve possibilities for meaningful innovation. [Work supported by AAHF, FGI, and CHD.]

Earthward electric field in the magnetotail: Cluster observations and theoretical estimates

In this paper we present an experimental evidence of the existence of the earthward electric field in the thin current sheet of the Earth magnetotail. This field plays an essential role in the redistribution of observed intensities of cross‐tail proton and electron currents. We consider the statistics of 59 thin current sheet crossings observed by CLUSTER spacecraft. It is shown that the sum of electron diamagnetic and curvature drifts can explain less than a half of the value of electron bulk velocity. The remaining part of electron velocity is thus related to the Ex × Bz cross field drift. The measurements of the typically negative shift of the central part of proton velocity distribution also confirm the existence of positive Ex field. Finally we suggest the mechanism of Ex formation in the thin current sheet of the Earth magnetotail.

Strength of knee flexor and extensor muscles in young male orienteers

In orienteering, a specially prepared map and a compass are used to navigate point to point in unfamiliar and uneven ground. Races test navigational skill, and running ability of the competitors. High levels of fitness and running speed are requested to cover long distances and climbs, and to compete successfully in international events. The strength of knee flexor and extensor muscles was investigated in young male orienteers. Eight junior Italian team orienteers (experimental group, EG, age, 19±1.6yr; weight, 62±7.0kg; height, 175±5.4cm; BMI, body mass index, 20±1.3kg/m2), and a control group (CG) of 8 cross country track and fields runners (20±4.5yr; 67±3.6kg; 179±3.5cm; 21±1.2kg/m2) volunteered. Right lower limb was dominant for all participants. Running capacities were tested on 3000m mean running speeds (EG, 17.8±1.0km/h; CG, 20.1±0.2km/h). Each athlete performed 5 repetitions of right and left knee flexion and extension at the angular speeds of 60-120-180-240-300deg/sec respectively. The peak torques of each movement at different angular speeds were measured by an isokinetic dynamometer. The obtained values were averaged within subject. Descriptive statistics were computed within group, movement, angular speed, and side. The differences between groups were compared by Mann-Whitney test; those within group, between sides were compared by Wilcoxon test. Statistical significance was set at 5% for all comparisons. Ages, weights, heights, and BMI of EG and CG did not differ (p>0.05, for all comparisons). CG runners were significantly faster than EG (p 0.05 for all comparisons). On average, EG performed peak torques larger than those obtained by CG, in both sides, and movements. The differences were significant in right knee flexor muscles at 60, 120, 300deg/sec (p<0.04; 0.03; 0.05 respectively), in left knee flexors at 60deg/sec (p<0.04), and in right knee extensor muscles at 60deg/sec (p<0.02). Further investigations into this matter should be extended to a larger group of participants and to other muscular districts. Data could be of interest for athletes, coaches, and physicians to allow a correct training planning, to prevent accidental injuries, and also to quantify the effects of rehabilitation.

Gyrokinetic Vlasov Equation in Three Dimensional Setting. Second Order Approximation

One of the main applications in plasma physics concerns the energy production through thermonuclear fusion. The controlled fusion requires the confinement of the plasma into a bounded domain, and for this we appeal to the magnetic confinement. Several models exist for describing the evolution of strongly magnetized plasmas. The subject matter of this paper is to provide a rigorous derivation of the guiding-center approximation in the general three dimensional setting under the action of large stationary inhomogeneous magnetic fields. The first order corrections are computed as well: electric cross field drift, magnetic gradient drift, magnetic curvature drift, etc. The mathematical analysis relies on average techniques and ergodicity.

Mixed-integer quadrangulation

We present a novel method for quadrangulating a given triangle mesh. After constructing an as smooth as possible symmetric cross field satisfying a sparse set of directional constraints (to capture the geometric structure of the surface), the mesh is cut open in order to enable a low distortion unfolding. Then a seamless globally smooth parametrization is computed whose iso-parameter lines follow the cross field directions. In contrast to previous methods, sparsely distributed directional constraints are sufficient to automatically determine the appropriate number, type and position of singularities in the quadrangulation. Both steps of the algorithm (cross field and parametrization) can be formulated as a mixed-integer problem which we solve very efficiently by an adaptive greedy solver. We show several complex examples where high quality quad meshes are generated in a fully automatic manner.

Relation between different theories for cosmic ray cross field diffusion

In the past few year several theories have been presented for describing cosmic ray scattering across the mean magnetic field. It is the purpose of the present article to discuss the relation between these different theories in order to improve our understanding of cosmic ray perpendicular scattering and to explore the parameter regimes for which these different theories are valid.