bluuebunny/crossref_metadata_2025 huggingface dataset:
Dosimetric IMRT verification with a flat‐panel EPID
Authors: Warkentin B. , Steciw S. , Rathee S. , Fallone B. G.
Published: December 2003

A convolution‐based calibration procedure has been developed to use an amorphous silicon flat‐panel electronic portal imaging device (EPID) for accurate dosimetric verification of intensity‐modulated radiotherapy (IMRT) treatments. Raw EPID images were deconvolved to accurate, high‐resolution 2‐D distributions of primary fluence using a scatter kernel composed of two elements: a Monte Carlo generated kernel describing dose deposition in the EPID phosphor, and an empirically derived kernel describing optical photon spreading. Relative fluence profiles measured with the EPID are in very good agreement with those measured with a diamond detector, and exhibit excellent spatial resolution required for IMRT verification. For dosimetric verification, the EPID‐measured primary fluences are convolved with a Monte Carlo kernel describing dose deposition in a solid water phantom, and cross‐calibrated with ion chamber measurements. Dose distributions measured using the EPID agree to within 2.1% with those measured with film for open fields of and Predictions of the EPID phantom scattering factors based on our scatter kernels are within 1% of the measured for open field sizes of up to Pretreatment verifications of step‐and‐shoot IMRT treatments using the EPID are in good agreement with those performed with film, with a mean percent difference of for three IMRT treatments (24 fields).
Determination of the two‐dimensional detective quantum efficiency of a computed radiography system
Authors: Båth Magnus , Håkansson Markus , Månsson Lars Gunnar
Published: December 2003

Based on a recently described method for determining the two‐dimensional presampling modulation transfer function (MTF), the aperture mask method, a method for determining the two‐dimensional detective quantum efficiency (DQE) of a digital radiographic system was developed. The method was applied to a new computed radiography (CR) system and comparisons with one‐dimensional determinations of the presampling MTF and the DQE were performed. The aperture mask method was shown to agree with the conventional tilted slit method for determining the presampling MTF along the axes. For the particular CR system studied, the mean of one‐dimensional determinations of the DQE in orthogonal directions led to a representative measure of the average DQE behavior of the system up to the Nyquist frequency along the axes, but a deviation was observed above this frequency. In conclusion, the method developed for determining the two‐dimensional DQE can be used to determine the imaging properties of a digital radiographic detector system over almost the entire frequency domain, the exception being the lowest frequencies at which the validity and the reliability of the method are low.
Clinical helical tomotherapy commissioning dosimetry
Authors: Balog John , Olivera Gustavo , Kapatoes Jeff
Published: December 2003

Helical tomotherapy presented many unique dosimetric challenges and solutions during the initial commissioning process, and some of them are presented. The dose calculation algorithm is convolution/superposition based. This requires that the energy fluence spectrum and magnitude be quantified. The methodology for doing so is described. Aspects of the energy fluence characterization that are unique to tomotherapy are highlighted. Many beam characteristics can be measured automatically by an included megavoltage computed tomography imaging system. This greatly improves data collection efficiency.
Monte Carlo model of the Studsvik BNCT clinical beam: Description and validation
Authors: Giusti Valerio , Munck af Rosenschöld Per M. , Sköld Kurt , Montagnini Bruno , Capala Jacek
Published: December 2003

The neutron beam at the Studsvik facility for boron neutron capture therapy (BNCT) and the validation of the related computational model developed for the MCNP‐4B Monte Carlo code are presented. Several measurements performed at the epithermal neutron port used for clinical trials have been made in order to validate the Monte Carlo computational model. The good general agreement between the MCNP calculations and the experimental results has provided an adequate check of the calculation procedure. In particular, at the nominal reactor power of 1 MW, the calculated in‐air epithermal neutron flux in the energy interval between 0.4 eV–10 keV is (±1.2% 1 std. dev.) while the measured value is (±5.0% 1 std. dev.). Furthermore, the calculated in‐phantom thermal neutron flux, equal to (±1.0% 1 std. dev.), and the corresponding measured value of (±5.3% 1 std. dev.) agree within their respective uncertainties. The only statistically significant disagreement is a discrepancy of 39% between the MCNP calculations of the in‐air photon kerma and the corresponding experimental value. Despite this, a quite acceptable overall in‐phantom beam performance was obtained, with a maximum value of the therapeutic ratio (the ratio between the local tumor dose and the maximum healthy tissue dose) equal to 6.7. The described MCNP model of the Studsvik facility has been deemed adequate to evaluate further improvements in the beam design as well as to plan experimental work.
Validation of target volume and position in respiratory gated CT planning and treatment
Authors: Shen Sui , Duan Jun , Fiveash John B. , Brezovich Ivan A. , Plant Brian A. , Spencer Sharon A. , Popple Richard A. , Pareek Prem N. , Bonner James A.
Published: December 2003

The capability of a commercial respiratory gating system based on video tracking of reflective markers to reduce motion‐induced CT planning and treatment errors was evaluated. Spherical plastic shells (2.8–82 cm3), simulating the gross target volume (GTV), were placed in a water‐filled body phantom that was moved sinusoidally along the longitudinal axis of the CT scanner and the accelerator for ±1 cm at 15–30 cycle/min. During gated CT imaging, the x‐ray exposure was initiated by the gating system shortly before the end of expiration (so that the imaging time would be centered at the end of expiration); it was terminated by the scanner after completion of each slice. In nongated CT images, the target appeared distorted and often broken up. GTVs volume errors ranged 16%–110% in axial scans, and 7%–36% in spiral scans. In gated CT images, the spheres appeared 3 and 5 mm longer than their actual diameters (volume errors 2%–16%), at the respective respiration rates of 15 and 20 cycles/min. At 30 cycles/min the target appeared 1 cm longer, and volume error ranged 25%–53%. During treatment, gating kept the beam on for a duration equal to the CT acquisition time of 1 s/slice. The difference in positional errors between gated CT and portal films was 1 mm, regardless the size of residual motion errors. Because of the potential of suboptimal placement of the gating window between CT imaging and treatment, an extra 1.5–2.5 mm safety margin can be added regardless of the size of residual motion error. For respiratory rates ⩾30 cycles/min, the effectiveness of gating is limited by large residual motion in the 1 s CT acquisition time.
A phantom study on the positioning accuracy of the Novalis Body system
Authors: Yan Hui , Yin Fang‐Fang , Kim Jae Ho
Published: December 2003

A phantom study was conducted to investigate inherent positioning accuracy of an image‐guided patient positioning system—the Novalis Body system for three‐dimensional (3‐D) conformal radiotherapy. This positioning system consists of two infrared (IR) cameras and one video camera and two kV x‐ray imaging devices. The initial patient setup was guided by the IR camera system and the target localization was accomplished using the kV x‐ray imaging system. In this study, the IR marker shift and phantom rotation were simulated and their effects on the positioning accuracy were examined by a Rando phantom. The effects of CT slice thickness and treatment sites on the positioning accuracy were tested. In addition, the internal target shift was simulated and its effect on the positioning accuracy was examined by a water tank. With the application of the Novalis Body system, the positioning error of the planned isocenter was significantly reduced. The experimental results with the simulated IR marker shifts indicated that the positioning errors of the planned isocenter were 0.6±0.3, 0.5±0.2, and 0.7±0.2 mm along the lateral, longitudinal, and vertical axes, respectively. The experimental results with the simulated phantom rotations indicated that the positioning errors of the planned isocenter were 0.6±0.3, 0.7±0.2, and 0.5±0.2 mm along the three axes, respectively. The experimental results with the simulated target shifts indicated that the positioning errors of the planned isocenter were 0.6±0.3, 0.7±0.2, and 0.5±0.2 mm along the three axes, respectively. On average, the positioning accuracy of 1 mm for the planned isocenter was achieved using the Novalis Body system.
Influence of scatter reduction method and monochromatic beams on image quality and dose in mammography
Authors: Moeckli Raphaël , Verdun Francis R. , Fiedler Stefan , Pachoud Marc , Bulling Shelley , Schnyder Pierre , Valley Jean‐François
Published: December 2003

In mammography, the image contrast and dose delivered to the patient are determined by the x‐ray spectrum and the scatter to primary ratio Thus the quality of the mammographic procedure is highly dependent on the choice of anode and filter material and on the method used to reduce the amount of scattered radiation reaching the detector. Synchrotron radiation is a useful tool to study the effect of beam energy on the optimization of the mammographic process because it delivers a high flux of monochromatic photons. Moreover, because the beam is naturally flat collimated in one direction, a slot can be used instead of a grid for scatter reduction. We have measured the ratio and the transmission factors for grids and slots for monoenergetic synchrotron radiation. In this way the effect of beam energy and scatter rejection method were separated, and their respective importance for image quality and dose analyzed. Our results show that conventional mammographic spectra are not far from optimum and that the use of a slot instead of a grid has an important effect on the optimization of the mammographic process. We propose a simple numerical model to quantify this effect.
In vivo diode dosimetry for routine quality assurance in IMRT
Authors: Higgins P. D. , Alaei P. , Gerbi B. J. , Dusenbery K. E.
Published: December 2003

Due to the complexity of IMRT dosimetry, dose delivery evaluation is generally done using a treatment plan in which the optimized fluence distribution has been transferred to a test phantom for accessibility and simplicity of measurement. The actual patient doses may be reconstructed in vivo through the use of electronic portal imaging devices or films, but the assessment of absolute dose from these measurements is time‐consuming and complicated. In our clinic we have instituted the use of routine diode dosimetry for IMRT patients following the same procedure used for standard radiation therapy patients in which each new treatment field is checked at the start of treatment. For standard cases the dose at is calculated as part of the monitor unit calculation. For the IMRT cases, the dose contribution to the depth for each field is taken from the treatment plan. We found that about 90% of the diode measurements agreed to within of the planned doses (45/51 fields) and 63% (32/51 fields) achieved agreement. By using this direct in vivo method to verify the clinical doses delivered, we have been able to make a uniform startup procedure for all patients while simplifying our IMRT QA process.
Summary and recommendations of a National Cancer Institute workshop on issues limiting the clinical use of Monte Carlo dose calculation algorithms for megavoltage external beam radiation therapy
Authors: Fraass Benedick A. , Smathers James , Deye James
Published: December 2003

Due to the significant interest in Monte Carlo dose calculations for external beam megavoltage radiation therapy from both the research and commercial communities, a workshop was held in October 2001 to assess the status of this computational method with regard to use for clinical treatment planning. The Radiation Research Program of the National Cancer Institute, in conjunction with the Nuclear Data and Analysis Group at the Oak Ridge National Laboratory, gathered a group of experts in clinical radiation therapy treatment planning and Monte Carlo dose calculations, and examined issues involved in clinical implementation of Monte Carlo dose calculation methods in clinical radiotherapy. The workshop examined the current status of Monte Carlo algorithms, the rationale for using Monte Carlo, algorithmic concerns, clinical issues, and verification methodologies. Based on these discussions, the workshop developed recommendations for future NCI‐funded research and development efforts. This paper briefly summarizes the issues presented at the workshop and the recommendations developed by the group.
Analysis on imaging features of mammography in computer radiography and investigation on gray scale transform and energy subtraction
Authors: Feng Shuli
Published: December 2003

In this dissertation, a novel transform method based on human visual response features for gray scale mammographic imaging in computer radiography (CR) is presented. The parameters for imaging quality on CR imaging for mammography were investigated experimentally. In addition, methods for image energy subtraction and a novel method of image registration for mammography of CR imaging are presented. Because the images are viewed and investigated by humans, the method of displaying differences in gray scale images is more convenient if the gray scale differences are displayed in a manner commensurate with human visual response principles. Through transformation of image gray scale with this method, the contrast of the image will be enhanced and the capability for humans to extract the useful information from the image will be increased. Tumors and microcalcifications are displayed in a form for humans to view more simply after transforming the image. The method is theoretically and experimentally investigated. Through measurement of the parameters of a geometrically blurred image, MTF, DQE, and ROC on CR imaging, and also comparison with the imaging quality of screen–film systems, the results indicate that CR imaging qualities in DQE and ROC are better than those of screen–film systems. In geometric blur of the image and MTF, the differences in image quality between CR and the screen–film system are very small. The results suggest that the CR system can replace the screen–film system for mammography imaging. In addition, the results show that the optimal imaging energy for CR mammography is about 24 kV. This condition indicates that the imaging energy of the CR system is lower than that of the screen–film system and, therefore, the x‐ray dose to the patient for mammography with the CR system is lower than that with the screen–film system. Based on the difference of penetrability of x ray with different wavelength, and the fact that the part of the x‐ray beam will pass through the image plate in the procedure of CR imaging, the method of subtraction of the two images which were taken in the same time with one exposure can increase the diagnostic information. Image registration for mammography with CR imaging is usually ignored because the two images are taken in one exposure time. This dissertation investigated the necessity of image registration for image energy subtraction in CR mammography imaging. A novel method for image registration that can reduce the computing time is established, based on the features of CR imaging for mammography.
An alternative derivation of Katsevich's cone‐beam reconstruction formula
Authors: Chen Guang‐Hong
Published: December 2003

In this paper an alternative derivation of Katsevich's cone‐beam image reconstruction algorithm is presented. The starting point is the classical Tuy's inversion formula. After (i) using the hidden symmetries of the intermediate functions, (ii) handling the redundant data by weighting them, (iii) changing the weighted average into an integral over the source trajectory parameter, and (iv) imposing an additional constraint on the weighting function, a filtered backprojection reconstruction formula from cone beam projections is derived. The following features are emphasized in the present paper: First, the nontangential condition in Tuy's original data sufficiency conditions has been relaxed. Second, a practical regularization scheme to handle the singularity is proposed. Third, the derivation in the cone beam case is in the same fashion as that in the fan‐beam case. Our final cone‐beam reconstruction formula is the same as the one discovered by Katsevich in his most recent paper. However, the data sufficiency conditions and the regularization scheme of singularities are different. A detailed comparison between these two methods is presented.
Model of metastatic growth valuable for radionuclide therapy
Authors: Bernhardt Peter , Ahlman Håkan , Forssell‐Aronsson Eva
Published: December 2003

The aim was to make a Monte Carlo simulation approach to estimate the distribution of tumor sizes and to study the curative potential of three candidate radionuclides for radionuclide therapy: the high‐energy electron emitter the medium‐energy electron emitter and the low‐energy electron emitter A patient with hepatocellular carcinoma with recently published serial CT data on tumor growth in the liver was used. From these data the growth of the primary tumor, and the metastatis formation rate, were estimated. Assuming the same tumor growth of the primary and all metastases and the same metastatis formation rate from both primary and metastases the metastatic size distribution was simulated for various time points. Tumor cure of the metastatic size distribution was simulated for uniform activity distribution of three radionuclides; the high‐energy electron emitter the mean‐energy electron emitter and the low‐energy electron emitter The simulation of a tumor cure was performed for various time points and tumor‐to‐normal tissue activity concentrations, TNC. It was demonstrated that it is important to start therapy as early as possible after diagnosis. It was of crucial importance to use an optimal radionuclide for therapy. These simulations demonstrated that was not suitable for systemic radionuclide therapy, due to the low absorbed fraction of the emitted electrons in small tumors If TNC was low was slightly better than For high TNC values low‐energy electron emitters, e.g., was the best choice for tumor cure. However, the short half‐life of (56 min) might not be optimal for therapy. Therefore, other low‐energy electron emitters, or alpha emitters, should be considered for systemic targeted therapy.
The Pendulum, Gravity, and that Number “9.8”
Authors: Clay Keith
Published: December 2003

A strange numerical coincidence lends itself to an exercise that can be an effective instruction and assessment tool. On the surface the exercise tests understanding of measurement. Due to the rich context of the problem, however, some former students report that it influenced their entire approach to science and problem solving.
Center of Mass of a Suspended Slinky: An Experiment
Authors: Toepker Terrence P.
Published: December 2003

Articles, notes, and letters1,2,3 in recent issues of The Physics Teacher have described the location of the center of mass of a Slinky™ spring toy suspended vertically. To determine the center of mass, we performed a simple experiment that is described here.
The World Year of Physics in 2005
Authors: Stone Chuck
Published: December 2003

The year 2005 has been designated the World Year of Physics (WYP) to commemorate the 100th anniversary of Albert Einstein's legendary papers on quantum theory, Brownian motion, and special relativity, first published in 1905. Organizations around the globe are planning a variety of programs to raise worldwide public awareness for physics in 2005. This paper provides a brief description of the WYP, discusses the significance of 1905, presents national objectives for the U.S. physics community, and outlines a variety of activities that individuals or teams can pursue to contribute to the success of this international campaign.
Energy and Momentum in the Gauss Accelerator
Authors: Kagan David
Published: December 2003

James Rabchuk's recent paper1 describes a method for measuring the kinetic energy changes in the Gauss accelerator, as well as a calculation of the change in potential energy. In this paper, a simple method for measuring both the change in potential energy and the change in kinetic energy will be presented. The measurements can be made with rulers, strings, and weights. In the process, your students will learn about the relationship between work and potential energy as well as the law of conservation of energy. Issues associated with the law of conservation of momentum in the accelerator will also be addressed.
Wheelies and Headers, or How to Keep Both Bicycle Wheels on the Ground
Authors: Wehrbein William M.
Published: December 2003

A “wheelie” is when a bicycle is ridden with its front wheel lifted from the ground. Riding the bicycle in a way to lift the rear wheel off the ground might lead to the cyclist tumbling over the handlebars, called a “header.” Other colorful terms for this situation are “endo” (short for “end-over-end”) and “face plant” (for landing face first on the ground). Let's determine the conditions required in order to keep both tires touching the ground at all times.
Teaching Tips
Authors: Hewitt Paul G.
Published: December 2003

If you asked Paul Hewitt to describe physics, he would probably say it is a study of the most basic rules by which nature operates, a way of seeing order and regularity in the world. His strong conviction that physics should be taught first at a conceptual level with emphasis on a qualitative grasp of concepts before they are considered for problem solving has made his name synonymous with the term “conceptual physics” in the physics education community. Drawing from the experience of a teaching career that began in the mid-60s, Paul offers beginning teachers some wonderful advice.
COUNTING THE NUMBER OF MINIMAL DFCA OBTAINED BY MERGING STATES
Authors: CÂMPEANU CEZAR , PĂUN ANDREI
Published: December 2003

Finite Deterministic Cover Automata (DFCA) can be obtained from Deterministic Finite Automata (DFA) using the similarity relation and a method of merging similar states. The DFCA minimization procedure can yield different results depending on the order of merging the similar states, because the minimal DFCA for a finite language is in general not unique.

We count the number of minimal DFCA that can be obtained from a given minimal DFA with n states by merging the similar states in the given DFA. We compute an upper-bound for this number and prove that in the worst case, it is n-1 for an unary alphabet, and [Formula: see text] for a non-unary alphabet. We prove that this upper-bound is reached, i.e., for any given positive integer n one can construct a minimal DFA with n states, which has the number of minimal DFCA obtained by merging similar states equal to this maximum expression.
LINEAR-TIME PRIME DECOMPOSITION OF REGULAR PREFIX CODES
Authors: CZYZOWICZ JUREK , FRACZAK WOJCIECH , PELC ANDRZEJ , RYTTER WOJCIECH
Published: December 2003

One of the new approaches to data classification uses prefix codes and finite state automata as representations of prefix codes. A prefix code is a (possibly infinite) set of strings such that no string is a prefix of another one. An important task driven by the need for the efficient storage of such automata in memory is the decomposition (in the sense of formal languages concatenation) of prefix codes into prime factors. We investigate properties of such prefix code decompositions. A prime decomposition is a decomposition of a prefix code into a concatenation of nontrivial prime prefix codes. A prefix code is prime if it cannot be decomposed into at least two nontrivial prefix codes. In the paper a linear time algorithm is designed which finds the prime decomposition F1F2…Fk of a regular prefix code F given by its minimal deterministic automaton. Our results are especially interesting for infinite regular prefix codes.
A TIME AND SPACE EFFICIENT ALGORITHM FOR MINIMIZING COVER AUTOMATA FOR FINITE LANGUAGES
Authors: KÖRNER HEIKO
Published: December 2003

A deterministic finite automaton (DFA) [Formula: see text] is called a cover automaton (DFCA) for a finite language L over some alphabet Σ if [Formula: see text], with l being the length of some longest word in L. Thus a word w ∈ Σ* is in L if and only if |w| ≤ l and [Formula: see text]. The DFCA [Formula: see text] is minimal if no DFCA for L has fewer states.

In this paper, we present an algorithm which converts an n–state DFA for some finite language L into a corresponding minimal DFCA, using only O(n log n) time and O(n) space. The best previously known algorithm requires O(n2) time and space. Furthermore, the new algorithm can also be used to minimize any DFCA, where the best previous method takes O(n4) time and space. Since the required data structure is rather complex, an implementation in the common programming language C/C++ is also provided.
NONDETERMINISTIC DESCRIPTIONAL COMPLEXITY OF REGULAR LANGUAGES
Authors: HOLZER MARKUS , KUTRIB MARTIN
Published: December 2003

We investigate the descriptional complexity of operations on finite and infinite regular languages over unary and arbitrary alphabets. The languages are represented by nondeterministic finite automata (NFA). In particular, we consider Boolean operations, catenation operations – concatenation, iteration, λ-free iteration – and the reversal. Most of the shown bounds are tight in the exact number of states, i.e. the number is sufficient and necessary in the worst case. Otherwise tight bounds in the order of magnitude are shown.
EFFICIENT AUTOMATON-BASED RECOGNITION FOR LINEAR CONJUNCTIVE LANGUAGES
Authors: OKHOTIN ALEXANDER
Published: December 2003

Linear conjunctive grammars have recently been proved computationally equivalent to triangular trellis automata. The relation between these grammars and these automata resembles that between regular expressions and finite automata: while the former are better suited for human use, the latter are considerably easier to implement. This paper studies efficient algorithms for converting a linear conjunctive grammar to an equivalent triangular trellis automaton, and also proposes a number of techniques of reducing the size of these automata.
REDUCED POWER AUTOMATA AND SOFIC SYSTEMS
Authors: SUTNER KLAUS
Published: December 2003

The state complexity of the cover language of sofic shifts arising from cellular automata is studied. It is shown that in the case where the underlying automaton is nearly a permutation automaton the deterministic automaton obtained by the classical Rabin-Scott construction is already reduced.
EFFICIENT ALGORITHMS FOR SELECTION AND SORTING OF LARGE DISTRIBUTED FILES ON DE BRUIJN AND HYPERCUBE STRUCTURES
Authors: WEI DAVID S. L. , RAJASEKARAN SANGUTHEVAR , NAIK KSHIRASAGAR , KUO SY-YEN
Published: December 2003

In this paper we show the power of sampling techniques in designing efficient distributed algorithms. In particular, we apply sampling techniques in the design of selection algorithms on the hypercube and de Bruijn networks, and show that the message complexity of selecting an item from a set (file) is less sensitive to the cardinality of the set (file). Given a file with n keys, our algorithm performs a selection on a p-node de Bruijn network or hypercube using only O(p log log n) messages and suffering a delay of O(τ log p log log n), with high probability. Our selection scheme outperforms the existing approaches in terms of both message complexity and communication delay. Because of the lesser sensitivity of message complexity and communication delay of our algorithms to the file size, our distributed selection schemes are very attractive in applications where very large database systems are involved. Using our selection algorithms, we also show that both quicksort-based sorting scheme and enumeration sorting scheme can be developed for sorting large distributed files on the hypercube and de Bruijn networks. Both of our sorting algorithms outperform the existing distributed sorting schemes in terms of both message complexity and communication delay.
BINARY TIME SERIES GENERATED BY CHAOTIC LOGISTIC MAPS
Authors: LAWRANCE A. J. , WOLFF RODNEY C.
Published: December 2003

This paper examines stochastic pairwise dependence structures in binary time series obtained from discretised versions of standard chaotic logistic maps. It is motivated by applications in communications modelling which make use of so-called chaotic binary sequences. The strength of non-linear stochastic dependence of the binary sequences is explored. In contrast to the original chaotic sequence, the binary version is non-chaotic with non-Markovian non-linear dependence, except in a special case. Marginal and joint probability distributions, and autocorrelation functions are elicited. Multivariate binary and more discretised time series from a single realisation of the logistic map are developed from the binary paradigm. Proposals for extension of the methodology to other cases of the general logistic map are developed. Finally, a brief illustration of the place of chaos-based binary processes in chaos communications is given.
STOCHASTIC PERTURBATIONS OF POSITION DEPENDENT RANDOM MAPS
Authors: BAHSOUN WAEL , GÓRA PAWEŁ , BOYARSKY ABRAHAM
Published: December 2003

A random map is a dynamical system consisting of a collection of maps which are selected randomly by means of fixed probabilities at each iteration. In this note, we consider absolutely continuous invariant measures of random maps with position dependent probabilities and prove that they are stable under small stochastic perturbations. This result depends on a new lemma which handles arbitrarily small extra partition elements that may arise from the perturbation of the random map. For perturbations satisfying additional conditions, we give precise estimates of the error in the invariant density.
RECURSIVE COMPUTATION OF THE INVARIANT DISTRIBUTION OF A DIFFUSION: THE CASE OF A WEAKLY MEAN REVERTING DRIFT
Authors: LAMBERTON DAMIEN , PAGÈS GILLES
Published: December 2003

We study a recursive procedure, based on the Euler scheme with decreasing step, for the computation of the invariant distribution of a Brownian diffusion process satisfying weak stability conditions. We are able to extend some of the results of [5] to diffusions for which the drift size at infinity is very small.
FURSTENBERG-TYPE FORMULAS OVER SHIFT SPACES
Authors: KOCH SUSANNE
Published: December 2003

We define a class of Markov chains of unbounded range on word spaces and deduce a Furstenberg-type integral representation for a subspace of the P-harmonic functions. As an application we obtain a Furstenberg-type formula for a set of continuous harmonic functions on p.c.f. self-similar sets.
LIMIT THEOREMS FOR SAMPLED DYNAMICAL SYSTEMS
Authors: GUILLOTIN-PLANTARD NADINE , SCHNEIDER DOMINIQUE
Published: December 2003

Let [Formula: see text] be a dynamical system where [Formula: see text] is a probability space and T an invertible transformation preserving the measure μ. Let (Sk)k≥0be a transient ℤ-random walk. Let f ∈ L2(μ) and H ∈ ]0,1[, we study the convergence in distribution of the sequence [Formula: see text] We also study the case when the random walk (Sk)k≥0is replaced by an increasing deterministic subsequence of integers.
Copper Barrier Properties of Low Dielectric Constant SiOCNH Film Deposited by Plasma-Enhanced CVD
Authors: Shioya Yoshimi , Ishimaru Tomomi , Ikakura Hiroshi , Nishimoto Yuko , Ohdaira Toshiyuki , Suzuki Ryoichi , Maeda Kazuo
Published: December 2003

We have developed a silicon oxi-carbide and nitride (SiOCNH) barrier film to protect against copper (Cu) thermal diffusion by plasma-enhanced chemical vapor deposition (PECVD) using hexamethyldisiloxane, nitrous oxide

(

N

2

O
)
,

and ammonia

(

NH

3

)

gases. We tried to enhance the Cu barrier property and etching selectivity for low dielectric constant (low-k) film by adding nitrogen (N) into the barrier silicon oxicarbide (SiOCH) film. The film protects against Cu thermal diffusion at 450°C for 4 h in

N

2

.

The k value is lower than that for PECVD silicon nitride (SiN) and silicon carbide (SiC) films, but is slightly larger than that of PECVD SiOCH film; it is in the range of 4.17 to 5.21. The leakage current is as low as the value of PECVD SiN film; it is in the range of

10

−
9

to

10

−
10

A
/

cm

2

at 1 MV/cm. This value decreases with increasing

NH

3

flow rate. However, Cu thermal diffusion increased with increasing

NH

3

flow rate. The diffusion depth is less than 20 nm. The diffusion behavior can be explained by the result that diffusion is controlled by the small pore size, high density, and small compressive stress in SiOCNH film. The average pore size is smaller than 0.49 nm, which is generally smaller than that of SiOCH film deposited using

N

2

O

gas. The film density is greater than 2.14 g/cm3, which is larger than that of SiOCH film. The etching selectivity to silicon oxide deposited by PECVD using tetraethoxysilane (PECVD tetraethylorthosiloxane, TEOS

SiO

2

)

film is ∼15. The dynamic hardness is almost the same as the value of quartz and is 2.0 to 2.5 times larger than the value of PECVD TEOS

SiO

2

film. The Young’s modulus was ∼2.0 and 2.5 times larger than the values of quartz and PECVD TEOS

SiO

2

film, respectively. The adhesion strength on Cu is the same as that of PECVD SiOCH film and slightly smaller than that of PECVD SiN film. The desorption of ammonium

(

NH

3

+

)

ions from SiOCNH film, which is known as the cause of poisoned via-holes, is very low. © 2003 The Electrochemical Society. All rights reserved.
A Possible Stimulatory Effect of FMRFamide on Neural Nitric Oxide Production in the Central Nervous System of Helix lucorum L.
Authors: Röszer Tamás , Jenei Zsolt , Gáll Tamás , Nagy Olivér , Czimmerer Zsolt , Serfözö Zoltán , Elekes Károly , Bánfalvi Gáspár
Published: December 2003

The anatomical and functional relationship between neurons expressing nitric oxide (NO) synthase and molluscan cardioexcitatory (FMRFamide)-like neuropeptides was studied in the central ganglia of Helix lucorum (Pulmonata, Gastropoda), applying NADPHdiaphorase (NADPHd) histochemistry to visualize NO synthase and immunocytochemistry to demonstrate FMRFamide (FMRFa) at the light microscopic level. The NO production of the ganglia was detected by the colorimetric Griess determination of nitrite, a breakdown product of NO. Effects of the NO synthase substrate amino acid L-arginine, the NO synthase inhibitor Nω-nitro-L-arginine (NOARG), synthetic FMRFa and the FMRFa sensitive ion channel blocker amiloride hydrochloride on nitrite production were also tested. NADPHd reaction labeled nerve cells and fibers in the procerebra, mesocerebra and metacerebra within the cerebral ganglia, and cell clusters in the postcerebral ganglia. FMRFa immunolabeling could be observed within subpopulations of NADPHd positive cells and in pericellular varicose fibers surrounding NADPHd stained neurons. Nitrite production of the ganglia was stimulated by L-arginine (10– 20 mM) but was decreased by NOARG (1–2 mM). Synthetic FMRFa (0.830–3.340 mM) increased the nitrite production in a dose dependent manner, but was ineffective in the presence of NOARG. Amiloride hydrochloride (7.890 mM) reduced the FMRFa evoked nitrite production in all ganglia. This is the first description of an anatomical relationship between putative NO producing and FMRFa containing cells, suggesting a possible regulatory role of FMRFa in the NO mediated signaling in an invertebrate nervous system.
The Decline of the Clinical Incidence of Cancers during Human Senescence
Authors: Macieira-Coelho Alvaro
Published: December 2003

Neoplastic growth occurs from the very beginning to the end of the human life span, with a predominant age span for the clinical incidence of each cancer. Most cancers are diagnosed during the second half of human life span, but their natural histories start much earlier than their clinical manifestations. The clinical incidence declines after ages 75–80 years. The histology, the evolution, and the distribution of the frequency of the different cancers during the human life span suggest that neoplastic growth is a dynamic process where new variables are continuously created, the result of the interaction of individual genetics, environmental aggressions, and the developmental stages of the human life span. Data suggest that in many instances tumor growth can be looked upon as a deviation from normal development. Mechanisms are described that can explain the decline of the incidence and the progression during senescence in terms of the changes occurring in the human organism during the last developmental stages.
Numbers of Neurons in the Retinal Ganglion Cell Layer of the Rat Do Not Change throughout Life
Authors: Harman Alison M. , MacDonald Alice , Meyer Peter , Ahmat Alicia
Published: December 2003

Background: There have been many assumptions made about neuronal loss in mammals due to aging. However, when we examined the retinal ganglion cell layer of a marsupial, the quokka, from 0.5 to 13.5 years of age, we found that the total neuron number did not decrease significantly even into extreme old age. The retinal area increased slowly throughout life, leading to a decrease in cell density. Neuronal death in the rat retina has been assumed, since the cell density has been seen to fall with age. However, a similar study to ours in the quokka has never been performed in the laboratory rat, the model for so many experimental investigations. Objective: We decided to test the hypothesis that rats do not lose neurons due to aging and that an increase in retinal area, and not cell death, as previously suggested, might underlie the decreasing cell density seen in aging animals such as rats. Methods: We kept laboratory rats under standard, unvarying conditions throughout the trial, sacrificing 3 animals every 3 months up to 30 months, and examined the retinal ganglion cell layer through adult life. Results: We found that the numbers of neurons did not decrease in this species, even in the oldest rats. We also saw that the retinal area increased slowly with a concomitant slow decrease in mean neuronal density. Soma diameters of neurons gradually increased throughout life. Conclusions: When rats are kept under standard conditions, there is no neuronal loss in the retina during aging, although the cell density does decrease as a result of retinal expansion. It is not sufficient to measure retinal cell density to determine cell loss. In addition, it is important to know that in normal conditions there is no cell loss in the retinal ganglion cell layer as a result of aging. Any loss that is seen must be a result of additional factors.
Aging Effects of Sympathetic Reflex Activities on Skin Nerves
Authors: Watanabe Harue , Shindo Kazumasa , Ida Haruyasu , Tanaka Haruyuki , Nagasaka Takamura , Shiozawa Zenji
Published: December 2003

Background: Muscle sympathetic nerve activity (MSNA) at rest is widely known to increase with aging, but changes in skin sympathetic nerve activity (SSNA) with aging are less well defined. We examined the aging effects of reflex activities on SSNA, sympathetic skin response (SSR), and sympathetic flow response (SFR). Objective: We studied the aging effect of reflex activities on SSNA, SSR and SFR. Methods: SSNA, SSR and SFR were simultaneously recorded during randomly administered electrical stimuli. Results: The mean SSNA reflex latency was 763.1 ± 39.8 ms, mean SSNA amplitude was 12.6 ± 6.3 µV, mean SSR reflex latency was 1,809.0 ± 90.6 ms, mean SSR reflex amplitude was 0.519 ± 0.449 mV, mean SFR reflex latency was 4,398.9 ± 761.7 ms, and mean SFR reflex amplitude was 8.21 ± 5.14 ml/min/100 g. None of these parameters were significantly affected by aging. The reflex bursts on SSNA could be recorded in all subjects studied. While the frequencies of SSR and SFR were recorded in more than 80% of young subjects under age 40 years, the frequencies of SSR were recorded in less than 25% of subjects over age 80 years, and the frequencies of SFR were recorded in less than 5%. Conclusion: There were no differences in electrical stimuli-induced reflex SSNA between young and older subjects, but effector organ responses such as SSR and SFR were diminished in older subjects.
Relationships between Plasma β-Amyloid Peptide 1–42 and Atherosclerotic Risk Factors in Community-Based Older Populations
Authors: Fujiwara Yoshinori , Takahashi Makoto , Tanaka Masaharu , Hoshi Tanji , Someya Toshiyuki , Shinkai Shoji
Published: December 2003

Background: Recent studies have suggested that atherosclerosis contributes to the development of dementia of the Alzheimer’s type (DAT). Convenient and valid biochemical markers of DAT are needed to control risk factors for this disease. The aims of the present study were thus (1) to determine the distribution of plasma β-amyloid peptide1–42 (Aβ1–42) levels in an older population and (2) to investigate factors correlating with plasma levels of this amyloid peptide. Our data support the hypothesis that atherosclerosis plays a role in the pathogenesis of DAT. Methods: 759 Japanese community residents participated in a municipal medical health evaluation; a subset of 280 was selected at random for the measurement of physiological, psychosocial and life-style variables, together with the analysis of blood specimens for cell counts, hematocrit, Aβ1–42, and other biochemical markers. Results: Log-transformed plasma Aβ1–42 concentrations showed a Gaussian distribution. Quartiles of log10 (Aβ1–42) concentrations correlated significantly with age categories, but not with other sociopsychological and life-style variables. Plasma Aβ1–42 was significantly correlated with systolic and diastolic blood pressure (DBP; r = 0.19, p = 0.002 and r = 0.16, p = 0.007, respectively), pulse pressure (r = 0.13, p = 0.036), total cholesterol (r = 0.15, p = 0.011), log10 (triacyl glycerol) (r = 0.14, p = 0.021), and log10 (hemoglobin A1c) [log10 (HbA1c)] (r = 0.14, p = 0.020). Stepwise multiple regression analysis showed significant independent effects of DBP, and log10 (HbA1c) on plasma Aβ1–42 concentrations. Conclusions: Our findings suggest that conventional atherosclerotic risk factors are associated with plasma Aβ1–42 levels. This observation may be important in the detection and prevention of DAT.
Red Wine Ingredient Resveratrol Protects from β-Amyloid Neurotoxicity
Authors: Savaskan Egemen , Olivieri Gianfranco , Meier Fides , Seifritz Erich , Wirz-Justice Anna , Müller-Spahn Franz
Published: December 2003

Background: β-Amyloid peptide (Aβ), a neutrotoxic substance, has been implicated to a great degree in cell death during the course of AD. Resveratrol, a natural polyphenol mainly found in red wine, has been shown to be cardioprotective and chemoprotective. Since a moderate wine intake correlates with a lower risk for Alzheimer disease (AD), an additional neuroprotective effect has been postulated for resveratrol. Objective: The present study aimed at elucidating the possible neuroprotective effects of resveratrol against Aβ-induced neurotoxicity. Methods: The neuroprotective capacity against Aβ-related oxidative stress was studied in a cell culture model suitable for studying such potentially neuroprotective substances. Results: Resveratrol maintains cell viability and exerts an anti-oxidative action by enhancing the intracellular free-radical scavenger glutathione. Conclusion: Our findings suggest that red wine may be neuroprotective through the actions of resveratrol.
Is Dementia a Disease?
Authors: Peng Fred C.C.
Published: December 2003

Background: It is customary for many neurologists to think that dementia is a disease. This view is based on the following reasons: (1) a brain disease is the cause of cognitive impairment; (2) therefore, such cognitive impairment is substituted for the disease, becoming dementia, which is then also regarded as a mental disease. Objective: In this brief article, I take exception to such a view, contrary to the common belief in the medical field, on the ground that senile plaques and/or neurofibrillary tangles or any other factors cause neuronal apoptosis but they do not cause dementia directly. Methods: Literature on dementia and aphasia are critically and briefly reviewed to get the historical perspective that it is the progressive neuronal losses, losing brain functions as a result, that cause dementia; that is, brain diseases cause neuronal losses which then result in the decrease of brain functions, thereby leading to dementia. Results: There is no direct cause-effect relationship between brain disease, be it caused by vascular factors or not, and dementia which is the consequence or sequela of neuronal losses. Conclusions: It is concluded that dementia is not a disease and yet it occurs not only in Parkinson’s disease, Alzheimer’s disease (AD), Huntington’s disease and Pick’s disease, but also in any other neurodegenerative disease, e.g., spinocerebellar ataxia, or vascular disease, e.g., Binswanger’s disease, as part of the process of aging; in fact, AD is now regarded by some as a vascular disorder with neurodegenerative consequence, rather than a neurodegenerative disorder with vascular consequence. But vascular disorder is misleading if AD includes both neurofibrillary tangles and senile plaques; on the other hand, AD cannot be a vascular disorder if it includes only neurofibrillary tangles, as it should. Dementia, in this context, is re-defined as the differential manifestation of deteriorating brain functions over time as a part of aging due to cell deaths in the brain caused by any neurodegenerative disease. Its prominent symptoms are language disorders which must be distinguished from aphasias. It is also suggested that in fairness to Fischer, senile plaques be designated as Fischer’s disease separate from neurofibrillary tangles for which AD was originally named as an eponym.
Cohort Difference in Sexual Orientation: Results from a Large Age-Stratified Population Sample
Authors: Jorm A.F. , Dear K.B.G. , Rodgers B. , Christensen H.
Published: December 2003

Background: There is some community survey evidence for a cohort difference in female sexual orientation. Objective: To determine whether there is a cohort difference in sexual orientation in Australia. Methods: A community survey was carried out with a sample of 7,447 adults from the age groups 20–24, 40–44 and 60–64 years. As part of this survey respondents were asked a question on sexual orientation which was answered privately. Results: A strong age cohort difference was found for women, with younger women more frequently reporting a homosexual or bisexual orientation. By contrast, no age cohort difference was found for men. Conclusion: These findings suggest that a heterosexual orientation may have become less common in younger cohorts of Australian women. This finding is consistent with data from other recent studies.
The Metaphysical Art of Giorgio de Chirico
Authors: Blanke Olaf , Landis Theodor
Published: December 2003

It has been suggested that the great Italian painter Giorgio de Chirico (1888–1978), who developed the unique style of ‘metaphysical art’, suffered from migraine and used some of his morbid manifestations as a source of inspiration for his paintings. Yet, whereas many of the symptoms that de Chirico described are rare in migraine, they are frequently encountered in patients with temporal lobe epilepsy. Here we rediscuss de Chirico’s symptoms critically and suggest that, if his symptoms were of neurological origin, they rather relate to temporal lobe epilepsy than migraine.