bluuebunny/crossref_metadata_2025 huggingface dataset:
An optimized mean first passage time approach for obtaining rates in activated processes
Authors: Shepherd Tricia D. , Hernandez Rigoberto
Published: November 2002

The mean first passage time has recently become a useful analytic and computational quantity for estimating reaction rates in many-dimensional activated processes. Unfortunately, the accuracy of this association is limited by the indeterminacy of the appropriate boundary surface with respect to which the first passage times are obtained. The standard choices for this boundary result in an overestimate of the rates in stochastic models using the Langevin equation in the low friction limit. We propose a boundary surface which is a subspace of phase space that results in rates that are accurate in the entire friction regime. It is to be contrasted with equally accurate mean-first-passage-time rates that are obtained using noninvariant subspaces of either the configuration space or phase space and hence are not amenable to nonnumerical analysis. The proposed boundary surface is also shown heuristically and numerically to result from a new kind of variational principle.
Monte Carlo simulation of vapor–liquid binodal of water
Authors: Yoo S. , Zeng X. C.
Published: November 2002

Gibbs ensemble Monte Carlo simulations were carried out to calculate the vapor–liquid coexistence densities (binodal curves) for two potential models of water, five-site transferable interaction potential (TIP5P) and four-site Dang–Chang potential. Both models were devised to improve a widely used water model—the four-site TIP4P model of water. Compared with the critical temperature of the TIP4P model (579 K), we found that the critical temperature of the TIP5P model (546 K) deviates further from experimental value (647 K). That of the Dang–Chang model (590 K), however, is in better agreement with the experiments.
Extension of the Wu–Jing equation of state for highly porous materials: Calculations to validate and compare the thermoelectron model
Authors: Huayun Geng , Qiang Wu , Hua Tan , Lingcang Cai , Fuqian Jing
Published: November 2002

In order to verify and validate the newly developed thermoelectron equation of state (EOS) model that is based on the Wu–Jing EOS [J. Appl. Phys. 80, 4343 (1996); Appl. Phys. Lett. 67, 49 (1995)], calculations of shock compression behavior have been made on five different porous metals: iron, copper, lead, tungsten, and aluminum which are commonly used as standards. The model was used to calculate the Hugoniot, shock temperature, sound velocity, and unloading isentrope for these materials and comparisons were made to previous calculations and available data. Based on these comparisons, it is felt that the model provides information in good agreement with the corresponding experimental and theoretical data published previously. This suggests that the new model can satisfactorily describe the properties of shocked porous materials over a wide range of pressure and porosity.
Extension of the Wu–Jing equation of state for highly porous materials: Thermoelectron based theoretical model
Authors: Huayun Geng , Qiang Wu , Hua Tan , Lingcang Cai , Fuqian Jing
Published: November 2002

A thermodynamic equation of state (EOS) for thermoelectrons is derived which is appropriate for investigating the thermodynamic variations along isobaric paths. By using this EOS and the Wu–Jing (WJ) model, [Q. Wu and F. Jing J. Appl. Phys. 80, 4343 (1996)] an extended Hugoniot EOS model is developed which can predict the compression behavior of highly porous materials. Theoretical relationships for the shock temperature, bulk sound velocity, and the isentrope are developed. This method has the advantage of being able to model the behavior of porous metals over the full range of applicability of pressure and porosity, whereas methods proposed in the past have been limited in their applicability.
Growth of highly strained germanium dots on Si(001) covered by a silicon nitride layer
Authors: Derivaz M. , Noé P. , Dianoux R. , Barski A. , Schülli T. , Metzger T. H.
Published: November 2002

We show that germanium dots can be directly grown by molecular beam epitaxy on a silicon (001) surface covered by a very thin (1.5 nm thick) silicon nitride layer. We describe the experimental procedure, which induces the growth of nano-metric size, isolated germanium dots. The germanium dots are in epitaxy with the silicon substrate. Using grazing incidence x-ray diffraction we show that for very small dots the in-plane lattice parameter inside the dots is very close to the silicon lattice parameter while a strong lattice relaxation and/or silicon inter-diffusion take place with increasing dot size.
Influence of low-energy electron beam irradiation on defects in activated Mg-doped GaN
Authors: Gelhausen O. , Klein H. N. , Phillips M. R. , Goldys E. M.
Published: November 2002

The effect of low-energy electron beam irradiation (LEEBI) on residual hydrogen impurities and native defects in activated metalorganic vapor phase epitaxy-grown Mg-doped (p-type) GaN layers was studied by cathodoluminescence (CL) microanalysis and spectroscopy at temperatures between 80 and 300 K. The LEEBI treatment dissociates (Mg–H)0 complexes producing (i) at 300 K, a significant increase in a free-to-bound transition (e,Mg0) centered at 3.26 eV and (ii) at 80 K, a substantial decrease in a H–Mg donor–acceptor pair emission at 3.27 eV. In-plane and depth-resolved CL imaging reveals a direct correlation between the spatial distribution of the injected carriers and the depth and lateral distribution of activated Mg acceptors. This finding strongly suggests that hydrogen dissociation results from electron-hole recombination at hydrogen defect complexes rather than heating by the electron beam. The results at 80 K indicate that the process of dissociation of hydrogen from (Mg–H)0 complexes is accompanied by a generation of additional defect centers. It is proposed that following LEEBI hydrogen does not leave the specimen, but instead associates with nitrogen vacancies, generating additional recombination channels.
Effect of medium permeability on the perpendicular recording process
Authors: Senanan K. , Victora R. H.
Published: November 2002

The importance of the small recording layer permeability in enabling the record process on thick perpendicular media is demonstrated. Approximate reluctance arguments are supported by detailed micromagnetic simulation that extracts the proper permeability for the nonlinear recording layer. We find that the effective permeability peaks at a value of 1+4πMs/Hk for exchange decoupled media.
Influence of crystal growth atmosphere on the formation of color centers in PbWO4 single crystals
Authors: Kim Tae Hoon , Cho Shinuk , Lee Kwanghee , Jang Min Su , Ro Ji Hyun
Published: November 2002

We report optical and steady-state photoconductivity spectra of two kinds of lead tungstate (PbWO4) crystals each grown in different atmosphere. When the crystals were grown in air by Czochralski method, they exhibit a yellowish tint with additional spectral responses around 2.9 and 3.5 eV as compared with the colorless crystals grown in argon. We attribute such additional features to a stoichiometric deficiency of Pb ions, resulting in the formation of two defect states of Pb3+ and O−. Those states act as color centers and also as trap sources for the exciton dissociation, thereby contributing to the photocurrent response in the visible-UV range.
Coherent longitudinal optical phonon and plasmon coupling in GaAs
Authors: Chang Y.-M. , Chang N.-A.
Published: November 2002

The coupling between femtosecond laser-excited coherent LO phonons and plasmon in GaAs was investigated in real time via two-pump time-resolved second-harmonic generation. The coherent LO phonon–plasmon coupling mode dominated the lattice oscillation when the photoexcited plasma density exceeded 3×1018/cm3. Its oscillation intensity showed sinusoidal dependence on the separation time between the two pumps and a phase shift from the initial LO phonon oscillation. These observations reveal the formation time of photoexcited plasmon and its coherent coupling with LO phonon in femtosecond time scale.
Generalized electron emission model for field, thermal, and photoemission
Authors: Jensen Kevin L. , O’Shea Patrick G. , Feldman Donald W.
Published: November 2002

Analysis of electron emission from photocathodes, field emitters under extreme fields, or thermionic emitters operated at reduced temperature, utilize thermionic (Richardson) or field emission (Fowler–Nordheim) approximations which become inaccurate for such atypical conditions. The computational overhead of advanced numerical transport models make them ill-suited for data analysis or simulations of extended areas of photocathode and thermionic emitters, or for nonplanar field emitters. In this letter, an analytic thermal-field emission equation is given for which the Fowler–Nordheim and Richardson–Laue–Dushman equations are asymptotic limits. The methodology can analytically address “warm” field and “cool” thermionic emission, photoemission, and electron transport between interfaces (e.g., Schottky barriers). The approximations developed are compared to an exact evaluation (the modified airy function approach).
Spectrotemporal response of 1.3 μm quantum-dot lasers
Authors: Kuntz M. , Ledentsov N. N. , Bimberg D. , Kovsh A. R. , Ustinov V. M. , Zhukov A. E. , Shernyakov Yu. M.
Published: November 2002

We report the spectrotemporal measurements on 1.3 μm quantum-dot lasers with picosecond time resolution. The relaxation oscillations of the various mode groups monitored separately are identical and thus allow us to examine the spectrally integrated transient of the laser pulse for its characteristics. A modulation bandwidth of 2.3 GHz at room temperature is determined, demonstrating the potential of high-speed operation of these devices at wavelengths relevant for optical data transmission. The differential gain at room temperature was measured to be g′=1×10−15 cm2, the gain compression factor is ε=1×10−15 cm3.
Analysis of coupling between two-dimensional photonic crystal waveguide and external waveguide
Authors: Miyai Eiji , Okano Makoto , Mochizuki Masamitsu , Noda Susumu
Published: November 2002

Coupling between conventional wire waveguide and two-dimensional photonic crystal waveguide was analyzed by means of a three-dimensional finite difference time domain method. We evaluated the transmittance corresponding to the coupling efficiency between two waveguides. By using SiO2 clad below the wire and setting the width of the wire to be an appropriate value, we obtained single mode guiding and a coupling efficiency over 80% for the wave length around 1.55 μm.
Experimental evidence for two thermodynamic length scales in neutralized polyacrylate gels
Authors: Horkay Ferenc , Hecht Anne-Marie , Grillo Isabelle , Basser Peter J. , Geissler Erik
Published: November 2002

The small angle neutron scattering (SANS) behavior of fully neutralized sodium polyacrylate gels is investigated in the presence of calcium ions. Analysis of the SANS response reveals the existence of three characteristic length scales, two of which are of thermodynamic origin, while the third length is associated with the frozen-in structural inhomogeneities. This latter contribution exhibits power law behavior with a slope of about −3.6, reflecting the presence of interfaces. The osmotically active component of the scattering signal is defined by two characteristic length scales, a correlation length ξ and a persistence length L.
The planar Cantor sets of zero analytic capacity and the local 𝑇(𝑏)-Theorem
Authors: Mateu Joan , Tolsa Xavier , Verdera Joan
Published: November 2002

In this paper we obtain rather precise estimates for the analytic capacity of a big class of planar Cantors sets. In fact, we show that analytic capacity and positive analytic capacity are comparable for these sets. The main tool for the proof is an appropriate version of the

T
(
b
)

T(b)

-Theorem.
Kazhdan-Lusztig polynomials and character formulae for the Lie superalgebra 𝔤𝔩(𝔪|𝔫)
Authors: Brundan Jonathan
Published: November 2002

We compute the characters of the finite dimensional irreducible representations of the Lie superalgebragl(m|n)\mathfrak {gl}(m|n), and determineExt{\operatorname {Ext}}’s between simple modules in the category of finite dimensional representations. We formulate conjectures for the analogous results in categoryO\mathcal O. The combinatorics parallels the combinatorics of certain canonical bases over the Lie algebragl(∞)\mathfrak {gl}(\infty ).
The perils of processed herbs and spices
Authors: White Richard
Published: November 2002

In recent years, consumer demand has very much been for fresh quality food at the point of delivery. An explosion in the range of processed foods available in the supermarket chiller cabinet has occurred to meet this demand. Chilled ready meals, pizzas, speciality sausages and other small goods all have to live up to consumer expectations of visual appearance, flavour and eating quality, whilst safely achieving a commercially acceptable shelf‐life. All these products contain one common flavouring ingredient, which can severely limit the time a food item can remain on display in the chiller cabinet – herbs and spices. This paper discusses the various strategies and processes currently in use to reduce the microbial loads of herbs and spices to acceptable levels, including improved agricultural methods product selection, irradiation, heat treatment, flavour extraction through steam distillation, and micro encapsulation.
Gender and authorship patterns in an African librarianship journal, 1991‐1997
Authors: Atinmo Morayo I. , Jimba Samuel W.
Published: November 2002

The authorship of AJLAIS over seven years was subjected to analysis by gender, collaboration and institutional affiliation. A total of 95 research articles contributed by 118 authors were analysed. Results indicated male dominance of single‐authored articles, 83.2 per cent to 16.8 per cent. Of the 16 co‐authored articles nine (56.25 per cent) were co‐authored by men only, one article (6.25 per cent) was co‐authored by women only, and gender mixture was found in six (37.5 per cent) of the articles. A cross‐tabulation of institutional affiliation with gender revealed that no woman contributed any article from special and public libraries while there was a relative gender mixture in academic libraries and library schools. There is a need to encourage female publication output in all sectors of librarianship and information science in Africa.
Delinquent readership in selected urban libraries in Nigeria
Authors: Momodu Margaret M.
Published: November 2002

The issue of delinquent readership has been recognised as a perennial problem in libraries. This study was conceived, therefore, on the premise that there is need for containing the problem, at least to the barest minimum. Questionnaire and interview methods were used to collect the necessary data and frequencies and percentages of responses to variables 1‐19 were reported. The study found that every library has the problem of delinquent readership, although to varying degrees. The administration in the urban libraries studied appreciate and try to solve the problem of delinquency in libraries.
Growing the top management team
Authors: Laske Otto E. , Maynes Barbara
Published: November 2002

We outline a developmental view of OD, showing on empirical grounds that Argyris’ “theory in use” notion points to different levels of mental growth as underpinnings of “the program in brain/mind” that determines personal theories of organizational action. Employing the developmental structure/process tool (DSPTTM), we explain the differences between two executives’ theory of action. We also analyze the dynamic of a six‐member team on developmental grounds. By way of close analysis, we show that theories of action are developmentally grounded, and are thus open both to maturation over the life span and to interventions like developmental coaching. We come to the conclusion that developmental assessment of executives and teams should become a vital part of in‐house development and of OD intervention.
On misdirecting management
Authors: Barabba Vincent , Pourdehnad John , Ackoff Russell L.
Published: November 2002

The authors argue that consultants are of two types: self‐promoting gurus and educators. Gurus that pontificate and promote their proprietary problem solving techniques do not educate their clients. They promote maxims that define rules of behavior but do not increase the competence of managers. They promote their proprietary solution as a fix for all problems instead of trying to increase managerial understanding of a particular corporate puzzle. They provide maxims that are really platitudes and panaceas without proof of effectiveness. A significant proportion of the advice produced by such management gurus is either incorrectly inferred from data (but nevertheless may be true) or is unsubstantiated by genuine evidence. Examples are drawn from the work of Peters, Covey, de Geus, and Hamel. Recommendations for providing management with defensive measures include: recognition that flawed research techniques produces flawed evidence; recognition that many seemingly wise maxims are really platitudes; and effective selection and use of internal and external consultants who perceive their mission to be the individualized education of managers and the solution of their organization’s particular problems.
Portfolio power: harnessing a group of brands to drive profitable growth
Authors: Pierce Andrew , Moukanas Hanna
Published: November 2002

Brand portfolio management is not just a marketing issue, in which a sub‐optimal portfolio dilutes marketing messages and confuses customers. It also directly affects corporate profitability. Ill‐defined and overlapping brands in a portfolio lead to erosion in price premiums, weaker manufacturing economies, and sub‐scale distribution. In a slower economy, the problems of an under performing portfolio are even more acute: While adding brands is easy, it becomes difficult to harvest the value in a brand or to divest it. Effective brand portfolio management starts by creating a fact base about the equity in each brand and the brand’s economic contribution. The application of analytical tools can inform decisions about individual and collective brand strategies from targeting and positioning to investments, partnerships, and extension opportunities. Linking the intangibles of brands to hard financial metrics allows companies to exploit the full potential of their brands and thereby gain a competitive advantage.
Gathering information for strategic decisions, routinely
Authors: McNeilly Mark
Published: November 2002

Leaders at all levels of the company need to institute a simple but effective routine for collecting the information needed to take strategic action. This article explains how to make that process pervasive and suggests some specific tools to help it work effectively in your organization. There are three basic steps to strategic decision‐making: getting the right information, making a good decision and then implementing that decision. Success in the information stage translates into knowing the types of information needed to make the decision, finding it, and transmitting it quickly to the decision‐makers. The information required falls in three categories: knowledge about the competition, knowledge about your own company, and knowledge about your marketplace. It is not enough to merely gather the information; an infrastructure must be in place to ensure that market information is getting back to the decision‐makers. Get the decision‐makers together regularly to close on important issues. Critical to making better decisions is to identify alternative courses of action rather than simply one proposal. In addition to basic strategic planning there are two ways to experience making decisions under simulated conditions: wargaming and scenario planning. Regularly tracking the successful implementation of decisions made is a key method of ensuring action.
Option pricing for real estate development: Hong Kong Disneyland
Authors: Leung Barbara Y.P. , Hui Eddie C.M.
Published: November 2002

It is well known that the traditional net present value (NPV) approach fails to take account of the multiple effects arising from the interactions of the operating and strategic flexibility during the course of a project. Option pricing theory (OPT) has been successfully applied in the valuation of both financial and real investments in the last two decades. However, it is still a relatively new approach in the valuation of real estate investments. This paper thus attempts to extend the application of OPT to the valuation of real estate development projects, providing insights into rectifying the limitations of traditional approaches. The paper starts with an overview of the development of OPT relating to real estate investments. It then examines the appraisal method adopted by the Government for Hong Kong Disneyland and explores the real options that may create added value to the project. A binomial option pricing model is proposed that estimates the potential values of the project with those options available. The study concludes that OPT is superior to NPV approach on the valuation of real estate investments in that it enhances upside potential as well as reducing downside risk.
Penetration Limit Velocity for Ogive-Nose Projectiles and Limestone Targets
Authors: Forrestal M. J. , Hanchak S. J.
Published: November 2002

We conducted depth-of-penetration experiments with ogive-nose steel projectiles and limestone targets to determine the penetration limit velocity. The penetration limit velocity is defined as the minimum striking velocity required to embed the projectile in the target. For striking velocities smaller than the penetration limit velocity, the projectile rebounds from the target.
A Note on the Application of the Flamant Solution of Classical Elasticity to Circular Domains
Authors: Levy A. J.
Published: November 2002

It is a well known fact that the Flamant solution of classical elasticity cannot be used at an interior point of an elastic body since the resulting displacement field would be multivalued. In this note we demonstrate that the solution to the problem of a concentrated force at a point on an interior circular boundary has a multivalued displacement component but that the exclusion of the point of application of the load from the domain renders the displacement field single-valued everywhere.
Scattering From an Elliptic Crack by an Integral Equation Method: Normal Loading
Authors: Saha T. K. , Roy A.
Published: November 2002

The scattering of normally incident elastic waves by an embedded elliptic crack in an infinite isotropic elastic medium has been solved using an analytical numerical method. The representation integral expressing the scattered displacement field has been reduced to an integral equation for the unknown crack-opening displacement. This integral equation has been further reduced to an infinite system of Fredholm integral equation of the second kind and the Fourier displacement potentials are expanded in terms of Jacobi’s orthogonal polynomials. Finally, proper use of orthogonality property of Jacobi’s polynomials produces an infinite system of algebraic equations connecting the expansion coefficients to the prescribed dynamic loading. The matrix elements contains singular integrals which are reduced to regular integrals through contour integration. The first term of the first equation of the system yields the low-frequency asymptotic expression for scattering cross section analytically which agrees completely with previous results. In the intermediate and high-frequency scattering regime the system has been truncated properly and solved numerically. Results of quantities of physical interest, such as the dynamic stress intensity factor, crack-opening displacement scattering cross section, and back-scattered displacement amplitude have been given and compared with earlier results.
A Closed Contour With No Warping: A Common Feature in all Confocally Elliptical Hollow Sections
Authors: Chen T. , Kung Y. J.
Published: November 2002

We show that for a confocally elliptical hollow section under Saint-Venant’s torsion, there always exists a confocally elliptical closed contour inside the section that exhibits no warping. This property is generally true without any regard to the thickness or the aspect ratio of the hollow section, as long as the inner and the outer ellipses are confocal. This property allows us to apply Packham and Shail’s (Packham, B. A, and Shail, R., 1978, “St. Venant Torsion of Composite Cylinders,” J. Elast., 8, pp. 393–407) superposition method for the torsion solutions of a two-phase elliptical hollow section. Previously, this superposition method is only applicable to symmetric compound sections with respect to a straight line or a circular arc.
Stress Behavior at the Interface Junction of an Elastic Inclusion
Authors: Qian Z. Q. , Akisanya A. R. , Thompson D. S.
Published: November 2002

The stress distribution at the interface junction of an elastic inclusion embedded in a brittle matrix is examined. Solutions are derived for the stress and displacement fields near the junction formed by the intersection of the interfaces between the inclusion and the matrix. The stress field consists of symmetric (mode I) and skew-symmetric (mode II) components. The magnitude of the intensity factor associated with each mode of deformation is determined using a combination of the finite element method and a contour integral. The numerical results of the stresses near the interface junction of two different inclusion geometries show that the asymptotic solutions of the stresses are in agreement with those from the finite element prediction when higher-order terms are considered. The implications of the results for the failure of particle-reinforced and two-phase brittle materials are discussed.
Thermal reaction of nickel and Si0.75Ge0.25 alloy
Authors: Pey K. L. , Choi W. K. , Chattopadhyay S. , Zhao H. B. , Fitzgerald E. A. , Antoniadis D. A. , Lee P. S.
Published: November 2002

The interfacial reactions and chemical phase formation between nickel and ultrahigh vacuum chemical vapor deposited Si0.75Ge0.25 alloy have been studied within the temperature range of 300–900 °C for forming low resistive and uniform silicide films for future application in SiGe based metal–oxide–semiconductor field effect transistor devices. The silicided films were characterized by the x-ray diffraction, Auger electron spectroscopy, scanning electron microscopy, transmission electron microscopy, and micro-Raman microscopy techniques. Smooth and uniform nickel monogermanosilicide NiSi0.75Ge0.25 films have been observed for samples annealed at around 400–500 °C. For annealing temperatures of 500 °C and above, Ge-rich Si1−zGez grains where z>0.25 were found among Ge deficient Niy(SiwGe1−w)1−y grains where w<0.25 and the Niy(Si1−wGew)1−y phase is thermally stable up to an annealing temperature of 800 °C. We found that the Ni/SiGe reaction is mainly diffusion controlled with Ge and Ni as the dominant diffusing species compared to Si during the annealing process. In addition, Ge has been found to promote agglomeration especially above 700 °C, leading to an abrupt increase in the sheet resistance.
Studies on electron behaviors at downstream region of a neutral loop discharge plasma
Authors: Sakoda Tatsuya , Sung Youl-Moon
Published: November 2002

The measurements of electron temperature, electron density, and ion current density at the plasma downstream region in a neutral loop discharge (NLD) plasma were performed using a double probe. Based on these results and the theoretical analyses of electron behaviors, the entire structure of the NLD plasma was discussed. It was concluded that the obtained profiles of the electron temperature, density, and ion current density at the downstream and throughout the intermediate regions were the mirror of profiles at the plasma source region. In addition, laser Thomson scattering measurements of the electron temperature and density at the downstream region were performed in order to include the quantitative evaluation phase.
Multiple cavity modes in the helicon plasma generated at very high radio frequency
Authors: Eom G. S. , Choe W.
Published: November 2002

Helicon plasma generated at very high radio frequency has almost the same properties as common high frequency helicon plasmas. By measurements of wave number and plasma potential, additional mode changes inside the helicon plasma were observed with increasing magnetic field. It was also observed that the wavelength of the helicon wave changes discretely with respect to the plasma length indicating strong restriction of the parallel wavelength to the plasma dimension. The dependence of plasma potential on magnetic field indicates that its change is not entirely due to capacitive coupling. The corresponding mode transition is related to the cavity modes driven by a helicon wave.
Surface morphology of ion-beam deposited carbon films under high temperature
Authors: Liao Meiyong , Chai Chunlin , Yang Shaoyan , Liu Zhikai , Qin Fuguang , Wang Zhanguo
Published: November 2002

Carbon films with an open-ended structure were obtained by mass-selected ion-beam deposition technique at 800 °C. Raman spectra show that these films are mainly sp2-bonded. In our case, threshold ion energy of 140 eV was found for the formation of such surface morphology. High deposition temperature and ion-beam current density are also responsible for the growth of this structure. Additionally, the growth mechanism of the carbon films is discussed in this article. It was found that the ions sputtered pits on the substrate in the initial stage play a key role in the tubular surface morphology.
X‐ray imaging with amorphous selenium: X‐ray to charge conversion gain and avalanche multiplication gain
Authors: Hunt Dylan C. , Kirby Sean S. , Rowlands J. A.
Published: November 2002

Fluoroscopy is a low dose imaging technique. As such, a very sensitive detector is required to create images of good quality. Present day flat panel active matrix read out systems introduce an amount of noise that inhibits present direct and indirect methods from producing optimal quality images at fluoroscopic exposure rates (0.1–10 μR per frame). The gain of the direct conversion approach using amorphous selenium (a‐Se) was investigated to determine whether by increasing the applied electric field, a gain sufficient to overcome the noise limitations of the active matrix could be achieved. Conversion gain and avalanche multiplication in a‐Se were investigated as a function of electric field from 10 to 100 V/μm. Our results show a factor of 4 increase in conversion gain is available by increasing electric field from the current standard of 10 V/μm to 100 V/μm. Furthermore, we show that avalanche multiplication can provide an additional gain of up to 25. This increase in signal is sufficient to overcome the noise level encountered in flat panel detectors and permit fully quantum noise limited operation across the whole fluoroscopic range of exposure.
A framework for noise‐power spectrum analysis of multidimensional images
Authors: Siewerdsen J. H. , Cunningham I. A. , Jaffray D. A.
Published: November 2002

A methodological framework for experimental analysis of the noise‐power spectrum (NPS) of multidimensional images is presented that employs well‐known properties of the n‐dimensional Fourier transform. The approach is generalized to n dimensions, reducing to familiar cases for (e.g., time series) and (e.g., projection radiography) and demonstrated experimentally for two cases in which (viz., using an active matrix flat‐panel imager for x‐ray fluoroscopy and cone‐beam CT to form three‐dimensional (3D) images in spatiotemporal and volumetric domains, respectively). The relationship between fully NPS analysis and various techniques for analyzing a “central slice” of the NPS is formulated in a manner that is directly applicable to measured data, highlights the effects of correlation, and renders issues of NPS normalization transparent. The spatiotemporal NPS of fluoroscopic images is analyzed under varying conditions of temporal correlation (image lag) to investigate the degree to which the NPS is reduced by such correlation. For first‐frame image lag of ∼5–8 %, the NPS is reduced by ∼20% compared to the lag‐free case. A simple model is presented that results in an approximate rule of thumb for computing the effect of image lag on NPS under conditions of spatiotemporal separability. The volumetric NPS of cone‐beam CT images is analyzed under varying conditions of spatial correlation, controlled by adjustment of the reconstruction filter. The volumetric NPS is found to be highly asymmetric, exhibiting a ramp characteristic in transverse planes (typical of filtered back‐projection) and a band‐limited characteristic in the longitudinal direction (resulting from low‐pass characteristics of the imager). Such asymmetry could have implications regarding the detectability of structures visualized in transverse versus sagittal or coronal planes. In all cases, appreciation of the full dimensionality of the image data is essential to obtaining meaningful NPS results. The framework may be applied to NPS analysis of image data of arbitrary dimensionality provided the system satisfies conditions of NPS existence.
Dosimetric accuracy of the ITP™ inverse treatment planning system
Authors: Olch Arthur J.
Published: November 2002

The dosimetric accuracy of the ITP™ system for intensity modulated radiation therapy was determined for 19 patient plans. Treatments were given with a Varian 2100C and a 120‐leaf multileaf collimator using step and shoot delivery. Both absolute dose, determined by an ionization chamber, and relative dose, determined by film, were assessed. It was found that absolute dose agreement was within isodoses in the high dose–low gradient region were within and the distance to agreement for isodoses between 20% and 90% was This agreement is at least as good as that found for standard wedged fields in most treatment planning systems.
Dose planning with comparison to in vivo dosimetry for epithermal neutron irradiation of the dog brain
Authors: Seppälä Tiina , Auterinen Iiro , Aschan Carita , Serén Tom , Benczik Judit , Snellman Marjatta , Huiskamp René , Ramadan Usama Abo , Kankaanranta Leena , Joensuu Heikki , Savolainen Sauli
Published: November 2002

Boron neutron capture therapy (BNCT) is an experimental type of radiotherapy, presently being used to treat glioblastoma and melanoma. To improve patient safety and to determine the radiobiological characteristics of the epithermal neutron beam of Finnish BNCT facility (FiR 1) dose‐response studies were carried on the brain of dogs before starting the clinical trials. A dose planning procedure was developed and uncertainties of the epithermal neutron‐induced doses were estimated. The accuracy of the method of computing physical doses was assessed by comparing with in vivo dosimetry. Individual radiation dose plans were computed using magnetic resonance images of the heads of 15 Beagle dogs and the computational model of the FiR 1 epithermal neutron beam. For in vivo dosimetry, the thermal neutron fluences were measured using Mn activation foils and the gamma‐ray doses with MCP‐7s type thermoluminescent detectors placed both on the skin surface of the head and in the oral cavity. The degree of uncertainty of the reference doses at the thermal neutron maximum was estimated using a dose‐planning program. The estimated uncertainty (±1 standard deviation) in the total physical reference dose was ±8.9%. The calculated and the measured dose values agreed within the uncertainties at the point of beam entry. The conclusion is that the dose delivery to the tissue can be verified in a practical and reliable fashion by placing an activation dosimeter and a TL detector at the beam entry point on the skin surface with homogeneous tissues below. However, the point doses cannot be calculated correctly in the inhomogeneous area near air cavities of the head model with this type of dose‐planning program. This calls for attention in dose planning in human clinical trials in the corresponding areas.
Mechanism study of skin tissue ablation by nanosecond laser pulses
Authors: Fang Qiyin
Published: November 2002

Understanding the fundamental mechanisms in laser tissue ablation is essential to improve clinical laser applications by reducing collateral damage and laser pulse energy requirements. In this dissertation, skin tissue ablation by nanosecond laser pulses has been studied from near infrared to ultraviolet for a clear understanding of the mechanism that can be used to enhance future design of pulsed lasers for dermatology and plastic surgery. Multiple laser and optical configurations have been constructed to generate 9–12 ns laser pulses at 1064, 532, 266, and 213 nm. Through histology and optical transmission measurements of ablation depth as a function of laser pulse energy, the 589 nm spectral line in the secondary radiation from ablated skin tissue samples was identified as the signature of the occurrence of ablation. Subsequently, this spectral signature has been used to investigate the probabilistic process of the ablation near the threshold at the four wavelengths. In addition, optical breakdown and backscattering in water were investigated along with a nonlinear refraction index measurement using a z‐scan technique. Preliminary studies on ablation of a gelatin based tissue phantom are also presented. The current theoretical models describing soft tissue ablation by short laser pulses were critically reviewed. A new plasma‐mediated model has subsequently been developed and a laser‐induced localized thermal ionization pathway has been investigated. It was found to have significant influence on the initial free electron density during plasma formation due to the combination of strong light absorption and subsequent confined temperature rise in chromophores. Good agreement has been found between the model and experimental results.
GEOMETRICAL CONSTRUCTION OF HETEROGENEOUS LOOP AMPLITUDES IN 2D GRAVITY
Authors: ANAZAWA MASAHIRO , ISHIKAWA ATUSHI
Published: November 2002

We study a disk amplitude which has a complicated heterogeneous matter configuration on the boundary in a system of the (3,4) conformal matter coupled to two-dimensional gravity. It is analyzed using the two-matrix chain model in the large N limit. We show that the disk amplitude calculated by Schwinger–Dyson equations can be completely reproduced through purely geometrical consideration. From this result, we speculate that all heterogeneous loop amplitudes can be derived from the geometrical consideration and the consistency among relevant amplitudes.
STATISTICAL ENTROPY OF KERR BLACK HOLE
Authors: ZHAO REN , ZHANG LICHUN
Published: November 2002

Using the method of quantum statistics, we directly derive the partition functions of bosonic and fermionic field in Kerr black hole with axial symmetry. Then via the improved brick-wall method for membrane model, we show that the entropy of the bosonic and fermionic field in the black hole is proportional to the area of the horizon. In our result, the stripped term and the divergent logarithmic term no longer exist. Hence the problem that the state density is divergent around the horizon doesn't exist. We also give the influence of the spining degeneracy of particles on the entropy of black hole. We offer a new simple and direct way of calculating the entropy of different complicated black holes.
STOCHASTIC ANALYSIS OF CELLULAR AUTOMATA WITH APPLICATION TO THE VOTER MODEL
Authors: MÜHLENBEIN HEINZ , HÖNS ROBIN
Published: November 2002

We perform a rigorous stochastic analysis of both deterministic and stochastic cellular automata. The theory uses a mesoscopic view, i.e. it works with probabilities instead of individual configurations used in micro-simulations. An exact stochastic analysis can be done using the theory of Markov processes. But this analysis is restricted to small problems only. For larger problems we compute the distribution using a factorization into marginals. These marginals are then approximated by the given marginals of low order with iterative proportional fitting using the maximum entropy principle. This method has been developed in probabilistic logic. Our method leads to a set of difference equations which have to be iterated numerically. We use the exact methods as well as our approximations to investigate the popular nonlinear voter model (NLVM). We show that the "phase transitions" regarded in recent papers are artifacts of the mean-field approximation. They do not show up in the real automata. There exist many mathematical peculiarities of the NLVM which raise doubts concerning the suitability of the model. As an alternative we propose the Exponential Voter Model which depends on a single parameter only, the inverse "temperature" β. Our proposed method to perform a stochastic analysis is not restricted to cellular automata, but can be applied to more general discrete stochastic systems.
The Pacific Salmon Wars: What Science Brings to the Challenge of Recovering Species
Authors: Ruckelshaus Mary H. , Levin Phil , Johnson Jerald B. , Kareiva Peter M.
Published: November 2002

▪ Abstract  Politicians, scientists, government agencies, and the public are all engaged in recovery planning for Pacific salmon. In order for science to fulfill its potential in the arena of salmon recovery planning, several shortcomings of the science and its application to decision-making must be rectified. The definition of conservation units using genetic and phylogenetic inference needs to be sharpened. Ecological analyses must get beyond casting blame for past declines in salmon numbers and examine mixed strategies of management that consider interactions between hatcheries, harvest, hydropower, and habitat factors as well as background natural stresses and invasive species. Glib acceptance of expert opinion and extrapolated or inferred data should be tempered. To deal with uncertainty, recovery teams should engage in scenario analyses in which a wide variety of assumptions are played out. Finally, there is a pressing need for analyses aimed at determining what circumstances and communication strategies give science an effective voice in decision-making.
The Energetic Metabolism of Societies Part I: Accounting Concepts
Authors: Haberl Helmut
Published: November 2002

Based upon the currently emerging international consensus on how to account for the materials flows of industrialized countries, this article proposes methods to account for the energetic metabolism of societies. It argues that, to fully exploit the potential of the metabolism approach in the context of sustainable development, both energetic and material aspects of societal metabolism have to be taken into account. The article proposes concepts to empirically describe energy input, internal energy transformations, and energy utilization of societies by extending commonly used notions of energy statistics in a way that is compatible with current methods of materials flow analysis. Whereas energy statistics include only the energy used in technical devices for providing heat, light, mechanical work, and data processing, an accounting system for the energetic metabolism of societies should also consider flows of nutritional energy for both livestock and humans. Moreover, in assessing the energy input of a society, all inputs of energy‐rich materials (and immaterial forms of energy such as electricity and light) that cross the boundary into the biophysical structures of society should be taken into consideration, regardless of the purpose for which they are eventually used. As a consequence, an energetic metabolism accounting system treats all biomass as energy input, instead of considering only the biomass used for technical energy generation, as energy statistics do. Part II in this set of articles will apply these concepts to different modes of societal organization and explore the significance of energetic metabolism for sustainable development. In particular, it will explore the significance for policies that aim at increasing the contribution of renewable energy, especially biomass.
Nitrogen's Role in Industrial Systems
Authors: Domene L. Alejandra Febre , Ayres Robert U.
Published: November 2002

Nitrogen is one of the key component elements in biological systems, but it also plays an increasingly important part in other areas of a modern industrial system. The starting point for almost all nitrogen‐based chemicals is ammonia. This article presents 1996 production and use statistics for ammonia and its most important derivatives. We also characterize the key production processes and emissions. Finally, we summarize losses and emissions of nitrogen within the sector.
The Introduction of Postconsumer Recycled Material into TYVEK® Production, Marketing, and Organizational Challenges
Authors: Sharfman Mark P. , Ellington Rex T. , Meo Mark
Published: November 2002

In the late 1980s, with the advent of increased consumer environmental awareness, DuPont faced a challenge with its TYVEK® family of nonwoven polyethylene textile products. TYVEK is used in a wide variety of applications ranging from house wrap to medical packaging. One of the most visible portions of the business is envelopes used by FedEx (previously known as Federal Express), the wellknown courier and delivery service and by the U.S. Postal Service. As early as 1988, end users began asking questions about the environmental characteristics of TYVEK envelopes. As these questions increased, DuPont began to address the concerns directly. In response to the market's concern and because of the increased availability of postconsumer‐recycled (PCR) polyethylene, DuPont decided to put PCR polyethylene into TYVEK, beginning with the envelope business. Further, DuPont developed a recycling infrastructure for TYVEK because, although TYVEK consists entirely of high‐density polyethylene, which is highly recyclable, no infrastructure was in place to recycle the material. These decisions produced a wide variety of technical and organizational challenges the firm had to overcome. This case study examines how DuPont made these choices and overcame the difficulties created by implementing needed changes. Whereas the envelope market for TYVEK embraced PCR polyethylene, other product markets resisted the innovation. The article closes with a discussion of the lessons learned from DuPont's experience.
Uplifting and Overturning of Equipment Anchored to a Base Foundation
Authors: Makris Nicos , Black Cameron J.
Published: November 2002

This paper concentrates on the rocking response of rigid equipment anchored on a foundation base with plan dimensions that are larger than the footprint of the equipment. With this configuration there are two distinct capacities to resist uplift and eventual overturning: (a) the equipment engages the base foundation into rocking motion, and (b) the restrainers fracture and the equipment subsequently rocks atop its foundation base. This study examines both moderate uplift (serviceability level) and overturning (ultimate state—failure). It is first shown that for specific equipment/base configurations, the high strength restrainers used in practice are sufficient to engage the foundation base into rocking motion for a wide range of recorded earthquake motions. Subsequently, the study uncovers that for earthquakes with long distinguishable pulses, the margin between exceeding the serviceability level of uplift and achieving overturning is minimal. None of the strong motions used in this study is capable of overturning the freestanding configurations examined. It is found that small values of the foundation protrusion from the footprint of the equipment reduces the uplift appreciably.