bluuebunny/crossref_metadata_2025 huggingface dataset:
On the highly accurate summation of certain series occurring in plate contact problems
Authors: MacDonald D.
Published: July 2002

The infinite series

R
p

=

∑

k
=
1

∞

(
2
k
−
1
)

−
p

x

2
k
−
1

R_p = \sum _{k=1}^\infty {(2 k - 1)}^{- p} \, x^{2 k - 1}

,

0
>
1
−
x
≪
1

0 >1-x\ll 1

,

p
=
2

p = 2

or

3
3

, and the related series
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="StartLayout 1st Row 1st Column upper C left-parenthesis x comma b comma 2 right-parenthesis 2nd Column a m p semicolon equals sigma-summation Underscript k equals 1 Overscript normal infinity Endscripts left-parenthesis 2 k minus 1 right-parenthesis Superscript negative 2 Baseline hyperbolic cosine left-parenthesis 2 k minus 1 right-parenthesis x slash hyperbolic cosine left-parenthesis 2 k minus 1 right-parenthesis b comma 0 greater-than 1 minus x slash b much-less-than 1 comma 2nd Row 1st Column upper S left-parenthesis x comma b comma 3 right-parenthesis 2nd Column a m p semicolon equals sigma-summation Underscript k equals 1 Overscript normal infinity Endscripts left-parenthesis 2 k minus 1 right-parenthesis Superscript negative 3 Baseline hyperbolic sine left-parenthesis 2 k minus 1 right-parenthesis x slash hyperbolic cosine left-parenthesis 2 k minus 1 right-parenthesis b comma EndLayout">

C
(
x
,
b
,
2
)

a
m
p
;
=

∑

k
=
1

∞

(
2
k
−
1
)

−
2

cosh
⁡
(
2
k
−
1
)
x

/

cosh
⁡
(
2
k
−
1
)
b
,

0
>
1
−
x

/

b
≪
1
,

S
(
x
,
b
,
3
)

a
m
p
;
=

∑

k
=
1

∞

(
2
k
−
1
)

−
3

sinh
⁡
(
2
k
−
1
)
x

/

cosh
⁡
(
2
k
−
1
)
b
,

\begin{equation*} \begin {split} C(x,b,2) &=\sum _{k=1}^\infty {(2k-1)}^{-2} \cosh (2k-1)x/\cosh (2k-1)b,\quad 0 >1-x/b \ll 1,\\ S(x,b,3)&=\sum _{k=1}^\infty {(2k-1)}^{-3} \sinh (2k-1)x/\cosh (2k-1)b, \end{split} \end{equation*}

are of interest in problems concerning contact between plates and unilateral supports. This article will re-examine a previously published result of Baratella and Gabutti for

R
p

R_p

, and will present new, rapidly convergent, series for

C
(
x
,
b
,
2
)

C(x,b,2)

and

S
(
x
,
b
,
3
)
.

S(x,b,3).
Modular forms which behave like theta series
Authors: Chakraborty K. , Lal A. , Ramakrishnan B.
Published: July 2002

In this paper, we determine all modular forms of weights

36
≤
k
≤
56

36\leq k\leq 56

,

4
∣
k

4\mid k

, for the full modular group

S

L
2

(

Z

)

SL_2(\mathbb Z)

which behave like theta series, i.e., which have in their Fourier expansions, the constant term

1
1

and all other Fourier coefficients are non–negative rational integers. In fact, we give convex regions in

R

3

{\mathbb R}^3

(resp. in

R

4

{\mathbb R}^4

) for the cases

k
=
36

k = 36

, 40, and 44 (resp. for the cases

k
=
48

k = 48

, 52, and 56). Corresponding to each lattice point in these regions, we get a modular form with the above property. As an application, we determine the possible exceptions of quadratic forms in the respective dimensions.
Vortex method for two dimensional Euler equations in bounded domains with boundary correction
Authors: Ying Lung-an
Published: July 2002

The vortex method for the initial-boundary value problems of the Euler equations for incompressible flow is studied. A boundary correction technique is introduced to generate second order accuracy. Convergence and error estimates are proved.
A priori 𝐿^{𝜌} error estimates for Galerkin approximations to porous medium and fast diffusion equations
Authors: Wei Dongming , Lefton Lew
Published: July 2002

Galerkin approximations to solutions of a Cauchy-Dirichlet problem governed by the generalized porous medium equation
\[
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="StartFraction partial-differential u Over partial-differential t EndFraction minus sigma-summation Underscript i equals 1 Overscript upper N Endscripts StartFraction partial-differential Over partial-differential x Subscript i Baseline EndFraction left-parenthesis StartAbsoluteValue u EndAbsoluteValue Superscript rho minus 2 Baseline StartFraction partial-differential u Over partial-differential x Subscript i Baseline EndFraction right-parenthesis equals f left-parenthesis x comma t right-parenthesis">

∂
u

∂
t

−

∑

i
=
1

N

∂

∂

x
i

(

|

u

|

ρ
−
2

∂
u

∂

x
i

)
=
f
(
x
,
t
)

\frac {\partial u}{\partial t}-\sum ^N_{i=1}\frac \partial {\partial x_i}(|u|^{\rho -2}\frac {\partial u}{ \partial x_i})=f(x,t)

\]
on bounded convex domains are considered. The range of the parameter

ρ
\rho

includes the fast diffusion case

1
>
ρ
>
2

1>\rho >2

. Using an Euler finite difference approximation in time, the semi-discrete solution is shown to converge to the exact solution in

L
∞

(
0
,
T
;

L
ρ

(
Ω
)
)

L^\infty (0,T;L^\rho (\Omega ))

norm with an error controlled by

O
(
Δ

t

1
4

)

O(\Delta t^{\frac 14})

for

1
>
ρ
>
2

1>\rho >2

and

O
(
Δ

t

1

2
ρ

)

O(\Delta t^{\frac 1{2\rho }})

for

2
≤
ρ
>
∞

2\le \rho >\infty

. For the fully discrete problem, a global convergence rate of

O
(
Δ

t

1
4

)

O(\Delta t^{\frac 14})

in

L
2

(
0
,
T
;

L
ρ

(
Ω
)
)

L^2(0,T;L^\rho (\Omega ))

norm is shown for the range

2
N

N
+
1

>
ρ
>
2

\frac {2N}{N+1}>\rho >2

. For

2
≤
ρ
>
∞

2\le \rho >\infty

, a rate of

O
(
Δ

t

1

2
ρ

)

O(\Delta t^{\frac 1{2\rho }})

is shown in

L
ρ

(
0
,
T
;

L
ρ

(
Ω
)
)

L^\rho (0,T;L^\rho (\Omega ))

norm.
Zeros of 2-adic 𝐿-functions and congruences for class numbers and fundamental units
Authors: Shanks Daniel , Sime Patrick , Washington Lawrence
Published: July 2002

We study the imaginary quadratic fields such that the Iwasawa

λ

2

\lambda _{2}

-invariant equals 1, obtaining information on zeros of

2
2

-adic

L
L

-functions and relating this to congruences for fundamental units and class numbers.
Homology of algebraic varieties: An introduction to the works of Suslin and Voevodsky
Authors: Levine Marc
Published: July 2002

We give an overview of the ideas Suslin and Voevodsky have introduced in their works on algebraic cycles and their relation to the mod-

n
n

homology of algebraic varieties.
The Schläfli formula in Einstein manifolds with boundary
Authors: Rivin Igor , Schlenker Jean-Marc
Published: July 2002

We give a smooth analogue of the classical Schläfli formula, relating the variation of the volume bounded by a hypersurface moving in a general Einstein manifold and the integral of the variation of the mean curvature. We extend it to variations of the metric in a Riemannian Einstein manifold with boundary, and apply it to Einstein cone-manifolds, to isometric deformations of Euclidean hypersurfaces, and to the rigidity of Ricci-flat manifolds with umbilic boundaries. Résumé. On donne un analogue régulier de la formule classique de Schläfli, reliant la variation du volume borné par une hypersurface se déplaçant dans une variété d’Einstein à l’intégrale de la variation de la courbure moyenne. Puis nous l’étendons aux variations de la métrique à l’intérieur d’une variété d’Einstein riemannienne à bord. On l’applique aux cone-variétés d’Einstein, aux déformations isométriques d’hypersurfaces de

E
n

E^n

, et à la rigidité des variétés Ricci-plates à bord ombilique.
The first eigenvalue of a Riemann surface
Authors: Brooks Robert , Makover Eran
Published: July 2002

We present a collection of results whose central theme is that the phenomenon of the first eigenvalue of the Laplacian being large is typical for Riemann surfaces. Our main analytic tool is a method for studying how the hyperbolic metric on a Riemann surface behaves under compactification of the surface. We make the notion of picking a Riemann surface at random by modeling this process on the process of picking a random

3
3

-regular graph. With this model, we show that there are positive constants

C
1

C_1

and

C
2

C_2

independent of the genus, such that with probability at least

C
1

C_1

, a randomly picked surface has first eigenvalue at least

C
2

C_2

.
Admissible nilpotent coadjoint orbits of p-adic reductive Lie groups
Authors: Nevins Monica
Published: July 2002

The orbit method conjectures a close relationship between the set of irreducible unitary representations of a Lie group

G
G

, and admissible coadjoint orbits in the dual of the Lie algebra. We define admissibility for nilpotent coadjoint orbits of

p
p

-adic reductive Lie groups, and compute the set of admissible orbits for a range of examples. We find that for unitary, symplectic, orthogonal, general linear and special linear groups over

p
p

-adic fields, the admissible nilpotent orbits coincide with the so-called special orbits defined by Lusztig and Spaltenstein in connection with the Springer correspondence.
Transcription, β–like DNA polymerases and hypermutation
Authors: Reynaud Claude–Agnès , Frey Stéphane , Aoufouchi Saïd , Faili Ahmad , Bertocci Barbara , Dahan Auriel , Flatter Eric , Delbos Frédéric , Storck Sébastien , Zober Carole , Weill Jean–Claude
Published: July 2002

This paper discusses two aspects of immunoglobulin (Ig) gene hypermutation. In the first approach, a transcription termination signal is introduced in an Ig light chain transgene acting as a mutation substrate, and transgenic lines are generated with control and mutant transgenes integrated in tandem. Analysis of transcription levels and mutation frequencies between mutant and control transgenes clearly dissociates transcription elongation and mutation, and therefore argues against models whereby specific pausing of the RNA polymerase during V gene transcription would trigger an error–prone repair process. The second part reports the identification of two novel β–like DNA polymerases named Pol λ and Pol μ, one of which (Pol μ) represents a good candidate for the Ig mutase due to its higher lymphoid expression and its similarity with the lymphoid enzyme terminal deoxynucleotidyl transferase. Peculiar features of the expression of this gene, including an unusual splicing variability and a splicing inhibition in response to DNA–damaging agents, are discussed.
Gene3D: Structural Assignment for Whole Genes and Genomes Using the CATH Domain Structure Database
Authors: Buchan Daniel W.A. , Shepherd Adrian J. , Lee David , Pearl Frances M.G. , Rison Stuart C.G. , Thornton Janet M. , Orengo Christine A.
Published: July 2002

We present a novel web-based resource,Gene3D, of precalculated structural assignments to gene sequences and whole genomes. This resource assigns structural domains from the CATH database to whole genes and links these to their curated functional and structural annotations within the CATH domain structure database, the functional Dictionary of Homologous Superfamilies (DHS) and PDBsum. CurrentlyGene3D provides annotation for 36 complete genomes (two eukaryotes, six archaea, and 28 bacteria). On average, between 30% and 40% of the genes of a given genome can be structurally annotated. Matches to structural domains are found using the profile-based method (PSI-BLAST). and a novel protocol, DRange, is used to resolve conflicts in matches involving different homologous superfamilies.
Classification of G‐protein coupled receptors by alignment‐independent extraction of principal chemical properties of primary amino acid sequences
Authors: Lapinsh Maris , Gutcaits Alexandrs , Prusis Peteris , Post Claes , Lundstedt Torbjörn , Wikberg Jarl E.S.
Published: July 2002

We have developed an alignment‐independent method for classification of G‐protein coupled receptors (GPCRs) according to the principal chemical properties of their amino acid sequences. The method relies on a multivariate approach where the primary amino acid sequences are translated into vectors based on the principal physicochemical properties of the amino acids and transformation of the data into a uniform matrix by applying a modified autocross‐covariance transform. The application of principal component analysis to a data set of 929 class A GPCRs showed a clear separation of the major classes of GPCRs. The application of partial least squares projection to latent structures created a highly valid model (cross‐validated correlation coefficient, Q2 = 0.895) that gave unambiguous classification of the GPCRs in the training set according to their ligand binding class. The model was further validated by external prediction of 535 novel GPCRs not included in the training set. Of the latter, only 14 sequences, confined in rapidly expanding GPCR classes, were mispredicted. Moreover, 90 orphan GPCRs out of 165 were tentatively identified to GPCR ligand binding class. The alignment‐independent method could be used to assess the importance of the principal chemical properties of every single amino acid in the protein sequences for their contributions in explaining GPCR family membership. It was then revealed that all amino acids in the unaligned sequences contributed to the classifications, albeit to varying extent; the most important amino acids being those that could also be determined to be conserved by using traditional alignment‐based methods.
A new three‐dimensional dose distribution reduction scheme for tubular organs
Authors: Zhou S. M. , Marks L. B. , Tracton G. S. , Sibley G. S. , Light K. L. , Maguire P. D. , Anscher M. S.
Published: July 2002

In tubular structures, spatial aspects of the dose distribution may be important in determining the normal tissue response. Conventional dose‐volume‐histograms (DVHs) and dose‐surface‐histograms (DSHs) lack spatial information and may not be adequate to represent the three‐dimensional (3D) dose data. A new 3D dose distribution data reduction scheme which preserves its longitudinal and circumferential character is presented. Dose distributions were generated at each axial level for esophagus or rectum in 123 patients with lung cancer or prostate cancer. Dose distribution histograms at each axial level were independently analyzed along the esophageal or rectal circumference to generate dose‐circumference‐histogram (DCH) sheets. Two types of plots were then generated from the DCH sheet. The first considered the percentage of the circumference at each axial level receiving various doses. The second considered the minimum dose delivered to any percentage of the circumference at each axial level. The DCH as a treatment planning tool can be easily implemented in a 3D planing system and is potentially useful for the study of the relationship between the complication risk and the longitudinal and circumferential dose distributions.
Practical aspects of in situ activation using a conventional medical accelerator for the purpose of perfusion imaging
Authors: Oldham M. , Sapareto S. A. , Li X. A. , Allen J. , Sutlief S. , Wong O. C. , Wong J. W.
Published: July 2002

We report investigations into the feasibility of generating radioactive oxygen a positron emitter, with half‐life 2.05 min) using a tuned Elekta SL25 accelerator, for the end purpose of imaging tumor perfusion. is produced by the “gamma, neutron,” (γ,n) reaction between high‐energy photons and normal oxygen in the body. As most in vivo is bound in water molecules the radio‐marker is produced in proportion to water content in tissue. Imaging the washout of the distribution using sensitive positron‐emission‐tomography (PET) technology can yield spatial information about blood perfusion in the tissue. The aim of this article was to determine the amount of activity that could be produced by the tuned medical accelerator. A further aim was to model the activation process using Monte Carlo and to investigate ways to optimize the amount of that could be generated. Increased activation was achieved by (i) tuning the beam to give higher‐energy electrons incident on the target of the accelerator, (ii) increasing dose rate by removing the conventional filtration in the beam and reducing the source to object distance, and (iii) reducing low‐energy photons by means of a carbon block absorber. The activity per‐unit‐dose produced by the tuned beam was measured by irradiating spheres of water to known doses and placing the spheres in a calibrated coincidence‐counting apparatus. Peak energy of the tuned bremsstrahlung beam was estimated at 29 MeV, and generated activity up to 0.24μCi/cc/3Gy in water. The measured amount of agreed to within 10% of the prediction from the Monte‐Carlo‐computed spectrum, indicating reasonable ability to model the activation process. The optimal thickness of the carbon absorber was found to be about 25 cm. The insertion of a carbon absorber improved spectral quality for activation purposes but at the cost of reduced dose rate. In conclusion, the viability of generating with an Elekta SL25 has been demonstrated. In conjunction with recent advances in high‐sensitivity portable PET imaging devices, real potential exists for imaging in situ activated washout as a surrogate measurement of macroscopic tumor perfusion.
Three‐dimensional tomosynthetic image restoration for brachytherapy source localization
Authors: Persons Timothy M.
Published: July 2002

Tomosynthetic image reconstruction allows for the production of a virtually infinite number of slices from a finite number of projection views of a subject. If the reconstructed image volume is viewed in toto, and the three‐dimensional (3D) impulse response is accurately known, then it is possible to solve the inverse problem (deconvolution) using canonical image restoration methods (such as Wiener filtering or solution by conjugate gradient least squares iteration) by extension to three dimensions in either the spatial or the frequency domains. This dissertation presents modified direct and iterative restoration methods for solving the inverse tomosynthetic imaging problem in 3D. The significant blur artifact that is common to tomosynthetic reconstructions is deconvolved by solving for the entire 3D image at once. The 3D impulse response is computed analytically using a fiducial reference schema as realized in a robust, self‐calibrating solution to generalized tomosynthesis. 3D modulation transfer function analysis is used to characterize the tomosynthetic resolution of the 3D reconstructions. The relevant clinical application of these methods is 3D imaging for brachytherapy source localization. Conventional localization schemes for brachytherapy implants using orthogonal or stereoscopic projection radiographs suffer from scaling distortions and poor visibility of implanted seeds, resulting in compromised source tracking (reported errors: 2–4 mm) and dosimetric inaccuracy. 3D image reconstruction (using a well‐chosen projection sampling scheme) and restoration of a prostate brachytherapy phantom is used for testing. The approaches presented in this work localize source centroids with submillimeter error in two Cartesian dimensions and just over one millimeter error in the third.
Brachytherapy dose–volume histogram computations using optimized stratified sampling methods
Authors: Karouzakis K. , Lahanas M. , Milickovic N. , Giannouli S. , Baltas D. , Zamboglou N.
Published: July 2002

A stratified sampling method for the efficient repeated computation of dose–volume histograms (DVHs) in brachytherapy is presented as used for anatomy based brachytherapy optimization methods. The aim of the method is to reduce the number of sampling points required for the calculation of DVHs for the body and the PTV. From the DVHs are derived the quantities such as Conformity Index COIN and COIN integrals. This is achieved by using partial uniform distributed sampling points with a density in each region obtained from a survey of the gradients or the variance of the dose distribution in these regions. The shape of the sampling regions is adapted to the patient anatomy and the shape and size of the implant. For the application of this method a single preprocessing step is necessary which requires only a few seconds. Ten clinical implants were used to study the appropriate number of sampling points, given a required accuracy for quantities such as cumulative DVHs, COIN indices and COIN integrals. We found that DVHs of very large tissue volumes surrounding the PTV, and also COIN distributions, can be obtained using a factor of 5–10 times smaller the number of sampling points in comparison with uniform distributed points.
C‐Arm imaging for brachytherapy source reconstruction: Geometrical accuracy
Authors: Fung Albert Y. C.
Published: July 2002

We study the accuracy of brachytherapy source reconstruction using C‐Arm images. We use a phantom embedded with dummy ribbons in a regular pattern, placed at the rotation center of the C‐Arm. With a commercial reconstruction jig, radiographic films are taken without the image intensifier. The average error in reconstructed seed coordinates is 0.1 cm. However, the jig is inconvenient for patient procedures. For C‐Arm reconstruction without the jig, the magnifications of the image intensifier along orthogonal directions are different. We “stretch” the image to equalize the magnifications. Afterward, seed reconstruction has an average error of 0.1 cm in all directions.
Empirical and theoretical investigation of the noise performance of indirect detection, active matrix flat‐panel imagers (AMFPIs) for diagnostic radiology
Authors: Siewerdsen J. H. , Antonuk L. E. , El‐Mohri Y. , Yorkston J. , Huang W. , Boudry J. M. , Cunningham I. A.
Published: July 2002

Noise properties of active matrix, flat‐panel imagers under conditions relevant to diagnostic radiology are investigated. These studies focus on imagers based upon arrays with pixels incorporating a discrete photodiode coupled to a thin‐film transistor, both fabricated from hydrogenated amorphous silicon. These optically sensitive arrays are operated with an overlying x‐ray converter to allow indirect detection of incident x rays. External electronics, including gate driver circuits and preamplification circuits, are also required to operate the arrays. A theoretical model describing the signal and noise transfer properties of the imagers under conditions relevant to diagnostic radiography, fluoroscopy, and mammography is developed. This frequency‐dependent model is based upon a cascaded systems analysis wherein the imager is conceptually divided into a series of stages having intrinsic gain and spreading properties. Predictions from the model are compared with x‐ray sensitivity and noise measurements obtained from individual pixels from an imager with a pixel format of 1536×1920 pixels at a pixel pitch of 127 μm. The model is shown to be in excellent agreement with measurements obtained with diagnostic x rays using various phosphor screens. The model is used to explore the potential performance of existing and hypothetical imagers for application in radiography, fluoroscopy, and mammography as a function of exposure, additive noise, and fill factor. These theoretical predictions suggest that imagers of this general design incorporating a CsI:Tl intensifying screen can be optimized to provide detective quantum efficiency (DQE) superior to existing screen‐film and storage phosphor systems for general radiography and mammography. For fluoroscopy, the model predicts that with further optimization of a‐Si:H imagers, DQE performance approaching that of the best x‐ray image intensifier systems may be possible. The results of this analysis suggest strategies for future improvements of this imaging technology.
X‐ray imaging with amorphous selenium: Theoretical feasibility of the liquid crystal light valve for radiography
Authors: Rieppo Pia‐Krista , Rowlands J. A.
Published: July 2002

A novel radiographic imaging system based on a liquid crystal light valve is described. A liquid crystal light valve is a photon addressed spatial light modulator that consists of a high resolution, solid‐state electrostatic detector (photoconductor) and an electro‐optic light modulator (liquid crystal cell) physically coupled in a sandwich structure. We propose a light valve with a thick, x‐ray sensitive photoconductive layer and call the system under study the x‐ray light valve (XLV). The image formation in the XLV is based on x‐ray exposure controlled modulation of light from an external source; the XLV is essentially an x‐ray image intensifier that allows the image brightness to be adjusted independently from the x‐ray exposure. Thus the XLV may be coupled to an optical imager, such as a charge coupled device (CCD), for image digitization without a secondary quantum sink. A model of the XLV operation is developed to investigate its sensitivity, speed, noise, and resolution. The imaging properties of the XLV are found to be time dependent, which leads to an unusual transmission versus exposure characteristic. The feasibility of clinical use of the XLV based on amorphous selenium (‐Se) photoconductor and a twisted nematic liquid crystal cell is analyzed, and the device is shown to be adaptable to a variety of radiographic imaging tasks.
Establishing minimum performance standards, calibration intervals, and optimal exposure values for a whole breast digital mammography unit
Authors: Kimme‐Smith C. , Lewis Candace , Beifuss Manuel , Williams Mark B. , Bassett L. W.
Published: July 2002

Methods are developed to establish minimum performance standards, calibration intervals, and criteria for exposure control for a whole breast digital mammography system. A prototype phantom was designed, and an automatic method programmed, to analyze CNR, resolution, and dynamic range between CCD components in the image receptor and over time. The phantom was imaged over a 5 month period and the results are analyzed to predict future performance. White field recalibration was analyzed by subtracting white fields obtained at different intervals. Exposure effects were compared by imaging the prototype phantom at different kVp, filtration (Mo vs Rh) and mAs. Calcification detection tests showed that phantom images, obtained at 28 kVp with a Mo/Mo anode/filter and low mAs technique, often could not depict specks 0.24 mm in diameter, while a 28 kVp Mo/Rh, higher mAs technique usually could. Stability of the system tested suggests that monthly phantom imaging may suffice. Differences in CCD performance are greater (12%) than differences in a single CCD over time (6%). White field recalibration is needed weekly because of pixel variations in sensitivity which occur if longer intervals between recalibration occur. When mean glandular dose is matched, Rh filtration gives better phantom performance at 28 kVp than Mo filtration at 26 kVp and is recommended for clinical exposures. An aluminum step wedge shows markedly increased dynamic range when exit exposure is increased by using a higher energy spectrum beam. Phantoms for digital mammography units should cover the entire image receptor, should test intersections between components of the receptor, and should be automatically analyzed.
In vivo dosimetry with a liquid‐filled electronic portal imaging device
Authors: Boellaard R.
Published: July 2002

The thesis describes the use of a liquid‐filled electronic portal imaging device, EPID, for in vivo dosimetry, i.e., for the verification of transmission, exit, and midplane dose. First, the application of the EPID to measure the transmission dose, i.e., the dose behind the patient, was investigated under various clinical conditions. For this purpose corrections for the nonlinear response of the EPID with dose and the effects of photon scatter in the EPID were performed. Next, a convolution model was developed to convert transmission dose images to exit and midplane dose distributions in the patient. Patient inhomogeneities are taken into account by using the radiological path length through the patient, which is derived from the measured transmission dose, i.e., without using patient data (CT). Finally, the accuracy of EPID exit and midplane dose measurements was determined for several homogeneous and inhomogeneous phantoms in open and wedged beams and for a few patients treated for larynx, breast, lung and prostate cancer. It was found that for most phantoms exit and midplane doses agree within 2% (1 s.d.) with ionization chamber measurements. EPID midplane dose measurements during patient treatment generally agreed within 2.5% with 3D treatment planning calculations. Occasionally larger differences were observed due to differences between the actual patient anatomy during treatment and the patient CT data, used for treatment planning. It is concluded that transmission dosimetry with a liquid‐filled EPID can be used to determine the 2D exit and midplane dose for several treatment sites in clinical practice and to quantify the influence of anatomical changes on the dose delivery.
Phenomenological dose model for therapeutic photon beams: Basic concepts and definitions
Authors: Nizin Paul S.
Published: July 2002

A model for central‐axis absorbed dose in therapeutic photon beams is developed. An expression for absorbed dose in a unit density material, including that in the regions of longitudinal and lateral electronic disequilibrium, is derived. The model is based on the concept of primary and scatter. Primary and scatter dose components are approximated using two identical analytical functions. Monte Carlo simulated dose data for gamma rays and 15 MV x rays in water are used to test the model. The accuracy of the model is demonstrated.
Beth’s experiment using optical tweezers
Authors: Moothoo D. N. , Arlt J. , Conroy R. S. , Akerboom F. , Voit A. , Dholakia K.
Published: July 2002

We show how a student may construct simple and versatile optical tweezers to manipulate micron-sized particles. The tweezers apparatus is used to set birefringent calcite particles into rotation using circularly polarized light. This demonstrates the mechanical transfer of the angular momentum associated with circularly polarized light from the laser beam to the trapped particle. This offers the student a method for performing Beth’s experiment qualitatively in the undergraduate laboratory.
Using video analysis to investigate intermediate concepts in classical mechanics
Authors: Wehrbein William M.
Published: July 2002

While used primarily in the introductory course to investigate basic principles, video analysis can be utilized to illustrate more advanced topics, such as the motion of a rigid body and the normal modes of coupled oscillators.
The quantum pendulum: Small and large
Authors: Baker G. L. , Blackburn J. A. , Smith H. J. T.
Published: July 2002

The quantum pendulum finds application in surprising contexts. We use commercially available software to numerically solve the Schrödinger equation for a microscopic pendulum subject to molecular (electromagnetic) restoring forces, and a macroscopic pendulum subject to a gravitational restoring force. The dynamics of the microscopic quantum pendulum are closely related to molecular motions known as hindered rotations. We use standard probabilistic methods to predict whether this motion is weakly or strongly hindered at ambient temperature and test the prediction against experimental data for C2H6 and K2PtCl6. For the macroscopic gravitational pendulum, we examine the uncertainty in position and find, not surprisingly, that it is too small to measure physically, but is nevertheless relatively large compared to present-day limits in computation. The latter juxtaposition of computational precision with quantum uncertainty has consequences for the study of chaotic dynamics.
Positronium in the undergraduate laboratory
Authors: Yuly M.
Published: July 2002

Positronium is an exotic atom formed by an electron and its antiparticle, the positron. Orthopositronium, which is the state with total spin 1, has a decay constant of about 7.05 μs−1 and decays primarily into three gamma rays. A relatively simple experiment is described which will allow students to detect and measure the lifetime of orthopositronium in gases using apparatus often found at undergraduate institutions. Other effects, such as parapositronium decay, pick-off, and thermalization, can also be demonstrated.
Harmonic and anharmonic oscillations investigated by using a microcomputer-based Atwood’s machine
Authors: Pecori Barbara , Torzo Giacomo , Sconza Andrea
Published: July 2002

We describe how the Atwood’s machine, interfaced to a personal computer through a rotary encoder, is suited for investigating harmonic and anharmonic oscillations, exploiting the buoyancy force acting on a body immersed in water. We report experimental studies of oscillators produced by driving forces of the type F=−kxn with n=1,2,3, and F=−k sgn(x). Finally we suggest how this apparatus can be used for showing to the students a macroscopic model of interatomic forces.
Resource Letter TF-1: Turbulence in fluids
Authors: Nelkin Mark
Published: July 2002

This Resource Letter provides a guide to the literature on fully developed turbulence in fluids. It is restricted to mechanically driven turbulence in an incompressible fluid described by the Navier–Stokes equations of hydrodynamics, and places greatest emphasis on fundamental physical questions. Journal articles and books are cited for the following topics: the Navier–Stokes equations, qualitative aspects of turbulence, the 1941 Kolmogorov theory, intermittency and small scale structure, time correlations and pressure; with brief mention of two-dimensional turbulence, passive scalars in turbulence, and the turbulent boundary layer. Turbulent fluid flows are ubiquitous in the atmosphere, the oceans, and the stars. They also occur in a wide variety of engineering applications. Most studies of turbulence have an applied objective, whether this application be to engineering, to geophysics, to astrophysics, or to weather predicition. But there is a basic problem in physics underlying all of these applications. This Resource Letter provides a guide to the literature relevant to this problem.
Investigating collisional broadening of spectral lines using a tuning fork: An undergraduate laboratory
Authors: Boreen Anne L. , Coons Renae L. , Ulness Darin J. , Luther Bryan A.
Published: July 2002

An intuitive laboratory experiment designed to study the phenomenon of collisional (or pressure) broadening is presented. Molecular collisions are modeled by striking a tuning fork with a mallet. The response of the tuning fork is recorded via microphone by a computer. These time domain data can be transformed numerically to reveal the frequency spectrum. Results corresponding to a range of pressures from 0 to 111 kPA are presented.
Compressibility effects on steady streaming from a noncompact rigid sphere
Authors: Gopinath Ashok , Trinh Eugene H.
Published: July 2002

The problem of steady streaming around a rigid isolated sphere in a plane standing acoustic field is considered. Existing results in the literature have been generalized to allow for noncompactness of the sphere, and the influence of fluid compressibility on the streaming behavior has been included. It is found that in the high-frequency limit of interest for which the streaming is strongest, the effective steady slip velocity at the edge of the inner boundary layer region that is responsible for driving the steady streaming in the bulk of the fluid in the outer region, has a complex variation over the surface of the sphere that depends on (i) the sphere position (with respect to the node/antinode of the acoustic field), (ii) the extent of sphere compactness, and (iii) on a well-defined function (representing compressibility effects) of the fluid Prandtl number and its ratio of specific heats. Not surprisingly, the contribution from this function is negligible when the host fluid is a liquid. The steady streaming behavior around the sphere is demonstrated with the help of flow streamlines for various cases in the diffusive limit of weak outer flow for low streaming Reynolds numbers.
Estimation of broadband acoustic power due to rib forces on a reinforced panel under turbulent boundary layer-like pressure excitation. I. Derivations using string model
Authors: Rumerman M. L.
Published: July 2002

This paper shows that, when the attachment forces on a rib-reinforced panel subjected to turbulent boundary layer (TBL) excitation can be considered to radiate independently, the rib-related acoustic power in a broad (e.g., one-third octave) frequency band can be estimated as the product of the average mean-squared force, the real part of the radiation admittance of an attachment force, and the number of ribs. Using a simple model of a string with point mass or spring attachments, an approach is developed for estimating the average mean-squared force in broad frequency bands. The results are in a form that can be applied to ribbed plates and shells. The following paper establishes the condition under which the ribs can be considered to radiate independently, and presents the results of validating calculations for steel plates in water.
A design study of an acoustic system suitable for differentiating between orange roughy and other New Zealand deep-water species
Authors: Barr Richard
Published: July 2002

Using the simple slab-cylinder acoustic model for fish, developed by Clay and Horne [J. Acoust. Soc. Am. 96, 1661–1668 (1994)], the target strengths of three of New Zealand’s deep-water fish species, namely orange roughy, black oreos, and smooth oreos, have been derived. The target strengths derived for the model fish have been found to be in reasonable agreement with currently accepted target strength values. These three model fish were used in a study to test the species discrimination of a chirp sonar system. Chirps of center frequencies 40, 80, and 160 kHz and bandwidth of 10, 20, and 40 kHz have been used to acoustically illuminate the three fish species listed above and the matched, filtered responses to the chirps determined. The effect of the response of transducer or system bandwidth has also been investigated. It has been found that the bandwidth of the chirp is much more important for resolving detail in a fish target than the chirp center frequency. A bandwidth of at least 20 kHz, and preferably 40 kHz, produces matched filtered responses for black and smooth oreos and orange roughy which are quite clearly species specific. Results suggest that with orange roughy it may be possible to size and even sex the targets acoustically.
Modeling elastic wave forward propagation and reflection using the complex screen method
Authors: Xie Xiao-Bi , Wu Ru-Shan
Published: July 2002

Formulation for calculating forward propagation and reflection in a 3D elastic structure based on the complex-screen method is given in this paper. The calculation of reflections is formulated based on the local Born approximation. When using a small angle approximation, the backscattering operator reduces to a screen operator which is similar to the forward screen propagator. Combining the forward propagator and backscattering operator together, the new method can properly handle the multiple forward scattering and single backscattering in a 3D heterogeneous model. Using a dual-domain technique, the new method is highly efficient in CPU time and memory savings. For models where reverberation and resonance scattering can be neglected, this method provides a fast and accurate algorithm. Synthetic seismograms for two-dimensional elastic models are calculated with this method and compared with those generated by the finite-difference method. The results show that the method works well for small to medium scattering angles and medium velocity contrasts.
An inverse dynamics approach to face animation
Authors: Pitermann Michel , Munhall Kevin G.
Published: July 2002

Muscle-based models of the human face produce high quality animation but rely on recorded muscle activity signals or synthetic muscle signals that are often derived by trial and error. This paper presents a dynamic inversion of a muscle-based model (Lucero and Munhall, 1999) that permits the animation to be created from kinematic recordings of facial movements. Using a nonlinear optimizer (Powell’s algorithm), the inversion produces a muscle activity set for seven muscles in the lower face that minimize the root mean square error between kinematic data recorded with OPTOTRAK and the corresponding nodes of the modeled facial mesh. This inverted muscle activity is then used to animate the facial model. In three tests of the inversion, strong correlations were observed for kinematics produced from synthetic muscle activity, for OPTOTRAK kinematics recorded from a talker for whom the facial model is morphologically adapted and finally for another talker with the model morphology adapted to a different individual. The correspondence between the animation kinematics and the three-dimensional OPTOTRAK data are very good and the animation is of high quality. Because the kinematic to electromyography (EMG) inversion is ill posed, there is no relation between the actual EMG and the inverted EMG. The overall redundancy of the motor system means that many different EMG patterns can produce the same kinematic output.
A new way to account for binaural detection as a function of interaural noise correlation
Authors: van der Heijden Marcel , Trahiotis Constantine
Published: July 2002

The purpose of this communication is to describe a new method for predicting masking level differences (MLDs) as a function of the interaural correlation of the masking noise. The general idea is to decompose a binaural noise masker having an arbitrary value of interaural correlation into two parts: an No constituent and an Nπ constituent. It is shown that the amount of masking produced by a noise having an arbitrary interaural correlation is equal to the addition of the masking effects produced by the No and Nπ constituents that compose the masker. The new approach was used to generate predictions of MLDs for NρSπ and NρSo conditions. Those predictions accounted for 98% of the variance in the classical data of Robinson and Jeffress [J. Acoust. Soc. Am. 35, 1947–1952 (1963)]. Finally, it is shown that the “additivity of masking” method is mathematically equivalent to assuming that binaural detection consists of a stage of errorless binaural processing preceded by a corrupted representation of the stimulus.
All-frequency normal-mode solution of the three-dimensional acoustic scattering from a vertical cylinder in a plane-horizontal waveguide
Authors: Athanassoulis Gerassimos A. , Belibassakis Konstadinos A.
Published: July 2002

The three-dimensional acoustic scattering from a vertical, impenetrable cylinder in a waveguide is studied. The analytical solution of the problem, for a Dirichlet or a Neumann boundary condition on the scatterer, has been derived recently by Athanassoulis and Prospathopoulos [J. Acoust. Soc. Am. 100, 206–218 (1996)] in the form of a double-infinite normal-mode series, representing the total acoustic field. In order to extend the applicability of this solution to higher frequencies, the total field is decomposed into the incident and the scattered parts. A series expansion for the scattered field is obtained, and the critical parameter controlling its azimuthal convergence is shown to be the nondimensional wave number ka based on the radius a of the cylinder. The general term of the series starts to decay exponentially immediately after the azimuthal index has exceeded the critical value ka, a fact justifying the introduction of the concept of azimuthal-evanescent modes. By exploiting the above decomposition, the direct numerical summation of the normal-mode series becomes feasible up to ka≈1000. For calculations at even higher frequencies (ka→∞), asymptotic expressions are derived by using appropriate integral representations of Bessel and Hankel functions, in conjunction with the method of stationary phase. The asymptotic analysis shows that the scattered field is obtained as a superposition of 2-D point sources lying on the boundary of the vertical cylinder, with appropriate amplitudes and phases. Excellent agreement between asymptotic and direct summation numerical results has been demonstrated, at moderate frequencies, where both representations are expected to be valid.
Numerical investigation of fracture interface waves
Authors: Gu Boliang , Nihei Kurt T. , Myer Larry R.
Published: July 2002

Two-dimensional boundary element simulations are conducted to investigate the properties of Rayleigh-type fracture interface waves generated by a line source located near a single fracture. The fracture is modeled as a displacement–discontinuity boundary condition between two elastic half-spaces with identical properties. Numerical simulations are performed for different fracture stiffnesses, source polarizations, and source depths. Symmetric and antisymmetric fracture interface waves are observed with amplitudes and velocities that are controlled by the ratio of the fracture impedance to the half-space shear wave impedance, as predicted by plane-wave theory [Gu et al., J. Geophys. Res. 101, 827–835 (1996); Pyrak-Nolte and Cook, Geophys. Res. Lett. 14, 1107–1110 (1987)]. When the source is located off the fracture, these waves develop at incidence angles that decrease with source depth.
Effect of the relative phase of amplitude modulation on the detection of modulation on two carriers
Authors: Furukawa Shigeto , Moore Brian C. J.
Published: July 2002

This study examined how effectively information about amplitude modulation (AM) on two carriers is combined, and whether the detection of AM depends on the relative phase of the AM across carriers. Psychometric functions were measured for detecting 5-Hz sinusoidal AM of carriers with frequencies 1100 and 1925 Hz, with a mean level 65 dB SPL for each carrier. The carriers had a duration of 400 ms with 50-ms raised-cosine ramps on either side of this. A single cycle of 5-Hz sinusoidal AM (200 ms in duration) was imposed on the temporal center of the stimulus, with 100-ms steady-state fringes before and after the modulation. The modulators for the two carriers were either in phase or in antiphase. The modulation of each carrier was equally detectable, as determined in a preliminary experiment. A continuous pink noise background was used to mask the outputs of auditory filters tuned between the two carrier frequencies. There was no effect of relative modulator phase. However, performance was consistently better than predicted from the assumption that information about AM from the two carriers is processed independently and combined optimally. The results are discussed in terms of (1) predictions using Dau’s “modulation filter bank model” [T. Dau et al., in Psychoacoustics, Speech and Hearing Aids, edited by B. Kollmeier (World Scientific, Singapore, 1996), pp. 45–48], and (2) the fact that relative modulator phase does have an effect on the detection of frequency modulation on two carriers, as found by Furukawa and Moore [J. Acoust. Soc. Am. 100, 2299–2311 (1996)].
Context effects in the auditory identification of Spanish fricatives /f/ and /θ/: Hyper and Hypospeech
Authors: Feijóo Sergio , Fernández Santiago , Balsa Ramón
Published: July 2002

Twenty-eight subjects heard 40 Spanish words in which the initial fricative was /f/ or /θ/, combined with vowels /e/ and /u/. Ten words were used for each particular combination (2 fricatives×2 vowels ×10 words). Two forms of speech (Hypo and Hyperspeech) and four conditions were considered: (1) Isolated fricative segment; (2) fricative segment + 51.2 ms of the following vowel; (3) fricative + whole following vowel; (4) whole word. The statistical analysis showed that, despite their differences in production and acoustic characteristics, isolated fricative segments were equally recognized in Hypo and Hyperspeech (cond. 1). Including the vowel ( conditions 2 and 3) significantly improved recognition of both fricatives for both forms of speech, except for the combination /f/+/e/: While fricative identification improves slightly in Hyperspeech, in Hypospeech, recognition decreases with respect to cond. (1). For this particular combination, an acceptable recognition rate is only achieved in the whole word condition for both forms of speech. The results indicate that: (a) Clear speech is not necessarily more intelligible than hypospeech; and (b) The role of vocalic context in the recognition of /f/ and /θ/ is similar for both forms of speech.
A note about acoustic streaming: Comparison of C. E. Bradley’s and W. L. Nyborg’s theories
Authors: Zhao Xiaoliang , Zhu Zhemin , Du Gonghuan
Published: July 2002

Some comparisons of C. E. Bradley’s and W. L. Nyborg’s theories on acoustic streaming are given.