bluuebunny/crossref_metadata_2025 huggingface dataset:
Dual Effects of Adp and Adenylylimidodiphosphate on Cftr Channel Kinetics Show Binding to Two Different Nucleotide Binding Sites
Authors: Weinreich Frank , Riordan John R. , Nagel Georg
Published: July 2002

The CFTR chloride channel is regulated by phosphorylation by protein kinases, especially PKA, and by nucleotides interacting with the two nucleotide binding domains, NBD-A and NBD-B. Giant excised inside-out membrane patches from Xenopus oocytes expressing human epithelial cystic fibrosis transmembrane conductance regulator (CFTR) were tested for their chloride conductance in response to the application of PKA and nucleotides. Rapid changes in the concentration of ATP, its nonhydrolyzable analogue adenylylimidodiphosphate (AMP-PNP), its photolabile derivative ATP-P3-[1-(2-nitrophenyl)ethyl]ester, or ADP led to changes in chloride conductance with characteristic time constants, which reflected interaction of CFTR with these nucleotides. The conductance changes of strongly phosphorylated channels were slower than those of partially phosphorylated CFTR. AMP-PNP decelerated relaxations of conductance increase and decay, whereas ATP-P3-[1-(2-nitrophenyl)ethyl]ester only decelerated the conductance increase upon ATP addition. ADP decelerated the conductance increase upon ATP addition and accelerated the conductance decay upon ATP withdrawal. The results present the first direct evidence that AMP-PNP binds to two sites on the CFTR. The effects of ADP also suggest two different binding sites because of the two different modes of inhibition observed: it competes with ATP for binding (to NBD-A) on the closed channel, but it also binds to channels opened by ATP, which might either reflect binding to NBD-A (i.e., product inhibition in the hydrolysis cycle) or allosteric binding to NBD-B, which accelerates the hydrolysis cycle at NBD-A.
Berezin Quantization and Reproducing Kernels on Complex Domains
Authors: Englis Miroslav
Published: July 2002

LetΩ\Omegabe a non-compact complex manifold of dimensionnn,ω=∂∂¯Ψ\omega =\partial \overline \partial \Psia Kähler form onΩ\Omega, andKα(x,y¯)K_\alpha ( x,\overline y)the reproducing kernel for the Bergman spaceAα2A^2_\alphaof all analytic functions onΩ\Omegasquare-integrable against the measuree−αΨ|ωn|e^{-\alpha \Psi } |\omega ^n|. Under the condition\[Kα(x,x¯)=λαeαΨ(x)K_\alpha ( x,\overline x)= \lambda _\alpha e^{\alpha \Psi (x)}\]F. A. Berezin [Math. USSR Izvestiya 8 (1974), 1109–1163] was able to establish a quantization procedure on(Ω,ω)(\Omega ,\omega )which has recently attracted some interest. The only known instances when the above condition is satisfied, however, are justΩ=Cn\Omega = \mathbf {C} ^nandΩ\Omegaa bounded symmetric domain (with the euclidean and the Bergman metric, respectively). In this paper, we extend the quantization procedure to the case when the above condition is satisfied only asymptotically, in an appropriate sense, asα→+∞\alpha \to +\infty. This makes the procedure applicable to a wide class of complex Kähler manifolds, including all planar domains with the Poincaré metric (if the domain is of hyperbolic type) or the euclidean metric (in the remaining cases) and some pseudoconvex domains inCn\mathbf {C}^n. Along the way, we also fix two gaps in Berezin’s original paper, and discuss, forΩ\Omegaa domain inCn\mathbf {C}^n, a variant of the quantization which uses weighted Bergman spaces with respect to the Lebesgue measure instead of the Kähler-Liouville measure|ωn||\omega ^n|.
Quality local refinement of tetrahedral meshes based on 8-subtetrahedron subdivision
Authors: Liu Anwei , Joe Barry
Published: July 2002

Let

T

\mathcal {T}

be a tetrahedral mesh. We present a 3-D local refinement algorithm for

T

\mathcal {T}

which is mainly based on an 8-subtetrahedron subdivision procedure, and discuss the quality of refined meshes generated by the algorithm. It is proved that any tetrahedron

T

∈

T

\mathbf {T} \in \mathcal {T}

produces a finite number of classes of similar tetrahedra, independent of the number of refinement levels. Furthermore,

η
(

T

i

n

)
≥
c
η
(

T

)

\eta (\mathbf {T}_i^{n}) \geq c \eta (\mathbf {T})

, where

T

∈

T

\mathbf {T} \in \mathcal {T}

,

c
c

is a positive constant independent of

T

\mathcal {T}

and the number of refinement levels,

T

i

n

\mathbf {T}_i^{n}

is any refined tetrahedron of

T

\mathbf {T}

, and

η
\eta

is a tetrahedron shape measure. It is also proved that local refinements on tetrahedra can be smoothly extended to their neighbors to maintain a conforming mesh. Experimental results show that the ratio of the number of tetrahedra actually refined to the number of tetrahedra chosen for refinement is bounded above by a small constant.
Finding finite 𝐵₂-sequences faster
Authors: Lindström Bernt
Published: July 2002

A

B
2

B_2

-sequence is a sequence

a
1

>

a
2

>
⋯
>

a
r

a_1>a_2>\cdots >a_r

of positive integers such that the sums

a
i

+

a
j

a_i+a_j

,

1
≤
i
≤
j
≤
r

1\le i\le j\le r

, are different. When

q
q

is a power of a prime and

θ
\theta

is a primitive element in

G
F
(

q
2

)

GF(q^2)

then there are

B
2

B_2

-sequences

A
(
q
,
θ
)

A(q,\theta )

of size

q
q

with

a
q

>

q
2

a_q>q^2

, which were discovered by R. C. Bose and S. Chowla. In Theorem 2.1 I will give a faster alternative to the definition. In Theorem 2.2 I will prove that multiplying a sequence

A
(
q
,
θ
)

A(q,\theta )

by integers relatively prime to the modulus is equivalent to varying

θ
\theta

. Theorem 3.1 is my main result. It contains a fast method to find primitive quadratic polynomials over

G
F
(
p
)

GF(p)

when

p
p

is an odd prime. For fields of characteristic 2 there is a similar, but different, criterion, which I will consider in “Primitive quadratics reflected in

B
2

B_2

-sequences”, to appear in Portugaliae Mathematica (1999).
New Fibonacci and Lucas primes
Authors: Dubner Harvey , Keller Wilfrid
Published: July 2002

Extending previous searches for prime Fibonacci and Lucas numbers, all probable prime Fibonacci numbers

F

n

F_{n}

have been determined for

6000
>
n
≤
50000

6000 > n \le 50000

and all probable prime Lucas numbers

L

n

L_{n}

have been determined for

1000
>
n
≤
50000

1000 > n \le 50000

. A rigorous proof of primality is given for

F

9311

F_{9311}

and for numbers

L

n

L_{n}

with

n
=
1097

n = 1097

,

1361
1361

,

4787
4787

,

4793
4793

,

5851
5851

,

7741
7741

,

10691
10691

,

14449
14449

, the prime

L

14449

L_{14449}

having 3020 digits. Primitive parts

F

n

∗

F^{*}_{n}

and

L

n

∗

L^{*}_{n}

of composite numbers

F

n

F_{n}

and

L

n

L_{n}

have also been tested for probable primality. Actual primality has been established for many of them, including 22 with more than 1000 digits. In a Supplement to the paper, factorizations of numbers

F

n

F_{n}

and

L

n

L_{n}

are given for

n
>
1000

n > 1000

as far as they have been completed, adding information to existing factor tables covering

n
≤
1000

n \le 1000

.
Hyphal Elongation Is Regulated Independently of Cell Cycle inCandida albicans
Authors: Hazan Idit , Sepulveda-Becerra Marisa , Liu Haoping
Published: July 2002

The mechanism for apical growth during hyphal morphogenesis inCandida albicans is unknown. Studies fromSaccharomyces cerevisiae indicate that cell morphogenesis may involve cell cycle regulation by cyclin-dependent kinase. To examine whether this is the mechanism for hyphal morphogenesis, the temporal appearance of different spindle pole body and spindle structures, the cell cycle-regulated rearrangements of the actin cytoskeleton, and the phosphorylation state of the conserved Tyr19 of Cdc28 during the cell cycle were compared and found to be similar between yeast and serum-induced hyphal apical cells. These data suggest that hyphal elongation is not mediated by altering cell cycle progression or through phosphorylation of Tyr19 of Cdc28. We have also shown that germ tubes can evaginate before spindle pole body duplication, chitin ring formation, and DNA replication. Similarly, tip-associated actin polarization in each hypha occurs before the events of the G1/S transition and persists throughout the cell cycle, whereas cell cycle-regulated actin assemblies come and go. We have also shown that cells in phases other than G1can be induced to form hyphae. Hyphae induced from G1cells have no constrictions, and the first chitin ring is positioned in the germ tube at various distances from the base. Hyphae induced from budded cells have a constriction and a chitin ring at the bud neck, beyond which the hyphae continue to elongate with no further constrictions. Our data suggest that hyphal elongation and cell cycle morphogenesis programs are uncoupled, and each contributes to different aspects of cell morphogenesis.
Allergen and dust exposure as determinants of work-related symptoms and sensitization in a cohort of flour-exposed workers; a case–control analysis
Authors: Cullinan Paul , Cook Adrian , Nieuwenhuijsen Mark J. , Sandiford Colin , Tee Rosemary D. , Venables Katherine M. , McDonald J. Corbett , Taylor Anthony J. Newman
Published: July 2002

Objectives: To estimate the incidence of specific IgE sensitization and allergic respiratory symptoms among UK bakery and flour mill workers; and to examine the roles of flour aeroallergen and total dust exposures in determining these outcomes.

Methods: A cohort of 300 new employees, without previous occupational exposure to flour, were followed prospectively for a median (range) of 40 (1–91) months. Cases—defined as those developing work-related symptoms or a positive skin prick test to flour or α-amylase during follow up—were compared with controls, matched for duration of employment. Exposures to flour aeroallergen and total inhalable dust were estimated using a questionnaire and personal sampling techniques.

Results: Incidence rates for work-related eye/nose and chest symptoms were 11.8 and 4.1cases per 100person years (py), respectively. Fewer employees developed positive skin prick tests to flour (2.2cases per 100py) or α-amylase (2.5cases per 100py). Positive skin tests to occupational allergens were more common among those with new work-related symptoms. There were clear relationships between the risks of developing work-related symptoms or a positive skin prick test and three categories of estimated exposure to total dust or flour aeroallergen. Atopic employees were more likely to develop a positive skin prick test—but not work-related symptoms. These findings were unaffected by age, sex or cigarette smoking.

Conclusions: In this population, many work-related symptoms which develop after first employment in modern UK bakeries or flour mills were not accompanied by evidence of IgE sensitization to flour or α-amylase. Although average dust exposures were within current occupational standards, the risks of development of upper and lower respiratory symptoms and of specific sensitization were clearly related to total dust and/or flour aeroallergen exposure. The incidence of work-related chest symptoms in the presence of a positive skin test to flour or α-amylase in this setting was approximately 1case per 100py.
POLINA: detection and evaluation of single amino acid substitutions in protein superfamilies.
Authors: Levin S , Satir B H
Published: July 2002

MOTIVATION AND RESULTS: An algorithm is described for the quick identification and evaluation of amino acid substitutions in multiple protein sequence alignment. The strategy is based on the calculation of a relative conservation index for an amino acid at each position of the alignment. The algorithm is implemented in the computer program POLINA (Protein Oriented LINear Analysis) which provides a summary of analysis in a format suitable for import into a graphing program. AVAILABILITY: A copy of source code is available upon request from the authors or can be downloaded via the WWW at http://www.geocities.com/Athens/4654/POLINA.h tml. CONTACT: slevin@aecom.yu.edu; bsatir@aecom.yu.edu
CoPE: a collaborative pedigree drawing environment.
Authors: Brun-Samarcq L , Gallina S , Philippi A , Demenais F , Vaysseix G , Barillot E
Published: July 2002

SUMMARY: We developed a collaborative pedigree environment called CoPE. This environment includes a Java program for drawing pedigrees and a standardized system for pedigree storage. Unlike other existing pedigree programs, this software is particularly intended for epidemiologists in the sense that it allows customized automatic drawing of large numbers of pedigrees and remote and distributed consultation of pedigrees. AVAILABILITY: At http://www.infobiogen.fr/services/CoPE
PNAD-CSS: a workbench for constructing a protein name
abbreviation dictionary
Authors: Yoshida Mikio , Fukuda Ken-ichiro , Takagi Toshihisa
Published: July 2002

Motivation: Since their initial development, integration and construction of databases for molecular-level data have progressed. Though biological molecules are related to each other and form a complex system, the information is stored in the vast archives of the literature or in diverse databases. There is no unified naming convention for biological object, and biological terms may be ambiguous or polysemic. This makes the integration and interaction of databases difficult. In order to eliminate these problems, machine-readable natural language resources appear to be quite promising. We have developed a workbench for protein name abbreviation dictionary (PNAD) building.

Results: We have developed PNAD Construction Support System (PNAD-CSS), which offers various convenient facilities to decrease the construction costs of a protein name abbreviation dictionary of which entries are collected from abstracts in biomedical papers. The system allows the users to concentrate on higher level interpretation by removing some troublesome tasks, e.g. management of abstracts, extracting protein names and their abbreviations, and so on. To extract a pair of protein names and abbreviations, we have developed a hybrid system composed of the PROPER System and the PNAD System. The PNAD System can extract the pairs from parenthetical-paraphrases involved in protein names, the PROPER System identified these pairs, with 98.95% precision, 95.56% recall and 97.58% complete precision.

Availability: PROPER System is freely available from http://www.hgc.ims.u-tokyo.ac.jp/service/tooldoc/KeX/intro.html. The other software are also available on request. Contact the authors.

Contact: mikio@ims.u-tokyo.ac.jp
A higher-order background model improves the detection of
promoter regulatory elements by Gibbs sampling
Authors: Thijs Gert , Lescot Magali , Marchal Kathleen , Rombauts Stephane , De Moor Bart , Rouzé Pierre , Moreau Yves
Published: July 2002

Motivation: Transcriptome analysis allows detection and clustering of genes that are coexpressed under various biological circumstances. Under the assumption that coregulated genes share cis-acting regulatory elements, it is important to investigate the upstream sequences controlling the transcription of these genes. To improve the robustness of the Gibbs sampling algorithm to noisy data sets we propose an extension of this algorithm for motif finding with a higher-order background model.

Results: Simulated data and real biological data sets with well-described regulatory elements are used to test the influence of the different background models on the performance of the motif detection algorithm. We show that the use of a higher-order model considerably enhances the performance of our motif finding algorithm in the presence of noisy data. For Arabidopsis thaliana, a reliable background model based on a set of carefully selected intergenic sequences was constructed.

Availability: Our implementation of the Gibbs sampler called the Motif Sampler can be used through a web interface: http://www.esat.kuleuven.ac.be/~thijs/Work/MotifSampler.html.

Contact: gert.thijs@esat.kuleuven.ac.be; yves.moreau@esat.kuleuven.ac.be

* To whom correspondence should be addressed.
FINANCIAL MARKET RESPONSES TO MONETARY POLICY CHANGES IN THE 1990S
Authors: Urich Thomas , Wachtel Paul
Published: July 2002

The operating target for monetary policy in the United States has changed from borrowings in the late 1980s to a target range for the fed funds rate to a specific fed funds target. In addition, secrecy about the policy target has largely disappeared, and since 1994 policy targets have been announced immediately. This article explores the impact of policy decisions on short‐term interest rates as the policy announcements have changed. The authors find that the policy changes had a larger impact when the Fed moved to a specific emphasis on the fed funds rate. However, since the Fed began to announce the targets, policy changes have had a lesser effect on rates.
Majoritarian Management of the Commons
Authors: Buchanan James M. , Yoon Yong J.
Published: July 2002

This article analyzes usage of a common property resource, “the commons,” under collectivization as compared with more familiar privatization institutional arrangements. Particular emphasis is on majority decision rules. When separate majority coalitions may authorize simultaneous usage of a common resource, total value is dissipated, but the interdependencies introduced by possible membership in differing coalitions to an extent reduce the incentives for exploitation. The formal analysis is analogous to that familiar in Cournot‐Nash duopoly‐oligopoly models but with differing efficiency implications. The argument has relevance for differential‐benefit public spending from general tax sources, as well as other applications.
A Quality‐of‐Play Model of a Professional Sports League
Authors: Cyrenne Philippe
Published: July 2002

Assuming that consumers value both the absolute and relative quality of play, I compare the choice of ticket prices, team qualities, and number of games played in a noncooperative outcome versus that chosen by a social planner. I find that the nature of consumer preferences regarding the quality of play determines whether the demand for talented players are strategic complements or substitutes. A strong preference by fans for a superior team makes players strategic substitutes, and a concern for a high quality of play and competitive balance make players strategic complements. Moreover, when fans only value the relative quality of play, there is an overemployment of talented players in the noncooperative outcome versus the socially optimal outcome; when they only value the absolute quality of play then there is an underemployment of talented players in the noncooperative outcome.
A rotary molecular motor that can work at near 100% efficiency
Authors: Kinosita Kazuhiko , Yasuda Ryohei , Noji Hiroyuki , Adachi Kengo
Published: July 2002

A single molecule of F
1
–ATPase is by itself a rotary motor in which a central γ–subunit rotates against a surrounding cylinder made of α
3
β
3
–subunits. Driven by the three βs that sequentially hydrolyse ATP, the motor rotates in discrete 120° steps, as demonstrated in video images of the movement of an actin filament bound, as a marker, to the central γ–subunit. Over a broad range of load (hydrodynamic friction against the rotating actin filament) and speed, the F motor produces a constant torque of
ca
. 40 pN nm. The work done in a 120° step, or the work per ATP molecule, is thus
ca
. 80 pN nm. In cells, the free energy of ATP hydrolysis is
ca
. 90 pN nm per ATP molecule, suggesting that the F
1
motor can work at near 100% efficiency. We confirmed
in vitro
that F
1
indeed does
ca
. 80 pN nm of work under the condition where the free energy per ATP is 90 pN nm. The high efficiency may be related to the fully reversible nature of the F
1
motor: the ATP synthase, of which F
1
is a part, is considered to synthesize ATP from ADP and phosphate by reverse rotation of the F motor. Possible mechanisms of F
1
rotation are discussed.
An ERK2 docking site in the Pointed domain distinguishes a subset of ETS transcription factors
Authors: Seidel Jeffrey J. , Graves Barbara J.
Published: July 2002

The ETS transcription factors perform distinct biological functions despite conserving a highly similar DNA-binding domain. One distinguishing property of a subset of ETS proteins is a conserved region of 80 amino acids termed the Pointed (PNT) domain. Using enzyme kinetics we determined that the Ets-1 PNT domain contains an ERK2 docking site. The docking site enhances the efficiency of phosphorylation of a mitogen-activated protein kinase (MAPK) site N-terminal to the PNT domain. The site enhances ERK2 binding rather than catalysis. Three hydrophobic residues are involved in docking, and the previously determined NMR structure indicates that these residues are clustered on the surface of the Ets-1 PNT domain. The docking site function is conserved in the PNT domain of the highly related Ets-2 but not in the ets family member GABPα. Ablation of the docking site in Ets-1 and Ets-2 prevented Ras pathway-mediated enhancement of the transactivation function of these proteins. This study provides structural insight into the function of a MAPK docking site and describes a unique activity for the PNT domain among a subset of ets family members.
A quantitative investigation of additive noise reduction for active matrix flat‐panel imagers using compensation lines
Authors: El‐Mohri Y. , Antonuk L. E. , Zhao Q. , Maolinbay M. , Rong X. , Jee K.‐W. , Nassif S. , Cionca C.
Published: July 2002

A quantitative investigation of a technique for reducing correlated noise in indirect detection active matrix flat‐panel imagers has been reported. Correlated noise in such systems arises from the coupling of electronic noise, originating from fluctuations in external sources such as power supplies and ambient electromagnetic sources, to the imaging array via its address lines. The noise reduction technique involves the use of signals from columns of compensation line pixels located in relatively close proximity to the columns of normal imaging pixels on the array. Compensation line pixels are designed to be as sensitive to externally‐coupled noise as columns of normal imaging pixels but are insensitive to incident radiation. For each imaging pixel, correlated noise is removed by subtracting from the imaging pixel signal a signal derived from compensation line pixels located on the same row. The effectiveness of various implementations of this correction has been examined through measurements of signal and noise from individual pixels as well as of noise power spectra. These measurements were performed both in the absence of radiation as well as with x rays. The effectiveness of the correction was also demonstrated qualitatively by means of an image of a hand phantom. It was found that the use of a single compensation line dramatically reduces external noise through removal of the correlated noise component. While this form of the correction increases non‐radiation‐related uncorrelated noise, the effect can be largely reduced through the introduction of multiple compensation lines. Finally, a position‐dependent correction based on compensation lines on both sides of the array was found to be effective when the magnitude of the correlated noise varied linearly across the array.
Magnetic resonance imaging based correction and reconstruction of positron emission tomography images (in English)
Authors: Oakley Jonathan David
Published: July 2002

Reconstruction of positron emission tomography (PET) images with good quantitative and qualitative resolution is a difficult problem. Mathematically the problem is ill‐posed, and a regularization of the reconstruction solution is necessary. Such constraints range from simply smoothing the data to the use of elaborate models employed within a Bayesian framework. The goal of optimum resolution, however, is typically not compatible with any of these schemes. This thesis presents new methods for dealing with the projection data on an anisotropic basis. This is done in order to compromise the need for regularization and the drive toward better resolutions. An appropriate resolution is chosen in accordance to either the quality of the projection data (based on local estimates of noise), or known regions of interest (taken, for example, from associated anatomical images). As such it addresses the issues of noise artifact whilst avoiding any unnecessary loss in resolution. A second key element is the development of a Bayesian algorithm to improve resolution in order to address the so‐called partial volume effect. Magnetic resonance imaging (MRI) data provides significant information about the expected distribution of radioactivity in the brain. Using this explicit information, corrections to the PET image can be made in a quantitative manner, but one must be cautious in its application. The thesis describes how to incorporate MRI data into the reconstruction process of the PET image in an adaptive manner. The adaptational nature of the process is driven solely by good heuristics designed to avoid both an overbiased usage of the a priori information and any assumptions made on the [supposed] homogeneous characteristic of the activity distribution.
Patella lead x‐ray fluorescence measurements are independent of sample orientation
Authors: Todd Andrew C. , Godbold James H. , Moshier Erin L. , Khan Fuad A.
Published: July 2002

In vivo x‐ray fluorescence bone lead measurements assess long‐term lead exposure. Tibia, calcaneus, and patella are the most commonly sampled bones. Patella measurements also include lead signals from the distal femur, proximal tibia, and synovium. It is therefore important to know whether the orientation of the patella relative to the measurement system substantially affects the measured patella lead concentrations and their measurement uncertainties. This study examined whether these parameters exhibited a dependence on the orientation of the patella with respect to the measurement system, a dependence that could arise from varying nonpatella contributions. There was no effect of orientation on measured patella lead concentration, but there was a highly significant effect of orientation on the measurement uncertainty. These data do not conclusively show that there are no nonpatella contributions to a patella lead measurement; rather, that any such contributions are not a function of measurement orientation over the range of orientations considered. Further study is required if the contribution of nonpatella tissues to a patella lead XRF‐measured concentration is to be fully addressed. This study also filled a gap in the literature by quantifying the within‐patella (29%) and between‐patella (71%) variability of measured patella lead concentrations from replicate measures of nine patellæ.
Monte Carlo characterization of a source for intravascular brachytherapy
Authors: Wang Ruqing , Li X. Allen
Published: July 2002

In this work, we have calculated the two‐dimensional dose distribution in water for a intravascular brachytherapy source wire using the EGSnrc Monte Carlo code. The beta source (Guidant Vascular Intervention) has a radioactive core with a length of 27 mm and a diameter of 0.24 mm. The dose parameters required by the AAPM TG‐60 formalism are discussed and calculated. Dose rate evaluated at the reference point is For the beta source studied, the dose distribution is uniform along the axial direction z for a given radial position ρ for and In such a dose‐uniformity region, the dose field can be characterized by one‐dimensional dose distribution, the dose distribution on the transverse axis. Beyond this region a two‐dimensional (2D) description is necessary. However, for the long beta source wire the anisotropy function proposed by the TG‐60 formalism becomes indefinable when the radial distance exceeds penetration depth of beta electrons. We have proposed that the anisotropy function be expressed in the cylindrical coordinate system, instead of a polar system, to remedy this deficiency. For practical purposes, the entire 2D dose distribution and the dose parameters calculated in the work are tabulated for ease of use.
Dosimetric characteristics of the Best® double‐wall brachytherapy source
Authors: Meigooni A. S. , Bharucha Z. , Yoe‐Sein M. , Sowards Keith
Published: July 2002

and brachytherapy sources are being used for interstitial implants in tumor sites such as the prostate. Recently, a double‐wall source has been introduced, which has a design different from that of sources presently on the market. Dosimetric characteristics (dose rate constant, radial dose function, and anisotropy function) of this source were experimentally and theoretically determined following the AAPM Task Group 43 recommendations and were related to the October 10, 2000 revision of the NIST 1999 Standard for Measurements were performed in a Solid Water™ phantom using LiF thermoluminescent dosimeters. For these measurements, slabs of Solid Water™ phantom material were machined to accommodate the source and LiF TLD chips of dimensions (3.1×3.1×0.8 and (1.0×1.0×1.0 The TLD chips were surrounded by at least 10 cm of Solid Water™ phantom material to provide full scattering conditions. The Monte Carlo simulations were performed in Solid Water™ and liquid water using the PTRAN code. The results of this investigation show an excellent agreement (within 5%) between the measured (0.67±8% and calculated (to be 0.65±3% dose rate constant in Solid Water™. The Monte Carlo calculated dose rate constant of the Best® in water was found to be 0.67±0.02 The radial dose function, of the new source was measured at distances ranging from 0.5 and 7 cm using LiF TLD in Solid Water™ phantom material. Moreover, the radial dose function of the new source was calculated in liquid water and Solid Water™ at distances ranging from 0.1 to 7 cm using the PTRAN Monte Carlo Code. The anisotropy function, of the new source was also measured in Solid Water™ and calculated in both Solid Water™ and water phantom material. From the anisotropy functions, the anisotropy factors, and anisotropy constant were calculated for each medium. The results indicated that the measured anisotropy constant of the Best® source in Solid Water™ was 0.89±5%. Complete dosimetric data are described in this manuscript.
Investigation on basic imaging properties in medical radiography and its application (in Japanese)
Authors: Morishita Junji
Published: July 2002

The focus of this study was to investigate basic imaging properties of medical radiography and to develop a computer‐aided diagnosis (CAD) scheme for automated detection and classification of interstitial infiltrates in chest radiographs.\sThis dissertation included the following four topics:\s(1) comparison of two methods for accurate measurement of modulation transfer functions (MTFs) of screen‐film systems with a slit and a square‐wave test pattern; (2) evaluation of an asymmetric screen‐film system for chest radiography; (3) investigation of basic imaging properties of a computed radiographic system with photostimulable phosphors; and (4) development of the CAD scheme for automated detection and classification of interstitial infiltrates with consideration of optical‐density dependence on texture measures as an application of basic imaging properties.\sIn this disseration, problems concerning resolution propertites of screen‐film systems were discussed in detail. Moreover, effective methods to measure the presampling MTFs of a computed radiographic system as well as characteristic curves and noise properties were shown.\sAlso, an application of the imaging properties to the development of the CAD scheme for interstitial infiltrates in chest radiographs was effective to improve the performance.\sThis research clearly shows the importance of understanding basic imaging properties of analog and digital imaging systems in medical radiography.
The performance of digital x‐ray imaging systems in detection of subtle lung nodules
Authors: Samei Ehsan
Published: July 2002

Subtle lung nodules (SLNs) are lesions that are commonly missed in radiologic examinations of the chest. This thesis explores three factors that influence the detection of these lesions: contrast‐diameter characteristics of SLNs, physical performance of the imaging system, and structured noise in the chest radiographs. The contrast‐diameter characteristics of SLNs were determined from radiographs containing confirmed lesions. The nodules were found to have similar subject contrast profiles with diverse variability in peak contrast (0.02–0.13) and diameter (3–16 mm). The physical performance of a digital chest radiographic system was assessed by measuring its Modulation Transfer Function (MTF), Noise Power Spectrum (NPS), and Detective Quantum Efficiency (DQE) responses. The results showed that the system only minimally blurs the appearance of SLNs, and that for a typical chest exposure, the quantum mottle is low enough not to obscure the visibility of even the smallest SLNs. The relative influence of the structured and quantum noise was explored in a Receiver Operating Characteristic (ROC) study in which simulated tissue‐equivalent nodules were superimposed on images of either structured or quantum noise backgrounds. The detection threshold =0.8) was achieved for nodules 4.5 mm in diameter against structured backgrounds, and for nodules 1.0 mm in diameter against quantum noise backgrounds. The results indicate that anatomical structured noise is the main factor limiting the detection of SLNs in chest radiographs.
Evaluation of optimized compensators on a 3D planning system
Authors: Basran P. S. , Ansbacher W. , Field G. C. , Murray B. R.
Published: July 2002

A commercially available treatment planning system contains several functions that allow for the automation of missing tissue and optimized compensators, where the former retracts the bolus toward the source, and the latter attempts, by iteration, to establish a uniform dose at some user defined depth. The intent of this paper is to report on the compensators designed by the system and to compare them to those devised through conventional techniques. It is demonstrated that the system can model the dosimetric effects of compensators with a high degree of accuracy; measured and predicted doses agree to within 3%. Optimized compensators show slightly improved dose uniformity over thickness reduced compensators. Both show significantly improved uniformity over compensators that simply retract the bolus geometry. In cases where internal inhomogeneities exist, however, the dose uniformity from the optimized compensators vary by as much as 6% at the target depth. These deviations are comparable to the errors of the inhomogeneity algorithm itself. The pathlength reduction technique has been applied to both missing tissue and inhomogeneity compensation, and it has been found that for inhomogeneity compensation, the pathlength reduced compensators produce more uniform distributions than those generated by the optimization algorithm.
Bell inequalities and quantum mechanics
Authors: Eberly J. H.
Published: July 2002

We employ an arrangement of polarization analyzer loops to derive several simple Bell inequalities and then discuss the violation of one of them in light of quantum and classical interpretations of the data recorded.
A curious and useful theorem in two-dimensional electrostatics
Authors: Jackson J. D.
Published: July 2002

In 1956 metrologists Thompson and Lampard established a new theorem in two-dimensional electrostatics that gives calculable capacitances for practical systems possessing a certain symmetry. The theorem is well known among those concerned with electrical standards, but not so well known beyond. This paper brings the theorem to a wider audience with a pedagogical discussion of it, first by treating a simple example by standard methods of electrostatics, then proving the Riemann mapping theorem on which the theorem is based. The Thompson–Lampard theorem and its generalization are then proved and its use in metrology described. Along the way, some curious results about series and products are exhibited.
Magnetic birefringence in a liquid crystal: An experiment for the advanced undergraduate laboratory
Authors: Moses Thomas , Durall Brian , Frankowiak Gregory
Published: July 2002

We describe an experiment involving an exciting phenomenon in liquid crystals, the magnetic field induced birefringence. We present a theoretical description accessible to junior- or senior-level physics majors, and we describe experiments for measuring the field and temperature dependence of the magnetic birefringence. The apparatus required for the experiment is inexpensive and/or easily constructed.
Scattering of antiplane shear waves by a circular cylinder in a traction-free plate
Authors: Wang Xiao-Min , Ying C. F. , Li Ming-Xuan
Published: July 2002

Following a well-established formula used by many researchers, the scattering of an anti-plane shear wave by an infinite elastic cylinder of arbitrary relative radius centered in a traction-free two-dimensional isotropic plate has been examined. The plate is divided into three regions by introducing two imaginary planes located symmetrically away from the surface of the cylinder and perpendicular to surfaces of the plate. The wave field is expanded into cylinder wave modes in the central bounded region containing the cylinder, while the fields in the other two outer regions are expanded into plate wave modes. A system of equations determining the expansion coefficients is obtained according to the traction-free boundary conditions on the plate walls and the stress and displacement continuity conditions across the imaginary planes. By taking an appropriate finite number of terms of the infinite expansion series and a few selected points on the two properly chosen virtual planes and the surfaces of the plate through convergence and precision tests, a matrix equation to numerically evaluate the expansion coefficients is found. The method of how to choose the locations of the imaginary planes and the terms of the expansion series as well as the points on each respective boundary is given in Sec. III in detail. Curves of the reflection and transmission coefficients against the relative radius of the cylinder in welded and slip or cracked interfacial conditions are shown. Analysis on the contrast variations of the reflection and transmission coefficients for a cylinder in bonded and debonded interfacial situations is made. The relative errors estimated by the deviation of the numerical results from the principle of the conservation of energy are found to be less than 2%.
Analysis of an asymmetrical piezoelectric annular bimorph using impedance and admittance matrices
Authors: Ha Sung K. , Kim Young H.
Published: July 2002

A theoretical model is presented for the analysis of an asymmetrical piezoelectric annular bimorph (APAB) in dynamic harmonic motion. The APAB is assumed to be so thin that the thickness dependent stresses vanish throughout. The conjugate parameters of the admittance and impedance matrices are derived using the variational principle. Both the extensional and flexural motions are considered in deriving the motional equations and the boundary conditions. By using the symmetry characteristic of the admittance matrix, the derivation procedure for the impedance and admittance matrices is thus greatly simplified. The resonance and antiresonance frequencies and the effective electromechanical coupling factors are calculated using the matrices. These present methods are applied to three special cases: a single piezoelectric ring in extensional motion, a triple-layer APAB in series or parallel connection, and a triple-layer APAB with sensor and actuator. The results are compared with previous publication and finite element methods, and it is found that the present methods are very effective in analyzing the piezoelectric multilayer annular transducers.
Rhythmic masking release: Contribution of cues for perceptual organization to the cross-spectral fusion of concurrent narrow-band noises
Authors: Turgeon Martine , Bregman Albert S. , Ahad Pierre A.
Published: July 2002

The contribution of temporal asynchrony, spatial separation, and frequency separation to the cross-spectral fusion of temporally contiguous brief narrow-band noise bursts was studied using the Rhythmic Masking Release paradigm (RMR). RMR involves the discrimination of one of two possible rhythms, despite perceptual masking of the rhythm by an irregular sequence of sounds identical to the rhythmic bursts, interleaved among them. The release of the rhythm from masking can be induced by causing the fusion of the irregular interfering sounds with concurrent “flanking” sounds situated in different frequency regions. The accuracy and the rated clarity of the identified rhythm in a 2-AFC procedure were employed to estimate the degree of fusion of the interferring sounds with flanking sounds. The results suggest that while synchrony fully fuses short-duration noise bursts across frequency and across space (i.e., across ears and loudspeakers), an asynchrony of 20–40 ms produces no fusion. Intermediate asynchronies of 10–20 ms produce partial fusion, where the presence of other cues is critical for unambiguous grouping. Though frequency and spatial separation reduced fusion, neither of these manipulations was sufficient to abolish it. For the parameters varied in this study, stimulus onset asynchrony was the dominant cue determining fusion, but there were additive effects of the other cues. Temporal synchrony appears to be critical in determining whether brief sounds with abrupt onsets and offsets are heard as one event or more than one.
Maximum likelihood estimation of structural wave components from noisy data
Authors: Halliday Peter J. , Grosh Karl
Published: July 2002

In this paper, a general framework is developed for determining the underlying parameters of general signal models through the application of maximum likelihood estimation theory for functions whose variables separate. This method extends previous work in sinusoidal and exponential estimation to include models with other functional bases, such as exponential functions with nonconstant amplitudes and Bessel functions. Nonuniform spatial sampling is also possible with this technique. The maximum likelihood method is applied to the identification of wave components along one-dimensional structural elements. Results are given which demonstrate the viability and accuracy of the technique estimating exponential and Bessel function model parameters from noisy simulation data.
Actively created quiet zones by multiple control sources in free space
Authors: Guo Jingnan , Pan Jie , Bao Chaoying
Published: July 2002

Local attenuation of sound pressure, which creates a zone of quiet, seems to be the only option if primary and secondary sources are well separated. Two major indexes of local control, the size of the quiet zone and the total sound power output, are mainly determined by the arrangement of primary sources, secondary sources, and error sensors. It has been found that the size of the quiet zone created by the control system with multiple secondary sources and error sensors is not simply the summation of quiet zones created by each individual control source. The interactions of the control sources, which are determined by the configuration of the system, play a very important role in the system performance. In this paper, a typical control arrangement with multiple secondary sources and multiple error sensors equally spaced in two parallel lines is examined. Results from computer simulation and experiments in an anechoic chamber show that there exists a range of optimal spacing for the secondary sources and error sensors. The control system will create the largest quiet zone and suffer the least increase of total sound power output in the optimal configuration.
An investigation of stop place of articulation as a function of syllable position: A locus equation perspective
Authors: Sussman Harvey M. , Bessell Nicola , Dalston Eileen , Majors Tivoli
Published: July 2002

Locus equations were employed to phonetically describe stop place categories as a function of syllable-initial, -medial, and -final position. Ten speakers, five male and five female, produced a total of 2700 CVC and 4500 VCV utterances that were acoustically analyzed to obtain F2 onset, F2 vowel, and F2 offset frequencies for locus equation regression analyses. In general, degree of coarticulation, as indexed by locus equation slope, was reduced for post-vocalic (VC) stops relative to pre-vocalic stops (pooled data from initial and medial positions), but significant differences were observed as a function of stop consonant. All stops showed significantly reduced R2 values and increased standard errors of estimate for VC relative to CV productions. Separability of stop place categories in a higher-order slope X y-intercept acoustic space also diminished for VC vs CV stop productions. The degradation of classic locus equation form (high correlation and linearity) for VC relative to CV productions was attributed to greater articulatory precision in the production of pre-vocalic compared to post-vocalic stops. This greater articulatory precision was interpreted as reflecting a greater need to normalize vowel context-induced variability of the F2 transition for syllable onset relative to final stops. The decline in acoustic lawfulness of syllable-final stops is discussed in terms of coarticulatory interactions and expected perceptual correlates.
The coupled mode parabolic equation
Authors: Abawi Ahmad T. , Kuperman W. A. , Collins Michael D.
Published: July 2002

The coupled mode parabolic equation (PE) is a generalization of the adiabatic mode PE that includes mode coupling terms. It is practical to apply this approach to large-scale problems involving coupling of energy between both modes and azimuths. The solution is expressed in terms of the normal modes and mode coefficients, which satisfy coupled horizontal wave equations. The coupled mode PE may be solved efficiently with the splitting method. The first step is equivalent to solving the adiabatic mode PE over one range step. The second step involves the integration of the coupling term. The coupling mode PE solution conserves energy, which is an important aspect of a range-dependent propagation model. The derivation of the coupled mode PE, which involves completing the square of an operator, is related to the derivation of an adiabatic mode PE that accounts for ambient flow. Examples are presented to illustrate the accuracy of the coupled mode PE.
Decorrelation of intravascular echo signals: Potentials for blood velocity estimation
Authors: Li Wenguang , Lancée Charles T. , Céspedes E. Ignacio , van der Steen Antonius F. W. , Bom Nicolaas
Published: July 2002

When blood particles travel through an intravascular ultrasound imaging plane, the received echo signals decorrelate at a rate that is related to the flow velocity. In this paper, the feasibility of extracting blood velocity from the decorrelation function of radio frequency signals was investigated through theoretical analysis and computer simulation. A computer model based on the impulse response method was developed to generate the ultrasound field of a 30-MHz intravascular transducer. The decorrelation due to the scatterer displacement as well as other nonmotion related decorrelation sources were studied. The computer simulations show that the decorrelation function is linearly related to the lateral displacement. The monotonic relationship between correlation and displacement provides possibilities to estimate flow velocity with decorrelation measurements. Because of the complexity of the beam profile in the near field, assessment of local velocities requires detailed knowledge of the decorrelation at each axial beam position. Sources of signal decorrelation other than the lateral displacement may cause a bias in the decorrelation based velocity measurements. For localized decorrelation estimation, measurement variations in small range windows present a major challenge. An approach based on multiple decorrelation measurements should be adopted in order to reduce the variations. In conclusion, results of this study suggest that it is feasible to measure flow velocity by quantifying the decorrelation of intravascular ultrasound signals from blood.