bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparisons of general linear groups and their metaplectic coverings II
Authors: Mezo Paul
Published: July 2002

Let

A

\mathbf {A}

be the adele ring of a number field containing the

n
n

th roots of unity, and let

G
L

~

(
r
,

A

)

\widetilde {\mathrm {GL}}(r,\mathbf {A})

be an

n
n

-fold metaplectic covering of

G
L

(
r
,

A

)

\mathrm {GL}(r,\mathbf {A})

. Under an assumption on

n
n

, we prove identities between all of the terms in Arthur’s invariant trace formulas for

G
L

~

(
r
,

A

)

\widetilde {\mathrm {GL}}(r,\mathbf {A})

and

G
L

(
r
,

A

)

\mathrm {GL}(r,\mathbf {A})

. We then establish a correspondence between the automorphic representations of these groups.
Semisymmetric polynomials and the invariant theory of matrix vector pairs
Authors: Knop Friedrich
Published: July 2002

We introduce and investigate a one-parameter family of multivariate polynomials

R
λ

R_\lambda

. They form a basis of the space of semisymmetric polynomials, i.e., those polynomials which are symmetric in the variables with odd and even index separately. For two values of the parameter

r
r

, namely

r
=

1
2

r=\frac 12

and

r
=
1

r=1

, the polynomials have a representation theoretic meaning related to matrix-vector pairs. In general, they form the semisymmetric analogue of (shifted) Jack polynomials. Our main result is that the

R
λ

R_\lambda

are joint eigenfunctions of certain difference operators. From this we deduce, among others, the Extra Vanishing Theorem, Triangularity, and Pieri Formulas.
The fine structure of translation functors
Authors: Günzl Karen
Published: July 2002

LetEEbe a simple finite-dimensional representation of a semisimple Lie algebra with extremal weightν\nuand let0≠e∈Eν0 \neq e \in E_{\nu }. LetM(τ)M(\tau )be the Verma module with highest weightτ\tauand0≠vτ∈M(τ)τ0 \neq v_{\tau } \in M(\tau )_{\tau }. We investigate the projection ofe⊗vτ∈E⊗M(τ)e \otimes v_{\tau } \in E \otimes M(\tau )on the central characterχ(τ+ν)\chi (\tau +\nu ). This is a rational function inτ\tauand we calculate its poles and zeros. We then apply this result in order to compare translation functors.
Ford and Dirichlet domains for cyclic subgroups of 𝑃𝑆𝐿₂(ℂ) acting on ℍ³_{ℝ} and ∂ℍ³_{ℝ}
Authors: Drumm Todd , Poritz Jonathan
Published: July 2002

Let

Γ
\Gamma

be a cyclic subgroup of

P
S

L
2

(

C

)

PSL_2({\mathbb C})

generated by a loxodromic element. The Ford and Dirichlet fundamental domains for the action of

Γ
\Gamma

on

H

R

3

{{\mathbb H}^3_{\mathbb R}}

are the complements of configurations of half-balls centered on the plane at infinity

∂

H

R

3

{\partial }{{\mathbb H}^3_{\mathbb R}}

. Jørgensen (On cyclic groups of Möbius transformations, Math. Scand. 33 (1973), 250–260) proved that the boundary of the intersection of the Ford fundamental domain with

∂

H

R

3

{\partial }{{\mathbb H}^3_{\mathbb R}}

always consists of either two, four, or six circular arcs and stated that an arbitrarily large number of hemispheres could contribute faces to the Ford domain in the interior of

H

R

3

{{\mathbb H}^3_{\mathbb R}}

. We give new proofs of Jørgensen’s results, prove analogous facts for Dirichlet domains and for Ford and Dirichlet domains in the interior of

H

R

3

{{\mathbb H}^3_{\mathbb R}}

, and give a complete decomposition of the parameter space by the combinatorial type of the corresponding fundamental domain.
DrosophilaStathmin: A Microtubule-destabilizing Factor Involved in Nervous System Formation
Authors: Ozon Sylvie , Guichet Antoine , Gavet Olivier , Roth Siegfried , Sobel André
Published: July 2002

Stathmin is a ubiquitous regulatory phosphoprotein, the generic element of a family of neural phosphoproteins in vertebrates that possess the capacity to bind tubulin and interfere with microtubule dynamics. Although stathmin and the other proteins of the family have been associated with numerous cell regulations, their biological roles remain elusive, as in particular inactivation of the stathmin gene in the mouse resulted in no clear deleterious phenotype. We identified stathmin phosphoproteins inDrosophila, encoded by a unique gene sharing the intron/exon structure of the vertebrate stathmin andstathmin family genes. They interfere with microtubule assembly in vitro, and in vivo when expressed in HeLa cells. Drosophila stathmin expression is regulated during embryogenesis: it is high in the migrating germ cells and in the central and peripheral nervous systems, a pattern resembling that of mammalian stathmin. Furthermore, RNA interference inactivation ofDrosophila stathmin expression resulted in germ cell migration arrest at stage 14. It also induced important anomalies in nervous system development, such as loss of commissures and longitudinal connectives in the ventral cord, or abnormal chordotonal neuron organization. In conclusion, a single Drosophilagene encodes phosphoproteins homologous to the entire vertebrate stathmin family. We demonstrate for the first time their direct involvement in major biological processes such as development of the reproductive and nervous systems.
POPSIM: a general population simulation program.
Authors: Hampe J , Wienker T , Schreiber S , N√ºrnberg P
Published: July 2002

MOTIVATION: The investigation of common disorders of polygenic inheritance using both population-based association designs and non-parametric linkage analysis within families is gaining increasing importance. We have created a program that allows for the flexible simulation of populations as a tool to investigate the properties of population-based mapping approaches. RESULTS: We have created a population simulation program, POPSIM, that (i) creates a virtual representation of every individual, (ii) makes no prior assumptions but the Mendelian rules and (iii) allows populations of several million individuals in size to be generated and to be followed over hundreds of generations. The parameters of the disease model, population structure and population expansion rate can be specified. Flexible sampling options exist that allow samples of families and individuals to be drawn at any given point during the population history. The program may be a useful tool in the study of the influence of genetic drift, recombination and admixture on the generation and maintenance of linkage disequilibrium in populations, as well as the evaluation of stochastic sampling characteristics of families and individuals conditional on a complex genetic phenotype from homogeneous and heterogeneous populations. AVAILABILITY: The source code as well as Sun and Windows NT4.0 console executables of the program are available under http://www.ukrv. de/ch/medgen/html/benutzer/j.hampe/popsim. html. CONTACT: J. Hampe@mucosa.de
Protein domain decomposition using a graph-theoretic approach
Authors: Xu Ying , Xu Dong , Gabow Harold N.
Published: July 2002

Motivation: Automatic decomposition of a multi-domain protein into individual domains represents a highly interesting and unsolved problem. As the number of protein structures in PDB is growing at an exponential rate, there is clearly a need for more reliable and efficient methods for protein domain decomposition simply to keep the domain databases up-to-date.

Results: We present a new algorithm for solving the domain decomposition problem, using a graph-theoretic approach. We have formulated the problem as a network flow problem, in which each residue of a protein is represented as a node of the network and each residue–residue contact is represented as an edge with a particular capacity , depending on the type of the contact. A two-domain decomposition problem is solved by finding a bottleneck (or a minimum cut) of the network, which minimizes the total cross-edge capacity, using the classical Ford–Fulkerson algorithm. A multi-domain decomposition problem is solved through repeatedly solving a series of two-domain problems. The algorithm has been implemented as a computer program, called DomainParser. We have tested the program on a commonly used test set consisting of 55 proteins. The decomposition results are 78.2% in agreement with the literature on both the number of decomposed domains and the assignments of residues to each domain, which compares favorably to existing programs. On the subset of two-domain proteins (20 in number), the program assigned 96.7% of the residues correctly when we require that the number of decomposed domains is two.

Availability: The executable of DomainParser and its web server are available at http://compbio.ornl.gov/structure/domainparser/.

Contact: xyn@ornl.gov

* To whom correspondence should be addressed.
Habitual and Occasional Lobbyers in the U.S. Steel Industry: An Em Algorithm Pooling Approach
Authors: Morck Randall , Sepanski Jungsywan , Yeung Bernard
Published: July 2002

Using U.S. steel firm data, we find that lobbying for import protection appears to be habit‐forming. To identify heterogeneity in lobbying behavior among firms, we use an expectation‐maximization algorithm to sort our firms into groups with different propensities to lobby and estimate the determinants of lobbying in each group. A two‐pool model emerges: occasional lobbyers' lobbying depends on their market performance, and habitual lobbyers' lobbying only depends on past lobbying. The latter tends to be larger steel firms whose business is more focused in steel. Our evidence is consistent with dynamic economies of scale in protection seeking breeding protection‐dependent firms.
African American Migration to the North: New Evidence for the 1910s
Authors: Maloney Thomas N.
Published: July 2002

The years between 1910 and 1920 witnessed the first wave of the “Great Migration” of African Americans to the North. This article uses new census data from the Integrated Public Use Microdata Series project to study self‐selection patterns in African American migration during this important decade. The results indicate that, contrary to contemporary accounts, migration rates rose at least as much among the literate as among the illiterate (and perhaps more), and migration increased more for married African Americans than for the unmarried.
Product Development of Branded, Packaged Household Goods in Britain, 1870–1914: Colman’s, Reckitt’s, and Lever Brothers
Authors: Church Roy , Clark Christine
Published: July 2002

The three companies whose history forms the subject of this article became leaders in a sector of the British economy—consumer goods—generally regarded as one of the most successful in the late nineteenth and early twentieth centuries. Product innovation and development, achieved internally or through acquisition, enabled these firms to become market leaders. We therefore analyze the processes of product development within the three firms, using a systematic framework that allows us to offer generalizations about the process of product innovation and development in the consumer goods sector in Britain. We conclude that gradual modification, rather than revolutionary innovation, was characteristic of product development in the household goods trade, and that technology was less important for success than marketing skill.
Climate signals in Palaeozoic land plants
Authors: Edwards Dianne
Published: July 2002

The Palaeozoic is regarded as a period in which it is difficult to recognize climate signals in land plants because they have few or no close extant relatives. In addition early, predominantly axial, representatives lack the features, e.g. leaf laminae, secondary growth, used later as qualitative and quantitive measures of past climates. Exceptions are stomata, and the preliminary results of a case study of a single taxon present throughout the Devonian, and analysis of stomatal complex anatomy attempt to disentangle evolutionary, taxonomic, habitat and atmospheric effects on stomatal frequencies. Ordovician–Silurian vegetation is represented mainly by spores whose widespread global distribution on palaeocontinental reconstructions with inferred climates suggest that the producers were independent of major climate variables, probably employing the physiology and behavioural strategies of extant bryophytes, further characterized by small size. Growth–ring studies, first possible on Mid–Devonian plants, have proved most informative in elucidating the climate at high palaeolatitudes in Late Permian Gondwana. Changes in the composition of Carboniferous–Permian low–latitude wetland vegetation are discussed in relation to tectonic activity and glaciation, with most confidence placed on the conclusion that major extinctions at the Westphalian–Stephanian boundary in Euramerica resulted from increased seasonality created by changes in circulation patterns at low latitudes imposed by the decrease of glaciations in most parts of Gondwana.
Size and scale effects as constraints in insect sound communication
Authors: Bennet-Clark H. C.
Published: July 2002

For optimal transfer of power to the surrounding medium, a sound source should have a radius of 1/6 to 1/4 of the sound wavelength. Sound-waves propagate from the source as compressions and rarefactions of the fluid medium, which decay by spreading and viscous losses. Higher frequencies are more easily refracted and reflected by objects in the environment, causing degradation of signal structure. In open air or water, the sound spreads spherically and decays by the inverse square law. If the sound is restricted to two dimensions rather than three, it decays as the inverse of range, whereas waves within a rod decay largely due to viscous losses; such calls are usually rather simple pulses and rely on the initial time of arrival because of multiple pathlengths or different propagation velocities in the environment. Because of the relationship between calling success and reproductive success, singing insects are under selective pressure to optimize the range, and to maintain the specificity, of their calls. Smaller insects have less muscle power; because of their small sound sources, higher frequencies will be radiated more efficiently than lower frequencies, but in order to produce brief loud pulses from a long-duration muscle contraction they may use both a frequency multiplier mechanism and a mechanical power amplifier. Airborne insect sounds in the range from 1 to 5 kHz tend to have sustained puretone components and a specific pattern of pulses which propagate accurately. Where the song frequency is higher, the pulses tend to become briefer, with a rapid initial build-up that gives a reliable time of onset through obstructed transmission pathways. These scale effects may be related both to the sound-producing mechanism and the auditory system of the receiver. Tiny insects have the special acoustic problem of communicating with only a small amount of available power. Some, such as fruit flies, communicate at low frequencies, at close range, by generating air currents; these currents may also be used to waft specific pheromones. Other small insects, such as Hemiptera, beetles, etc., communicate using substrate vibration. This enables long-range communication, but signal structure degrades with distance from the source; vibration signals tend to be confined to certain types of linear substrate, such as vegetation.
Field biology of the platypus (Ornithorhynchus anatinus): historical and current perspectives
Authors: Grant T. R. , Temple–Smith P. D.
Published: July 2002

The field biology of the platypus,Ornithorhynchus anatinus, was first studied by a number of expatriate biologists who visited the Australian colonies to collect specimens in the 1800s. Their work was followed in the early to mid–1900s by a group of resident natural historians and later by an increasing number of academic biologists. All of these workers contributed significantly to the current understanding of the field biology of this unique Australian species. The platypus occupies much the same general distribution as it did prior to European occupation of Australia, except for its loss from the state of South Australia. However, local changes and fragmentation of distribution due to human modification of its habitat are documented. The species currently inhabits eastern Australia from around Cooktown in the north to Tasmania in the south. Although not found in the west–flowing rivers of northern Queensland, it inhabits the upper reaches of rivers flowing to the west and north of the dividing ranges in the south of the state and in New South Wales and Victoria. Its current and historical abundance, however, is less well known and it has probably declined in numbers, although still being considered as common over most of its current range. The species was extensively hunted for its fur until around this turn of this century. The platypus is mostly nocturnal in its foraging activities, being predominantly an opportunistic carnivore of benthic invertebrates. The species is homeothermic, maintaining its low body temperature (32°C), even while foraging for hours in water below 5°C. Its major habitat requirements include both riverine and riparian features which maintain a supply of benthic prey species and consolidated banks into which resting and nesting burrows can be excavated. The species exhibits a single breeding season, with mating occurring in late winter or spring and young first emerging into the water after 3—4 months of nurture by the lactating females in the nesting burrows. Natural history observations, mark and recapture studies and preliminary investigations of population genetics indicate the possibility of resident and transient members of populations and suggest a polygynous mating system. Recent field studies have largely confirmed and extended the work of the early biologists and natural historians.
How ancient DNA may help in understanding the origin and spread of agriculture
Authors: Brown Terence A.
Published: July 2002

The origin and spread of agriculture have been central questions in archaeology for the last 75 years and are increasingly being addressed by a multidisciplinary approach involving biologists, ecologists, geographers and anthropologists as well as archaeologists. Molecular genetics has the potential to make an important contribution, especially by enabling the number of times that a crop or animal was domesticated to be determined. Molecular genetics can also assign approximate dates to domestication events, identify the wild progenitor of a domesticate, and provide new forms of evidence relevant to agricultural spread. With wheat, molecular genetical studies of modern plants have suggested that einkorn was domesticated just once but that emmer might have been domesticated more than once. Ancient DNA studies of animal remains have benefited from progress made with equivalent analyses of human bones, and with plant material there have been clear demonstrations of DNA preservation in desiccated seeds. Charred remains have also been shown to contain ancient DNA but this finding is unexpected in view of the high temperatures to which these seeds have supposedly been exposed. Ancient DNA studies of wheat remains have been used in taxonomic identification and in assessment of the possible bread–making quality of the wheat grown at an Early Bronze Age site in Greece.
Neuromuscular control: introduction and overview
Authors: Leeuwen Johan L.
Published: July 2002

This paper introduces some basic concepts of the interdisciplinary field of neuromuscular control, without the intention to be complete. The complexity and multifaceted nature of neuromuscular control systems is briefly addressed. Principles of stability and planning of motion trajectories are discussed. Closed–loop and open–loop control are considered, together with the inherent stability properties of muscles and the geometrical design of animal bodies. Various modelling approaches such as inverse and forward dynamics are outlined, as used by several authors in the Philosophical Transactions of the Royal Society of London, series B, May 1999 issue. An introductory overview is presented of the other contributions in that issue.
The portable UNIX programming system (PUPS) and CANTOR: a computational environment for dynamical representation and analysis of complex neurobiological data
Authors: O'Neill M. A. , Hilgetag C. C.
Published: July 2002

Many problems in analytical biology, such as the classification of organisms, the modelling of macromolecules, or the structural analysis of metabolic or neural networks, involve complex relational data. Here, we describe a software environment, the portable UNIX programming system (PUPS), which has been developed to allow efficient computational representation and analysis of such data. The system can also be used as a general development tool for database and classification applications. As the complexity of analytical biology problems may lead to computation times of several days or weeks even on powerful computer hardware, the PUPS environment gives support for persistent computations by providing mechanisms for dynamic interaction and homeostatic protection of processes. Biological objects and their interrelations are also represented in a homeostatic way in PUPS. Object relationships are maintained and updated by the objects themselves, thus providing a flexible, scalable and current data representation. Based on the PUPS environment, we have developed an optimization package, CANTOR, which can be applied to a wide range of relational data and which has been employed in different analyses of neuroanatomical connectivity. The CANTOR package makes use of the PUPS system features by modifying candidate arrangements of objects within the system's database. This restructuring is carried out via optimization algorithms that are based on user–defined cost functions, thus providing flexible and powerful tools for the structural analysis of the database content. The use of stochastic optimization also enables the CANTOR system to deal effectively with incomplete and inconsistent data. Prototypical forms of PUPS and CANTOR have been coded and used successfully in the analysis of anatomical and functional mammalian brain connectivity, involving complex and inconsistent experimental data. In addition, PUPS has been used for solving multivariate engineering optimization problems and to implement the digital identification system (DAISY), a system for the automated classification of biological objects. PUPS is implemented in ANSI–C under the POSIX.1 standard and is to a great extent architecture– and operating–system independent. The software is supported by systems libraries that allow multi–threading (the concurrent processing of several database operations), as well as the distribution of the dynamic data objects and library operations over clusters of computers. These attributes make the system easily scalable, and in principle allow the representation and analysis of arbitrarily large sets of relational data. PUPS and CANTOR are freely distributed (http://www.pups.org.uk) as open–source software under the GNU license agreement.
Molecular Fossils in the Human Genome: Identification and Analysis of the Pseudogenes in Chromosomes 21 and 22
Authors: Harrison Paul M. , Hegyi Hedi , Balasubramanian Suganthi , Luscombe Nicholas M. , Bertone Paul , Echols Nathaniel , Johnson Ted , Gerstein Mark
Published: July 2002

We have developed an initial approach for annotating and surveying pseudogenes in the human genome. We search human genomic DNA for regions that are similar to known protein sequences and contain obvious disablements (i.e., mid-sequence stop codons or frameshifts), while ensuring minimal overlap with annotations of known genes. Pseudogenes can be divided into “processed” and “nonprocessed”; the former are reverse transcribed from mRNA (and therefore have no intron structure), whereas the latter presumably arise from genomic duplications. We annotate putative processed pseudogenes based on whether there is a continuous span of homology that is >70% of the length of the closest matching human protein (i.e., with introns removed), or whether there is evidence of polyadenylation. We have applied our approach to chromosomes 21 and 22, the first parts of the human genome completely sequenced, finding 190 new pseudogene annotations beyond the 264 reported by the sequencing centers. In total, on chromosomes 21 and 22, there are 189 processed pseudogenes, 195 nonprocessed pseudogenes, and, additionally, 70 pseudogenic immunoglobulin gene segments. (Detailed assignments are available athttp://bioinfo.mbb.yale.edu/genome/pseudogeneorhttp://genecensus.org/pseudogene.) By extrapolation, we predict that there could be up to ∼20,000 pseudogenes in the whole human genome, with a little more than half of them processed. We have determined the main populations and clusters of pseudogenes on chromosomes 21 and 22. There are notable excesses of pseudogenes relative to genes near the centromeres of both chromosomes, indicating the existence of pseudogenic “hot-spots” in the genome. We have looked at the distribution of InterPro families and Gene Ontology (GO) functional categories in our pseudogenes. Overall, the families in both processed and nonprocessed pseudogene populations occur according to a similar power–law distribution as that found for the occurrence of gene families, with a few big families and many small ones. The processed population is, in particular, enriched in highly expressed ribosomal–protein sequences (∼20%), which appear fairly evenly distributed across the chromosomes. We compared processed pseudogenes of different evolutionary ages, observing a high degree of similarity between “ancient” and “modern” subpopulations. This may be attributable to the consistently high expression of ribosomal proteins over evolutionary time. Finally, we find that chromosome 22 pseudogene population is dominated by immunoglobulin segments, which have a greater rate of disablement per amino acid than the other pseudogene populations and are also substantially more diverged.
Determination of three‐dimensional positions of known sparse objects from a single projection
Authors: Hoffmann Kenneth R. , Esthappan Jacqueline
Published: July 2002

A new technique is developed for accurate determination of the three‐dimensional position and orientation of known sparse objects, e.g., a configuration of points, from a single‐perspective projection. In this technique, a computer model of the known object is translated and rotated so as to align it optimally in a least‐squares sense with the projection lines connecting the image points with the focal spot by using a modification of the projection‐Procrustes technique. The translational and rotational adjustments are repeated iteratively until the angular change between iterations is less than 0.25°. Simulations indicate that, for rms input image errors of 0.03 cm, the three‐dimensional positions and orientations can be determined to within approximately 0.2 cm and 0.3° for a wide range of initially guessed positions and orientations, and positions can be determined with an accuracy of approximately 0.3 cm for objects having as few as four points. In phantom experiments, three‐dimensional positions and orientations of a cube phantom were reproducibly determined to within 0.23 cm and 0.13°. The entire calculation requires only 10 s on a VAX 3500 to converge to the solution. The accuracy, precision, and speed of the technique indicate that it will be a useful tool for determination of three‐dimensional positions and orientations of known sparse objects.
A new approach to film dosimetry for high energy photon beams: Lateral scatter filtering
Authors: Burch Sandra E. , Kearfott Kimberlee J. , Trueblood Jon H. , Sheils W. Chris , Yeo J. Inhwan , Wang C. K. Chris
Published: July 2002

A method of film dosimetry for high energy photon beams is proposed which reduces the required film calibration exposures to a set of films obtained for a small radiation field size and shallow depth at 5 cm depth). It involves modification of a compression type polystyrene film phantom to include thin lead foils parallel to the vertical film plane at approximately 1 cm from both sides of the film emulsion. The foils act as high atomic number filters which remove low energy Compton scatter photons that otherwise would cause the film sensitivity to change with field size and depth. The proposed method is best described as “lateral scatter filtering.” To validate the proposed method, central axis depth doses and isodose curves for a 4 MV photon beam were determined from films exposed within the modified phantom and the results compared with ionization chamber measurements. When no lateral filtering was used, for field sizes of and this comparison demonstrated up to a 65% difference between film and ionization chamber central axis depth dose measurements. When using the lateral scatter filtering technique, less than a 4% difference was observed for these field sizes.
An introduction to wavelet theory and application for the radiological physicist
Authors: Harpen Michael D.
Published: July 2002

The wavelet transform, part of a rapidly advancing new area of mathematics, has become an important technique for image compression, noise suppression, and feature extraction. As a result, the radiological physicist can expect to be confronted with elements of wavelet theory as diagnostic radiology advances into teleradiology, PACS, and computer aided feature extraction and diagnosis. With this in mind we present a primer on wavelet theory geared specifically for the radiological physicist. The mathematical treatment is free of the details of mathematical rigor, which are found in most other treatments of the subject and which are of little interest to physicists, yet is sufficient to convey a reasonably deep working knowledge of wavelet theory.
Anisotropy functions for and sources
Authors: Weaver Keith
Published: July 2002

The anisotropy function was defined by AAPM Task Group 43 in a recent report, and reference data were provided. However, some of the data appeared to have large experimental errors. In this work, anisotropy functions are presented for three low‐energy photon‐emitting sources commonly used for brachytherapy:source models 6702 and 6711, and the model 200source. The data were generated via a two‐step process: the sources' intrinsic radiation emission pattern was determined from in‐air measurements, and these data were used as input to Monte Carlo calculations of the fluence distribution in water. The new anisotropy function values for iodine compare well with earlier data from diode measurements, and seem more physically realistic than some data provided by TG43. Previous palladium data measured with TLDs are more variable, but on the average are similar to the data presented here. The new data have estimated uncertainties of 3%–6%; this level of accuracy should be completely adequate for clinical calculations.
A simple model for examining issues in radiotherapy optimization
Authors: Shepard David M. , Olivera Gustavo , Angelos Lisa , Sauer Otto , Reckwerdt Paul , Mackie T. Rockwell
Published: July 2002

Convolution/superposition software has been used to produce a library of photon pencil beam dose matrices. This library of pencil beams is designed to serve as a tool for both education and investigation in the field of radiotherapy optimization. The elegance of this pencil beam model stems from its cylindrical symmetry. Because of the symmetry, the dose distribution for a pencil beam from any arbitrary angle can be determined through a simple rotation of a pre‐computed dose matrix. Rapid dose calculations can thus be performed while maintaining the accuracy of a convolution/superposition based dose computation. The pencil beam data sets have been made publicly available. It is hoped that the data sets will facilitate a comparison of a variety of optimization and delivery approaches. This paper will present a number of studies designed to demonstrate the usefulness of the pencil beam data sets. These studies include an examination of the extent to which a treatment plan can be improved through either an increase in the number of beam angles and/or a decrease in the collimator size. A few insights into the significance of heterogeneity corrections for treatment planning for intensity modulated radiotherapy will also be presented.
Photon scatter in portal images: Accuracy of a fluence based pencil beam superposition algorithm
Authors: McCurdy B. M. C. , Pistorius S.
Published: July 2002

The accuracy of a pencil beam algorithm to predict scattered photon fluence into portal imaging systems was studied. A data base of pencil beam kernels describing scattered photon fluence behind homogeneous water slabs (1–50 cm thick) at various air gap distances (0–100 cm) was generated using the EGS Monte Carlo code. Scatter kernels were partitioned according to particle history: singly‐scattered, multiply‐scattered, and bremsstrahlung and positron annihilation photons. Mean energy and mean angle with respect to the incident photon pencil beam were also scored. This data allows fluence, mean energy, and mean angular data for each history type to be predicted using the pencil beam algorithm. Pencil beam algorithm predictions for 6 and 24 MV incident photon beams were compared against full Monte Carlo simulations for several inhomogeneous phantoms, including approximations to a lateral neck, and a mediastinum treatment. The accuracy of predicted scattered photon fluence, mean energy, and mean angle was investigated as a function of air gap, field size, photon history, incident beam resolution, and phantom geometry. Maximum errors in mean energies were 0.65 and 0.25 MeV for the higher and lower energy spectra, respectively, and 15° for mean angles. The ability of the pencil beam algorithm to predict scatter fluence decreases with decreasing air gap, with the largest error for each phantom occurring at the exit surface. The maximum predictive error was found to be 6.9% with respect to the total fluence on the central axis. By maintaining even a small air gap (∼10 cm), the error in predicted scatter fluence may be kept under 3% for the phantoms and beam energies studied here. It is concluded that this pencil beam algorithm is sufficiently accurate (using International Commission on Radiation Units and Measurements Report No. 24 guidelines for absorbed dose) over the majority of clinically relevant air gaps, for further investigation in a portal dose prediction algorithm.
A systematic evaluation of air cavity dose perturbation in megavoltage x‐ray beams
Authors: Li X. Allen , Yu Cedric , Holmes Timothy
Published: July 2002

The EGS4 Monte Carlo radiation transport code was used to systematically study the dose perturbation near planar and cylindrical air cavities in a water medium irradiated by megavoltage x‐ray beams. The variables of the problem included x‐ray energy, cavity shape and dimension, and depth of the cavity in water. The Monte Carlo code was initially validated against published measurements and its results were found to agree within 2% with the published measurements. The study results indicate that the dose perturbation is strongly dependent on x‐ray energy, field size, depth, and size of cavity in water. For example, the Monte Carlo calculations show dose reductions of 42% and 18% at 0.05 and 2 mm, respectively, beyond the air–water interface distal to the radiation source for a 3 cm thick air slab irradiated by a single 5×5 cm215 MV beam. The dose reductions are smaller for a parallel‐opposed pair of 5×5 cm215 MV x‐ray beams, being 21% and 11% for the same depths. The combined set of Monte Carlo calculations showed that the dose reduction near an air cavity is greater for: (a) Smaller x‐ray field size, (b) higher x‐ray energy, (c) larger air‐cavity size, and (d) smaller depth in water where the air cavity is situated. A potential clinical application of these results to the treatment of prostate cancer is discussed.
In vivo dosimetry: Intercomparison between p‐type based and n‐type based diodes for the 16–25 MV energy range
Authors: Jornet N. , Ribas M. , Eudaldo T.
Published: July 2002

This paper compares two different types of diodes designed to cover the energy range from 16 to 25 MV, one n‐type (diode‐A) and the other p‐type (diode‐B). A 18 MV x‐ray beam has been used for all tests. Signal stability postirradiation, intrinsic precision and linearity of response with dose, front–back symmetry, and dose decrease under the diode were studied. Also, the water equivalent thickness of the build up caps was determined. Both types of diodes were calibrated to give entrance dose. Entrance correction factors for field size, tray, source skin distance, angle, and wedge were determined. Finally, the effect of dose rate, temperature and accumulated dose on the diode's response were studied. Only diode‐A had full build‐up for 18 MV x rays and standard irradiation conditions. Field size correction factor was about 2%–4% for field sizes bigger than 20×20 cm2 for both diodes. Tray correction factor was negligible for diode‐A while diode‐B would overestimate the dose by a 2% for a 40×40 cm2 field size if the correction factor was not applied. Wedge correction factors are only relevant for the 60° wedge, being the correction factor for diode‐A significantly higher than for diode‐B. Diode‐A showed less temperature dependence than diode‐B. Sensitivity dependence on dose per pulse was a 1.5% higher for diode‐A than for diode‐B and therefore a higher SSD dependence was found for diode‐A. The loss of sensitivity with accumulated radiation dose was only about 0.3% for diode‐A, after 300 Gy, while it amounted to 8% for diode‐B. Weighing the different correction factors for both types of diodes no conclusions about which type is better can be driven. From these results it can be also seen that the dependence of the diode response on dose rate in a pulsed beam does not seem to be associated with the fact of being n‐type or p‐type but could be related to the doping level of the diodes.
The van der Waals interaction
Authors: Holstein Barry R.
Published: July 2002

The interaction between two neutral but polarizable systems at separation R, usually called the van der Waals force, is discussed from different points of view. The change in character from 1/R6 to 1/R7 due to retardation is explained.
Full-wave modeling of therapeutic ultrasound: Nonlinear ultrasound propagation in ideal fluids
Authors: Ginter Siegfried , Liebler Marko , Steiger Eckard , Dreyer Thomas , Riedlinger Rainer E.
Published: July 2002

The number of applications of high-intense, focused ultrasound for therapeutic purposes is growing. Besides established applications like lithotripsy, new applications like ultrasound in orthopedics or for the treatment of tumors arise. Therefore, new devices have to be developed which provide pressure waveforms and distributions in the focal zone specifically for the application. In this paper, a nonlinear full-wave simulation model is presented which predicts the therapeutically important characteristics of the generated ultrasound field for a given transducer and initial pressure signal. A nonlinear acoustic approximation in conservation form of the original hydrodynamic equations for ideal fluids rather than a wave equation provides the base for the nonlinear model. The equations are implemented with an explicit high-order finite-difference time-domain algorithm. The necessary coefficients are derived according to the dispersion relation preserving method. Simulation results are presented for two different therapeutic transducers: a self-focusing piezoelectric and one with reflector focusing. The computational results are validated by comparison with analytical solutions and measurements. An agreement of about 10% is observed between the simulation and experimental results.
Acoustic correlates of English and French nasalized vowels
Authors: Chen Marilyn Y.
Published: July 2002

Acoustic analysis of nasalized vowels in the frequency domain indicates the presence of extra peaks: one between the first two formants with amplitude P1 and one at lower frequencies, often below the first formant, with amplitude P0. The first-formant amplitude A1 is also reduced relative to its amplitude for an oral vowel. These acoustic characteristics can be explained by speech production theory. The objective of this study was to determine the values for the acoustic correlates A1-P1 and A1-P0 (dB) for quantifying nasalization. They were tested as measures of nasalization by comparing vowels between nasal consonants and those between stop consonants for English speakers. Also, portions of nasal vowels following a stop consonant were compared for speakers of French, which makes a linguistic distinction between oral and nasal vowels. In the analysis of English, the mean difference of A1-P1 measured in oral vowels and nasalized vowels had a range of 10 dB–15 dB; the difference of A1-P0 had a range of 6 dB–8 dB. In the study of French, the difference of A1-P1 measured between the least-nasalized portion and the most-nasalized portion of the vowel had a range of 9 dB–12 dB; for A1-P0, the difference ranged between 3 dB and 9 dB. In order to obtain an absolute acoustic measure of nasalization that was independent of vowel type, normalized parameters were calculated by adjusting for the influence of the vowel formant frequencies.
On the derivation of boundary integral equations for scattering by an infinite one-dimensional rough surface
Authors: DeSanto J. A. , Martin P. A.
Published: July 2002

A crucial ingredient in the formulation of boundary-value problems for acoustic scattering of time-harmonic waves is the radiation condition. This is well understood when the scatterer is a bounded obstacle. For plane-wave scattering by an infinite, rough, impenetrable surface S, the physics of the problem suggests that all scattered waves must travel away from (or along) the surface. This condition is used, together with Green’s theorem and the free-space Green’s function, to derive boundary integral equations over S. This requires careful consideration of certain integrals over a large semicircle of radius r; it is known that these integrals vanish as r→∞ if the scattered field satisfies the Sommerfeld radiation condition, but that is not the case here—reflected plane waves must be present. The integral equations obtained are Helmholtz integral equations; they must be modified for grazing incident waves. As such integral equations are often claimed to be exact, and are often used to generate benchmark numerical solutions, it seems worthwhile to establish their validity or otherwise.
On a mechanism of target disintegration at a shock wave focusing in ESWL systems
Authors: Kedrinskii Valery K.
Published: July 2002

It is well known how the lithotriptors operate and the discussion concerning the mechanisms of target disintegration are continued. Meanwhile, to understand these mechanisms means to obtain a possibility to influence on the fracture process. The spall mechanism, as a result of acting with the shear forces, the crack growth inside a stone, and an erosion mechanism (impacts of cumulative microjets forming at bubble collapse in the cavitation zone near a target wall), were suggested by Sturtevant, Kuwahara, Delius, Takayama, Groenig, Crum, and others to explain the disintegration effects observed. At the same time, all authors do not deny a rise of the cavitation zone in the vicinity of a focus under the action of a negative pressure phase in ‘‘a tail’’ of a shock wave. However, the role of the cavitation cluster is interpreted in different ways assuming that this effect is a secondary one. This paper proposes an approach to the estimation of the disintegration mechanism, which is based on the development and dynamics of the cavity cluster in a focus vicinity. Within the framework of a two-phase model of cavitating liquid the problem of bubbly cluster development and its collapse on a solid wall are considered. The experimental data on a simulation of cavity cluster pulsation on a target and the idea that hydraulic impacts generated by cluster can determine the mechanics of target disintegration in a focusing zone of shock wave and its rarefaction phase are discussed.
Experimental detection of a subharmonic route to chaos in acoustic cavitation through the tuning of a piezoelectric cavity
Authors: Cabeza C. , Sicardi-Schifino A. C. , Negreira C. , Montaldo G.
Published: July 2002

Experimental observation is reported of a subharmonic route to chaos through the tuning of a piezoelectric cavity. The emission spectrum of bubbles generated in a liquid contained in the cavity through the application of a pressure ultrasonic field of constant frequency is analyzed. The cavity height is used as control parameter to vary the resonance frequency of the cavity. In the emission spectrum of the bubbles subharmonics of the excitation frequency are observed. This phenomenon is identified as a period-doubling bifurcation and is explained on the basis of a simple model of resonance in the cavity. The appearance of subharmonics is highly sensitive to changes in the cavity height.
Sound attenuation in a cylindrical tube due to evaporation–condensation
Authors: Mao Yi
Published: July 2002

The influence of evaporation–condensation processes on sound propagation in a cylindrical tube was studied in an attempt to understand sound attenuation in porous materials. In this theoretical model, the tube wall is assumed to be rigid and kept at constant temperature. Water in a very thin layer on the wall is allowed to evaporate into or condense from the gas/vapor mixture due to the sound field propagating in the tube. In addition to the acoustical, thermal, and vorticity modes in Kirchhoff’s theory, there exists a mass-diffusion mode. Sound attenuation was obtained after applying the boundary conditions at the tube wall for these four modes. Analytical expressions for the asymptotic behavior in both high- and low-frequency limits were derived. While the sound attenuation due to viscosity could be identified, those due to thermal conduction and evaporation–condensation were coupled. The sound attenuation due to the evaporation–condensation process was significant when the concentration of vapor in the tube was high, but it still underestimated the experimental results in porous materials.
Scale Effects in the Study of Earth Tides
Authors: Gruntfest I. J. , Shaw H. R.
Published: July 2002

Some new conceptions of the current condition of our planet emerge from analyses of the tidal motions of the earth which take into account the effect of scale on the mechanical behavior of materials. In particular, mechanisms for the production of earthquakes, volcanoes, and continental drift are suggested. The results are compatible with available data and suggest new observations and experiments which might be useful for earthquake prediction or for the discovery of geothermal energy sources.
The 19S proteasome subunit Rpt5 reversibly associates with cold‐stable microtubules in glial cells at low temperatures
Authors: Flores‐Martin Jésica Belén , Bonnet Laura Vanesa , Palandri Anabela , Zamanillo‐Hermida Sofía , Hallak Marta Elena , Galiano Mauricio Raul
Published: February 2022

The ubiquitin–proteasome system (UPS) degrades intracellular proteins through the 26S proteasome. We analysed how cold stress affects the UPS in glial cells. Together with a reduction in the 20S proteolytic activity and increased levels of polyubiquitinated proteins, exposure of glial cell cultures to cold induces a partial disassembly of the 26S proteasome. In particular, we found that Rpt5, a subunit of the 19S proteasome, relocates to cold‐stable microtubules, although no apparent cytoskeletal redistribution was detected for other analysed subunits of the 19S or 20S complexes. Furthermore, we demonstrate that both the expression of the microtubule‐associated protein MAP6 and the post‐translational acetylation of α‐tubulin modulate the association of Rpt5 with microtubules. This reversible association could be related to functional preservation of the proteolytic complex during cold stress.