bluuebunny/crossref_metadata_2025 huggingface dataset:
Defective Development of γ/δ T Cells in Interleukin 7 Receptor–Deficient Mice Is Due to Impaired Expression of T Cell Receptor γ Genes
Authors: Kang Joonsoo , Coles Mark , Raulet David H.
Published: July 2002

Mice lacking the interleukin 7 receptor (IL-7R) generate α/β T cells at a detectable but greatly reduced rate, but γ/δ T cells are completely absent. The special role of IL-7R signaling in γ/δ T cell development has remained unclear. IL-7Rα−/− mice exhibit a paucity of γ gene rearrangements. This striking observation can be explained by a defect in T cell receptor (TCR)-γ gene rearrangement, a defect in TCR-γ gene transcription leading to death of γ/δ lineage cells, and/or a requirement for IL-7R in commitment of cells to the γ/δ lineage. To determine the role of IL-7R signaling in γ/δ T cell development, we examined transcription of a prerearranged TCR-γ transgene in IL-7Rα−/− mice, as well as the effects of IL-7 on transcription of endogenous, rearranged TCR-γ genes in α/β lineage cells. The results demonstrate that IL-7R–mediated signals are necessary for the normal expression of rearranged TCR-γ genes. Equally significant, the results show that the poor expression of TCR-γ genes in IL-7Rα−/− mice is responsible for the selective deficit in γ/δ cells in these mice, since a high copy TCR-γ transgene exhibited sufficient residual expression in IL-7Rα−/− mice to drive γ/δ cell development. The results indicate that the absence of γ/δ T cells in IL-7Rα−/− mice is due to insufficient TCR-γ gene expression.
The Role of Peptides in T Cell Alloreactivity Is Determined by Self–Major Histocompatibility Complex Molecules
Authors: Obst Reinhard , Netuschil Nikolai , Klopfer Karsten , Stevanović Stefan , Rammensee Hans-Georg
Published: July 2002

By analyzing T cell responses against foreign major histocompatibility complex (MHC) molecules loaded with peptide libraries and defined self- and viral peptides, we demonstrate a profound influence of self-MHC molecules on the repertoire of alloreactive T cells: the closer the foreign MHC molecule is related to the T cell's MHC, the higher is the proportion of peptide-specific, alloreactive (“allorestricted”) T cells versus T cells recognizing the foreign MHC molecule without regard to the peptide in the groove. Thus, the peptide repertoire of alloreactive T cells must be influenced by self-MHC molecules during positive or negative thymic selection or peripheral survival, much like the repertoire of the self-restricted T cells. In consequence, allorestricted, peptide-specific T cells (that are of interest for clinical applications) are easier to obtain if T cells and target cells express related MHC molecules.
Dap10 and Dap12 Form Distinct, but Functionally Cooperative, Receptor Complexes in Natural Killer Cells
Authors: Wu Jun , Cherwinski Holly , Spies Thomas , Phillips Joseph H. , Lanier Lewis L.
Published: July 2002

Many of the activating receptors on natural killer (NK) cells are multisubunit complexes composed of ligand-binding receptors that are noncovalently associated with membrane-bound signaling adaptor proteins, including CD3ζ, FcεRIγ, DAP12, and DAP10. Because the DAP10 and DAP12 genes are closely linked, expressed in NK cells, and have remarkably similar transmembrane segments, it was of interest to determine the specificity of their interactions with ligand-binding receptors and to examine their signaling properties. Despite their similarities, DAP10, DAP12, FcεRIγ, and CD3ζ form specific receptor complexes with their ligand-binding partners in NK cells and transfectants. The transmembrane regions of DAP10 and DAP12 are sufficient to confer specific association with their partners. Although cross-linking of either DAP10- or DAP12-associated receptors has been shown to be sufficient to trigger NK cell–mediated cytotoxicity against Fc receptor–bearing cells, substantial synergy was observed in the induction of cytokine production when both receptors were engaged. Activation of the Syk/ZAP70 tyrosine kinases by the immunoreceptor tyrosine-based activation motif–containing DAP12 adaptor and of the phosphatidylinositol 3-kinase pathway by the YxNM-containing DAP10 adaptor may play an important role in the stimulation of NK cells and T cells.
Genetic Modulation of T Cell Receptor Gene Segment Usage during Somatic Recombination
Authors: Livak Ferenc , Burtrum Douglas B. , Rowen Lee , Schatz David G. , Petrie Howard T.
Published: July 2002

Lymphocyte antigen receptors are not encoded by germline genes, but rather are produced by combinatorial joining between clusters of gene segments in somatic cells. Within a given cluster, gene segment usage during recombination is thought to be largely random, with biased representation in mature T lymphocytes resulting from protein-mediated selection of a subset of the total repertoire. Here we show that T cell receptor Dβ and Jβ gene segment usage is not random, but is patterned at the time of recombination. The hierarchy of gene segment usage is independent of gene segment proximity, but rather is influenced by the ability of the flanking recombination signal sequences (RSS) to bind the recombinase and/or to form a paired synaptic complex. Importantly, the relative frequency of gene segment usage established during recombination is very similar to that found after protein-mediated selection, suggesting that in addition to targeting recombinase activity, the RSS may have evolved to bias the naive repertoire in favor of useful gene products.
The Use of Lymphocyte Function–Associated Antigen (Lfa)-1–Deficient Mice to Determine the Role of Lfa-1, Mac-1, and α4 Integrin in the Inflammatory Response of Neutrophils
Authors: Henderson Robert B. , Lim Lina H.K. , Tessier Philippe A. , Gavins Felicity N.E. , Mathies Meg , Perretti Mauro , Hogg Nancy
Published: July 2002

After injury or infection, neutrophils rapidly migrate from the circulation into tissues by means of an orderly progression of adhesion receptor engagements. Neutrophils have been previously considered to use selectins exclusively to roll on vessels before an adhesion step mediated by the β2 integrins, lymphocyte function–associated antigen (LFA)-1, and Mac-1. Here we use LFA-1−/− mice, function blocking monoclonal antibodies, and intravital microscopy to investigate the roles of LFA-1, Mac-1, and α4 integrins in neutrophil recruitment in vivo. For the first time, we show that LFA-1 makes a contribution to neutrophil rolling by stabilizing the transient attachment or tethering phase of rolling. In contrast, Mac-1 does not appear to be important for either rolling or firm adhesion, but instead contributes to emigration from the vessel. Blocking Mac-1 in the presence of LFA-1 significantly reduces emigration, suggesting cooperation between these two integrins. Low levels of α4β1 integrin can be detected on neutrophils from LFA-1+/+ and −/− mice. These cells make use of α4β1 during the rolling phase, particularly in the absence of LFA-1. Thus LFA-1 and α4β1, together with the selectins, are involved in the rolling phase of neutrophil recruitment, and, in turn, affect the later stages of the transmigration event.
The Absence of Interleukin 9 Does Not Affect the Development of Allergen-induced Pulmonary Inflammation nor Airway Hyperreactivity
Authors: McMillan Sarah J. , Bishop Benjamin , Townsend Michael J. , McKenzie Andrew N. , Lloyd Clare M.
Published: July 2002

Interleukin (IL)-9 is a pleiotropic cytokine secreted by T helper (Th)2 cells and has been proposed as a candidate gene for asthma and allergy. We have used mice genetically deficient in IL-9 to determine the role of this cytokine in the pathophysiologic features of the allergic pulmonary response–airway hyperreactivity (AHR) and eosinophilia. We have demonstrated that IL-9 is not required for the development of a robust Th2 response to allergen in sensitized mice. IL-9 knockout mice developed a similar degree of eosinophilic inflammation and AHR to their wild-type littermates. Goblet cell hyperplasia and immunoglobulin (Ig) E production were also unaffected by the lack of IL-9. Moreover, levels of bronchoalveolar lavage (BAL) IL-4, IL-5, and IL-13 were comparable between wild-type and knockout mice. These findings indicate that IL-9 is not obligatory for the development of eosinophilia and AHR, and imply that other Th2 cytokines can act in a compensatory fashion.
Control of Rectification and Gating of Cloned KATP Channels by the Kir6.2 Subunit
Authors: Shyng S.-L. , Ferrigni T. , Nichols C.G.
Published: July 2002

KATP channels are a functional complex of sulphonylurea receptor (SUR1, SUR2) and inward rectifier K+ (Kir6.1, Kir6.2) channel subunits. We have studied the role of the putative pore forming subunit (Kir6.2) in regulation of rectification and gating of KATP channels generated by transfection of SUR1 and Kir6.2 cDNAs in COSm6 cells. In the absence of internal polyvalent cations, the current-voltage relationship is sigmoidal. Mg2+ or spermine4+ (spm) each induces a mild inward rectification. Mutation of the asparagine at position 160 in Kir6.2 to aspartate (N160D) or glutamate (N160E) increases the degree of rectification induced by Mg2+ or spermine4+, whereas wild-type rectification is still observed after mutation to other neutral residues (alanine–N160A, glutamine–N160Q). These results are consistent with this residue lining the pore of the channel and contributing to the binding of these cations, as demonstrated for the equivalent site in homomeric ROMK1 (Kir1.1) channels. Since Kir6.2 contains no consensus ATP binding site, whereas SUR1 does, inhibition by ATP has been assumed to depend on interactions with SUR1. However, we found that the [ATP] causing half-maximal inhibition of current (Ki) was affected by mutation of N160. Channels formed from N160D or N160Q mutant subunits had lower apparent sensitivity to ATP (Ki,N160D = 46.1 μM; Ki,N160Q = 62.9 μM) than wild-type, N160E, or N160A channels (Ki = 10.4, 17.7, 6.4 μM, respectively). This might suggest that ATP binding to the channel complex was altered, although examination of channel open probabilities indicates instead that the residue at position 160 alters the ATP-independent open probability, i.e., it controls the free energy of the open state, thereby affecting the “coupling” of ATP binding to channel inhibition. The results can be interpreted in terms of a kinetic scheme whereby the residue at Kir6.2 position 160 controls the rate constants governing transitions to and from the open state, without directly affecting ATP binding or unbinding transitions.
Synergistic Activation of G Protein–Gated Inwardly Rectifying Potassium Channels by the βγ Subunits of G Proteins and Na+ and Mg2+ Ions
Authors: Petit-Jacques Jérôme , Sui Jin Liang , Logothetis Diomedes E.
Published: July 2002

Native and recombinant G protein–gated inwardly rectifying potassium (GIRK) channels are directly activated by the βγ subunits of GTP-binding (G) proteins. The presence of phosphatidylinositol-bis-phosphate (PIP2) is required for G protein activation. Formation (via hydrolysis of ATP) of endogenous PIP2 or application of exogenous PIP2 increases the mean open time of GIRK channels and sensitizes them to gating by internal Na+ ions. In the present study, we show that the activity of ATP- or PIP2-modified channels could also be stimulated by intracellular Mg2+ ions. In addition, Mg2+ ions reduced the single-channel conductance of GIRK channels, independently of their gating ability. Both Na+ and Mg2+ ions exert their gating effects independently of each other or of the activation by the Gβγ subunits. At high levels of PIP2, synergistic interactions among Na+, Mg2+, and Gβγ subunits resulted in severalfold stimulated levels of channel activity. Changes in ionic concentrations and/or G protein subunits in the local environment of these K+ channels could provide a rapid amplification mechanism for generation of graded activity, thereby adjusting the level of excitability of the cells.
Light Adaptation in Drosophila Photoreceptors
Authors: Juusola Mikko , Hardie Roger C.
Published: July 2002

It is known that an increase in both the mean light intensity and temperature can speed up photoreceptor signals, but it is not known whether a simultaneous increase of these physical factors enhances information capacity or leads to coding errors. We studied the voltage responses of light-adapted Drosophila photoreceptors in vivo from 15 to 30°C, and found that an increase in temperature accelerated both the phototransduction cascade and photoreceptor membrane dynamics, broadening the bandwidth of reliable signaling with an effective Q10 for information capacity of 6.5. The increased fidelity and reliability of the voltage responses was a result of four factors: (1) an increased rate of elementary response, i.e., quantum bump production; (2) a temperature-dependent acceleration of the early phototransduction reactions causing a quicker and narrower dispersion of bump latencies; (3) a relatively temperature-insensitive light-adapted bump waveform; and (4) a decrease in the time constant of the light-adapted photoreceptor membrane, whose filtering matched the dynamic properties of the phototransduction noise. Because faster neural processing allows faster behavioral responses, this improved performance of Drosophila photoreceptors suggests that a suitably high body temperature offers significant advantages in visual performance.
Global lower bound for the heat kernel of -Δ+\frac{𝑐}|𝑥|²
Authors: Zhang Qi
Published: July 2002

We obtain global in time and qualitatively sharp lower bounds for the heat kernel of the singular Schrödinger operator

−
Δ
+

a

|

x

|

2

-\Delta + \frac {a}{|x|^2}

with

a
>
0

a>0

. Here

Δ
\Delta

is either the Laplace-Beltrami operator or the Laplacian on the Heisenberg group. This complements a recent paper by P. D. Milman and Yu. A. Semenov in which an upper bound was found. The above potential is interesting because it is a border line case where both the strong maximum principle and Gaussian bounds fail.
On the Darboux theorem for weak symplectic manifolds
Authors: Bambusi Dario
Published: July 2002

A new tool to study reducibility of a weak symplectic form to a constant one is introduced and used to prove a version of the Darboux theorem more general than previous ones. More precisely, at each point of the considered manifold a Banach space is associated to the symplectic form (dual of the phase space with respect to the symplectic form), and it is shown that the Darboux theorem holds if such a space is locally constant. The following application is given. Consider a weak symplectic manifold

M
M

on which the Darboux theorem is assumed to hold (e.g. a symplectic vector space). It is proved that the Darboux theorem holds also for any finite codimension symplectic submanifolds of

M
M

, and for symplectic manifolds obtained from

M
M

by the Marsden–Weinstein reduction procedure.
Sums of squares of regular functions on real algebraic varieties
Authors: Scheiderer Claus
Published: July 2002

Let

V
V

be an affine algebraic variety over

R

\mathbb {R}

(or any other real closed field

R
R

). We ask when it is true that every positive semidefinite (psd) polynomial function on

V
V

is a sum of squares (sos). We show that for

dim
⁡
V
≥
3

\dim V\ge 3

the answer is always negative if

V
V

has a real point. Also, if

V
V

is a smooth non-rational curve all of whose points at infinity are real, the answer is again negative. The same holds if

V
V

is a smooth surface with only real divisors at infinity. The “compact” case is harder. We completely settle the case of smooth curves of genus

≤
1

\le 1

: If such a curve has a complex point at infinity, then every psd function is sos, provided the field

R
R

is archimedean. If

R
R

is not archimedean, there are counter-examples of genus 

1
1

.
Null Mutation ofAtCUL1Causes Arrest in Early Embryogenesis inArabidopsis
Authors: Shen Wen-Hui , Parmentier Yves , Hellmann Hanjo , Lechner Esther , Dong Aiwu , Masson Jean , Granier Fabienne , Lepiniec Loı̈c , Estelle Mark , Genschik Pascal
Published: July 2002

The SCF (for SKP1, Cullin/CDC53,F-box protein) ubiquitin ligase targets a number of cell cycle regulators, transcription factors, and other proteins for degradation in yeast and mammalian cells. Recent genetic studies demonstrate that plant F-box proteins are involved in auxin responses, jasmonate signaling, flower morphogenesis, photocontrol of circadian clocks, and leaf senescence, implying a large spectrum of functions for the SCF pathway in plant development. Here, we present a molecular and functional characterization of plant cullins. TheArabidopsis genome contains 11 cullin-related genes. Complementation assays revealed that AtCUL1 but not AtCUL4 can functionally complement the yeast cdc53 mutant.Arabidopsis mutants containing transfer DNA (T-DNA) insertions in the AtCUL1 gene were shown to display an arrest in early embryogenesis. Consistently, both the transcript and the protein of the AtCUL1 gene were found to accumulate in embryos. The AtCUL1 protein localized mainly in the nucleus but also weakly in the cytoplasm during interphase and colocalized with the mitotic spindle in metaphase. Our results demonstrate a critical role for the SCF ubiquitin ligase inArabidopsis embryogenesis.
MEF2‐mediated recruitment of class II HDAC at the EBV immediate early gene BZLF1 links latency and chromatin remodeling
Authors: Gruffat H , Manet E , Sergeant A
Published: July 2002

In B lymphocytes induced to proliferate in vitro by the Epstein–Barr virus (EBV), extra‐chromosomal viral episomes packaged in chromatin persist in the nucleus, and there is no productive cycle. A switch from this latency to the productive cycle is observed after induced expression of the EBV BZLF1 gene product, the transcription factor EB1. We present evidence that, during latency, proteins of the myocyte enhancer binding factor 2 (MEF2) family are bound to the BZLF1 promoter and recruit class II histone deacetylases. Furthermore, we propose that latency is determined primarily by a specific and local recruitment of class II histone deacetylase (HDAC) by MEF2D to the BZLF1 gene promoter. The switch from latency to the productive cycle could be due in part to post‐translational modification of MEF2 proteins and changes in the local acetylation state of the chromatin.
Initial activation of cyclin‐B1–cdc2 kinase requires phosphorylation of cyclin B1
Authors: Peter Marion , Le Peuch Christian , Labbé Jean‐Claude , Meyer April N , Donoghue Daniel J , Dorée Marcel
Published: July 2002

At the G2/M transition of the cell cycle, the cdc25c phosphatase dephosphorylates inhibitory residues of cdc2, and cyclin‐B–cdc2 kinase (MPF) is activated. Phosphorylation of cyclin B1 induces its nuclear accumulation, and, since cdc25c is also believed to accumulate and activate shortly before G2/M in the nucleus, it has been proposed that this induces cyclin‐B1–cdc2 kinase activation. We demonstrate that cyclin B1 phosphorylation has another essential function in vivo: it is required for cdc25c and MPF activation, which does not require nuclear accumulation of cyclin B1, and occurs in the cytoplasm.
Heterogeneity of fish taste bud ultrastructure as demonstrated in the holosteans
Amia calva
and
Lepisosteus oculatus
Authors: Reutter Klaus , Boudriot Friederike , Witt Martin
Published: July 2002

Taste buds are the peripheral sensory organs of the gustatory system. They occur in all taxa of vertebrates and are pear–shaped intra–epithelial organs of about 80 μm height and 50 μm width. Taste buds mainly consist of specialized epithelial cells, which synapse at their bases and therefore are secondary sensory cells. Taste buds have been described based on studies of teleostean species, but it turned out that the ultrastructure of teleostean taste buds may differ between distinct systematic groups and that this description is not representative of those taste buds in other main taxa of fishes, such as selachians, holosteans and dipnoans. Furthermore, it is not known how variable the micromorphologies of non–teleostean taste buds are. For this reason the taste buds of two holosteans,
Lepisosteus oculatus
and
Amia calva
, were investigated and compared. While in both species the taste buds are of the same shapes and sizes, the cellular components of their sensory epithelia differ: in
Lepisosteus
taste buds comprise two types of elongated light cells and one type of dark cells. In contrast,
Amia
taste buds contain only one type of light, but two types of dark elongated cells. Afferent synapses are common in the buds of both species, efferent synapses occur only in
Lepisosteus
taste buds. These differences show that even in the small group of holostean fishes the taste buds are differently organized. Consequently, a representative type of fish taste buds does not exist.
Genetic approaches to studying virulence and pathogenesis inToxoplasma gondii
Authors: Sibley L. David , Mordue Dana G. , Su Chunlei , Robben Paul M. , Howe Dan K.
Published: July 2002

Toxoplasma gondiiis a common protozoan parasite that causes disease in immunocompromised humans. Equipped with a wide array of experimental tools,T. gondiihas rapidly developed as a model parasite for genetic studies. The population structure ofT. gondiiis highly clonal, consisting of three distinct lineages that differ dramatically in virulence. Acute virulence is probably mediated by the genetic differences that distinguish strain types. We have utilized a combination of genetic approaches to investigate the acute virulence of toxoplasmosis using the mouse model. These studies reveal the surprising finding that pathogenicity is due to the over–stimulation of normally protective immune responses. Classical genetic linkage mapping studies indicate that genes that mediate acute virulence are linked to chromosome VII in the parasite. To increase the resolution of genetic mapping studies, single–nucleotide polymorphisms are being developed based on an extensive database of expressed sequence tags (ESTs) fromT. gondii. Separately, DNA microarray studies are being used to examine the expression of parasite and host genes during infection. Collectively, these approaches should improve current understanding of virulence and pathogenicity in toxoplasmosis.
Identification of Multiple Genetic Loci Linked to the Propensity for “Behavioral Despair” in Mice
Authors: Yoshikawa Takeo , Watanabe Akiko , Ishitsuka Yuichi , Nakaya Akihiro , Nakatani Noriaki
Published: July 2002

The forced swim test (FST) and tail suspension test (TST) are widely used and well established screening paradigms for antidepressants. A variety of antidepressive agents are known to reduce immobility time in both FST and TST. To identify genetic determinants of immobility duration in both tests, we analyzed 560 F2 mice from an intercross between C57BL/6 (B6) and C3H/He (C3) strains. Composite interval mapping revealed five major loci (suggestive and significant linkage) affecting immobility in the FST, and four loci for the TST. The quantitative trait loci (QTL) on chromosomes 8 and 11 overlap between the two behavioral measures. Genome-wide interaction analysis, which was developed to identify locus pairs that may contribute epistatically to a phenotype, detected two pairs of chromosomal loci for the TST. The QTL on chromosome 11 and its associated epistatic TST–QTL on chromosome X encode γ-aminobutyric acid type A (GABAA) receptor subunits as candidates. Sequence and expression analyses of these genes from the two parental strains revealed a significantly lower expression of the α1 subunit gene in the frontal cortex of B6 mice compared to C3 mice. The present quantitative trait study should open up avenues for identifying novel molecular targets for antidepressants and unraveling the complex genetic mechanisms of depressive and anxiety disorders.
A neural network approach to breast cancer diagnosis as a constraint satisfaction problem
Authors: Tourassi Georgia D. , Markey Mia K. , Lo Joseph Y. , Floyd Carey E.
Published: July 2002

A constraint satisfaction neural network (CSNN) approach is proposed for breast cancer diagnosis using mammographic and patient history findings. Initially, the diagnostic decision to biopsy was formulated as a constraint satisfaction problem. Then, an associative memory type neural network was applied to solve the problem. The proposed network has a flexible, nonhierarchical architecture that allows it to operate not only as a predictive tool but also as an analysis tool for knowledge discovery of association rules. The CSNN was developed and evaluated using a database of 500 nonpalpable breast lesions with definitive histopathological diagnosis. The CSNN diagnostic performance was evaluated using receiver operating characteristic analysis (ROC). The results of the study showed that the CSNN ROC area index was The CSNN predictive performance is competitive with that achieved by experienced radiologists and backpropagation artificial neural networks (BP‐ANNs) presented before. Furthermore, the study illustrates how CSNN can be used as a knowledge discovery tool overcoming some of the well‐known limitations of BP‐ANNs.
Monte Carlo and TLD dosimetry of an high dose‐rate brachytherapy source
Authors: Karaiskos P. , Angelopoulos A. , Sakelliou L. , Sandilos P. , Antypas C. , Vlachos L. , Koutsouveli E.
Published: July 2002

An analytical Monte Carlo simulation code has been used to perform dosimetry calculations around an high dose‐rate brachytherapy source utilized in the widely used microSelectron afterloaded system. Radial dose functions, dose rate constant and anisotropy functions, utilized in the AAPM Task Group 43 dose estimation formalism, have been calculated. In addition, measurements of anisotropy functions using LiF TLD‐100 rods have been performed in a polystyrene phantom to support our Monte Carlo calculations. The energy dependence of LiF TLD response was investigated over the whole range of measurement distances and angles. TLD measurements and Monte Carlo calculations are in agreement to each other and agree with published data. The influence of phantom dimensions on calculations was also investigated. Radial dose functions were found to depend significantly on phantom dimensions at radial distances near phantom edges. Deviations of up to 25% are observed at these distances due to the lack of full scattering conditions, indicating that body dimensions should be taken into account in treatment planning when the absorbed dose is calculated near body edges. On the other hand, anisotropy functions do not demonstrate a strong dependence on phantom dimensions. However, these functions depend on radial distance at angles close to the longitudinal axis of the source, where deviations of up to 20% are observed.
Measurement of radiotherapy x‐ray skin dose on a chest wall phantom
Authors: Quach K. Y. , Morales J. , Butson M. J. , Rosenfeld A. B. , Metcalfe P. E.
Published: July 2002

Sufficient skin dose needs to be delivered by a radiotherapy chest wall treatment regimen to ensure the probability of a near surface tumor recurrence is minimized. To simulate a chest wall treatment a hemicylindrical solid water phantom of 7.5 cm radius was irradiated with 6 MV x‐rays using and fields at 100 cm source surface distance (SSD) to the base of the phantom. A surface dose profile was obtained from 0 to 180°, in 10° increments around the circumference of the phantom. Dosimetry results obtained from radiochromic film (effective depth of 0.17 mm) were used in the investigation, the superficial doses were found to be 28% (of at the 0° beam entry position and 58% at the 90° oblique beam position. Superficial dose results were also obtained using extra thin thermoluminescent dosimeters (TLD) (effective depth 0.14 mm) of 30% at 0°, 57% at 90°, and a metal oxide semiconductor field effect transistor (MOSFET) detector (effective depth 0.5 mm) of 43% at 0°, 62% at 90°. Because the differences in measured superficial doses were significant and beyond those related to experimental error, these differences are assumed to be mostly attributable to the effective depth of measurement of each detector. We numerically simulated a bolus on/bolus off technique and found we could increase the coverage to the skin. Using an alternate “bolus on,” “bolus off” regimen, the skin would receive 36.8 Gy at 0° incidence and 46.4 Gy at 90° incidence for a prescribed midpoint dose of 50 Gy. From this work it is evident that, as the circumference of the phantom is traversed the SSD increases and hence there is an inverse square fluence fall‐off, this is more than offset by the increase in skin dose due to surface curvature to a plateau at about 90°. Beyond this angle it is assumed that beam attenuation through the phantom and inverse square fall‐off is causing the surface dose to reduce.
Screening of a point charge by an anisotropic medium: Anamorphoses in the method of images
Authors: Mele E. J.
Published: July 2002

We extend the classical dielectric image problem for an external point charge interacting with a semi-infinite medium to the case of an anisotropic dielectric. We show that the exterior potential is a solution to an unconventional image problem. By contrast the interior potential is not a solution to any simple image system; instead it can be obtained through an anamorphic transformation of an image solution. We calculate the volume bound charge density that is induced within the anisotropic dielectric and distinguishes it from an isotropic medium where the volume density vanishes. This solution provides a very simple and physically relevant example in which the physics of the surface and volume bound charge densities in a polarized dielectric can be analyzed.
A simple experiment for measuring the surface tension of soap solutions
Authors: Román F. L. , Faro J. , Velasco S.
Published: July 2002

A simple experimental method for measuring the surface tension of a soap solution is proposed. In the experiment, a soap solution bubble is inflated by a syringe that is also connected to a precision manometer. By measuring the pressure change inside the bubble the surface tension can be calculated using the Young–Laplace equation. Experimental results for both toilet and dishwasher soap solutions are obtained.
Teaching scientific thinking skills: Students and computers coaching each other
Authors: Reif Frederick , Scott Lisa A.
Published: July 2002

Our attempts to improve physics instruction have led us to analyze thought processes needed to apply scientific principles to problems—and to recognize that reliable performance requires the basic cognitive functions of deciding, implementing, and assessing. Using a reciprocal-teaching strategy to teach such thought processes explicitly, we have developed computer programs called PALs (P_ersonal A_ssistants for L_earning) in which computers and students alternately coach each other. These computer-implemented tutorials make it practically feasible to provide students with individual guidance and feedback ordinarily unavailable in most courses. We constructed PALs specifically designed to teach the application of Newton’s laws. In a comparative experimental study these computer tutorials were found to be nearly as effective as individual tutoring by expert teachers—and considerably more effective than the instruction provided in a well-taught physics class. Furthermore, almost all of the students using the PALs perceived them as very helpful to their learning. These results suggest that the proposed instructional approach could fruitfully be extended to improve instruction in various practically realistic contexts.
A class of inverse problems in physics
Authors: Carter Ashley H.
Published: July 2002

If physics students are exposed at all to inverse problems, it is usually in the context of specialized treatments of quantum scattering processes. Inverse problems are, however, important in a wide variety of applications, such as gravitational lensing, seismological exploration, and underwater acoustic tomography. Students can be introduced to inverse problems in undergraduate courses in mechanics, optics, and quantum mechanics. This paper presents some simple examples whose solution in each case involves Abel’s integral equation, illustrating the ubiquity of this mathematical relation in diverse areas of physics.
A software model to estimate zones of impact on marine mammals around anthropogenic noise
Authors: Erbe Christine , Farmer David M.
Published: July 2002

Anthropogenic noise impacts marine mammals in a variety of ways. In order to estimate over which ranges this happens, we first need to understand the propagation of noise through the ocean away from the noise source, and, second, understand the relationship between received noise levels and impact thresholds. A software package combining both aspects is presented. (1) A sound propagation model based on ray theory was developed to calculate received noise levels as a function of range, depth, and frequency. (2) Current knowledge of noise impact thresholds for marine mammals was gathered and included in software routines predicting zones of impact on marine mammals around industrial underwater noise sources. As input parameters, this software package requires the source level and spectrum of the noise of interest; physical oceanography data about the local ocean environment such as bathymetry, bottom and surface loss data, and sound speed profiles; and bioacoustical information about the target species in the form of an audiogram, critical auditory bandwidths, spectra of typical animal vocalizations, reported sound levels of disturbance, and criteria for hearing damage. As output, the software produces data files and plots of the zones of audibility, masking, disturbance, and potential hearing damage around a noise source.
On the relationship between identification and discrimination of non-native nasal consonants
Authors: Harnsberger James D.
Published: July 2002

To examine the relationship between the identification and discrimination of non-native sounds, nasal consonants varying in place of articulation from Malayalam, Marathi, and Oriya were presented in two experiments to seven listener groups varying in their native nasal consonant inventory: Malayalam, Marathi, Punjabi, Tamil, Oriya, Bengali, and American English. The experiments consisted of a categorial AXB discrimination test and a forced-choice identification test with category goodness ratings. The identification test results were used to classify the non-native contrasts as one of five “assimilation types” of the Perceptual Assimilation Model (PAM) that are predicted to vary in their relative discriminability: two-category (TC), uncategorizable–categorizable (UC), both uncategorizable (UU), category-goodness (CG), and single-category (SC). The results showed that the mean percent correct discrimination scores of the assimilation types, but not the range of scores, were accurately predicted. Furthermore, differences in category goodness ratings in the CG and SC assimilations that were predicted to correlate with discrimination showed a weak, but significant correlation (r=0.31, p<0.05). The implications of the results for models of cross-language speech perception were discussed, and an alternative model of cross-language speech perception was outlined, in which the discriminability of non-native contrasts is a function of the similarity of non-native sounds to each other in a multidimensional, phonologized perceptual space.
Peripheral auditory processing and investigations of the “precedence effect” which utilize successive transient stimuli
Authors: Hartung Klaus , Trahiotis Constantine
Published: July 2002

This article addresses how a consideration of peripheral auditory processing can help to understand experiments concerning binaural precedence that employ successive binaural transients. It appears that much of the patterning of the behavioral data is amenable to an explanation based on peripheral interactions that result from auditory filtering and the functioning of auditory hair cells in combination with a binaural model based on cross correlation. A noteworthy aspect of this approach is that it does not include inhibitory mechanisms like those commonly invoked to explain binaural precedence.
Acoustic propagation and atmosphere characteristics derived from infrasonic waves generated by the Concorde
Authors: Le Pichon Alexis , Garcés Milton , Blanc Elisabeth , Barthélémy Maud , Drob Doug P.
Published: July 2002

Infrasonic signals generated by daily supersonic Concorde flights between North America and Europe have been consistently recorded by an array of microbarographs in France. These signals are used to investigate the effects of atmospheric variability on long-range sound propagation. Statistical analysis of wave parameters shows seasonal and daily variations associated with changes in the wind structure of the atmosphere. The measurements are compared to the predictions obtained by tracing rays through realistic atmospheric models. Theoretical ray paths allow a consistent interpretation of the observed wave parameters. Variations in the reflection level, travel time, azimuth deviation and propagation range are explained by the source and propagation models. The angular deviation of a ray’s azimuth direction, due to the seasonal and diurnal fluctuations of the transverse wind component, is found to be ∼5° from the initial launch direction. One application of the seasonal and diurnal variations of the observed phase parameters is the use of ground measurements to estimate fluctuations in the wind velocity at the reflection heights. The simulations point out that care must be taken when ascribing a phase velocity to a turning height. Ray path simulations which allow the correct computation of reflection heights are essential for accurate phase identifications.
A study of the transmission of ultrasound across solid–rubber interfaces
Authors: Drinkwater Bruce , Dwyer-Joyce Rob , Cawley Peter
Published: July 2002

The reflection coefficient at the solid–rubber interface of a rubber coupled ultrasonic transducer may be used as a measure of its coupling performance; the lower the solid–rubber reflection coefficient, the better the coupling. An experimental and theoretical study of the transmission of ultrasound across dry coupled solid–rubber interfaces, and in particular the effect of surface roughness and particulate contaminants on solid coupling, is described. The effect of surface roughness is modeled using a numerical contact model of the solid–rubber interface from which the static stiffness is calculated. The calculated interfacial stiffness is then used in a spring model of the interface to predict the solid–rubber reflection coefficient behavior. By repeating this process for different loads applied to the solid–rubber interface the variation of reflection coefficient with interfacial pressure is found. The agreement between these predictions and the experiments is shown to be reasonable in general and good at higher pressures. The numerical contact model is then used to predict the pressure required to achieve a given level of coupling on a variety of surfaces. This modeling procedure can now be used to provide the operator of a dry coupled system with an estimate of the pressure which must be applied to a dry coupled transducer on a given system to achieve the required coupling. The effect of dust and dirt on the transmission of ultrasound across solid–rubber interfaces has been considered experimentally. These experiments showed that particulate contaminants at a solid coupled interface significantly reduce the degree of coupling and this effect is quantified.
Spatial coherence of sound in convergence zones and shallow zones in the South China Sea
Authors: Guan Dinghua , Zhang Renhe , Sun Zhenge , Wang Yan
Published: July 2002

Some results of a horizontal spatial coherence experiment of sound propagation in the South China Sea were presented. Average water depth is over 4000 m and the depth of axis of the underwater sound channel is 1200 m. Explosive sources were discharged at depths of 7, 100, 200, and 1000 m. Signals were received at a horizontal receiving array of seven hydrophones with an overall length 410 m at a depth of 200 m. Distances between hydrophones are 10, 20, 40, 80, 160, and 1000 m. It is found that at the direct arrival zone and the convergence zones the sound field has good horizontal coherence. At the direct arrival zone the radius of coherence is larger than 200 m. At the first convergence zone the radius of coherence is larger than 250 m. At the second, third, and fourth convergence zones for frequencies lower than 1000 Hz the radii of coherence are larger than 250 m. When the sound source is placed at the shadow zones, the radius of horizontal coherence is less than 100 m, much lower than at the convergence zones. This experiment shows that a horizontal array can be used for beam forming with high spatial gain and good directivities at convergence zones.
The new Konzertsaal of the KKL Center, Lucerne, Switzerland. I. Acoustics design
Authors: Johnson Russell , Kahle Eckhard
Published: July 2002

The 1840 seat concert hall is the first of three halls that will eventually make up the Culture and Convention Center in Lucerne. It was inaugurated on 19 August 1998 to widespread critical acclaim. The hall is the home of the Lucerne International Music Festival, one of the most prestigious international festivals dedicated to symphonic music. The room will first be presented and illustrated, and an outline will be given of the basic acoustics design features such as room shape, seat count, and balcony design. Then, focus will shift to more specific acoustic design features, such as the reverberance chamber surrounding the main audience chamber, the two-part moving canopy with both horizontal and vertical reflecting surfaces, and the acoustically diffusing surface finish on most of the side wall area of the hall.
Experimental study of a fractal acoustical cavity
Authors: Hébert B. , Sapoval B. , Russ S.
Published: July 2002

The resonance properties of a prefractal cavity are studied in an acoustical transmission experiment. Resonance frequencies and quality factors are measured and compared to theory. All the delocalized modes are detected, and their measured eigenfrequencies closely fit numerical predictions. Most of the localized modes appear to be missing in the experimental spectra because of their weak coupling with the acoustic excitation and detection. The measurement of the quality factor of the acoustic resonances confirms the existence of increased damping due to the irregular shape of the cavity. This constitutes the first experimental evidence for the damping power of fractal structures.
Measurements and predictions of the phase velocity and attenuation coefficient in suspensions of elastic microspheres
Authors: Mobley Joel , Waters Kendall R. , Hall Christopher S. , Marsh Jon N. , Hughes Michael S. , Brandenburger Gary H. , Miller James G.
Published: July 2002

The phase velocities and attenuation coefficients for suspensions of narrowly sized polymer microspheres are reported over a broadband spectrum from 3 to 30 MHz. The six suspensions used in this work contain microspheres with respective average diameters near 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, and 100 μm. The results of these measurements are compared with theoretical expressions for the phase velocity and attenuation coefficient derived from the scattering properties of an elastic sphere in water using the weak scattering limit of the Waterman and Truell dispersion relation [J. Math. Phys. 2, 512–537 (1961)]. This single-scattering limit of the theory is found to be sufficient for predicting the ultrasonic transport properties of these suspensions to a considerable degree of accuracy.
Acoustical performance of an electrostrictive polymer film loudspeaker
Authors: Heydt Richard , Pelrine Ron , Joseph Jose , Eckerle Joseph , Kornbluh Roy
Published: July 2002

A new type of loudspeaker that generates sound by means of the electrostrictive response of a thin polymer film is described. Electrostrictive polymer film (EPF) loudspeakers are constructed with inexpensive, lightweight materials and have a very low profile. The films are typically silicone and are coated with compliant electrodes to allow large film deformations. Acoustical frequency response measurements from 5×5 cm (planar dimensions) prototype EPF loudspeakers are presented. Measurements of harmonic distortion are also shown, along with results demonstrating reduced harmonic distortion achieved with square-root wave shaping. Applications of EPF loudspeakers include active noise control and general-purpose flat-panel loudspeakers.
The radial motion of a sonoluminescence bubble driven with multiple harmonics
Authors: Hargreaves Kirk , Matula Thomas J.
Published: July 2002

Harmonic excitation has been reported to enhance the light emission of a single sonoluminescing bubble by as much as 300% [J. Holzfuss, M. Rüggeberg, and R. Mettin, Phys. Rev. Lett. 81, 1961–1964 (1998)]. In this paper it is shown that the effect of harmonic excitation on the radial motion of the bubble is consistent with bubble dynamics predictions. Also, it has been suggested that the energetic collapse of a sonoluminescence bubble can be enhanced with the addition of an acoustic “spike” drive [W. C. Moss et al., Phys. Lett. A 211, 69–74 (1996)]. Preliminary attempts to spike the bubble with an acoustic pulse (positive and negative) resulted in a temporary increase in light intensity of ≈ 200%; however, a strong acoustic radiation force pushes the bubble away from the antinodal region, suggesting that “spiking” the bubble each and every acoustic cycle may not be feasible.
Perceptual classification based on the component structure of song in European starlings
Authors: Gentner Timothy Q. , Hulse Stewart H.
Published: July 2002

The ability to recognize individuals based on their vocalizations is common among many species of songbirds. Examining the psychological and neural basis of this functionally relevant behavior can provide insight into the perceptual processing of acoustically complex, real-world, communication signals. In one species of songbird, European starlings (Sturnus vulgaris), males sing long and acoustically complex songs composed of small stereotyped note clusters called motifs. Previous studies demonstrate that starlings are capable of individual vocal recognition, and suggest that vocal recognition results from the association of specific motifs with specific individuals. The present study tests this possibility by examining how variation among the motifs that comprise a song affect its discrimination and classification. Starlings were trained, using operant techniques, to associate multiple songs from a single male starling with one response, and songs from four other male starlings with another response. The level of stimulus control exerted by motif variation was then measured by having subjects classify three sets of novel song bouts in which motifs from the training songs were systematically recombined. The results demonstrate a significant, and approximately linear, relationship between song classification and the relative proportions of familiar motifs from different singers that compose a bout. The results also indicate that the motif proportion effects on song classification are primary to retroactive interference in the recall for specific motifs, and independent of any biases due to the syntactic organization of motifs within a bout. Together, the results of this study suggest that starlings organize the complex vocalizations of conspecifics by memorizing large numbers of unique song components (i.e., motifs) that are then associated with different classes. Because individual starlings tend to possess unique motif repertoires, it is likely that under natural conditions such classes will correspond to individual identity. Thus, it is likely that perceptual processing mechanisms similar to those described by the results of the present study form the basis for individual vocal recognition in starlings.