bluuebunny/crossref_metadata_2025 huggingface dataset:
Subsets of Human Dendritic Cell Precursors Express Different Toll-like Receptors and Respond to Different Microbial Antigens
Authors: Kadowaki Norimitsu , Ho Stephen , Antonenko Svetlana , de Waal Malefyt Rene , Kastelein Robert A. , Bazan Fernando , Liu Yong-Jun
Published: July 2002

Toll-like receptors (TLRs) are ancient microbial pattern recognition receptors highly conserved from Drosophila to humans. To investigate if subsets of human dendritic cell precursors (pre-DC), including monocytes (pre-DC1), plasmacytoid DC precursors (pre-DC2), and CD11c+ immature DCs (imDCs) are developed to recognize different microbes or microbial antigens, we studied their TLR expression and responses to microbial antigens. We demonstrate that whereas monocytes preferentially express TLR 1, 2, 4, 5, and 8, plasmacytoid pre-DC strongly express TLR 7 and 9. In accordance with these TLR expression profiles, monocytes respond to the known microbial ligands for TLR2 (peptidoglycan [PGN], lipoteichoic acid) and TLR4 (lipopolysaccharide), by producing tumor necrosis factor (TNF)-α and interleukin (IL)-6. In contrast, plasmacytoid pre-DCs only respond to the microbial TLR9-ligand, CpG-ODNs (oligodeoxynucleotides [ODNs] containing unmethylated CpG motifs), by producing IFN-α. CD11c+ imDCs preferentially express TLR 1, 2, and 3 and respond to TLR 2-ligand PGN by producing large amounts of TNF-α, and to viral double-stranded RNA-like molecule poly I:C, by producing IFN-α and IL-12. The expression of distinct sets of TLRs and the corresponding difference in reactivity to microbial molecules among subsets of pre-DCs and imDCs support the concept that they have developed through distinct evolutionary pathways to recognize different microbial antigens.
Positive and Negative Coupling of the Metabotropic Glutamate Receptors to a G Protein–activated K+ Channel, GIRK, in Xenopus Oocytes
Authors: Sharon Dahlia , Vorobiov Dmitry , Dascal Nathan
Published: July 2002

Metabotropic glutamate receptors (mGluRs) control intracellular signaling cascades through activation of G proteins. The inwardly rectifying K+ channel, GIRK, is activated by the βγ subunits of Gi proteins and is widely expressed in the brain. We investigated whether an interaction between mGluRs and GIRK is possible, using Xenopus oocytes expressing mGluRs and a cardiac/brain subunit of GIRK, GIRK1, with or without another brain subunit, GIRK2. mGluRs known to inhibit adenylyl cyclase (types 2, 3, 4, 6, and 7) activated the GIRK channel. The strongest response was observed with mGluR2; it was inhibited by pertussis toxin (PTX). This is consistent with the activation of GIRK by Gi/Go-coupled receptors. In contrast, mGluR1a and mGluR5 receptors known to activate phospholipase C, presumably via G proteins of the Gq class, inhibited the channel's activity. The inhibition was preceded by an initial weak activation, which was more prominent at higher levels of mGluR1a expression. The inhibition of GIRK activity by mGluR1a was suppressed by a broad-specificity protein kinase inhibitor, staurosporine, and by a specific protein kinase C (PKC) inhibitor, bis-indolylmaleimide, but not by PTX, Ca2+ chelation, or calphostin C. Thus, mGluR1a inhibits the GIRK channel primarily via a pathway involving activation of a PTX-insensitive G protein and, eventually, of a subtype of PKC, possibly PKC-μ. In contrast, the initial activation of GIRK1 caused by mGluR1a was suppressed by PTX but not by the protein kinase inhibitors. Thus, this activation probably results from a promiscuous coupling of mGluR1a to a Gi/Go protein. The observed modulations may be involved in the mGluRs' effects on neuronal excitability in the brain. Inhibition of GIRK by phospholipase C–activating mGluRs bears upon the problem of specificity of G protein (GIRK interaction) helping to explain why receptors coupled to Gq are inefficient in activating GIRK.
Sudden atom-molecule collisions: CsF scattered by Ne, Ar, Kr and Xe
Authors: A S Dickinson  , D Richards
Published: July 2002

The sudden approximation in conjunction with the body-fixed and semiclassical approximations provides a simple method of calculating differential state-to-state cross sections. These approximations overestimate the mod Delta j mod =1 cross section by 5-15% and the mod Delta j mod =2 cross section by 25-35%. Various Lennard-Jones (12,6) spherical potentials and the leading terms of the long-range anisotropic potential are used. The results of this theory are compared with measurements of partial cross sections for jm to j'm' transitions in CsF scattered by Ne, Ar, Ke and Xe. The calculated values are consistent with about 40% of the observations.
Measurements of relative transition probabilities and the variation of the electronic transition moment for N2C3Πu-B3Πgsecond positive system
Authors: G Hartmann  , P C Johnson
Published: July 2002

Accurate values of the relative transition probabilities Aupsilon ' upsilon ''for 41 bands in the N2second positive system have been measured using single-photon counting techniques on a repetitive pulsed source. A computer code simulating the band structure, including multiplet splitting, and intensity distribution enables any band intensity to be deduced from the fractional intensity seen at the peak in the P branch (band-head). The variation of the electronic transition moment with internuclear separation Re(r) is obtained from the measured Aupsilon ' upsilon ''by means of a weighted least-squares curve-fitting procedure based on nth moment r centroids. It is best represented by a polynomial of degree 2, (1-1.336r+0.487r2) whose curvature is in the opposite sense to previously derived fits.
Dielectronic recombination of the multiply charged Li-like ion Fe23+via the 2s-3d transition
Authors: V P Zhdanov
Published: July 2002

It has been shown that dielectronic recombination (DR) via the optically forbidden 2s-3d transition is the most important process of recombination of the multiply charged Li-like ion Fe23+in a high-temperature low-density plasma.
Rotational excitation of N2, CO and H2O by low-energy electron collisions
Authors: K Jung  , T Antoni  , R Muller  , K -H Kochem  , H Ehrhardt
Published: July 2002

Absolute total and differential rotational and rotational-vibrational cross sections have been measured for N2(weak quadrupole), CO (weak dipole), and H2O (strong dipole). In the beam experiments, the range of collision energies of the electrons was chosen between 0.5 and 6 eV, and the range of scattering angles from 15 to 105 degrees was covered. The overall energy inhomogeneity of the electron spectrometer was between 10 and 18 meV FWHM, depending on the experiment. Direct and resonant rotational excitation has been measured. In the case of N2the rotational branches with Delta J=0, +or-2, +or-4 have been fitted to energy-loss spectra and for each branch a cross section is given. The authors have proceeded similarly in the case of CO (for dipole excitation Delta J=0, +or-1, for excitation via the2Pi resonance Delta J=0, +or-1, ..., +or-4) and in the case of H2O ( Delta J=0, +or-1). For N2and CO the results are compared with calculated angular dependences. Finally, the cross sections are listed according to the different types of interaction potentials and interaction mechanisms.
Depolarisation in Na-Ar optical collisions
Authors: W Behmenburg  , V Kroop  , F Rebentrost
Published: July 2002

The depolarisation of the redistributed Na D1and D2line fluorescence caused by Na-Ar collisions after far-wing excitation was investigated. In the limit of zero Ar density the J=1/2orientation and J=3/2alignment reflect the distribution among Zeeman sublevels of Na 32PJproduced after absorption of a photon into one or several excited Na-Ar molecular states at small internuclear separation, followed by a mixing between these states during dissociation. Measurements of these quantities as functions of the detuning up to Delta omegaJ=50 cm-1in the red wings are compared with quantum-mechanical coupled-channel (CC) calculations using realistic molecular potentials and thermal averaging, and with predictions from the factorisation approximation (FA) of the theory of redistribution. Fair agreement with CC calculations and FA predictions was obtained within the impact region, proving the validity of the factorisation assumption there. Outside this region the overall depolarisation is primarily due to reorientation of the Na 3P electronic angular momentum and is reproduced qualitatively by the CC calculations but not by the FA theory. Additional depolarisation connected with the fine-structure coupling was observed.
Classical trajectory calculations for anisotropy-dependent cross sections for He-N2mixtures
Authors: A S Dickinson  , M S Lee
Published: July 2002

The classical expressions for kinetic theory cross sections which are related to the Senftleben-Beenakker effect on viscosity, diffusion, conductivity and thermal diffusion are evaluated using the HFD1 surface (R. Fuchs et al. (1984)) in the temperature range 77.3-1100K. The depolarised Rayleigh scattering and rotational-relaxation cross sections are also obtained. Comparisons with experiment show that the authors' values for these cross sections are 10-80% larger than the measurements. These consistent discrepancies suggest that this potential surface is too anisotropic.
The structure factor for liquid metals II. Results for liquid Zn, Tl, Pb, Sn and Bi
Authors: D M North  , J E Enderby  , P A Egelstaff
Published: July 2002

The structure factors for four liquid metals (Zn, Tl, Sn and Bi) at temperatures close to the melting point have been determined by means of neutron diffraction and the data used to calculate the total correlation functions. In addition a detailed study has been made of liquid Pb as a function of temperature. Data are given for the structure factors, the total correlation functions and the direct correlation functions at four temperatures in the range 340 °c to 1100 °c. The total and direct correlation functions were used in the Percus-Yevick and hyper-netted chain equations to calculate the interionic potential. The structure factors were applied to the Ziman theory of electron transport in liquid metals. It is shown that the predicted temperature dependence of resistivity and thermoelectric power is in good agreement with experiment.
NMR relaxation and self-diffusion in PbF2
Authors: R E Gordon  , J H Strange
Published: July 2002

The19F-self-diffusion has been investigated in PbF2, up to the melting point, by NMR techniques. Relaxation time measurements (T1, T2and T1 rho) have been made from 300 to 1095K. Anomalous behaviour above 500K, similar to that reported in previous investigations, is found to be due to paramagnetic impurity produced as a result of the high reactivity of PbF2at these temperatures. Direct F-diffusion measurements have been made using NMR spin echoes from 570K to 1005K. These results are compared with those of ionic conductivity and are found to be 0.88+or-0.10 eV, assuming a vacancy mechanism of self-diffusion is operative. Above the phase transition at 705K the F-diffusion coefficient changes more slowly with temperature, being characterised by an activation energy of 0.20+or-0.02 eV, which is typical of a fast ion conductor.
Short-wavelength approximation to multiple scattering in MEED
Authors: N Masud
Published: July 2002

In medium-energy electron diffraction (MEED) strong multiple scattering takes place in the forward direction. The short-wavelength approximation to forward multiple scattering in MEED is studied using the chain scattering formula of intensity calculation for the purpose of investigating the feasibility of describing scattering within a layer of atoms by a pseudodynamic theory and thus reducing calculation times. In a test calculation on a Si(111) surface, it is found that such an approximation is allowed in a part of the angular range and a pseudodynamic theory, based on the short-wavelength approximation to multiple scattering, can be used to this range.
Theoretical study of metal overlayer thickness effects on the electronic properties of metal-semiconductor interfaces
Authors: P Masri  , P Langlade
Published: July 2002

The authors present a theory based upon a Green function method to study the evolution of the electronic properties of a metal-semiconductor interface as a function of the metal thickness. The results show trends consistent with the experimental observations: existence of metal-induced interface states in the semiconductor gap near the Fermi level. The corresponding levels are pushed up towards higher energies by increasing the metal thickness. Interactions of semiconductor and growing metal bands occur leading to localised and resonant interface states that are very sensitive to metal coverage changes.
Level crossing between NQR and tunnel systems in (NH4)2SnCl6
Authors: J J van der Klink  , C Dimitropoulos
Published: July 2002

The authors have observed a peculiar behaviour in the NQR relaxation of both chlorine isotopes in (NH4)2SnCl6below 80K. An unusual ratio T1(37Cl)/T1(35Cl) approximately=2.4 at low temperatures can be explained by the dipolar coupling to the tunnelling ammonium protons causing relaxation by a mechanism similar to that for the proton NMR relaxation, but at slower rates. A very large maximum value around 55K is ascribed to relaxation of the tunnel system towards the lattice, after resonant transfer of energy from the NQR system. It is argued that this relaxation time should be of the same order of magnitude as the proton T1at similar frequencies and temperatures.
The entropy of formation of anion Frenkel defects in fluorites: a quasiharmonic calculation for calcium fluoride
Authors: P W M Jacobs  , M A H Nerenberg  , J Govindarajan  , T M Haridasan
Published: July 2002

A Green function formalism, as first used by Govindarajan et al. (1979) for Schottky defects in alkali halides, has been reformulated on a more rigorous basis and then applied to the calculation of the entropy of formation of an interstitial and of an anion vacancy in the alkaline earth fluoride, CaF2. The relevant lattice Green functions are calculated using a shell model. The force constant changes are obtained from the coordinates of the relaxed ions which are computed using the Hades program due to Norgett (1974) and the potential parameters of Catlow, Norgett and Ross (1977). This calculation of the entropy of formation of a Frenkel defect in CaF2is a quasiharmonic one at the temperatures 300, 1000 and 1500K. The calculated values are significantly lower than experimental results. The principal reason for this discrepancy is that the calculations refer to the entropy of formation at constant volume (sv) whereas the experiments measure the entropy of formation at constant pressure (sp). A calculation of sp-svis presented and it is demonstrated that this term is an important component of sp.
Landau theory interpretation of the commensurate superlattice structure of 2H-TaSe2
Authors: D M Bird  , R L Withers
Published: July 2002

The Landau theory of charge density wave states in 2H-TaSe2is re-examined in the light of the commensurate superlattice structure determination by Bird, McKernan and Steeds (1985). It is shown that interlayer interactions play a far more important role in determining the phasing of the CDW/PSD than has been previously assumed. Some consequences of this for the nature of incommensurate states and the interpretation of previous experimental data are also discussed.
Theory of LEED in crystals with defects
Authors: O Litzman  , P Dub
Published: July 2002

Formulae for LEED can be put in a suitable matrix form which enables the authors to use a matrix algebra procedure to deduce exact formulae for the diffraction of a plane wave on a slab with isolated defects. The general theory is applied to the case of substitutional foreign atoms and/or vacancies which cause no lattice deformation. A generalisation to more complex defects is briefly mentioned.
Further calculations of the energies of formation of Schottky defects in NaCl structure ionic crystals
Authors: I M Boswarva
Published: July 2002

The author presents the results of calculations of the energy of formation of Schottky defects in some alkali halides and alkaline earth oxides. It is shown that the basic Born-Mayer model of an ionic solid, which treats each ion as a point polarizable dipole, remains very adequate for defect energy calculations so long as the repulsive potential is chosen to give correctly the static dielectric constant of the substance it represents. The derived values for the alkali halides are in good agreement with experimental ones, particularly for those substances for which the latter are well documented, namely the potassium halides.
A Hall-effect apparatus for the measurement of simple shear in polymers
Authors: E L V Lewis  , I D Richardson  , I M Ward
Published: July 2002

A device for measuring the mechanical properties of polymers in shear has been devised, built and tested. The type of deformation employed is that of simple shear of flat sheets and the displacements are measured using a Hall-effect extensometer. The method has been tested using isotropic samples of low-density polyethylene and the results for shear compliance are found to agree satisfactorily with those obtained from conventional extension tests. Continuous records of shear strain or compliance against time have been obtained, as have measurements of the variation of compliance with strain. The method is quick and simple and gives direct results for shear compliances, time dependences and strain dependences, the last two properties being very difficult to measure using conventional torsional techniques.
Reliable high speed transfer with the Le Croy CAMAC-GPIB interface
Authors: J -P Lanquart
Published: July 2002

The author presents modifications to the original instructions, which make it possible to have a reliable high speed transfer from a CAMAC transient recorder to a computer by means of a Le Croy CAMAC-GPIB interface.
Ion kinetic energy spectrometry
Authors: J H Beynon  , R G Cooks
Published: July 2002

The principles upon which accurate measurements of kinetic energy of kilovolt ions are based are illustrated, and the design of an instrument for focusing the ions formed by reactions in a field-free region is described. Reactions that have been studied include spontaneous decompositions as well as charge-stripping, charge-exchange and charge- inversion both for rare gases and for organic compounds. The results give information on the energies of excited states, on double ionization potentials and on electron affinities.
An improved circular camera for elastic light scattering experiments
Authors: R L Addleman  , G F Harding  , F M Willmouth
Published: July 2002

A cylindrical camera and spherical glass cell system is described, which permits measurement in two dimensions within the range 4-173 degrees ; angular resolution is better than in a previous design, and errors due to reflections have been eliminated.
On upper bounds for high order Neumann eigenvalues of convex domains in Euclidean space
Authors: Kröger Pawel
Published: July 2002

We derive sharp upper bounds for eigenvalues of the Laplacian under Neumann boundary conditions on convex domains with given diameter in Euclidean space. We use the Brunn-Minkowski theorem in order to reduce the problem to a question about eigenvalues of certain classes of Sturm-Liouville problems.
Expansive Subdynamics
Authors: Boyle Mike , Lind Douglas
Published: July 2002

This paper provides a framework for studying the dynamics of commuting homeomorphisms. Let

α
\alpha

be a continuous action of

Z

d

\mathbb {Z}^d

on an infinite compact metric space. For each subspace

V
V

of

R

d

\mathbb {R}^d

we introduce a notion of expansiveness for

α
\alpha

along

V
V

, and show that there are nonexpansive subspaces in every dimension

≤
d
−
1

\le d-1

. For each

k
≤
d

k\le d

the set

E

k

(
α
)

\mathbb {E}_k(\alpha )

of expansive

k
k

-dimensional subspaces is open in the Grassmann manifold of all

k
k

-dimensional subspaces of

R

d

\mathbb {R}^d

. Various dynamical properties of

α
\alpha

are constant, or vary nicely, within a connected component of

E

k

(
α
)

\mathbb {E}_k(\alpha )

, but change abruptly when passing from one expansive component to another. We give several examples of this sort of “phase transition,” including the topological and measure-theoretic directional entropies studied by Milnor, zeta functions, and dimension groups. For

d
=
2

d=2

we show that, except for one unresolved case, every open set of directions whose complement is nonempty can arise as an

E

1

(
α
)

\mathbb {E}_1(\alpha )

. The unresolved case is that of the complement of a single irrational direction. Algebraic examples using commuting automorphisms of compact abelian groups are an important source of phenomena, and we study several instances in detail. We conclude with a set of problems and research directions suggested by our analysis.
A monotone finite element scheme for convection-diffusion equations
Authors: Xu Jinchao , Zikatanov Ludmil
Published: July 2002

A simple technique is given in this paper for the construction and analysis of a class of finite element discretizations for convection-diffusion problems in any spatial dimension by properly averaging the PDE coefficients on element edges. The resulting finite element stiffness matrix is an

M
M

-matrix under some mild assumption for the underlying (generally unstructured) finite element grids. As a consequence the proposed edge-averaged finite element scheme is particularly interesting for the discretization of convection dominated problems. This scheme admits a simple variational formulation, it is easy to analyze, and it is also suitable for problems with a relatively smooth flux variable. Some simple numerical examples are given to demonstrate its effectiveness for convection dominated problems.
CRAWview: for viewing splicing variation, gene families, and polymorphism in clusters of ESTs and full-length sequences.
Authors: Chou A , Burke J
Published: July 2002

MOTIVATION: DNA sequence clustering has become a valuable method in support of gene discovery and gene expression analysis. Our interest lies in leveraging the sequence diversity within clusters of expressed sequence tags (ESTs) to model gene structure for the study of gene variants that arise from, among other things, alternative mRNA splicing, polymorphism, and divergence after gene duplication, fusion, and translocation events. In previous work, CRAW was developed to discover gene variants from assembled clusters of ESTs. Most importantly, novel gene features (the differing units between gene variants, for example alternative exons, polymorphisms, transposable elements, etc.) that are specialized to tissue, disease, population, or developmental states can be identified when these tools collate DNA source information with gene variant discrimination. While the goal is complete automation of novel feature and gene variant detection, current methods are far from perfect and hence the development of effective tools for visualization and exploratory data analysis are of paramount importance in the process of sifting through candidate genes and validating targets. RESULTS: We present CRAWview, a Java based visualization extension to CRAW. Features that vary between gene forms are displayed using an automatically generated color coded index. The reporting format of CRAWview gives a brief, high level summary report to display overlap and divergence within clusters of sequences as well as the ability to 'drill down' and see detailed information concerning regions of interest. Additionally, the alignment viewing and editing capabilities of CRAWview make it possible to interactively correct frame-shifts and otherwise edit cluster assemblies. We have implemented CRAWview as a Java application across windows NT/95 and UNIX platforms. AVAILABILITY: A beta version of CRAWview will be freely available to academic users from Pangea Systems (http://www.pangeasystems.com). Contact :
Ubiquitin‐associated (UBA) domains in Rad23 bind ubiquitin and promote inhibition of multi‐ubiquitin chain assembly
Authors: Chen Li , Shinde Ujwal , Ortolan Tatiana G , Madura Kiran
Published: July 2002

Rad23 is a DNA repair protein that promotes the assembly of the nucleotide excision repair complex. Rad23 can interact with the 26S proteasome through an N‐terminal ubiquitin‐like domain, and inhibits the assembly of substrate‐linked multi‐ubiquitin (multi‐Ub) chains in vitro and in vivo. Significantly, Rad23 can bind a proteolytic substrate that is conjugated to a few ubiquitin (Ub) moieties. We report here that two ubiquitin‐associated (UBA) domains in Rad23 form non‐covalent interactions with Ub. A mutant that lacked either UBA sequence was capable of blocking the assembly of substrate‐linked multi‐Ub chains, although a mutant that lacked both UBA domains was significantly impaired. These studies suggest that the interaction with Ub is required for Rad23 activity, and that other UBA‐containing proteins may have a similar function.
The evolution of insecticide resistance in the peach–potato aphid, Myzus persicae
Authors: Devonshire A. L. , Field L. M. , Foster S. P. , Moores G. D. , Williamson M. S. , Blackman R. L.
Published: July 2002

The peach–potato aphid
Myzus persicae
(Sulzer) can resist a wide range of insecticides, but until recently (1990) the only mechanism identified was the increased production of carboxylesterases (E4 or FE4), which cause enhanced degradation and sequestration of insecticidal esters. We have now identified two forms of target–site resistance involving changes in the acetylcholinesterase (
AChE
) and sodium channel (
kdr
) genes. Biochemical and DNA diagnostic methods can be used to identify all three mechanisms in individual aphids, and thereby establish their spatial distributions and temporal dynamics. Amplified genes underlie the increased production of esterases but their expression is modulated by DNA methylation. Amplification of the
E4
gene is in strong linkage disequilibrium with the kdr mechanism. This may reflect strong insecticidal selection favouring aphids with multiple mechanisms, tight chromosomal linkage and/or the prominence of parthenogenesis in many
M. persicae
populations. The decreased fitness of resistant aphids under winter conditions may be a consequence of the altered sodium–channel gene affecting behaviour and/or the perception of external stimuli.
Tetanus and botulinum neurotoxins: mechanism of action and therapeutic uses
Authors: Pellizzari Rossella , Rossetto Ornella , Schiavo Giampietro , Montecucco Cesare
Published: July 2002

The clostridial neurotoxins responsible for tetanus and botulism are proteins consisting of three domains endowed with different functions: neurospecific binding, membrane translocation and proteolysis for specific components of the neuroexocytosis apparatus. Tetanus neurotoxin (TeNT) binds to the presynaptic membrane of the neuromuscular junction, is internalized and transported retroaxonally to the spinal cord. The spastic paralysis induced by the toxin is due to the blockade of neurotransmitter release from spinal inhibitory interneurons. In contrast, the seven serotypes of botulinum neurotoxins (BoNTs) act at the periphery by inducing a flaccid paralysis due to the inhibition of acetylcholine release at the neuromuscular junction. TeNT and BoNT serotypes B, D, F and G cleave specifically at single but different peptide bonds, of the vesicle associated membrane protein (VAMP) synaptobrevin, a membrane protein of small synaptic vesicles (SSVs). BoNT types A, C and E cleave SNAP–25 at different sites located within the carboxyl–terminus, while BoNT type C additionally cleaves syntaxin. The remarkable specificity of BoNTs is exploited in the treatment of human diseases characterized by an hyperfunction of cholinergic terminals.
From genomes to vaccines:Leishmaniaas a model
Authors: Almeida Renata , Norrish Alan , Levick Mark , Vetrie David , Freeman Tom , Vilo Jaak , Ivens Alasdair , Lange Uta , Stober Carmel , McCann Sharon , Blackwell Jenefer M.
Published: July 2002

The 35 Mb genome ofLeishmaniashould be sequenced by late 2002. It contains approximately 8500 genes that will probably translate into more than 10 000 proteins. In the laboratory we have been piloting strategies to try to harness the power of the genome–proteome for rapid screening of new vaccine candidate. To this end, microarray analysis of 1094 unique genes identified using an EST analysis of 2091 cDNA clones from spliced leader libraries prepared from different developmental stages ofLeishmaniahas been employed. The plan was to identify amastigote–expressed genes that could be used in high–throughput DNA–vaccine screens to identify potential new vaccine candidates. Despite the lack of transcriptional regulation that polycistronic transcription inLeishmaniadictates, the data provide evidence for a high level of post–transcriptional regulation of RNA abundance during the developmental cycle of promastigotes in culture and in lesion–derived amastigotes ofLeishmania major. This has provided 147 candidates from the 1094 unique genes that are specifically upregulated in amastigotes and are being used in vaccine studies. Using DNA vaccination, it was demonstrated that pooling strategies can work to identify protective vaccines, but it was found that some potentially protective antigens are masked by other disease–exacerbatory antigens in the pool. A total of 100 new vaccine candidates are currently being tested separately and in pools to extend this analysis, and to facilitate retrospective bioinformatic analysis to develop predictive algorithms for sequences that constitute potentially protective antigens. We are also working with other members of theLeishmaniaGenome Network to determine whether RNA expression determined by microarray analyses parallels expression at the protein level. We believe we are making good progress in developing strategies that will allow rapid translation of the sequence ofLeishmaniainto potential interventions for disease control in humans.
Generalized multi‐dimensional adaptive filtering for conventional and spiral single‐slice, multi‐slice, and cone‐beam CT
Authors: Kachelrieß Marc , Watzke Oliver , Kalender Willi A.
Published: July 2002

In modern computed tomography (CT) there is a strong desire to reduce patient dose and/or to improve image quality by increasing spatial resolution and decreasing image noise. These are conflicting demands since increasing resolution at a constant noise level or decreasing noise at a constant resolution level implies a higher demand on x‐ray power and an increase of patient dose. X‐ray tube power is limited due to technical reasons. We therefore developed a generalized multi‐dimensional adaptive filtering approach that applies nonlinear filters in up to three dimensions in the raw data domain. This new method differs from approaches in the literature since our nonlinear filters are applied not only in the detector row direction but also in the view and in the z‐direction. This true three‐dimensional filtering improves the quantum statistics of a measured projection value proportional to the third power of the filter size. Resolution tradeoffs are shared among these three dimensions and thus are considerably smaller as compared to one‐dimensional smoothing approaches. Patient data of spiral and sequential single‐ and multi‐slice CT scans as well as simulated spiral cone‐beam data were processed to evaluate these new approaches. Image quality was assessed by evaluation of difference images, by measuring the image noise and the noise reduction, and by calculating the image resolution using point spread functions. The use of generalized adaptive filters helps to reduce image noise or, alternatively, patient dose. Image noise structures, typically along the direction of the highest attenuation, are effectively reduced. Noise reduction values of typically 30%–60% can be achieved in noncylindrical body regions like the shoulder. The loss in image resolution remains below 5% for all cases. In addition, the new method has a great potential to reduce metal artifacts, e.g., in the hip region.
A compact ridge filter for spread out Bragg peak production in pulsed proton clinical beams
Authors: Kostjuchenko Valeri , Nichiporov Dmitri , Luckjashin Victor
Published: July 2002

A number of designs have been proposed for ridge filters and range modulators used in proton therapy to modify the beam in order to spread out the Bragg peak. Despite the variety of solutions, no simple design capable of providing large fields and easy variation of the spread out Bragg peak (SOBP) length in a pulsed beam has been developed. We propose a compact ridge filter that can be used in a proton beam of any time structure. It allows the production of depth dose distributions that meet the requirements of therapy dose fields.
Monte Carlo dosimetry of the selectSeed interstitial brachytherapy seed
Authors: Karaiskos P. , Papagiannis P. , Sakelliou L. , Anagnostopoulos G. , Baltas D.
Published: July 2002

This work provides full dosimetric data for the new selectSeed prostate seed source to be distributed by Nucletron B.V. The AAPM TG‐43 dosimetric formalism and the new 1999 NIST air kerma strength calibration standard have been followed. Air kerma strength, dose rate constant, radial dose functions, anisotropy functions, and anisotropy factors were calculated using Monte Carlo simulation. Corresponding calculations were also performed for the commercially available 6711 seed source, which is of similar design, for reasons of comparison. The calculated dose rate constant of the selectSeed was 0.954±0.005 compared to 0.953±0.005 for the 6711 source design. The latter value for the 6711 source suggests that the correction factor proposed by NIST for conversion of dose rate constants to the new 1999 NIST calibration standard may be overestimated by 2–3%. Radial dose functions of the two sources were found in good agreement for radial distances up to 4 cm, the selectSeed being less penetrating at greater radial distances (∼4% at 10 cm). The selectSeed source presents similar anisotropy characteristics with the 6711 source design. For both source designs, a distance and polar angle dependent discontinuity of anisotropy function values was observed owing to the dose contribution of radioactivity distributed on the ends of the cylindrical source cores. Variation of dosimetric parameters with possible variation in radioactive silver halide coating thickness of the silver source core of the new source was also investigated.
Oersted Medal Lecture 2001: “Physics Education Research—The Key to Student Learning”
Authors: McDermott Lillian Christie
Published: July 2002

Research on the learning and teaching of physics is essential for cumulative improvement in physics instruction. Pursuing this goal through systematic research is efficient and greatly increases the likelihood that innovations will be effective beyond a particular instructor or institutional setting. The perspective taken is that teaching is a science as well as an art. Research conducted by physicists who are actively engaged in teaching can be the key to setting high (yet realistic) standards, to helping students meet expectations, and to assessing the extent to which real learning takes place.
Perceptual calibration of F0 production: Evidence from feedback perturbation
Authors: Jones Jeffery A. , Munhall K. G.
Published: July 2002

Hearing one’s own speech is important for language learning and maintenance of accurate articulation. For example, people with postlinguistically acquired deafness often show a gradual deterioration of many aspects of speech production. In this manuscript, data are presented that address the role played by acoustic feedback in the control of voice fundamental frequency (F0). Eighteen subjects produced vowels under a control (normal F0 feedback) and two experimental conditions: F0 shifted up and F0 shifted down. In each experimental condition subjects produced vowels during a training period in which their F0 was slowly shifted without their awareness. Following this exposure to transformed F0, their acoustic feedback was returned to normal. Two effects were observed. Subjects compensated for the change in F0 and showed negative aftereffects. When F0 feedback was returned to normal, the subjects modified their produced F0 in the opposite direction to the shift. The results suggest that fundamental frequency is controlled using auditory feedback and with reference to an internal pitch representation. This is consistent with current work on internal models of speech motor control.
Binaural processing model based on contralateral inhibition. I. Model structure
Authors: Breebaart Jeroen , van de Par Steven , Kohlrausch Armin
Published: July 2002

This article presents a quantitative binaural signal detection model which extends the monaural model described by Dau et al. [J. Acoust. Soc. Am. 99, 3615–3622 (1996)]. The model is divided into three stages. The first stage comprises peripheral preprocessing in the right and left monaural channels. The second stage is a binaural processor which produces a time-dependent internal representation of the binaurally presented stimuli. This stage is based on the Jeffress delay line extended with tapped attenuator lines. Through this extension, the internal representation codes both interaural time and intensity differences. In contrast to most present-day models, which are based on excitatory–excitatory interaction, the binaural interaction in the present model is based on contralateral inhibition of ipsilateral signals. The last stage, a central processor, extracts a decision variable that can be used to detect the presence of a signal in a detection task, but could also derive information about the position and the compactness of a sound source. In two accompanying articles, the model predictions are compared with data obtained with human observers in a great variety of experimental conditions.
Maximum speed of pitch change and how it may relate to speech
Authors: Xu Yi , Sun Xuejing
Published: July 2002

How fast speakers can change pitch voluntarily is potentially an important articulatory constraint for speech production. Previous attempts at assessing the maximum speed of pitch change have helped improve understanding of certain aspects of pitch production in speech. However, since only “response time”—time needed to complete the middle 75% of a pitch shift—was measured in previous studies, direct comparisons with speech data have been difficult. In the present study, a new experimental paradigm was adopted in which subjects produced rapid successions of pitch shifts by imitating synthesized model pitch undulation patterns. This permitted the measurement of the duration of entire pitch shifts. Native speakers of English and Mandarin participated as subjects. The speed of pitch change was measured both in terms of response time and excursion time—time needed to complete the entire pitch shift. Results show that excursion time is nearly twice as long as response time. This suggests that physiological limitation on the speed of pitch movement is greater than has been recognized. Also, it is found that the maximum speed of pitch change varies quite linearly with excursion size, and that it is different for pitch rises and falls. Comparisons of present data with data on speed of pitch change from studies of real speech found them to be largely comparable. This suggests that the maximum speed of pitch change is often approached in speech, and that the role of physiological constraints in determining the shape and alignment of F0 contours in speech is probably greater than has been appreciated.
Acoustics of friction
Authors: Akay Adnan
Published: July 2002

This article presents an overview of the acoustics of friction by covering friction sounds, friction-induced vibrations and waves in solids, and descriptions of other frictional phenomena related to acoustics. Friction, resulting from the sliding contact of solids, often gives rise to diverse forms of waves and oscillations within solids which frequently lead to radiation of sound to the surrounding media. Among the many everyday examples of friction sounds, violin music and brake noise in automobiles represent the two extremes in terms of the sounds they produce and the mechanisms by which they are generated. Of the multiple examples of friction sounds in nature, insect sounds are prominent. Friction also provides a means by which energy dissipation takes place at the interface of solids. Friction damping that develops between surfaces, such as joints and connections, in some cases requires only microscopic motion to dissipate energy. Modeling of friction-induced vibrations and friction damping in mechanical systems requires an accurate description of friction for which only approximations exist. While many of the components that contribute to friction can be modeled, computational requirements become prohibitive for their contemporaneous calculation. Furthermore, quantification of friction at the atomic scale still remains elusive. At the atomic scale, friction becomes a mechanism that converts the kinetic energy associated with the relative motion of surfaces to thermal energy. However, the description of the conversion to thermal energy represented by a disordered state of oscillations of atoms in a solid is still not well understood. At the macroscopic level, friction interacts with the vibrations and waves that it causes. Such interaction sets up a feedback between the friction force and waves at the surfaces, thereby making friction and surface motion interdependent. Such interdependence forms the basis for friction-induced motion as in the case of ultrasonic motors and other examples. Last, when considered phenomenologically, friction and boundary layer turbulence exhibit analogous properties and, when compared, each may provide clues to a better understanding of the other.
Global attenuation of broadband noise fields using energy density control
Authors: Park Young C. , Sommerfeldt Scott D.
Published: July 2002

The performance of the energy density control algorithm for controlling a broadband noise is evaluated in a one-dimensional enclosure. To avoid the noncausality problem of the control filter, which often happens in a frequency domain optimization, analyses presented in this paper are undertaken in the time domain. This approach provides the form of the causally constrained optimal controller. Numerical results are presented to predict the performance of the active noise control system, and indicate that improved global attenuation of the broadband noise can be achieved by minimizing the energy density, rather than the squared pressure. It is shown that minimizing the energy density at a single location yields global attenuation results that are comparable to minimizing the potential energy. Furthermore, unlike controlling the squared pressure, the energy density control does not demonstrate any dependence on the error sensor location for this one-dimensional field. A practical implementation of the energy-based control algorithm is presented. Results show that the energy density control algorithm can be implemented using the two sensor technique with a tolerable margin of performance degradation.
Acoustic interactions of the voice source with the lower vocal tract
Authors: Titze Ingo R. , Story Brad H.
Published: July 2002

The linear source-filter theory of speech production assumes that vocal fold vibration is independent of the vocal tract. The justification is that the glottis often behaves as a high-impedance (constant flow) source. Recent imaging of the vocal tract has demonstrated, however, that the epilarynx tube is quite narrow, making the input impedance to the vocal tract comparable to the glottal impedance. Strong interactions can exist, therefore. In particular, the inertance of the vocal tract facilitates vocal fold vibration by lowering the oscillation threshold pressure. This has a significant impact on singing. Not only does the epilarynx tube produce the desirable singer’s formant (vocal ring), but it acts like the mouthpiece of a trumpet to shape the flow and influence the mode of vibration. Effects of the piriform sinuses, pharynx expansion, and nasal coupling are also discussed.
Active control of structurally radiated sound from plates
Authors: Sung Chia-Chi , Jan C. T.
Published: July 2002

Active control of sound radiation from a clamped rectangular plate by piezoelectric moments is investigated both analytically and experimentally. A new theoretical derivation for the dynamic response of a plate excited by steady-state harmonic point forces, couples, and piezomoments is presented. Four point moments, simulating a piezoceramic patch bonded directly on the surface of the plate, are used to achieve the control. Control gain is obtained by minimizing the sound radiation power. The sound radiation measurement is conducted in a reverberation room equipped with an anechoic chamber. The results indicate that this research not only provides an accurate and efficient approach to theoretically predict the response of a clamped rectangular plate subjected to piezomoment excitation but also achieves effective global attenuation of sound radiation power. The highest reduction of the total power radiated from the plate was approximately 24 dB.
Phonation onset: Vocal fold modeling and high-speed glottography
Authors: Mergell Patrick , Herzel Hanspeter , Wittenberg Thomas , Tigges Monika , Eysholdt Ulrich
Published: July 2002

Phonation onset is discussed in the framework of dynamical systems as a Hopf bifurcation, i.e., as a transition from damped to sustained vocal fold oscillations due to changes of parameters defining the underlying laryngeal configuration (e.g., adduction, subglottal pressure, muscular activity). An analytic envelope curve of the oscillation onset is deduced by analyzing the Hopf bifurcation in mathematical models of the vocal folds. It is governed by a single time constant which can be identified with the physiological parameter phonation onset time. This parameter reflects the laryngeal state prior to phonation and can be used as a quantitative classification criterion in order to assess the phonation onset in clinical diagnosis. The extraction of the phonation onset time from simulated time series using a simplified two-mass model and from digital high-speed videos is described in detail. It shows a good agreement between theory and measurement.
Recognizing transient low-frequency whale sounds by spectrogram correlation
Authors: Mellinger David K. , Clark Christopher W.
Published: July 2002

A method is described for the automatic recognition of transient animal sounds. Automatic recognition can be used in wild animal research, including studies of behavior, population, and impact of anthropogenic noise. The method described here, spectrogram correlation, is well-suited to recognition of animal sounds consisting of tones and frequency sweeps. For a sound type of interest, a two-dimensional synthetic kernel is constructed and cross-correlated with a spectrogram of a recording, producing a recognition function—the likelihood at each point in time that the sound type was present. A threshold is applied to this function to obtain discrete detection events, instants at which the sound type of interest was likely to be present. An extension of this method handles the temporal variation commonly present in animal sounds. Spectrogram correlation was compared to three other methods that have been used for automatic call recognition: matched filters, neural networks, and hidden Markov models. The test data set consisted of bowhead whale (Balaena mysticetus) end notes from songs recorded in Alaska in 1986 and 1988. The method had a success rate of about 97.5% on this problem, and the comparison indicated that it could be especially useful for detecting a call type when relatively few (5–200) instances of the call type are known.