bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonstochastic Coexpression of Activation Receptors on Murine Natural Killer Cells
Authors: Smith Hamish R.C. , Chuang Hubert H. , Wang Lawrence L. , Salcedo Margarita , Heusel Jonathan W. , Yokoyama Wayne M.
Published: July 2002

Murine natural killer cells (NK) express lectin-like activation and inhibitory receptors, including the CD94/NKG2 family of receptors that bind Qa-1, and the Ly-49 family that recognizes major histocompatibility complex class I molecules. Here, we demonstrate that cross-linking of NK cells with a new specific anti–Ly-49H mAb induced NK cell cytotoxicity and cytokine production. Ly-49H is expressed on a subset of NK cells and can be coexpressed with Ly-49 inhibitory receptors. However, unlike Ly-49 inhibitory receptors, Ly-49H is not detectable on naive splenic CD3+ T cells, indicating that Ly-49H may be an NK cell–specific activation receptor. In further contrast to the stochastically expressed Ly-49 inhibitory receptors, Ly-49H is preferentially expressed with the Ly-49D activation receptor, and expression of both Ly-49H and Ly-49D is augmented on NK cells that lack receptors for Qa-1 tetramers. On developing splenic NK1.1+ cells, Ly-49D and Ly-49H are expressed later than the inhibitory receptors. These results directly demonstrate that Ly-49H activates primary NK cells, and suggest that expression of Ly-49 activation receptors by NK cells may be specifically regulated on NK cell subsets. The simultaneous expression of multiple activation receptors by individual NK cells contrasts with that of T cell antigen receptors and is relevant to the role of NK cells in innate immunity.
Aberrant in Vivo T Helper Type 2 Cell Response and Impaired Eosinophil Recruitment in Cc Chemokine Receptor 8 Knockout Mice
Authors: Chensue Stephen W. , Lukacs Nicholas W. , Yang Tong-Yuan , Shang Xiaozhou , Frait Kirsten A. , Kunkel Steven L. , Kung Ted , Wiekowski Maria T. , Hedrick Joseph A. , Cook Donald N. , Zingoni Alessandra , Narula Satwant K. , Zlotnik Albert , Barrat Franck J. , O'Garra Anne , Napolitano Monica , Lira Sergio A.
Published: July 2002

Chemokine receptors transduce signals important for the function and trafficking of leukocytes. Recently, it has been shown that CC chemokine receptor (CCR)8 is selectively expressed by Th2 subsets, but its functional relevance is unclear. To address the biological role of CCR8, we generated CCR8 deficient (−/−) mice. Here we report defective T helper type 2 (Th2) immune responses in vivo in CCR8−/− mice in models of Schistosoma mansoni soluble egg antigen (SEA)-induced granuloma formation as well as ovalbumin (OVA)- and cockroach antigen (CRA)-induced allergic airway inflammation. In these mice, the response to SEA, OVA, and CRA showed impaired Th2 cytokine production that was associated with aberrant type 2 inflammation displaying a 50 to 80% reduction in eosinophils. In contrast, a prototypical Th1 immune response, elicited by Mycobacteria bovis purified protein derivative (PPD) was unaffected by CCR8 deficiency. Mechanistic analyses indicated that Th2 cells developed normally and that the reduction in eosinophil recruitment was likely due to systemic reduction in interleukin 5. These results indicate an important role for CCR8 in Th2 functional responses in vivo.
Zinc Finger Protein, Hzf, Is Required for Megakaryocyte Development and Hemostasis
Authors: Kimura Yuki , Hart Adam , Hirashima Masanori , Wang Chen , Holmyard Doug , Pittman Jackie , Pang Xin-Li , Jackson Carl W. , Bernstein Alan
Published: July 2002

Using an expression gene trapping strategy, we recently identified a novel gene, hematopoietic zinc finger (Hzf), which encodes a protein containing three C2H2-type zinc fingers that is predominantly expressed in megakaryocytes. Here, we have examined the in vivo function of Hzf by gene targeting and demonstrated that Hzf is essential for megakaryopoiesis and hemostasis in vivo. Hzf-deficient mice exhibited a pronounced tendency to rebleed and had reduced α-granule substances in both megakaryocytes and platelets. These mice also had large, faintly stained platelets, whereas the numbers of both megakaryocytes and platelets were normal. These results indicate that Hzf plays important roles in regulating the synthesis of α-granule substances and/or their packing into α-granules during the process of megakaryopoiesis.
CD8α2 CD11b+ Dendritic Cells Present Exogenous Virus-like Particles to CD8+ T Cells and Subsequently Express CD8α and CD205 Molecules
Authors: Morón Gabriel , Rueda Paloma , Casal Ignacio , Leclerc Claude
Published: July 2002

Recombinant porcine parvovirus virus-like particles (PPV-VLPs) are particulate exogenous antigens that induce a strong, specific cytotoxic T lymphocyte (CTL) response in the absence of adjuvant. In the present report, we demonstrate in vivo that dendritic cells (DCs) present PPV-VLPs to CD8+ T cells after intracellular processing. PPV-VLPs are captured by DCs with a high efficacy, which results in the delivery of these exogenous antigens to 50% of the whole spleen DC population. In vivo, a few hours after injection, PPV-VLPs are presented exclusively to CD8+ T cells by CD8α− DCs, whereas 15 hours later they are presented mainly by CD8α+ DCs. After PPV-VLPs processing, a fraction of CD11b+ DCs undergo phenotypic changes, i.e., the up-regulation of CD8α and CD205 and the loss of CD4 molecules on their surface. The failure to detect mRNA coding for CD8α in CD11b+ DCs suggests that CD8α expression by these cells is not due to de novo synthesis. In recombination-activating gene knockout mice (Rag−/−), CD11b+ DCs did not express CD8α and PPV-VLPs presentation by CD8α+ DCs was severely diminished. These results indicate that both CD8α− and CD8α+ DCs play an important role in the induction of CTL responses by exogenous antigens, such as VLP.
Separation of Gating Properties from Permeation and Block in mslo Large Conductance Ca-activated K+ Channels
Authors: Cox D.H. , Cui J. , Aldrich R.W.
Published: July 2002

In this and the following paper we have examined the kinetic and steady-state properties of macroscopic mslo Ca-activated K+ currents in order to interpret these currents in terms of the gating behavior of the mslo channel. To do so, however, it was necessary to first find conditions by which we could separate the effects that changes in Ca2+ concentration or membrane voltage have on channel permeation from the effects these stimuli have on channel gating. In this study we investigate three phenomena which are unrelated to gating but are manifest in macroscopic current records: a saturation of single channel current at high voltage, a rapid voltage-dependent Ca2+ block, and a slow voltage-dependent Ba2+ block. Where possible methods are described by which these phenomena can be separated from the effects that changes in Ca2+ concentration and membrane voltage have on channel gating. Where this is not possible, some assessment of the impact these effects have on gating parameters determined from macroscopic current measurements is provided. We have also found that without considering the effects of Ca2+ and voltage on channel permeation and block, macroscopic current measurements suggest that mslo channels do not reach the same maximum open probability at all Ca2+ concentrations. Taking into account permeation and blocking effects, however, we find that this is not the case. The maximum open probability of the mslo channel is the same or very similar over a Ca2+ concentration range spanning three orders of magnitude indicating that over this range the internal Ca2+ concentration does not limit the ability of the channel to be activated by voltage.
Calcium Signaling in Transgenic Mice Overexpressing Cardiac Na+-Ca2+ Exchanger
Authors: Adachi-Akahane Satomi , Lu Liyan , Li Zhaoping , Frank J.S. , Philipson Kenneth D. , Morad Martin
Published: July 2002

We have produced transgenic mice which overexpress cardiac Na+-Ca2+ exchange activity. Overexpression has been assessed by Western blot, Northern blot, and immunofluorescence. Functional overexpression was analyzed using membrane vesicles and isolated ventricular myocytes. In whole cell clamped myocytes dialyzed with 0.1–0.2 mM Fura-2, the magnitude of ICa and Ca2+i -transient triggered by ICa or caffeine were not significantly different in transgenic vs. control myocytes. In transgenic myocytes, activation of ICa, however, was followed by a large slowly inactivating transient inward current representing INa-Ca. This current depended on Ca2+ release as it was abolished when sarcoplasmic reticulum (SR) Ca2+ was depleted using thapsigargin. Cai-transients triggered by rapid application of 5 mM caffeine, even though equivalent in control and transgenic myocytes, activated larger INa-Ca (∼5 pA/pF at −90 mV) in transgenic vs. control myocytes (1.5 pA/pF). The decay rate of caffeine-induced Ca2+i -transient and INa-Ca was 2.5 times faster in transgenic than in control myocytes. 5 mM Ni2+ was equally effective in blocking INa-Ca in control or transgenic myocytes. In 9 out of 26 transgenic myocytes, but none of the controls, Ca2+ influx via the exchanger measured at +80 mV caused a slow rise in [Ca2+]i triggering rapid release of Ca2+ from the SR. SR Ca2+ release triggered by the exchanger at such potentials was accompanied by activation of transient current in the inward direction. In 2 mM Fura-2–dialyzed transgenic myocytes caffeine-triggered Cai-transients failed to activate INa-Ca, even though the kinetics of inactivation of ICa slowed significantly in caffeine-treated myocytes. In 0.1 mM Fura-2–dialyzed transgenic myocytes 100 μM Cd2+ effectively blocked ICa and suppressed Cai-transients at −10 or +50 mV. Our data suggests that in myocytes overexpressing the exchanger, the content of intracellular Ca2+ pools and the signaling of its release by the Ca2+ channel vis-à-vis the Na+-Ca2+ exchanger were not significantly altered despite an up to ninefold increase in the exchanger activity. We conclude that the exchanger remains functionally excluded from the Ca2+ microdomains surrounding the DHP/ryanodine receptor complex.
Nitric Oxide Links the Apical Na+ Transport to the Basolateral K+ Conductance in the Rat Cortical Collecting Duct
Authors: Lu Ming , Giebisch Gerhard , Wang WenHui
Published: July 2002

We have used the patch clamp technique to study the effects of inhibiting the apical Na+ transport on the basolateral small-conductance K+ channel (SK) in cell-attached patches in cortical collecting duct (CCD) of the rat kidney. Application of 50 μM amiloride decreased the activity of SK, defined as nPo (a product of channel open probability and channel number), to 61% of the control value. Application of 1 μM benzamil, a specific Na+ channel blocker, mimicked the effects of amiloride and decreased the activity of the SK to 62% of the control value. In addition, benzamil reduced intracellular Na+ concentration from 15 to 11 mM. The effect of amiloride was not the result of a decrease in intracellular pH, since addition 50 μM 5-(n-ethyl-n-isopropyl) amiloride (EIPA), an agent that specifically blocks the Na/H exchanger, did not alter the channel activity. The inhibitory effect of amiloride depends on extracellular Ca2+ because removal of Ca2+ from the bath abolished the effect. Using Fura-2 AM to measure the intracellular Ca2+, we observed that amiloride and benzamil significantly decreased intracellular Ca2+ in the Ca2+-containing solution but had no effect in a Ca2+-free bath. Furthermore, raising intracellular Ca2+ from 10 to 50 and 100 nM with ionomycin increased the activity of the SK in cell-attached patches but not in excised patches, suggesting that changes in intracellular Ca2+ are responsible for the effects on SK activity of inhibition of the Na+ transport. Since the neuronal form of nitric oxide synthase (nNOS) is expressed in the CCD and the function of the nNOS is Ca2+ dependent, we examined whether the effects of amiloride or benzamil were mediated by the NO-cGMP–dependent pathways. Addition of 10 μM S-nitroso-n-acetyl-penicillamine (SNAP) or 100 μM 8-bromoguanosine 3′:5′-cyclic monophosphate (8Br-cGMP) completely restored channel activity when it had been decreased by either amiloride or benzamil. Finally, addition of SNAP caused a significant increase in channel activity in the Ca2+-free bath solution. We conclude that Ca2+-dependent NO generation mediates the effect of inhibiting the apical Na+ transport on the basolateral SK in the rat CCD.
Modulation of GABAC Response by Ca2+ and Other Divalent Cations in Horizontal Cells of the Catfish Retina
Authors: Kaneda M. , Mochizuki M. , Aoki K. , Kaneko A.
Published: July 2002

GABAC responses were recorded in cultured cone-driven horizontal cells from the catfish retina using the patch clamp technique. At a holding potential of −49 mV, a bicuculline-resistant inward current (IGABA) was observed when 10 μM GABA was applied. The amplitude of IGABA increased as the extracellular Ca2+ ([Ca2+]o) was increased. Concentration–response curves of IGABA at 2.5 and 10 mM [Ca2+]o had similar EC50 (3.0 and 3.1 μM) and Hill coefficients (1.54 and 1.24). However, the maximal response estimated at 10 mM [Ca2+]o was larger than the maximal response at 2.5 mM [Ca2+]o. Increasing Ca influx through voltage-gated Ca channels and the resulting rise in the intracellular Ca2+ concentration had no effects on IGABA. However, IGABA was inhibited by extracellular divalent cations, with the following order of the inhibitory potency: Zn2+ > Ni2+ > Cd2+ > Co2+. The inhibitory action of Zn2+ on the [Ca2+]o-dependent IGABA increase was noncompetitive. The action of [Ca2+]o on IGABA was mimicked by Ba2+ or Sr2+. These results demonstrate that the extracellular domain of GABAC receptors has two functionally distinct binding sites represented by Ca2+ (facilitation) and Zn2+ (inhibition). Since [Ca2+]o and [Zn2+]o change into the opposite direction by light, it seems likely that they modify cooperatively the efficacy of the positive feedback consisting of the GABAC receptor.
A spectral method for the Stokes problem in three-dimensional unbounded domains
Authors: Halpern L.
Published: July 2002

We present a method for solving the Stokes problem in unbounded domains. It relies on the coupling of the transparent boundary operator and a spectral method in spherical coordinates. It is done explicitly by the use of vector-valued spherical harmonics. A uniform inf-sup condition is proved, which provides an optimal error estimate.
Applications of optimally local interpolation to interpolatory approximants and compactly supported wavelets
Authors: Chui Charles , De Villiers Johan
Published: July 2002

The objective of this paper is to introduce a general scheme for the construction of interpolatory approximation formulas and compactly supported wavelets by using spline functions with arbitrary (nonuniform) knots. Both construction procedures are based on certain “optimally local” interpolatory fundamental spline functions which are not required to possess any approximation property.
Interior penalty preconditioners for mixed finite element approximations of elliptic problems
Authors: Rusten Torgeir , Vassilevski Panayot , Winther Ragnar
Published: July 2002

It is established that an interior penalty method applied to second-order elliptic problems gives rise to a local operator which is spectrally equivalent to the corresponding nonlocal operator arising from the mixed finite element method. This relation can be utilized in order to construct preconditioners for the discrete mixed system. As an example, a family of additive Schwarz preconditioners for these systems is constructed. Numerical examples which confirm the theoretical results are also presented.
Finite subdivision rules
Authors: Cannon J. , Floyd W. , Parry W.
Published: July 2002

We introduce and study finite subdivision rules. A finite subdivision rule

R

\mathcal {R}

consists of a finite 2-dimensional CW complex

S

R

S_{\mathcal {R}}

, a subdivision

R

(

S

R

)

\mathcal {R}(S_{\mathcal {R}})

of

S

R

S_{\mathcal {R}}

, and a continuous cellular map

φ

R

:

R

(

S

R

)
→

S

R

\varphi _{\mathcal {R}}\colon \thinspace \mathcal {R}(S_{\mathcal {R}}) \to S_{\mathcal {R}}

whose restriction to each open cell is a homeomorphism. If

R

\mathcal {R}

is a finite subdivision rule,

X
X

is a 2-dimensional CW complex, and

f
:

X
→

S

R

f\colon \thinspace X\to S_{\mathcal {R}}

is a continuous cellular map whose restriction to each open cell is a homeomorphism, then we can recursively subdivide

X
X

to obtain an infinite sequence of tilings. We wish to determine when this sequence of tilings is conformal in the sense of Cannon’s combinatorial Riemann mapping theorem. In this setting, it is proved that the two axioms of conformality can be replaced by a single axiom which is implied by either of them, and that it suffices to check conformality for finitely many test annuli. Theorems are given which show how to exploit symmetry, and many examples are computed.
RNAi inDictyostelium:The Role of RNA-directed RNA Polymerases and Double-stranded RNase
Authors: Martens Henrik , Novotny Jindrich , Oberstrass Jürgen , Steck Theodore L. , Postlethwait Pamela , Nellen Wolfgang
Published: July 2002

We show that in Dictyostelium discoideum an endogenous gene as well as a transgene can be silenced by introduction of a gene construct that is transcribed into a hairpin RNA. Gene silencing was accompanied by the appearance of sequence-specific RNA ∼23mers and seemed to have a limited capacity. The threeDictyostelium homologues of the RNA-directed RNA polymerase (RrpA, RrpB, and DosA) all contain an N-terminal helicase domain homologous to the one in the dicer nuclease, suggesting exon shuffling between RNA-directed RNA polymerase and the dicer homologue. Only the knock-out of rrpA resulted in a loss of the hairpin RNA effect and simultaneously in a loss of detectable ∼23mers. However, ∼23mers were still generated by theDictyostelium dsRNase in vitro with extracts from rrpA−, rrpB−, and DosA−cells. Both RrpA and a target gene were required for production of detectable amounts of ∼23mers, suggesting that target sequences are involved in ∼23mer amplification.
Transforming Growth Factor-β–induced Mobilization of Actin Cytoskeleton Requires Signaling by Small GTPases Cdc42 and RhoA
Authors: Edlund Sofia , Landström Maréne , Heldin Carl-Henrik , Aspenström Pontus
Published: July 2002

Transforming growth factor-β (TGF-β) is a potent regulator of cell growth and differentiation in many cell types. The Smad signaling pathway constitutes a main signal transduction route downstream of TGF-β receptors. We studied TGF-β–induced rearrangements of the actin filament system and found that TGF-β1 treatment of PC-3U human prostate carcinoma cells resulted in a rapid formation of lamellipodia. Interestingly, this response was shown to be independent of the Smad signaling pathway; instead, it required the activity of the Rho GTPases Cdc42 and RhoA, because ectopic expression of dominant negative mutant Cdc42 and RhoA abrogated the response. Long-term stimulation with TGF-β1 resulted in an assembly of stress fibers; this response required both signaling via Cdc42 and RhoA, and Smad proteins. A known downstream effector of Cdc42 is p38MAPK; treatment of the cells with the p38MAPKinhibitor 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(pyridyl)1H-imidazole (SB203580), as well as ectopic expression of a kinase-inactive p38MAPK, abrogated the TGF-β–induced actin reorganization. Moreover, treatment of cells with the inhibitors of the RhoA target-protein Rho-associated coiled-coil kinase (+)-R-trans-4-(aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide (Y-27632) and 1-5(-isoquinolinesulfonyl)homopiperazine (HA-1077), as well as ectopic expression of kinase-inactive Rho coiled-coil kinase-1, abrogated the TGF-β1–induced formation of stress fibers. Collectively, these data indicate that TGF-β–induced membrane ruffles occur via Rho GTPase-dependent pathways, whereas long-term effects require cooperation between Smad and Rho GTPase signaling pathways.
A-Cell: graphical user interface for the construction of

biochemical reaction models
Authors: Ichikawa Kazuhisa
Published: July 2002

Summary: A-Cell is a tool for constructing models of complex and complicated biochemical reactions. An important feature of A-Cell is its graphical user interface for constructing biochemical reactions. In addition, it has a capability of importing previously constructed models, combining them, and constructing a comprehensive model. The simulation program for the model is automatically generated by A-Cell.

Availability: http://www.fujixerox.co.jp/crc/cng/A-Cell/

Contact: kazuhisa.ichikawa@fujixerox.co.jp
Yarrowia lipolytica Pex20p, Saccharomyces cerevisiae Pex18p/Pex21p and mammalian Pex5pL fulfil a common function in the early steps of the peroxisomal PTS2 import pathway
Authors: Einwächter Henrik , Sowinski Stefanie , Kunau Wolf‐H , Schliebs Wolfgang
Published: July 2002

Import of peroxisomal matrix proteins is essential for peroxisome biogenesis. Genetic and biochemical studies using a variety of different model systems have led to the discovery of 23 PEX genes required for this process. Although it is generally believed that, in contrast to mitochondria and chloroplasts, translocation of proteins into peroxisomes involves a receptor cycle, there are reported differences of an evolutionary conservation of this cycle either with respect to the components or the steps involved in different organisms. We show here that the early steps of protein import into peroxisomes exhibit a greater similarity than was thought previously to be the case. Pex20p of Yarrowia lipolytica, Pex18p and Pex21p of Saccharomyces cerevisiae and mammalian Pex5pL fulfil a common function in the PTS2 pathway of their respective organisms. These non‐orthologous proteins possess a conserved sequence region that most likely represents a common PTS2‐receptor binding site and di‐aromatic pentapeptide motifs that could be involved in binding of the putative docking proteins. We propose that not necessarily the same proteins but functional modules of them are conserved in the early steps of peroxisomal protein import.
Standard Bearers: Material Culture and Middle-Class Communities at the Turn of the Twentieth Century
Authors: Moskowitz Marina
Published: July 2002

A generation of historians, working at the intersection of business history and cultural history, has examined the consumer culture that flourished in the United States in the nineteenth and twentieth centuries. In studies of advertising, marketing, department stores, credit systems, and other aspects of selling and buying, these scholars have shown that American businesses not only produced consumer goods but also created consumer desire.
Plumbers of the Internet: The Creation and Evolution of the LAN Industry
Authors: Burg Urs Von
Published: July 2002

In 1973 at Xerox's Palo Alto Research Center (Xerox PARC), one of the first local area networking (LAN) technologies was invented: Ethernet. Today, Ethernet is the dominant LAN standard but, as is the case with most other information technologies, Ethernet was neither the only available alternative nor a technology well suited for all networking needs from the outset. In fact, when it was first commercialized in 1980, Ethernet was a relatively expensive, high-end technology, suited for connecting minicomputers or workstations but too expensive for connecting microcomputers or personal computers (PCs), soon to be the largest LAN market.
Molecular mechanisms of sleep–wake regulation: a role of prostaglandin D
2
Authors: Hayaishi Osamu
Published: July 2002

Prostaglandin (PG) D
2
is a major prostanoid in the brains of rats and other mammals, including humans. When PGD synthase (PGDS), the enzyme that produces PGD
2
in the brain, was inhibited by the intracerebroventricular infusion of its selective inhibitors, i.e. tetravalent selenium compounds, the amount of sleep decreased both time and dose dependently. The amount of sleep of transgenic mice, in which the human PGDS gene had been incorporated, increased several fold under appropriate conditions. These data indicate that PGDS is a key enzyme in sleep regulation.
In situ
hybridization, immunoperoxidase staining and direct enzyme activity determination of tissue samples revealed that PGDS is hardly detectable in the brain parenchyma but is localized in the membrane systems surrounding the brain, namely, the arachnoid membrane and choroid plexus, from which it is secreted into the cerebrospinal fluid (CSF) to become β–trace, a major protein component of the CSF. PGD
2
exerts its somnogenic activity by binding to PGD
2
receptors exclusively localized at the ventrorostral surface of the basal forebrain. When PGD
2
was infused into the subarachnoid space below the rostral basal forebrain, striking expression of proto–oncogene Fos immunoreactivity (FosIR) was observed in the ventrolateral preoptic area (VLPO), a putative sleep centre, concurrent with sleep induction. Fos expression in the VLPO was positively correlated with the preceding amount of sleep and negatively correlated with Fos expression in the tuberomammillary nucleus (TMN), a putative wake centre. These observations suggest that PGD
2
may induce sleep via leptomeningeal PGD
2
receptors with subsequent activation of the VLPO neurons and downregulation of the wake neurons in the TMN area. Adenosine may be involved in the signal transduction associated with PGD
2
.
The control of chemotactic cell movement duringDictyosteliummorphogenesis
Authors: Dormann Dirk , Vasiev Bakhtier , Weijer Cornelis J.
Published: July 2002

Differential cell movement is an important mechanism in the development and morphogenesis of many organisms. In many cases there are indications that chemotaxis is a key mechanism controlling differential cell movement. This can be particularly well studied in the starvation–induced multicellular development of the social amoebaDictyostelium discoideum. Upon starvation, up to 105individual amoebae aggregate to form a fruiting body. The cells aggregate by chemotaxis in response to propagating waves of cAMP, initiated by an aggregation centre. During their chemotactic aggregation the cells start to differentiate into prestalk and prespore cells, precursors to the stalk and spores that form the fruiting body. These cells enter the aggregate in a random order but then sort out to form a simple axial pattern in the slug. Our experiments strongly suggest that the multicellular aggregates (mounds) and slugs are also organized by propagating cAMP waves and, furthermore, that cell–type–specific differences in signalling and chemotaxis result in cell sorting, slug formation and movement.
Odour discrimination in the olfactory bulb of goldfish: contrasting interactions between mitral cells and ruffed cells
Authors: Zippel H. P. , Gloger M. , Nasser S. , Wilcke S.
Published: July 2002

Anatomical differences characterizing mitral cells and ruffed cells have been published by T. Kosaka and K. Hama in three teleost species. Physiological responses from both types of relay neurons were recorded extracellularly and simultaneously in the plexiform layer, using a single tungsten microelectrode. During interstimulus intervals mitral cells responded with higher, frequently burst-like impulse rates triggered by the activity of epithelial receptor neurons. Mitral cell activity could be totally suppressed by local anaesthesia of the olfactory epithelium. Ruffed cell impulse rates were low, and each action potential triggered a long-lasting (3-5 ms), continuously varying, summed granule cell potential. During olfactory stimulation with non-familiar stimuli and important biological stimuli such as amino acids, preovulatory and ovulatory pheromones, and a probable alarm pheromone, contrasting interactions between mitral cells and ruffed cells were recorded frequently, which resulted in a drastic intensification of centrally transmitted information. An excitation of mitral cells' activity via granule cells laterally inhibited the ruffed cells' activity, and an inhibition of mitral cells' activity simultaneously ‘released’ an excitation of ruffed cells.
Structural insights into human serum albumin‐mediated prostaglandin catalysis
Authors: Yang Jinsheng , Petersen Charles E. , Ha Chung‐Eun , Bhagavan Nadhipuram V.
Published: July 2002

Previous studies have shown that many arachidonic acid metabolites bind to human serum albumin (HSA) and that the metabolism of these molecules is altered as a result of binding. The present study attempted to gain insights into the mechanisms by which prostaglandins bound to subdomain 2A of HSA are metabolized by catalytic processes. The breakdown of the prostaglandin 15‐keto‐PGE2 to 15‐keto‐PGA2 and 15‐keto‐PGB2 in the presence of wild‐type HSA and a number of subdomain 2A mutants was examined using a previously validated spectroscopic method which monitors absorbance at 505 nm. The species examined using this method were wild‐type HSA, K195M, K199M, F211V, W214L, R218M, R218P, R218H, R222M, H242V, R257M, and bovine serum albumin. Previous studies of HSA‐mediated catalysis indicated that the breakdown of HSA‐bound prostaglandins results from an alkaline microenvironment in the binding site. Our results show that the catalytic breakdown of HSA‐bound 15‐keto‐PGE2 to 15‐keto‐PGB2 results from two specific processes which are modulated by specific amino acid residues. Specifically, some amino acid residues modulate the rate of step 1, the conversion of 15‐keto‐PGE2 to 15‐keto‐PGA2, while other residues modulate the rate of step 2, the conversion of 15‐keto‐PGA2 to 15‐keto‐PGB2. Some residues modulate the rate of steps 1 and 2. In total, while our results support the involvement of certain basic amino acid residues in the catabolism of HSA‐bound 15‐keto‐PGE2, our data suggest that metabolism of HSA‐bound prostaglandins may be a more complex and specific process than previously thought.
Constants of the motion for nonslipping tippe tops and other tops with round pegs
Authors: Gray C. G. , Nickel B. G.
Published: July 2002

New and more illuminating derivations are given for the three constants of the motion of a nonsliding tippe top and other symmetric tops with a spherical peg in contact with a horizontal plane. Some rigorous conclusions about the motion can be drawn immediately from these constants. It is shown that the system is integrable, and provides a valuable pedagogical example of such systems. The equation for the tipping rate is reduced to one-dimensional form. The question of sliding versus nonsliding is considered. A careful literature study of the work over the past century on this problem has been done. The classic work of Routh has been rescued from obscurity, and some misstatements in the literature are corrected.
Understanding probabilistic interpretations of physical systems: A prerequisite to learning quantum physics
Authors: Bao Lei , Redish Edward F.
Published: July 2002

Probability plays a critical role in making sense of quantum physics, but most science and engineering undergraduates have very little experience with the topic. A probabilistic interpretation of a physical system, even at a classical level, is often completely new to them, and the relevant fundamental concepts such as the probability distribution and probability density are rarely understood. To address these difficulties and to help students build a model of how to think about probability in physical systems, we have developed a set of hands-on tutorial activities appropriate for use in a modern physics course for engineers. We discuss some student difficulties with probability concepts and an instructional approach that uses a random picture metaphor and digital video technology.
Resource Letter: AOA-1: Adaptive optics for astronomy
Authors: Milonni Peter W.
Published: July 2002

But soft! what light through yonder window breaks?

It is the east, and Juliet is the sun!

This is a guide to the basic concepts and the literature on adaptive optics for astronomy.
Extension of the mode method for viscoelastic media and focused ultrasonic beams
Authors: Vandeputte J. , Leroy O. , Briers R. , Shkerdin G.
Published: July 2002

In the present study viscoelasticity is introduced in the mode model and the orthogonality condition is adapted for viscous media. The expansion of convergent acoustic Gaussian beams in terms of radiation modes for viscoelastic media is studied as well. The effects on the reflected and transmitted profiles of acoustic beams incident from an ideal liquid onto a viscoelastic plate are shown and physically explained. It is shown that focusing the incident beam can suppress divergence effects and gives the possibility to measure shear wave attenuation coefficients.
Failure to unlearn the precedence effect
Authors: Litovsky R. Y. , Hawley M. L. , Fligor B. J. , Zurek P. M.
Published: July 2002

Studies of the precedence effect using two binaural clicks have shown that listeners’ ability to discriminate changes in the interaural time difference (ITD) of the lagging click is much poorer than that for the leading click [e.g., Zurek, J. Acoust. Soc. Am. 67, 952–964 (1980)]. This difference is thought to reflect an auditory process that suppresses directional information from the lagging sound and attributes greater perceptual weight to directional information contained in the leading one. A report by Saberi and Perrott [J. Acoust. Soc. Am. 87, 1732–1737 (1990)] suggested that listeners can “unlearn” this suppression of the lag’s directional information after training with an adaptive psychophysical procedure involving 100 reversals and extremely small step sizes. Here, an attempt was made to find a similar effect using psychophysical procedures that are more common to precedence studies. Eight subjects were rigorously trained on the precedence task using either a blocked procedure or an adaptive procedure to vary ITD. Listeners showed no sign of unlearning. After 9–31 h of participating in the task, all subjects maintained high lag just-noticeable differences (jnd’s) and low single source jnd’s. This failure to train away the precedence effect (as manifested in discrimination suppression) suggests that directional information contained in the lagging source is not easily accessed. Several possible explanations for the discrepancies between the present study and Saberi and Perrott’s finding are discussed.
Thermal wave harmonics generation in the hydrodynamical heat transport in thermoacoustics
Authors: Gusev Vitalyi , Lotton Pierrick , Bailliet Hélène , Job Stéphane , Bruneau Michel
Published: July 2002

It is demonstrated that the temperature oscillations near the edge of the thermoacoustic stack are highly anharmonic even in the case of harmonic acoustic oscillations in the thermoacoustic engines. In the optimum regime for the acoustically induced heat transfer, the amplitude of the second harmonic of the temperature oscillations is comparable to that of the fundamental frequency.
Simulation of jet-noise excitation in an acoustic progressive wave tube facility
Authors: Steinwolf Alexander , White Robert G. , Wolfe Howard F.
Published: July 2002

Acoustic excitation produced by jet-engine effluxes was simulated in a progressive wave tube (APWT) facility with a computer-based control system. The APWT siren is driven by a signal generated numerically in a PC and then converted into analog form. Characteristics of the acoustic pressure measured by a microphone are analyzed in digital form and compared with those prescribed for simulation. Divergence is compensated by immediate modification of the driving signal and this action is repeated in the form of iterative process until the test specification is attained. Typical power spectral density (PSD) shapes with maxima at low and high frequencies were simulated. A “tailoring” approach has been also achieved when a test specification was determined directly from field measurements for the particular aircraft under consideration. Since acoustic pressure signals of high level differ from the Gaussian random process model, particularly in terms of asymmetric probability density function, a method has been developed to make the driving signal also non-Gaussian by simulating skewness and kurtosis parameters of the APWT acoustic excitation simultaneously with PSD control. Experimental results with Gaussian and non-Gaussian characteristics obtained for various PSD specifications including sharp and narrow peaks are presented in the paper.
Relationships among calcaneal backscatter, attenuation, sound speed, hip bone mineral density, and age in normal adult women
Authors: Wear Keith A. , Armstrong David W.
Published: July 2002

The present study was undertaken in order to investigate the use of calcaneal ultrasonic backscatter for the application of diagnosis of osteoporosis. Broadband ultrasonic attenuation (BUA), speed of sound (SOS), the average backscatter coefficient (ABC), and the hip bone mineral density (BMD) were measured in calcanea in 47 women (average age: 58 years, standard deviation: 13 years). All three ultrasound variables had comparable correlations with hip BMD (around 0.5). As reported previously by others, BUA and SOS were rather highly correlated with each other. The logarithm of the ABC was only moderately correlated with the other two. The three ultrasound parameters exhibited similar moderate negative correlations with age. These results taken collectively suggest that the ABC may carry important diagnostic information independent of that contained in BUA and SOS and, therefore, may be useful as an adjunct measurement in the diagnosis of osteoporosis.
Noisy speech recognition using de-noised multiresolution analysis acoustic features
Authors: Chan C. P. , Ching P. C. , Lee Tan
Published: July 2002

This paper describes a novel application of multiresolution analysis (MRA) in extracting acoustic features that possess de-noising capability for robust speech recognition. The MRA algorithm is used to construct a mel-scaled wavelet packet filter-bank, from which subband powers are computed as the feature parameters for speech recognition. Wiener filtering is applied to a few selected subbands at some intermediate stages of decomposition. For high-frequency bands, Wiener filters are designed based on a reduced fraction of the estimated noise power, making the consonant features much more prominent and contrastive. The proposed method is evaluated in phone recognition experiments with the TIMIT database. In the presence of stationary white noise at 10-dB SNR, the de-noised MRA features attain a phone recognition rate of 32%. There is a noticeable improvement compared with the accuracy of 29% and 20% attained by the commonly used mel-frequency cepstral coefficients (MFCC) with and without cepstral mean normalization (CMN), respectively. The effectiveness of the MRA features is also verified by the fact that they exhibit smaller distortion from clean speech.
Effects of reversible noise exposure on the suppression tuning of rabbit distortion-product otoacoustic emissions
Authors: Howard MacKenzie A. , Stagner Barden B. , Lonsbury-Martin Brenda L. , Martin Glen K.
Published: July 2002

Distortion-product otoacoustic emissions (DPOAEs) at 2f1-f2 can be suppressed by the introduction of a third “suppressor” tone. Plotting the suppression of the DPOAE level against the changing frequency and level of the suppressor produces frequency-tuning functions referred to as suppression tuning curves (STCs). The dominant features of STCs, including their shape, are similar to the features of neural tuning curves (NTCs) recorded from single auditory nerve fibers. However, recent findings using reversible diuretics suggest that STCs do not provide the same measure of cochlear frequency selectivity as provided by NTCs. To determine if STCs are also insensitive to the adverse effects of excessive sounds, the present study exposed rabbits to a moderate-level noise that produced temporary threshold shift-like (TTS) effects on DPOAEs, and examined the influence of such exposures on STCs. DPOAEs were produced using primary tones with geometric-mean frequencies centered at 2.8 or 4 kHz, and with L1 and L2 values of 45/45, 50/35, 50/50, and 55/45 dB SPL. STCs were obtained before and during recovery for a period of approximately 2 h immediately following, and at 1, 2, 3, and 7 d post-exposure to a 2 kHz octave band noise, at levels and durations sufficient to cause significant but reversible reductions in DPOAE levels. STC data included tip center frequency, tip threshold, and Q10dB measures of tuning for suppression criteria of 3, 6, 9, and 12 dB. Recovery was variable between animals, but all rabbits recovered fully by 7 d post-exposure. STC center frequencies measured during the TTS typically tuned to a slightly higher frequency, while tip thresholds tended to decrease and Q10dB increase. Together, the results indicate that, despite similarities in the general properties of STCs and NTCs, these two types of tuning curves are affected differently following reversible cochlear insult.
The mechanical waveform of the basilar membrane. IV. Tone and noise stimuli
Authors: de Boer Egbert , Nuttall Alfred L.
Published: July 2002

Analysis of mechanical cochlear responses to wide bands of random noise clarifies many effects of cochlear nonlinearity. The previous paper [de Boer and Nuttall, J. Acoust. Soc. Am. 107, 1497–1507 (2000)] illustrates how closely results of computations in a nonlinear cochlear model agree with responses from physiological experiments. In the present paper results for tone stimuli are reported. It was found that the measured frequency response for pure tones differs little from the frequency response associated with a noise signal. For strong stimuli, well into the nonlinear region, tones have to be presented at a specific level with respect to the noise for this to be true. In this report the nonlinear cochlear model originally developed for noise analysis was modified to accommodate pure tones. For this purpose the efficiency with which outer hair cells modify the basilar-membrane response was made into a function of cochlear location based on local excitation. For each experiment, the modified model is able to account for the experimental findings, within 1 or 2 dB. Therefore, the model explains why the type of filtering that tones undergo in the cochlea is essentially the same as that for noise signals (provided the tones are presented at the appropriate level).
Perception of nonlinear and linear formant trajectories
Authors: Nábělek Anna K. , Ovchinnikov Alexandra
Published: July 2002

Perception of F2 trajectories in synthetic vowels was investigated. Perceptual boundaries (50% response points of identification functions) of 20-step /ʊ–ɪ/ continua with various shapes of F2 trajectories were determined and compared with the boundary for vowels with steady-state F2. In experiment 1, the vowels were synthesized in either /j–j/ or /w–w/ context resulting in parabolic trajectories, then the stimuli were split into halves resulting in quadratic F2 trajectories. All stimuli were 200 ms long. For the /wVw/, and /wV/ stimuli, the boundaries were at lower stimulus numbers than for the stimuli with steady-state F2, indicating that the nonlinear F2 trajectories were perceived as having frequencies beyond the extreme values actually synthesized in the stimuli. This type of signal processing has been termed “perceptual compensation.” For the /jVj/ stimuli, there was only a trend for perceptual compensation of F2 trajectories. For the /Vw/, /Vj/, and /jV/ stimuli, the boundaries were at stimulus numbers corresponding to frequencies of the relatively steady-state vowel-like segments. In experiment 2, the quadratic F2 trajectories of the /wV/ stimuli were changed to linear trajectories and F1 and F3 trajectories were either quadratic, linear, or steady state. The results indicated that the shape of F1 and F3 trajectories had no effect on the boundaries. For the linear F2 trajectories, as for the quadratic F2 trajectories in the /wV/ stimuli, the boundaries were at lower stimulus numbers than for the stimulus with steady-state F2, indicating presence of perceptual compensation. In the experiment 3, the F1 and F3 were steady state and the linear F2 trajectories had three different values of frequency difference, ΔF, between the initial and final frequencies. The perceptual compensation was found for the 200-ms stimuli with large ΔF up to 500 Hz over 200-ms stimulus duration, and perceptual enhancement of final frequencies was found for the stimuli with ΔF=280 Hz.
Modeling of piezoelectric ceramic vibrators including thermal effects. Part IV. Development and experimental evaluation of a bond graph model of the thickness vibrator
Authors: Moon Won-kyu , Busch-Vishniac Ilene J.
Published: July 2002

This article develops a model of the piezoelectric ceramic vibrator which includes thermal energy exchange on an equal footing with the electrical and mechanical energy. By use of an isentropically linear model for the material and the bond graph models for a piezoelectric thickness vibrator and heat conduction previously developed by the authors, a thermodynamically complete model is developed. For a simple case, the predicted results from the developed model are compared with the results from experiments. Predictions are found to compare very favorably with these measurements.
A model of auditory streaming
Authors: McCabe Susan L. , Denham Michael J.
Published: July 2002

An essential feature of intelligent sensory processing is the ability to focus on the part of the signal of interest against a background of distracting signals, and to be able to direct this focus at will. In this paper the problem of auditory streaming is considered and a model of the early stages of the process is proposed. The behavior of the model is shown to be in agreement with a number of well-known psychophysical results, including the relationship between presentation rate, frequency separation and streaming, the temporal development of streaming, and the effect of background organization on streaming. The principal contribution of this model is that it demonstrates how streaming might result from interactions between the tonotopic patterns of activity of incoming signals and traces of previous activity which feed back and influence the way in which subsequent signals are processed. The significance of these results for auditory scene analysis is considered and a framework for the integration of simultaneous and sequential grouping cues in the perception of auditory objects is proposed.
The modulated–unmodulated difference: Effects of signal frequency and masker modulation depth
Authors: Bacon Sid P. , Lee Jungmee
Published: July 2002

The masked threshold for a signal is oftentimes lower when the masker is modulated than when it is unmodulated. The difference in masked thresholds is referred to as the modulated–unmodulated difference, or MUD. The purpose of the present study was to follow up on the results of a previous study [Bacon et al., J. Acoust. Soc. Am. 101, 1600–1610 (1997)] which showed that the MUD is larger for high than for low signal frequencies, both when the masker is no wider than a critical band (and the processing is solely within channel) and when it is broadband (and the processing may be both within and across channel). The present results indicate that the effects of signal frequency primarily exist only when the modulated masker is modulated at a depth greater than about 0.75, and that at these large depths, thresholds in the presence of the modulated masker are governed largely by forward masking. By far, the effect of signal frequency is larger with the broadband masker than with the critical-band masker, suggesting that there may be an across-channel process whose contribution is greater at high than at low signal frequencies. It is argued here that this across-channel process may be related to psychophysical suppression.