bluuebunny/crossref_metadata_2025 huggingface dataset:
Bad Boys and Good Girls? Patterns of Interaction and Response in Whole Class Teaching
Authors: Myhill Debra
Published: July 2002

Abstract The article describes the findings of a cross‐phase study into boys' underachievement which investigated patterns of classroom interaction by boys and girls. The data illustrate how underachievers, of either gender, are the least likely group to be participating positively in the classroom and most likely to be engaged in off‐task interactions. The underachieving boys' reluctance to participate emerges in year 1, but by year 4 the underachieving girl is behaving in the same way. To a lesser extent, the older high‐achieving boy begins to exhibit similar interaction patterns to the underachievers. By contrast, the high‐achieving girl remains consistently actively participant and on‐task. The article questions the extent to which whole class teaching is benefiting the learning experience of underachievers and challenges the current tendency to construct underachievement in terms of gender.
Modulation of β1A Integrin Functions by Tyrosine Residues in the β1 Cytoplasmic Domain
Authors: Sakai Takao , Zhang Qinghong , Fässler Reinhard , Mosher Deane F.
Published: July 2002

β1A integrin subunits with point mutations of the cytoplasmic domain were expressed in fibroblasts derived from β1-null stem cells. β1A in which one or both of the tyrosines of the two NPXY motifs (Y783, Y795) were changed to phenylalanines formed active α5β1 and α6β1 integrins that mediated cell adhesion and supported assembly of fibronectin. Mutation of the proline in either motif (P781, P793) to an alanine or of a threonine in the inter-motif sequence (T788) to a proline resulted in poorly expressed, inactive β1A. Y783,795F cells developed numerous fine focal contacts and exhibited motility on a surface. When compared with cells expressing wild-type β1A or β1A with the D759A activating mutation of a conserved membrane–proximal aspartate, Y783,795F cells had impaired ability to transverse filters in chemotaxis assays. Analysis of cells expressing β1A with single Tyr to Phe substitutions indicated that both Y783 and Y795 are important for directed migration. Actin-containing microfilaments of Y783,795F cells were shorter and more peripheral than microfilaments of cells expressing wild-type β1A. These results indicate that change of the phenol side chains in the NPXY motifs to phenyl groups (which cannot be phosphorylated) has major effects on the organization of focal contacts and cytoskeleton and on directed cell motility.
Cathepsin S Controls the Trafficking and Maturation of Mhc Class II Molecules in Dendritic Cells
Authors: Driessen Christoph , Bryant Rebecca A.R. , Lennon-Duménil Ana-Maria , Villadangos José A. , Bryant Paula Wolf , Shi Guo-Ping , Chapman Harold A. , Ploegh Hidde L.
Published: July 2002

Before a class II molecule can be loaded with antigenic material and reach the surface to engage CD4+ T cells, its chaperone, the class II-associated invariant chain (Ii), is degraded in a stepwise fashion by proteases in endocytic compartments. We have dissected the role of cathepsin S (CatS) in the trafficking and maturation of class II molecules by combining the use of dendritic cells (DC) from CatS−/− mice with a new active site–directed probe for direct visualization of active CatS. Our data demonstrate that CatS is active along the entire endocytic route, and that cleavage of the lysosomal sorting signal of Ii by CatS can occur there in mature DC. Genetic disruption of CatS dramatically reduces the flow of class II molecules to the cell surface. In CatS−/− DC, the bulk of major histocompatibility complex (MHC) class II molecules is retained in late endocytic compartments, although paradoxically, surface expression of class II is largely unaffected. The greatly diminished but continuous flow of class II molecules to the cell surface, in conjunction with their long half-life, can account for the latter observation. We conclude that in DC, CatS is a major determinant in the regulation of intracellular trafficking of MHC class II molecules.
Isoenzyme-Specific Interaction of Muscle-Type Creatine Kinase with the Sarcomeric M-Line Is Mediated by Nh2-Terminal Lysine Charge-Clamps
Authors: Hornemann Thorsten , Stolz Martin , Wallimann Theo
Published: July 2002

Creatine kinase (CK) is located in an isoenzyme-specific manner at subcellular sites of energy production and consumption. In muscle cells, the muscle-type CK isoform (MM-CK) specifically interacts with the sarcomeric M-line, while the highly homologous brain-type CK isoform (BB-CK) does not share this property. Sequence comparison revealed two pairs of lysine residues that are highly conserved in M-CK but are not present in B-CK. The role of these lysines in mediating M-line interaction was tested with a set of M-CK and B-CK point mutants and chimeras. We found that all four lysine residues are involved in the isoenzyme-specific M-line interaction, acting pair-wise as strong (K104/K115) and weak interaction sites (K8/K24). An exchange of these lysines in MM-CK led to a loss of M-line binding, whereas the introduction of the very same lysines into BB-CK led to a gain of function by transforming BB-CK into a fully competent M-line–binding protein. The role of the four lysines in MM-CK is discussed within the context of the recently solved x-ray structures of MM-CK and BB-CK.
Telomere Length, Telomerase Activity, and Replicative Potential in HIV Infection: Analysis of CD4+ and CD8+T Cells from HIV-discordant Monozygotic Twins
Authors: Palmer Larry D. , Weng Nan-ping , Levine Bruce L. , June Carl H. , Lane H. Clifford , Hodes Richard J.
Published: July 2002

To address the possible role of replicative senescence in human immunodeficiency virus (HIV) infection, telomere length, telomerase activity, and in vitro replicative capacity were assessed in peripheral blood T cells from HIV+ and HIV− donors. Genetic and age-specific effects on these parameters were controlled by studying HIV-discordant pairs of monozygotic twins. Telomere terminal restriction fragment (TRF) lengths from CD4+ T cells of HIV+ donors were significantly greater than those from HIV− twins. In contrast, telomere lengths in CD8+ T cells from HIV+ donors were shorter than in HIV− donors. The in vitro replicative capacity of CD4+ cells from HIV+ donors was equivalent to that of HIV− donors in response to stimulation through T cell receptor CD3 and CD28. Little or no telomerase activity was detected in freshly isolated CD4+ or CD8+ lymphocytes from HIV+ or HIV− donors, but was induced by in vitro stimulation of both HIV+ and HIV− donor cells. These results suggest that HIV infection is associated with alterations in the population dynamics of both CD4+ and CD8+ T cells, but fail to provide evidence for clonal exhaustion or replicative senescence as a mechanism underlying the decline in CD4+ T cells of HIV-infected donors.
The Iron Transport Protein NRAMP2 Is an Integral Membrane Glycoprotein That Colocalizes with Transferrin in Recycling Endosomes
Authors: Gruenheid Samantha , Canonne-Hergaux François , Gauthier Susan , Hackam David J. , Grinstein Sergio , Gros Philippe
Published: July 2002

The natural resistance associated macrophage protein (Nramp) gene family is composed of two members in mammals, Nramp1 and Nramp2. Nramp1 is expressed primarily in macrophages and mutations at this locus cause susceptibility to infectious diseases. Nramp2 has a much broader range of tissue expression and mutations at Nramp2 result in iron deficiency, indicating a role for Nramp2 in iron metabolism. To get further insight into the function and mechanism of action of Nramp proteins, we have generated isoform specific anti-Nramp1 and anti-Nramp2 antisera. Immunoblotting experiments indicate that Nramp2 is present in a number of cell types, including hemopoietic precursors, and is coexpressed with Nramp1 in primary macrophages and macrophage cell lines. Nramp2 is expressed as a 90–100-kD integral membrane protein extensively modified by glycosylation (>40% of molecular mass). Subcellular localization studies by immunofluorescence and confocal microscopy indicate distinct and nonoverlapping localization for Nramp1 and Nramp2. Nramp1 is expressed in the lysosomal compartment, whereas Nramp2 is not detectable in the lysosomes but is expressed primarily in recycling endosomes and also, to a lower extent, at the plasma membrane, colocalizing with transferrin. These findings suggest that Nramp2 plays a key role in the metabolism of transferrin-bound iron by transporting free Fe2+ across the endosomal membrane and into the cytoplasm.
A Novel Gene Coding for a Fas Apoptosis Inhibitory Molecule (FAIM) Isolated from Inducibly Fas-resistant B Lymphocytes
Authors: Schneider Thomas J. , Fischer Gavin M. , Donohoe Terrence J. , Colarusso Thomas P. , Rothstein Thomas L.
Published: July 2002

The sensitivity of primary splenic B cells to Fas-mediated apoptosis is modulated in a receptor-specific fashion. Here we used a differential display strategy to detect cDNAs present in B cells rendered Fas resistant but absent in those rendered Fas sensitive. This led to the cloning and characterization of a novel 1.2-kb gene that encodes a Fas apoptosis inhibitory molecule (FAIM). faim-transfected BAL-17 B lymphoma cells were less sensitive by half or more to Fas-mediated apoptosis than were vector-transfected controls, using Fas ligand–bearing T cells or a cytotoxic anti-Fas antibody to trigger Fas, and this was associated with inhibition of Fas- induced poly-ADP ribose polymerase (PARP) cleavage. In primary B cells, the time course of faim mRNA and FAIM protein expression correlated with the induction of Fas resistance by surface (s)Ig engagement. Thus, FAIM is an inducible effector molecule that mediates Fas resistance produced by sIg engagement in B cells. However, faim is broadly expressed in various tissues and the faim sequence is highly conserved evolutionarily, suggesting that its role extends beyond lymphocyte homeostasis. As FAIM has no significant regions of homology to other gene products that modulate Fas killing, it appears to represent a distinct, new class of antiapoptotic protein.
Protective T Cell–Independent Antiviral Antibody Responses Are Dependent on Complement
Authors: Ochsenbein Adrian F. , Pinschewer Daniel D. , Odermatt Bernhard , Carroll Michael C. , Hengartner Hans , Zinkernagel Rolf M.
Published: July 2002

Complement is part of the innate immune system and one of the first lines of host defense against infections. Its importance was evaluated in this study in virus infections in mice deficient either in soluble complement factors (C3−/−, C4−/−) or in the complement signaling complex (complement receptor [CR]2−/−, CD19−/−). The induction of the initial T cell–independent neutralizing immunoglobulin (Ig)M antibody response to vesicular stomatitis virus (VSV), poliomyelitis virus, and recombinant vaccinia virus depended on efficient antigen trapping by CR3 and -4–expressing macrophages of the splenic marginal zone. Neutralizing IgM and IgG antibody responses were largely independent of CR2-mediated stimulation of B cells when mice were infected with live virus. In contrast, immunizations with nonreplicating antigens revealed an important role of B cell stimulation via CR2 in the switch to IgG. The complement cascade was activated after infection with VSV via the classical pathway, and active complement cleavage products augmented the effector function of neutralizing IgM and IgG antibodies to VSV by a factor of 10–100. Absence of the early neutralizing antibody responses, together with the reduced efficiency of neutralizing IgM in C3−/− mice, led to a drastically enhanced susceptibility to disease after infection with VSV.
Suppression of Tumorigenicity in Breast Cancer Cells by the Microfilament Protein Profilin 1
Authors: Janke Jürgen , Schlüter Kathrin , Jandrig Burkhard , Theile Michael , Kölble Konrad , Arnold Wolfgang , Grinstein Edgar , Schwartz Arnfried , Estevéz-Schwarz Lope , Schlag Peter M. , Jockusch Brigitte M. , Scherneck Siegfried
Published: July 2002

Differential display screening was used to reveal differential gene expression between the tumorigenic breast cancer cell line CAL51 and nontumorigenic microcell hybrids obtained after transfer of human chromosome 17 into CAL51. The human profilin 1 (PFN1) gene was found overexpressed in the microcell hybrid clones compared with the parental line, which displayed a low profilin 1 level. A comparison between several different tumorigenic breast cancer cell lines with nontumorigenic lines showed consistently lower profilin 1 levels in the tumor cells. Transfection of PFN1 cDNA into CAL51 cells raised the profilin 1 level, had a prominent effect on cell growth, cytoskeletal organization and spreading, and suppressed tumorigenicity of the stable, PFN1-overexpressing cell clones in nude mice. Immunohistochemical analysis revealed intermediate and low levels of profilin 1 in different human breast cancers. These results suggest profilin 1 as a suppressor of the tumorigenic phenotype of breast cancer cells.
Role of Lipooligosaccharide in Opa-Independent Invasion of Neisseria gonorrhoeae into Human Epithelial Cells
Authors: Song Wenxia , Ma Lang , Chen Ruiwu , Stein Daniel C.
Published: July 2002

Lipooligosaccharide (LOS) has been implicated in the adhesion and invasion of host epithelial cells. We examined the adhesive and invasive abilities of isogenic gonococcal opacity-associated outer membrane protein–negative, pilus-positive (Opa−Pil+) Neisseria gonorrhoeae strains expressing genetically defined LOS. Strain F62 (Opa−Pil+), expressing the lacto-N-neotetraose and the galNac-lacto-N-neotetraose LOS, and its isogenic derivative that expressed only the lacto-N-neotetraose LOS (F62ΔlgtD), adhered to, and invaded, to the same extent the human cervical epidermoid carcinoma cell line, ME180. While the adhesive abilities of Opa−Pil+ isogenic strains that express LOS molecules lacking the lacto-N-neotetraose structure were similar to that seen for F62, their invasive abilities were much lower than the strains expressing lacto-N-neotetraose. Fluorescence microscopy studies showed that the adherence of F62, but not the strains lacking lacto-N-neotetraose, induced the rearrangement of actin filaments under the adherent sites. Electron microscopy studies demonstrated that F62, but not the strains lacking lacto-N-neotetraose, formed extensive and intimate associations with epithelial cell membranes. Thus, in the absence of detectable Opa protein, the lacto-N-neotetraose LOS promotes gonococcal invasion into ME180 cells. The data also suggest that LOS is involved in the mobilization of actin filaments in host cells, and in the formation of a direct interaction between the bacterial outer membrane and the plasma membrane of ME180 cells.
Sensory Adaptation in Naive Peripheral CD4 T Cells
Authors: Smith Katy , Seddon Benedict , Purbhoo Marco A. , Zamoyska Rose , Fisher Amanda G. , Merkenschlager Matthias
Published: July 2002

T cell receptor interactions with peptide/major histocompatibility complex (pMHC) ligands control the selection of T cells in the thymus as well as their homeostasis in peripheral lymphoid organs. Here we show that pMHC contact modulates the expression of CD5 by naive CD4 T cells in a process that requires the continued expression of p56lck. Reduced CD5 levels in T cells deprived of pMHC contact are predictive of elevated Ca2+ responses to subsequent TCR engagement by anti-CD3 or nominal antigen. Adaptation to peripheral pMHC contact may be important for regulating naive CD4 T cell responsiveness.
A unified approach to evaluation algorithms for multivariate polynomials
Authors: Lodha Suresh , Goldman Ron
Published: July 2002

We present a unified framework for most of the known and a few new evaluation algorithms for multivariate polynomials expressed in a wide variety of bases including the Bernstein-Bézier, multinomial (or Taylor), Lagrange and Newton bases. This unification is achieved by considering evaluation algorithms for multivariate polynomials expressed in terms of L-bases, a class of bases that include the Bernstein-Bézier, multinomial, and a rich subclass of Lagrange and Newton bases. All of the known evaluation algorithms can be generated either by considering up recursive evaluation algorithms for L-bases or by examining change of basis algorithms for L-bases. For polynomials of degree

n
n

in

s
s

variables, the class of up recursive evaluation algorithms includes a parallel up recurrence algorithm with computational complexity

O
(

n

s
+
1

)

O(n^{s+1})

, a nested multiplication algorithm with computational complexity

O
(

n
s

log
⁡
n
)

O(n^s \log n)

and a ladder recurrence algorithm with computational complexity

O
(

n
s

)

O(n^s)

. These algorithms also generate a new generalization of the Aitken-Neville algorithm for evaluation of multivariate polynomials expressed in terms of Lagrange L-bases. The second class of algorithms, based on certain change of basis algorithms between L-bases, include a nested multiplication algorithm with computational complexity

O
(

n
s

)

O(n^s)

, a divided difference algorithm, a forward difference algorithm, and a Lagrange evaluation algorithm with computational complexities

O
(

n
s

)

O(n^s)

,

O
(

n
s

)

O(n^s)

and

O
(
n
)

O(n)

per point respectively for the evaluation of multivariate polynomials at several points.
The autonomy of the visual systems and the modularity of conscious vision
Authors:   The American Association for Research into Nervous and Mental Diseases, Zeki S. , Bartels A.
Published: July 2002

Anatomical and physiological evidence shows that the primate visual brain consists of many distributed processing systems, acting in parallel. Psychophysical studies show that the activity in each of the parallel systems reaches its perceptual end–point at a different time, thus leading to a perceptual asynchrony in vision. This, together with clinical and human imaging evidence, suggests strongly that the processing systems are also perceptual systems and that the different processing–perceptual systems can act more or less autonomously. Moreover, activity in each can have a conscious correlate without necessarily involving activity in other visual systems. This leads us to conclude not only that visual consciousness is itself modular, reflecting the basic modular organization of the visual brain, but that the binding of cellular activity in the processing–perceptual systems is more properly thought of as a binding of the consciousnesses generated by each of them. It is this binding that gives us our integrated image of the visual world.
Levels and loops: the future of artificial intelligence and neuroscience
Authors: Bell Anthony J.
Published: July 2002

In discussing artificial intelligence and neuroscience, I will focus on two themes. The first is the universality of cycles (or loops): sets of variables that affect each other in such a way that any feed–forward account of causality and control, while informative, is misleading. The second theme is based around the observation that a computer is an intrinsically dualistic entity, with its physical set–up designed so as not to interfere with its logical set–up, which executes the computation. The brain is different. When analysed empirically at several different levels (cellular, molecular), it appears that there is no satisfactory way to separate a physical brain model (or algorithm, or representation), from a physical implementational substrate. When program and implementation are inseparable and thus interfere with each other, a dualistic point–of–view is impossible. Forced by empiricism into a monistic perspective, the brain–mind appears as neither embodied by or embedded in physical reality, but rather as identical to physical reality. This perspective has implications for the future of science and society. I will approach these from a negative point–of–view, by critiquing some of our millennial culture's popular projected futures.
On the functions of double eyes in midwater animals
Authors: Land Michael F.
Published: July 2002

Midwater predators often have double eyes consisting of a large upward–pointing part with a narrow field of view and high resolution, and a small downward–pointing part with a wide field of view and low resolution. In crustaceans with compound eyes the different eye parts are of basically similar construction, but in fishes the downward–pointing regions may employ unusual optical systems with unknown image–forming capabilities. It has been suggested that the upward–directed parts are used to detect silhouettes of animals against the residual daylight, whereas the lower parts look out for luminescent organisms. Here I calculate the sizes that apposition compound eyes would need to attain in order to fulfil these tasks, and the way that size should vary with depth. It is concluded that silhouette detection is much the more demanding task, and becomes increasingly difficult as light levels decrease. For this reason the upward–pointing parts must increase rapidly with depth. This is not the case with luminescence detectors, where the task is most difficult near the surface because of upwelling background light, and becomes easier with depth. On the whole these predictions fit well with the sizes and shapes of real midwater eyes, especially in the case of the hyperiid amphipods.
Chromatin-specific regulation of LEF-1–β-catenin transcription activation and inhibition in vitro
Authors: Tutter Antonin V. , Fryer Christy J. , Jones Katherine A.
Published: July 2002

Transcriptional activation of Wnt/Wg-responsive genes requires the stabilization and nuclear accumulation of β-catenin, a dedicated coactivator of LEF/TCF enhancer-binding proteins. Here we report that recombinant β-catenin strongly enhances binding and transactivation by LEF-1 on chromatin templates in vitro. Interestingly, different LEF-1 isoforms vary in their ability to bind nucleosomal templates in the absence of β-catenin, owing to N-terminal residues that repress binding to chromatin, but not nonchromatin, templates. Transcriptional activation in vitro requires both the armadillo (ARM) repeats and the C terminus of β-catenin, whereas the phosphorylated N terminus is inhibitory to transcription. A fragment spanning the C terminus (CT) and ARM repeats 11 and 12 (CT–ARM), but not the CT alone, functions as a dominant negative inhibitor of LEF-1–β-cat activity in vitro and can block ATP-dependent binding of the complex to chromatin. LEF-1–β-cat transactivation in vitro was also repressed by inhibitor of β-catenin and Tcf-4 (ICAT), a physiological inhibitor of Wnt/Wg signaling that interacts with ARM repeats 11 and 12, and by the nonsteroidal anti-inflammatory compound, sulindac. None of these transcription inhibitors (CT–ARM, ICAT, or sulindac) could disrupt the LEF-1–β-cat complex after it was stably bound to chromatin. We conclude that the CT–ARM region of β-catenin functions as a chromatin-specific activation domain, and that several inhibitors of the Wnt/Wg pathway directly modulate LEF-1–β-cat activity on chromatin.
Monte Carlo calculation of dose rate distributions around 0.5 and 0.6 mm in diameter wires
Authors: Pérez‐Calatayud J. , Lliso F. , Carmona V. , Ballester F. , Hernández C.
Published: July 2002

Monte Carlo simulations of absolute dose rate in liquid water are presented in the form of away‐along tables for 1 and 5 cm wires of 0.5 and 0.6 mm diameter. Simulated absolute dose rate values can be used as benchmark data to verify the calculation results of treatment planning systems or directly as input data for treatment planning. Best fit value of an attenuation coefficient suitable for use in Sievert integral‐type calculations has been derived based on Monte Carlo simulation results. For the treatment planning systems that are based on the TG43 formalism we have also computed the required dosimetry parameters.
Two charged particles in a one-dimensional well
Authors: Salter Edward A. , Trucks Gary W. , Cyphert Daniel S.
Published: July 2002

We present numerically exact solutions of the time-independent Schrödinger equation for the following system: two particles of the same charge, repelled by the Coulomb force, confined to a one-dimensional infinite well. The eigenfunctions are expanded in a basis set of product delta functions; the expansion allows the removal of the Coulomb potential’s singularity. We report and discuss our findings regarding correlated behavior in the lowest energy states of a well of length 3 bohr (1 bohr=1 Bohr radius≈0.52 Å).
Gas bubble pulsation in a semiconfined space subjected to ultrasound
Authors: Krasovitski Boris , Kimmel Eitan
Published: July 2002

In the case of ultrasound application in biological tissues, gas bubbles might form and collapse within cells, in the intercellular spaces and on tissue surfaces. In this work the effect of confined space on the behavior of the gas bubble in the presence of ultrasonic field is studied. A numerical model for bubble pulsation in a planar liquid layer, bounded by two rigid walls, is developed. Surface tension at the interface between the host liquid and the gas in the bubble is considered as well. A mathematical statement and solution technique based on the boundary integral method are presented. In some cases, the bubble divides into two symmetrical parts and high-velocity jets are generated, aimed at the walls. The final velocity of the jets strongly depends on the surface tension of the host liquid. Two new parameters that predict the occurrence of jet formation are developed.
Locus equations in the light of articulatory modeling
Authors: Chennoukh Samir , Carré René , Lindblom Björn
Published: July 2002

This paper examines the significance of the so-called “locus equation” by means of articulatory simulations of V1CV2 utterances with different intergestural timing, and, therefore, with varying degrees of consonant–vowel coarticulation. Movement toward the vowel V2 started (i) at the beginning of the transition to the consonant, (ii) at the beginning of the complete consonant closure, or (iii) at the beginning of the release of the consonant. For each combination of vowels and each consonant, F2 onset of V2 as a function of F2 of V2 was adequately described by straight lines corresponding to locus equations (referred to as first-order locus equations). The findings show that the derived locus equations depend on the consonant place on the one hand and on the degree of coarticulation on the other. The effect of varying intergestural timing was compared with published data on locus equation coefficients for individual speakers using the format of y-intercept plotted versus slope for each place of articulation (referred to as a second-order locus equation). These comparisons demonstrate that the model adequately captures the natural place-dependent variations in slope and intercept. Also it provides accurate numerical matches with their speaker-specific ranges suggesting the hypothesis that the variability derives, to a significant extent, from individual differences in intergestural timing.
Sound radiation of 3-MHz driven gas bubbles
Authors: Grossmann Siegfried , Hilgenfeldt Sascha , Lohse Detlef , Zomack Michael
Published: July 2002

The sound radiation of 3-MHz acoustically driven air bubbles in liquid is analyzed with respect to possible applications in second harmonic ultrasound diagnostics devices, which have recently come into clinical use. In the forcing pressure amplitude Pa=1–10 atm and ambient radius R0=0.5–5 μm parameter domain, a narrow regime around the resonance radius R0∼1–1.5 μm and relatively modest Pa∼2–2.5 atm is identified in which optimal sound yield in the second harmonic is achieved while maintaining spherical stability of the bubble. For smaller Pa and larger R0 hardly any sound is radiated; for larger Pa bubbles become unstable toward nonspherical shape oscillations of their surface. The computation of these instabilities is essential for the evaluation of the optimal parameter regime. A region of slightly smaller R0 and Pa∼1–3 atm is best suited to achieve large ratios of the second harmonic to the fundamental intensity. Spherical stability is guaranteed in the suggested regimes for liquids with an enhanced viscosity compared to water, such as blood.
Acoustic wave generation in viscoelastic rods by time-gated microwaves
Authors: Bacon Christophe , Hosten Bernard , Bernard Pierre-Alain
Published: July 2002

A one-dimensional model is developed to predict the acoustic waves generated in viscoelastic rods by electromagnetic microwave pulses. The wave generation is due to the rapid thermal expansion caused by microwave absorption. The distribution of the temperature rise along the rod is taken to be either uniform or linear. The effects of this distribution and of the microwave pulsewidth are investigated numerically. Some tests are carried out on PVC rods instrumented with accelerometers. The presence of the accelerometer mass at the end of the rod is taken into account in the model. The comparison between the experimental and the theoretical accelerations leads to the evaluation of the maximum temperature rise during one pulse. Although this temperature rise is found to be extremely low, it produces acoustic waves easily detectable with the accelerometer. The inverse problem to estimate the viscoelastic properties of the rod and the temperature rise is approached by means of a numerical minimization technique.
Statistical characterization of high-frequency shallow-water seafloor backscatter
Authors: Lyons Anthony P. , Abraham Douglas A.
Published: July 2002

Knowledge of the background reverberation environment is a prerequisite for the design of any target detection scheme. While the problem of understanding and predicting high-frequency background seafloor reverberation level or mean energy scattered per unit area of the seabed has received considerable attention, studies of high-frequency reverberation amplitude statistics are relatively scarce. Of these studies, many have dealt with scattering from more or less homogeneous seafloors in terms of bottom type, whereas most shallow-water areas will not be homogeneous but will have patchiness in space and time which will have a strong influence on scattered amplitude statistics. In this work, a comparison is presented between 80-kHz seafloor backscatter statistics obtained at shallow-water sites around Sardinia and Sicily. The data include measurements from several distinct bottom provinces, including sites with Posidonia Oceanica sea grass and sites covered with live shellfish. Results of the analysis are cast both in terms of mean power level or backscattering coefficient as well as of the amplitude statistics. The reverberation statistics did not always exhibit a Rayleigh probability distribution function (PDF), but exhibited statistical distributions with heavier tails. Several more appropriate models of reverberation PDF were examined in order to better describe the measured amplitude distributions. The Rayleigh mixture and the K models were found to be the most robust in describing the observed data.
NMR flow imaging of aqueous polysaccharide solutions
Authors: Gibbs S. J. , Xing D. , Carpenter T. A. , Hall L. D. , Ablett S. , Evans I. D. , Frith W. , Haycock D. E.
Published: July 2002

Nuclear-magnetic-resonance (NMR) flow imaging with spatial resolution of the order of 200 μm is used to measure the velocity fields in aqueous solutions of 0.2% and 1% xanthan gum and 1% guar gum for steady flow in a 1.2 cm internal diameter cylindrical polymethylmethacrylate pipe. The velocity fields show little evidence of apparent wall slip and are differentiated to obtain relationships between shear stress and shear rate which span over four decades in shear rate for the xanthan solutions and approximately three decades for the guar solution; these data agree well with those obtained by cone-and-plate viscometry. The behavior of the xanthan solutions is well described by a power-law dependence of shear stress on shear rate, and the guar solution is better described by a Cross-type relationship. The implications of these studies for future NMR flow imaging studies of more complex systems are discussed.
ERBB and P‐glycoprotein inhibitors break resistance in relapsed neuroblastoma models through P‐glycoprotein
Authors: Rösch Lisa , Herter Sonja , Najafi Sara , Ridinger Johannes , Peterziel Heike , Cinatl Jindrich , Jones David T. W. , Michaelis Martin , Witt Olaf , Oehme Ina
Published: October 2022

Chemotherapy resistance is a persistent clinical problem in relapsed high‐risk neuroblastomas. We tested a panel of 15 drugs for sensitization of neuroblastoma cells to the conventional chemotherapeutic vincristine, identifying tariquidar, an inhibitor of the transmembrane pump P‐glycoprotein (P‐gp/ABCB1), and the ERBB family inhibitor afatinib as the top resistance breakers. Both compounds were efficient in sensitizing neuroblastoma cells to vincristine in trypan blue exclusion assays and in inducing apoptotic cell death. The evaluation of ERBB signaling revealed no functional inhibition, that is, dephosphorylation of the downstream pathways upon afatinib treatment but direct off‐target interference with P‐gp function. Depletion of ABCB1, but not ERRB4, sensitized cells to vincristine treatment. P‐gp inhibition substantially broke vincristine resistance in vitro and in vivo (zebrafish embryo xenograft). The analysis of gene expression datasets of more than 50 different neuroblastoma cell lines (primary and relapsed) and more than 160 neuroblastoma patient samples from the pediatric precision medicine platform INFORM (Individualized Therapy For Relapsed Malignancies in Childhood) confirmed a pivotal role of P‐gp specifically in neuroblastoma resistance at relapse, while the ERBB family appears to play a minor part.
Electrochemical Palladium‐Catalyzed CH Functionalization
Authors: Yang Qi‐Liang , Guo Hai‐Ming , Mei Tian‐Sheng
Published: October 2022

Palladium‐catalyzed site‐selective functionalization of inert CH bonds has emerged as a versatile and transformative synthetic approach in modern organic synthesis, enabling tremendous possibility in the application of drug design, natural products synthesis, and material sciences. Despite significant progress, until recently, the oxidative functionalization of CH bonds predominantly relied on the use of stoichiometric amounts of sacrificial chemical oxidants that lead to the generation of undesired waste, thus compromising the environmental merits deriving from the CH activation chemistry. The recently developed electrooxidative CH functionalization via catalyst control strategy using transition‐metals as redox catalysts and electricity as an environmentally benign oxidant, offers a promising alternative to minimizes waste production, thereby providing a more sustainable and efficient pathway toward the catalytic conversion of CH bonds. In this article, we focus specifically on the progressive discoveries of electrochemical CH bond functionalizations catalyzed by palladium‐based catalysts, highlighting the enormous potential of this exciting field of synthetic chemistry, capable of offering increasingly efficient and sustainable routes for organic syntheses. These pallada‐electrocatalyzed CH bond transformations are presented in terms of CC and C–heteroatom bonds formation.
Palladium‐Catalyzed CH Arylation
Authors: Zhao Yingsheng , Ju Guodong
Published: October 2022

CH activation catalyzed by transition metals is one of the more challenging and important research topics in organic chemistry, and direct arylation of the CH bond plays an important role. Recent CH activation developments include considerable progress toward CH arylation. This article summarizes many of the strategies and corresponding mechanistic investigations toward the realization of CH arylation, including directing group, transient directing, extended template strategies, and norbornene as transient mediator strategy.
Pd‐Catalyzed CH Functionalization Leading to Alkene Difunctionalization
Authors: Barve Balaji D. , Kuo Yao‐Haur , Li Wen‐Tai
Published: October 2022

Owing to their natural abundance, alkene has been widely employed in the preparation of various synthetic frameworks and for practical industrial production purposes. Pd‐catalyzed CH functionalization has emerged as one of the most important tools for constructing CC or CX bonds via the generation of different heterocycles, which include pharmaceutically important molecules. Compared with the significant research into transition metal‐catalyzed olefin difunctionalization using activated, preinstalled, and halide substrates, the application of palladium catalysis in CH bond functionalization to afford alkene difunctionalization is less explored, despite being synthetically important. In this article, we provide an overview of recent advancements in olefin difunctionalization resulting from Pd‐catalyzed CH functionalization.
Rhodium(II)‐Carboxylate‐Catalyzed Carbene Transfer Reactions: Toward CH Functionalizations
Authors: Hota Sudhir K. , Meher Prahallad , Murarka Sandip
Published: October 2022

The direct CH functionalizations have garnered immense popularity in the chemical community as they offer novel strategic approaches to introduce new functional entities into small organic molecules. One of the most promising reaction technologies for CH functionalization is the dirhodium carboxylate‐catalyzed insertion of transient metal carbenes into CH bonds. Over the years, this area has witnessed tremendous growth and dirhodium carboxylates have evolved as powerful catalysts allowing site‐ and stereoselective CH insertion reactions. This article delineates all these developments made in the last 10 years in the field of rhodium(II) carboxylate‐catalyzed intra‐ and intermolecular insertion of metal carbenes into Csp
2
H and Csp
3
H bonds with representative examples. A particular emphasis has been given to illustrate the effectiveness of dirhodium catalysts in controlling the site‐ and stereoselectivity in CH insertions of a diverse variety of substrates, including applications in the synthesis and late‐stage functionalization of biologically active compounds, pharmaceuticals, and natural products.
Ruthenium‐Catalyzed C–Heteroatom Bond Formation Through C(sp
2
)H Functionalization
Authors: Song Li‐Rui , (Ruthy) Zhang Ruisi , Lu Heng , Zhang Ao
Published: October 2022

This article describes recent advances in C–heteroatom bond formation via ruthenium‐catalyzed proximal or remote C(sp
2
)H functionalization. This ruthenium catalysis is particularly fascinating not only because of the low cost of the metal, but also because it allows for a wide range of transformations. The excellent reactivity of the ruthenium catalysts is attributed to the highly active CH ruthenated intermediate, which can perform oxidative addition or electrophilic substitution at the ortho position as well as radical addition at distal meta or para positions. Diverse strongly or weakly coordinating directing groups, such as
N
‐containing heterocycles, aldehydes, ketones, carboxylic acids, amides, sulfamides, carbamates, and phosphines, can assist the ruthenium‐catalyzed functionalization of ortho, meta, and even, para positions via CN, CO, C–halogen, CSi, CS/Se, and CB bond‐forming reactions. Typically, [RuCl
2
(
p
‐cymene)]
2
is used for C–heteroatom bond construction, but the octahedral Ru catalysts RuHCl(CO)(PPh
3
)
3
and Ru
3
(CO)
12
have been used for
ortho
CSi and
meta
CN bond formation, respectively. In addition, this article details representative applications of Ru‐catalyzed C(sp
2
)H functionalization in the preparation and late‐stage modification of important synthetic building blocks and pharmaceuticals.
Ni‐Catalyzed C(sp
2
)H Bond Functionalization: Trifluoromethylation, Thiolation, and Selenylation
Authors: Garg Nidhi , Garai Bholanath , Sundararaju Basker
Published: October 2022

This article is intended to provide a concise review of the seminal work on nickel‐catalyzed direct “sp
2
” CH bond functionalizations, with a particular focus on trifluoromethylation, thiolation, and selenylation. The current mechanistic hypotheses were described for a deeper understanding that should aid in the future design of various other efficient transformations. We anticipate that the continued research in this area should help to extend applications in late‐stage functionalization of various bioactive molecules.
Transition Metal‐Catalyzed CH Functionalizations Using a Transient Directing Group Approach
Authors: Das Animesh , Aditya Netai , Maji Biplab
Published: October 2022

Transition metal‐catalyzed CH bond functionalization reactions are among the cutting‐edge synthetic tool for step‐economical construction of complex‐molecular architectures. In this realm, the key challenge lies in harnessing the site‐selective activation of the inert CH bonds. Although covalently tethered directing groups rendered reliable results in obtaining positional selectivity, their preinstallation and removal entail multiple steps restricting their applicability. An alternative approach is developed to fill this gap where a transient ligand enables the formation of the directing group in situ and dissociates after the reaction's completion. This strategy is widely known as the transient directing group (TDG) approach. Diverse functionalization such as arylation, alkylation, amination, halogenation, etc., could be achieved using TDG as a powerful means. Moreover, asymmetric functionalization has also been realized utilizing this technique. However, this strategy remained only applicable to aldehydes, ketones, amines, and phenol substrates.
α‐Functionalization of Aliphatic Carboxylic Acid Equivalents via Direct CH Oxidation
Authors: Rahaman Ajijur , Gupta Aniket , Kumar Jogendra , Bhadra Sukalyan
Published: October 2022

The α‐functionalization of aliphatic carboxylic acids and equivalents thereof including amides and esters is among the highly important synthetic transformations of organic synthesis. Traditional approaches are largely dominated by enolate chemistry demanding (over) stoichiometric quantity of a strong base with respect to the carbonyl precursor to obtain a nucleophilic enolate equivalent and an electrophilic coupling partner to form a new CC and/or C–heteroatom bond. Modern progresses demonstrate that the α‐CH bond of carboxylic acids, amides, esters, and other synthons can be also triggered in the presence or absence of a transition metal catalyst under oxidative conditions. The external oxidant is known to play a crucial role in the α‐CH bond oxidation process. The current article describes the oxidative α‐CH bond functionalizations of carboxylic acids/equivalents by nucleophiles using transition metal catalysts or organic mediators. Consequently, (i) α‐CH transformations with the participation of an enolate equivalent from the carboxylate counterpart; (ii) Lewis acid‐catalyzed α‐functionalization approaches; (iii) α‐functionalization with concomitant decarboxylation, etc. are beyond the scope of this article.
Annulative π‐Extension (APEX) of Indole to Carbazole Through CH Activation
Authors: Das Pritha , Dinda Enakshi , Jana Ranjan
Published: October 2022

The annulative π‐extension (APEX) reaction through CH bond activation has emerged as a powerful technique for the rapid synthesis of fused aromatic systems from simple aromatic compounds in a single operation. This cutting‐edge technology can transform the conventional, tedious multistep protocols into a user‐friendly one‐pot procedure for the synthesis of functionalized materials useful in high‐tech materials for material science applications, bioimaging for biomedical research, and agro‐ and pharmaceutical industries. Furthermore, CH activation strategy does not require prefunctionalization steps, which allows for the late‐stage modification of the functional molecule to achieve requisite molecular properties. Owing to their unique photophysical properties, carbazoles are widely used in photovoltaic cells, biomedical imaging, fluorescent polymer, organic light‐emitting diodes (OLEDs), liquid crystals, etc. They are also ubiquitously found in many natural products, agrochemicals, and privileged medicinal scaffolds. Hence, π‐extension of indole to carbazole via CH functionalization has proven as a straightforward and robust technique in the past decades. The fundamental mechanistic aspect behind this cascade π‐extension strategy is the facile electrophilic metalation at the C‐3 position of the indole moiety, 1,2‐ migration, and electrocyclization. Furthermore, acid‐catalyzed electrocyclization under metal‐free conditions has also been explored.
Iron‐Catalyzed Heterocycle Synthesis by CH Functionalization
Authors: Sekar Govindasamy , Sundaravelu Nallappan , Nair Vysakh V.
Published: October 2022

The synthetic perspective of CH activation was first revealed using ruthenium catalysis and is now extensively studied by the use of several other transition metals. Iron‐catalyzed CH functionalization reactions have gained paramount attention in organic synthesis due to their low cost, low toxicity, and good functional group tolerance. Recently, iron‐catalyzed CH bond functionalization has achieved significant progress in the synthesis of heterocycles through CH activation followed by inter/intramolecular cyclization reactions on treatment with various electrophiles. This article mainly focuses on iron‐catalyzed C–heteroatom bond (CN, CO, CS, etc.) formation through sp
2
and sp
3
CH functionalization to access biologically valuable heterocycles and their mechanistic insights.
Cp*Co(III)‐Catalyzed CH Functionalization Mediated by Oxidizing Directing Groups toward the Synthesis of Heterocycles
Authors: Aher Yogesh N. , Mondal Bhaskar , Pawar Amit B.
Published: October 2022

The utilization of oxidizing directing group for CH activation/functionalization is a unique strategy for the synthesis of a versatile range of heterocycles under redox‐neutral conditions. In this approach, the directing group plays a dual role; controls the product selectivity through its chelation property, and a part of the directing group functions as an internal oxidant. The oxidizing property of the directing groups is due to the oxidizing ability of the NO, NN, NS, NCl bonds. Overall, this synthetic strategy precludes the need for external oxidants, thereby making the process environmentally benign. This article describes significant developments in this area focusing on the Cp*Co(III)‐catalyzed CH functionalization using the oxidizing directing group strategy for the synthesis of heterocycles. The emphasis has been given to the scope and generality of the reactions along with their mechanistic understanding.
Chromium‐Catalyzed CH Functionalization
Authors: Shang Rui
Published: October 2022

Chromium salts have long been used in organic synthesis for oxidation/reduction, polymerization, carbon–carbon bond formation in the renowned Nozaki–Hiyama–Kishi reactions, and in recent decades as catalysts for carbon–carbon cross‐couplings. However, the potential of this abundant first‐row transition metal as a tool in the field of catalytic CH functionalization has been unknown until several years ago. This article summarizes literature examples of chromium‐catalyzed CH bond functionalization with a focus on examples involving organochromium species generated after CH bond cleavage. The article starts with describing literature examples of chromium metallacycles (chromacycles), which are related to intermediates in directed CH activation, and stoichiometric CH activation of chromium(III) complex. Examples of catalytic CH functionalization in this article were categorized by the coupling partners used, including organometallic nucleophiles, electrophiles, alkenes, and alkynes. Chromium‐catalyzed CH oxidation reactions were also briefly discussed. Current limitations and future opportunities in this emerging research field were lastly discussed with a hope to stimulate future research interest to explore catalytic utility of this abundant metal in the field of CH activation.