bluuebunny/crossref_metadata_2025 huggingface dataset:
REFORMING BANK CAPITAL REGULATION: USING SUBORDINATED DEBT TO ENHANCE MARKET AND SUPERVISORY DISCIPLINE
Authors: Evanoff Douglas D. , Wall Larry D.
Published: July 2002

In 1988 the Basel Capital Accord introduced minimum risk‐weighted capital requirements for internationally active banks. In recent years there has been a growing realization that there are significant problems with the capital guidelines. As financial firms have become more sophisticated and complex they have effectively arbitraged the requirements and have become so good at it that the regulations have essentially ceased being a safety and soundness issue for supervisors and have become more of a compliance issue. Indeed, the Basel Committee is now evaluating reforms to the capital accord and is considering various means to improve the risk‐capital relationship and to increase the role of market discipline. The authors argue that many of the problems that currently exist can be addressed, and some additional benefits not previously possible under the current capital guidelines can be realized, by increasing the role of subordinated debt in the bank capital structure. The authors discuss the potential benefits and offer a capital reform proposal that would improve both market and supervisory oversight. This should lead to more prudent risk management behavior by the larger, more complex banking organizations, resulting in a safer industry with less potential for systemic problems.
OFFSETTING BEHAVIOR EFFECTS OF THE CORPORATE AVERAGE FUEL ECONOMY STANDARDS
Authors: Yun John M.
Published: July 2002

Research has concluded that regulatory attempts to improve fuel economy, such as the Corporate Average Fuel Economy (CAFE) Standards, lower the average weight of an automobile. Ceteris paribus, this reduction in weight is detrimental to the overall level of vehicle safety. However, this study attempts to explicitly measure possible behavioral responses on the part of drivers that could offset some of the loss in safety. The results indicate that CAFE, although increasing the vulnerability rate by approximately 20%, has reduced the accident rate by 26%. The net effect on the fatality rate is a decrease of approximately 6%.
ASYMMETRY IN THE EFFECTS OF MONETARY AND GOVERNMENT SPENDING SHOCKS: CONTRASTING EVIDENCE AND IMPLICATIONS
Authors: Kandil Magda
Published: July 2002

Using quarterly data for the United States, demand contraction exceeds expansion in the face of monetary and government spending shocks. Demand contraction in the face of government spending shocks, is absorbed in nominal wage and price deflation. The variability of government spending shocks decreases average wage and price inflation. In contrast, the upward flexibility of price appears in sharp contrast to its downward rigidity in the face of monetary shocks. Furthermore, output contraction is notably larger relative to expansion in the face of monetary shocks. Monetary variability accelerates average price inflation and decreases average output and real wage growth.
Sphingosine 1‐phosphate released from platelets during clotting accounts for the potent endothelial cell chemotactic activity of blood serum and provides a novel link between hemostasis and angiogenesis
Authors: English Denis , Welch Zachary , Kovala A. Thomas , Harvey Kevin , Volpert Olga V. , Brindley David N. , Garcia Joe G. N.
Published: July 2002

ABSTRACT Recent studies have identified factors responsible for angiogenesis within developing tumors, but mediators of vessel formation at sites of trauma, injury, and wound healing are not clearly established. Here we show that sphingosine 1‐phosphate (S1P) released by platelets during blood clotting is a potent, specific, and selective endothelial cell chemoattractant that accounts for most of the strong endothelial cell chemotactic activity of blood serum, an activity that is markedly diminished in plasma. Preincubation of endothelial cells with pertussis toxin inhibited this effect of S1P, demonstrating the involvement of a Gαi‐coupled receptor. After S1P‐induced migration, endothelial cells proliferated avidly and differentiated forming multicellular structures suggestive of early blood vessel formation. S1P was strikingly effective in enhancing the ability of fibroblast growth factor to induce angiogenesis in the avascular mouse cornea. Our results show that blood coagulation initiates endothelial cell angiogenic responses through the release of S1P, a potent endothelial cell chemoattractant that exerts its effects by activating a receptor‐dependent process.—English, D., Welch, Z., Kovala, A. T., Harvey, K., Volpert, O. V., Brindley, D. N., Garcia, J. G. N. Sphingosine 1‐phosphate released from platelets during clotting accounts for the potent endothelial cell chemotactic activity of blood serum and provides a novel link between hemostasis and angiogenesis. FASEB J. 14, 2255–2265 (2000)
Lysosomal sphingomyelinase is not solicited for apoptosis signaling
Authors: Bezombes Christine , Ségui Bruno , Cuvillier Olivier , Bruno Alain P. , Uro‐Coste Emmanuelle , Gouazé Valérie , Andrieu‐Abadie Nathalie , Carpentier Stéphane , Laurent Guy , Salvayre Robert , Jaffrézou Jean‐Pierre , Levade Thierry
Published: July 2002

Stress‐induced activation of an acidic sphingomyelinase leading to generation of ceramide, an important lipid mediator, has been associated with apoptosis; however, the implication of this hydrolase has been questioned. The present study aimed at re‐evaluating the role of this lysosomal enzyme in apoptosis initiated by different apoptotic inducers. The sensitivity of a series of acid sphingomyelinase‐deficient cell lines derived from Niemann‐Pick disease patients to stress‐induced apoptosis was investigated. We have now shown that stress stimuli, such as anthracyclines, ionizing radiation, and Fas ligation trigger similar apoptotic hallmarks in normal and acid sphingomyelinase‐deficient cell lines. Retrovirus‐mediated gene correction of enzyme deficiency in Niemann‐Pick cells does not modify response to apoptosis. Ceramide production is comparable in normal and Niemann‐Pick cells, and increased activity of neutral sphingomyelinase is observed. Thus, our findings cast serious doubts that lysosomal sphingomyelinase activation is responsible for stress‐induced apoptosis of cultured cells.
Consciousness and the structure of neuronal representations
Authors:   The American Association for Research into Nervous and Mental Diseases, Singer W.
Published: July 2002

The hypothesis is defended that brains expressing phenomenal awareness are capable of generating metarepresentations of their cognitive processes, these metarepresentations resulting from an iteration of self–similar cortical operations. Search for the neuronal substrate of awareness therefore converges with the search for the nature of neuronal representations. It is proposed that evolved brains use two complementary representational strategies. One consists of the generation of neurons responding selectively to a particular constellation of features and is based on selective recombination of inputs in hierarchically structured feedforward architectures. The other relies on the dynamic association of feature–specific cells into functionally coherent cell assemblies that, as a whole, represent the constellation of features defining a particular perceptual object. Arguments are presented that favour the notion that the metarepresentations supporting awareness are established in accordance with the second strategy. Experimental data are reviewed that are compatible with the hypothesis that evolved brains use assembly codes for the representation of contents and that these assemblies become organized through transient synchronization of the discharges of associated neurons. It is argued that central states favouring the formation of assembly–based representations are similar to those favouring awareness.
The neuronal basis for consciousness
Authors:   The American Association for Research into Nervous and Mental Diseases, Llinás R. , Ribary U. , Contreras D. , Pedroarena C.
Published: July 2002

Attempting to understand how the brain, as a whole, might be organized seems, for the first time, to be a serious topic of inquiry. One aspect of its neuronal organization that seems particularly central to global function is the rich thalamocortical interconnectivity, and most particularly the reciprocal nature of the thalamocortical neuronal loop function. Moreover, the interaction between the specific and non-specific thalamic loops suggests that rather than a gate into the brain, the thalamus represents a hub from which any site in the cortex can communicate with any other such site or sites. The goal of this paper is to explore the basic assumption that large–scale, temporal coincidence of specific and non–specific thalamic activity generates the functional states that characterize human cognition.
Episodic–like memory in animals: psychological criteria, neural mechanisms and the value of episodic–like tasks to investigate animal models of neurodegenerative disease
Authors: Morris Richard G. M.
Published: July 2002

The question of whether any non–human species displays episodic memory is controversial. Associative accounts of animal learning recognize that behaviour can change in response to single events but this does not imply that animals need or are later able to recall representations of unique events at a different time and place. The lack of language is also relevant, being the usual medium for communicating about the world, but whether it is critical for the capacity to represent and recall events is a separate matter. One reason for suspecting that certain animals possess an episodic–like memory system is that a variety of learning and memory tasks have been developed that, even though they do not meet the strict criteria required for episodic memory, have an ‘episodic–like’ character. These include certain one–trial learning tasks, scene–specific discrimination learning, multiple reversal learning, delayed matching and non–matching tasks and, most recently, tasks demanding recollection of ‘what, where and when’ an event happened. Another reason is that the neuronal architecture of brain areas thought to be involved in episodic memory (including the hippocampal formation) are substantially similar in mammals and, arguably, all vertebrates. Third, our developing understanding of activity–dependent synaptic plasticity (which is a candidate neuronal mechanism for encoding memory traces) suggests that its expression reflects certain physiological characteristics that are ideal components of a neuronal episodic memory system. These include the apparently digital character of synaptic change at individual terminals and the variable persistence of potentiation accounted for by the synaptic tag hypothesis. A further value of studying episodic–like memory in animals is the opportunity it affords to model certain kinds of neurodegenerative disease that, in humans, affect episodic memory. An example is recent work on a transgenic mouse that over–expresses a mutation of human amyloid precursor protein (APP) that occurs in familial Alzheimer's disease, under the control of platelet derived (PD) growth factor promoter (the PDAPP mouse). A striking age– and amyloid plaque–related deficit is seen using a task in which the mice have to keep changing their memory representation of the world rather than learn a single fact.
Dissociations in cognitive memory: the syndrome of developmental amnesia
Authors: Vargha-Khadem Faraneh , Gadian David G. , Mishkin Mortimer
Published: July 2002

The dearth of studies on amnesia in children has led to the assumption that when damage to the medial temporal lobe system occurs early in life, the compensatory capacity of the immature brain rescues memory functions. An alternative view is that such damage so interferes with the development of learning and memory that it results not in selective cognitive impairments but in general mental retardation. Data will be presented to counter both of these arguments. Results obtained from a series of 11 amnesic patients with a history of hypoxic ischaemic damage sustained perinatally or during childhood indicate that regardless of age at onset of hippocampal pathology, there is a pronounced dissociation between episodic memory, which is severely impaired, and semantic memory, which is relatively preserved. A second dissociation is characterized by markedly impaired recall and relatively spared recognition leading to a distinction between recollection–based versus familiarity–based judgements. These findings are discussed in terms of the locus and extent of neuropathology associated with hypoxic ischaemic damage, the neural basis of ‘remembering’ versus ‘knowing’, and a hierarchical model of cognitive memory.
Antifreeze protein from shorthorn sculpin: Identification of the ice‐binding surface
Authors: Baardsnes Jason , Jelokhani‐Niaraki Masood , Kondejewski Leslie H. , Kuiper Michael J. , Kay Cyril M. , Hodges Robert S. , Davies Peter L.
Published: July 2002

Shorthorn sculpins, Myoxocephalus scorpius, are protected from freezing in icy seawater by alanine‐rich, α‐helical antifreeze proteins (AFPs). The major serum isoform (SS‐8) has been reisolated and analyzed to establish its correct sequence. Over most of its length, this 42 amino acid protein is predicted to be an amphipathic α‐helix with one face entirely composed of Ala residues. The other side of the helix, which is more heterogeneous and hydrophilic, contains several Lys. Computer simulations had suggested previously that these Lys residues were involved in binding of the peptide to the {11–20} plane of ice in the <−1102> direction. To test this hypothesis, a series of SS‐8 variants were generated with single Ala to Lys substitutions at various points around the helix. All of the peptides retained significant α‐helicity and remained as monomers in solution. Substitutions on the hydrophilic helix face at position 16, 19, or 22 had no obvious effect, but those on the adjacent Ala‐rich surface at positions 17, 21, and 25 abolished antifreeze activity. These results, with support from our own modeling and docking studies, show that the helix interacts with the ice surface via the conserved alanine face, and lend support to the emerging idea that the interaction of fish AFPs with ice involves appreciable hydrophobic interactions. Furthermore, our modeling suggests a new N terminus cap structure, which helps to stabilize the helix, whereas the role of the lysines on the hydrophilic face may be to enhance solubility of the protein.
Deterministic calculations of photon spectra for clinical accelerator targets
Authors: Williams M. L. , Sajo E.
Published: July 2002

A method is proposed to compute photon energy spectra produced in clinical electron accelerator targets, based on the deterministic solution of the Boltzmann equation for coupled electron–photon transport in one‐dimensional (1‐D) slab geometry. It is shown that the deterministic method gives similar results as Monte Carlo calculations over the angular range of interest for therapy applications. Relative energy spectra computed by deterministic and 3‐D Monte Carlo methods, respectively, are compared for several realistic target materials and different electron beams, and are found to give similar photon energy distributions and mean energies. The deterministic calculations typically require 1–2 mins of execution time on a Sun Workstation, compared to 2–36 h for the Monte Carlo runs.
A new approach to electron‐beam reference dosimetry
Authors: Rogers D. W. O.
Published: July 2002

A new approach is proposed for electron‐beam dosimetry under reference conditions and data necessary to use this approach are presented. The approach has the following features: it uses ion chambers and starts from an absorbed‐dose calibration factor for to be consistent with the present proposal for the new AAPM photon‐beam protocol; it uses to specify the beam quality and the reference depth, (all quantities in cm), recommended by Burns et al. [Med. Phys. 23, 383–388 (1996)]; it has a formalism which is parallel to the formalism for photon‐beam dosimetry; it fully accounts for the impact on stopping‐power ratios of realistic electron beams; it allows an easy transition to using primary standards for absorbed dose to water in electron beams when these are available. The equation for dose to water under reference conditions is: The term is not needed with plane‐parallel chambers but corrects for gradient effects with cylindrical chambers and is measured in the user's beam. The parameter is associated with converting the absorbed‐dose calibration factor into one for an electron beam of quality and contains most of the chamber to chamber variation. Calculated values of are presented as well as Monte Carlo calculated values for plane‐parallel chambers in a water phantom irradiated by a beam since these are needed to calculate The factor is a function of and converts the absorbed‐dose calibration factor to that for the electron‐beam quality of interest. Two analytical expressions are presented which are close to universal expressions for all cylindrical Farmer‐like chambers and for well‐guarded plane‐parallel chambers respectively. Calculated values are presented graphically for electron beams with energies between 5 and 50 MeV.
Self‐normalizing method to measure the detective quantum efficiency of a wide range of x‐ray detectors
Authors: Stierstorfer Karl , Spahn Martin
Published: July 2002

The detective quantum efficiency (DQE) is widely accepted as the most relevant parameter to characterize the image quality of medical x‐ray systems. In this article we describe a solid method to measure the DQE. The strength of the method lies in the fact that it is self‐normalizing so measurements at very low spatial frequencies are not needed. Furthermore, it works on any system with a response function which is linear in the small‐signal approximation. We decompose the DQE into several easily accessible quantities and discuss in detail how they can be measured. At the end we lead the interested reader through an example. Noise equivalent quanta and normalized contrast values are tabulated for standard radiation qualities.
A Monte Carlo dosimetry‐based evaluation of the reaction near threshold for accelerator boron neutron capture therapy
Authors: Lee C. L. , Zhou X.‐L. , Kudchadker R. J. , Harmon F. , Harker Y. D.
Published: July 2002

Advanced methods of boron neutron capture therapy (BNCT) use an epithermal neutron beam in conjunction with tumor‐targeting boron compounds for irradiation of glioblastomas and metastatic melanomas. A common neutron‐producing reaction considered for accelerator‐based BNCT is whose cross section increases very rapidly within several tens of keV of the reaction threshold at 1.88 MeV. Operation in the proton energy region near threshold will have an appreciable thick target neutron yield, but the neutrons produced will have relatively low energies that require little moderation to reach the epithermal range desirable for BNCT. Because of its relatively low projected accelerator cost and the portability of the neutron source/target assembly, BNCT based on the near‐threshold technique is considered an attractive candidate for widespread hospital use. A systematic Monte Carlo N‐Particle (MCNP) investigation of the dosimetric properties of near‐threshold neutron beams has been performed. Results of these studies indicate that accelerator proton energies between 1.93 and 1.99 MeV, using 5 cm of moderator followed by thin and Pb shields, can provide therapeutically useful beams with treatment times less than one hour and accelerator currents less than 5 mA.
Partition functions and symmetric polynomials
Authors: Schmidt Heinz-Jürgen , Schnack Jürgen
Published: July 2002

We find a close correspondence between the partition functions of ideal quantum gases and certain symmetric polynomials. From this correspondence, it can be shown that a number of thermodynamic identities that have recently been considered in the literature are essentially of combinatorial origin and have been known for a long time as theorems on symmetric polynomials. For example, a recurrence relation for partition functions in the textbook by P. Landsberg is Newton’s identity in disguised form. Conversely, a theorem on symmetric polynomials translates into a new and unexpected relation between fermion and boson partition functions, which can be used to express the former by means of the latter and vice versa.
On the time domain version of the optical theorem
Authors: Karlsson Anders
Published: July 2002

The time domain version of the optical theorem is discussed. The theorem relates the sum of the scattered and absorbed energies, for a plane pulse that is scattered from a bounded obstacle, to the far field amplitude in the forward direction. Several fundamental results concerning the scattered and absorbed energies that follow from the theorem and from causality are discussed. Some results are verified by numerical calculations.
The lower limit of pitch as determined by rate discrimination
Authors: Krumbholz Katrin , Patterson Roy D. , Pressnitzer Daniel
Published: July 2002

This paper is concerned with the lower limit of pitch for complex, harmonic sounds, like the notes produced by low-pitched musical instruments. The lower limit of pitch is investigated by measuring rate discrimination thresholds for harmonic tones filtered into 1.2-kHz-wide bands with a lower cutoff frequency, Fc, ranging from 0.2 to 6.4 kHz. When Fc is below 1 kHz and the harmonics are in cosine phase, rate discrimination threshold exhibits a rapid, tenfold decrease as the repetition rate is increased from 16 to 64 Hz, and over this range, the perceptual quality of the stimuli changes from flutter to pitch. When Fc is increased above 1 kHz, the slope of the transition from high to low thresholds becomes shallower and occurs at progressively higher rates. A quantitative comparison of the cosine-phase thresholds with subjective estimates of the existence region of pitch from the literature shows that the transition in rate discrimination occurs at approximately the same rate as the lower limit of pitch. The rate discrimination experiment was then repeated with alternating-phase harmonic tones whose envelopes repeat at twice the repetition rate of the waveform. In this case, when Fc is below 1 kHz, the transition in rate discrimination is shifted downward by almost an octave relative to the transition in the cosine-phase thresholds. The results support the hypothesis that in the low-frequency region, the pitch limit is determined by a temporal mechanism, which analyzes time intervals between peaks in the neural activity pattern. It seems that temporal processing of pitch is limited to time intervals less than 33 ms, corresponding to a pitch limit of about 30 Hz.
Characterizing frequency selectivity for envelope fluctuations
Authors: Ewert Stephan D. , Dau Torsten
Published: July 2002

Three experimental paradigms were used to specify the auditory system’s frequency selectivity for amplitude modulation (AM). In the first experiment, masked-threshold patterns were obtained for signal-modulation frequencies of 4, 16, 64, and 256 Hz in the presence of a half-octave-wide modulation masker, both applied to the same noise carrier with a bandwidth ranging from 1 to 4 kHz. In the second experiment, psychophysical tuning curves (PTCs) were obtained for signal-modulation frequencies of 16 and 64 Hz imposed on a noise carrier as in the first experiment. In the third experiment, masked thresholds for signal-modulation frequencies of 8, 16, 32, and 64 Hz were obtained according to the “classical” band-widening paradigm, where the bandwidth of the modulation masker ranged from 18 to 4 octaves, geometrically centered on the signal frequency. The first two experiments allowed a direct derivation of the shape of the modulation filters while the latter paradigm only provided an indirect estimate of the filter bandwidth. Thresholds from the experiments were predicted on the basis of an envelope power-spectrum model (EPSM) which integrates the envelope power of the modulation masker in the passband of a modulation filter tuned to the signal-modulation frequency. The Q-value of second-order bandpass modulation filters was fitted to the masking patterns from the first experiment using a least-squares algorithm. Q-values of about 1 for frequencies up to 64 Hz suggest an even weaker selectivity for modulation than assumed in earlier studies. The same model also accounted reasonably well for the shape of the temporal modulation transfer function (TMTF) obtained for carrier bandwidths in the range from 1 to 6000 Hz. Peripheral filtering and effects of peripheral compression were also investigated using a multi-channel version of the model. Waveform compression did not influence the simulated results. Peripheral bandpass filtering only influenced thresholds for high modulation frequencies when signal information was strongly attenuated by the transfer function of the peripheral filters.
Whistles of boto, Inia geoffrensis, and tucuxi, Sotalia fluviatilis
Authors: Ding Wang , Würsig Bernd , Leatherwood Stephen
Published: July 2002

Whistles were recorded and analyzed from free-ranging single or mixed species groups of boto and tucuxi in the Peruvian Amazon, with sonograms presented. Analysis revealed whistles recorded falling into two discrete groups: a low-frequency group with maximum frequency below 5 kHz, and a high-frequency group with maximum frequencies above 8 kHz and usually above 10 kHz. Whistles in the two groups differed significantly in all five measured variables (beginning frequency, end frequency, minimum frequency, maximum frequency, and duration). Comparisons with published details of whistles by other platanistoid river dolphins and by oceanic dolphins suggest that the low-frequency whistles were produced by boto, the high-frequency whistles by tucuxi. Tape recordings obtained on three occasions when only one species was present tentatively support this conclusion, but it is emphasized that this is based on few data.
Relations between intelligibility of narrow-band speech and auditory functions, both in the 1-kHz frequency region
Authors: Noordhoek Ingrid M. , Houtgast Tammo , Festen Joost M.
Published: July 2002

Relations between perception of suprathreshold speech and auditory functions were examined in 24 hearing-impaired listeners and 12 normal-hearing listeners. The speech intelligibility index (SII) was used to account for audibility. The auditory functions included detection efficiency, temporal and spectral resolution, temporal and spectral integration, and discrimination of intensity, frequency, rhythm, and spectro-temporal shape. All auditory functions were measured at 1 kHz. Speech intelligibility was assessed with the speech-reception threshold (SRT) in quiet and in noise, and with the speech-reception bandwidth threshold (SRBT), previously developed for investigating speech perception in a limited frequency region around 1 kHz. The results showed that the elevated SRT in quiet could be explained on the basis of audibility. Audibility could only partly account for the elevated SRT values in noise and the deviant SRBT values, suggesting that suprathreshold deficits affected intelligibility in these conditions. SII predictions for the SRBT improved significantly by including the individually measured upward spread of masking in the SII model. Reduced spectral resolution, reduced temporal resolution, and reduced frequency discrimination appeared to be related to speech perception deficits. Loss of peripheral compression appeared to have the smallest effect on the intelligibility of suprathreshold speech.
Analysis of different boundary condition models for study of wave scattering from fiber–matrix interphases
Authors: Huang W. , Rokhlin S. I. , Wang Y. J.
Published: July 2002

In this paper different approximate boundary conditions (BC) describing a thin fiber–matrix interphase are used to study ultrasonic wave scattering from a multiphase fiber embedded in a solid matrix. To facilitate the analysis of scattering from a multilayered fiber, a matrix differential equation is derived for elastic fields in a cylindrical medium with radially-dependent properties. From this equation the transfer matrix for each intermediate layer between the fiber core and matrix, relating the stress and displacement fields on the inner and outer boundaries of the layer, is obtained. To describe the effect of the interphase the first- and second-order asymptotic and the spring boundary conditions are derived using an asymptotic expansion of the transfer matrix for a thin fiber–matrix interphase. Analysis performed for different models of spring boundary conditions shows the advantage of preserving the interphase gap connected by springs versus the spring BC defined on an infinitely thin interface, after eliminating the interphase layer and filling the remaining gap by matrix or fiber material. In the last two cases the geometry of the system changes due to change of the scattering surface radius, leading to error in the scattering amplitude. Numerical examples are given for scattering cross sections of longitudinal and shear waves from a multiphase SiC fiber in titanium. It is shown that the spring BC can be used to represent a thin interphase layer with elastic moduli smaller than those of the fiber.
A boundary integral method for acoustic radiation and scattering
Authors: Hwang W. S.
Published: July 2002

In this article, a computational method is proposed for computing the Helmholtz integral equation for acoustic radiation and scattering problems with a three-dimensional body shape. Unlike the previous boundary element method, the integration of acoustic properties is based on the global body surface instead of local elements. The approximation function of body geometry and the weighting function of numerical integration are independently chosen. When the singular kernels of Helmholtz equation are regularized as bounded, discontinuous functions, the order of integration polynomials for acoustic properties can be arbitrarily chosen, therefore, the accuracy and efficiency of computation can be increased.
Multiple-scattering theory for mean responses in a plate with sprung masses
Authors: Weaver Richard L.
Published: July 2002

Diagrammatic multiple-scattering theory is applied to the case of an infinite homogeneous plate in flexure attached to a random distribution of sprung masses. This system is a prototypical example of a wave-bearing master structure with a locally reacting “fuzzy” substructure. Results for mean fields are obtained from the first-order smoothing approximation, the Foldy average t-matrix approximation, and Soven’s coherent-potential approximation. The study of mean-square responses is reserved to a later paper. It is found that the attenuation as calculated by Pierce et al. [J. Vib. Acoustics 117, 339–348 (1995)] differs from that of the multiple-scattering theory by a fractional amount which is small if the individual sprung masses are weak.
A simplified model for linear and nonlinear processes in thermoacoustic prime movers. Part I. Model and linear theory
Authors: Watanabe M. , Prosperetti A. , Yuan H.
Published: July 2002

A simplified quasi-one-dimensional model of thermoacoustic devices is formulated by averaging the conservation equations over the cross section. Heat transfer and drag effects are introduced by means of suitable coefficients. While the primary motivation for this work is the development of a model approximately valid in the nonlinear regime, the focus of this paper is the proper formulation of the transfer coefficients and the analysis of the linear problem. The accuracy of the model is demonstrated by comparison with existing more precise theories and data. Examples of devices with variable cross section demonstrate the flexibility of the approach.
Vocal tract length and formant frequency dispersion correlate with body size in rhesus macaques
Authors: Fitch W. Tecumseh
Published: July 2002

Body weight, length, and vocal tract length were measured for 23 rhesus macaques (Macaca mulatta) of various sizes using radiographs and computer graphic techniques. Linear predictive coding analysis of tape-recorded threat vocalizations was used to determine vocal tract resonance frequencies (“formants”) for the same animals. A new acoustic variable is proposed, “formant dispersion,” which should theoretically depend upon vocal tract length. Formant dispersion is the averaged difference between successive formant frequencies, and was found to be closely tied to both vocal tract length and body size. Despite the common claim that voice fundamental frequency (F0)provides an acoustic indication of body size, repeated investigations have failed to support such a relationship in many vertebrate species including humans. Formant dispersion, unlike voice pitch, is proposed to be a reliable predictor of body size in macaques, and probably many other species.
Effect on ultrasonic signals of viscous pore fluids in unconsolidated sand
Authors: Seifert Patricia K. , Kaelin Bruno , Johnson Lane R.
Published: July 2002

Ultrasonic attenuation measurements in unconsolidated sand with pore fluids ranging in viscosity between 0.001 and 1 Pa⋅s were compared with the predictions of fluid flow and scattering theories. Laboratory experiments were performed for P waves propagating through sand samples saturated with water, castor oil and two different silicone oils. The attenuation shows a frequency squared dependence for all measurements, regardless of viscosity, in the range between 100 and 1000 kHz. The results show that for unconsolidated sand, fluid flow models which imply significant effects of the viscous pore fluids on ultrasonic waves cannot explain the laboratory measurements. The main attenuation effects observed in the laboratory can be simulated with a three-dimensional generalized dynamic composite elastic medium model, which includes scattering from the pores and grains as well as intrinsic attenuation caused by the viscous pore fluids. For the studied sand samples, scattering is the main attenuation mechanism for ultrasonic P waves.
Design and construction of a solar-powdered, thermoacoustically driven, thermoacoustic refrigerator
Authors: Adeff Jay A. , Hofler Thomas J.
Published: July 2002

A thermoacoustically driven thermoacoustic refrigerator powered by solar thermal energy has been successfully built and tested. A 0.457 m diameter Fresnel lens focuses sunlight onto the hot end of a 0.0254 m diameter reticulated vitreous carbon prime mover stack, heating it to 475 °C, thereby eliminating the need for the most troublesome component in a heat driven prime mover, the hot heat exchanger. The high intensity sound waves produced by the prime mover drive a thermoacoustic refrigerator to produce 2.5 watts of cooling power at a cold temperature of 5 °C and a temperature span of 18 °C.
The effect of aging on horizontal plane sound localization
Authors: Abel Sharon M. , Giguère Christian , Consoli Angela , Papsin Blake C.
Published: July 2002

An experiment was conducted to determine the effect of aging on sound localization. Seven groups of 16 subjects, aged 10–81 years, were tested. Sound localization was assessed using six different arrays of four or eight loudspeakers that surrounded the subject in the horizontal plane, at a distance of 1 m. For two 4-speaker arrays, one loudspeaker was positioned in each spatial quadrant, on either side of the midline or the interaural axis, respectively. For four 8-speaker arrays, two loudspeakers were positioned in each quadrant, one close to the midline and the second separated from the first by 15°, 30°, 45°, or 60°. Three different 300-ms stimuli were localized: two one-third-octave noise bands, centered at 0.5 and 4 kHz, and broadband noise. The stimulus level (75 dB SPL) was well above hearing threshold for all subjects tested. Over the age range studied, percent-correct sound-source identification judgments decreased by 12%–15%. Performance decrements were apparent as early as the third decade of life. Broadband noise was easiest to localize (both binaural and spectral cues were available), and the 0.5-kHz noise band, the most difficult to localize (primarily interaural temporal difference cue available). Accuracy was relatively higher in front of than behind the head, and errors were largely front/back mirror image reversals. A left-sided superiority was evident until the fifth decade of life. The results support the conclusions that the processing of spectral information becomes progressively less efficient with aging, and is generally worse for sources on the right side of space.
Stress and birefringence measurements during the uniaxial elongation of polystyrene melts
Authors: Venerus D. C. , Zhu S.-H. , Öttinger H. C.
Published: July 2002

A rheometer for generating uniaxial elongations in molten polymers has been modified to allow for the simultaneous measurement of stress and flow-induced birefringence. Tensile stress σ and birefringence Δn′ data in flows at constant strain rates up to 1 s−1 were collected on a polydisperse polystyrene melt at temperatures of 160 and 170 °C. From these data, the stress-optic rule was followed for stresses below roughly 1 MPa. For stresses less than 1 MPa, the stress-optic coefficient |C|=|Δn′|/σ was found to have a value of 4.8×10−9 Pa−1, which was independent of strain, strain rate, and temperature. At stress levels higher than 1 MPa, |C| decreased indicating a failure of the stress-optic rule. A criteria for failure of the stress-optic rule was formulated using simple arguments from network models and characteristic times suggested by the tube model. This criteria, which is based on the hypothesis that failure of the stress-optic rule is the result of significant chain stretching, was found to be consistent with the data reported in this study and with data from previous studies on polystyrene melts.
Targeted Adjusting Molecular Arrangement in Organic Solar Cells via a Universal Solid Additive
Authors: Zhang Difei , Li Yuanfeng , Li Meijing , Zhong Wenkai , Heumüller Thomas , Li Ning , Ying Lei , Brabec Christoph J. , Huang Fei
Published: July 2022

The incorporation of solid additive has been considered as an effective strategy for developing organic photovoltaics with multi‐components, which is independent of dynamics, playing unique roles in morphology adjustment. However, their complex working mechanisms involving specific chemical structures are selective to material systems, hence limiting their university and flexibility in application. Herein, an inert small‐molecular compound naphtho[1,2‐c:5,6‐c′]bis[1,2,5]thiadiazole (NT) is introduced into the bulk‐heterojunction blend as the solid additive, which can function with various material systems and solvents, depending on its simple π‐conjugated structure and S⋯N interaction for adjusting molecular alignment. It is interesting to note that the introduced NT can not only improve device performance, but also simplify complicated pre‐ or post‐processing methods, reduce impact from batch‐to‐batch differences, construct sufficient energy transfer channel as well as improve device stability. The resulting devices based on PTzBI‐dF:Y6‐BO system show an impressive power conversion efficiency of 17.4% with obviously enhanced T80 lifetime of >1200 h. These findings provide useful guidelines for exploring potential universal solid additives benefitting toward commercial application.
A Versatile Approach for Preparing Shape‐Morphing Bilayer Films by Simply Adhering Two SEBS/Paraffin Films with Different Deformability and Melting Temperatures
Authors: Ren Sijia , Feng Jiachun
Published: July 2022

Shape‐morphing materials that can exhibit various shape deformations are highly desirable. In this work, shape‐morphing materials with diverse deformation modes are prepared via a facile approach of constructing bilayer structures of SEBS/paraffin blends with different melting temperatures. The bilayer films are prepared using a simple solvent‐coating adhesion method, either by adhering two single‐layers together and stretching or by adhering two pre‐stretched single‐layers. These bilayer films show strong interfacial adhesion due to the similar chemical composition of the two layers. By adjusting the programming method, stretching strain, and thickness ratio, the shape deformation behaviors of the resultant bilayer films can be flexibly tuned. To demonstrate the wide applicability of this approach, several 2D sheets with hinge structures as well as a smart dressing are prepared, in which the former can be transformed into 3D configurations and the latter can automatically fit to the human body and peel off. Owing to the advantages of low cost, easy and large‐scale preparation, recyclability, and high designability, the approach for preparing shape‐morphing bilayer films proposed by this work is versatile and the obtained bilayer films have the potential to satisfy the demands of divergent application fields.
Regioselective Dearomatization of N‐Alkylquinolinium and Pyridinium Salts under Morita‐Baylis‐Hillman Conditions
Authors: Pareek Abhishek , Kalek Marcin
Published: July 2022

Morita‐Baylis‐Hillman reaction employing N‐alkylquinolinium salts as electrophiles has been developed. The reaction is promoted by DBU, which acts both as a catalyst activating the electron‐poor olefin as well as a base. The dearomatization occurs regioselectively at the C‐2 position, delivering a broad range of α‐(1,2‐dihydroquinolin‐2‐yl)vinyl esters, ketones, and sulfones. The scope of the transformation has also been extended to N‐alkylpyridinium salts. For this class of substrates a presence of at least moderately electron‐withdrawing substituent in the ring is necessary to attain good reactivity. In particular, N‐alkylpyridinium salts containing an ester group undergo the dearomatization regioselectively at the C‐4 position, while nitrile and nitro moieties cause the non‐selective formation of products of the C‐2 and C‐6 additions.

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Carbonylative Suzuki Coupling Catalyzed by Pd Complexes Based on [N,P]‐Pyrrole Ligands: Direct Access to 2‐Hydroxybenzophenones
Authors: Cortés‐Mendoza Salvador , Adamczyk Dorian , Badillo‐Goméz Joel I. , Urrutigoïty Martine , Ortega‐Alfaro M. Carmen , López‐Cortés José G.
Published: July 2022

The Suzuki‐Miyaura cross‐coupling is one of the most useful synthetic tools to build C−C bonds, but the use of hydroxyaryl halides to direct access hydroxy‐byaryls still remains a challenge. For the carbonylative version of the reaction, the synthesis of hydroxybiaryl ketones is commonly solved by protecting group strategies. In this work, we report a protocol of carbonylative Suzuki‐ Miyaura coupling catalysed by a [N,P]‐PdCl2complex using aryl halides, various aryl boronic acids and CO. We were able at first to obtain biphenyls, finding a singular reactivity towards 2‐bromophenol, that later was extended to the carbonylation reaction, resulting in methodology that allows the obtention of 2‐hydroxybiaryl ketones, with a functional group tolerance toward amines, alkoxy, ketones, esters, and halides.

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Palladium‐Catalyzed Reaction of 2,3‐Allenols with Amines: Synthesis of [3]Dendralenes and 1,3‐Dienes Containing Allylic Amino and Hydroxy Groups
Authors: Xu Guang‐Li , Wang Zhong‐Xia
Published: July 2022

Palladium‐catalyzed reaction of 2,3‐allenols with amines was carried out to construct conjugated polyenes with allylic amino and hydroxy groups. [Pd(π‐allyl)Cl]2/P(2‐furyl)3‐catalyzed reaction in MeOH led to (Z)‐configurated [3]dendralene derivatives and Pd(OAc)2/P(2‐furyl)3‐catalyzed reaction in iPrOH resulted in (1Z,3E)‐1,3‐diene derivatives.

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3D Hierarchical Graphene‐CNT Anode for Sodium‐Ion Batteries: a First‐Principles Assessment
Authors: Ma Jiachen , Yang Chen , Li Qiuhui , Liu Shiqi , Xu Linqiang , Fang Shibo , Sun Xiaotian , Quhe Ruge , Pan Feng , Lu Jing
Published: July 2022

A thermodynamically and kinetically stable 3D hierarchical carbonaceous nanostructure is constructed to examine its potential as an anode for sodium‐ion batteries (SIBs). Heptagonal and quadrilateral staggered carbon rings are formed where the graphite layers and the CNT interconnect vertically. Based on first‐principles calculations, such a graphite‐CNT hybrid with expanded interlayer spacing allows effective binding to Na atoms and contributes a high specific capacity of 324.3 mAh g−1. It maintains a great electronic conductivity for both pristine and Na‐adsorbed graphite‐CNT along the expanded graphite layers, and constructs a 3D electronic transport network when a large number of Na atoms are adsorbed. This hierarchical nanostructure predicts a fast inner 3D Na‐ion transport network, with energy barriers of 0.56 and 0.50 eV along the expanded graphite layer and the CNT channel, respectively. This research manifests the feasibility of obtaining well‐performed graphite‐based anodes for SIBs through purposeful microcosmic morphology modification.
Ultrathin Plasma Polymer Passivation of Perovskite Solar Cells for Improved Stability and Reproducibility
Authors: Obrero‐Perez Jose M. , Contreras‐Bernal Lidia , Nuñez‐Galvez Fernando , Castillo‐Seoane Javier , Valadez‐Villalobos Karen , Aparicio Francisco J. , Anta Juan A. , Borras Ana , Sanchez‐Valencia Juan R. , Barranco Angel
Published: July 2022

Despite the youthfulness of hybrid halide perovskite solar cells, their efficiencies are currently comparable to commercial silicon and have surpassed quantum‐dots solar cells. Yet, the scalability of these devices is a challenge due to their low reproducibility and stability under environmental conditions. However, the techniques reported to date to tackle such issues recurrently involve the use of solvent methods that would further complicate their transfer to industry. Herein a reliable alternative relaying in the implementation of an ultrathin plasma polymer as a passivation interface between the electron transport layer and the hybrid perovskite layer is presented. Such a nanoengineered interface provides solar devices with increased long‐term stability under ambient conditions. Thus, without involving any additional encapsulation step, the cells retain more than 80% of their efficiency after being exposed to the ambient atmosphere for more than 1000 h. Moreover, this plasma polymer passivation strategy significantly improves the coverage of the mesoporous scaffold by the perovskite layer, providing the solar cells with enhanced performance, with a champion efficiency of 19.2%, a remarkable value for Li‐free standard mesoporous n‐i‐p architectures, as well as significantly improved reproducibility.