bluuebunny/crossref_metadata_2025 huggingface dataset:
On segmentation of lung parenchyma in quantitative computed tomography of the lung
Authors: Kemerink Gerrit J. , Lamers Rob J. S. , Pellis Bas J. , Kruize Han H. , van Engelshoven J. M. A.
Published: July 2002

Our purpose in this study was to investigate the influence of segmentation threshold and number of erosions on parameters used in quantitative computed tomography (CT) of the lung (erosions are shrink operations on the segmented area). Parameters assessed were mean lung density, area of the segmented lung, two percentiles, and the pixel index, which is the relative area of the histogram below −905 Hounsfield Units (HU). We analyzed images of ten emphysematous and ten nonemphysematous patients, that had been scanned at carina level in inspiration and expiration, using sections of 1, 2, 3, 5, and 10 mm in combination with a standard, a smooth, and an ultrasmooth reconstruction kernel. The lungs were segmented using pixel tracing at thresholds of −200, −400, and −600 HU with 0–4 erosions, followed by histogram analysis. The area of the segmented lungs decreased with 0.9%–3.2% per 100 HU decrease in threshold and with 2.2%–3.1% per erosion, dependent on patient group and respiratory status. Estimated mean lung density changed up to 30% by changing the threshold and the number of erosions. The pixel index and the 10th percentile depended only slightly on threshold and number of erosions, but the 90th percentile showed a strong dependence of up to 40%. It is concluded that the segmentation protocol can have a large impact on densitometric parameters and that standardization is mandatory for obtaining comparable results. Ideally a threshold equal to the average of the densities of lung and soft tissue should be used, but −400 HU will do in a limited but common density range (−910 to −790 HU). For densitometry two erosions are recommended, for volumetry zero erosions should be used.
A computer program to visualize gravitational lenses
Authors: Alfaro Francisco Frutos
Published: July 2002

Gravitational lenses presently play an important role in astrophysics. By means of these lenses the parameters of the deflector such as its mass, ellipticity, etc., and Hubble’s constant can be determined. Using C, XFORMS, MESA, and IMLIB, a computer program to visualize this lens effect has been developed. This program has been applied to generate sequences of images of a source object and its corresponding images. It has also been used to visually test different models of gravitational lenses.
Masking period patterns of Schroeder-phase complexes: Effects of level, number of components, and phase of flanking components
Authors: Carlyon Robert P. , Datta A. Jaysurya
Published: July 2002

Masking period patterns (MPPs) were obtained for maskers consisting of harmonics 2–20 of a 100-Hz fundamental. The signal was always a 5-ms 1100-Hz sinusoid presented 152, 154, 156, 158, or 160 ms after the start of a 400-ms masker. Experiment 1 replicated the finding that, for a masker level of 69 dB component, the shape of the MPP depended strongly on the phases of the components: Summing them in positive Schroeder phase led to a threshold variation of about 18 dB across the MPP, but summing them in negative Schroeder phase produced a flat MPP [A. Kohlrausch and A. Sander, J. Acoust. Soc. Am. 97, 1817–1829 (1995)]. Reducing the level of the positive-phase masker resulted in a systematic flattening of the MPP, whereas the negative-phase MPPs were flat both at high and at low levels. Experiment 2 showed that removing all components of a positive-phase masker except those close to the signal raised thresholds at the minimum of the MPP. In contrast, a similar manipulation applied to the negative-phase masker produced a uniform elevation of the MPP. Experiment 3 showed that an analogous effect could be obtained by manipulating the phases of masker components remote from the signal. It is shown that several features of the data can be simulated using a nonlinear model of the auditory periphery [C. Giguère and P. C. Woodland, J. Acoust. Soc. Am. 95, 331–342 (1994)].
Hypersingular boundary integral equations for exterior acoustic problems
Authors: Hwang W. S.
Published: July 2002

A bounded form of the hypersingular Helmholtz integral equation for 3-D acoustic problems is developed in this paper. All integrals with singular kernels are regularized within each regular surface element, in the sense of Kellogg, with twice continuous differentiability. The standard Gaussian quadrature formula is applied without any special treatment for all the computational points. The collocation points are chosen to be the Gauss–Legendre nodes and no interpolation function is assumed for acoustic variables.
Green’s tensor function for Lamb’s problem: The general anisotropic case
Authors: Spies Martin
Published: July 2002

The complete solution of Lamb’s three-dimensional problem of determining the elastic disturbance resulting from a point force in a half-space is addressed. The derived expression for the half-space Green’s function is valid for a general anisotropic medium and is given in a two-dimensional space–time spectral representation, which is well-suited for numerical evaluation. It is expressed with respect to the displacement and traction vectors involved as well as the full-space Green’s dyadic (or displacement tensor) and triadic (or stress tensor) functions.
Collective and localized modes of mono-coupled multi-span beams with large deterministic disorders
Authors: Bansal A. S.
Published: July 2002

Natural frequencies of two-span beams have been studied in the presence of different amounts of deterministic disorder (mistuning) arising from displacement of the intermediate simple support (prop) to different locations away from its tuned (periodic) position. The two beam-segments are assumed to be fully (strongly) coupled in the absence of any torsional constraint offered by the prop. Conditions under which the beam systems with different end conditions and support locations have the same natural frequencies have been identified and explained. Unlike the tuned multi-span beams, the natural frequencies of disordered beams with extreme ends simply supported and clamped have been found to coincide even when they do not belong to the same group(s) of natural frequencies. The deflection mode shapes and the phenomenon of normal mode localization have been presented and discussed for some specific prop locations. Conditions have been identified under which the disordered beams can behave as ordered (tuned, periodic) beams and their normal modes become perfectly collective with peak deflections exactly the same in both spans. Normal modes of fully coupled multi-span beams can become and appear to be strongly localized only if they are strongly disordered. Just as in the case of periodic beams, study of natural modes of two-span disordered beams is also helpful in understanding the natural modes of disordered beams having more than two spans.
Study of energy distribution of guided waves in multilayered media
Authors: Zhang Bixing , Xiong Wei , Yu M. , Lan C. Q. , Li Long
Published: July 2002

The energy distributions of guided waves in multilayered elastic solid media are investigated in three dimensions. A guided wave is the result of the interaction of the acoustic source and the interfaces in the material structure, and does not lose energy in the course of propagation along the horizontal direction. It should be pointed out that the guided wave cannot be excited alone by a practical acoustic source in this paper. The mean energy flux density of the guided waves (excited by a nonaxisymmetric acoustic source) has the tangential component except the radial component, but the effective part of the mean energy flux density has only the radial component. Only in the case that the propagation distance is greater than the wavelength, is the propagation velocity of the mean value of the total energy equal to the group velocity of the guided wave. It is found that the propagation velocity of the mean energy density is equal to the phase velocity of the guided wave in the lowest layer medium in the multilayered media, but in other layers, the propagation velocity of the mean energy density is related to the distance from the free surface to the receiving point. Two categories of guided waves, Rayleigh and trapped waves, are also numerically investigated in this paper in the multilayered media in which a low-velocity area is comprised. It is also found that one category of the guided waves decays rapidly with the distance from the free surface while the another category of guided waves concentrates its energy within the low-velocity area and decays with the distance from the low-velocity area. These two categories of guided waves have different energy distributions and propagation characteristics. However, since they are closely related, it is not always easy to distinguish them from each other. The excitation and propagation mechanism of the guided waves are useful for exploring the structures of the interfaces and the low-velocity area under the free surface.
An equivalent source technique for calculating the sound in enclosures
Authors: Johnson Marty E. , Elliott Stephen J. , Baek Kwang-Hyun , Garcia-Bonito Juan
Published: July 2002

The equivalent source method has previously been used to calculate the exterior sound field radiated or scattered from bodies in the free-field. In this work the method is used to calculate the internal pressure field for an enclosure which can have arbitrary boundary conditions and may include internal scattering objects. The normal velocity on the surfaces of the scattering objects and the enclosure walls is evaluated at a larger number of positions than there are equivalent sources. The sum of the squared difference between this velocity and that expected because of the admittance of the boundary is minimized by adjusting the strengths of the equivalent sources. Example results are presented for the sound field and frequency response inside a damped rectangular enclosure, which compare very well with the conventional modal model. The effect of having rigid spheres inside the enclosure are then investigated, and it is found that the effect is significant even some distance from the spheres and at frequencies for which the size of the sphere is small compared to a wavelength. Finally, the effect of a nonlocally reacting boundary condition is illustrated by assuming that one of the walls of the enclosure is an elastic plate. [Work conducted at the ISVR.]
Piezoelectric thin shell theoretical model and eigenfunction analysis of radially polarized ceramic cylinders
Authors: Ebenezer D. D. , Abraham Pushpa
Published: July 2002

A piezoelectric thin shell theoretical model of radially polarized ceramic cylinders is first developed. An eigenfunction approach is then used to determine the displacement, stress, electric field, and input electrical admittance of the cylinder. In the model, the effect of bending strain is included and it is assumed that the electric field varies linearly between the electrodes. It is then shown that the displacement and electric field are uncoupled, i.e., it is possible to first determine the displacement and then determine the electric field. It is also noted that, irrespective of the dimensions of the cylinder and the boundary conditions, the electric field can be much greater than the ratio of the applied voltage to the distance between electrodes. Next, the equations of motion and the boundary conditions are derived by using Hamilton’s variational principle. They are solved by using the eigenfunction approach. The eigenfunctions are determined here by using a general method and, therefore, cylinders with arbitrary boundary conditions can be analyzed. The same method can be used even if other thin shell theories are used. It is shown that experimental resonance frequencies and input electrical admittance of free–free cylinders are in good agreement with those computed using the present model. It is also shown that the electric field is in good agreement with the work of other investigators.
Detection of phase- or frequency-modulated signals in reverberation noise
Authors: Carmillet Valérie , Amblard Pierre-Olivier , Jourdain Geneviève
Published: July 2002

This paper is devoted to the detection of phase- or frequency-modulated signals corrupted by the reverberation noise they have created. When the reverberation is modeled as a time-varying stochastic filtering of the emitted signal, the optimal detector consists of prewhitening the observation before applying a matched filter. This theory is very difficult to implement because of the nonstationarity of the reverberation noise. In this paper, a suboptimal detector proposed by Kay and Salisbury in 1990 is generalized to phase or frequency modulated signals. The reverberation is assumed locally stationary; the signal is cut into blocks and the whitening is performed as follows: An autoregressive (AR) modeling of one block allows the whitening of the following block. After whitening, an appropriate matched filter is applied. This scheme is explained in detail. The local stationarity assumption of the reverberation noise is discussed in light of the Itakura spectral distance. Performance of the proposed approach is evaluated theoretically when all parameters are known, and experimentally using three different real-data sets.
Computer models for masked hearing experiments with beluga whales (Delphinapterus leucas)
Authors: Erbe Christine , King Andrew R. , Yedlin Matthew , Farmer David M.
Published: July 2002

Environmental assessments of manmade noise and its effects on marine mammals need to address the question of how noise interferes with animal vocalizations. Seeking the answer with animal experiments is very time consuming, costly, and often infeasible. This article examines the possibility of estimating results with software models. A matched filter, spectrogram cross-correlation, critical band cross-correlation, and a back-propagation neural network detected a beluga vocalization in three types of ocean noise. Performance was compared to masked hearing experiments with a beluga whale [C. Erbe and D. M. Farmer, Deep-Sea Res. II 45, 1373–1388 (1998)]. The artificial neural network simulated the animal data most closely and raised confidence in its ability to predict the interference of a variety of noise sources with a variety of vocalizations.
Effect of acoustic dynamic range on phoneme recognition in quiet and noise by cochlear implant users
Authors: Fu Qian-Jie , Shannon Robert V.
Published: July 2002

The present study measured phoneme recognition in cochlear implant users when the dynamic range of the input speech signals was reduced by either peak clipping or center clipping. In quiet, reducing the acoustic dynamic range to 30 dB still provides sufficient speech information for phoneme identification in cochlear implant users with 4-channel continuous interleaved sampler strategy and normal-hearing listeners listening to correspondingly degraded speech. Phoneme recognition decreased when the dynamic range was reduced below 30 dB: peak clipping was more detrimental to vowel recognition and center clipping was more detrimental to consonant recognition. However, in background noise, center clipping produced a small increase in speech recognition for cochlear implant listeners.
Backscattering enhancements for tilted solid plastic cylinders in water due to the caustic merging transition: Observations and theory
Authors: Blonigen Florian J. , Marston Philip L.
Published: July 2002

Bulk shear and longitudinal waves give rise to important contributions to the scattering of ultrasound by tilted finite plastic and rubber cylinders in water. This occurs in situations where either the shear or longitudinal speed is less than the speed of sound in the surrounding water. At a certain critical tilt angle, large backscattering enhancements are observed for finite cylinders, where the wave vector can reverse direction upon reflection from the cylinder truncation. The scattering process is analogous to the enhancement produced by the merging of rainbow caustics of primary rainbow rays in the scattering of light by long dielectric cylinders, also known as the caustic merging transition [C. M. Mount, D. B. Thiessen, and P. L. Marston, Appl. Opt. 37, 1534–1539 (1998)]. A ray theory was developed to model the backscattering mechanism at the critical tilt angle. It employs the idea of the Bravais effective refractive index, convenient for constructing ray diagrams for the projections of rays in the base plane of the cylinder. There is general agreement between the theory and the experiment down to relatively low ultrasonic frequencies (ka as small as 10). The enhancement is the most significant backscattering contribution for a wide range of tilt angles.
Scale model experiments on the insertion loss of wide and double barriers
Authors: Wadsworth Glenn J. , Chambers James P.
Published: July 2002

The insertion loss of wide and double barriers is investigated through scale model experiments. Such configurations appear in outdoor sound propagation problems such as highway noise reduction and community noise control. The Biot–Tolstoy–Medwin (BTM) time domain wedge formulation for multiple diffraction [J. Acoust. Soc. Am. 72, 1005–1013 (1982)] is used to predict the acoustic response of an impulsive source. Evaluation of the insertion loss at discrete frequencies is accomplished via the fast Fourier transform (FFT). Good agreement has been found between the BTM model and experimental data for all configurations tested.
Finite Deformations under Pressurization in an Infinitely Long, Thick-Walled, Elastic Cylinder Ideally Bonded to a Thin Elastic Case
Authors: Baltrukonis J. H. , Vaishnav R. N.
Published: July 2002

Using the tensor-analytic approach of Green and Zerna, an expression relating the internal pressure in an infinitely long, hollow, elastic cylinder with a thin elastic casing to the geometry of the cylinder in the strained and unstrained states, has been derived. Assumption of incompressibility is made. The strains in the elastic case are assumed to be infinitesimal, whereas, as long as they are consistent with the above requirement, no restriction is placed on the magnitude of the strains in the cylinder. The result is specialized for the case of a Mooney material for which expressions of stresses and strains in the cylinder are also presented. In the latter case, an additional restriction is placed on the magnitude of the strains in the cylinder, namely, that of being within the limits of validity of the Mooney expression for the strain energy function. The results of the analysis are applied in the solution of a practical problem, and in this case, the discrepancies between finite and infinitesimal strain theories are discussed.
Time, Temperature, and Molecular Weight Effects in Environmental Stress Cracking
Authors: Fulmer Glenn E.
Published: July 2002

A parametric study was made of the stress relaxation of linear polyethylene in air and a stress cracking environment, Igepal. Breaking time is shown to be a function of reduced variables of time, temperature, and molecular weight. Acreleration of tests for failure time can be achieved if the test temperature is raised, since for 0.96 density P.E. over the range of 50–110°C no mechanism change occurs. Stress relaxation measurements are shown to give results similar to the bent strip stress cracking test (ASTM D 1693-60T). This latter test can also be accelerated 80 times for 0.96 density polyethylene and 1500 times for 0.95 density polyethylene. A slight modification of the test procedure is required to obtain meaningful results. Some effects of strain, thickness, and presoaking are also reported.
Some Experimental Observations on the Stored Energy Function for Small Values of Strain Invariants
Authors: San Miguel Anthony , Landel Robert F.
Published: July 2002

In order to evaluate the stored energy function W for elastomeric materials, at least biaxial experiments must be made. Two of the biaxial testers developed at the Jet Propulsion Laboratory are an inflated cylinder device and a second biaxial sheet tester. Some preliminary experimental results obtained with these two devices at small values of strain invariants are presented for a polyurethane elastomer. These results are analyzed without making the assumption that the elastomer is incompressible, a fact which modifies the analysis of multiaxial or large-strain behavior. The results from the biaxial sheet tester are consistent with those obtained from an inflated cylinder of the same material, though experimental difficulties prevent a detailed comparison. Nevertheless, both series of experiments show that all three terms, ∂W/∂Ii, where Ii are the three strain invariants, depend strongly on the invariants. Moreover, ∂W/∂I2 is negative, in agreement with theoretical expectations. Thus, the form of W in the region where Ii<4 is very complex.
Partially Crystalline Polyethylene: Flow and Optical Properties
Authors: Johnson Julian F. , Barrall Edward M. , Porter Roger S.
Published: July 2002

Viscosity-shear rate measurements have been made on two branched polyethylenes with molecular weights of 3300 and 8300 over a temperature range extending from above to below the nominal melting point and well into the region of partial crystallinity. Calculation of flow activation energies at different shear rates shows several distinct temperature regions for flow of the polymer with molecular weight of 3300. The polymer with a molecular weight of 8300, above the entanglement composition, also shows distinct temperature regions of flow but with considerably different flow activation energies. Certain activation energies are independent of shear rate within experimental error. Depolarized light intensity measurements and photomicroscopy confirm that physical changes occur at the temperatures where the flow properties exhibit transitions.
Rolling Friction on Viscoelastic Substrates
Authors: Gent A. N. , Henry R. L.
Published: July 2002

Apparatus has been constructed to carry out precise measurements of rolling friction for rigid balls rolling over soft viscoelastic substrates, using a wide range of ball size, normal load, and rolling speed. Measurements are reported for two viscoelastic substrates, representing high and low energy loss elastomers. Measurements of the energy loss factor were also carried out for each substrate, using a simple rebound arrangement with a wide range of initial velocity and impact mass so that the contact time varied substantially. The rolling friction measurements were somewhat higher under all circumstances than the theoretical values, calculated using an energy loss factor appropriate to the contact time in rolling. The discrepancy at low rolling speeds was about the same magnitude as that reported previously by Greenwood, Minshall, and Tabor, and attributed by them to additional energy losses in complex strain cycles like those involved in rolling.
Response of Viscoelastic Materials to Piecewise Continuous Excitations
Authors: Yagii K. , Tschoegl N. W.
Published: July 2002

A general method is presented for predicting the response of a linear viscoelastic material to piecewise continuous excitations in terms of its known response to the standard excitation functions, i.e., in terms of the relaxation modulus and the creep compliance in case of non-periodic excitations, or the real and imaginary parts of the complex modulus and complex compliance in case of the steady-state response to a periodic non-sinusoidal excitation. To illustrate typical behavior, the response is used of a three-parameter Maxwell model to staircase, pyramid, triangular pulse, and triangular pulse train excitations.
Theoretical and Experimental Treatment of Fracture in an Adhesive Interlayer
Authors: Burton J. D. , Jones W. B. , Williams M. L.
Published: July 2002

From the viewpoint of continuum mechanics, cohesive and adhesive fracture have been shown to be similar. The energy approach to adhesive fracture has provided a method of interpreting the results from a convenient “blister” test that may be used quantitatively to evaluate bond strengths for particular bi-material bond systems. Inquiring further into adhesive fracture, the effect of including an elastic adhesive interlayer between the two other materials is investigated analytically and experimentally. The experimental system is typical of the propellant-liner-steel combination frequently encountered in a solid rocket motor.
Torque Reduction in Finite Amplitude Secondary Flows of Dilute Polymer Solutions
Authors: Denn M. M. , Sun Z.-S. , Rushton B. D.
Published: July 2002

When a dilute polymer solution is sheared between concentric cylinders with the inner cylinder rotating and the outer fixed, the onset of cellular secondary flows (Taylor vortices) is usually delayed relative to a Newtonian liquid of the same kinematic viscosity, and the extra torque in the polymer solution following instability is less than that for the Newtonian liquid at the same relative Taylor Number. This torque reduction is explained here by means of a finite amplitude analysis of the secondary motion in a second-order fluid using the energy equilibrium approach of Landau and Stuart. The theoretical calculations are in general agreement with data of Denn and Roisman for a 0.5% solution of polyisobutylene in decalin. Using these calculations and the linearized stability theory it is possible to estimate the three rheological parameters for a second-order fluid from a single set of torque-rotational speed data in a Couette viscometer.
Internal Viscosity Effects on Transient Elongational Behavior of Dilute Polymer Solutions (Elastic dumbbell model)
Authors: Acierno D. , Titomanlio G. , Marrucci G.
Published: July 2002

The transient elongational viscosity of dumbbell suspensions is calculated accounting for the effect of an internal viscosity in the dumbbell. The calculations are relative to conditions of sufficiently large stretching rates for the effect of Brownian motions to be neglibible. Large extensions of the dumbbell are considered and the resulting nonlinear elastic behavior is accounted for. Both numerical and approximate analytical solutions are provided.
The Drainage of Non-Newtonian Liquids Entrained on a Vertical Surface
Authors: Denson C. D.
Published: July 2002

The drainage behavior of a wide variety of non-Newtonian liquids has been studied under circumstances when “free-drainage” conditions apply. Experimental values for the time-variant film thicknesses were obtained while drainage proceeded using a light absorption technique, and an analytic expression relating film thickness to drainage time was derived for fluids described by the Ellis model. Deviations between the experimental and theoretical results are interpreted in light of the Ellis model's inability to describe the elastic properties of the liquids studied.
Investigation of Stability of Plane Couette Flow of a Second-Order Fluid by the Energy Method
Authors: Kundu Pijush K.
Published: July 2002

The classical energy method of Orr is used to investigate the stability of a plane Couette flow of a viscoelastic fluid obeying the constitutive equation of the so-called second-order fluid. For two-dimensional disturbances of any magnitude, the presence of elasticity has been found to stabilize the flow. For small three-dimensional disturbances invariant in the flow direction, the presence of elasticity has been found to affect the stability either way, depending on the relative values of the constants in the constitutive equation.
A Thermomechanical Theory for Structured Materials
Authors: Sarti G. C. , Astarita G.
Published: July 2002

Materials are considered with an instantaneous molecular structure describable in terms of some distribution function φ(R,t). For such materials, a general thermodynamic theory based on the Clausius-Duhem inequality is developed, along the lines of the thermodynamic theory for simple materials with fading memory developed by Coleman. The problem of the restrictions imposed on molecular model building by the requirement that they yield results compatible with Coleman's theory is discussed in some detail, and certain general conclusions are obtained.
Simulation of the nonlinear rheological properties of gluten dough using the Wagner constitutive model
Authors: Wang C. F. , Kokini J. L.
Published: July 2002

The Wagner theory was used for gluten dough with 55% moisture content. Using the generalized Maxwell model with 24 parameters it was possible to simulate the linear memory function required in the Wagner formulation. The generalized Maxwell model also allowed prediction of the dynamic viscosity η′ and the out-of-phase component of the complex viscosity divided by frequency η′/ω in the frequency range studied. A damping function with two exponential terms was found to be suitable to simulate the nonlinear properties. With the incorporation of the linear memory function and the damping function, the Wagner model is able to predict the nonlinear relaxation modulus as well as the steady viscosity.
The 2000 Materials Research Society (MRS) Fall Meeting Report
Authors: Wong-Ng Winnie
Published: July 2002

Keeping with tradition, the 2000 MRS annual meeting again took place in Boston Copely Plaza from November 27 to December 1. The 2000 meeting was well organized and well attended, with a total of 4600 attendees representing industrial, academic, and government sectors. The rich technical program was multi-disciplinary (41 symposia) to meet the needs of the attendees. A total of 4000 papers were presented. There were a number of memorable lectures, several special seminars on policy and funding, an award ceremony, a new educational seminar series that focused on the scientific basis and practical application of commercial tools. The meeting also highlighted an elaborate exhibit, poster sessions and other well organized events. This report summarizes various events which took place at the meeting.
Chemical Recycling of Poly(Cyclohexene Carbonate) Using a Di‐MgII Catalyst
Authors: Singer Frances N. , Deacy Arron C. , McGuire Thomas M. , Williams Charlotte K. , Buchard Antoine
Published: April 2022

Chemical recycling of polymers to true monomers is pivotal for a circular plastics economy. Here, the first catalyzed chemical recycling of the widely investigated carbon dioxide derived polymer, poly(cyclohexene carbonate), to cyclohexene oxide and carbon dioxide is reported. The reaction requires dinuclear catalysis, with the di‐MgII catalyst showing both high monomer selectivity (>98 %) and activity (TOF=150 h−1, 0.33 mol %, 120 °C). The depolymerization occurs via a chain‐end catalyzed depolymerization mechanism and DFT calculations indicate the high selectivity arises from Mg‐alkoxide catalyzed epoxide extrusion being kinetically favorable compared to cyclic carbonate formation.
Manipulating the Water Dissociation Electrocatalytic Sites of Bimetallic Nickel‐Based Alloys for Highly Efficient Alkaline Hydrogen Evolution
Authors: Wang Jinsong , Xin Sisi , Xiao Yao , Zhang Zhengfu , Li Zhimin , Zhang Wang , Li Caiju , Bao Rui , Peng Jian , Yi Jianhong , Chou Shulei
Published: April 2022

Transition‐metal alloys are currently drawing increasing attention as promising electrocatalysts for the alkaline hydrogen evolution reaction (HER). However, traditional density‐functional‐theory‐derived d‐band theory fails to describe the hydrogen adsorption energy (ΔGH) on hollow sites. Herein, by studying the ΔGH for a series of Ni−M (M=Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Mo, W) bimetallic alloys, an improved d‐band center was provided and a potential NiCu electrocatalyst with a near‐optimal ΔGH was discovered. Moreover, oxygen atoms were introduced into Ni−M (O−NiM) to balance the adsorption/desorption of hydroxyl species. The tailored electrocatalytic sites for water dissociation can synergistically accelerate the multi‐step alkaline HER. The prepared O−NiCu shows the optimum HER activity with a low overpotential of 23 mV at 10 mA cm−2. This work not only broadens the applicability of d‐band theory, but also provides crucial understanding for designing efficient HER electrocatalysts.
Amine‐Catalyzed Copper‐Mediated C−H Sulfonylation of Benzaldehydes via a Transient Imine Directing Group**
Authors: Higham Joe I. , Bull James A.
Published: April 2022

Transient directing groups (TDGs) can provide a powerful means for C−H functionalization without requiring additional steps for directing group introduction and removal. We report the first use of a TDG in combination with copper to effect C−H functionalization. The regioselective copper mediated β−C(sp2)−H sulfonylation of aldehydes with sulfinate salts is accomplished using catalytic β‐alanine to form a transient imine. A broad range of sulfonylated benzaldehydes are prepared using copper fluoride as both copper source and oxidant, involving a [5,6] cupracyclic intermediate. γ‐(peri)‐Sulfonylation of napthyl and phenanthrenyl carboxaldehydes is achieved through [6,6] cupracyclic intermediates. Further derivatisation of the aldehyde products is demonstrated. Kinetic experiments and Hammett analysis suggest the turnover limiting step to be a concerted asynchronous C−H cleavage via a dearomative Wheland‐type transition state.
Layered Organic Metal Chalcogenides (OMCs): From Bulk to Two‐Dimensional Materials
Authors: Wang Guan‐E , Luo ShaoZhen , Di Tuo , Fu ZhiHua , Xu Gang
Published: April 2022

The modification of inorganic two‐dimensional (2D) materials with organic functional motifs is in high demand for the optimization of their properties, but it is still a daunting challenge. Organic metal chalcogenides (OMCs) are a type of newly emerging 2D materials, with metal chalcogenide layers covalently anchored by long‐range ordered organic functional motifs, these materials are extremely desirable but impossible to realize by traditional methods. Both the inorganic layer and organic functional motifs of OMCs are highly designable and thus provide this type of 2D materials with enormous variety in terms of their structure and properties. This Minireview aims to review the latest developments in OMCs and their bulk precursors. Firstly, the structure types of the bulk precursors for OMCs are introduced. Second, the synthesis and applications of OMC 2D materials in photoelectricity, catalysis, sensors, and energy transfer are explored. Finally, the challenges and perspectives for future research on OMCs are discussed.
Iridium‐Catalyzed Ligand‐Controlled Remote para‐Selective C−H Activation and Borylation of Twisted Aromatic Amides
Authors: Hoque Md Emdadul , Bisht Ranjana , Unnikrishnan Anju , Dey Sayan , Mahamudul Hassan Mirja Md , Guria Saikat , Rai Rama Nand , Sunoj Raghavan B. , Chattopadhyay Buddhadeb
Published: April 2022

A method of para‐selective borylation of aromatic amides is described. The borylation proceeded via an unprecedented substrate–ligand distortion between the twisted aromatic amides and a newly designed ligand framework (defa) that is different from the traditionally used ligand (dtbpy) for the C−H borylation reactions. The designed ligand framework (defa) has led to the development of a new type of catalytic system that shows excellent para selectivity for a range of aromatic amides. Moreover, the designed ligand has shown excellent reactivity and selectivity for a range of heterocyclic aromatic amides. The identification of key transition states and intermediates using the DFT computations associated with the three regio‐isomeric pathways revealed that the most efficient catalytic pathway with the defa ligand leads to the para borylation while in the case of bpy the borylation at the para and meta sites compete.
Scalable Nitrate Treatment for Constructing Integrated Surface Structures to Mitigate Capacity Fading and Voltage Decay of Li‐Rich Layered Oxides
Authors: Luo Dong , Xie Huixian , Tan Fulin , Ding Xiaokai , Cui Jiaxiang , Xie Xiaoyan , Liu Chenyu , Lin Zhan
Published: April 2022

Capacity fading and voltage decay is one of the biggest obstacles for the practical application of Li‐rich layered oxides due to the serious surface‐related detrimental reactions. Herein, we develop a versatile and scalable method to construct a robust surface‐integrated structure. All the designed samples deliver outstanding capacity and voltage stability, among which the Zn‐treated sample possesses the best electrochemical performance. Its capacity retention is larger than 90 % after 400 cycles with a voltage decay ratio as small as 0.73 mV per cycle. What is more, the rules of surface‐integrated structure with different cations in terms of capacity and voltage stability is further deciphered by combining with density function theory (DFT) calculations. It is found that to obtain advanced Li‐rich layered oxide cathodes, cations in Li‐sites should firstly ensure the binding energy of the surface‐integrated structure in a lower level and then provide Bader charge for the nearest O atoms as small as possible.
Tetracoordinate Boron‐Based Multifunctional Chiral Thermally Activated Delayed Fluorescence Emitters
Authors: Zhou Ling , Ni Fan , Li Nan , Wang Kai , Xie Guohua , Yang Chuluo
Published: April 2022

Purely organic emitters have shown great potential but still suffer from low efficiency in near‐infrared organic light‐emitting diodes (NIR‐OLEDs) due to the intensive non‐radiative recombination. In this contribution, two pairs of thermally activated delayed fluorescence (TADF) enantiomers (R/S‐DOBP and R/S‐HDOBP) with tetracoordinate boron geometries were designed and synthesized. The TADF emitters simultaneously showed aggregation‐induced emission, circularly polarized luminescence, high‐contrast mechanochromism, and piezochromism behaviors. More importantly, R/S‐DOBP and R/S‐HDOBP revealed high photoluminescence quantum yields and efficient reverse intersystem crossing in neat films. The nondoped solution‐processed OLEDs based on these unique emitters revealed the NIR emission (peaking at 716 nm) with a maximum external quantum efficiency of 1.9 % and high exciton utilization efficiency of 86 %, which represent one of the best solution‐processed nondoped NIR‐OLEDs.
Biomacromolecule‐Fueled Transient Volume Phase Transition of a Hydrogel
Authors: Nakamoto Masahiko , Kitano Shiro , Matsusaki Michiya
Published: April 2022

A metabolic cycle‐inspired hydrogel which exhibits the biomacromolecule‐fueled transient volume phase transition is reported. This hydrogel has the affinity and digestive capacity for a fuel α‐poly‐L‐lysine by incorporating acrylic acid and trypsin. The hydrogel captured fuel and transiently shrank owing to the construction of electrostatic cross‐linkages. This process was inherently connected with the digestion of these cross‐linkages and the release of oligo‐lysine as waste, which induced the reswelling of the hydrogel at equilibrium. The transient volume change of the hydrogel realized the fuel‐stimulated transient release of a payload. This study provides a strategy for engineering materials with biomacromolecule‐fueled dynamic functions under the out‐of‐equilibrium condition.
Beyond Bioisosteres: Divergent Synthesis of Azabicyclohexanes and Cyclobutenyl Amines from Bicyclobutanes**
Authors: Dhake Kushal , Woelk Kyla J. , Becica Joseph , Un Andy , Jenny Sarah E. , Leitch David C.
Published: April 2022

The development of two divergent and complementary Lewis acid catalyzed additions of bicyclobutanes to imines is described. Microscale high‐throughput experimentation was integral to the discovery and optimization of both reactions. N‐arylimines undergo formal (3+2) cycloaddition with bicyclobutanes to yield azabicyclo[2.1.1]hexanes in a single step; in contrast, N‐alkylimines undergo an addition/elimination sequence to generate cyclobutenyl methanamine products with high diastereoselectivity. These new products contain a variety of synthetic handles for further elaboration, including many functional groups relevant to pharmaceutical synthesis. The divergent reactivity observed is attributed to differences in basicity and nucleophilicity of the nitrogen atom in a common carbocation intermediate, leading to either nucleophilic attack (N‐aryl) or E1 elimination (N‐alkyl).
Fixed‐time backstepping distributed cooperative control for multiple unmanned aerial vehicles
Authors: Cui Lei , Zhou Qi , Jin Nan
Published: April 2022

This paper proposes a fixed‐time backstepping distributed cooperative control scheme based on fixed‐time extended state observer (FxTESO) for multiple unmanned aerial vehicles (UAVs). A fixed‐time ESO, which is convergent independently of initial conditions, is designed to estimate and compensate the external disturbances in tracking process. Moreover, to eliminate the “explosion of complexity” in the traditional backstepping architecture, a nonlinear first‐order filter is adopted to construct the distributed fixed‐time control scheme. Based on the local information of neighboring UAVs, a fixed‐time backstepping cooperative controller is designed. The proposed formation algorithm can be shown practicable for the UAV control system by using of Lyapunov stability theory and graph theory. Simulation results are given to demonstrate the effectiveness of the proposed control scheme.
Genauigkeitsgrenzen modularer Betontragwerke – Teil 2: Probabilistische Bewertung der Montage mit Schraubenverbindung
Authors: Stindt Jan , Frey Alex Maximilian , Forman Patrick , Lanza Gisela , Mark Peter
Published: April 2022

Der Beitrag behandelt die Montage von modulartigen Betonfertigteilen mit Fachwerkknoten aus Stahl. Dazu werden Wabenstrukturen betrachtet, die aus vielen Fertigteilen mit Y‐Form bestehen. Der Beitrag baut auf der für die Wabenstrukturen im Teil 1 abgeleiteten Bewegungskinematik zwischen den einzelnen Modulen auf, wobei Schwinddehnungen Verformungen in den Modularmen erzeugen. Für die Montage werden Schraubenverbindungen betrachtet, die entweder klassisches Lochspiel besitzen oder gleitfest fixiert werden. Bei Letzterem kompensiert ein Ausrichten vor dem Fixieren einen Teil von Abweichungen. Die Zuverlässigkeit der Montage wird mit probabilistischen Methoden auf Grundlage von Monte‐Carlo‐Simulationen überprüft. Es zeigt sich, dass reine Lochleibungsverbindungen nur für sehr wenige zu kombinierende Module geeignet sind. Gleitfeste Verbindungen mit kompensatorischem Ausrichten sind mit einem Konfidenzintervall vierfacher Standardabweichung geeignet, Wabenstrukturen bis ca. 60 m Höhe und Breite zuverlässig zusammenzusetzen.
Preparation and application of taste bud organoids in biomedicine towards chemical sensation mechanisms
Authors: Liu Shuge , Zhu Ping , Tian Yulan , Chen Yating , Liu Yage , Chen Wei , Du Liping , Wu Chunsheng
Published: April 2022

Taste is one of the most basic and important sensations that is able to monitor the food quality and avoid intake of potential danger materials. Whether as an inevitable symptom of aging or a complication of cancer treatment, taste loss very seriously affects the patient's life quality. Taste bud organoids provide an alternative and convenient approach for the research of taste functions and the underlying mechanisms due to their characteristics of availability, strong maneuverability, and high similarity to the in‐vivo taste buds. This review gives a systemic and comprehensive introduction to the preparation and application of taste bud organoids towards chemical sensing mechanisms. First, the basic structures and functions of taste buds will be briefly introduced. Then, the currently available approaches for the preparation of taste bud organoids are summarized and discussed, which are mainly divided into two categories, that is, the stem/progenitor cell‐derived approach and the tissue‐derived approach. Next, different applications of taste bud organoids in biomedicine are outlined based on their central roles such as disease modeling, biological sensing, gene regulation, and signal transduction. Finally, the current challenges, future development trends, and prospects of research in taste bud organoids are proposed and discussed.
Biosynthesis of 1,3‐propanodiol and 2,3‐butanodiol from residual glycerol in continuous cell‐immobilized Klebsiella pneumoniae bioreactors
Authors: Damasceno Ana Paula Klaus , Rossi Daniele Misturini , Ayub Marco Antônio Záchia
Published: April 2022

In recent years, residual glycerol from biodiesel synthesis made this chemical a cheap, readily available carbon source to bioprocess, which is also a form to reduce costs in the fuel industry. We propose and describe a bioprocess using fluidized and packed‐bed continuous bioreactors to convert this residual glycerol into value‐added products such as 1,3‐propanediol (1,3‐PD) and 2,3‐butanediol (2,3‐BD), largely used in the chemical industry. The bacterium Klebsiella pneumoniae BLh‐1, strain isolated by us, was immobilized in the permeable support of polyvinyl alcohol (LentiKats®). After testing different dilution rates (D) for all bioreactor configurations, the best obtained productivities of 1,3‐PD was 8.69 g L−1 h−1 at a D = 0.45 h−1, and 2.99 g L−1 h−1 at a D = 0.30 h−1 for 2,3‐BD, both in the packed‐bed configuration. In the fluidized‐bed reactor, the highest productivity values achieved were 4.48 and 1.16 g L−1 h−1 for 1,3‐PD and 2,3‐BD, respectively, both at D = 0.33 h−1. These results show the potential of setting up a bioprocess based on continuous cultures using immobilized K. pneumoniae BLh‐1 in PVA matrices in order to efficiently convert the abundant surplus of glycerol into commercially important chemicals such as 1,3‐PD and 2,3‐BD.
Clipping costs
Authors: Drosou Maria E. , Gray William A.
Published: April 2022

Key Points

Early data on mitral TEER indicate that decrease in cost trends is primarily attributed to decrease in length of index hospitalization and relatively stable 30‐day readmission rates.

The addition of functional MR in the population set and a more stable, less expansive operator pool will affect outcomes over the following years and should be included in cost analyses.

Additional baseline patient characteristics, optimal medical therapy and longer follow up will provide more information regarding mitral TEER outcomes and costs.
Step back to see the complete picture: Complete versus incomplete revascularization of multivessel coronary disease
Authors: Grines Cindy L. , Marshall J. Jeffrey
Published: April 2022

Key Points

Multivessel disease patients who are incompletely revascularized with PCI have have worse clinical outcomes including death and need for subsequent revascularization

The mechanism of increased mortality with incomplete revascularization is uncertain, and is confounded by higher atherosclerotic burden and more comorbidities

Although we recommend complete revascularization, there are no randomized trials except in the STEMI population.
Ileal gastrointestinal stromal tumor causing mesenteric gangrene
Authors: Beji Hazem , Bouassida Mahdi , Zribi Slim , Touinsi Hassen
Published: April 2022

To our knowledge, this is one of the rare literature reports of an ileal GIST complicated with mesenteric gangrene. We reported successful surgical treatment. Infection of GIST is an extremely rare complication that should be treated with no delays to avoid rupture and peritonitis.
Photoactivatable V‐Shaped Bifunctional Quinone Methide Precursors as a New Class of Selective G‐quadruplex Alkylating Agents
Authors: Lena Alberto , Benassi Alessandra , Stasi Michele , Saint‐Pierre Christine , Freccero Mauro , Gasparutto Didier , Bombard Sophie , Doria Filippo , Verga Daniela
Published: April 2022

Combining the selectivity of G‐quadruplex (G4) ligands with the spatial and temporal control of photochemistry is an emerging strategy to elucidate the biological relevance of these structures. In this work, we developed six novel V‐shaped G4 ligands that can, upon irradiation, form stable covalent adducts with G4 structures via the reactive intermediate, quinone methide (QM). We thoroughly investigated the photochemical properties of the ligands and their ability to generate QMs. Subsequently, we analyzed their specificity for various topologies of G4 and discovered a preferential binding towards the human telomeric sequence. Finally, we tested the ligand ability to act as photochemical alkylating agents, identifying the covalent adducts with G4 structures. This work introduces a novel molecular tool in the chemical biology toolkit for G4s.