bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculating output factors for photon beam radiotherapy using a convolution/superposition method based on a dual source photon beam model
Authors: Liu H. Helen , Mackie T. Rock , McCullough Edwin C.
Published: July 2002

A realistic photon beam model based on Monte Carlo simulation of clinical linear accelerators was implemented in a convolution/superposition dose calculation algorithm. A primary and an extra‐focal sources were used in this beam model to represent the direct photons from the target and the scattered photons from other head structures, respectively. The effect of the finite size of the extra‐focal source was modeled by a convolution of the source fluence distribution with the collimator aperture function. Relative photon output in air and in phantom were computed using the convolution method with this new photon beam model. Our results showed that in a 10 MV photon beam, the (phantom scatter factor), and factors increased by 11%, 10%, and 22%, respectively, as the field size changed from to The variation of the factor was contributed mostly by an increase of the extra‐focal radiation with field size. The radiation backscattered into the monitor chamber inside the accelerator head affected the by about 2% in the same field range. The output factors in elongated fields, asymmetric fields, and blocked fields were also investigated in this study. Our results showed that if the effect of the backscattered radiation was taken into account, output factors in these treatment fields can be predicted accurately by our convolution algorithm using the dual source photon beam model.
Report on the dosimetry of a new design brachytherapy source
Authors: Wallace Robert E. , Fan Jay J.
Published: July 2002

Dosimetric measurements were performed to characterize a new source that is a variant design of an existing source, designated as MED3631‐A/S, and that has application in interstitial brachytherapy. The new source, designated as MED3631‐A/M, has centralized radio‐opaque markers. In the original MED3631‐A/S source, the radio‐opaque markers are separated. Thermoluminescent dosimeters were placed in phantom to measure transverse axis and angular dose profiles over a range of distances from 0.5 to 7 cm. The data were analyzed in terms of parameters recommended by AAPM Task Group No. 43. Tabular data evaluated in liquid water are provided for the dose‐rate constant, Λ, radial dose function, the anisotropy function, the anisotropy factor, the point‐source approximation anisotropy constant, The dose‐rate constant was determined by an absolute method using a Cobalt‐60 reference and by relative measurements using calibrated source(s). Values of the dose‐rate constant are provided for both the 1985 and 1999 NIST air‐kerma strength standards. The new source is comparable to both the MED3631‐A/S and the model 6702 source designs, demonstrating equivalent radial dose function, Differences in the value of the dose‐rate constant, Λ, and the anisotropy of the dose distributions in phantom are discussed in light of the improved isotropy of the new design, the MED3631‐A/M source, and the uncertainty involved in the dose measurement using a Cobalt‐60 reference.
Space-time exchange invariance: Special relativity as a symmetry principle
Authors: Field J. H.
Published: July 2002

Special relativity is reformulated as a symmetry property of space-time: space-time exchange invariance. The additional hypothesis of spatial homogeneity is then sufficient to derive the Lorentz transformation without reference to the traditional form of the Principle of Special Relativity. The kinematical version of the latter is shown to be a consequence of the Lorentz transformation. As a dynamical application, the laws of electrodynamics and magnetodynamics are derived from those of electrostatics and magnetostatics respectively. The four-vector nature of the electromagnetic potential plays a crucial role in the last two derivations.
Perturbation of infinite networks of resistors
Authors: Cserti József , Dávid Gyula , Piróth Attila
Published: July 2002

The resistance between arbitrary nodes of an infinite network of resistors is calculated when the network is perturbed by removing one bond from the perfect lattice. A relation is given between the resistance and the lattice Green’s function of the perturbed resistor network. By solving the Dyson equation, the Green’s function and the resistance of the perturbed lattice are expressed in terms of those of the perfect lattice. Numerical results are presented for a square lattice.
On the superconducting sphere in an external magnetic field
Authors: Matute Ernesto A.
Published: July 2002

The magnetic field inside and outside a superconducting sphere in an external magnetic field is determined solving the Maxwell–London equations by standard mathematical methods, which formally explain the ansatz used in a number of textbooks.
Perturbation theory applied to sound propagation in flowing media confined by a cylindrical waveguide
Authors: Willatzen M.
Published: July 2002

First-order perturbation theory is employed to examine sound propagation in flowing media confined by a cylindrical waveguide. The use of perturbation theory allows examination of mode phase-speed changes due to any radially dependent flow w(r) as long as the flow magnitude is sufficiently small. The condition to be fulfilled is satisfied in the flow range: 0–0.3 m/s for the specific values of cylinder radius, ultrasound frequency, and sound speed analyzed in the present work [in the general case, however, the condition in Eq. (1) of the present work must be fulfilled]. This freedom of choice, i.e., the possibility to handle any radial flow profile, is used to analyze two flow profile cases: (1) where w(r) is a linear combination of a laminar flow profile and a flat profile corresponding to turbulent flow, and (2) where w(r) is a linear combination of a laminar flow profile and a more realistic logarithmic-dependent turbulent flow profile. In both cases, it is shown that large errors may result in ultrasound flow measurements if several modes are excited by the transmitting transducer, and that a logarithmic flow profile in the turbulent regime leads to somewhat larger measurement errors at high flow values as compared to assuming a simple flat profile in the turbulent regime.
On the sound sources of screech tones radiated from choked circular jets
Authors: Umeda Yoshikuni , Ishii Ryuji
Published: July 2002

The generation mechanism of the screech tone in the helical oscillation mode is mainly investigated using a series of instantaneous schlieren photographs. From the photographs, five evanescent sound sources are observed as prominent points along the jet axis. The sound source for the dominant helical oscillation mode is found to be the second prominent point which moves along a circular orbit in a plane perpendicular to the jet axis and just downstream of the rear edge of the third shock cell. It is shown that the speed of a moving sound source is supersonic and that the Mach cone generated by the moving sound source forms the helical-shaped wave front of the screech tone for the helical oscillation mode of the jet. This idea of the moving sound source is well supported by a measured directionality of the screech tone. Sound sources of the other oscillation modes appearing in the other pressure ratio ranges are also described.
Experimental evaluation of leaky least-mean-square algorithms for active noise reduction in communication headsets
Authors: Cartes David A. , Ray Laura R. , Collier Robert D.
Published: July 2002

An adaptive leaky normalized least-mean-square (NLMS) algorithm has been developed to optimize stability and performance of active noise cancellation systems. The research addresses LMS filter performance issues related to insufficient excitation, nonstationary noise fields, and time-varying signal-to-noise ratio. The adaptive leaky NLMS algorithm is based on a Lyapunov tuning approach in which three candidate algorithms, each of which is a function of the instantaneous measured reference input, measurement noise variance, and filter length, are shown to provide varying degrees of tradeoff between stability and noise reduction performance. Each algorithm is evaluated experimentally for reduction of low frequency noise in communication headsets, and stability and noise reduction performance are compared with that of traditional NLMS and fixed-leakage NLMS algorithms. Acoustic measurements are made in a specially designed acoustic test cell which is based on the original work of Ryan et al. [“Enclosure for low frequency assessment of active noise reducing circumaural headsets and hearing protection,” Can. Acoust. 21, 19–20 (1993)] and which provides a highly controlled and uniform acoustic environment. The stability and performance of the active noise reduction system, including a prototype communication headset, are investigated for a variety of noise sources ranging from stationary tonal noise to highly nonstationary measured F-16 aircraft noise over a 20 dB dynamic range. Results demonstrate significant improvements in stability of Lyapunov-tuned LMS algorithms over traditional leaky or nonleaky normalized algorithms, while providing noise reduction performance equivalent to that of the NLMS algorithm for idealized noise fields.
Incorporating linear viscoelasticity into acoustic scattering theory
Authors: Hipp Alexander K. , Adjadj Laurent P. , Storti Giuseppe , Morbidelli Massimo
Published: July 2002

The scattering theory of Epstein and Carhart [J. Acoust. Soc. Am. 25, 553–565 (1953)] and Allegra and Hawley [J. Acoust. Soc. Am. 51, 1545–1564 (1972)] is a well-established approach for the prediction of the acoustic attenuation and sound speed in suspensions and emulsions. The original theory assumes that each phase is either an elastic solid or a Newtonian liquid; incorporation of other rheological behavior generally requires rederivation of the model equations. An exception is the case of linear viscoelasticity: using a suitable stress–strain relation, the original model equations also hold for this case. In this work, it is shown that Ḡ*=G′−iG″, where G′ and G″ are the storage and loss moduli of a viscoelastic material, is analogous to the shear modulus G (elastic solids) and −iωη (Newtonian liquids). Viscoelasticity can thus be introduced simply by using Ḡ* in place of G.
An investigation of the small slope approximation for scattering from rough surfaces. Part II. Numerical studies
Authors: Broschat Shira Lynn , Thorsos Eric I.
Published: July 2002

The small slope approximation (SSA) of Voronovich [Sov. Phys. JETP 62, 65–70 (1985)] is a promising method for modeling wave scattering from rough surfaces. The SSA T-matrix series, which can be interpreted as an expansion in a generalized surface slope, satisfies the appropriate reciprocity condition at each order and reduces to the standard perturbation series for small surface roughness. When the SSA T matrix is found to second order in generalized slope, it reduces to that of the Kirchhoff approximation as the frequency is increased. In an earlier paper [E. I. Thorsos and S. L. Broschat, J. Acoust. Soc. Am. 97, 2082–2093 (1995)] the derivation of the SSA for surfaces subject to the Dirichlet boundary condition was examined in detail. In this paper the accuracy of the SSA for the Dirichlet problem is investigated through comparison with exact results. Expressions for the first three terms of the SSA incoherent bistatic scattering cross-section series are presented, followed by numerical results for one-dimensional surfaces with Gaussian statistics and a Gaussian roughness spectrum. Surfaces with rms slope angles up to 45° are considered. It is found that, for the numerous cases studied, the SSA results agree well with the exact results over a broad range of scattering angles. When the lowest-order results are inaccurate, successive addition of each higher-order term generally yields improvement. The range of scattering angles over which the SSA results are accurate depends on both the rms slope angle and the surface correlation length, as well as on the angle of incidence. A simple rule of thumb, however, is that for an incident angle of 45°, the highest-order SSA scattering cross section examined here is accurate to within ±1 dB from backscatter to a forward grazing angle of 5° for rms slope angles less than about 30°. When the surface roughness is such that perturbation theory is accurate, the SSA is accurate over the full range of scattering angles for small to moderate slopes.
Low Strouhal number instabilities of flow over apertures and wall cavities
Authors: Howe M. S.
Published: July 2002

A theory is developed to predict the frequency of self-sustained oscillations of flow over an aperture in a plane wall and over a shallow wall cavity. The Mach number is sufficiently small that motion in the aperture or cavity may be regarded as incompressible. The shear layer thickness is small enough to permit it to be modeled by a vortex sheet, which is taken to be linearly disturbed from its equilibrium planar form. The motion of this sheet is discussed for circular and rectangular wall apertures, and numerical predictions are given for the Rayleigh conductivity KR(ω) as a function of the radian frequency ω of the motion. Instabilities of the aperture flow are determined by poles of KR(ω) in the upper complex frequency plane, and it is argued that the real parts of these complex frequencies correspond to the Strouhal numbers of self-sustained oscillations. An approximate method is given for determining the pole that corresponds to the minimum frequency, self-sustained oscillation. For incompressible flow there can be no net volume flux into a shallow wall cavity, and oscillations are in this case related to poles of a frequency-dependent drag coefficient. The predicted minimum Strouhal number for the cavity is close to measured values for the first stage of self-sustained oscillations of wall apertures and shallow cavities at very low Mach number.
Interactions among F0, duration, and amplitude in the perception of focus
Authors: Bunnell H. Timothy , Hoskins Steven R. , Yarrington Debra
Published: July 2002

F0, amplitude, and durational cues are considered the primary acoustic correlates of focus or sentence-level stress. However, questions remain regarding: (a) the degree to which each of these cues are necessary or sufficient for signaling focus; (b) the relative importance of each of these cues; and (c) how they interact in the perception of focus. Natural productions of the sentence ‘‘Bob bought Bogg’s box,’’ in which focus was varied over each of the four words of the sentence were altered to produce prosodic cue neutralized versions. The alterations were applied singly and in all possible combinations to form eight experimental versions of each original sentence (the original and seven cue-neutralized versions). The sentences were presented to listeners with the task of identifying the focused item in the sentence. Results indicated that: (a) neutralizing any acoustic cue produced some degradation in performance, but even with all cues nullified, performance remained above chance for at least some words; (b) overall, F0 was more important than either amplitude or duration in signaling focus; and (c) F0 was more important early in the sentence while amplitude and duration played relatively more prominent roles late in the sentence. [Work supported by NIDRR and Nemours.]
Measurement of acoustic stop bands in two-dimensional periodic scattering arrays
Authors: Robertson W. M. , Rudy J. F.
Published: July 2002

The experimental observation of acoustic stop bands in two-dimensional periodic arrays using an impulse response technique is reported. The frequencies of the stop-band centers are consistent with simple theoretical considerations based on the spacing between layers along the high symmetry directions of the regular arrays. The phase information extracted from the Fourier analysis is used to construct the acoustic dispersion relation for frequencies above and below the stop band. Measurements are reported for both square and triangular scattering arrays.
Phantom echo generation: A new technique for investigating dolphin echolocation
Authors: Aubauer Roland , Au Whitlow W. L.
Published: July 2002

In behavioral experiments where real targets are used to investigate dolphin echolocation, it is often very difficult to extract the relevant echo parameters that the animals use to discriminate or classify. The complex relationship between the physical dimensions and the reflection characteristic of real targets prevents separate control of various echo parameters of the stimuli presented in an echolocation experiment. A new echo simulation method presented in this paper avoids this problem. Dolphin echolocation sounds are transformed with the target impulse response into artificial echoes, which are played back to the animal. The phantom echo system is implemented on a digital signal processing board and gives an experimenter fully programmable control over the echo generating process and the echo structure itself. Echoes of several underwater targets were simulated to evaluate the quality of the method. A comparison of simulated echoes with the original echoes demonstrated very good agreement independent of the incident signal (cross-correlation coefficient >0.95). The method has tremendous potential for investigating animal echolocation and understanding biosonar signal processing.
Near-caustic behavior in a 270-km acoustical experiment
Authors: Simmen Jeffrey A. , Flatté Stanley M. , DeFerrari Harry A. , Nguyen Hien , Williams Neil J.
Published: July 2002

Data from a pulse-propagation experiment are analyzed to quantify fluctuations in the transmitted acoustic signal. In the experiment a bottom-moored, broadband source having a 460-Hz center frequency transmitted 273 km away to a bottom-moored, vertical hydrophone array spanning 180 m of the water column. Pulses were transmitted every 12 min for a total duration of nearly 100 h. Because the minimal hydrophone separation at the receiving array was less than 2 m, vertical behavior on small scales could be observed. Furthermore, the vertical position of the receiving array enabled an examination of the near-caustic portion of wavefronts, and in some cases, the caustics themselves. Unfortunately, because instrument motion measurements were unsuccessful, relative rather than absolute signal fluctuations were the principal observable in this analysis.
Steady-state air-flow and acoustic measurement of the resistivity of loose granular materials
Authors: Iannace Gino , Ianniello Carmine , Maffei Luigi , Romano Rosario
Published: July 2002

In the course of a study for characterizing the acoustic properties of some loose granulates made of limestone chips, the authors have measured their resistivity in a very simple way by a steady-state air-flow technique. The results of these tests are compared with the corresponding values obtained by an acoustic technique. The latter relies on the assumption that at very low frequencies the real part of the normal-incidence flow impedance of a thin porous layer is very close to its steady-state air-flow resistance. The measurements results confirmed the above mentioned assumption to a certain degree. To the knowledge of the authors, no previous comparison of steady-state air-flow versus oscillating air-flow measurement of the resistivity of the considered granulates has been published yet.
The use of partially measured source data in near-field acoustical holography based on the BEM
Authors: Kang Sung-Chon , Ih Jeong-Guon
Published: July 2002

In applying the conformal near-field acoustical holography (NAH) to actual source identification problems, it is often possible to determine the velocity at certain points of the source surface in advance. This partially known velocity data would reduce the problem size and permit better reconstruction accuracy. In this paper, the effectiveness of using partially measured source data in the conformal NAH is investigated, which uses the boundary element method. A vibro-acoustic transfer matrix and measured field pressure data, which is involved with the boundary integral equation, are reorganized in order to deal with the partially measured surface velocities. For a baffled vibrating panel, simulations were performed by varying the number of velocity-known nodes. In addition, the effect of measurement error is investigated for two extreme positioning methods of velocity-known nodes. Without regularization, the reconstructed error can be reduced considerably by employing some of the source data and this error can be further reduced by increasing those surface points. However, the velocity reconstruction error is not reduced substantially when the number of velocity-known nodes is less than 30%–40% of the total nodes. The reduction in the reconstruction error is not large if the regularization technique is applied to the restored field.
A review of active control of combustion instabilities
Authors: Zinn Ben T.
Published: July 2002

This paper presents an overview of active control of combustion instabilities. First, the paper will use a simple model to present the rationale that motivated the development of active control systems (ACS) for unstable combustors. Next, the design and performance of earlier ACS will be discussed to identify control system components and control approaches that offer the most promise for practical applications. The bulk of the paper will discuss active control research at Georgia Tech, conducted by the author and colleagues. It will describe the architecture of the developed ACS, adaptive and nonadaptive active control approaches, and the performance of critical ACS components. Emphasis will be placed upon the performance of the observer that determines the state of the unstable combustor in real time and the fuel injector actuator that can modulate the injection rate of a fuel stream over a wide frequency range (e.g., 0–2000 Hz). This will be followed by descriptions of the performance of this ACS under different modes of operation when applied to different combustors. These results will show that the developed ACS can rapidly damp combustion instabilities whose characteristics vary with time and are not known a priori. The paper will close with a discussion of needed research and development efforts.
Auditory perception of objects by blind persons, using a bioacoustic high resolution air sonar
Authors: Kay Leslie
Published: July 2002

A high-resolution octave band air sonar for spatial sensing and object imaging by blind persons is described. The system has wide-angle overlapping peripheral fields of view with a narrow central field superposed. It is noninvasively coupled to the auditory system for neural processing and spatial imaging. Blind persons learn to comprehend the auditory cortical multiple-object image that is created. The real-time synchronous relationship between hearing a change in the sensor sounds and the sensed motor actions causing the change seems to aid the learning process. Computer based testing of the sensor system is described so as to relate the physical system performance with the time-varying human auditory perception. This is so that the basic psychometric experiments studying the sensor bio-acoustic spatial resolution, resulting from the superposition of two wide-angle peripheral fields with one central narrow field, may be better understood. These tests confirm that the auditory ability of subjects to resolve close objects using the combined fields is significantly improved relative to using the peripheral fields alone. These measurements are supported by blind children learning to use the sensor system.
Intrinsic Errors in Pressure-Hole Measurements
Authors: Tanner R. I. , Pipkin A. C.
Published: July 2002

A convenient way of measuring normal thrusts on fluid-immersed surfaces is by use of a pressure gauge attached to a hole in the surface. With viscoelastic fluids exhibiting normal stress effects, it is shown that a systematic error exists, independent of hole size, but dependent on wall shear stress. Experiments were made in an open channel with various holes from 132 in. to 14 in. diameter, and also with an 18 in. wide slot. Errors were small with 30P silicone fluid, but with two viscoelastic solutions errors were always negative and of the order of 25% of the first normal stress difference. No significant difference has been seen yet between sharp-edged holes of different sizes or between holes and slots. A theoretical treatment for plane creeping flow over a deep slot predicts that the error is negative, independent of slot width, and 25% of the first normal stress difference. Some implications for normal stress measurements are considered.
The continuous chain model for the elastic extension of polymer fibers in the glassy state
Authors: Baltussen J. J. M. , Northolt M. G. , van der Hout R.
Published: July 2002

Fibers of linear polymers below the glass transition show a strong nonlinear deformation behavior even at small strains. The elastic modulus is a fast increasing function of the strain. A new model for the description of the deformation of these fibers is presented. It is assumed that the fiber consists of long and continuous polymer chains which do not break during the extension of the fiber. The deformation of the fiber is calculated for finite strains and arbitrary values of the orientation parameter. Equations for the elastic stress versus strain curve and modulus versus strain curve have been derived. The model can be used for the calculation of the modulus of isotropic fibers and sheets with uniplanar orientation as well.
Evaluating dosimetric accuracy of the 6 MV calibration on EBT3 film in the use of Ir‐192 high dose rate brachytherapy
Authors: Huang Lyu , Gaballa Hani , Chang Jenghwa
Published: February 2022

Purpose

To evaluate the dosimetric accuracy of EBT3 film calibrated with a 6 MV beam for high dose rate brachytherapy and propose a novel method for direct film calibration with an Ir‐192 source.

Methods

The 6 MV calibration was performed in water on a linear accelerator (linac). The Ir‐192 calibration was accomplished by irradiating the film wrapped around a cylinder applicator with an Ir‐192 source. All films were scanned 1‐day post‐irradiation to acquire calibration curves for all three (red, blue, and green) channels. The Ir‐192 calibration films were also used for single‐dose comparison. Moreover, an independent test film under a H.A.M. applicator was irradiated and the 2D dose distribution was obtained separately for each calibration using the red channel data. Gamma analysis and point‐by‐point profile comparison were performed to evaluate the performance of both calibrations. The uncertainty budget for each calibration system was analyzed.

Results

The red channel had the best performance for both calibration systems in the single‐dose comparison. We found a significant 4.89% difference from the reference for doses <250 cGy using the 6 MV calibration, while the difference was only 0.87% for doses >600 cGy. Gamma analysis of the 2D dose distribution showed the Ir‐192 calibration had a higher passing rate of 91.9% for the 1 mm/2% criterion, compared to 83.5% for the 6 MV calibration. Most failing points were in the low‐dose region (<200 cGy). The point‐by‐point profile comparison reported a discrepancy of 2%–3.6% between the Ir‐192 and 6 MV calibrations in this low‐dose region. The linac‐ and Ir‐192‐based dosimetry systems had an uncertainty of 4.1% (k = 2) and 5.66% (k = 2), respectively.

Conclusions

Direct calibration of EBT3 films with an Ir‐192 source is feasible and reliable, while the dosimetric accuracy of 6 MV calibration depends on the dose range. The Ir‐192 calibration should be used when the measurement dose range is below 250 cGy.
Damage Trajectories in Systemic Sclerosis Using Group‐Based Trajectory Modeling
Authors: Barbacki Ariane , Baron Murray , Wang Mianbo , Zhang Yuqing , Stevens Wendy , Sahhar Joanne , Proudman Susanna , Nikpour Mandana , Man Ada ,   the Australian Scleroderma Interest Group and the Canadian Scleroderma Research Group
Published: February 2022

Objective

Systemic sclerosis (SSc) is an autoimmune disease characterized by progressive organ damage, which can be measured using the Scleroderma Clinical Trials Consortium Damage Index (SCTC‐DI). We aimed to identify whether distinct trajectories of damage accrual exist and to determine which variables are associated with different trajectory groups.

Methods

Incident cases of SSc (<2 years) were identified in the Australian Scleroderma Interest Group and Canadian Scleroderma Research Group prospective registries. Group‐based trajectory modeling was used to identify SCTC‐DI trajectories over the cohort's first 5 annual visits. Baseline variables associated with trajectory membership in a univariate analysis were examined in multivariable models.

Results

A total of 410 patients were included. Three trajectory groups were identified: low (54.6%), medium (36.2%), and high (10.3%) damage. Patients with faster damage accrual had higher baseline SCTC‐DI scores. Older age (odds ratio [OR] 1.57 [95% confidence interval (95% CI) 1.18–2.10]), male sex (OR 2.55 [95% CI 1.10–5.88]), diffuse disease (OR 6.7 [95% CI 2.57–17.48]), tendon friction rubs (OR 5.4 [95% CI 1.86–15.66]), and elevated C‐reactive protein level (OR 1.98 [95% CI 1.49–2.63]) increased the odds of being in the high‐damage group versus the reference (low damage), whereas White ethnicity (OR 0.31 [95% CI 0.12–0.75]) and anticentromere antibodies (OR 0.24 [95% CI 0.07–0.77]) decreased the odds.

Conclusion

We identified 3 trajectories of damage accrual in a combined incident SSc cohort. Several characteristics increased the odds of belonging to worse trajectories. These findings may be helpful in recognizing patients in whom early aggressive treatment is necessary.
Tribovoltaic Nanogenerators Based on MXene–Silicon Heterojunctions for Highly Stable Self‐Powered Speed, Displacement, Tension, Oscillation Angle, and Vibration Sensors
Authors: Luo Xiongxin , Liu Lindong , Wang Yi‐Chi , Li Jiayu , Berbille Andy , Zhu Laipan , Wang Zhong Lin
Published: February 2022

Tribovoltaic nanogenerators (TVNGs), an emerging high‐entropy energy harvesting technique, present great features such as low matching resistance, high current density, and continuous output performance. Here, an MXene layer and a semiconducting silicon wafer are assembled into a tribovoltaic nanogenerator (named MS‐TVNG). The output peak current of the MS‐TVNG reaches up to 22 µA for a P‐type (0.1–0.5 Ω cm) silicon wafer under a normal force of 4.56 N and a sliding speed of 2 m s−1. Owing to the unique metal characteristics of the MXene layer, the performance is superior to those previously reported TVNGs using traditional metals. The layered structure of MXene endows the real‐time MS‐TVNG with outstanding wear‐resistance and stable output properties. The performance of the MS‐TVNG can be tuned by the doping type and concentration of the silicon wafer, as well as by the pressure and the relative sliding speed between two friction surfaces. The MS‐TVNG has proven to be a solid foundation for high‐performance self‐powered speed sensors and has excellent potentials for applications in displacement, tension, oscillation angle, and vibration detection.
Bilayer Lubricant‐Infused Particulate Films as Slippery Protective Coatings with Durable Anticorrosion and Antifouling Performance
Authors: Chien Chih‐Hsuan , Chen Ting‐Lun , Wu Xiao‐Yan , Chen Yi‐Chen , Lee Pin‐Yan , Lin Lu‐Yin , Wang Wei‐Lung , Hsueh Han‐Yu
Published: February 2022

In this study, durable slippery colloidal coatings are created through the infiltration of particulate films with bilayer lubricant; the coatings exhibit remarkable surface‐protective performance, including anticorrosion, antifouling, self‐healing, anti‐icing, and self‐cleaning properties. Materials with low surface energy, namely polytetrafluoroethylene or polydimethylsiloxane, are used to form micelle dispersions, with particulate films then obtained through spray coating. In particular, the thermally driven viscous surfactants can serve as a bottom adhesive primer after thermal treatment, which significantly improve durability. After lubricant infusion as a top protective layer, bilayer lubricant‐infused slippery coatings are obtained without a complex hole‐making process being required. The anticorrosion and antifouling performance of colloid coatings infused with various functional lubricants—ionic liquid, silicone oil, and perfluoropolyether oils—is investigated. This study is the first to create bilayer lubricant‐infused colloid‐based surface systems (i.e., primer and protective lubricants) as protective coatings. The coatings can be employed in various applications, such as fuel transport, self‐cleaning windows, anticorrosion protection, nontoxic coatings for medical devices, and optical instruments.
In Situ Fabrication, Manipulation, and Mechanical Characterization of Free‐Standing Silica Thin Films Using Focused Ion Beam Scanning Electron Microscopy
Authors: Soleimani Mohammad , Maddala Sai P. , Wismans Martijn , Liao Wei‐Chih , van Breemen Lambèrt C. A. , van Benthem Rolf A. T. M. , Friedrich Heiner
Published: February 2022

Determination of mechanical properties of (silica) thin films is important for the development of new applications. However, a versatile approach for small‐scale sample fabrication and in situ mechanical testing of these materials is currently lacking which can overcome the existing difficulties in conventional testing approaches. Here, it is shown that by combining focused ion beam scanning electron microscopy (FIB‐SEM) with micromanipulators free‐standing silica beams of the desired dimensions can be fabricated. Using in situ bending tests on such beams inside the SEM and finite element method simulations, the Young's modulus of thin‐film silica and the effects of gallium ion beam radiation on Young's modulus are determined. Furthermore, the effects of controlled relative humidity on the mechanical behavior of silica beams are investigated. The demonstrated FIB‐SEM approach can be extended to other materials and preparation conditions to measure, model, and optimize mechanical properties of thin films for a wide range of (coating) applications.
Ultrasensitive Detection of Heavy Metal Ions with Scalable Singular Phase Thin Film Optical Coatings
Authors: Rao Anirudha R. , Sreekanth Kandammathe Valiyaveedu , Sreejith Sivaramapanicker , Jose Vishal , Pethe Shreyas , Singh Ranjan
Published: February 2022

Identification of spectroscopically silent heavy‐metal ions in environmental and bio‐analytical samples has gained immense importance. Lowering the limit of detection of these ions at low concentrations is crucial for biomedicine and food safety applications. Optical chemical sensors have shown great potential in improving the sensing solutions for heavy‐metal ions because of their fast and label‐free detection capabilities. However, achieving high sensitivity without compromising on scalability and simplicity is challenging. Here, we experimentally demonstrate the detection of heavy metal ions at ultralow concentrations using lithography‐free scalable thin film optical coatings that show singular behavior of phase of light at the point‐of‐darkness. Since the phase‐sensitive optical techniques have shown superior sensitivity over traditional sensing techniques based on spectroscopy, we use this extreme phase change to detect zinc ions concentration down to femtomolar. In particular, it allows us to monitor very small changes in refractive index due to the real‐time binding of zinc ions on a poly (lactic‐co‐glycolic acid) functionalized sensor surface. This cost‐effective extreme sensitivity sensing platform can be used for the label‐free detection of various heavy metal ions by properly functionalizing the sensor surface.
Stimuli‐Responsive Antibacterial Materials: Molecular Structures, Design Principles, and Biomedical Applications
Authors: Wang Xianghong , Shan Mengyao , Zhang Shike , Chen Xin , Liu Wentao , Chen Jinzhou , Liu Xuying
Published: February 2022

Infections are regarded as the most severe complication associated with human health, which are urgent to be solved. Stimuli‐responsive materials are appealing therapeutic platforms for antibacterial treatments, which provide great potential for accurate theranostics. In this review, the advantages, the response mechanisms, and the key design principles of stimuli‐responsive antibacterial materials are highlighted. The biomedical applications, the current challenges, and future directions of stimuli‐responsive antibacterial materials are also discussed. First, the categories of stimuli‐responsive antibacterial materials are comprehensively itemized based on different sources of stimuli, including external physical environmental stimuli (e.g., temperature, light, electricity, salt, etc.) and bacterial metabolites stimuli (e.g., acid, enzyme, redox, etc.). Second, structural characteristics, design principles, and biomedical applications of the responsive materials are discussed, and the underlying interrelationships are revealed. The molecular structures and design principles are closely related to the sources of stimuli. Finally, the challenging issues of stimuli‐responsive materials are proposed. This review will provide scientific guidance to promote the clinical applications of stimuli‐responsive antibacterial materials.
Static and Dynamic Disorder of Charge Transfer States Probed by Optical Spectroscopy
Authors: Kahle Frank‐Julian , Rudnick Alexander , Wedler Stefan , Saxena Rishabh , Ammenhäuser Robin , Scherf Ullrich , Bagnich Sergey , Bässler Heinz , Köhler Anna
Published: February 2022

Since the key role of charge transfers (CT) states has been identified for organic solar cells (OSCs), research into their properties is a timely topic. Conventionally, their absorption and emission spectra are described in terms of Marcus’ electron transfer theory. This is a single site approach with the essential parameter being the reorganization energy. Thus, it ignores ensemble effects, notably the role of static disorder that is inevitably present in a spin‐coated OSC film. Here time dependent photoluminescence spectroscopy is applied on blends of the polymeric donor MeLPPP with either the non‐fullerene acceptor SF‐PDI2 or with PC61BM within a temperature range from 295 to 5 K. The authors monitor how initially excited singlet states are converted to emissive CT states. Concomitantly, emission from residual singlets on the acceptor is observed rather than hybrid CT‐states. The role of spectral diffusion in this process is discussed. From the temperature and time dependent linewidths of absorption, fluorescence, and CT emission, the static and dynamic contributions to the total disorder are inferred. In both blends, at 295 K, the contribution of static disorder is comparable to the dynamic disorder.
Pd‐Catalyzed Chemoselective Bis‐Allylic Substitution of Allylic Dicarbonates with Arylated Nitromethanes: A Route to 1,2‐Oxazine N‐Oxides
Authors: Zhao Can , Li Tao , Khan Ijaz , Zhang Yong Jian
Published: February 2022

An efficient method for the construction of 1,2‐oxazine N‐oxides has been developed via Pd‐catalyzed chemoselective bis‐allylic substitution of 2‐methylenepropane‐1,3‐diol dicarbonates with arylated nitroalkanes through sequential C‐ and O‐nucleophilic allylic substitution in one‐pot manipulation. By using Pd(PPh3)4 as a catalyst under mild reaction conditions, the process allows rapid access to 3‐aryl‐5,6‐dihydro‐4H‐1,2‐oxazine N‐oxides in high yields with excellent chemoselectivities.
Remote blood collection from older adults in the Brain Health Registry for plasma biomarker and genetic analysis
Authors: Fockler Juliet , Ashford Miriam T. , Eichenbaum Joseph , Howell Taylor , Ekanem Aniekan , Flenniken Derek , Happ Alexander , Truran Diana , Mackin R. Scott , Blennow Kaj , Halperin Eran , Coppola Giovanni , Weiner Michael W. , Nosheny Rachel L.
Published: February 2022

Introduction

Use of online registries to efficiently identify older adults with cognitive decline and Alzheimer's disease (AD) is an approach with growing evidence for feasibility and validity. Linked biomarker and registry data can facilitate AD clinical research.

Methods

We collected blood for plasma biomarker and genetic analysis from older adult Brain Health Registry (BHR) participants, evaluated feasibility, and estimated associations between demographic variables and study participation.

Results

Of 7150 participants invited to the study, 864 (12%) enrolled and 629 (73%) completed remote blood draws. Participants reported high study acceptability. Those from underrepresented ethnocultural and educational groups were less likely to participate.

Discussion

This study demonstrates the challenges of remote blood collection from a large representative sample of older adults. Remote blood collection from > 600 participants within a short timeframe demonstrates the feasibility of our approach, which can be expanded for efficient collection of plasma AD biomarker and genetic data.
Cystine Knot Peptides with Tuneable Activity and Mechanism
Authors: Li Choi Yi , Rehm Fabian B. H. , Yap Kuok , Zdenek Christina N. , Harding Maxim D. , Fry Bryan G. , Durek Thomas , Craik David J. , de Veer Simon J.
Published: February 2022

Knottins are topologically complex peptides that are stabilised by a cystine knot and have exceptionally diverse functions, including protease inhibition. However, approaches for tuning their activity in situ are limited. Here, we demonstrate separate approaches for tuning the activity of knottin protease inhibitors using light or streptavidin. We show that the inhibitory activity and selectivity of an engineered knottin can be controlled with light by activating a second mode of action that switches the inhibitor ON against new targets. Guided by a knottin library screen, we also identify a position in the inhibitor's binding loop that permits insertion of a biotin tag without impairing activity. Using streptavidin, biotinylated knottins with nanomolar affinity can be switched OFF in activity assays, and the anticoagulant activity of a factor XIIa inhibitor can be rapidly switched OFF in human plasma. Our findings expand the scope of engineered knottins for precisely controlling protein function.
Catalytic Enantioselective Pictet–Spengler Reaction of α‐Ketoamides Catalyzed by a Single H‐Bond Donor Organocatalyst
Authors: Andres Rémi , Wang Qian , Zhu Jieping
Published: February 2022

The asymmetric Pictet–Spengler reaction (PSR) with aldehydes is well known. However, PSR involving ketones as electrophilic partners is far‐less developed. We report herein the first examples of catalytic enantioselective PSR of tryptamines with α‐ketoamides. A new class of easily accessible prolyl‐urea organocatalysts bearing a single H‐bond donor function catalyzes the title reaction to afford 1,1‐disubstituted tetrahydro‐β‐carbolines in excellent yields and enantioselectivities. The kinetic isotope effect using C2‐deuterium‐labelled tryptamine indicates that the rearomatization of the pentahydro‐β‐carbolinium ion intermediate might be the rate‐ and the enantioselectivity‐determining step.
Site‐Specific Protein Modification with Reducing Carbohydrates
Authors: Wu Qifan , Dong Weidong , Miao Hui , Wang Qian , Dong Suwei , Xuan Weimin
Published: February 2022

Protein glycosylation plays critical roles in many biological processes. However, the fundamental study and application of glycobiology are hindered by the heterogeneousness of oligosaccharides in natural glycoproteins and the difficulty in constructing glycoproteins of human design. Herein, we describe a semisynthetic method to site‐specifically modify proteins with reducing carbohydrates. The method involves the genetic incorporation of a side‐chain‐esterified aspartate, which was subsequently quantitatively converted into alanine‐β‐hydrazide (Aβz), and chemoselective conjugation of Aβz with a range of readily available reducing carbohydrates. The resulting Aβz‐linked GlcNAc is a close mimic of native N‐GlcNAc and could be installed on various proteins, including IL‐17A and RNase A. Notably, Aβz‐linked GlcNAc on proteins reacted with biantennary oligosaccharide oxazoline derivatives through endoglycosidase‐catalyzed transglycosylation reactions to enable the assembly of homogeneous glycans on proteins.
Host‐Assisted Delivery of a Model Drug to Genomic DNA: Key Information from Ultrafast Spectroscopy and in silico Study
Authors: Ghosh Ria , Singh Soumendra , Mukherjee Dipanjan , Mondal Susmita , Das Monojit , Pal Uttam , Adhikari Aniruddha , Bhushan Aman , Bose Surajit , Bhattacharyya Siddharth Sankar , Pal Debasish , Saha‐Dasgupta Tanusri , Bhattacharyya Maitree , Bhattacharyya Debasis , Mallick Asim Kumar , Das Ranjan , Pal Samir Kumar
Published: February 2022

Drug delivery to a target without adverse effects is one of the major criteria for clinical use. Herein, we have made an attempt to explore the delivery efficacy of SDS surfactant in a monomer and micellar stage during the delivery of the model drug, Toluidine Blue (TB) from the micellar cavity to DNA. Molecular recognition of pre‐micellar SDS encapsulated TB with DNA occurs at a rate constant of k1 ∼652 s−1. However, no significant release of encapsulated TB at micellar concentration was observed within the experimental time frame. This originated from the higher binding affinity of TB towards the nano‐cavity of SDS at micellar concentration which does not allow the delivery of TB from the nano‐cavity of SDS micelles to DNA. Thus, molecular recognition controls the extent of DNA recognition by TB which in turn modulates the rate of delivery of TB from SDS in a concentration‐dependent manner.
A Combined Sodium Intercalation and Copper Extrusion Mechanism in the Thiophosphate Family: CuCrP2S6 as Anode Material in Sodium‐Ion Batteries
Authors: van Dinter Jonas , Grantz David , Bitter Alexander , Bensch Wolfgang
Published: February 2022

The layered hypothiophosphate CuCrP2S6 was identified as promising candidate for the application as anode in sodium‐ion batteries exhibiting an appropriate electrochemical performance (409 mAh g−1 after 200 cycles @ 1 A g−1). The electrochemical long‐term experiments suggest that the reaction mechanism changed upon repeated discharging and charging. The initial discharge and charge process was studied by X‐ray diffraction evidencing that at the early discharge stages, Na+ was intercalated into the interlayer space accompanied by a simultaneous reduction of Cu+ to metallic Cu, which was extruded from the host. At later stages of discharge, a conversion of the intermediate phase to Cu0, amorphous Cr0 and P0 embedded in nanocrystalline Na2S occurred. After recharging, only reflections of nanocrystalline NaF could be identified, which is part of the generated solid electrolyte interphase (SEI) layer. In contrast to observation made in literature, elemental Cu seems to be oxidized during the charge process again.