bluuebunny/crossref_metadata_2025 huggingface dataset:
Exposure and dose in panoramic radiology
Authors: Goldstein Albert
Published: July 2002

Panoramic radiology entrance skin exposure (ESE) was measured for a Siemens Orthopantomograph 10 E using a thimble chamber and TLDs. Thimble chamber measurements are shown to be inaccurate for the moving, narrow beam panoramic scan geometry due to partial volume and partial charged‐particle equilibrium effects. For 75 KVp, 8 mA panoramic scans the TLD measured beam central ray ESE on the scan central plane (patient midsagittal plane) was an approximately constant 20 mR for the first 7.5 cm from the entrance slit. A theoretical model of central plane ESE for a fixed rotation center agrees very well with the TLD measurements and is consistent with all of the known ESE (and dose) properties near rotation centers. Head phantom skin dose measurements demonstrate the dependence of skin dose on exact equipment mode of use and patient anatomy. Central plane, beam central ray ESE is judged to be a convenient, universal measure of panoramic radiology radiation output.
Computerized analysis of breast lesions in three dimensions using dynamic magnetic‐resonance imaging
Authors: Gilhuijs Kenneth G. A. , Giger Maryellen L. , Bick Ulrich
Published: July 2002

Contrast‐enhanced magnetic resonance imaging (MRI) of the breast is known to reveal breast cancer with higher sensitivity than mammography alone. The specificity is, however, compromised by the observation that several benign masses take up contrast agent in addition to malignant lesions. The aim of this study is to increase the objectivity of breast cancer diagnosis in contrast‐enhanced MRI by developing automated methods for computer‐aided diagnosis. Our database consists of 27 MR studies from 27 patients. In each study, at least four MR series of both breasts are obtained using FLASH three‐dimensional (3D) acquisition at 90 s time intervals after injection of Gadopentetate dimeglumine (Gd‐DTPA) contrast agent. Each series consists of 64 coronal slices with a typical thickness of 2 mm, and a pixel size of 1.25 mm. The study contains 13 benign and 15 malignant lesions from which features are automatically extracted in 3D. These features include margin descriptors and radial gradient analysis as a function of time and space. Stepwise multiple regression is employed to obtain an effective subset of combined features. A final estimate of likelihood of malignancy is determined by linear discriminant analysis, and the performance of classification by round‐robin testing and receiver operating characteristics (ROC) analysis. To assess the efficacy of 3D analysis, the study is repeated in two‐dimensions (2D) using a representative slice through the middle of the lesion. In 2D and in 3D, radial gradient analysis and analysis of margin sharpness were found to be an effective combination to distinguish between benign and malignant masses (resulting area under the ROC curve: 0.96). Feature analysis in 3D was found to result in higher performance of lesion characterization than 2D feature analysis for the majority of single and combined features. In conclusion, automated feature extraction and classification has the potential to complement the interpretation of radiologists in an objective, consistent, and accurate way.
Half‐value layer and intensity variations as a function of position in the radiation field for film‐screen mammography
Authors: Terry James A. , Waggener Robert G. , Miller Blough Melissa A.
Published: July 2002

Differences in half‐value layer (HVL) and radiation intensity are investigated as a function of position in the mammographic radiation field. Sources of systematic variation include the heel effect, the inverse square law, and differential photon path lengths through thicknesses of inherent and added filtration. The combination of these effects can increase the HVL by as much as 9% and reduce intensity by as much as 40% along the cathode‐anode axis. To the left and right of the x‐ray field central axis, reductions in radiation intensity of up to 9% and minor increases in HVL are noted as well. Optical density variations as a function of position in the field correlate well with the measured radiation intensity changes.
Dose calculation for asymmetric photon fields with independent jaws and multileaf collimators
Authors: Araki Fujio , Ikeda Ryuji , Moribe Nobuyuki , Shirakawa Yuichi , Hatemura Masahiro , Shimonobou Toshiaki , Hirata Yukinori , Takada Takao , Takahashi Mutsumasa , Matoba Masaru
Published: July 2002

We have developed a simple method for dose calculation in dual asymmetric open and irregular fields with four independent jaws and multileaf collimators. Our calculation method extends the scatter correction method of Kwa et al. [Med. Phys. 21, 1599–1604 (1994)] based on the principle of Day's equivalent‐field calculation. The scatter correction factor was determined by the ratio of the derived doses of a smaller asymmetric open field or irregular field to a larger symmetric field. The algorithm with the scatter correction method can be calculated from output factors, tissue maximum ratios, and off‐axis ratios for conventional symmetric fields. The doses calculated by this method were compared with the measured doses for various asymmetric open and irregular fields. The agreement between the calculated and measured doses for 4 and 10 MV photon beams was within 0.5% at the geometric center of the asymmetric open fields. For the asymmetric irregular fields with the same geometrical center, agreement within 1% was found in most cases.
Dose calculation and verification of intensity modulation generated by dynamic multileaf collimators
Authors: Papatheodorou Spiridon , Rosenwald Jean‐Claude , Zefkili Sofia , Murillo Marie‐Claude , Drouard Jean , Gaboriaud Geneviève
Published: July 2002

While the development of inverse planning tools for optimizing dose distributions has come to a level of maturity, intensity modulation has not yet been widely implemented in clinical use because of problems related to its practical delivery and a lack of verification tools and quality assurance (QA) procedures. One of the prerequisites is a dose calculation algorithm that achieves good accuracy. The purpose of this work was twofold. A primary‐scatter separation dose model has been extended to account for intensity modulation generated by a dynamic multileaf collimator (MLC). Then the calculation procedures have been tested by comparison with carefully carried out experiments. Intensity modulation is being accounted for by means of a 2D (two‐dimensional) matrix of correction factors that modifies the spatial fluence distribution, incident to the patient. The dose calculation for the corresponding open field is then affected by those correction factors. They are used in order to weight separately the primary and the scatter component of the dose at a given point. In order to verify that the calculated dose distributions are in good agreement with measurements on our machine, we have designed a set of test intensity distributions and performed measurements with 6 and 20 MV photons on a Varian Clinac 2300C/D linear accelerator equipped with a 40 leaf pair dynamic MLC. Comparison between calculated and measured dose distributions for a number of representative cases shows, in general, good agreement (within 3% of the normalization in low dose gradient regions and within 3 mm distance‐to‐dose in high dose gradient regions). For absolute dose calculations (monitor unit calculations), comparison between calculation and measurement reveals good agreement (within 2%) for all tested cases (with the condition that the prescription point is not located on a high dose gradient region).
Wave packet spreading: Temperature and squeezing effects with applications to quantum measurement and decoherence
Authors: Ford G. W. , O’Connell R. F.
Published: July 2002

A localized free particle is represented by a wave packet and its motion is discussed in most quantum mechanics textbooks. Implicit in these discussions is the assumption of zero temperature. We discuss how the effects of finite temperature and squeezing can be incorporated in an elementary manner. The results show how the introduction of simple tools and ideas can bring the reader into contact with topics at the frontiers of research in quantum mechanics. We discuss the standard quantum limit, which is of interest in the measurement of small forces, and decoherence of a mixed (“Schrödinger cat”) state, which has implications for current research in quantum computation, entanglement, and the quantum-classical interface.
Infinite resistive lattices
Authors: Atkinson D. , van Steenwijk F. J.
Published: July 2002

The resistance between two arbitrary nodes in an infinite square lattice of identical resistors is calculated. The method is generalized to infinite triangular and hexagonal lattices in two dimensions, and also to infinite cubic and hypercubic lattices in three and more dimensions.
The intriguing properties of the equivalent resistances of n equal resistors combined in series and in parallel
Authors: Amengual Antoni
Published: July 2002

We found that the different values of equivalent resistance of all the possible combinations of n equal unitary resistors in series and/or in parallel form a list composed by a set of numbers and their inverses. This property is demonstrated and used to justify the symmetry and the peaks and valleys observed in the histogram representing the distribution of the values on the real axis. The number of different values obtained with n resistors is approximately 2.55n, defining a geometric series with a ratio smaller than the one that could be expected. The characteristics of the histograms, when some connections other than series or parallel as well as when nonplanar arrangements are allowed, is also suggested.
Second-harmonic generation in sound beams reflected from, and transmitted through, immersed elastic solids
Authors: Landsberger B. J. , Hamilton M. F.
Published: July 2002

Second-harmonic generation in sound beams reflected from and transmitted through thick isotropic elastic solids is investigated experimentally. Measurements of diffraction patterns are compared with a theoretical model based on integral solutions for harmonic generation in sound beams. The solutions are connected by classical linear theory for reflection and transmission at fluid–solid interfaces. Nonspecular phenomena associated with rapid phase variations near critical angles are accurately described. The principal restriction is that the solid is sufficiently thick that internal reflections may be ignored.
A theoretical study of passive control of duct noise using panels of varying compliance
Authors: Huang Lixi
Published: July 2002

It is theoretically demonstrated that, in a duct, a substantial amount of sound energy can be transferred to flexural waves on a finite wall panel when the upstream portion of the panel is made to couple strongly with sound. The flexural wave then loses its energy either through radiating reflection sound waves or by internal friction. The effectiveness of the energy transfer and damping is greatly enhanced if the panel has a gradually decreasing in vacuo wave speed, which, in this study, is achieved by using a tapered membrane under tension. A high noise attenuation rate is possible with the usual viscoelastic materials such as rubber. The transmission loss has a broadband spectrum, and it offers an alternative to conventional duct lining where a smooth air passage is desired and nonacoustical considerations, such as chemical contamination or cost of operation maintenance, are important. Another advantage of the tapered panel is that, at very low frequencies, typically 5% of the first cut-on frequency of the duct, sound reflection occurs over the entire panel length. This supplements the inevitable drop in sound absorption coefficient, and a high transmission loss may still be obtained at very low frequencies.
Frequency specificity of the human auditory brainstem and middle latency responses using notched noise masking
Authors: Oates Peggy A. , Purdy Suzanne C.
Published: July 2002

This study investigated the frequency specificity of the auditory brainstem and middle latency responses to 80 and 90 dB ppe SPL 500-Hz and 90 dB ppe SPL 2000-Hz tonebursts. The stimuli were brief (2-1-2 cycle) linear-gated tonebursts. ABR/MLRs were recorded using two electrode montages: (1) Cz-nape of neck and (2) Cz-ipsilateral earlobe. Cochlear contributions to ABR wave V-Na and MLR waves Na-Pa and Pa-Nb were assessed by plotting notched noise tuning curves which showed amplitudes and latencies as a function of center frequency of the noise masker [Abdala and Folsom, J. Acoust. Soc. Am. 97, 2394 (1995); ibid. 98, 921 (1995)]. Maxima in the response amplitude profiles for the ABR and MLR to 80 dB ppe SPL tonebursts occurred within one-half octave of the nominal stimulus frequency, with minimal contributions to the responses from frequencies greater than one octave away. At 90 dB ppe SPL, contributions came from a slightly broader frequency region for both stimulus frequencies. Thus, the ABR/MLR to 80 dB ppe SPL tonebursts shows good frequency specificity which decreases at 90 dB ppe SPL. No significant differences exist in frequency specificity of: (1) ABR wave V-Na versus MLR waves Na-Pa and Pa- Nb at either stimulus frequency or intensity; and (2) ABR/MLRs recorded using the two electrode montages.
On the sound insulation of wood stud exterior walls
Authors: Bradley J. S. , Birta J. A.
Published: July 2002

This article reports the results of a series of measurements of the sound transmission loss of exterior wood stud walls. The measurements were made using standard laboratory procedures in which the walls were built between two reverberation chambers. The outdoor–indoor transmission class is used to rate the relative effectiveness of the various constructions. The measurement results are used to illustrate the influence of key parameters of the constructions on measured sound transmission loss values and to give guidance for future designs. The overall sound insulation of these wood stud walls, to typical outdoor noises, is shown to be limited by two types of low-frequency resonances. An understanding of these low-frequency limitations can most effectively lead to superior sound insulation in similar wood stud walls.
Robust feedback control of flow-induced structural radiation of sound
Authors: Heatwole Craig M. , Franchek Matthew A. , Bernhard Robert J.
Published: July 2002

A significant amount of the interior noise of aircraft and automobiles is a result of turbulent boundary layer excitation of the vehicular structure. In this investigation, the feasibility of active robust feedback control of the noise due to this type of excitation is studied. The structural sound radiation system investigated is comprised of a simply supported panel excited by turbulent flow. An analytical model of this system is developed to evaluate the robust feedback control system design strategy. The model consists of a modal description of the excitation of the plate by a turbulent boundary layer, a modal representation of the plate vibrations, and an acoustic model of the sound radiated from the plate. Parametric uncertainties of 1% variation in the natural frequencies and 5% variation in the damping ratio are considered. A frequency domain controller design approach is utilized to develop a robust controller. Performance objectives are specified which include output performance of the sound radiated by the plate and control effort constraints on the force applied to the plate by the controller. Plate acceleration feedback is used in an effort to reduce the sound-pressure level. Approximately 16 and 8 dB of sound-pressure level reduction were achieved at the first and third resonances, respectively.
Propagation of transverse waves on piezoelectric plates supporting single or double side metal strip gratings
Authors: Ballandras S. , Briot J. B. , Gavignet E. , Bigler E.
Published: July 2002

A theoretical model of transverse waves propagating on piezoelectric plates of finite thickness under metal strip gratings is proposed. Different mechanical and electrical boundary conditions are considered and their influence on the propagation characteristics of the waves is emphasized. In all the cases, the dispersion curve relating the angular frequency to the wave number exhibits more than only one stopband as found in the usual analysis of surface transverse waves on semi-infinite substrates. This model has been used to calculate the resonance frequencies of synchronous devices on AT-cut and Z-cut quartz plates. These theoretical predictions are compared to experimental results obtained using synchronous devices built on 128-μm-thick Z-cut plate of quartz and AT-cut plate of quartz and operating at frequency range 80–150 MHz.
Organization and discrimination of repeating sound sequences by newborn infants
Authors: McAdams Stephen , Bertoncini Josiane
Published: July 2002

A study was conducted to determine whether newborn infants organize auditory streams in a manner similar to that of adults. A series of three experiments investigated the ability of 3- to 4-day-old infants to discriminate repeated rising and falling four-tone sequences in two configurations of source timbre and spatial position. It was hypothesized that if the sequences were organized into two auditory streams on the basis of timbre and spatial position, one of the configurations should be discriminable from its reversal while the other should not. The sequences were tested with different pitch and temporal intervals separating the tones. Sequences were discriminated for the first configuration by adults at both fast tempo/small interval and slow tempo/large interval combinations, while only the latter was discriminated by newborns as measured with a non-nutritive high-amplitude sucking paradigm. Neither adults nor infants could discriminate the sequence reversals for the second configuration. The results suggest that newborn infants organize auditory streams on the basis of source timbre and/or spatial position. They also suggest that newborns have limits in temporal and/or pitch resolution when discriminating tone sequences.
Using acoustic radiation force as a concentration method for erythrocytes
Authors: Yasuda Kenji , Haupt Stephan Shuichi , Umemura Shin-ichiro , Yagi Toshiki , Nishida Masaharu , Shibata Yasuhisa
Published: July 2002

We investigated the potential damage inflicted on erythrocytes by acoustic radiation force when the cells are concentrated by a 500-kHz ultrasonic standing wave at the pressure node. The extent of the damage was estimated from the concentrations of potassium ions, iron complexes, and lactate dehydrogenase released from the cells. After 2 min of ultrasound irradiation at 12.8 mJ/m3, the cells concentrated on the pressure node, with a cell distribution half-width of 138 μm; no significant release of intracellular components was detected, even after 15 min of irradiation. The results indicate that even small ions like potassium are not released as a result of ultrasound irradiation on cell membranes without cavitation, and they demonstrate the potential use of acoustic radiation force for concentrating living cells in biomedical applications.
A note on differential equations of coupled-mode propagation in fluids
Authors: Godin Oleg A.
Published: July 2002

There is a significant discrepancy between bathymetric contributions to ocean acoustic mode coupling matrix elements derived by various authors. In this paper, the discrepancy is shown to be due to incorrectness of the traditional approach to mode coupling theory, originated by A. D. Pierce [J. Acoust. Soc. Am. 37, 19–27 (1965)] and D. M. Milder [J. Acoust. Soc. Am. 46, 1259–1263 (1969)], in the presence of a sloping interface or a range-dependent rigid boundary. Physically, their approach is consistent with neither energy conservation nor reciprocity. Mathematically, the problem with the traditional approach consists of formal, unjustified, term-by-term differentiation of a series representing the acoustic pressure in terms of local normal modes. The series is poorly convergent when a nonhorizontal interface of fluids with distinct densities is present. A rigorous derivation of the acoustic mode coupling equations in media with piecewise continuous density and sound speed is given here on the basis of the reciprocity principle. Necessary corrections to the results presented recently by B. E. McDonald [J. Acoust. Soc. Am. 100, 219–224 (1996)] are discussed.
Sound radiation by a simply supported unbaffled plate
Authors: Laulagnet B.
Published: July 2002

Sound radiation by a simply supported unbaffled plate is presented using a double layer integral representation of the acoustic pressure. Both the pressure jump and the plate displacement are developed in series of the simply supported plate modes. This leads to modal coupling coefficients, which are numerically calculated for this specific unbaffled problem. The unbaffled problem is then transformed in the presentation of the baffled one which allows us to define original modal radiation impedance coefficients to the unbaffled plate. Baffled and unbaffled radiation impedances are then compared versus nondimensional frequency, in real and imaginary parts for a set of representative modes. An approximate expression for the direct unbaffled radiation impedance is presented, which is useful for light fluid loading. Finally, the influence of the baffle on sound radiation both in light and in heavy fluid, on the acoustic radiated power, the plate velocity, and the radiation factor is investigated.
One tone, two ears, three dimensions: A robotic investigation of pinnae movements used by rhinolophid and hipposiderid bats
Authors: Walker V. A. , Peremans H. , Hallam J. C. T.
Published: July 2002

Bats, which echolocate using broadband calls, are believed to employ the passive acoustic filtering properties of the head and pinnae to provide spectral cues which encode 3-D target angle. Microchiropteran species whose calls consist of a single, constant frequency harmonic (i.e., some species in the families Rhinolophidae and Hipposideridae) may create additional acoustic localization cues via vigorous pinna movements. In this work, two types of echolocation cues generated by moving a pair of receivers aboard a model sensor head are investigated. In the first case, it is supposed that a common 3-D echolocation principle employed by all bats is the creation of alternative viewing perspectives, and that constant frequency (CF) echolocators use pinna movement rather than morphology to alter the acoustic axes of their perceptual systems. Alternatively, it is possible rhinolophids and hipposiderids move their ears to create dynamic cues—in the form of frequency and amplitude modulations—which vary systematically with target elevation. Here the use of binaural and monaural timing cues derived from amplitude modulated echo envelopes are investigated. In this case, pinna mobility provides an echolocator with a mechanism for creating dramatic temporal cues for directional sensing which, unlike interaural timing differences, do not degrade with head size.
On bistatic sea surface scattering: Field measurements and modeling
Authors: Dahl Peter H.
Published: July 2002

The bistatic scattering cross section of the sea surface, σ, is studied, along with a model for σ and its comparison with field data. The data are horizontal spatial coherence and ensemble-averaged intensity, which represent integral measures of sea surface bistatic scattering, and the model for σ is used to generate these same properties for comparison with the field data. The data are from an experiment conducted in shallow waters off southern Florida, using a sound frequency of 30 kHz. Directional wave measurements were made with a wave buoy positioned within 100 m of the acoustic measurements, with the environment characterized by rms wave heights of O(10) cm and wind speeds of 1–4 m/s. In the model σ is divided into two components: σr associated with scattering from the rough, air/sea interface, and σb associated with scattering from near-surface bubbles. The second-order small slope approximation is used to compute σr, which is a much improved approach over the traditionally used composite roughness model. The primary advantage in the small slope approximation was the resulting smooth behavior in σr over a broad range of scattering angles. Directional wave data obtained by the wave buoy were converted to an estimate of the 2-D spatial correlation function of sea surface roughness, C(ξ,final_sigma), for use in the scattering calculations. An analysis of the effective correlation properties of C(ξ,final_sigma) suggested that an isotropic correlation function C(ρ), based on the directionally averaged wave-number spectrum, would be equally effective in the scattering calculations. Model-data agreement was quite satisfactory, regardless of whether C(ξ,final_sigma) or C(ρ) was used in the scattering calculations.
Radius of curvature estimation and localization of targets using multiple sonar sensors
Authors: Barshan Billur , Sekmen Ali Şafak
Published: July 2002

Acoustic sensors have been widely used in time-of-flight ranging systems since they are inexpensive and convenient to use. One of the most important limitations of these sensors is their low angular resolution. To improve the angular resolution and the accuracy, a novel, flexible, and adaptive three-dimensional (3-D) multi-sensor sonar system is described for estimating the radius of curvature and location of cylindrical and spherical targets. Point, line, and planar targets are included as limiting cases which are important for the characterization of typical environments. Sensitivity analysis of the curvature estimate with respect to measurement errors and certain system parameters is provided. The analysis and the simulations are verified by experiments in 2-D with specularly reflecting cylindrical and planar targets, using a real sonar system. Typical accuracies in range and azimuth are 0.18 mm and 0.1°, respectively. Accuracy of the curvature estimation depends on the target type and system parameters such as transducer separation and operating range. The adaptive configuration brings an improvement varying between 35% and 45% in the accuracy of the curvature estimate. The presented results are useful for target differentiation and tracking applications.
The perceptual effects of current pulse duration in electrical stimulation of the auditory nerve
Authors: McKay Colette M. , McDermott Hugh J.
Published: July 2002

In cochlear implants employing pulsatile stimulation, loudness is controlled by current amplitude and/or pulse duration. Five experiments were conducted with cochlear implantees to investigate the hypothesis that perceptual effects other than loudness result from changes in pulse duration for durations from 50 to 266 μs. In experiment 1, five subjects’ ability to discriminate equally loud pulse trains employing differing pulse durations was measured at four electrode positions. In 11 of the 20 cases, subjects could significantly discriminate these stimuli. In experiments 2 and 3, discrimination was measured of dual-electrode stimuli which differed in overall temporal pattern but had an equal temporal pattern on each of the individual electrodes (separated by 0 to 9 mm). Discrimination was compared for stimuli employing short or long pulse durations and, in experiment 3, employing different pulse durations on each electrode. When the pulse duration was longer, six out of seven subjects could either combine temporal information across electrode positions at wider electrode separations (experiment 2) or had better discrimination at the same electrode separation (experiment 3). This result was consistent with the hypothesis that longer pulse durations result in a greater spread of excitation than equally loud stimuli using shorter pulse durations. In experiment 4, pulse rate discrimination was compared for stimuli with differing pulse durations, and in four out of five subjects, there was no effect of pulse duration. Finally, the dB change in current per doubling of pulse duration for threshold and equally loud stimuli was calculated for nine subjects (52 electrodes). Values ranged from −5.9 to −2.0 dB/doubling, and were significantly correlated with the absolute intensity of the stimulus. This result was hypothesized to be due to a relationship between the neural charging characteristics and the distance of the excited neural elements from the electrode.
Matched-field processing using measured replica fields
Authors: Fialkowski Laurie T. , Collins Michael D. , Kuperman W. A. , Perkins John S. , Kelly Lesley J. , Larsson Ashley , Fawcett John A. , Hall Lindsay H.
Published: July 2002

An approach for avoiding the problem of environmental uncertainty is tested using data from the TESPEX experiments. Acoustic data basing is an alternative to the difficult task of characterizing the environment by performing direct measurements and solving inverse problems. A source is towed throughout the region of interest to obtain a database of the acoustic field on an array of receivers. With this approach, there is no need to determine environmental parameters or solve the wave equation. Replica fields from an acoustic database are used to perform environmental source tracking [J. Acoust. Soc. Am. 94, 3335–3341 (1993)], which exploits environmental complexity and source motion.
The role of magnesium in the susceptibility of soldiers to noise-induced hearing loss
Authors: Walden Brian E. , Henselman Lynn W. , Morris Elena R.
Published: July 2002

A number of studies have demonstrated that magnesium, administered prophylactically, can reduce the amount of hearing loss resulting from noise exposure. This study explored the possible role of naturally occurring body magnesium concentration in susceptibility of soldiers to noise-induced hearing loss. Participants were 68 adult males who had received extensive noise exposure over several years as a result of training with weapon systems. Each participant provided a pure-tone audiogram, blood sample, and noise-exposure history. A variety of pure-tone indices was correlated with serum magnesium levels as determined by atomic absorption spectroscopy. No significant correlations were observed between any audiometric index and body magnesium. The results of this study, therefore, do not support the hypothesis that there is a strong association between naturally occurring body magnesium and susceptibility to noise-induced hearing loss.
Bessel beams of finite amplitude in absorbing fluids
Authors: Cunningham Kevin B. , Hamilton Mark F.
Published: July 2002

Second-harmonic generation in a Bessel beam is investigated analytically, with emphasis on the effect of absorption. It is shown that absorption has a strong influence on the far-field beam profile. Numerical results are presented for higher harmonics and for waveform distortion in a Bessel beam that forms a shock.
Molecular Weight Dependency of Rheological Characteristics of Linear Low Density Polyethylene
Authors: Acierno D. , Brancaccio A. , Curto D. , La Mantia F. P. , Valenza A.
Published: July 2002

Five samples of linear low density polyethylene, polymerized with l-butene as comonomer and having different molecular weights but similar molecular weight distributions, have been characterized in shear and nonisothermal elongational flow. From the experimental data, generalized relationships have been found for the zero shear viscosity, the shift factors of the whole viscosity curve, the critical shear rate, the melt strength and the breaking-stretching ratio. It is then possible to predict with very good confidence values for the most important rheological characteristics of any LLDPE of similar polydispersity from the sole knowledge of the weight average molecular weight, in the range of temperature and flow conditions of industrial interest.
Melt rheology of randomly branched polystyrenes
Authors: Ferri Dino , Lomellini Paolo
Published: July 2002

Melt rheological properties of different homologous series of linear polystyrenes (LPS) and randomly branched polystyrenes (RBPS) in both linear and nonlinear viscoelastic response regions are presented. In the linear regime, the master curves of the experimentally determined viscoelastic functions reveal that the temperature dependence of the shift factors aT for all the samples follow the Vogel–Tammann–Fulcher equation: aT∝exp[B/(T−T0)]. The value of the apparent activation energy B is found to increase slightly with an increasing degree of branching, reflecting a stronger temperature dependence of the viscosity of RBPS with respect to that of LPS. This difference is approached within the framework of both Ngai’s coupling model and free volume theory. In the nonlinear regime, the shear rate dependence of the steady state viscosity η(γ̇), corrected for both non-Newtonian and entrance effects, was measured. A comparison with the angular frequency dependence of the dynamic complex viscosity |η*(ω)| reveals interesting behavior concerning the Cox–Merz rule. In the non-Newtonian flow region, for LPS the relationship η(γ̇) < |η*(ω)| is found to hold. On the other hand, RBPS exhibit an unusual failure of the rule characterized by the relationship η(γ̇) > |η*(ω)|. Elongational behavior of RBPS is also presented. Assuming a Wagner type single integral constitutive equation for the RBPS, a generalized time–temperature superposition principle in the field of nonlinear viscoelasticity is attempted: elongational stress curves measured at different temperatures are found to qualitatively match the same master curve if both the time and strain rate are reduced by an appropriate shift factor.
Childhood maltreatment: The role of concurrent advantageous experiences on adolescents' psychosocial adjustment
Authors: Ronzón‐Tirado Román , Redondo Natalia , Muñoz‐Rivas Marina J.
Published: August 2022

Despite the growing body of evidence concerning the harmful effects of childhood maltreatment, intimate partner violence exposure (IPVE) and their correlates, little is currently known about the effects of co‐occurring advantageous family conditions (e.g., instrumental support, inductive parenting, positive communication) and how they may serve to offset the detrimental effects of maltreatment and IPVE. The present study applied a three‐step latent class analysis to identify the co‐occurrence patterns of childhood maltreatment and advantageous family conditions among 1379 Spanish adolescents. The study also sought to identify the sociodemographic risk markers and psychosocial adjustment associated with each latent class membership. The analyses revealed four classes, namely (1) violent family context, (2) emotionally neglectful family context, (3) adverse and advantageous family conditions, and (4) positive family context. Having a lower socioeconomic status and being a migrant were both risk markers for membership to the violent family context as well as to the adverse and advantageous family conditions class. Adolescents who were exposed to advantageous family conditions (e.g., the positive family context or the adverse and advantageous family conditions) exhibited fewer psychosocial problems (e.g., depression, anxiety, somatisation) and lower frequencies of teen dating violence (TDV) when compared with those in the violent family context. Moreover, membership to the emotionally neglectful family context class was related to more psychological symptoms and a higher prevalence of TDV when compared with membership to the positive family context class, despite the absence of IPVE and maltreatment. Overall, the results provide evidence that advantageous family conditions contribute to better psychosocial adjustment on the part of adolescents even when exposed to IPV and maltreatment. Identifying the experiences that contribute to adolescents' psychosocial adjustment could help clinical and governmental interventions tailor their often‐limited resources to children who are at greater risk of negative outcomes.
Evidence‐based region of interest (ROI) definition for surface‐guided radiotherapy (SGRT) of abdominal cancers using deep‐inspiration breath‐hold (DIBH)
Authors: Song Yulin , Zhai Xingchen , Liang Yubei , Zeng Chuan , Mueller Boris , Li Guang
Published: August 2022

To define and evaluate the appropriate abdominal region of interest (ROI) as a surrogate of diaphragm positioning in deep‐inspiration breath‐hold (DIBH) for surface‐guided radiotherapy (SGRT) of abdominal cancers using 3D optical surface imaging (OSI). Six potential abdominal ROIs were evaluated to calculate their correlations with the diaphragm position using 4DCT images of 20 abdominal patients. Twelve points of interest (POIs) were defined (six on the central soft tissue and six on the bilateral ribs) at three superior–inferior levels, and different sub‐groups represented different ROIs. ROI‐1 was the largest, containing all 12 POIs from the xiphoid to the umbilicus and between the lateral body midlines while ROI‐2 had only eight inferior POIs, ROI‐3 had six lateral POIs, and ROI‐4 had four superior‐lateral POIs over the ribs, ROI‐5 contained six central and two most inferior‐lateral POIs and ROI‐6 contained six central and four inferior‐lateral POIs. Internally, the right diaphragm dome was used to represent its positions in 4DCT (0% and 50% within the cycle). The Pearson correlation coefficients were calculated between the diaphragm dome and all 12 external POIs individually or grouped as six ROIs. The quality of the abdominal ROIs was evaluated as potential internal surrogates and, therefore, potential ROIs for SGRT DIBH setup. The four most inferior POIs show the highest mean correlation (r = 0.75) with diaphragmatic motion, and the correlation decreases as POIs move superiorly. The mean correlations are the highest for ROIs with little or no rib support: r = 0.67 for ROI‐2, r = 0.64 for ROI‐5, and r = 0.63 for ROI‐6, while lower for ROIs with rib support: ROI‐1 has r = 0.60, ROI‐3 has r = 0.50, and ROI‐4 has only r = 0.28. This study demonstrates that the rectangular/triangular soft‐tissue ROI (with little rib support) is an optimal surrogate for body positioning and diaphragmatic motion, even when treating tumors under the rib cage. This evidence‐based ROI definition should be utilized when treating abdominal cancers with free‐breathing (FB) and/or DIBH setup.
Bubble‐Mediated Mass Production of Graphene: A Review
Authors: Shi Zhiyuan , He Peng , Wang Ningzhen , Liu Yuan , Chen Xiang , Li Yanxiang , Ding Guqiao , Yu Qingkai , Xie Xiaoming
Published: August 2022

The large‐scale industrial applications of graphene highly depend on its mass production with efficiency (high‐yield, time‐saving, and low‐cost) and controllability (high‐quality, safe, and environmentally friendly). However, this requirement can hardly be satisfied by incumbent chemical exfoliation methods exploiting liquid–solid interactions. Recently, many studies have demonstrated that the usage of bubbling as a new tool makes a big difference in multiple aspects of graphene production. Benefiting from their unique properties, the bubbles can be employed as the driving force to cleave graphite layers for graphene preparation or as the favorite interface for graphene growth at a high temperature. Therefore, the bubble‐mediated technique represents a new strategy promising to achieve efficient and controllable preparation of graphene. Here, the formation and evolution of bubbles in liquid media are first analyzed. Then, two routes including “top‐down” and “bottom‐up” toward mass production of graphene with the assistance of bubbles are summarized and discussed. This review sheds light on the introduction of gas to realize the mass production of graphene for the development of graphene's applications on large scale.
Reversibly Compressible Supramolecular Aerogels with Low Density and Sound Insulation Performance
Authors: Chen Yong , Li Yuangang , Li Huajing , Liu Minghua
Published: August 2022

It is still a great challenge for supramolecular materials to be used as polymer systems. Here, reversibly compressible supramolecular aerogels with low density and sound insulation performance are reported, which are exclusively composed of small molecules. It is found that the mixture of melamine and isonicotinic acid can form supramolecular hydrogel. Then it could be transformed into aerogel via a simple freeze‐drying method to allow gas to replace the position of water in the 3D network skeleton pores of the hydrogel. This supramolecular aerogel is characterized of low density (1.2 mg cm‐3), high porosity (99.9%), and no volume shrinkage. In addition, the supramolecular aerogel exhibits intrinsically elastic and strong fatigue resistance under compress loading/unloading cycles. The mechanical efficiency of the supramolecular aerogel can be maintained in a wide density range without significant stiffness degradation. Remarkably, such supramolecular aerogel can be used as a sound insulator and exhibits a good sound insulation performance. Compared with the polymeric foam insulation materials, the supramolecular aerogel is environmentally friendly, easy to be fabricated and disposed. This work demonstrates the fabrication of supramolecular aerogel and expands the application of self‐assembled supramolecular materials.
Nanostructured α‐Fe2O3 Photoelectrodes with Transparent and Conducting Sb‐Doped SnO2 Films Deposited by Atomic Layer Deposition
Authors: Kim Eunsoo , Yang Hyunwoo , Seo Seongrok , Park Jong Hyeok , Shin Hyunjung
Published: August 2022

Antimony (Sb)‐doped tin oxide (ATO), as a transparent conducting oxide, is successfully deposited through atomic layer deposition (ALD). Thin films (≈270 nm) with various dopant concentrations are fabricated by sequential mixing of Sn‐ and Sb‐containing oxide layers in each ALD supercycle. The crystal structure, chemical composition, and morphologies of different films are characterized. Increasing the dopant concentration decreases the lattice parameter along the c‐axis and the overall grain size, as observed from X‐ray diffraction patterns and scanning electron microscopy images. X‐ray photoelectron spectroscopy spectra show increasing Sb content with increasing Sb to Sn subcycle ratio. The plasmonic loss feature, which is usually observed in highly doped degenerate semiconductors, is also found. Hall measurements are carried out to determine the electrical properties of each film, and films with ≈5% dopant concentration show the optimal conductivity. The carrier concentration continues to increase with increasing dopant concentration in the range of 0–20%, while the mobility decreases, which leads to a trade‐off and results in an increase in resistance if the dopant concentration exceeds 5%. The optimized ATO ALD process is demonstrated to fabricate core–shell structured nanotube arrays, which show its potential usage for photoelectrochemical applications.
Reagent‐Controlled Chemodivergent Approach to Thiazolines and Thiazines from α‐N‐Hydroxyimino Dithioesters
Authors: Ray Subhasish , Singh Saurabh , Kumar Ganesh , Shukla Gaurav , Shankar Singh Maya
Published: August 2022

A chemoselective route to thiazolines and thiazines has been devised by heterocyclization of viable α‐N‐hydroxyimino‐β‐oxodithioesters with 2‐chloroethylamine hydrochloride/3‐chloropropylamine hydrochloride, which does not require metals or additives and proceeds at 0–60 °C. The overall transformation involves base mediated intramolecular cyclization of α‐N‐hydroxyimino‐β‐oxodithioesters to 4‐membered oxazete‐4‐thione intermediates followed by coupling with chloroalkyl amines via tandem ring cleavage and C−N/C−S bonds formation enabling the construction of thiazolines/thiazines in one‐pot. This strategy allows broadening the arsenal of synthetic methods to obtain N,S‐heterocycles utilizing substrates prepared according to reported procedures.

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Decoupling gaseous hydrogen production from liquid water using a magnetic‐photo‐thermal coupling reactor
Authors: Wang Shujian , Lu Kejian , Hu Anlan , Li Naixu , Feng Yeti , Jing Dengwei , Liu Maochang
Published: August 2022

Taking monolithic TiO2/nickel foam as a model photocatalytic material, we hereby report the application of magnetic‐photo‐thermal coupling field toward enhanced solar photocatalytic hydrogen production. This enhancement is attributed to the increased temperature induced by eddy current effect and effective charge separation caused by the electric field force under the alternating magnetic field condition. Particularly, we demonstrate that a proper set of the position of the monolithic catalyst relative to the reaction solution, that is, at the water‐air interface, will lead to a further enhancement of the photocatalytic activity because of the improved mass transfer property of the reactants, with a hydrogen evolution rate of 104.3 μmol h−1. Specifically, the increased temperature of the catalyst leads to the rapid evaporation of water. Hydrogen generation is thus decoupled from liquid water, avoiding kinetically disfavored bubble formation. This work provides a novel strategy to facilitate photocatalytic performance with the application of external field.
Active learning boosted computational discovery of covalent–organic frameworks for ultrahighCH4storage
Authors: Tang Hongjian , Jiang Jianwen
Published: August 2022

As an environmental‐benign fuel, methane (CH4) has received considerable interest for developing high‐capacity energy storage systems. Herein, we aim to rapidly discover covalent–organic frameworks (COFs) for ultrahigh CH4storage among 530,000+ COFs, including one experimental (Curated) and two hypothetical (Berkeley and Genomic) databases. First, the feature space of all the three COF databases is projected by t‐Distributed Stochastic Neighbor Embedding (t‐SNE) technique, which reveals a potential but unexplored regime in Genomic COFs. Subsequently, an active learning (AL) approach is developed by integrating parallel acquisition with molecular simulation to efficiently explore Genomic COFs. The parallel AL model demonstrates remarkable screening efficiency and shortlists top COFs by evaluating only 50 out of 445,845 Genomic COFs. A record‐breaking Genomic COF is identified with CH4deliverable capacity of 222.2 v/v, surpassing the current world record (208.0 v/v from experiment and 217.9 v/v from simulation). Our AL approach is significantly faster than brute‐force simulation and conventional machine learning, it would accelerate the discovery of advanced porous materials for broad applications.
Nahinfrarotlicht‐induzierte radikalische Polymerisation in Wasser
Authors: Neidinger Philipp , Davis Joshua , Voll Dominik , Jaatinen Esa A. , Walden Sarah L. , Unterreiner Andreas N. , Barner‐Kowollik Christopher
Published: August 2022

Wir stellen eine auf Goldnanostäbchen (AuNR) basierende Methode vor, um eine radikalische Polymerisation in Wasser mit Nahinfrarotlicht (800 nm) zu induzieren. Der Prozess nutzt die photothermische Umwandlung in AuNR und die anschließende Wärmeübertragung auf einen Radikalinitiator (hier Azobisisobutyronitril) für die primäre Radikalbildung. Es wurde ein breites Spektrum an Reaktionsbedingungen untersucht, wobei die Kontrolle über das Molekulargewicht und den Reaktionsumsatz von Dimethylacrylamidpolymeren mit Hilfe der kernmagnetischen Resonanzspektroskopie nachgewiesen wurde. Wir untermauern unsere experimentellen Daten mit einer Finite‐Elemente‐Simulation des räumlich‐zeitlichen Temperaturprofils in der Umgebung der AuNR direkt nach der Anregung durch Femtosekunden‐Laserpulse. Wir weisen nach, dass die Polymerisation, aufgrund erhöhter Eindringtiefe des Nahinfrarotlichts, durch biologisches Gewebe induziert werden kann. Wir sind der Meinung, dass der vorgestellte Initiierungsmechanismus in wässrigen Systemen vielversprechend für die radikale Polymerisation in biologischen Umgebungen, einschließlich Zellen, ist.