bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of Be diffusion in molecular beam epitaxy GaAs
Authors: Miller Jeffrey N. , Collins Douglas M. , Moll Nicolas J.
Published: July 2002

After molecular beam epitaxy GaAs is grown at 585 °C, substantial diffusion of Be occurs during growth of subsequent layers or during subsequent in situ annealing at 700 °C. By using an order of magnitude larger As4 flux than commonly used during growth and annealing, we were able to lower the Be diffusion coefficient by an order of magnitude. We also show that the Be diffusion coefficient is strongly dependent on the Be concentration. Different specimens were prepared with varying Be doping density, As4:Ga beam flux ratio, and annealing temperature. In these experiments, the Be concentration profiles were measured by secondary ion mass spectrometry and from them Be diffusion coefficients were calculated.
Measurement of population inversions and gain in carbon fiber plasmas
Authors: Milchberg H. , Skinner C. H. , Suckewer S. , Voorhees D.
Published: July 2002

A CO2 laser (∼0.5 kJ energy, 50–80 ns pulse width) was focused onto the end of an axially oriented, thick (35–350 μ) carbon fiber with or without a magnetic field present along the laser-fiber axis. We present evidence for axial-to-transverse enhancement of the C VI 182 Å (n=3–2) transition, which is correlated with the appearance of a population inversion between levels n=3 and 2. For the B=0 kG, zero field case, the maximum gain length product of kl≊3 (k≊6 cm−1) was measured for a carbon fiber coated with a thin layer of aluminum (for additional radiation cooling). The results are interpreted in terms of fast recombination due mostly to thermal conduction from the plasma to the cold fiber core.
X
2Σ→B2Σ absorption band of HgBr: Optically pumped 502-nm laser
Authors: Greene D. P. , Killeen K. P. , Eden J. G.
Published: July 2002

The X2Σ+1/2→B2Σ+1/2 absorption band of HgBr has been observed in the afterglow of a pulsed Ne-N2-HgBr2 discharge. Peaking in the ultraviolet (UV) near 350 nm, this continuum degrades slowly to the red and at 410 nm the absorption coefficient is 30% of its maximum value. Upon exciting the X→B band with an XeF (351 nm) or frequency tripled Nd:YAG (355 nm) laser, intense lasing is observed in the blue-green (λ∼502 nm). For λpump=351 nm, the energy conversion efficiency (UV to green) is 22% which corresponds to a photon conversion efficiency of 32%. The quantum efficiency for this four level system is 71%.
Generation of high magnetic fields using a gas-puff Z pinch
Authors: Wessel F. J. , Felber F. S. , Wild N. C. , Rahman H. U. , Fisher A. , Ruden E.
Published: July 2002

The imploding plasma column of a gas-puff Z pinch was used to compress an embedded axial magnetic field. Field compression ratios up to 180 times and peak compressed fields up to 1.6 MG were measured by Faraday rotation. Field compression by this method has the advantage of high repetition rate for applications in the controlled production of high-energy densities, solid-state studies, generation of short-wavelength radiation, reducing the ignition threshold for fusion, and particle acceleration.
Waveguiding in soft x-ray laser experiments
Authors: Lunney James G.
Published: July 2002

In soft x-ray laser experiments using laser produced plasmas on thick targets the steep electron density gradients in the plasma can cause refraction of the soft x rays out of the region of gain. It is shown how this refraction problem can be overcome by bending the target to a concave cylindrical or toroidal surface. The possibility of waveguiding in these soft x-ray laser schemes is also examined.
Simulation studies of bifurcation and chaos in semiconductor lasers
Authors: Tang Ming , Wang Shyh
Published: July 2002

We apply the phase portrait analysis for photon density and carrier density to analyze simulation results obtained from the rate equations for semiconductor lasers. On the two-dimensional bifurcation diagram of modulation depth and modulation frequency, there are six regions: periodic pulse, continuous oscillation wave, chaos, period doubling of single period, period multiplying of single period, and period doubling of two period. The region of chaos is located below the region of periodic pulse. By properly choosing the modulation frequency, chaotic behavior can be avoided. A normalized two-dimensional bifurcation diagram defining the periodic pulse region is presented for the purpose of locating the suitable region for modulation of a semiconductor laser.
Passive mode locking of a continuous wave dye laser operating in the blue-green spectral region
Authors: French P. M. W. , Taylor J. R.
Published: July 2002

The passive mode locking of a continuous wave dye laser operating in the blue-green spectral region is reported for the first time. In a simple linear configuration with no optimization of the intracavity dispersion, coumarin 102, excited by the ultraviolet lines of an argon ion laser, has been mode locked using 3,3′-diethyl oxacarbocyanine iodide over the spectral range 487–508 nm, yielding pulses as short as 580 fs duration at 498 nm.
Low-frequency excess noise in Nb-Al2O3-Nb Josephson tunnel junctions
Authors: Savo Bonaventura , Wellstood Frederick C. , Clarke John
Published: July 2002

A fabrication technique for Nb-Al2O3-Nb Josephson tunnel junctions is described that is an alternative to the trilayer method generally used. At 4.2 K the magnitude of the low-frequency noise in the critical current I0 of four junctions with areas 𝒜 ranging from 7.8 to 115 μm2 was characterized by S1/2I0𝒜1/2/I0 =(14±6)pA μm/μA Hz1/2, where SI0 is the spectral density of the excess noise at 1 Hz. The noise power spectrum of one 3×3 μm2 junction exhibited a Lorentzian feature associated with the emptying and filling of a single trap in the barrier. The low level of noise makes these junctions attractive for use in superconducting quantum interference devices.
Degradation of band-gap photoluminescence in GaAs
Authors: Guidotti D. , Hasan Eram , Hovel H. J. , Albert Marc
Published: July 2002

Evidence is presented to show that the degradation of near-band-gap photoluminescence emission in GaAs with time of exposure to low power, cw laser excitation can be attributed to a surface mechanism that is independent of surface oxidation and may involve an interaction between crystal point defects and the photogenerated electron-hole plasma near the surface.
Epitaxy of orthorhombic gadolinium disilicide on 〈100〉 silicon
Authors: Geröcs I. , Molnár G. , Jároli E. , Zsoldos E. , Petö G. , Gyulai J. , Bugiel E.
Published: July 2002

Epitaxial orthorhombic GdSi2 was grown by in situ vacuum annealing of a 50-nm Gd layer on 〈100〉 silicon. The epitaxy was proved by x-ray diffraction, electron diffraction, and ion channeling measurements. The lattice mismatch between the orthorhombic GdSi2 and 〈100〉 silicon substrate was found to be 4%.
Operation of Schottky-barrier field-effect transistors of 3C-SiC up to 400 °C
Authors: Daimon H. , Yamanaka M. , Shinohara M. , Sakuma E. , Misawa S. , Endo K. , Yoshida S.
Published: July 2002

Schottky-barrier field-effect transistors have been fabricated from 3C-SiC and transistor operation has been studied at temperatures up to 400 °C. B-doped high-resistivity and undoped n-type 3C-SiC epilayers were successively grown on p-type Si substrates by chemical vapor deposition. Au and Al electrodes were used for Schottky-barrier gate contacts and source and drain contacts for n-type 3C-SiC, respectively. Transconductances of 1.7 and 0.15 mS/mm were obtained at room temperature and 400 °C, respectively.
Femtosecond luminescence spectroscopy with 60 fs compressed pulses
Authors: Damen T. C. , Shah Jagdeep
Published: July 2002

We report compression of the pulses from a synchronously pumped Rh 6G dye laser to 60 fs using a fiber-prism compressor. Average power in excess of 150 mW has been obtained. Using this compressed laser and the sum-frequency-generation technique, we have demonstrated the capability of measuring luminescence spectra with 65 fs time resolution. Initial results on GaAs and AlGaAs are presented.
Amorphous chalcogenide thin-film Schottky barrier (Bi/As2Se3:Bi) solar cell
Authors: Kumar Sunil , Mehta B. R. , Kashyap Subhash C. , Chopra K. L.
Published: July 2002

A thin-film metal-amorphous chalcogenide semiconductor Schottky barrier solar cell between Bi and n-type As2Se3:Bi has been fabricated by low-temperature diffusion of vacuum evaporated bismuth into a p-type a-As2Se3 film. The dominant current transport mechanism in the junction is established to be tunneling via recombination states. Typical open circuit voltage and short circuit current density of the solar cell are 300 mV and 140 μA/cm2, respectively.
Reflectance line shapes from GaAs/Ga1−xAlxAs quantum well structures
Authors: Zheng X. L. , Heiman D. , Lax B. , Chambers F. A.
Published: July 2002

Reflectance experiments on GaAs/Ga1−xAlxAs single quantum well structures were performed at 4.2 K, with different thicknesses of the front GaAlAs barrier layer (100–1000 Å). The observed exciton reflectance line shapes depend strongly on the thickness of the front barrier layer due to the interferences between the reflected waves from the front surface and the quantum well interfaces. Calculations of the reflectance line shapes show good agreement with the observations. The absorption coefficient for the electron heavy-hole exciton transition in a single quantum well sample is determined. Our study also provides a new understanding of the line shapes measured in photoreflectance experiments.
Novel adiabatic bifilar helical wiggler entrance for free-electron laser applications
Authors: Hartemann F. , Buzzi J. M. , Lamain H.
Published: July 2002

A new adabatic bifilar helical wiggler entrance is presented. This introduction region is obtained by using a liquid shunt resistance to progressively shunt the current circulating in the wiggler helical windings. We have built a prototype wiggler and measured the field profiles obtained with this new scheme. The results agree very well with computer calculations and show that, indeed, one obtains a high quality adiabatic wiggler with this method.
Picosecond switching time measurement of a resonant tunneling diode
Authors: Whitaker J. F. , Mourou G. A. , Sollner T. C. L. G. , Goodhue W. D.
Published: July 2002

Picosecond bistable operation has been experimentally observed for the first time in a double-barrier resonant tunneling diode. A rise time of 2 ps was measured using the electro-optic sampling technique; this is the fastest switching event yet observed for an electronic device. This time domain measurement adds necessary information to the understanding of the transport mechanisms in the resonant tunneling diode and is consistent with switching time limitations computed for the device. It also demonstrates that appropriately designed double-barrier quantum well diodes have a response time comparable to that of the fastest all-optical logic elements, and that they may be very useful in high-speed logic applications.
Shear stress regulates the endothelial Kir2.1 ion channel
Authors: Hoger Jeff H. , Ilyin Victor I. , Forsyth Scott , Hoger Anne
Published: July 2002

Endothelial cells (ECs) line the mammalian vascular system and respond to the hemodynamic stimulus of fluid shear stress, the frictional force produced by blood flow. When ECs are exposed to shear stress, one of the fastest responses is an increase of K
+
conductance, which suggests that ion channels are involved in the early shear stress response. Here we show that an applied shear stress induces a K
+
ion current in cells expressing the endothelial Kir2.1 channel. This ion current shares the properties of the shear-induced current found in ECs. In addition, the shear current induction can be specifically prevented by tyrosine kinase inhibition. Our findings identify the Kir2.1 channel as an early component of the endothelial shear response mechanism.
Overexpression of cellular glutathione peroxidase rescues homocyst(e)ine-induced endothelial dysfunction
Authors: Weiss Norbert , Zhang Ying-Yi , Heydrick Stanley , Bierl Charlene , Loscalzo Joseph
Published: July 2002

Homocyst(e)ine (Hcy) inhibits the expression of the antioxidant enzyme cellular glutathione peroxidase (GPx-1)
in vitro
and
in vivo
, which can lead to an increase in reactive oxygen species that inactivate NO and promote endothelial dysfunction. In this study, we tested the hypothesis that overexpression of GPx-1 can restore the normal endothelial phenotype in hyperhomocyst(e)inemic states. Heterozygous cystathionine β-synthase-deficient (CBS
(−/+)
) mice and their wild-type littermates (CBS
(+/+)
) were crossbred with mice that overexpress GPx-1 [GPx-1
(tg+)
mice]. GPx-1 activity was 28% lower in CBS
(−/+)
/GPx-1
(tg−)
compared with CBS
(+/+)
/GPx-1
(tg−)
mice (
P
< 0.05), and CBS
(−/+)
and CBS
(+/+)
mice overexpressing GPx-1 had 1.5-fold higher GPx-1 activity compared with GPx-1 nontransgenic mice (
P
< 0.05). Mesenteric arterioles of CBS
(−/+)
/GPx-1
(tg−)
mice showed vasoconstriction to superfusion with β-methacholine and bradykinin (
P
< 0.001 vs. all other groups), whereas nonhyperhomocyst(e)inemic mice [CBS
(+/+)
/GPx-1
(tg−)
and CBS
(+/+)
/GPx-1
(tg+)
mice] demonstrated dose-dependent vasodilation in response to both agonists. Overexpression of GPx-1 in hyperhomocyst(e)inemic mice restored the normal endothelium-dependent vasodilator response. Bovine aortic endothelial cells (BAEC) were transiently transfected with GPx-1 and incubated with
dl
-homocysteine (HcyH) or
l
-cysteine. HcyH incubation decreased GPx-1 activity in sham-transfected BAEC (
P
< 0.005) but not in GPx-1-transfected cells. Nitric oxide release from BAEC was significantly decreased by HcyH but not cysteine, and GPx-1 overexpression attenuated this decrease. These findings demonstrate that overexpression of GPx-1 can compensate for the adverse effects of Hcy on endothelial function and suggest that the adverse vascular effects of Hcy are at least partly mediated by oxidative inactivation of NO.
Increased histone H1 phosphorylation and relaxed chromatin structure in Rb-deficient fibroblasts.
Authors: Herrera R E , Chen F , Weinberg R A
Published: July 2002

Fibroblasts derived from embryos homozygous for a disruption of the retinoblastoma gene (Rb) exhibit a shorter G1 than their wild-type counterparts, apparently due to highly elevated levels of cyclin E protein and deregulated cyclin-dependent kinase 2 (CDK2) activity. Here we demonstrate that the Rb-/- fibroblasts display higher levels of phosphorylated H1 throughout G1 with the maximum being 10-fold higher than that of the Rb+/+ fibroblasts. This profile of intracellular H1 phosphorylation corresponds with deregulated CDK2 activity observed in in vitro assays, suggesting that CDK2 may be directly responsible for the in vivo phosphorylation of H1. H1 phosphorylation has been proposed to lead to a relaxation of chromatin structure due to a decreased affinity of this protein for chromatin after phosphorylation. In accord with this, chromatin from the Rb-/- cells is more susceptible to micrococcal nuclease digestion than that from Rb+/+ fibroblasts. Increased H1 phosphorylation and relaxed chromatin structure have also been observed in cells expressing several oncogenes, suggesting a common mechanism in oncogene and tumor suppressor gene function.
Rapid evolution in plant chitinases: Molecular targets of selection in plant-pathogen coevolution
Authors: Bishop J. G. , Dean A. M. , Mitchell-Olds T.
Published: July 2002

Many pathogen recognition genes, such as plant
R
-genes, undergo rapid adaptive evolution, providing evidence that these genes play a critical role in plant-pathogen coevolution. Surprisingly, whether rapid adaptive evolution also occurs in genes encoding other kinds of plant defense proteins is unknown. Unlike recognition proteins, plant chitinases attack pathogens directly, conferring disease resistance by degrading chitin, a component of fungal cell walls. Here, we show that nonsynonymous substitution rates in plant class I chitinase often exceed synonymous rates in the plant genus
Arabis
(Cruciferae) and in other dicots, indicating a succession of adaptively driven amino acid replacements. We identify individual residues that are likely subject to positive selection by using codon substitution models and determine the location of these residues on the three-dimensional structure of class I chitinase. In contrast to primate lysozymes and plant class III chitinases, structural and functional relatives of class I chitinase, the adaptive replacements of class I chitinase occur disproportionately in the active site cleft. This highly unusual pattern of replacements suggests that fungi directly defend against chitinolytic activity through enzymatic inhibition or other forms of chemical resistance and identifies target residues for manipulating chitinolytic activity. These data also provide empirical evidence that plant defense proteins not involved in pathogen recognition also evolve in a manner consistent with rapid coevolutionary interactions.
Selecting between Competitors in Multiplication Tasks: An Explanation of the Errors Produced by Adolescents with Learning Difficulties
Authors: Barrouillet Pierre , Fayol Michel , Lathulière Eric
Published: July 2002

Two experiments were conducted in order to determine the nature of the difficulties encountered by learning disabled (LD) adolescents in the resolution of multiplication problems ( a b, where a and b vary between 2 and 9). A response production task (Experiment 1) revealed that the incorrect responses generally belonged to the table of one of the two operands, and that the order of difficulty of the problems was the same for the LDs as for normal children, adolescents, and educated adults as reported in the literature. This result suggests that the difficulties are not solely due to memory problems. Experiment 2 tested the hypothesis that these difficulties were caused by a problem in inhibiting the incorrect responses from a set of possible responses. Subjects completed a multiple response task in which the correct response was presented along with three distractors. The level of interference between the correct response and the distractors was varied by manipulating the nature of the distractors (Null Interference, NI: numbers that did not belong to the multiplication table; Weak Interference, WI: numbers belonging to other tables than those of a and b; Strong Interference, SI: numbers belonging to the tables of either a or b). The SI condition resulted in a higher level of errors than the NI and WI conditions and there was no difference between these latter two conditions. This result suggests that the main difficulty encountered by LD subjects is associated with inefficient inhibition of incorrect responses. Thus, the mobilisation of inhibitory processes seems to be an important stage in the development of multiplication skills.
The Differential Effects of Medication on Mood, Sleep Disturbance, and Work Ability in Outpatient Alcohol Detoxification
Authors: Malcolm Robert , Myrick Hugh , Roberts James , Wang Wei , Anton Raymond F.
Published: July 2002

A double‐blind, randomized controlled trial of patients (n = 136) meeting DSM‐IV criteria for alcohol withdrawal and stratified based on detoxification history were treated with carbamazepine or lorazepam for 5 days on a fixed dose tapering schedule. Mood symptoms improved for all subjects regardless of medication or detoxification history. There was a significant main effect favoring carbamazepine in reducing anxiety (p = 0.0007). Anxiety was highest in those individuals who had multiple previous detoxifications (p = 0.02). Visual analog measures of sleep quality indicated a statistically significant main effect of medication on sleep that again favored carbamazepine (p = 0.0186). Visual analog rating of perceived ability to return to work was decreased in individuals who had multiple previous detoxifications (p= 0.025). In this study of out‐patients with mild to moderate alcohol withdrawal, carbamazepine was superior to lorazepam in reducing anxiety and improving sleep.
Introduction to Brain mechanisms of selective perception and action. Proceedings of a Discussion Meeting held at the Royal Society of London on 19 and 20 November 1997.
Authors: Humphreys Glyn W. , Duncan John , Treisman Anne
Published: July 2002

The world is full of objects. Some may be static, others not. Some may be partially occluded, others standing alone. Some may emit sounds, others not. Some we may be touching (hands resting on a table), others out of reach. At a sensory level, the means by which the world comes to be organized into objects is a far from trivial problem, since stimulus information is typically ambiguous as to which local parts of a scene ‘belong’ together. It is also unclear how different forms of sensory information combineödoes each sense operate independently, or is information integrated in forms of multi-modal representation (Driver, this issue)? Furthermore, the behavioural responses we are equipped to make are inherently limited.We may only name one object at a time; we can reach at most to two objects. The information available to our senses needs to be selected, so that only elevant parts of the world are represented for action. In this way, action may interact in important ways with perceptual processing. Scenes may be parsed in different ways according to our intended behaviour. Perception and action may be linked through processes of selective attention (Milner, this issue; Tipper et al., this issue).
An introduction to three papers on human migration by Coleman, Laczko and Myers
Authors: Tickell Crispin , Zeki Semir
Published: July 2002

Human migration is an activity that is as old as humanity itself. Yet it remains a sensitive and politically charged subject, creating tensions in societies that experience it. It is closely linked to economic, environmental, demographic and political factors. It has become a conspicuous feature of the world political and demographic scene, with an estimated number of 22 million migrants in the past year. It shows every sign of accelerating in the future, not only because of poverty, civil war and politics, but also from environmental reasons that, in the future, may cause still larger–scale migration. Migration will be influenced by a host of such factors as climate change, sea–level rise, desertification, and environmental degradation generally.
Shear wave focusing for three-dimensional sonoelastography
Authors: Wu Zhe , Taylor Lawrence S. , Rubens Deborah J. , Parker Kevin J.
Published: July 2002

A new vibration scheme is shown to provide localized vibration fields for three-dimensional sonoelastography imaging. The theoretical vibration distributions of double strip loads vibrating normally to the surface of a semi-infinite elastic space are calculated. A localization or focusing of shear waves inbetween the double-strip loads is predicted. Experimentally, two parallel rigid rectangular cross-section bars are mounted on an electromagnetic shaker. Driven by the signal source, the bars vibrate against the surface of a tissue-mimicking phantom. The double-bar source is also used to propagate shear wave into an ex vivo prostate phantom with a 6 mm “tumor” in it. A combination of high frequencies (400–600 Hz) is used to drive the double-bar applicator. In the phantom experiments, a shear wave focal zone with higher vibration amplitude and uniformity predicted by the theory was confirmed. The position of the focal zone is controllable when adjusting the separation of the bars as the theory shows. When this vibration scheme was used in a prostate phantom experiment, high-resolution tumor images with clear boundaries are obtained. The parallel bar is an ideal applicator to create more uniform vibration within a controllable localized volume. The field has uniformity especially in the direction along the bars.
Nonlinear acoustic scattering from a gassy poroelastic seabed
Authors: Boyle Frank A. , Chotiros Nicholas P.
Published: July 2002

A model for difference frequency backscatter from trapped bubbles in sandy sediments was developed. A nonlinear volume scattering coefficient was computed via a technique similar to that of Ostrovsky and Sutin [“Nonlinear sound scattering from subsurface bubble layers,” in Natural Physical Sources of Underwater Sound, edited by B. R. Kerman (Kluwer, Dordrecht, 1993), pp. 363–373], which treats the case of bubbles surrounded by water. Biot’s poroelastic theory is incorporated to model the acoustics of the sediment. Biot fast and slow waves are included by modeling the pore fluid as a superposition of two acoustic fluids with effective densities that differ from the pore fluid’s actual density and account for its confinement within sediment pores. The principle of acoustic reciprocity is employed to develop an expression for the backscattering strength. Model behavior is consistent with expectations, based on the known behavior of bubbles in simpler fluid media.
Theoretical and experimental study of transducers aimed at low-frequency ultrasonic atomization of liquids
Authors: Sindayihebura Daniel , Bolle Léon , Cornet Alain , Joannes Luc
Published: July 2002

The fine atomization of liquids by means of low-frequency ultrasonic atomizers (about 50 kHz) results from unstable surface waves generated on the free surface of a thin liquid film. This thin liquid film develops as the liquid spreads fast over the atomizing surface of the atomizer. The displacement amplitude of the atomizing surface must be greater than 2 μm to initiate the atomization process. This may be achieved using a displacement amplitude transformer. The present study focuses on an analytical analysis of the longitudinal oscillations stimulated by the piezoelectric elements in a stepped horn which operates as an amplitude transformer. A sizing method of the stepped horn is established and experimentally tested. The influence of the materials’ mechanical damping on the displacement amplitude of the atomizing surface is investigated. The comparison between theoretical and experimental results allows the determination of the internal damping coefficient.
Generalized material model for lead magnesium niobate (PMN) and an associated electromechanical equivalent circuit
Authors: Piquette Jean C. , Forsythe Stephen E.
Published: July 2002

An existing one-dimensional nonlinear material model of lead magnesium niobate [J. C. Piquette and S. E. Forsythe, “A nonlinear model of lead magnesium niobate (PMN),” J Acoust. Soc. Am. 101, 289–296 (1997)] is generalized to three dimensions. The resulting theory is applied to two practical systems: the “thickness expander plate” and the “length expander bar.” Linearizing the theory results in an electromechanical equivalent circuit that is applicable to predicting the first-order behavior of transducers based on either of these practical systems. The methods used are sufficiently general that the circuit is also appropriate for piezoelectric, and even for electrostatic, transducers. Preliminary experimental data that confirm the validity of the circuit are presented. Connections between the constants of the theory and those of piezoelectricity are derived, and a general expression for the coupling coefficient is obtained. Known theoretical coupling coefficients for piezoelectric and electrostatic transducers are recovered as special cases. The coupling coefficient of the PMN bar at zero prestress and zero remanent polarization is examined in some detail. For this case it is found that, to a good approximation, the bias voltage of the optimal (i.e., maximum) coupling coefficient is √ times the bias voltage which produces the maximum effective piezoelectric d33. A simple formula for estimating second harmonic distortion at zero stress and remanent polarization is given. The D field for the bar is obtained in terms of a Maclaurin series in stress. This series is asymptotic in the electric field, and is useful for estimating harmonic distortion when the stress or remanent polarization are nonzero.
Characteristics of Thixotropic Behavior
Authors: Joye Donald D. , Poehlein Gary W.
Published: July 2002

The shear stress-shear rate behavior of a thixotropic hectorite clay-water suspension was studied in a Couette viscometer under a wide variety of rest and shear rate histories. Shear stress decay and build-up transients resulting from step changes in shear rate were measured. The transient stress data were used to construct equilibrium and constant structure flow curves. The constant structure curves could be described by the Power Law model with a constant exponent but varying coefficient. Normalized stress transients could be described by an exponential time series similar to those used in stress relaxation studies on viscoelastic polymers. This method was applicable to literature data and to data obtained for other fluids in our laboratory. The transient behavior of thixotropic fluids is heavily influenced by past history of deformation. Structural rebuilding during rest seemed to begin with the formation of a weak gel structure. Structural rebuilding was also observed under shear rate. In experiments with a short rest period, stresses measured after reapplication of shear rate returned quickly to the values measured before the rest period.
Creep behavior of electrorheological fluids
Authors: Otsubo Yasufumi , Edamura Kazuya
Published: July 2002

Composite particles consisting of a polymer core and an inorganic shell were formed by suspension polymerization. For suspensions in a silicone oil, the steady-shear viscosity and creep behavior were measured in electric fields up to 2.0 kV mm−1. Although the polymer core is not ER active, the suspensions of composite particles show a striking increase in the steady-shear viscosity and the flow curve changes from Newtonian to Bingham profiles. The ER effects can be attributed to the shell layers on the polymer surfaces. The creep curves at low stresses are composed of instantaneous elastic, retarded elastic, and viscous regions. With increasing stress the retarded elastic and viscous components decrease. At some critical stress the strain almost instantaneously increases and reaches the equilibrium without viscous flow. After the removal of the critical stress, the suspensions show no elastic recovery. Therefore the creep and recovery behavior is purely plastic and the critical stress corresponds to the static yield value. The application of stresses above the static yield value causes the suspensions to flow. The development of yield stress (plateau value) in steady shear can be derived from the ideal chain model in which the particles all align into chains of single particle width and equal spacing. However, the model cannot predict the instantaneous deformation without recovery below the yield stress. The thick column formed by several chains may be responsible for purely plastic responses.
Digital Cognitive Behavioral Therapy for Insomnia Using a Smartphone Application in China
Authors: Zhang Cheng , Liu Yuxuan , Guo Xiaoming , Liu Yanan , Shen Yane , Ma Jing
Published: March 2023

Importance

Digital cognitive behavioral therapy for insomnia (DCBT-I) requires adaptation to different sociocultural contexts. Moreover, studies comparing DCBT-I and sleep education in the same operating interface are lacking.

Objective

To investigate the efficacy of a smartphone-based Chinese culture–adapted DCBT-I application (app) for insomnia compared with sleep education using the same app.

Design, Setting, and Participants

This was a single-blinded, randomized clinical trial conducted from March 2021 to January 2022. Screening and randomization were conducted at Peking University First Hospital. Follow-up visits were performed online or in the same hospital. After assessing for eligibility, eligible participants were enrolled and allocated (1:1) to DCBT-I or sleep education groups. Data were analyzed from January to February 2022.

Interventions

A Chinese smartphone-based app with the same interface was used in both DCBT-I and sleep education groups over 6 weeks, with 1-, 3-, and 6-month follow-ups.

Main Outcomes and Measures

The primary outcome was Insomnia Severity Index (ISI) scores with the intention-to-treat principle. Secondary and exploratory outcomes included sleep diary measures; self-reported scales assessing dysfunctional beliefs about sleep, mental health, and quality of life; and smart bracelet measures.

Results

Of 82 participants (mean [SD] age, 49.67 [14.49] years; 61 [74.4%] females), with 41 randomized to sleep education and 41 randomized to DCBT-I; 77 participants completed the 6-week intervention (39 participants in the sleep education group and 38 participants in the DCBT-I group; full analysis data set) and 73 completed the 6-month follow-up (per protocol data set). Mean (SD) ISI scores in the DCBT-I group were significantly lower than those in the sleep education group after the 6-week intervention (12.7 [4.8] points vs 14.9 [5.0] points; Cohen d = 0.458; P = .048) and at the 3-month follow-up (12.1 [5.4] points vs 14.8 [5.5] points; Cohen d = 0.489; P = .04). There were significant improvements from before to after the intervention for both the sleep education and DCBT-I groups, with large effect sizes(sleep education: d = 1.13; DCBT-I: d = 1.71). Some of the sleep diary measures and self-reported scales showed more improvements in the DCBT-I group than sleep education group, such as total sleep time (mean [SD]: 3 months, 403.9 [57.6] minutes vs 363.2 [72.3] minutes; 6 months, 420.3 [58.0] minutes vs 389.7 [59.4] minutes) and sleep efficiency (mean [SD]: 3 months, 87.4% [8.3%] vs 76.7% [12.1%]; 6 months, 87.5% [8.2%] vs 78.1% [10.9%]).

Conclusions and Relevance

In this randomized clinical trial, the smartphone-based Chinese culture-adapted DCBT-I improved insomnia severity compared with sleep education. Future multicenter clinical trials with large sample sizes are needed to validate its effectiveness in the Chinese population.

Trial Registration

ClinicalTrials.gov Identifier: NCT04779372
Out-of-Pocket Spending for Non–Birth-Related Hospitalizations of Privately Insured US Children, 2017 to 2019
Authors: Carlton Erin F. , Becker Nora V. , Moniz Michelle H. , Scott John W. , Prescott Hallie C. , Chua Kao-Ping
Published: March 2023

Importance

Privately insured US children account for 40% of non–birth-related pediatric hospitalizations. However, there are no national data on the magnitude or correlates of out-of-pocket spending for these hospitalizations.

Objective

To estimate out-of-pocket spending for non–birth-related hospitalizations among privately insured children and identify factors associated with this spending.

Design, Setting, and Participants

This study is a cross-sectional analysis of the IBM MarketScan Commercial Database, which reports claims from 25 to 27 million privately insured enrollees annually. In the primary analysis, all non–birth-related hospitalizations of children 18 years and younger from 2017 through 2019 were included. In a secondary analysis focused on insurance benefit design, hospitalizations that could be linked to the IBM MarketScan Benefit Plan Design Database and were covered by plans with a family deductible and inpatient coinsurance requirements were analyzed.

Main Outcomes and Measures

In the primary analysis, factors associated with out-of-pocket spending per hospitalization (sum of deductibles, coinsurance, and copayments) were identified using a generalized linear model. In the secondary analysis, variation in out-of-pocket spending was assessed by level of deductible and inpatient coinsurance requirements.

Results

Among 183 780 hospitalizations in the primary analysis, 93 186 (50.7%) were for female children, and the median (IQR) age of hospitalized children was 12 (4-16) years. A total of 145 108 hospitalizations (79.0%) were for children with a chronic condition and 44 282 (24.1%) were covered by a high-deductible health plan. Mean (SD) total spending per hospitalization was $28 425 ($74 715). Mean (SD) and median (IQR) out-of-pocket spending per hospitalization were $1313 ($1734) and $656 ($0-$2011), respectively. Out-of-pocket spending exceeded $3000 for 25 700 hospitalizations (14.0%). Factors associated with higher out-of-pocket spending included hospitalization in quarter 1 compared with quarter 4 (average marginal effect [AME], $637; 99% CI, $609-$665) and lack of chronic conditions compared with having a complex chronic condition (AME, $732; 99% CI, $696-$767). The secondary analysis included 72 165 hospitalizations. Among hospitalizations covered by the least generous plans (deductible of $3000 or more and coinsurance of 20% or more) and most generous plans (deductible less than $1000 and coinsurance of 1% to 19%), mean (SD) out-of-pocket spending was $1974 ($1999) and $826 ($798), respectively (AME, $1123; 99% CI, $1069-$1179).

Conclusions and Relevance

In this cross-sectional study, out-of-pocket spending for non–birth-related pediatric hospitalizations were substantial, especially when they occurred early in the year, involved children without chronic conditions, or were covered by plans with high cost-sharing requirements.
Hyaluronic Acid‐Based Bioconjugate Systems, Scaffolds, and Their Therapeutic Potential
Authors: Kotla Niranjan G. , Mohd Isa Isma Liza , Larrañaga Aitor , Maddiboyina Balaji , Swamy Samantha K. , Sivaraman Gandhi , Vemula Praveen K.
Published: March 2023

In recent years, the development of hyaluronic acid or hyaluronan (HA) based scaffolds, medical devices, bioconjugate systems have expanded into a broad range of research and clinical applications. Research findings over the last two decades suggest that the abundance of HA in most mammalian tissues with distinctive biological roles and chemical simplicity for modifications have made it an attractive material with a rapidly growing global market. Besides its use as native forms, HA has received much interest on so‐called “HA‐bioconjugates” and “modified‐HA systems”. In this review, the importance of chemical modifications of HA, underlying rationale approaches, and various advancements of bioconjugate derivatives with their potential physicochemical, and pharmacological advantages are summarized. This review also highlights the current and emerging HA‐based conjugates of small molecules, macromolecules, crosslinked systems, and surface coating strategies with their biological implications, including their potentials and key challenges discussed in detail.
Recent Advances in Organ‐on‐Chips Integrated with Bioprinting Technologies for Drug Screening
Authors: Tabatabaei Rezaei Nima , Kumar Hitendra , Liu Hongqun , Lee Samuel S. , Park Simon S. , Kim Keekyoung
Published: March 2023

Currently, the demand for more reliable drug screening devices has made scientists and researchers develop novel potential approaches to offer an alternative to animal studies. Organ‐on‐chips are newly emerged platforms for drug screening and disease metabolism investigation. These microfluidic devices attempt to recapitulate the physiological and biological properties of different organs and tissues using human‐derived cells. Recently, the synergistic combination of additive manufacturing and microfluidics has shown a promising impact on improving a wide array of biological models. In this review, different methods are classified using bioprinting to achieve the relevant biomimetic models in organ‐on‐chips, boosting the efficiency of these devices to produce more reliable data for drug investigations. In addition to the tissue models, the influence of additive manufacturing on microfluidic chip fabrication is discussed, and their biomedical applications are reviewed.
Polymeric Memristor Based Artificial Synapses with Ultra‐Wide Operating Temperature
Authors: Li Jiayu , Qian Yangzhou , Li Wen , Yu Songcheng , Ke Yunxin , Qian Haowen , Lin Yen‐Hung , Hou Cheng‐Hung , Shyue Jing‐Jong , Zhou Jia , Chen Ye , Xu Jiangping , Zhu Jintao , Yi Mingdong , Huang Wei
Published: March 2023

Neuromorphic electronics, being inspired by how the brain works, hold great promise to the successful implementation of smart artificial systems. Among several neuromorphic hardware issues, a robust device functionality under extreme temperature is of particular importance for practical applications. Given that the organic memristors for artificial synapse applications are demonstrated under room temperature, achieving a robust device performance at extremely low or high temperature is still utterly challenging. In this work, the temperature issue is addressed by tuning the functionality of the solution‐based organic polymeric memristor. The optimized memristor demonstrates a reliable performance under both the cryogenic and high‐temperature environments. The unencapsulated organic polymeric memristor shows a robust memristive response under test temperature ranging from 77 to 573 K. Utilizing X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary‐ion mass spectrometry (ToF‐SIMS) depth profiling, the device working mechanism is unveiled by comparing the compositional profiles of the fresh and written organic polymeric memristors. A reversible ion migration induced by an applied voltage contributes to the characteristic switching behavior of the memristor. Herein, both the robust memristive response achieved at extreme temperatures and the verified device working mechanism will remarkably accelerate the development of memristors in neuromorphic systems.
Single‐Atom Nano‐Islands (SANIs): A Robust Atomic–Nano System for Versatile Heterogeneous Catalysis Applications
Authors: Li Zesheng , Li Bolin , Li Qingyu
Published: March 2023

Academician Tao Zhang from China and co‐workers designed the first Pt1/FeOx single‐atom catalysts (SACs) in 2011, and they proposed the concept of “single‐atom catalysis” in the field of heterogeneous catalysis. Generally, it is easy for active metal single‐atom sites on a carrier to migrate and aggregate, which results in poor performance; or the chemical bond between the metal atom and carrier is too strong (immovable), which results in passivation of the active site. Recently, “nano‐island” type SACs were designed, in which the active metal atoms are isolated on the “islands”, and can move within the respective “island”, but the migration across the “island” is blocked, to achieve a dynamic confinement design of single atoms (that is, a “moving but not aggregating” design philosophy). Herein, a new concept of “single‐atom nano‐islands (SANIs)” is proposed to describe these congeneric “atomic–nano” systems in heterogeneous catalysis fields. Particularly, the SANIs are divided into three categories: “one‐island–one‐atom”, “one‐island–multi‐atoms”, and “island–sea synergism” architectures. The scientific significance and application principles of SANIs in versatile heterogeneous catalysis fields (i.e., thermocatalysis, electrocatalysis, and photocatalysis) are summarized. The challenges and proposals of SANIs are also provided.
TexSe1–x Photodiode Shortwave Infrared Detection and Imaging
Authors: Fu Liuchong , He Yuming , Zheng Jiajia , Hu Yuxuan , Xue Jiayou , Li Sen , Ge Ciyu , Yang Xuke , Peng Meng , Li Kanghua , Zeng Xiangbin , Wei Jinchao , Xue Ding‐jiang , Song Haisheng , Chen Chao , Tang Jiang
Published: March 2023

Short‐wave infrared detectors are increasingly important in the fields of autonomous driving, food safety, disease diagnosis, and scientific research. However, mature short‐wave infrared cameras such as InGaAs have the disadvantage of complex heterogeneous integration with complementary metal–oxide–semiconductor (CMOS) readout circuits, leading to high cost and low imaging resolution. Herein, a low‐cost, high‐performance, and high‐stability TexSe1–x short‐wave infrared photodiode detector is reported. The TexSe1–x thin film is fabricated through CMOS‐compatible low‐temperature evaporation and post‐annealing process, showcasing the potential of direct integration on the readout circuit. The device demonstrates a broad‐spectrum response of 300–1600 nm, a room‐temperature specific detectivity of 1.0 × 1010 Jones, a −3 dB bandwidth up to 116 kHz, and a linear dynamic range of over 55 dB, achieving the fastest response among Te‐based photodiode devices and a dark current density 7 orders of magnitude smaller than Te‐based photoconductive and field‐effect transistor devices. With a simple Si3N4 packaging, the detector shows high electric stability and thermal stability, meeting the requirements for vehicular applications. Based on the optimized TexSe1–x photodiode detector, the applications in material identification and masking imaging is demonstrated. This work paves a new way for CMOS‐compatible infrared imaging chips.
2D Perovskite Mn2+‐Doped Cs2CdBr2Cl2 Scintillator for Low‐Dose High‐Resolution X‐ray Imaging
Authors: Xu Haiping , Liang Wenqing , Zhang Zhizhuan , Cao Chi , Yang Wensheng , Zeng Hongmei , Lin Zhien , Zhao Dewei , Zou Guohong
Published: March 2023

High‐performance X‐ray scintillators with low detection limits and high light yield are of great importance and are a challenge for low‐dose X‐ray imaging in medical diagnosis and industrial detection. In this work, the synthesis of a new 2D perovskite, Cs2CdBr2Cl2, via hydrothermal reaction is reported. By doping Mn2+ into the perovskite, a yellow emission located at 593 nm is obtained, and the photoluminescence quantum yield (PLQY) of Cs2CdBr2Cl2:5%Mn2+ perovskite reaches the highest value of 98.52%. The near‐unity PLQY and negligible self‐absorption of Cs2CdBr2Cl2:5%Mn2+ enable excellent X‐ray scintillation performance with a high light yield of 64 950 photons MeV−1 and low detection limit of 17.82 nGyair s−1. Moreover, combining Cs2CdBr2Cl2:5%Mn2+ with poly(dimethylsiloxane) to fabricate a flexible scintillator screen achieves low‐dose X‐ray imaging with a high resolution of 12.3 line pairs (lp) mm−1. The results suggest that Cs2CdBr2Cl2:5%Mn2+ is a promising candidate for low‐dose and high‐resolution X‐ray imaging. The study presents a new approach to designing high‐performance scintillators through metal‐ion doping.
PF6− Pseudohalides Anion Based Metal‐Free Perovskite Single Crystal for Stable X‐Ray Detector to Attain Record Sensitivity
Authors: Li Zhizai , Li ZhenHua , Peng Guoqiang , Shi Chang , Wang Haoxu , Ding San‐Yuan , Wang Qian , Liu Zitong , Jin Zhiwen
Published: March 2023

Metal‐free perovskites (MFPs) possess excellent photophysical properties of perovskites while avoiding the introduction of toxic metal ions and organic solvents, and have been expanded to X‐ray detection. However, iodine‐based high‐performance MFPs are tended to oxidation, corrosion, and uncontrolled ion migration, resulting in poor material stability and device performance. Herein, the strongly electronegative PF6− pseudohalide is used to fabricate the large‐size MDABCO‐NH4(PF6)3 (MDBACO = methyl‐N′‐diazabicyclo[2.2.2]octonium) single crystals (SCs) for solving the problems of iodine ions. After the introduction of PF6− pseudohalides, the Coulomb interaction and hydrogen bonding strength are enhanced to alleviate the ion‐migration and stability problems. Moreover, combined with theoretical calculations, PF6− pseudohalides increase the ion‐migration barrier, and affect the contribution of its components to the energy band for a broadening bandgap. Meanwhile, the improved physical properties, such as large activation energy of ionic migration, high resistivity, and low current drift, further expand its application in low‐dose and sensitive X‐ray detection. Finally, the X‐ray detector based on MDABCO‐NH4(PF6)3 SCs achieves a sensitivity of 2078 µC Gyair−1 cm−2 (highest among metal‐free SCs‐based detectors) and the lowest detectable dose rate (16.3 nGyair s−1). This work has expanded the selection of MFPs for X‐ray detectors and somewhat advanced the development of high‐performance devices.