bluuebunny/crossref_metadata_2025 huggingface dataset:
Phase transition of spin-1 frustrated model on square-lattice bilayer
Authors: Qing Yu-Lin , Peng Xiao-Li , Hu Ai-Yuan ,   College of Physics and Electronic Engineering, Chongqing Normal University, Chongqing 401331, China
Published: February 2022

In this paper, we investigate the phase transition of the spin-1 frustrated model on a square-lattice bilayer by the double-time Green’s function method. The effects of the interlayer coupling parameter \begin{document}$ {J_c} $\end{document} and single-ion anisotropy D on phase transformation between the Nèel state (AF1) and collinear state (AF2) are explored. Our results show that if only the parameters \begin{document}$ {J_c} $\end{document} and D are not equal to zero at the same time, the two states can exist and have the same critical temperature at \begin{document}$ {J_2} = {J_1}/2 $\end{document}, which represents the nearest neighbor exchange. Under such parameters, a first-order phase transformation between these two states below the critical point can occur. For \begin{document}$ {J_2} \ne {J_1}/2 $\end{document}, although both states may exist, their Neel temperatures differ from each other. If the Nèel point of the AF1 (AF2) state is larger, then at very low temperature, the AF1 (AF2) state is more stable. Thus, in an intermediate temperature, a first-order phase transition between these two states may also occur.
Experimental research progress of electronic band structure and low temperature transport based on molybdenum disulfide
Authors: Wu Fan-Fan , Ji Yi-Ru , Yang Wei , Zhang Guang-Yu ,   Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China,   School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China,   Songshan Lake Materials Laboratory, Dongguan 523808, China
Published: February 2022

Molybdenum disulfide is a layered transition metal chalcogenide semiconductor. It has many applications in the fields of two-dimensional spintronics, valleytronics and optoelectronics. In this review, molybdenum disulfide is taken as a representative to systematically introduce the energy band structures of single layer, bilayer and twisted bilayer molybdenum disulfide, as well as the latest experimental progress of its realization and low-temperature electrical transport, such as superconductivity and strong correlation phenomenon. Finally, two-dimensional transition metal chalcogenide moiré superlattice’s challenges in optimizing contact and sample quality are analyzed and the future development of this field is also presented.
Charge density waves in low-dimensional material
Authors: Fan Jin-Ze , Fang Zhan-Bo , Luo Chao-Jie , Zhang Hui ,   Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei 230026, China,   Department of Physics, University of Science and Technology of China, Hefei 230026, China
Published: February 2022

Charge density waves (CDWs) have triggered off extensive research in low-dimensional systems. The discovery of CDW offers a new crucial clue to understanding the intrinsic mechanisms of low-dimensional electron-phonon coupling and electron correlation. In addition, the physical properties of low-dimensional material such as magnetism and superconductivity can be fine-tuned with accurately and effectively controlled CDW phase. At the beginning,we briefly introduce the basic properties of CDW in one-dimensional and quasi one-dimensional materials, revealing the physical proprieties of the CDW, for instance, the excited state and the manipulation technologies. Then, focusing on the CDW in a two-dimensional system, we mainly introduce the recent research progress and the generation mechanism of CDW of two-dimensional materials. The interaction between CDW and Mott insulator and between superconductivity and other orders such as spin density wave and pair density wave provide a new perspective to research the multi-electron collective excitation and electron interaction. The manipulation of multi-electron collective excitation and electron-phonon interaction in CDW through doping, high pressure and laser pulse is also introduced and shares similarity with the one-dimensional system. Finally, in this article we propose a potential research application of two dimensional CDW.
Response of bacterial community structure to different ecological niches and their functions in Korean pine forests
Authors: Ji Rui-Qing , Xie Meng-Le , Li Guan-Lin , Xu Yang , Gao Ting-Ting , Xing Peng-Jie , Meng Li-Peng , Liu Shu-Yan
Published: February 2022

A healthy plant microbiome is diverse, taxonomically-structured, and gives its plant host moderate advantages in growth, development, stress tolerance, and disease resistance. The plant microbiome varies with ecological niches and is influenced by variables that are complex and difficult to separate from each other, such as the plant species, soil, and environmental factors. To explore the composition, diversity, and functions of the bacterial community of Korean pine forests, we used high-throughput sequencing to study five areas with different forest ages from June to October 2017 in northeast China. We obtained 3,247 operational taxonomic units (OTUs) based on 16S rRNA gene sequencing via an Illumina Hi-seq platform. A total of 36 phyla and 159 known genera were classified. The Shannon index of the bacterial community from the rhizospheric soil was significantly higher (p < 0.01, n = 10) than that of the root tips. Beta-diversity analysis confirmed that the bacterial community of the rhizospheric soil was significantly different (p < 0.001) from the root tips. Nine bacterial phyla were dominant (relative richness > 1%) in the rhizospheric soil, but there were six dominant phyla in the root tips. Proteobacteria was the core flora in the root tips with a relative abundance of more than 50%. It is known that the formation of bacterial communities in the rhizospheric soil or the root is mainly caused by the processes of selection, and we found a relatively high abundance of a few dominant species. We further analyzed the correlations between the bacterial community from the rhizospheric soil with that of the root tips, as well as the correlations of the bacterial community with soil physicochemical properties and climate factors. We used Functional Annotation of the Prokaryotic Tax (FAPROTAX) to predict the functions of the bacterial community in the rhizospheric soil and root tips. Five related phototrophic functions, nine nitrogen cycle functions, two related chemoheterotrophic functions, and two others were predicted. The abundance of the bacteria phyla performing relevant functions was different in the rhizospheric soil than in the root tips. These functions were significantly influenced by the contents of nitrogen, phosphorus, and potassium in the soil habitat. The bacterial composition and functions in the rhizospheric soil and root tips of Korean pine were analyzed, and the results demonstrated the importance of soil and plant species on the bacterial community in the below ground plant microbiome.
Performance Assessment of Two Horizontal Shroud Tidal Current Energy Converter using Hydraulic Experiment
Authors: Lee Uk-Jae , Choi Hyuk-Jin , Ko Dong-Hui
Published: February 2022

In this study, the two horizontal shroud tidal current energy converter, which can generate power even under low flow speed conditions, was developed. In order to determine the shape of the shroud system, a three-dimensional numerical simulation test was conducted, and a 1/6 scale down model was made to perform a hydraulic model experiment. The hydraulic model experiment was performed under four flow conditions, and the flow speed, torque, and RPM were measured for each experimental case. As a result of the numerical simulation test, it was found that the flow speeds passing through the nozzle were increased by about 2~3 times in the cylinder, and when the extension ratio was 2:1, the highest flow speed was shown. In addition, it was found that the flow speeds increased 2.8 times when the diameter ratio between the nozzle and the cylinder was 1.5:1. Meanwhile, as a result of the hydraulic model experiment, it was found that when the tip speed ratio was between 1.75 and 2, the power coefficient was 0.32 to 0.34.
Use of a constrain phage displayed‐peptide library for the isolation of peptides binding to HIV‐1 nucleocapsid protein (NCp7)
Authors: Lener D. , Benarous R. , Calogero R.A.
Published: July 2002

It has been shown that peptide libraries are powerful tools for the identification of peptides showing new binding specificity. This technology was applied to the isolation of peptides binding to HIV‐1 nucleocapsid protein (NCp7). Three different prolin reach peptide sequences, interacting with NCp7, were isolated, from a constrained phage displayed‐peptide library of 108 independent clones. The three peptide sequences, isolated from the peptide library, were shown to bind NCp7 in the region 30–52. Moreover, two of them share the PP‐(D/E)R consensus sequence.
Site‐directed mutagenesis of histidine residues in the Δ12 acyl‐lipid desaturase of Synechocystis
Authors: Avelange-Macherel Marie-Hélène , Macherel David , Wada Hajime , Murata Norio
Published: July 2002

In the cyanobacterium Synechocystis sp. PCC 6803, there are four acyl‐lipid desaturases that are, respectively, specific to the Δ6, Δ9, Δ12 and ω3 positions of fatty acids. The desA gene for the Δ12 acyl‐lipid desaturase was modified by site‐directed mutagenesis, such that four of the histidine residues that are conserved in the four desaturases and one histidine residue that is not conserved were replaced by arginine, and the mutated desA genes were overexpressed in Escherichia coli. All of these mutations eliminated the Δ12 desaturase activity. These results demonstrate that the five histidine residues are essential for the activity of the Δ12 desaturase, perhaps by providing the ligands for the catalytic Fe center.
Pressure‐induced molten globule state of cholinesterase
Authors: Cléry C. , Renault F. , Masson P.
Published: July 2002

The denaturing effect of pressure on the structure of human butyrylcholinesterase was examined by gel electrophoresis under pressure and by 8‐anilino‐1‐naphthalene sulfonate (ANS) binding. It was found that the fluorescence intensity of bound ANS is increased by pressure between 0.5 and 1.5 kbar and that the hydrodynamic volume of the enzyme swells when pressures around 1.5 kbar are applied. These findings indicate that pressure denaturation of butyrylcholinesterase is a multi‐step process and that the observed transient pressure‐denatured states have characteristics of molten globules.
Characterization of recombinant mustard trypsin inhibitor 2 (MTI2) expressed in Pichia pastoris
Authors: Volpicella M. , Schipper A. , Jongsma M.A. , Spoto N. , Gallerani R. , Ceci L.R.
Published: July 2002

The mustard trypsin inhibitor MTI2 was expressed as secretory protein in the yeast Pichia pastoris. In order to evaluate the influence of the C‐terminal amino acids of the precursor form on the inhibitor activity, the C‐terminal precursor and the mature protein were both expressed. A third His‐tagged construct was also designed to compare alternative purification procedures. Proteins were efficiently expressed at levels of 40–160 mg/l in shake flasks. Equilibrium dissociation constants demonstrated that the mature protein was a stronger inhibitor of bovine β‐trypsin compared to the precursor and His‐tagged forms (0.01 nM vs. 0.58 nM and 0.71 nM, respectively). The recombinant proteins were active inhibitors of Spodoptera exigua gut proteases.
The chaperonin‐related protein Tcm62p ensures mitochondrial gene expresssion under heat stress
Authors: Klanner Carola , Neupert Walter , Langer Thomas
Published: July 2002

Tcm62p, distantly related to chaperonins, is required for the assembly of succinate dehydrogenase in mitochondria of Saccharomyces cerevisiae and was proposed to exert chaperone activity. We demonstrate here crucial functions of Tcm62p under heat stress. It ensures mitochondrial gene expression at elevated temperatures and prevents heat‐aggregation of the ribosomal subunit Var1p. Similar to chaperonins, Tcm62p forms a high molecular mass protein complex of approximately 850 kDa in the mitochondrial matrix space. These results suggest a more general chaperone function of Tcm62p in mitochondria.
The reduction potential of the β‐carotene+/β‐carotene couple in an aqueous micro‐heterogeneous environment
Authors: Edge Ruth , Land Edward J. , McGarvey David J. , Burke Marc , Truscott T.George
Published: July 2002

There is a resurgence of interest in the role of electron transfer reactions involving β‐carotene in photosynthesis. There is also current debate on the health benefits of dietary carotenoids and the possible deleterious effects on certain sub‐populations such as smokers. The impact of dietary carotenoids on health may well be also related to radical reactions. A key parameter in biological systems is therefore the one‐electron reduction potential of the carotenoid radical cation, now reported for the first time in a model biological aqueous environment. The value obtained is 1.06±0.01 V and is sufficiently high to oxidise cell membrane proteins, but is low enough to repair P680+in the photosynthetic reaction centre.
A central role for the endothelial NADPH oxidase in atherosclerosis
Authors: Meyer Jamie W. , Schmitt Mark E.
Published: July 2002

An increasing body of evidence has demonstrated that NADPH oxidase plays a critical role in several early steps leading toward the development of atherosclerosis. These effects appear to be carried out by both the ability of O2
− to act as a small second messenger molecule, and potentially the oxidation of low density lipoprotein by O2
−. We describe a model for the initiation and development of atherosclerosis that suggests targeted inhibition of NADPH oxidase as a powerful site for prevention and treatment of this disease.
Mitochondrial DNA depletion causes morphological changes in the mitochondrial reticulum of cultured human cells
Authors: Gilkerson Robert W , Margineantu Daciana H , Capaldi Roderick A , Selker Jeanne M.L
Published: July 2002

Depletion of mitochondrial DNA (mtDNA) causes defects in respiratory activity and energy production. Recent studies have shown mitochondria to exist primarily as reticular networks, having tubular cristae. Using fluorescence microscopy and transmission electron microscopy, we have examined mitochondrial morphology and interior structure in wildtype and mtDNA‐depleted ρ0 human fibroblasts and 143B osteosarcoma cell lines. MtDNA depletion results in compromise of the mitochondrial continuum and causes a reduction in amount of cristal membranes, often prompting the remaining cristae to adopt a circular appearance in the mitochondrial interior. These changes emphasize the tight relationship between mitochondrial structure and function.
Protein synthesis is required for stabilization of hsp70 mRNA upon exposure to both hydrostatic pressurization and elevated temperature
Authors: Kaarniranta Kai , Holmberg Carina I. , Helminen Heikki J. , Eriksson John E. , Sistonen Lea , Lammi Mikko J.
Published: July 2002

We have recently described that in chondrocytic cells high hydrostatic pressure (HP) causes a heat shock response via mRNA stabilization without a transcriptional activation of the hsp70 gene. In this study, we investigated whether this exceptional regulatory mechanism occurs more generally in different types of cells. Indeed, hsp70 mRNA and protein accumulated in HeLa, HaCat and MG‐63 cells under 30 MPa HP, without DNA‐binding of heat shock transcription factor 1 (HSF1) to the heat shock element of the hsp70 gene or formation of nuclear HSF1 granules, revealing a lack of transcriptional activation. Moreover, we observed that protein synthesis is needed for mRNA stabilization. Thus, high HP offers a model to study the mechanisms of hsp70 mRNA stabilization without HSF1‐mediated induction of the heat shock gene response.
Methadone induces CCR5 and promotes AIDS virus infection
Authors: Suzuki Shunji , Carlos Maria P , Chuang Linda F , Torres José V , Doi Roy H , Chuang Ronald Y
Published: July 2002

Methadone, a regimen for the treatment of opioid dependency, was found to induce the expression of CCR5, a co‐receptor for human immunodeficiency virus (HIV)/simian form of HIV (SIV) entry, on human CEM x174 lymphocytes. Both CCR5 mRNA and protein were elevated in methadone‐treated cells. A concomitant increase of mu opioid receptors was also observed. Upon methadone exposure, SIVmac239‐infected CEM x174 cells released greater amounts of virus particles as revealed by both the number of syncytia formation and reverse transcriptase activities. Similar methadone effect was not observed on CEM x174 cells infected with other simian retroviruses that do not depend on CCR5 for cellular entry. These studies raise concerns considering methadone as an innocuous morphine substitute.
Cold signalling associated with vernalization in Arabidopsis thaliana does not involve CBF1 or abscisic acid
Authors: Liu Jiayou , Gilmour Sarah J. , Thomashow Michael F. , Van Nocker Steven
Published: July 2002

In genotypes of Arabidopsis that exhibit a winter‐annual flowering habit, floral induction in response to extended cold exposure (vernalization) is mediated by repression of the flowering‐inhibitor gene FLC. We are interested in identifying components of the cold signal transduction pathway leading to FLC repression. We examined the potential involvement of two factors that are known to play roles in plant cold responses: (1) CBF1, a cold‐responsive transcription factor that is involved in activating the cold acclimation response, and (2) the phytohormone abscisic acid (ABA), which has traditionally been associated with plant cold responses. We introduced a transgene driving constitutive expression of CBF1 into a winter‐annual genotype of Arabidopsis. In transgenic lines expressing CBF1 mRNA to high levels, FLC mRNA expression was not repressed, and flowering was not accelerated relative to control plants. We also introduced mutations that compromise ABA biosynthesis or sensitivity into a winter‐annual genotype and found that the vernalization response was not affected. Finally, we found that presumed increases in ABA levels, as a result of direct application of the hormone or severe water stress, were insufficient to substitute for cold to induce flowering. Taken together, these findings indicate that vernalization involves a pathway that is distinct from cold‐response mechanisms involving CBF1, cold‐regulated genes under CBF1 control, and ABA.
Oxidation of nitric oxide by oxomanganese–salen complexes: a new mechanism for cellular protection by superoxide dismutase/catalase mimetics
Authors: SHARPE Martyn A. , OLLOSSON Richard , STEWART Victoria C. , CLARK John B.
Published: July 2002

Manganese—salen complexes (Mn-Salen), including EUK-8 [manganese N,N′-bis(salicylidene)ethylenediamine chloride] and EUK-134 [manganese 3-methoxy N,N′-bis(salicylidene)ethylenediamine chloride], have been reported to possess combined superoxide dismutase (SOD) and catalase mimetic functions. Because of this SOD/catalase mimicry, EUK-8 and EUK-134 have been investigated as possible therapeutic agents in neurological disorders resulting from oxidative stress, including Alzheimer's disease, Parkinson's disease, stroke and multiple sclerosis. These actions have been explained by the ability of the Mn-Salen to remove deleterious superoxide (O2−) and H2O2. However, in addition to oxidative stress, cells in models for neurodegenerative diseases may also be subjected to damage from reactive nitrogen oxides (nitrosative stress), resulting from elevated levels of NO and sister compounds, including peroxynitrite (ONOO−). We have been examining the interaction of EUK-8 and EUK-134 with NO and ONOO−. We find that in the presence of a per-species (H2O2, ONOO−, peracetate and persulphate), the Mn-Salen complexes are oxidized to the corresponding oxo-species (oxoMn-Salen). OxoMn-Salens are potent oxidants, and we demonstrate that they can rapidly oxidize NO to NO2 and also oxidize nitrite (NO2− to nitrate (NO2−). Thus these Mn-Salens have the potential to ameliorate cellular damage caused by both oxidative and nitrosative stresses, by the catalytic breakdown of O2−, H2O2, ONOO− and NO to benign species: O2, H2O, NO2− and NO3−.
Increased susceptibility of Eucalyptus marginata to stem infection by Phytophthora cinnamomi resulting from root hypoxia
Authors: Burgess T. , McComb J. A. , Colquhoun I. , Hardy G. E. StJ.
Published: July 2002

Eucalyptus marginata growing on rehabilitated bauxite mines may be exposed to waterlogging (hypoxia) at the roots, as well as ponding around the stems at the soil surface. This paper examines whether these conditions may predispose stems of E. marginata to infection by Phytophthora cinnamomi. Plants of E. marginata clones resistant and susceptible to P. cinnamomi were grown in an aeroponics system that could be sealed to allow the manipulation of oxygen levels in the root zone to simulate waterlogging. Plants grown under normal oxygen conditions were compared with those whose root zone was exposed to hypoxia (2 mg O2 L−1) before, during or after the stems were inoculated with zoospores of P. cinnamomi. Inoculation was achieved by constructing receptacles around the stems that could hold water and zoospores.

Stomatal conductance increased in plants whose roots had been exposed to hypoxia. This effect lasted for at least 2 weeks after the resumption of normal oxygen conditions. P. cinnamomi entered and colonized ponded stems; however, there were no visible lesions on stems 14 days after inoculation. For any given clone of E. marginata, the extent of colonization was significantly greater in stems whose root zone had been exposed to hypoxia than in control stems. The activity of the plant defence‐associated enzymes PAL, 4‐CL and CAD and the concentrations of soluble phenolics were higher in the stems of plants whose roots were exposed to hypoxia, but the increase in activity in response to colonization was much greater for plants whose roots were under normal aerobic conditions. The greatest difference between colonized and noninoculated plants was observed at the colonization front. Peroxidase activity increased after tissues were colonized, rather than preceding the colonization as seen with the other enzymes.

The stress induced by root hypoxia remained after roots were returned to normal oxygen conditions. Plants with root hypoxia showed greater stem colonization by P. cinnamomi and seemed less able to recognize the pathogen and switch on rapid defence responses.
Transurethral electrovaporization of the prostate — a possible alternative to transurethral resection: a one‐year follow‐up of a prospective randomized trial
Authors: Hammadeh  , Fowlis  , Singh  , Philp
Published: July 2002

Objective

 To compare the efficacy, safety and durability of transurethral electrovaporization of the prostate (TUVP) with standard transurethral resection (TURP) in a prospective randomized trial.

Patients and methods

 The study included 104 consecutive men with symptomatic benign prostatic hyperplasia (BPH) admitted for surgery who were randomized to TUVP or TURP. The variables evaluated included the duration of surgery, catheterization and hospital stay, the International Prostate Symptom Score (IPSS), a quality‐of‐life assessment (QOL), the maximum urinary flow rate (Qmax ) and the postvoid residual urine volume (PVR).

Results

 Both groups showed a comparable significant and maintained decline in the mean IPSS, from 26.5 to 4.4 (TUVP) and from 26.6 to 5.9 (TURP), and increase in mean Qmax , from 8.9 to 22.5 mL/s (TUVP) and 8.6 to 22.8 mL/s (TURP) after 1 year. However, there were significant differences in the mean duration of catheterization (TUVP 20.9 h, TURP 46.6 h, P<0.001), hospital stay (TUVP 2.2 day, TURP 3.1 days, P<0.001), and the duration and volume of post‐operative irrigation (TUVP none, TURP 18.1 h with 17.5 L of saline). Two patients in each group developed urethral strictures (4%) and two patients in each group required re‐operation for residual adenoma (4%); two patients undergoing TURP had a bladder neck stricture (4%).

Conclusion

 The results suggest that TUVP is as effective as standard TURP in the treatment of moderate‐sized BPH. TUVP offers the advantage of using established instruments, has excellent peri‐operative haemostasis and requires a shorter hospital stay.
Bladder neck strictures after radical retropubic prostatectomy: still an unsolved problem
Authors: Tomschi  , Suster  , HÖltl
Published: July 2002

Objective

 To investigate the factors responsible for anastomotic strictures of the bladder neck after radical retropubic prostatectomy.

Patients and methods

 Of 239 consecutive patients who underwent radical retropubic prostatectomy between 1987 and 1996, 36 (15%) developed anastomotic strictures after surgery. The influence of tumour stage, previous prostatic surgery, urinary extravasation and postoperative bacteriuria were assessed.

Results

 In 21 patients (58%), the bladder neck stricture occurred within 3 months of surgery, in 11 (30%) at 4–12 months after surgery and in four (11%) more than 12 months after surgery; three of these also had local recurrence. Advanced tumour stage and positive margins did not correlate with a higher stricture rate, nor was there a significant difference in stricture rates with three or four anastomotic sutures. However, extravasation at the time of catheter removal (16 of 36 patients (44%) with vs 34 of 183 patients without (19%) stricture, bacteriuria of >106 c.f.u./mL at the time of catheter removal (stricture group 21 of 36 patients (58%) stricture with vs 71 of 203 (35%) without) and previous prostatic surgery (TURP or open surgery, stricture in 28% of those previously operated vs 13% with no previous surgery) were significant risk factors.

Conclusion

 There are three risk factors for anastomotic stricture after radical prostatectomy; previous operations on the prostate, extravasation and asymptomatic bacteriuria.
Quantum interference in time-dependent tunneling
Authors: Zhang Chao , Tzoar Narkis
Published: July 2002

The frequency-dependent transmission coefficient of a particle tunneling through a time-dependent barrier is calculated taking into account the quantum interference effect. We consider a rectangular barrier of height V0 with a time-dependent modulation of single frequency ω. For small modulation amplitude V1, our result is exact up to order V21 for any barrier width. In the low transmission region, our result is consistent with those obtained using a semiclassical method. We find that quantum interference (two modulation quanta process) makes a significant contribution to the tunneling current. In the static approximation, ωτ≪1, where τ is the barrier transit time, the contribution to the current from interference process is to cancel one-half of the tunneling current from first-order process (one modulation quantum process). To the lowest order in power series of V1/ℏω, the tunneling current is reduced due to interference.
Spectroscopic study of plasma-assisted laser deposition of Y-Ba-Cu-O
Authors: Ying Q. Y. , Shaw D. T. , Kwok H. S.
Published: July 2002

Photoluminescence spectroscopy of the plasma plume during plasma-assisted laser deposition of YBa2Cu3O7−x was performed. The spectrum in the range of 355–900 nm was measured at several spatial positions using an optical multichannel analyzer. It was found that both atomic and molecular components were present. Rich emission lines of O, O+, Y, Y+, Ba, Ba+, and Cu were observed, from which the plasma temperature could be estimated. Cu+ emission was conspicuously absent. The mechanism of the plasma process and its relevance to thin-film formation is discussed.
I
n s
i
t
u formation of superconducting YBa2Cu3O7−x thin films using pure ozone vapor oxidation
Authors: Berkley D. D. , Johnson B. R. , Anand N. , Beauchamp K. M. , Conroy L. E. , Goldman A. M. , Maps J. , Mauersberger K. , Mecartney M. L. , Morton J. , Tuominen M. , Zhang Y-J.
Published: July 2002

Superconducting YBa2Cu3O7−x thin films have been prepared by coevaporation using an ozone vapor jet as an oxygen source. Films exhibiting zero resistance at 82 K have been fabricated in situ under high vacuum conditions using substrate temperatures of 700 °C without a post-evaporation anneal in oxygen. This process has implications for in situ measurements of fully superconducting surfaces using a variety of probes as well as for the fabrication of devices and structures whose properties are dependent on surfaces and interfaces.
Endothermic reaction aided crystal growth of 2-methyl-4-nitroaniline and their electro-optic properties
Authors: Kubota Yoshinobu , Yoshimura Tetsuzo
Published: July 2002

We investigated relationships between the electro-optic properties and the growth conditions for 2-methyl-4-nitroaniline (MNA) thin-film crystals. The crystal is grown by melt growth between two quartz substrates with a newly developed automatic control of the crystal growth, which utilizes an endothermic reaction. The electro-optic effect decreases with increases in the maximum melt temperature. When MNA thin-film crystals are grown from the melt at temperatures near the melting point, the figure of merit for electro-optic phase retardation is the greatest. The value is twice that of the LiNbO3 crystal. By annealing, the figure of merit becomes three times as large as that of the LiNbO3 crystal. This is consistent with the expectations from second-harmonic generation measurements. We also investigated the purity dependence of the electro-optic effect. The electro-optic effect drastically decreases with impurity, especially for purities <99.9%.
GaAs growth properties on V-grooved Si substrates
Authors: Hashimoto A. , Fukunaga T. , Watanabe N.
Published: July 2002

GaAs growth properties and first successful maskless selective growth on the etched groove Si substrates are reported. No crystal growth occurs on the {111} Si sidewalls of the V grooves, and the GaAs layers grow only on the {100} planes. The cross-sectional shapes of the selective grown layer depend on the direction of the V grooves. The selectivity also remains even in Al0.3Ga0.7As-grown layers. The selective growth mechanisms are discussed.
Photoluminescence enhancement in post-growth hydrogenated Ga1−xAlxAs (0≤x≤0.32) and GaAs/GaAlAs multilayer structures
Authors: Pavesi L. , Martelli F. , Martin D. , Reinhart F. K.
Published: July 2002

Low-temperature photoluminescence measurements in undoped Ga1−xAlxAs (0≤x≤0.32) and GaAs/GaAlAs quantum structures grown by molecular beam epitaxy are performed before and after hydrogen plasma exposure. In both cases we observe a strong enhancement of the luminescence after the exposure. In the GaAlAs epilayers this enhancement clearly depends on the Al concentration in the alloy. The results are explained in terms of passivation of nonradiative traps in the GaAlAs that increases the carriers’ lifetime and diffusion length allowing, in the case of the multilayers, a greater number of carriers to recombine in the quantum well.
Optical characterization of stress in narrow GaAs stripes on patterned Si substrates
Authors: De Boeck J. , Deneffe K. , Christen J. , Arent D. J. , Borghs G.
Published: July 2002

Photoluminescence (PL) and spatially resolved cathodoluminescence (CL) techniques are used to characterize the stress in narrow GaAs stripes grown on Si platforms. Since no overgrowth occurs over the recess edges, the GaAs stripes are grown unconstrained along one dimension. A duplication of the optical transitions is found in the PL spectrum from a region containing embedded GaAs and stripes. The peaks in the high-energy shoulders of the PL spectrum are identified by CL measurements with high spatial resolution as the luminescence contribution of the GaAs stripes. They are submitted to lower internal stress values. A study on the geometrical dependence of the strain regime shows that a nonuniform biaxial strain field with a dominant longitudinal component is present in the stripes. The uniform biaxial strain, found in GaAs on Si (001), is present at stripe intersections.
On the precursor in laser-generated ultrasound waveforms in metals
Authors: McDonald F. Alan
Published: July 2002

A laser pulse, when focused on a metal sample, produces characteristic elastic waveforms, which depend on whether thermoelastic or ablative/evaporative mechanisms dominate the generation process. In the thermoelastic regime, with an unconstrained surface, the predominant axial displacement is opposite to the direction of propagation (negative), but there is typically a small transient positive displacement. This precursor is not predicted by elastic point source models, but is predicted by models including thermal diffusion. A recent formulation of pulsed photoacoustic generation is used to show how the precursor arises from interaction of the thermal and elastic modes at the illuminated surface.
Transform-limited 1.4 ps optical pulses from a monolithic colliding-pulse mode-locked quantum well laser
Authors: Wu M. C. , Chen Y. K. , Tanbun-Ek T. , Logan R. A. , Chin M. A. , Raybon G.
Published: July 2002

We report the generation of short optical pulses from novel monolithic colliding-pulse mode-locked quantum well lasers. Transform-limited pulses with durations of 1.4 ps at a repetition rate of 32.6 GHz have been achieved, with nearly 100% intensity modulation depth and a peak optical power of 10 mW. This is the shortest transform-limited pulse directly generated from monolithic mode-locked lasers (time-bandwidth product =0.3).
Investigation of the temperature dependence of the threshold current density of GaInP/AlGaInP double-heterostructure lasers
Authors: Hagen S. H. , Valster A. , Boermans M. J. B. , van der Heyden J.
Published: July 2002

The temperature dependence of the threshold current density of GaInP/AlGaInP double-heterostructure lasers is investigated over a wide temperature range. Using a theoretical calculation of the temperature dependence of the recombination rate in the active layer, the experimentally obtained threshold current density is separated into a component due to recombination in the active layer and an additional component responsible for an increased temperature dependence at higher temperature. For the additional component, a thermal activation energy of 0.27 eV is found. It is argued that this value is too low for a simple explanation based on carrier leakage.
Epitaxial yttria-stabilized zirconia on hydrogen-terminated Si by pulsed laser deposition
Authors: Fork D. K. , Fenner D. B. , Connell G. A. N. , Phillips Julia M. , Geballe T. H.
Published: July 2002

Epitaxial yttria-stabilized zirconia films were grown on Si (100) and Si (111) by pulsed laser deposition. Rutherford backscattering spectroscopy indicates a high degree of crystalline perfection with a channeling minimum yield of 5.3%. A necessary predeposition process is removal of native silicon oxide from the Si prior to film growth. This is done outside the deposition chamber at 23 °C using a wet-chemical hydrogen-termination procedure. Epitaxial YBa2Cu3O7−δ films have been grown on these films.
High critical current densities in YBa2Cu3O7−x films on polycrystalline zirconia
Authors: Norton David P. , Lowndes Douglas H. , Budai J. D. , Christen D. K. , Jones E. C. , Lay K. W. , Tkaczyk J. E.
Published: July 2002

We report the growth on polycrystalline yttria-stabilized zirconia substrates of YBa2Cu3O7−x films with Jc (77 K)=11 000 A/cm2 and Jc (4.2 K)=122 000 A/cm2 by pulsed laser ablation. These Jc values are among the highest reported for YBa2Cu3O7−x on any polycrystalline substrate and approach the intrinsic upper limit for films with large-angle grain boundaries, as indicated by recent bicrystal experiments. We find that the substrate temperature during film growth is most important in obtaining high Jc polycrystalline films. Although the magnetic field dependence of Jc indicates the presence of weak links, the behavior of Jc (4.2 K, H) suggests that a percolative path consisting of low-angle grain boundaries exists in the films, resulting in Jc (4.2 K, 60 kOe)=4100 A/cm2.
Permanent increase of the electrical conductivity of polymers induced by ultraviolet laser radiation
Authors: Schumann M. , Sauerbrey R. , Smayling M. C.
Published: July 2002

When polyimide (Kapton) or polybenzimidazole (PBI) are irradiated by a 248 nm KrF laser, their electrical conductivity is increased permanently. Conductivity increases of up to fifteen orders of magnitude were observed, and conductivities on the order of 1–10 Ω−1 cm−1 were obtained. The laser-induced conductivity increase of polyimide depends on the fluence per laser shot and the total fluence delivered (dosage) and exhibits a fluence threshold of ∼20 mJ cm−2 per laser shot, as well as a dosage threshold.
Structural and optical properties of ferroelectric Bi4Ti3O12 thin films by sol-gel technique
Authors: Joshi P. C. , Mansingh Abhai , Kamalasanan M. N. , Chandra Subhas
Published: July 2002

Ferroelectric thin films of Bi4Ti3O12 were fabricated on several types of substrates, including quartz, steel plates, and indium-tin-oxide coated glass slides, by sol-gel technique. Crystalline, transparent, and crack-free films of 5000 Å thickness were fabricated by spinning and post-deposition annealing at a temperature of 550 °C. Ferroelectric properties were confirmed by P-E hysteresis loops. The dielectric constant and optical transmission were also measured.
Modeling of the sp3/sp2 ratio in ion beam and plasma-deposited carbon films
Authors: Möller W.
Published: July 2002

Model calculations are described which predict the fraction of tetrahedral (sp3) versus graphitic (sp2) bonding in ion beam or plasma-deposited amorphous carbon films on the basis of the preferential displacement of sp2 atoms. Displacement yields obtained from static trim simulations are used as input data for a simple analytical growing layer model of ion beam deposition. The sp3/sp2 ratio is found to increase with increasing carbon ion energy between 30 eV and 1 keV. Assuming equal probabilities for a free (implanted or displaced) atom to become trapped at either sp2 or sp3 sites results in sp3/sp2 ratios between 1 and 3.5. More refined dynamic simulations with tridyn confirm the trends with slightly lower sp3/sp2 ratios for ion beam or plasma deposition, also involving hydrogen. A decrease of the sp3/sp2 ratio towards high energies cannot be explained by preferential displacement only, in contrast to proposals in recent literature.
Photolithographic fabrication of micron-dimension porous Si structures exhibiting visible luminescence
Authors: Doan Vincent V. , Sailor Michael J.
Published: July 2002

A procedure for the patterned synthesis of porous Si exhibiting visible luminescence is described. Anodic electrochemical etch of n- or p-type Si in ethanol/HF solution leads directly to porous Si that luminesces with λmax between 750 and 650 nm. Positive and negative patterns of luminescent porous Si are etched into n- and p-type Si samples, respectively, by projecting a high-contrast image on the electrode surface during the etching process. Lithographic resolution obtained is on the order of 20 μm.
Demonstration of photoluminescence in nonanodized silicon
Authors: Sarathy J. , Shih S. , Jung Kim , Tsai C. , Li K. -H. , Kwong D. -L. , Campbell J. C. , Yau Shueh-Lin , Bard A. J.
Published: July 2002

The formation of photoluminescent porous Si in an etchant solution made from the HF-HNO3-CH3COOH system is reported. The porous Si is characterized on the basis of its photoluminescence (PL) spectra and the degradation of the PL during exposure to laser irradiation. The surface topography as characterized by atomic force microscopy (AFM) reveals features on the order of 400–600 Å. The effect of annealing the porous Si in vacuum on the PL intensity is described and correlated to the breakdown of Si—H bonds on the porous Si surface.
Optical trapping of a metal particle and a water droplet by a scanning laser beam
Authors: Sasaki Keiji , Koshioka Masanori , Misawa Hiroaki , Kitamura Noboru , Masuhara Hiroshi
Published: July 2002

Laser trapping of a metal particle in water or a water droplet in liquid paraffin, which cannot be attained by irradiation of a TEM00 mode focused laser beam, was experimentally confirmed based on a scanning laser trapping technique. Although a metal particle or a water droplet experiences repulsive radiation force from a laser beam (1064 nm, focused into a ∼1 μm spot), scanning of the laser beam circularly around the particle was successful to optically trap and tweezer the particle. Water and ethylene glycol droplets dispersed in liquid paraffin were also shown to be manipulated independently by scanning double laser-beam trapping.
Near-infrared optical parametric oscillation in a N-(4-nitrophenyl)-L-prolinol molecular crystal
Authors: Josse D. , Dou S. X. , Zyss J. , Andreazza P. , Périgaud A.
Published: July 2002

Optical parametric oscillation has been achieved in a 1.9-mm-thick organic nonlinear optical crystal of NPP [N-(4-nitrophenyl)-L-prolinol]. Tunability from 0.9 to 1.7 μm is obtained for the first time in an organic crystal with a maximum total conversion efficiency of about 5%. Considerable possibilities for further optimization are available.
Partially exposed polymer dispersed liquid crystals for boundary layer investigations
Authors: Parmar Devendra S. , Singh Jag J.
Published: July 2002

A new configuration termed partially exposed polymer dispersed liquid crystal in which the liquid crystal microdroplets dispersed in a rigid polymer matrix are partially entrapped on the free surface of the thin film deposited on a glass substrate is reported. Optical transmission characteristics of the partially exposed polymer dispersed liquid crystal thin film in response to an air flow induced shear stress field reveal its potential as a sensor for gas flow and boundary layer investigations.
Femtosecond thermomodulation measurements of Co/Cu and Ag/Cu multilayer films
Authors: Liu Ding , He Ping , Alexander D. R.
Published: July 2002

Femtosecond transient reflectivities of Co/Cu and Ag/Cu multilayer films were measured to study the electron-lattice relaxation in these systems. The measurement results suggest that the thickness of Cu layers does not influence the electron relaxation time. A slow decaying signal, which is absent in Ag/Cu films, was observed in Co/Cu films and it is attributed to the spin excitations in the Co layers.
Reactive sputtering deposition of low temperature tantalum suboxide thin films
Authors: Wu X. M. , Wu P. K. , Lu T.-M. , Rymaszewski E. J.
Published: July 2002

A relatively simple direct current sputtering deposition scheme has been employed to deposit 1000 Å tantalum oxide thin films at low temperature. At ≂190 °C substrate temperature, without further annealing, tantalum oxide films with a dielectric constant of 21–22 and a leakage current density as low as 10 nA/cm2 at 0.5 MV/cm electrical field strength (∼5 V of applied voltage) are obtained. These properties are achieved over a wide range of O2/Ar ratios when the total flow rate is kept constant. XPS measurements reveal that these films are nonstoichiometric with a composition of TaOx where x≂1.5. These low temperature, high dielectric constant thin films have potential applications as decoupling capacitors in very high speed electronic circuits and packaging.
Characterization of thin films using numerical inversion of the generalized Lamb wave dispersion relation
Authors: Behrend O. , Kulik A. , Gremaud G.
Published: July 2002

A numerical inversion procedure based on the simplex algorithm was implemented and tested for the dispersion relation of generalized Lamb waves propagating in a thin film on a semi-infinite substrate. This procedure allows for the determination of up to three parameters of the thin film (transverse elastic wave velocity, density, and thickness). Continuous wave scanning acoustic microscopy was used to measure the dispersion curves of surface waves in a gold film sputtered on a fused silica substrate. The inversion of the data yielded the thickness of the gold film, a Young’s modulus of 80.55 GPa and a Poisson coefficient of 0.418.
Novel platinum-tin oxide-silicon nitride-silicon dioxide-silicon gas sensing component for oxygen and carbon monoxide gases at low temperature
Authors: Kang W. P. , Kim C. K.
Published: July 2002

A novel gas sensing component based on a platinum-tin oxide-silicon nitride-silicon dioxide-silicon metal-insulator-semiconductor (MIS) capacitor has been developed. The new approach to integrate the catalytic properties of platinum (Pt) and the gas sensing properties of tin oxide (SnOx) with the surface-sensitive silicon MIS capacitor enhances the gas detection at lower temperature. The device is capable of detecting oxygen (O2) and carbon monoxide (CO) gases at room ambient and at temperature much lower than the operating temperature of the conventional solid state gas detectors. The gas sensing characteristics of the device and its detection mechanism for O2 and CO at 27–100 °C are presented.
Preparation of (In,Mn)As/(Ga,Al)Sb magnetic semiconductor heterostructures and their ferromagnetic characteristics
Authors: Munekata H. , Zaslavsky A. , Fumagalli P. , Gambino R. J.
Published: July 2002

A series of III-V-based magnetic semiconductor heterostructures, p-type (In,Mn)As/(Ga,Al)Sb, has been grown by molecular beam epitaxy. Studies on magnetotransport and magneto-optical properties show that perpendicular ferromagnetic order occurs in the heterostructures with thin (In,Mn)As layers. The origin is discussed in terms of both carrier- and strain-induced effects.
External diode-laser-array cavity with mode-selecting mirror
Authors: Leger James R. , Mowry Greg
Published: July 2002

A new external optical cavity employing a mode-selecting mirror is used to tailor the amplitude and phase of the fundamental array mode and discriminate between higher-order modes. We explore the ability of this phase-coded mirror to select a particular mode and compare it with a conventional Talbot cavity. Diffraction-limited performance of the in-phase fundamental mode is shown.
Optoelectronic applications of porous polycrystalline silicon
Authors: Kalkhoran Nader M. , Namavar Fereydoon , Maruska H. Paul
Published: July 2002

We report visible light emission from porous structures formed in bulk and thin-film polycrystalline silicon materials by anodic etching in an HF:ethanol solution. Our results indicate photoluminescence (PL) peaks at wavelengths between 650 and 655 nm and with intensities comparable to those typically obtained from porous samples of single-crystal silicon. The analyses of the surface morphology of porous polycrystalline silicon (PPSI) layers suggest that the etch rate could be preferentially greater at the grain boundaries. We have illuminated PPSI films formed on quartz substrates from both the front and rear of the samples and have measured PL emission from the same corresponding sides. Luminescent polycrystalline silicon films offer the possibility of integrating a novel Si-based flat-panel display along with the recently developed thin-film transistor (TFT) driver circuitry on a glass substrate. In addition, nanostructures originating from polycrystalline silicon substrates may enable low-cost fabrication of highly efficient photovoltaic cells.
dc SQUID magnetometers from single layers of YBa2Cu3O7−x
Authors: Koelle D. , Miklich A. H. , Ludwig F. , Dantsker E. , Nemeth D. T. , Clarke John
Published: July 2002

We have fabricated magnetometers patterned in a single layer of YBa2Cu3O7−x involving dc superconducting quantum interference devices (SQUIDs) with bicrystalline grain boundary junctions. The magnetometers consist of either a SQUID with a large area square washer or a single turn pickup loop coupled directly to the body of a small area SQUID. We found that the transfer function falls off with increasing SQUID inductance much more rapidly than predicted; implications for magnetometer performance are discussed. When operated at 77 K with a bias reversal technique a directly coupled magnetometer had a noise of (105±10) fT Hz−1/2 at 1 kHz, increasing to (145±10) fT Hz−1/2 at 1 Hz.