bluuebunny/crossref_metadata_2025 huggingface dataset:
Revisiting the genetic diversity and population structure of the endangered Green Sea Turtle (Chelonia mydas) breeding populations in the Xisha (Paracel) Islands, South China Sea
Authors: Li Meimei , Zhang Ting , Liu Yunteng , Li Yupei , Fong Jonathan J. , Yu Yangfei , Wang Jichao , Shi Hai-tao , Lin Liu
Published: March 2023

The Green Sea Turtle (Chelonia mydas) is an umbrella species in the South China Sea, a Chinese national first-level protected wild animal, and the only sea turtle that nests in waters around China. The largest C. mydas nesting ground is distributed in the Xisha (Paracel) Islands, which plays a vital role in the survival of sea turtle populations in the region. This study reveals the genetic diversity and population structure of the breeding population of C. mydas in the Xisha (Paracel) Islands using three mitochondrial markers. A total of 15 D-loop, five Cytochrome b (Cyt b), and seven Cytochrome C Oxidase subunit I (COI) haplotypes were identified in the breeding population of C. mydas in the Xisha (Paracel) Islands. D-loop haplotypes are distributed in clades III, IV, and VIII of the C. mydas mitochondrial control region. It is the first time that one haplotype from Clade IV was found in this C. mydas population, and five new D-loop haplotypes were also identified. The haplotype and nucleotide diversity were calculated for each marker: D-loop (0.415 haplotype diversity, 0.00204 nucleotide diversity), Cyt b (0.140, 0.00038) and COI (0.308, 0.00083). The average genetic distance (p) of each molecular marker was less than 0.01. Neutral detection and nucleotide mismatch analysis suggested that the breeding population of C. mydas in the Xisha (Paracel) Islands did not experience a population expansion event in recent history. It is recommended that a sea turtle protection area be established in the Xisha (Paracel) Islands area to strengthen protection and effectively protect the uniqueness and sustainability of the breeding population of C. mydas in the South China Sea.
Climate change response : input adjustment in agriculture
Authors:   ,   Pontificia Universidad Católica de Chile, Figari Leiva Sebastián
Published: March 2023

Can farmers mitigate the impact of climate change? Using medium-term fluctuations of temperature and precipitation in Chile, this research tests the hypothesis of factor adjustment as a mechanism to attenuate the effects of extreme heat. I find that extreme heat leads to reallocation of land from fruit to forestry and primary activities. This readjustment leads to a reduction in labor and physical capital allocation in agriculture but also increases labor productivity and aggregate agricultural output. I conclude that this result is due to fruit sector is more labor-intensive than forestry and primary sectors, thus a reduction of this subsector drives away labor from the agriculture, but also leads to reallocation gains sufficiently high to compensate the direct losses due to extreme heat. These findings are consistent with farmers using input adjustments as a medium-term mechanism to attenuate the effects of extreme heat and highlight that accounting for land reallocation is essential to quantify the mitigation of the damages associated with climate change.
Essays in sovereign debt and default
Authors:   ,   Pontificia Universidad Católica de Chile. Instituto de Economía, Cobas Barquet Adriana Jennifer
Published: March 2023

Mi tesis se enmarca dentro de la literatura teórica de deuda soberana y aborda dos aspectos relevantes que tienen que ver con el proceso de reestructuración de deuda en default. El primer capítulo presenta aspectos de la reciente desintermediación del mercado de deuda soberana en economías emergentes y propone un modelo multietapas de teoría de juegos para determinar cómo impacta en el resultado de la restructuración. Se demuestra que en este contexto surgen costos de coordinación de magnitud significativa que debe enfrentar el gobierno para lograr una negociación exitosa. El segundo capítulo se enfoca en el periodo de exclusión luego del default y en particular en el tiempo que se extiende entre la restructuración y el retorno final al mercado de capitales. Se propone un modelo cuantitativo standard de default soberano para analizar la contribución de costos de emisión fijos y variables a la duración de este periodo, así como para comprender los principales mecanismos que en él participan.
Decisiones curriculares para el desarrollo de la argumentación en las clases de matemática
Authors:   ,   Pontificia Universidad Católica de Chile, Martínez Martínez Cherie Elvira
Published: March 2023

El objetivo de esta investigación es analizar las decisiones curriculares para el desarrollo de la argumentación en la clase de matemática. Luego se caracterizan las decisiones curriculares que favorecen y obstaculizan la promoción de la argumentación. También las condiciones en las cuales los estudiantes la desarrollan esta habilidad. En un inicio, se realizó un trabajo con el programa de estudio de Matemática de 3º año básico, en donde nos centramos en una de las habilidades mencionadas en las Bases Curriculares y uno de los focos de trabajo, la Argumentación, realizando la selección de todos los Objetivos de Aprendizaje, de las distintas unidades didácticas, que declaraba el desarrollo de esta habilidad. Luego se realizó una preparación con una profesora de manera que ella tomara decisiones curriculares para la promoción de la argumentación, por medio de la planificación y posteriormente en la ejecución de la clase. Por lo tanto se hizo un análisis de las decisiones curriculares para el desarrollo de la argumentación en las clases de matemática, tomando el caso de un 3º año básico, en donde se evidenció la importancia de cada una de las decisiones curriculares que la profesora gestiona, concluyendo la relevancia en el diseño de la tarea matemática, por ejemplo, de la selección esta, en cuya actividad existan diversos procedimientos, respuestas abiertas, permita variadas posturas. También el diseño de las tareas matemáticas deben caracterizarse por las estrategias comunicativas, entregándoles oportunidades de participación a todos los estudiantes para que tengan la posibilidad de aportar, en caso que un estudiante responda de forma errónea, gestionar para obtener un nuevo conocimiento y de igual forma, es de relevancia el tipo de preguntas, en donde el profesor estimule la habilidad a trabajar. La tercera y última característica, en cuanto al diseño de la tarea matemática es el plan de clase, en donde el docente debe anticiparse a posibles respuestas, procedimientos, hallazgos, posturas, procesos argumentativos y acciones adecuadas para la promoción de la argumentación.
Test de competencia moral : evidencia de validez basada en el proceso de respuesta
Authors:   ,   Pontificia Universidad Católica de Chile, Lavados Sepúlveda Manuel Andrés
Published: March 2023

El Test de Competencia Moral (MCT, por sus siglas en inglés) es una prueba utilizada para medir el impacto de programas de educación moral. Pese a contar con evidencia relativa al contenido del test, su estructura interna y las relaciones con otras variables, la construcción de su argumento de validez carece de evidencia basada en los procesos de respuesta. En esta indagación, se utilizan entrevistas cognitivas para examinar los procesos de respuesta de 5 estudiantes chilenos de pedagogía a 13 ítems del MCT. En el marco de modelos cognitivos acerca del procesamiento de información en pruebas con ítems de auto-reporte y de la formación del juicio moral, se indaga el nivel de ajuste entre el proceso cognitivo intencionado por los diseñadores y los procesos de respuesta reales de los sujetos entrevistados. Se concluye que las preguntas del MCT producen procesos de razonamiento moral. Sin embargo, la ocurrencia de errores de comprensión y la influencia de estrategias heurísticas indican que las inferencias realizadas a partir de los resultados del test podrían no ser siempre válidas. Finalmente, se realizan algunas recomendaciones de diseño y de administración para reducir la incidencia de estos errores, y se explicitan los desafíos que resultan de estos hallazgos preliminares para futuras investigaciones.
"Nuestro afligido reino" : la representación de la voz indígena en el "Cautiverio feliz" de Núñez de Pineda y Bascuñán
Authors:   ,   Pontificia Universidad Católica de Chile. Facultad de Letras, Rojas Rojas Ángel Matías
Published: March 2023

Esta tesis explora la representación de voces indígenas mapuches en el Cautiverio Feliz (1673) de Francisco Núñez de Pineda y Bascuñán. Para esto, se describen las características retóricas y discursivas de las intervenciones mapuches en la obra, a la luz de su contexto colonial; se identifican las situaciones y temas que tratan en sus conversaciones y parlamentos; y se analizan críticamente las denuncias y demandas indígenas que incorpora el autor criollo en el marco de la Guerra de Arauco, con el fin de comprender las implicancias discursivas y políticas que tiene su incorporación de la voz indígena en el cuestionamiento del orden colonial de Chile del siglo XVII.
Oral Stimulation by 3-D Printed Speech-sensory Appliance Series to Evaluate Speech and Associated Oral Sensory Difficulties in Children with Autism Spectrum Disorder: Protocol for Randomised Controlled Trial
Authors: Chaware Sachin Haribhau , Dubey Surekha , Thakare Vrushali , kakatkar Vinay , Darekar Abhishek
Published: March 2023

Introduction: Oral sensory problems in Autism Spectrum Disorder (ASD) are mainly due to lack of sensory-motor synchronisation and incomplete neuromuscular development. Direct oral stimulation can play a significant role as a part of oral therapy, because the speech outcome by Speech Therapy (ST) has subjective variation and requires a long period of time. The other oral muscular therapy has lack of specificity and sensitivity. However, the direct oral stimulation in the form of appliance therapy has not yet been investigated. Aim: To explore the precise role of Speech-sensory Appliance (SSA) on speech disorder and associated oral sensory problems in ASD children. Materials and Methods: In this single-arm, Randomised Controlled Trial (RCT), 40 ASD-diagnosed children between the ages of 4 and 11 will be involved. The study participants will be split into two groups of 20 each at random. While the other group will be exposed to SSA+ST therapy, one of the groups will undergo SSA therapy. The speech therapist was unaware of the group of children who received both therapies (blind). Analyses of the results will be conducted utilising voice recordings and Visual Analogue Scales (VAS). Before and after therapy, the voice recording graph will be collected. Parents will be given a short questionnaire as part of the VAS to track any changes in feeding behaviour. Expected Results: SSA therapy that is 3D printed will result in better speaking outcomes and feeding behaviour. Conclusion: If the current study’s hypothesis is confirmed, direct oral stimulation can be employed either alone or in conjunction with ST to improve participants with ASD’s speech outcomes and feeding behaviour.
Can Auditory and Vestibular Findings Differentiate Vestibular Migraine and Meniere’s Disease?
Authors: Yaman Handan , Polat Burcu , Şerbetçioğlu Mustafa Bülent
Published: March 2023

Background and Objectives: Besides evaluating the auditory and vestibular systems of patients with vestibular migraine (VM) and Meniere’s disease (MD), this study aimed to examine the clinical overlaps between these two conditions by detailed evaluation of the patient’s symptoms.Subjects and Methods: The ears of the patients with VM and MD were evaluated and patients’ vestibular and auditory complaints were questioned particularly. Pure tone audiometry, vestibular evoked myogenic potential (VEMP) responses, and caloric test results were evaluated for objective measurements.Results: The VM group had better air-conduction and boneconduction threshold and speech reception threshold and speech discrimination score test values (p<0.05). Regarding the interaural N1-P1 asymmetry ratio, the cervical VEMP between the groups had significant differences (p=0.019). The MD group had more unilateral tinnitus and ear fullness complaints and canal paresis results (p<0.01). The VM group had more motion sickness complaints (p<0.01).Conclusions: If only ears with hearing loss are evaluated; there was no significant difference between VM and MD, but regardless of hearing level or only the patients with normal hearing were evaluated, the VM group had better hearing levels. It should be considered that patients with VM may have VM-independent hearing loss, and patient complaints should be sufficiently detailed to make an accurate distinction from MD.
Fournier’s Gangrene: A Report of Two Cases and Literature Review
Authors: Dan-Jumbo A. , Dienye N. P. , Uriah S. S. , Dienye P. O. , Atata C. T. , Nnadi N. O.
Published: March 2023

Fournier's gangrene is a severe surgical emergency that occurs worldwide. The mortality and morbidity of this condition have greatly decreased over time due to improvements in surgical methods and critical care treatment. For a successful result and to lessen the high mortality and morbidity of this condition, an early diagnosis that includes evaluation of predisposing and etiological factors, metabolic and physiological parameters, prompt resuscitation, aggressive surgical debridement, broad-spectrum antibiotic coverage, and continuous monitoring of all the parameters is essential.

In this study, we present two patients who reported to the hospital with Fournier’s gangrene.  Our first patient was a 47 year-old alcoholic whose gangrene involved the scrotum and perianal area and was successfully managed. The second case involved a 67-year-old man, a known diabetic on irregular treatment who presented with Fournier’s gangrene involving the scrotum. He made a full recovery, though the postoperative period was turbulent and prolonged.
Fixed Points of \(\xi\) - (\(\alpha\), \(\beta\))- Contractive Mappings in b-Metric Spaces
Authors: Jain Kapil , Kaur Jatinderdeep , Bhatia Satvinder Singh
Published: March 2023

In the paper [Some new observations on Geraghty and \(\acute{C}\)iri\(\acute{c}\) type results in b-metric spaces, Mathematics, 7, (2019), doi: 10.3390/math7070643] Mlaiki et al. introduced (\(\alpha\), \(\beta\))-type contraction in order to generalize the contraction mapping defined by Pant and Panicker. Also, in the paper [Some fixed point results in b- metric spaces and b-metric-like spaces with new contractive mappings, Axioms, 10(2), (2021), 15 pages, doi: 10.3390/axioms10020055] Jain and Kaur presented the concepts of \(\xi\) -contractive mappings. Now, the aim of the present article is to introduce \(\xi\) - (\(\alpha\), \(\beta\)) -contractive mappings in b-metric spaces by combining the concepts (\(\alpha\), \(\beta\))-type contraction and \(\xi\)-contractive mappings. Also, we establish some fixed point results for newly defined mappings. Our results generalize various theorems in literature. In support, we provide an example.
Inhibition of the DNA‐binding activity of NF‐κB by gold compounds in vitro
Authors: Yang Jian-Ping , Merin Jocelyn P. , Nakano Tatsunori , Kato Tetsuji , Kitade Yukio , Okamoto Takashi
Published: July 2002

Nuclear factor κB (NF‐κB) is a transcription factor that is critical for the inducible expression of multiple cellular and viral genes. DNA binding activity is essential for its function. Here, we report that gold compounds, especially aurothioglucose (AuTG), have a strong inhibitory effect on NF‐κB‐DNA binding. Our finding also reveals that Zn2+ is a necessary component of NF‐κB for its DNA binding activity and that gold ion can efficiently block NF‐κB‐DNA binding, presumably through oxidation of the cysteins associated with zinc. This redox mechanism may provide an explanation for the observed efficacy of gold compounds in the treatment of rheumatoid arthritis.
Functional characterization of human sphingosine kinase‐1
Authors: Nava Victor E. , Lacana’ Emanuela , Poulton Samantha , Liu Hong , Sugiura Masako , Kono Keita , Milstien Sheldon , Kohama Takafumi , Spiegel Sarah
Published: July 2002

Sphingosine kinase catalyzes the phosphorylation of sphingosine to form sphingosine 1‐phosphate (SPP), a novel lipid mediator with both intra‐ and extracellular functions. Based on sequence identity to murine sphingosine kinase (mSPHK1a), we cloned and characterized the first human sphingosine kinase (hSPHK1). The open reading frame of hSPHK1 encodes a 384 amino acid protein with 85% identity and 92% similarity to mSPHK1a at the amino acid level. Similar to mSPHK1a, when HEK293 cells were transfected with hSPHK1, there were marked increases in sphingosine kinase activity resulting in elevated SPP levels. hSPHK1 also specifically phosphorylated D‐erythro‐sphingosine and to a lesser extent sphinganine, but not other lipids, such as D,L‐threo‐dihydrosphingosine, N,N‐dimethylsphingosine, diacylglycerol, ceramide, or phosphatidylinositol. Northern analysis revealed that hSPHK1 was widely expressed with highest levels in adult liver, kidney, heart and skeletal muscle. Thus, hSPHK1 belongs to a highly conserved unique lipid kinase family that regulates diverse biological functions.
Highly divergent sequences of the pollen self‐incompatibility (S) gene in class‐I S haplotypes of Brassica campestris (syn. rapa) L
Authors: Watanabe Masao , Ito Akiko , Takada Yoshinobu , Ninomiya Chie , Kakizaki Tomohiro , Takahata Yoshihito , Hatakeyama Katsunori , Hinata Kokichi , Suzuki Go , Takasaki Takeshi , Satta Yoko , Shiba Hiroshi , Takayama Seiji , Isogai Akira
Published: July 2002

Self‐incompatibility (SI) enables flowering plants to discriminate between self‐ and non‐self‐pollen. In Brassica, SI is controlled by the highly polymorphic S locus. The recently identified male determinant, termed SP11 or SCR, is thought to be the ligand of S receptor kinase, the female determinant. To examine functional and evolutionary properties of SP11, we cloned 14 alleles from class‐I S haplotypes of Brassica campestris and carried out sequence analyses. The sequences of mature SP11 proteins are highly divergent, except for the presence of conserved cysteines. The phylogenetic trees suggest possible co‐evolution of the genes encoding the male and female determinants.
From the Special Issue Editor
Authors: Vihtelic Jill Lynn
Published: July 2002

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Index Vol 8
Authors: Lahey Karen Eilers
Published: July 2002

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Single‐center experience with mycophenolate mofetil in pediatric renal transplant recipients
Authors: Virji Mumtaz , Carter James E. , Lirenman David S.
Published: July 2002

Abstract: Mycophenolate mofetil (MMF), a potent and specific inhibitor of guanosine nucleotide synthesis, is a new immunosuppressive drug used to prevent rejection in transplant patients. Extensive data on its utility and efficacy exists in adult patients but there is limited experience in pediatrics. Twenty‐four children (14 male, 10 female; 2–19 yr of age), eight of whom had received living‐related donor (LRD) transplants and 16 of whom had received cadaveric donor (CD) transplants, have been treated with MMF in our institution since September 1996. MMF was administered for a duration ranging from 13 weeks to 38 months, at an average dose of 600 mg/m2 (range: 200–1,000 mg/dose) every 12 h, for a total experience of 304 patient months. MMF capsules were used in 16 patients and/or pediatric suspension in eight. Five patients were switched to MMF from azathioprine as a result of rejection episodes or inability to taper prednisone, between 5 weeks and 3.5 yr post‐transplant. All patients received prednisone, cyclosporin A (CsA), and induction therapy with anti‐lymphocyte globulin (19 patients), anti‐thymocyte globulin (one patient) or daclizumab (four patients). In 12 patients started on MMF at the time of CD transplant, five (42%) had an acute rejection episode. In seven who received a LRD transplant, one (14%) had an acute rejection episode. No patients who were converted to MMF were treated for acute rejection following conversion to MMF. One LRD graft was lost at 19 days following injury to the donor artery at the time of retrieval. At the last follow‐up, the average creatinine level was 93 µmol/L and average urea level was 8.6 mmol/L. One patient developed epigastric distress. Three patients developed diarrhea/abdominal pain requiring dose adjustment. Five episodes of leukopenia and one episode of thrombocytopenia required dose adjustment. Two patients developed symptomatic cytomegalovirus (CMV) infection, one while on acyclovir prophylaxis. No malignancy has been encountered to date. Hence, MMF can be administered safely to children with good effect and with an acceptable side‐effect profile.
Experimental study of electrolysis-induced hepatic necrosis
Authors: Robertson G S M , Wemyss-Holden S A , Dennison A R , Hall P De La M , Baxter P , Maddern G J
Published: July 2002

Background

One of the most promising but unexplored methods for treating patients with irresectable liver tumours is electrolysis. This study examined the effect of increasing ‘current dose’ on the volume of the lesion induced in normal rat liver.

Methods

A direct current generator, connected to platinum electrodes implanted in the rat liver, was used to examine the effect of (1) varying current doses from 1 to 5 coulombs and (2) electrode separation (2 or 20 mm), on the volume of liver necrosis.

Results

There was a significant correlation (P < 0·001) between the current dose and the volume of necrosis produced for each electrode separation. Placing the electrodes 2 mm apart resulted in smaller total volumes of necrosis than placing them 20 mm apart when anode lesions were significantly larger than cathode lesions (P < 0·05). Liver enzymes (aspartate aminotransferase, alanine aminotransferase) were significantly raised 1 day after treatment (P < 0·001) and predicted the total volume of hepatic necrosis (P < 0·001).

Conclusion

Predictable and reproducible areas of liver necrosis are produced with electrolysis. If these results extrapolate to larger animal models, this technique has potential for patients with irresectable primary and secondary liver tumours.
Intrahepatic peripheral cholangiocarcinoma: mode of spread and choice of surgical treatment
Authors: Sasaki A , Aramaki M , Kawano K , Morii Y , Nakashima K , Yoshida T , Kitano S
Published: July 2002

Background

Classification of macroscopic appearance and standard operative procedures for intrahepatic cholangiocarcinoma (ICC) are still controversial.

Methods

The mode of spread of 12 resected ICCs was examined by light microscopy, and the appropriate operative procedures for the various tumours were considered.

Results

Macroscopically, nine tumours were classified as mass-forming type and three as periductal infiltrating type. All patients were treated by major hepatectomy; resection of the extrahepatic bile duct was included in two cases of the periductal infiltrating type. Microscopically, invasion into the portal vein, intrahepatic metastasis and perineural or lymphatic vessel invasion occurred in none, one and all of three tumours of the periductal infiltrating type and in eight, six and six of nine tumours of the mass-forming type.

Conclusion

ICC of the periductal infiltrating type has a tendency to spread along Glisson's sheath via lymphatic vessels. By contrast, ICC of the mass-forming type tends to invade the liver via the portal vein system; such tumours begin to invade Glisson's sheath through the lymphatic vessels when the tumour has increased in size. Therefore, major hepatectomy with combined resection of the extrahepatic bile duct should be performed for all ICCs of the periductal infiltrating type and for those of the mass-forming type with invasion of Glisson's sheath.
Clinical aspects of ocular leptospirosis in New Caledonia (South Pacific)
Authors: Md Erica Mancel , Vetd Fabrice Merien , Pesenti Laurent , PhD Dominique Salino Md , Md Gilles Angibaud , PhD Philippe Perolat Md
Published: July 2002

Purpose: The incidence of leptospirosis is very high in New Caledonia (average annual incidence rate: 180/100 000 of the population). To investigate the role of pathogenic leptospires as an aetiological agent of ocular diseases, we report the results of a 5‐year survey in New Caledonia.

Methods: We reviewed 13 patients (corresponding to 17 investigated pathologic eyes) retrospectively. The selection of patients was based on epidemiological data, initial clinical examination, biological confirmation of leptospirosis according to reference procedures and a specific polymerase chain reaction assay. The anatomic criteria of uveitis and the criteria describing the evolution of the disease were those recommended by the International Uveitis Study Group.

Results: Consequent rates of optic neuritis (65%), posterior uveitis (35%), secluded pupil (24%), interstitial keratitis (18%) and pars planitis (12%) were found. Our rates of recurrence (46%) and of ophthalmic complications (82%) were substantial; some symptoms indicated brain involvement. The final visual damage was severe in 35% of eyes.

Conclusions: Microagglutination and polymerase chain reaction hybridization are complementary tests for the diagnosis of Leptospira‐induced ophthalmic lesions. Before deciding on treatment, one must consider the ability of virulent leptospires to persist in immunologically privileged sites such as aqueous humor, cerebrospinal fluid and eukaryotic cells. Polymerase chain reaction is a useful tool for the diagnosis of Leptospira‐induced ocular complications, which are probably misdiagnosed if based only on routine laboratory tests. It enables early diagnosis and early specific treatment that now consists of quinolone and cyclines.
Evolution of Filamentous Ascomycetes Inferred from LSU rDNA Sequence Data
Authors: Lumbsch H. T. , Lindemuth R. , Schmitt I.
Published: July 2002

Abstract: The nuclear LSU rRNA gene was examined in order to evaluate the current phylogeny of ascomycetes, which is mainly based on nuclear SSU rRNA data. Partial LSU rRNA gene sequences of 19 ascomycetes were determined and aligned with the corresponding sequences of 13 other ascomycetes retrieved from Genbank, including all classes traditionally distinguished and most of the recently accepted classes. The classification based on SSU rDNA data and morphological characters is supported, while the traditional classification and classifications based on the ascus type are rejected. Ascomycetes with perithecia and cleistothecia form monophyletic groups, while the discomycetes are a paraphyletic assemblage. The Pezizales are basal to all other filamentous ascomycetes. The monophyly of Loculoascomycetes is uncertain. The results of the LSU rDNA analysis agree with those of the SSU rDNA and RPB2 gene analyses, suggesting that most classes circumscribed in the filamentous ascomycetes are monophyletic. The branching order and relationships among these classes, however, cannot be elucidated with any of these data sets.
Infrared spectroscopy of thin silicon dioxide on silicon
Authors: Olsen J. E. , Shimura F.
Published: July 2002

An infrared technique has been devised to study the structure of very thin films on substrates of high refractive index. Optical spectrum amplification of three orders of magnitude is theoretically available. A series of refractive index enhanced multiple internal reflection spectra reveals a clear thickness-dependent structural transformation in thermal SiO2. The spectra suggest a shift in ring statistics, from smaller to larger, with increasing distance from the oxide-silicon interface.
High-field transport in GaAs transistors
Authors: Berthold K. , Levi A. F. J. , Walker J. , Malik R. J.
Published: July 2002

Resonant tunneling is used to explore the dynamics of electron transport in the electric field of reverse-biased GaAs n-p-n heterojunction bipolar transistor collectors. Extreme velocity overshoot is observed in a fraction of a percent of electrons which are accelerated ballistically in the Γ valley to energies greater than 1.5 eV. In addition, we show that Γ–X valley transfer is the dominant scattering mechanism for high-energy Γ valley electrons.
Activation of Zn and Cd acceptors in InP grown by metalorganic vapor phase epitaxy
Authors: Glade M. , Grützmacher D. , Meyer R. , Woelk E. G. , Balk P.
Published: July 2002

We have investigated the activation by post-deposition annealing of Zn and Cd acceptors incorporated in InP during epitaxial growth using metalorganic vapor phase epitaxy. Growth was carried out at 20 mbar and atmospheric pressure for Zn- and Cd-doped samples, respectively, using TMI, PH3, DEZn, and DMCd as sources. Post-epitaxial annealing in a N2 atmosphere at temperatures in the range of 370–470 °C leads to complete activation of the acceptors. This process is strongly temperature dependent and a distinct effect of a GaInAs overlayer was observed. The activation energy is the same for Zn- and Cd-doped samples. It is suggested that the diffusion of vacancies plays a determining role in activating the dopant.
Quantitative resonant tunneling spectroscopy: Current-voltage characteristics of precisely characterized resonant tunneling diodes
Authors: Reed M. A. , Frensley W. R. , Duncan W. M. , Matyi R. J. , Seabaugh A. C. , Tsai H.-L.
Published: July 2002

A systematic comparison of precisely characterized resonant tunneling structures is presented. A self-consistent band bending calculation is used to model the experimentally observed resonant peak positions. lt is found that the peak positions can be accurately modeled if the nominal characterization parameters are allowed to vary within the measurement accuracy of the characterization. As a result, it is found that the asymmetries in the current-voltage characteristics are solely explainable by tunnel barrier thickness fluctuations.
Interaction of picosecond optical pulses with high T
c superconducting films
Authors: Donaldson W. R. , Kadin A. M. , Ballentine P. H. , Sobolewski R.
Published: July 2002

Infrared pulses (1.06 μm wavelength, ≊150 ps long) from a Nd:YAG laser illuminated a superconducting YBa2Cu3O7 granular film, 0.7 μm thick. This caused the film to switch from the superconducting to the normal (resistive) state in less than 2 ns, followed by a much slower recovery ∼1 μs. The initial fast switching may be explained by nonequilibrium hot-electron energy transfer from the top absorbing layer (≊100 nm thick) through the film, followed by an essentially bolometric response and cooldown via equilibrium thermal conduction out of the film.
Reversible light-induced reactivation of acceptors in p-type hydrogenated GaAs
Authors: Szafranek I. , Bose S. S. , Stillman G. E.
Published: July 2002

We report a new effect in which hydrogen-passivated acceptor impurities in p-type GaAs are reactivated by low-intensity, above band gap illumination. Low-temperature photolumines cence was used to monitor the acceptor reactivation process. The light-induced reactivation is persistent at cryogenic temperatures, but the material relaxes back to the hydrogen-passivated state after annealing at moderate temperatures. Preliminary kinetic considerations, as well as the implications of this phenomenon on the fundamental and technological aspects of hydrogen passivation in semiconductors, are briefly discussed.
Optical fiber switch employing a Sagnac interferometer
Authors: Farries M. C. , Payne D. N.
Published: July 2002

Switching in less than 1 ns of an optical signal at 632 nm is demonstrated in a 1 m optical fiber Sagnac interferometer. Full signal modulation was obtained with a pump power of 24 W at a wavelength of 532 nm.
Two-wavelength demultiplexing p-i-n GaAs/AlAs photodetector using partially disordered multiple quantum well structures
Authors: Miyazawa T. , Kagawa T. , Iwamura H. , Mikami O. , Naganuma M.
Published: July 2002

A novel two-wavelength p-i-n demultiplexer is proposed and fabricated using dopant-free partial disordering of GaAs/AlAs quantum wells by rapid thermal annealing. A crosstalk attenuation of 41 dB and an interchannel spacing of 69 nm were achieved in the 0.8 μm wavelength region.
Very low threshold InGaAs/InGaAsP graded index separate confinement heterostructure quantum well lasers grown by atmospheric pressure metalorganic vapor phase epitaxy
Authors: Tanbun-Ek T. , Logan R. A. , Temkin H. , Berthold K. , Levi A. F. J. , Chu S. N. G.
Published: July 2002

Record low threshold current densities have been achieved in InGaAs/InGaAsP step graded index sep[AV:arate confinement (GRIN SCH) quantum well lasers emitting close to 1.50 μm. Single (SQW) and multiple (MQW) quantum well lasers with 300–500 μm long cavities had threshold current densities as low as 1.9 and 0.9 kA/cm2, respectively. In longer cavity devices, threshold current densities as low as 750 and 450 A/cm2 have been measured in SQW and MQW lasers, respectively. These lasers show no significant change in threshold current density with well thicknesses varying from 5 to 25 nm which demonstrate the effectiveness of the graded index in the carrier capture process. Buried-heterostructure GRIN SCH SQW and MQW with active layer widths of ∼2 μm show threshold currents of 15 and 9 mA, respectively.
Molecular beam epitaxial growth of CdTe and HgCdTe on Si (100)
Authors: Sporken R. , Sivananthan S. , Mahavadi K. K. , Monfroy G. , Boukerche M. , Faurie J. P.
Published: July 2002

CdTe has been grown on Si(100) by molecular beam epitaxy. Two orientations can be obtained: (111)B CdTe when the CdTe is deposited directly on the Si(100) substrates, and (100)CdTe when an intermediate layer of ZnTe is grown first. The (111)B oriented layers are made of two domains which are rotated by 90°. A layer with only one domain can be grown on Si(100) misoriented by 8°, but the best misorientation for this purpose still needs to be found. These layers were characterized by reflection high-energy electron diffraction, photoluminescence spectroscopy, scanning electron microscopy, and x-ray diffraction. Hg1−xCdxTe has also been grown by molecular beam epitaxy on (111)B CdTe on Si(100).
Measurement of the nonlinear refractive index of single-crystal polydiacetylene channel waveguides
Authors: Krol D. M. , Thakur M.
Published: July 2002

We have measured the nonlinear refractive index (n2) of single crystalline poly(bis(p-toluene sulfonate) of 2,4-hexadiyn-1,6-diol) (PTS) polydiacetylene channel waveguides at 1.06 μm using two different techniques. The first method employs a Mach–Zehnder interferometer to determine the intensity-induced phase shift in the waveguide. In the second case n2 is derived from the intensity-dependent birefringence, which is measured with a Babinet–Soleil compensator. With both measurements the value of n2 in the direction of the PTS polymer chain axis is found to be ∼3×10−11 cm2/W. Such a large value of n2 would allow all-optical device applications of this material at low-power levels.
Femtosecond excited-state dynamics of polydiacetylene
Authors: Huxley J. M. , Mataloni P. , Schoenlein R. W. , Fujimoto J. G. , Ippen E. P. , Carter G. M.
Published: July 2002

Femtosecond time-resolved absorption spectroscopy measurements were performed on polydiacetylene 15-8 and polydiacetylene p-toluene sulfonate. The relaxation of the singlet exciton was measured to be a two-component process with an initial relaxation in ∼95 fs followed by complete recovery in ∼1.5 ps. The rapid formation of broadband photoinduced absorption was observed with recovery in a few picoseconds.
Electric field dependent photocurrent and electroreflectance spectra of InGaAs/AlGaAs multiple strained quantum well structures
Authors: Fritz I. J. , Brennan T. M. , Wendt J. R. , Ginley D. S.
Published: July 2002

We present results on excitonic transitions and confinement at high electric fields from photocurrent and electroreflectance spectra of an In0.17Ga0.83As/Al0.3Ga0.7As strained quantum well structure fabricated into a Schottky barrier diode. Up to the highest field attained, 1.7×105 V/cm, we observe a well-defined exciton line at the band edge (in contrast to data on similar GaAs/Al0.3Ga0.7As structures), a feature important for potential optoelectronic applications. At low fields, ‘‘allowed’’ (Δn=0) transitions dominate the photocurrent spectra, but with increasing field ‘‘forbidden’’ transitions (allowed because of reduced symmetry and valence-band mixing) grow in intensity and eventually dominate the above-gap response. In the electroreflectance spectra, the forbidden transitions are relatively strong, even at low field. The allowed above-gap transitions nearly vanish at low temperature because of the small field dependence of the higher lying quantum well energy levels.
High current plasma based electron source
Authors: Bauer H. R. , Gundersen M. A.
Published: July 2002

This letter analyzes the transport of an electron beam that is produced during the conductive phase operation in the cathode fall of a pseudospark or back lighted thyratron for applications that require a high brightness electron source. The beam is estimated to traverse the device without thermalization if the plasma density is ≤2.5×1015 cm−3. High brightness electron sources are necessary for various new plasma based devices, and these results encourage consideration of this electron beam as a new candidate for applications including microwave generation sources, electron sources for accelerators, and plasma based accelerators which require improved cathodes.
Nonlinear optical properties of molecular beam epitaxy grown Bi1−xSbx
Authors: Youngdale E. R. , Meyer J. R. , Hoffman C. A. , Bartoli F. J. , Partin D. L. , Thrush C. M. , Heremans J. P.
Published: July 2002

We discuss the first investigation of Bi1−xSbx as an infrared nonlinear optical material. Nondegenerate four-wave mixing experiments at CO2 laser wavelengths yield a large nonlinearity (χ(3)≊3×10−4 esu) which does not saturate at power densities up to 0.5 MW/cm2. Both the ambient and substrate interfaces of the film are highly reflective and the étalon they form is found to have a large effect on the transmission and reflectivity spectra of the as-grown films. This suggests the possibility that constructive interference of the film’s internal optical fields could be used to considerably enhance the nonlinear signal.
Experimental observations of L- and M-shell spectra emitted from plasmas produced by the irradiation of solid targets with single 3.5 ps, KrF laser pulses
Authors: Edwards J. , Barrow V. , Willi O. , Rose S. J.
Published: July 2002

L- and M-shell x-ray spectra obtained when solid targets were irradiated by single, 3.5 ps, KrF laser pulses with irradiances above 1016 W cm−2 are presented. Modeling of the experimental conditions with a one-dimensional hydrocode and time-dependent atomic physics is shown to be consistent with the experimental results.
Electronic properties of metal/sol-gel SiO2/indium-phosphode capacitor
Authors: Shacham-Diamand Y. , Moriya N. , Bahir G.
Published: July 2002

This work reports on the electrical properties of metal-oxide-semiconductor (MOS) capacitors made with a spin-on-glass (SOG) SiO2 layer, doped with 2% phosphorus, deposited on InP substrate by spin casting followed by a low-temperature (<260 °C) anneal. The capacitance versus voltage behavior as well as the dielectric constant of the SOG layer was analyzed as a function of the frequency. The stability of the relevant parameters was checked after a long period of time (four weeks), compared with fresh devices, and revealed a significant increase in the dielectric constant and a slight increase in the leakage current. It is shown that the use of SOG as the dielectric material in the MOS structure leads to a relatively low fixed charge (less than 2×1011 cm−2) and low fast state concentration.
Soliton generation at 10 MW level in the very high frequency band
Authors: Ikezi H. , DeGrassie J. S. , Drake J.
Published: July 2002

Eletromagnetic solitions at a 10 MW level in a frequency band of several hundred megahertz are generated in a transmission line loaded by a nonlinear ceramic dielectric in the para- electric phase.
Multiple flame deposition of diamond films
Authors: Tzeng Y. , Phillips R. , Cutshaw C. , Srivinyunon T. , Loo B. H. , Wang P.
Published: July 2002

A multiple flame burner has been used to deposit diamond films of up to 20 mm in diameter from an oxygen-acetylene mixture. The burner consists of nine equally spaced linear holes each sustaining its own flame and rotates under a water-cooled substrate. The diamond film’s quality is characterized as a function of its radial distance from the center of the film by scanning electron microscopy, Raman spectroscopy, and photoluminescence spectroscopy. Typical films exhibit variations in thickness and crystal structure with an increasing graphitic component present towards the edge of the film as evidenced by Raman analysis. Photoluminescence spectra exhibit defect bands at 1.95 eV present near the outer edge of the film and at 2.16 eV present near the center of the film. These luminescence bands are discussed and attributed to defects induced from the flame’s chemistry.
Nanosecond laser-induced cavitation in carbon microparticle suspensions: Applications in nonlinear interface switching
Authors: Lawson C. M. , Euliss G. W. , Michael R. R.
Published: July 2002

Nanosecond transmission to total internal reflection switching has been demonstrated using a thin absorbing film of carbon microparticles suspended in ethanol. The switching results from laser-induced cavitation and the large refractive index mismatch that occurs when the vapor bubble meets the surrounding glass substrate. This extraordinarily large refractive index change (≳0.3) causes the incident beam to be totally internally reflected at the glass-vapor interface. Switching energies below 1 μJ have been measured using a 5 ns doubled Nd:YAG laser (λ=0.532 μm) pulse. We have investigated the effects that particle concentration, film thickness, and bias temperature have on switching performance.
Novel far-infrared-photoconductor based on photon-induced interedge channel scattering
Authors: Dießel E. , Müller G. , Weiss D. , von Klitzing K. , Ploog K. , Nickel H. , Schlapp W. , Lösch R.
Published: July 2002

We demonstrate experimentally that the far-infrared photoresponse of GaAs/AlGaAs heterostructures at photon energies corresponding to cyclotron resonance absorption is strongly enhanced in the adiabatic transport regime of the quantum Hall effect (QHE). Ideal adiabatic transport is characterized within the edge channel picture of the QHE by the absence of interedge channel scattering. We realize adiabatic transport by the means of a multiple gate finger structure, which is used for a selective population of the edge channels. The cyclotron resonance absorption is interpreted as an additional interchannel scattering process increasing the magnetoresistance.
Superconductivities of n-type Nd1.85Ce0.15CuO4−y prepared under high pressure
Authors: Jin C. Q. , Yao Y. S. , Wu B. Q. , Xu Y. F. , Liu S. C. , Wang W. K.
Published: July 2002

In this work we provide the report on the preparation of a bulk n-type NdCeCuO superconductor using a high-pressure high-temperature sintering procedure. The superconductor was obtained by sintering as-prepared material at 4.0 GPa at 530 °C for 20 min and required no additional reducing treating. The sample shows a higher onset temperature Tcon (32 K), a higher zero resistance temperature Tc0 (22 K), and a much lower resistivity than a standard bulk sample. Indeed the room-temperature resistivity and the quasimetallic resistivity in the normal state for our polycrystalline sample are similar to those of single crystals. This high-pressure sintering procedure reduces weak link effects and opens the possibility of preparing high-quality bulk n-type superconductors.
High electron mobility in modulation-doped Si/SiGe quantum well structures
Authors: Schuberth G. , Schäffler F. , Besson M. , Abstreiter G. , Gornik E.
Published: July 2002

Modulation-doped multiple quantum well structures based on Si/SiGe have been grown by molecular beam epitaxy. Low-temperature electron mobilities up to 17 000 cm2/V s have been achieved in narrow Si quantum wells. The electronic properties of the strain symmetrized Si/SiGe multilayer structures were studied by magnetotransport and cyclotron resonance experiments. The results are consistent with subband calculations which take the strain-induced splitting of the conduction band and the lowering of two valleys into account.
Pressure dependence of Bi-Sr-Ca-Cu-O phases with laser deposition technique
Authors: Narumi E. , Lee J. , Li C. , Hosokawa S. , Patel S. , Shaw D. T.
Published: July 2002

Superconducting Bi2Sr2Can−1CunOx (n=1,2,3) films, with the c-axis perpendicular to the films, were fabricated by laser deposition. Oxygen pressure was found to be important to control the phases, and a unique pressure dependence of Bi-Sr-Ca-Cu-O phases was shown by these films. Tc of 76 K and Jc of 1.5×105 A/cm2 at 40 K were achieved for the in situ Bi2Sr2CaCu2Ox film. The critical-current densities in the external magnetic field up to 5 T with the fields parallel and perpendicular to the c-axis of the film were measured.
Possibility of infrared laser in a resonant tunneling structure
Authors: Kastalsky A. , Goldman V. J. , Abeles J. H.
Published: July 2002

We analyze the possibility of creating population inversion and optical gain in a specially designed resonant tunneling superstructure when the energy between active quantum levels is greater than the optical phonon energy. Each of twenty periods of the structure represents a complete resonant tunneling, double quantum well diode designed to provide escape time from the lower level of the active well much shorter than the electron-optical phonon relaxation time. Three heterostructure materials are considered: InAs/AlSb, InGaAs/AlAs, and GaAs/AlAs. In all three cases optical gains of 50–90 cm−1 were calculated to be present for the photon energy of ≊0.1 eV.
Suppression of nucleation during crystallization of amorphous thin Si films
Authors: Im James S. , Shin Jung H. , Atwater Harry A.
Published: July 2002

The ability to selectively suppress crystal nucleation during the crystallization of amorphous Si films is often desirable, but is not generally possible. We demonstrate that a periodic two-step process−involving intermediate temperature ion irradiation followed by high-temperature isothermal annealing−can suppress nucleation in amorphous regions without destroying existing crystals or inhibiting crystal growth. When interpreted in the context of transient nucleation theory, our results indicate that the size distribution of critical and subcritical-sized clusters is modified by exposure to intermediate temperature high-energy ion irradiation. The reduction in the population of critical-sized clusters, which presumably occurs via an interfacial amorphization process, in turn leads to a prolonged incubation period in the subsequent thermal annealing step during which nucleation is negligible but crystal growth is substantial.
Low-frequency noise in InP-based NnPnN double heterojunction bipolar transistors
Authors: Su Y. K. , Shei S. C. , Chen C. H.
Published: July 2002

This letter deals with the low-frequency noise in an InGaAs(P)/InP double heterojunction bipolar transistor at room temperature. The recombination is mainly responsible for the noise. The current dependence of the base noise with floating collector was of the form IB3 and the shot noise of base current corresponding to 3.2×10−24 A2/Hz for f=10 Hz. The current dependence of the collector noise with high frequency short circuited was of the form Ic1.55 and the shot noise of collector current corresponding to 3.2×10−24 A2/Hz for f=10 Hz.
Growth of face-centered-cubic single crystals of C60 from boiling benzene
Authors: Yosida Yositaka , Arai Takeshi , Suematsu Hiroyoshi
Published: July 2002

We report a new synthesis technique of face-centered-cubic single crystals of C60 with a macroscopic dimension of 0.3×0.3×0.5 mm3. The crystals are grown from a benzene heated above 80 °C. The mosaic spread of the crystal is about 0.5°.