bluuebunny/crossref_metadata_2025 huggingface dataset:
O TRABALHO INFANTIL NO BRASIL CONTEMPORÂNEO
Authors: Moreira de Carvalho Inaiá Maria
Published: August 2022

Este trabalho analisa o panorama atual do trabalho infantil na sociedade brasileira, abordando a sua origem, trajetória recente, efeitos sobre as crianças e adolescentes e políticas que vêm sendo desenvolvidas para combatê-lo. Baseando-se em tabulações especiais da PNAD de 2006, ele mostra a dimensão do fenômeno e como a atividade precoce se diferencia conforme a idade, o sexo, a residência rural e urbana e as grandes regiões, assinalando suas condições de atividade e seus impactos perversos sobre a educação e a saúde dos pequenos trabalhadores. Considerando tanto os determinantes econômicos como os valores e representações simbólicas que estão na base da sua reprodução, o texto conclui destacando como, nas condições do desenvolvimento brasileiro, esse é um fenômeno de difícil erradicação. PALAVRAS CHAVE: trabalho infantil, crianças e adolescentes, desigualdade social, Brasil. THE CHILD LABOR IN BRASILTHE CHILD LABOR IN BRASIL CONTEMPORÂNEO Inaiá Maria Moreira de Carvalho This paper analyzes the current panorama of the child labor in the Brazilian society, approaching its origins, recent trajectory, effects on the children and adolescents and policies developed to combat it. Based on special tabulations of PNAD 2006, it shows the dimension of the phenomenon and how precocious activity differs according to age, sex, place of residence, rural and urban, and the geographical regions, marking their conditions of activity and the perverse impacts on the small workers education and health. Considering as much the economical determinant to child labor as the values and symbolic representations that are in the base of its reproduction, the text concludes highlighting as, in the conditions of the Brazilian development, that it is a phenomenon of difficult eradication. KEYWORDS: child labor, children and adolescents, social inequality, Brazil. LE TRAVAIL DES ENFANTS AU SEIN DU BRESIL CONTEMPORAIN Inaiá Maria Moreira de Carvalho Cette étude se propose d’analyser le panorama actuel du travail des enfants dans la société brésilienne, son origine, sa trajectoire récente, ses effets sur les enfants et les adolescents ainsi que les politiques mises en oeuvre pour le combattre. Basée sur des analyses de données spécifiques de la PNAD 2006, elle permet de montrer la dimension du phénomène et combien l’activité précoce change en fonction de l’âge, du sexe, du lieu de résidence en zone rurale ou urbaine et des grandes régions. On y met en évidence les conditions de travail et leurs impacts pervers sur la scolarité et la santé des petits travailleurs. En prenant en considération autant les déterminants économiques que les valeurs et les représentations symboliques qui sont à la base de sa reproduction, pour conclure, cette analyse démontre combien il est difficile d’éliminer ce phénomène dans les conditions du développement brésilien. MOTS-CLÉS: travail des enfants, enfants et adolescents, inégalités sociales, Brésil. Publicação Online do Caderno CRH: http://www.cadernocrh.ufba.br
QUANDO INOVAR É APELAR À TRADIÇÃO - a condição baiana frente à modernização turística
Authors: Farias Edson
Published: August 2022

O objetivo deste artigo é enfocar a tônica depositada na tradição como componente de uma dinâmica sócio-histórica tramada entre distintos grupos em Salvador, mas cujo efeito definiu um modo de modernização concatenado com o cruzamento de identidades de grupos, patrimônios imateriais e arquitetônicos, os trânsitos de imagens e o capitalismo informacional. Tal modo de modernização definiu uma experiência turística marcada pelos usos, da e na cidade, que se fazem do espaço, da memória e das expressões culturais, recursos que são decisivos e, ao mesmo tempo, revolvem um terreno de contradições sociosimbólicas que alimentam a economia simbólica das cidades contemporâneas. PALAVRAS-CHAVE: inovação, tradição baiana, modernização turística, serviços. WHEN INNOVATING IS APPEALING TO TRADITION. THE BAHIAN CONDITION FACING TOURIST MODERNIZATION Edson Farias The objective of this paper is to focus the role accorded to tradition as a component of a socialhistorical dynamics schemed among different groups in Salvador, but whose effect defined a way of modernization connected with the crossing of group identities, immaterial and architectural patrimonies, the transit of images and the informational capitalism. Such way of modernization defined a touristic experience marked by the uses, by the city and in the city, that are made of space, of memory and of cultural expressions, resources that are decisive and, at the same time, they revolve a land of social-symbolic contradictions that feed the symbolic economy. KEYWORDS: innovation, bahian tradition, touristic modernization, services. QUAND INNOVER, C’EST FAIRE APPEL À LA TRADITION. BAHIA ET SA CONDITION FACE À LA MODERNISATION TOURISTIQUE Edson Farias L’objectif de cet article est de cibler l’accent mis sur la tradition en tant que composante d’une dynamique socio-historique tissée entre des groupes distincts à Salvador, mais dont l’effet a été de définir un mode de modernisation lié au croisement d’identités de groupes, de patrimoines immatériels et architectoniques, aux transits d’images et au capitalisme informationnel. Un tel mode de modernisation a engendré une expérience touristique marquée par les us et coutumes, de la ville et dans la ville, qui transforment l’espace, la mémoire et les expressions culturelles en ressources décisives mais qui, en même temps, retournent un terrain parsemé de contradictions socio symboliques qui soutiennent l’économie symbolique. MOTS-CLÉS: innovation, tradition bahianaise, modernisation touristique, services. Publicação Online do Caderno CRH: http://www.cadernocrh.ufba.br
FINANÇAS, POLÍTICA E TERRITÓRIO - INTRODUÇÃO
Authors: Christina Dias Leila
Published: August 2022

55todos

Publicação

Online do Caderno CRH: http://www.cadernocrh.ufba.br
Nitrite and nitric oxide reduction in Paracoccus denitrificans is under the control of NNR, a regulatory protein that belongs to the FNR family of transcriptional activators
Authors: Van Spanning Rob J.M , De Boer Anthonius P.N , Reijnders Willem N.M , Spiro Stephen , Westerhoff Hans V , Stouthamer Adriaan H , Van der Oost John
Published: July 2002

The nir and nor genes, which encode nitrite and nitric oxide reductase, lie close together on the DNA of Paracoccus denitrificans. We here identify an adjacent gene, nnr, which is involved in the expression of nir and nor under anaerobic conditions. The corresponding protein of 224 amino acids is homologous with the family of FNR proteins, although it lacks the N‐terminal cysteines. A mutation in the nnr gene had a negative effect on the expression of nitrite and nitric oxide reductase. Synthesis of membrane bound nitrate reductase, of nitrous oxide reductase, and of the cbb
3‐type cytochrome c oxidase were not affected by mutation of this gene. These results suggest that denitrification in P. denitrificans may be governed by a signal transduction network that is similar to that involved in oxygen regulation of nitrogen metabolism in other organisms.
Role of lysine‐195 in the KMSKS sequence of E. coli tryptophanyl‐tRNA synthetase
Authors: Chan Kim W. , Koeppe Roger E.
Published: July 2002

Lysine 195 in the K195 MSKS sequence of E. coli tryptophanyl‐tRNA synthetase (TrpRS) was replaced with alanine. The resulting K195A mutant TrpRS had essentially unchanged Km values for ATP and Trp, but a 1500‐fold decreased k
cat in a pyrophosphate‐ATP exchange reaction. This large decrease in k
cat reduces the rate of aminoacyladenylate formation (step 1) to a rate comparable to the rate of aminoacylation of tRNATTrp (step 2) by the K195A mutant enzyme. Both the TIGN and KMSKS sequences are important for step 1 of class I aminoacyl‐tRNA synthetase reactions.
Anionic phospholipids can mediate membrane insertion of the anionic part of a bound peptide
Authors: Leenhouts J.M. , van den Wijngaard P.W.J. , de Kroon A.I.P.M. , de Kruijff B.
Published: July 2002

The effect of anionic lipids on the membrane insertion of a carboxyl group on a specially designed palmitoylated peptide was studied, using tryptophan fluorescence. It is demonstrated that the negatively charged membrane surface of mixed phosphatidylcholine/phosphatidylglycerol small unilamellar vesicles enhances the protonation of the C‐terminal carboxyl group, and the subsequent insertion of that part of the peptide.
Characterization of the DNA triplex formed by d(TGGGTGGGTGGTTGGGTGGG) and a critical R · Y sequence located in the promoter of the murine Ki‐ras proto‐oncogene
Authors: Xodo Luigi E.
Published: July 2002

The binding of the G‐rich oligonucleotide d(TGGGTGGGTGGTTGGGTGGG) to a critical homopurine‐homopyrimidine sequence located in the promoter of the murine Ki‐ras proto‐oncogene has been investigated. The duplex and the oligonucleotide form a triple helix as evidenced by band‐shift electrophoresis, hydroxyapatite (HA) chromatography, UV‐melting and circular dichroism (CD) experiments. Upon thermal denaturation in 50 mM Tris‐acetate, pH 7.4, 50 mM NaCl, 10 mM MgCl2, 0.1 mM spermine the triplex exhibits two cooperative transitions: one of these is attributed to the triplex‐to‐duplex transformation, the other to the duplex‐to‐coil transformation. The thermodynamic parameters of triplex formation have been determined by a van't Hoff analysis of the UV‐melting curves which provided values of ΔH = 79 ± 8 kcal/mol, δS = 224 22 e.u., ΔG
298 = 12.2 ± 1.2 kcal/mol. These data are compared with those reported for the YRY triplex motif.
Beta‐blocker therapy in advanced heart failure: clinical characteristics and long‐term outcomes
Authors: O'Connor Christopher M. , Gattis Wendy A. , Zannad Faiez , McNulty Steven E. , Gheorghiade Mihai , Adams Kirkwood F. , Califf Robert M. , McKenna William J. , Soler‐Soler Jordi , Swedberg Karl
Published: July 2002

Aims:

To evaluate the clinical characteristics and long‐term outcomes of advanced heart failure patients (NYHA Class IIIb–IV) receiving beta‐blocker therapy vs. those patients not receiving beta‐blockers at randomization in the FIRST trial, a randomized, double‐blind, placebo‐controlled trial of epoprostenol vs. usual care in advanced heart failure.

Methods and results:

The patient population consisted of 471 patients enrolled in FIRST with Class IIIb–IV heart failure, left ventricular ejection fraction (LVEF) of < 30%, advanced hemodynamic abnormalities, and standard pharmacologic treatment of ACE‐inhibitor, diuretics, and/or digoxin. The study cohort consisted of 448 patients not receiving beta‐blockers and 23 patients receiving beta‐blockers at randomization for the FIRST trial. Patients in the beta‐blocker group had decreased rates of any clinical event (P = 0.03), worsening heart failure (P = 0.001), and death or worsening heart failure (P = 0.0008) than patients not receiving beta‐blockers. After adjusting for prognostically important variables, the favorable effect of beta‐blockers on worsening heart failure (P = 0.02) and death or worsening heart failure (P = 0.02) persisted.

Conclusion:

Patients with advanced heart failure who receive beta‐blocker therapy have a lower rate of hospitalization and are less likely to experience worsening heart failure or death at 6 months than patients who are not treated with beta‐blockers. These observational data contribute to the growing body of data demonstrating a favorable effect of beta‐blockers on clinical outcomes in heart failure.
Photodynamic effect in lysozyme: a kinetic study in different micellar media
Authors: Biasutti M.A. , Soltermann T.A. , García N.A.
Published: July 2002

Abstract: The influence of medium heterogeneity on the kinetics of the photodynamic effect on native protein lysozyme (Lyso), as well as the interaction of protein and the medium, anionic (SDS) micelles, neutral (Triton X‐100) micelles and reversed micelles of AOT, were investigated at pH 8. The interaction between Lyso, Triton X‐100 and SDS micelles was quantified by determining the respective associations constant (KLyso). Values were 37 m–1 for Triton X‐100 and 514 m–1 for SDS, indicating that the Lyso molecule binds Triton X‐100 micelles effectively and SDS micelles even more strongly. Time‐resolved phosphorescence detection (TRPD) indicates that the protein interacts with O2 (1Δg), with overall rate constants of the order of 108 m–1/s in direct micelles and 107 m–1/s in reverse micelles. Apparent reactive rate constants for eosin‐sensitized photo‐oxidation (singlet molecular oxygen [O2 (1Δg)]‐mediated) of the protein were determined through oxygen uptake experiments for the direct micelles, while the fade in the protein fluorescence spectrum upon sensitized irradiation was used in AOT. The results indicate that the O2 (1Δg) attack on the interior of Lyso on amino acid residues, was more effective in leading to a photo‐oxidative reaction in SDS and in Triton X‐100 at surfactant concentrations < 1 × 10–2 M than in a homogeneous solution. However, Lyso reactivity reached a maximum when the concentration of micelles was ≈ 1 × 10–5, the same as the protein concentration In AOT reverse micelles, the quenching rate constants decreased > 75% with respect to water. This effect can be attributed to the decrease in accessibility of the amino acid residues to O2 (1Δg).
COMPLICATIONS OF TRANS‐SPHENOIDAL SURGERY: THE WELLINGTON EXPERIENCE
Authors: Woollons A. C. , Balakrishnan V. , Hunn M. K. , Rajapaske Y. R.
Published: July 2002

Background: All patients who underwent trans‐sphenoidal surgery between January 1984 and December 1998 were reviewed to assess morbidity resulting from this operation.

Methods: There were 185 operations on 165 patients. The operative approach was sublabial in 80 cases and transnasal in 105. One surgeon (VB) performed the vast majority of operations.

Results: Complications included nasal perforation (7.6%), transient diabetes insipidus (4.9%), permanent diabetes insipidus (3.8%), cerebrospinal fluid fistula (4.3%), donor site haematoma (2.2%) and residual tumour haemorrhage (1.6%) causing ophthalmoplegia (1.1%) and loss of vision (1.1%). Other complications included epistaxis (1.1%), meningitis (0.5%) and sinusitis (0.5%). Injury to the anterior superior alveolar nerve also occurred in the sublabial approach in 6.3% of patients. There were no perioperative deaths.

Conclusions: There is a small but significant risk of a number of complications that should be considered for informed consent of this procedure.
Ultrasound contrast agent Levovist® in colour Doppler sonography of hepatocellular carcinoma in Chinese patients
Authors: Khong PL , Chau MT , Fan ST , Leong LLY
Published: July 2002

In a phase IIIb clinical trial of the ultrasound contrast agent Levovist® (Schering AG, Berlin, Germany), the role of Levovist® in the management of patients with clinically suspected hepatocellular carcinoma (HCC) was evaluated and its efficacy was assessed. The assessment included the duration of diagnostically usable Doppler signal enhancement, and safety and tolerance of intravenous administration. All patients with clinically suspected hepatocellular carcinoma were referred for Doppler sonographic examination over a 5‐month period and lesions with absent or suboptimal Doppler signals were included in the trial. A total of 300 mg/mL in concentration (8.5 mL) of Levovist® was administered through a peripheral vein while Doppler signal intensity in the lesion, based on a visual score, was recorded. Blood pressure and pulse were recorded before and after injection. Thirty‐eight patients were examined, of which 29 were included in the trial. The lesions were subsequently proven histologically to be 19 HCC, one cholangiocarcinoma, two regeneration nodules and one colonic metastasis. For six patients in whom histological proof was not available, the diagnosis of HCC was suggested based on markedly elevated serum alpha‐fetoprotein levels. All but one (96%) of the 25 HCC demonstrated increased Doppler signal after Levovist®. There were no Doppler signals before and after Levovist® injection in three non‐HCC lesions (two regeneration nodules and one colonic metastasis). Two patients (6.9%) suffered minor adverse reactions of nausea and vomiting. The results show that Levovist® is safe and is able to improve lesion characterization and increase diagnostic confidence of hepatocellular carcinoma by enhancing tumour vascularization Doppler signal intensity.
Temperature sensitivity of primary spermatocyte DNA synthesis in immature mice confirmed by bromodeoxyuridine labelling in vitro
Authors: Zhou  , Hutson  , Hasthorpe  , Farmer
Published: July 2002

Objective

 To investigate the relationship between temperature and DNA synthesis of immature germ cells and to determine whether the early primary spermatocytes proliferate at a ‘scrotal’ temperature of 32°C in vitro.

Materials and methods

 Day‐7 mouse testes (n=16) were cultured with 10% fetal calf serum (FCS) for 3 days at 32°C or 37°C and labelled by bromodeoxyuridine (BrDU) for a further hour. The BrDU‐labelled cells were detected by immunohistochemical staining using a monoclonal anti‐BrDU antibody. The numbers of primary spermatocytes with BrDU‐labelling or unlabelled in each tubule were determined as an index of spermatocyte DNA synthesis. In addition, the cultured media at different temperatures were collected and the testosterone levels measured by radioimmunoassay.

Results

 The numbers of primary spermatocytes (P<0.01) and the BrDU‐labelling index in primary spermatocytes per tubule at 32°C in vitro were significantly higher (P<0.001) than in the culture at 37°C. The testosterone levels in the culture media at 32°C were also markedly higher than in the culture at 37°C (P<0.01).

Conclusion

 These observations indicate that DNA synthesis of early primary spermatocytes and testosterone production can be stimulated by lower testicular temperature, even in immature mouse testes that are naturally located in the intra‐abdominal cavity.
Detection of local atomic ordering in high-resolution electron images of quasiamorphous materials
Authors: Timsit R. S. , Gallerneault C. , Barry J. C. , Landheer D.
Published: July 2002

This letter describes an image analysis technique capable of enhancing atomic ordering in high-resolution electron micrographs of quasiamorphous materials. The technique cross correlates the full micrograph with a template selected from the micrograph image field and examines the cross-correlation function (CCF) as a function of template dimension. A critical dimension is found for which the CCF yields evidence of local atomic ordering.
Effect of post-growth annealing on patterned GaAs on silicon
Authors: Matyi R. J. , Duncan W. M. , Shichijo H. , Tsai H. L.
Published: July 2002

We have investigated the effect of post-growth thermal annealing on the defect surface of patterned GaAs on silicon. Significant improvements in defect structure of the patterned GaAs were observed by transmission electron microscopy (TEM) after short anneal times (15 min) at temperatures as low as 750 °C. At anneal temperatures of 950 °C, long-range single-crystal lateral regrowth of the original polycrystalline GaAs deposited over the amorphous patterning mask was observed. Micro-Raman spectroscopic characterization of the GaAs grown on the oxide/nitride mask corroborated the TEM results by showing a significant improvement in the crystalline quality of patterned GaAs on silicon following post-growth annealing.
NbN Josephson tunnel junctions for terahertz local oscillators
Authors: Robertazzi R. P. , Buhrman R. A.
Published: July 2002

Rugged, high current density NbN1−xCx/MgO/NḃN1−xCx tunnel junctions have been fabricated and tested as voltage tunable Josephson junction terahertz oscillators. The emitted radiation from these junctions is detected on chip by a second junction which is capacitively coupled to the first. For oscillator junctions with a critical current density of Jc∼3.5×104 A/cm2 we find that the junction oscillates with a voltage amplitude of ∼1.5 mV. The detected rf voltage level remains essentially constant from 300 GHz to above 1 THz. The oscillator junction produces 0.5 μW of terahertz radiation of which, due to impedance mismatch, 0.01 μW is coupled into the detector junction.
Light hole interband transitions in HgTe-HgCdTe superlattices
Authors: Schulman J. N. , Wu O. K. , Patten E. A. , Han Jeong W. , Lansari Y. , Kim L. S. , Cook J. W. , Schetzina J. F.
Published: July 2002

The light hole to conduction band optical transition has been identified in the room-temperature absorption spectra of several high quality HgTe-HgCdTe superlattices, in addition to the familiar heavy hole to conduction band transitions. The observation of the light hole transition, coupled with a more accurate determination of the superlattice layer thicknesses, allows the superlattice band gap and the HgTe-HgCdTe valence band offset to be determined more precisely than previously possible. A two-band tight-binding model was used to calculate the transition energies to compare with the optical data. The valence band offset for the HgTe-Hg0.15 Cd0.85 Te interface was determined to be 300±25 meV.
Laser-induced selective copper deposition on polyimide
Authors: Cole H. S. , Liu Y. S. , Rose J. W. , Guida R.
Published: July 2002

Laser irradiation of organometallic palladium compounds with an argon ion laser at 351 nm is used to selectively deposit catalytic amounts of palladium on polyimide. Subsequent immersion of the irradiated samples in an electroless copper solution results in copper deposition. Since a few monolayers of palladium are sufficient to catalyze the electroless copper process, fast writing speeds of several centimeters per second are obtained.
Interfacial reactions between indium and anodic oxide of mercury cadmium telluride
Authors: Lau W. M.
Published: July 2002

The interfacial reaction between indium and anodic oxide of Hg0.8 Cd0.2 Te has been studied using x-ray photoelectron spectroscopy. It was found that the deposition of a thin layer (about 1 nm) of indium by either argon ion sputtering or by direct evaporation reduced some oxidized tellurium of the anodic oxide. The reduced tellurium was extracted to the indium overlayer and present as indium tellurides. However, the thin overlayer on the anodic oxide was found to be partially oxidized but not metallic.
Influence of a thin interfacial oxide layer on the ion beam assisted epitaxial crystallization of deposited Si
Authors: Priolo F. , La Ferla A. , Spinella C. , Rimini E. , Ferla G. , Baroetto F. , Licciardello A.
Published: July 2002

The epitaxial crystallization of chemical vapor deposited Si layers on 〈100〉 Si substrates with a thin interfacial oxide layer was induced by a 600 keV Kr beam in the temperature range 350–500 °C. During irradiation the single crystal-amorphous interface velocity was measured in situ by monitoring the reflectivity of He-Ne laser light. We show that a critical irradiation dose is needed before the interfacial oxide breaks down and epitaxial regrowth can take place. This critical dose depends exponentially on the reciprocal temperature with an activation energy of 0.44 eV.
Deposition of superconducting Y-Ba-Cu-O films at 400 °C without post-annealing
Authors: Witanachchi S. , Kwok H. S. , Wang X. W. , Shaw D. T.
Published: July 2002

Superconducting thin films of Y1Ba2Cu3O7−x were fabricated using the process of plasma-assisted laser deposition. The substrate temperature was as low as 400 °C and high-temperature post-annealing in an O2 atmosphere was not necessary. The as-deposited films have a Tc of ∼85 K, and are oriented mostly with the c axis perpendicular to the substrate surface. The measured Jc at 80 K was 105 A/cm2.
Optical spectra of a (Si4Ge4)5 quantum well structure in an external electric field
Authors: Wong K. B. , Jaros M.
Published: July 2002

We report the first account of the optical spectra in the presence of an external electric field of the Si-Ge structure studied by T. P. Pearsall, J. Berk, L. C. Feldman, A. Ourmazd, J. M. Bonar, and J. P. Mannaerts [Phys. Rev. Lett. 28, 729 (1987)]. We show that although there are some novel features in the electronic structure of the finite system, the optical spectrum is very similar to that obtained for an infinite superlattice. The effect of the electric field used in electroreflectance experiments is negligible.
Laser microfabrication of optical circuits in LiNbO3
Authors: Krauss T. , Speth A. , Oprysko M. M. , Fan B. , Grebe K.
Published: July 2002

Optical waveguides have been fabricated in x-cut LiNbO3 by direct laser patterning of ‘‘spin-on’’ organometallic inks. The technique has been used to repeatedly and rapidly produce single- and multimode waveguide structures, such as lines, y branches, and couplers. In addition, an entirely laser-delineated Mach–Zehnder interferometric modulator has been fabricated.
Plasma-enhanced chemical vapor deposited HgTe-CdTe epitaxial superlattices
Authors: Williams L. M. , Lu P.-Y. , Chu S. N. G.
Published: July 2002

For the first time, small-period epitaxial superlattices were grown using plasma-enhanced chemical vapor deposition. The superlattices were periods of HgTe-CdTe grown on CdTe substrates at 150 °C using dimethylcadmium, dimethylmercury, and dimethyltelluride. Cross-section transmission electron microscopy shows that layers as thin as 80 Å were obtained.
Temperature dependence of the dielectric constants of semi-insulating III-V compounds
Authors: Seeger Karlheinz
Published: July 2002

A microwave transmission interference method recently developed has been applied for a determination of the static dielectric constants of semi-insulating InP, GaP, and GaAs at temperatures of 77 and 300 K.
AlGaAs/GaAs single heterojunction bipolar transistors grown on InP by molecular beam epitaxy
Authors: Agarwala S. , Won T. , Morkoç H.
Published: July 2002

AlGaAs/GaAs single heterojunction bipolar transistors grown on InP substrates by molecular beam epitaxy have been fabricated and tested. An eight-period 25 Å/25 Å In0.53Ga0.47As/GaAs strained-layer superlattice is incorporated in the buffer structure to reduce dislocation propagation to the active region. Small-signal common emitter current gains of about 20 and 30 at a collector current density of 2×103 A/cm2 have been obtained for devices on InP as compared to about 60 and 150 for those on GaAs in structures with base thickness of 0.12 μm doped with Be to 1×1019 and 1×1018 cm−3, respectively. Current densities as high as 1×104 A/cm2 have been achieved in these devices with emitter area of 50×50 μm2 without degradation, demonstrating the excellent stability of this material. From the collector current dependence of the current gain, ideality factors of 1.3 and 1.2 for the emitter junctions have been obtained for devices on InP and GaAs, respectively.
Ultrafast two-laser pump-probe measurement using temporally incoherent lights
Authors: Minami Fujio , Hasegawa Atsushi
Published: July 2002

We propose a new type of pump-probe method to investigate picosecond and femtosecond processes. This method utilizes the intensity correlation between two different temporally incoherent lights. It is demonstrated theoretically that the time resolution is determined by the correlation time independently of the pump and probe pulse widths. The validity of the theoretical consideration is confirmed by lifetime measurements for excited dye molecules.
Compound cavity modes in semiconductor lasers with asymmetric optical feedback
Authors: Seo Dong-Sun , Park Jong-Dae , McInerney John G. , Osiński Marek
Published: July 2002

We describe a static model for determining the oscillating modes of an external cavity semiconductor laser with asymmetric feedback induced by external mirror misalignment. The most significant prediction of this model, the existence of double loss minima leading to compound cavity mode splitting, has been confirmed directly by spectral measurements. This result is important for analyzing complex dynamical phenomena in semiconductor lasers with optical feedback.
Folded acoustic phonons in InAs-AlAs strained-layer superlattices
Authors: Recio M. , Armelles G. , Ruiz A. , Mazuelas A. , Briones F.
Published: July 2002

Raman spectroscopy is used to characterize highly mismatched (7%) InAs-AlAs superlattices grown by atomic layer molecular beam epitaxy. In particular, folded acoustic modes are presented and compared with two different theoretical models (Rytov and linear chain). We find good agreement between theory and experiments. We estimate, with a simple model, the magnitude of the effect of the strain on the phonon frequency shifts.
Intermixing of InGaAs/InP multiple quantum well structures by Ga implantation
Authors: Sumida Hitoshi , Asahi Hajime , Yu S. Jae , Asami Kumiko , Gonda Shun-ichi , Tanoue Hisao
Published: July 2002

The effect of Ga implantation and thermal annealing on InGaAs/InP multiple quantum well structures is investigated by photoluminescence (PL) and sputtering Auger electron spectroscopy. It is found that the interdiffusion of both column III and column V atoms occurs at the interfaces between InP barrier and InGaAs well layers, but the degree of intermixing near the sample surface is small. The variations of PL peak energy shift with annealing and dose suggest that the PL peak shift is attributed to a combination of intermixing and stress.
Medium-energy sputtering of thin films: The approach to percolation
Authors: Papandreou N. , Nedellec P. , Rosenblatt J.
Published: July 2002

Thin Pd films are irradiated with 100 keV Xe ions and their resistance measured in situ. The evolution of resistance as a function of the fluence is found to display invariance properties, which lead to a characterization of the film structure and morphology. The calculations emphasize the role of two features of medium-energy sputtering: the thickness dependence of the sputtering yield and the applicability of Poisson statistics to the process of hole creation in the film.
Rapid, differential microthermometry using Zeeman interferometry
Authors: Johnston Roger G.
Published: July 2002

Zeeman interferometry, based on the two-frequency Zeeman effect laser, can be used for simple, noncontact differential thermometry. The thermometry is differential in both space and time. Small (0.73 μℓ ) laser-heated volumes were monitored with a Zeeman interferometer. Heating rates varied over six orders of magnitude from 180 μK/s to 330 K/s. Temporal resolution was 10 μs. Measured temperatures and measured rates of heating were compared with theory for slowly and rapidly heated samples, respectively.
Electro-optical switching and bistability in coupled quantum wells
Authors: Khurgin Jacob
Published: July 2002

A modulation-doped system of asymmetric-coupled quantum wells is shown theoretically to possess a large optical nonlinearity due to the change transfer associated with intersubband transition. The range of parameters leading to optical bistability is detetermined. A novel triple quantum well system is suggested, allowing a few orders of magnitude reduction in switching power density. Novel hybrid optoelectronic devices, incorporating the triple quantum well system into the channel of a modulation-doped field-effect transistor, are proposed with potential applications as optoelectronic switches and detectors.
Current-controlled negative differential resistance in four-terminal heterostructure devices
Authors: Kastalsky A. , Milshtein M. , Shantharama L. G. , Harbison J. , Florez L.
Published: July 2002

We demonstrate new effects of the current-controlled (S-shaped) negative differential resistance (NDR) in different circuit configurations of four-terminal modulation-doped AlGaAs/GaAs heterostructure devices, with the magnitude of the voltage drop varied by external electrodes. We observe two S-shaped instabilities having different physical origins. One effect arises due to an avalanche in the top AlGaAs layer underneath the reverse-biased gate region. Another phenomenon relies on the creation, during the avalanche, of nonequilibrium hot electrons at the conducting channel (quantum well). This dramatically enhances electron flow over the heterostructure barriers and gives rise to a strongly pronounced current-controlled NDR with a peak-to-valley ratio of ∼10.
Novel low-power optical nonlinearity in semiconductor quantum well electro-optic effect devices
Authors: Weber Ch. , Schlaad K.-H. , Klingshirn C. , Hoof C. v. , Borghs G. , Weimann G. , Schlapp W. , Nickel H.
Published: July 2002

We report a new type of GaAs/AlGaAs electro-optic effect device which offers a built-in optical nonlinearity at extremely low power operation working in the pW to μW regime. The device consists of semitransparent metal electrodes evaporated directly onto the undoped AlGaAs cladding layers of a multiple quantum well structure. We briefly characterize the optical nonlinearity which is based on the quantum-confined Stark effect and discuss the underlying physical mechanism which relies on the suppression of the internal electric fields of the biased sample. The use of such structures is proposed especially for applications as possible low-power and low-cost optical bistable switch.
Study of oxygen addition to CF3Br reactive ion etching plasmas: Effects on silicon surface chemistry and etching behavior
Authors: Bestwick T. D. , Oehrlein G. S. , Angell D. , Jones P. L. , Corbett J. W.
Published: July 2002

The etching of silicon in CF3Br/O2 plasmas has been examined. In situ x-ray photoelectron spectroscopy shows that silicon surfaces etched in CF3Br/O2 plasmas with a proportion of 30% O2 or less are covered with a reaction layer that is mainly due to bromine bonded to silicon. As the proportion of oxygen is increased above 30% the reaction layer becomes thicker and contains mainly fluorine and oxygen, and the silicon etch rate decreases simultaneously.
Novel photovoltaic δ-doped GaAs superlattice structure
Authors: Glass A. M. , Schubert E. F. , Wilson B. A. , Bonner C. E. , Cunningham J. E. , Olson D. H. , Jan W.
Published: July 2002

An asymmetric δ-doped GaAs structure is described which exhibits novel photovoltaic effects and low-intensity nonlinear optics. Of particular interest in this kind of structure is the ability to design the electro-optical and nonlinear optical properties and the material response time over a wide range by appropriate design of the doping profile.
Characterization of a top-illuminated p-i-n diode with an indium tin oxide contact
Authors: Zirngibl M. , Hu Y. , Sachot R. , Ilegems M.
Published: July 2002

The characteristics of a new type of AlGaAs/GaAs p-i-n photodiode are reported. Indium tin oxide forms the contact to the upper AlGaAs layer and serves also as an antireflection coating. Our devices show very low dark currents (20–300 pA at 5 V reverse bias for devices of 20–200 μm diameter), high speed (full width at half maximum <60 ps), and high sensitivity (61% external quantum efficiency) at 1 V bias. A microwave analysis of the diode is presented.
Hydrogen and boron concentrations in doped hydrogenated amorphous silicon-carbon films measured by nuclear reaction analysis
Authors: Zhang Fangqing , Chen Guanghua , He Deyan
Published: July 2002

Hydrogen concentration, boron concentration, and their depth profiles in boron-doped hydrogenated amorphous silicon-carbon films have been measured by nuclear reaction analysis. We find that the concentrations of hydrogen and boron in the films depend on the doping gas ratio of B2H6 to SiH4+CH4. With the increase of the boron doping gas ratio from 10−4 to 10−2, the hydrogen concentration decreases from 38.7 to 6.2 at. % and the boron concentration increases from 0.0094 to 1.2 wt. %. A simple discussion for the results obtained is also presented.
Effect of grain size on conduction mechanism in polycrystalline silicon
Authors: Sagara Kazuhiko , Murakami Eiichi
Published: July 2002

Amorphous silicon was deposited on SiO2 in ultrahigh vacuum and annealed for 8 h at 600 °C in a nitrogen atmosphere. Transmission electron microscopy shows a columnar structure of polycrystalline silicon with the average grain size of 2.5 μm. Boron doses of 3×1013–6×1014 cm−2 were implanted at 30 keV into those films and annealed for 20 min at 950 °C. Hall and resistivity measurements show that the carrier concentration was 100% of the doping concentration and the hole mobility was 20–60 cm2/V s. It was also found that the dependence of hole mobility on carrier concentration is in good agreement with that for the fine grain polycrystalline silicon.
Tunable far-infrared photovoltaic response in semiconductor field-effect devices
Authors: Batke E. , Kaminsky J. , Kotthaus J. P. , Spector J.
Published: July 2002

In semiconductor field-effect devices with quasi-two-dimensional electron channels we observe a novel resonant photovoltaic response to the high-power radiation of a far-infrared free-electron laser. A fast photovoltaic signal occurs when a laser pulse is resonantly absorbed by a plasmon in the two-dimensional electron system. The plasmon frequency and hence the resonant photovoltaic response can be voltage tuned via field effect.
Very low loss GaAs/AlGaAs miniature bending waveguide with curvature radii less than 1 mm
Authors: Takeuchi Hiroaki , Oe Kunishige
Published: July 2002

Very low loss GaAs/AlGaAs miniature bending waveguides with curvature radii less than 1 mm have been fabricated. Their propagation characteristics have been measured at wavelengths of 1.30 and 1.55 μm. Total loss of the fabricated S-bending waveguide shows no increase due to radiation loss even at small radii less than 1 mm. The measured total loss at a radius of 500 μm, for example, is 0.55 and 1.4 dB at wavelengths of 1.30 and 1.55 μm, respectively. These very low loss bending waveguides with small radii prove to be suitable for compact optical integrated circuits.
Laser diode with an auxiliary channel waveguide
Authors: Sheem Sang K.
Published: July 2002

When a laser diode and a directional coupler switch are combined into one structure, the device physics becomes complicated. This work reports some experimental results indicating that the switching function is accompanied by the lasing mode selection mechanism, and that it is enhanced by a longitudinal asymmetry between the coupling channels, namely, by making the lengths of two operating channels different. Such a device exhibits wavelength tunability and self-oscillation besides the enhanced switching effect.
Changes in composition and deposition rates in the reactive sputtering of copper, titanium, and yttrium exposed to oxygen
Authors: Ohwaki Takeshi , Taga Yasunori
Published: July 2002

Copper, titanium, and yttrium oxide films were prepared by reactive dc magnetron sputtering in an Ar-O2 plasma and the deposition rates and compositional changes were measured as a function of dc power. The deposition rates of Cu increased monotonically with increasing dc power, while those of Ti and Y increased abruptly by more than one order of magnitude at a critical dc power (Pc). Abrupt compositional changes of metal and oxygen in the thin films were also observed for Ti and Y at Pc. The compositional change curve for Cu had a plateau in dc power dependence. These results correlate with the differences of heat of oxide formation among Cu, Ti, and Y.
Mass and energy dependence of depth resolution in secondary-ion mass spectrometry experiments with iodine, oxygen, and cesium beams on AlGaAs/GaAs multilayer structures
Authors: Meuris M. , Vandervorst W. , De Bisschop P. , Avau D.
Published: July 2002

The use of an I+2 and I+ primary ion beam in secondary-ion mass spectrometry measurements was studied to investigate its depth profiling properties. A comparison with the results of a Cs+, O+2, and O+ primary beam was made. Experiments were performed with low impact energy (down to 1.7 keV) and glancing angle of incidence on molecular beam epitaxy AlGaAs-GaAs multilayer structures. The best obtainable decay length of the Al+ signal with an iodine primary beam is 1.1 nm. At low impact energies, no mass dependence on the depth resolution is observed. In these conditions, a useful yield for Al+ of approximately 5×10−5 was obtained with the Cs+ beam and 10−2 with the iodine and oxygen beams.
Compensation of the temperature dependence of the optical characteristics of twisted nematic liquid-crystal displays using a single chiral dopant
Authors: Leenhouts F. , Kelly S. , Villiger A.
Published: July 2002

Chiral dopants are reported which enable one to compensate for the temperature dependence of the optical characteristics of twisted nematic liquid-crystal displays. Temperature compensation is achieved by the addition of a small amount of only one chiral compound to the liquid-crystal mixture. This procedure is more precise and less laborious than a previously reported method, which utilizes two or more chiral dopants.
Radiation-induced interface phenomena: Decoration of high-energy density ion tracks
Authors: Ingemarsson P. Anders , Sundqvist Bo U. R. , Nieh C. W. , Tombrello Thomas A.
Published: July 2002

The effect of 20 MeV Cl4+ ions incident on Au-SiO2 and Ag-SiO2 interfaces was investigated using high-resolution transmission electron microscopy. Cross-sectional micrographs expose beam-induced gold interfacial transport and migration into the SiO2. No such migration was observed for silver films. The relevance of this phenomenon to the adhesion improvement found at corresponding irradiation doses is discussed.
Diffusion of Si in thin CoSi2 layers
Authors: Schowengerdt F. D. , Lin T. L. , Fathauer R. W. , Grunthaner P. J.
Published: July 2002

We present evidence of Si diffusion in 100 Å layers of CoSi2 grown by room-temperature codeposition and annealing on Si(111) substrates. By monitoring the intensity of the Co MVV and Si LVV Auger peaks, we find a Si-rich surface layer after annealing, in agreement with the results of others. We find that this layer can be removed by chemical etching and re-formed by subsequent annealing. By measuring the intensity of the plasmon energy loss peak associated with the Co L23 VV Auger peak, we conclude that the Si must exist on top of the CoSi2 and we obtain the effective Si overlayer thickness as a function of annealing temperature by calibrating the plasmon loss data against known overlayer thicknesses on unannealed samples. We find similar results on samples grown both with and without the addition of a 10 Å Si cap to prevent pinhole formation in the CoSi2 and we have indications that the same type of diffusion occurs also beneath the native oxide layer on samples that have not had the surface Si removed by chemical etching. In all of the samples studied, Si diffusion was observed to be non-negligible at temperatures on the order of 400 °C, which is well below the point where pinhole formation is first observed. This result suggests that the diffusion does not depend on the presence of observable pinholes as previously thought.
Formation of an interfacial AlN layer in an Al/Si3N4 thin-film system
Authors: Brener R. , Edelman F. , Gutmanas E. Y.
Published: July 2002

The formation of an interfacial AlN layer was observed in an Al/Si3 N4 thin-film system immediately after electron beam deposition of Al, employing Auger electron spectroscopy, x-ray diffraction, and transmission electron microscopy. Heat treatments up to 600 °C resulted in growth of this layer. The Si liberated by the direct reaction between Al and Si3 N4 was found to crystallize into small islands of peculiar fractal-like shape. The AlN layer acted as a diffusion barrier for diffusion of Al into Si3 N4 .
Anisotropic laser etching of oxidized (100) silicon
Authors: Arnone C. , Scelsi G. B.
Published: July 2002

Laser-induced anisotropic chemical etching of silicon is reported, by using a 488 nm Ar+ laser in direct write mode and high-pressure Cl2 process gas. Surface modifications directly comparable with conventional anisotropic wet etching methods have been obtained. A main role in the process is played by the masking effect due to a thin uniform SiO2 film grown on the Si substrate. An explanation of the etching mechanism is attempted.
Ion beam induced epitaxy of deposited amorphous Si and Si-Ge films
Authors: Yu A. J. , Mayer J. W. , Eaglesham D. J. , Poate J. M.
Published: July 2002

The epitaxial recrystallization of amorphous electron beam deposited silicon and silicon-germanium layers on 〈100〉 silicon substrates was induced by a 2.5 MeV Ar beam irradiation in the temperature range of 200–400 °C. Even in films with bulk oxygen concentration of 0.5 at. %, layer-by-layer regrowth was observed with an order of magnitude reduction in growth rate when compared to clean, implanted amorphous silicon. Irradiation of codeposited Si-Ge amorphous layers results in the layer-by-layer regrowth of a Si88Ge12 alloy. Ion beam assisted epitaxy of Si and Si-Ge was found to be sensitive to interfacial cleanliness, but layer-by-layer regrowth was observed for samples that did not demonstrate regrowth under conventional furnace annealing.
Preparation and superconducting properties of ultrathin YBa2Cu3O7−x films
Authors: Xi X. X. , Geerk J. , Linker G. , Li Q. , Meyer O.
Published: July 2002

Ultrathin films of YBa2Cu3O7−x with thicknesses down to 2 nm were grown on(100)SrTiO3 and (100)MgO by inverted cylindrical magnetron sputtering. Metallic behavior and zero resistance temperatures above 4.2 K were obtained in 3-nm-thick films on SrTiO3. Thinner films revealed temperature-activated conductivity and only partial transitions to superconductivity due to inhomogeneities in the film morphology. On MgO, the critical film thickness leading to deteriorations of the transport properties was 6 nm. An analysis of the fluctuation-enhanced conductivity near Tc in terms of the Aslamazov–Larkin theory [Phys. Lett. A 26, 238 (1968)] revealed three-dimensional behavior even in the thinnest fully superconducting films.
Electro-optic depolarization switch on y-cut LiNbO3 proton-exchanged channel waveguides
Authors: Chen Ray T.
Published: July 2002

We report the first electro-optic depolarization (TE guided mode to TM substrate modes) switch on y-cut LiNbO3 proton-exchanged channel waveguides operating at 632.8 nm. Tunability of the waveguide ordinary and extraordinary indices through thermal annealing provides an alternative way to reduce the drive voltage. An extinction ratio of 13.5 dB is achieved with 10 V applied voltage on a switch with 4 μm channel width and 3 mm electrode length. The measured capacitance of the electrode is 4.2 pF, which gives a theoretical modulation bandwidth of 1.5 GHz in a 50 Ω lumped electrode structure.
Acoustoelectric effects in ceramic high-temperature superconductors using a separate medium structure
Authors: Abedin M. N. , Tiersten S. C. , Das P.
Published: July 2002

The interaction of the surface acoustic wave (SAW) with a bulk ceramic high-temperature superconductor is investigated using a contactless separate medium structure. The superconductor is part of a sandwich structure consisting of a y-cut z-propagating LiNbO3 SAW delay line. An acoustoelectric voltage is observed across the superconductor above the transition temperature. The magnitude of this voltage exhibits large changes as a function of temperature. As the temperature decreases through the superconductive transition, the acoustoelectric voltage vanishes abruptly. The transition temperature for the acoustoelectric voltage is in agreement with resistivity measurements performed on the same sample.
Laser writing of high-purity gold lines
Authors: Jubber M. , Wilson J. I. B. , Davidson J. L. , Fernie P. A. , John P.
Published: July 2002

Gold tracks of better than 98% purity have been deposited onto oxidized silicon wafers from gaseous methyl(triethylphosphine) gold(I), AuMe(Et3 P), by using 514 nm radiation from a focused cw argon ion laser. Room-temperature resistivities of 4.2 μΩ cm, comparable with bulk gold, were attained at a writing speed of 35 μm s−1 . The track profiles suggest that deposition is more rapid on the gold surface than on the SiO2 substrate.