bluuebunny/crossref_metadata_2025 huggingface dataset:
Converging Lenses: PLE diagrams, PKM Workflows and Scholarly Ontologies
Authors: Cosgrave Michael
Published: January 2023

This paper reviews the emergence and development of three different perspectives on knowledge work – PLE (Personal Learning Environments), PKM (Personal Knowledge Management) and Scholarly Ontologies. Each is described briefly, followed by an overview of how they align and might usefully be used as approaches to introducing students to formal methods of knowledge processes in their learning.

Este artículo revisa el surgimiento y desarrollo de tres perspectivas diferentes sobre el trabajo del conocimiento: PLE (Entornos personales de aprendizaje), PKM (Gestión personal del conocimiento) y Ontologías académicas. Cada uno se describe brevemente, seguido de una descripción general de cómo se alinean y podrían usarse de manera útil como enfoques para presentar a los estudiantes métodos formales de procesos de conocimiento en su aprendizaje.
En este artículo se revisa la aparición y el desarrollo de tres perspectivas distintas para aproximarse al trabajo con el conocimiento: los PLE (Entornos Personales de Aprendizaje), las PKM (Redes de gestión del conocimiento) y las ontologías académicas. Cada una de las perspectivas se describe brevemente, y a continuación se presenta una visión general de cómo se armonizan, complementan y pueden ser útiles como enfoques para la introducción de los estudiantes en los métodos formales para procesar el conocimiento en sus diversos ámbitos de aprendizaje.
Diseño y validación de contenido de una rúbrica para medir el valor educativo de aplicaciones para dispositivos móviles
Authors: Expósito-López Jorge , Romero-Díaz de la Guardia José Javier , Olmedo-Moreno Eva María
Published: January 2023

Applications for mobile devices are increasingly a frequently used resource in different educational settings. The objective of this work was the design and validation of an instrument to measure the educational value of these applications, which has been called E-V-A (Educational Value Assessment). A process comprised of three phases was followed, according to a mixed methodology, considering the conceptual and theoretical design of the rubric, the functional design of dimensions, indicators and descriptors, as well as the subsequent validation of theoretical-practical content through expert judgment on relevance, clarity and adequacy, using the Delphi technique. The validation process allowed the formulation of an evaluation rubric for educational apps made up of 100 items structured into 21 blocks and 5 dimensions: personal development, cognitive and metacognitive development, learning and skills development; social development and technical dimension. This instrument can be very useful for teaching professionals who need to measure the educational value of an app through a structured and uniform protocol.

Las aplicaciones para dispositivos móviles son cada vez más un recurso frecuentemente utilizado en los diferentes escenarios educativos. El objetivo de este trabajo fue el diseño y validación de un instrumento para medir el valor educativo de estas aplicaciones, al que se ha denominado E-V-A (Educational Value Assessment). Se siguió un proceso estructurado en tres fases, acorde a una metodología mixta, contemplando el diseño conceptual y teórico de la rúbrica, diseño funcional de dimensiones, indicadores y descriptores de valoración y posterior validación de contenido teórico-práctica mediante juicio de expertos en torno a la pertinencia, claridad y adecuación, utilizando técnica Delphi. El proceso de validación permitió la formulación de una rúbrica de evaluación de app educativas compuesta por 100 ítems estructurados en 21 bloques y 5 dimensiones: desarrollo personal, desarrollo cognitivo y metacognitivo, desarrollo del aprendizaje y de competencias; desarrollo social y dimensión técnica. Este instrumento puede ser de gran utilidad para profesionales de la docencia que necesiten medir el valor educativo de una app mediante un protocolo estructurado y uniforme.
Los títulos de "El libro del conde Partinuplés" (siglo XVI)
Authors: Torralba Ruberte Ángela
Published: January 2023

El presente trabajo trata de analizar las características del título en las ediciones castellanas de la novela o historia caballeresca Partinuplés a lo largo del siglo xvi. Por un lado, lo estudiaremos en las diferentes portadas del relato en esta centuria, atendiendo tanto a los términos genéricos con que se inician las intitulaciones de los relatos caballerescos, como a su extensión, ya que los rótulos se fueron amplificando durante el Seiscientos. Por otro lado, examinaremos las referencias a la obra en el íncipit y el colofón, lo que posibilitará percibir la evolución y variabilidad de todas las alusiones, así como su relación con su desarrollo narrativo. De esta manera, los datos obtenidos nos permitirán comprender los diferentes factores que intervienen en la titulación de este relato.
El mito de la Fuente de la Juventud en el sermonario de san Vicente Ferrer: contra “poetes e altres faules”
Authors: Calvé Mascarell Óscar
Published: January 2023

El presente trabajo se aproxima, con el apoyo de la producción figurativa contemporánea, a la tensa relación del predicador dominico Vicent Ferrer (c. 1350-1419) con autores que no dedicaron su obra al adoctrinamiento de la fe cristiana, o si lo hicieron, no fue en la forma tradicional. En sus sermones Ferrer no dudó en descalificar forma y contenido de cualquier literatura ajena a la revelación del dogma, apuntando que el destino de gran parte de los poetas era arder en el infierno. Llegó a parodiarlos públicamente, pues sus textos «sólo resultan bien a los oídos y no reportan ningún fruto sino la cadencia tan, taran, etc.». Mayor enjundia presentan alusiones a motivos concretos como el de la «Font Jove», de especial arraigo en la ficción caballeresca: presentada por Ferrer como desviación literaria del sacramento del bautismo, gozó de enorme éxito figurativo. Este y otros casos informan sobre la recepción heterogénea de una determinada producción cultural del momento.
El presente trabajo se aproxima, con el apoyo de la producción figurativa contemporánea, a la tensa relación del predicador dominico Vicent Ferrer (c. 1350-1419) con autores que no dedicaron su obra al adoctrinamiento de la fe cristiana, o si lo hicieron, no fue en la forma tradicional. En sus sermones Ferrer no dudó en descalificar forma y contenido de cualquier literatura ajena a la revelación del dogma, apuntando que el destino de gran parte de los poetas era arder en el infierno. Llegó a parodiarlos públicamente, pues sus textos «sólo resultan bien a los oídos y no reportan ningún fruto sino la cadencia tan, taran, etc.». Mayor enjundia presentan alusiones a motivos concretos como el de la «Font Jove», de especial arraigo en la ficción caballeresca: presentada por Ferrer como desviación literaria del sacramento del bautismo, gozó de enorme éxito figurativo. Este y otros casos informan sobre la recepción heterogénea de una determinada producción cultural del momento.
La Orden de la Jarretera en la compilación de la "Historia de Inglaterra" (1504-1509) de Rodrigo de Cuero
Authors: Contreras Martín Antonio , Soriano Robles Lourdes
Published: January 2023

En los folios finales de los manuscritos que transmiten la Historia de Inglaterra con el fruto de los tiempos (1504 ante quem – 1509), Rodrigo de Cuero añadió al final de la obra un opúsculo sobre el origen de la Orden de la Jarretera, sus divisas y estatutos. En el presente trabajo, se ofrece la edición de la versión castellana, así como una propuesta de filiación textual a los estatutos revisados por Enrique VII, que fueron redactados en francés durante el último cuarto del siglo xv.
Ferrando Morales, Àngel Lluís, «El "Tirant lo Blanc" fet música», Alacant, Univ. d'Alacant, 2022
Authors: Hernàndez i Garcia Xavier
Published: January 2023

Ressenya de: "Ferrando Morales, Àngel Lluís, El Tirant lo Blanc fet música. Les composicions musicals inspirades en el Tirant lo Blanc, Alacant, Universitat d’Alacant, 2022"
Campos García Rojas, Axayácatl y Yordi Enrique Gutiérrez Barreto (eds.), «En línea caballeresca», Ciudad de México, UNAM, 2020
Authors: Pallardó Betlem
Published: January 2023

Ressenya de: Campos García Rojas, Axa y Jordi Gutiérrez Barreto (eds.), En línea caballeresca: lecciones del Seminario de Estudios sobre Narrativa Caballeresca, México, UNAM, 2020
Córdoba, Juan de, «Lidamor de Escocia», ed. Rafael Ramos, Alcalá de Henares, Universidad de Alcalá, 2020
Authors: García Álvarez Juan Pablo Mauricio
Published: January 2023

Córdoba, Juan de, Lidamor de Escocia, ed. Rafael Ramos, Alcalá de Henares, Universidad de Alcalá – Instituto Universitario de Investigación Miguel de Cervantes, 2020
Korpus Polsko-Niemiecki Uniwersytetu Warszawskiego i Uniwersytetu Gutenberga (PolGerCorp)
Authors: Łaziński Marek , Meger Andreas , Woźniak Michał
Published: January 2023

Celem artykułu jest prezentacja nowego korpusu polsko-niemieckiego PolGerCorp, zgromadzonego w latach 2018-2021 w ramach projektu Uniwersytetu Warszawskiego i Uniwersytetu Gutenberga w Moguncji. Korpus ma wielkość 10 mln słów w tekstach z lat 1750–2020. Teksty oryginalne polskie oraz niemieckie wraz z tłumaczeniami reprezentują prozę artystyczną, non-fiction, prasę i teksty prawne. Teksty zostały otagowane, zlematyzowane i wyrównane zdanie do zdania. W artykule prezentujemy interfejs przyjazny dla użytkownika niespecjalisty oraz możliwości wyszukiwania. Tagowanie odpowiedników aspektowych daje szczególną i unikalną szansę wyszukiwania w ramach par aspektowych z uwzględnieniem różnych formalnych typów wyznaczników aspektu.
Arsenic and mercury tolerant rhizobacteria that can improve phytoremediation of heavy metal contaminated soils
Authors: Rojas-Solis Daniel , Larsen John , Lindig-Cisneros Roberto
Published: January 2023

Background

Mining deposits often contain high levels of toxic elements such as mercury (Hg) and arsenic (As) representing strong environmental hazards. The purpose of this study was the isolation for plant growth promoting bacteria (PGPBs) that can improve phytoremediation of such mine waste deposits.

Methods

We isolated native soil bacteria from the rhizosphere of plants of mine waste deposits and agricultural land that was previously mine tailings from Tlalpujahua Michoacán, Mexico, and were identified by their fatty acid profile according to the MIDI Sherlock system. Plant growth promoting traits of all bacterial isolates were examined including production of 3-indoleacetic acid (IAA), siderophores, biofilm formation, and phosphate solubilization. Finally, the response of selected bacteria to mercury and arsenic was examined an in-vitro assay.

Results

A total 99 bacterial strains were isolated and 48 identified, representing 34 species belonging to 23 genera. Sixty six percent of the isolates produced IAA of which Pseudomonas fluorescens TL97 produced the most. Herbaspirillum huttiense TL36 performed best in terms of phosphate solubilization and production of siderophores. In terms of biofilm formation, Bacillus atrophaeus TL76 was the best.

Discussion

Most of the bacteria isolates showed high level of tolerance to the arsenic (as HAsNa2O4 and AsNaO2), whereas most isolates were susceptible to HgCl2. Three of the selected bacteria with PGP traits Herbispirillum huttiense TL36, Klebsiella oxytoca TL49 and Rhizobium radiobacter TL52 were also tolerant to high concentrations of mercury chloride, this might could be used for restoring or phytoremediating the adverse environmental conditions present in mine waste deposits.
Evaluation of fish density influence on the growth of the spotted rose snapper reared in floating net cages using growth models and non-parametric tests
Authors: Jurado-Molina Jesús , Hernández-López Carlos Humberto , Hernández Crisantema
Published: January 2023

In commercial fish farming, growth performance is the most influential factor in economic profitability; so, biomass optimization has become a growing concern. We analyzed the influence of 3 harvest densities (15, 20, and 22 kg·m–3) on the growth of spotted rose snappers reared in floating net cages during a production cycle. To assess the impact of stocking density on growth performance, we used 2 indicators: final total length-at-age (12 months) and the growth rate estimated from growth models (von Bertalanffy, logistic, and Gompertz). For the first indicator, we tested for normality. We did the Kruskal–Wallis and the post hoc Kruskal–Wallis tests to compare the mean total final length from each density. Accordingly, the means of densities D15 and D20 were the same (P value = 0.22). For the second indicator, we fitted the models with the subroutine optim of the R statistical package using the L-BFGS-B algorithm. Model selection was made with the Akaike and the Bayesian information criteria. Both criteria suggested that the logistic model fitted the data best. With the best model (logistic), we did 1,000 bootstrap simulations for each density scenario to determine the distribution of the maximum likelihood estimation for the instantaneous growth rate. Because the estimates were normally distributed, we used ANOVA to test the equality of the instantaneous growth. The Tukey HSD test suggested that all means were statistically different from each other. The fastest growth rate (K = 0.275) corresponded to the cage with a density of 20 kg·m–3. These findings demonstrate that the logistic model can predict the growth of spotted rose snappers under culture conditions using floating net cages. These results strengthen the productive potential and economic profitability of snapper aquaculture using floating cage and may help the start of commercial scale aquaculture.
Digital Marketing and Entrepreneurship in Women of El Porvenir District, Peru
Authors: Morales Ana Elizabeth Paredes
Published: January 2023

The objective of this research was to determine the impact of digital marketing on women's entrepreneurship in the district of El Porvenir 2022, the type of research was applied, with a quantitative research approach and a non-experimental research design with a cross-sectional and correlational approach. The sample consisted of 114 women entrepreneurs from the El Porvenir district. The questionnaire for digital marketing with a reliability of 0.983 and the questionnaire for business entrepreneurship with a reliability of 0.967 was used for data collection. The information was processed in SPSS Ver 26 software. As a result, digital marketing has a very high incidence in business entrepreneurship with a correlation coefficient of 0.950. It was determined that the normative framework has a very high incidence in business entrepreneurship with a correlation of 0.942, the referential framework has a very high incidence in business entrepreneurship with a correlation of 0.983, the conceptual framework has a very high incidence in business entrepreneurship with a correlation of 0.983, the conceptual framework has a high impact on entrepreneurial entrepreneurship with a correlation of 0.756, the theoretical framework also has a high impact on entrepreneurship with a correlation of 0.689 and the philosophical framework has a moderate impact with a correlation of 0.522 on entrepreneurship all at 1% significance.
A study of sustainable growing media through the utilization of agricultural by-products as organic substrates for tomato seedling production
Authors: Truong Ha Duy , Nin Le Thanh , Quynh An Nguyen
Published: January 2023

Tomato is a widely cultivated and consumed vegetable crop in the world. It is a valuable source of nutritional compositions and health-promoting phytochemicals. This study aimed to evaluate the growth response of tomato seedlings to the use of media mixtures formulated from rice husk ash (RHA), coir (C), canna residue (CR), and animal manures, including pig manure (PM), chicken manure (CKM), and cow manure (CM). Five treatments were applied at proportions: 25% RHA + 25% C + 25% CR + 25% PM (T1), 25% RHA + 25% C + 25% CR + 25% CKM (T2), 25% RHA + 25% C + 25% CR + 25% CM (T3), 25% RHA + 25% C + 25% CR + 25% peat (T4), and 100% TS2 (Kultursubstrat aus Weibtorf White Peat Potting Substrate) commercial product (T5). Our results suggested that, in comparison with the treatment of T5 the experimented media showed positive effects on the growth of tomato plants during the nursery stage. The best response was recorded in the treatment T1 with the highest germination rate (96.05%) after 10 days of sowing. Also, T1 obtained great values of plant height, leaf number, and root volume on day 30 after sowing, which were 7.85 cm, 3.5 leaves per plant, and 1.08 cm3, respectively. These findings indicated that the tested byproduct materials offer a viable and sustainable alternative to producing growing media for tomato seedling practices.

Keywords: Growing media, rice husk ash, coir, canna residue, and animal manures, tomato by-product.
Bacteriophage and host mutants causing the rolling‐circle λ DNA replication early after infection
Authors: Konopa Grażyna , Barańska Sylwia , Wegrzyn Alicja , Wegrzyn Grzegorz
Published: July 2002

There are two modes of bacteriophage λ DNA replication during its lytic development in Escherichia coli cells. The circle‐to‐circle (θ) replication predominates at early stages of the phage growth, whereas rolling‐circle (σ) replication occurs late after infection to produce long concatemers that serve as substrates for packaging of λ DNA into phage proheads. The mechanism regulating the switch from θ to σ replication remains unknown. Our previous genetic studies indicated that the bacteriophage λ Pts1πA66 mutant cannot replicate at 43°C in the wild‐type E. coli host, but it can replicate in the dnaA46(ts) mutant. Density shift experiments suggested that the parental DNA molecules of the infecting phage enter σ replication. Here, using electron microscopy, we demonstrate that as soon as 5 min after infection of the dnaA46(ts) mutant by the λPts1πA66 phage at 43°C, the σ replication intermediates are highly predominant over θ replication intermediates, contrary to the wild‐type conditions (wild‐type bacteria infected with the λP
+ phage). The initiation of replication of the λPts1πA66 mutant at 43°C was strongly inhibited in the dnaA
+ host, as demonstrated by electron microscopy and by pulse‐labeling of the phage‐derived plasmid replicon. Implications for the mechanism of the regulation of the switch from θ to σ replication mode are discussed.
Combination therapy with carvedilol and amiodarone in patients with severe heart failure
Authors: Nägele Herbert , Bohlmann Michael , Eck Ulrich , Petersen Ben , Rödiger Wilfried
Published: July 2002

Background:

Carvedilol and at least in some studies, amiodarone have been shown to improve symptoms and prognosis of patients with heart failure. There are no reports on the outcome of combined treatment with both drugs on top of angiotensin‐converting enzyme inhibitors (ACEI), diuretics and digitalis.

Methods and Results:

In 109 patients with severe heart failure submitted for heart transplantation at one single center between the years 1996 and 1998 [left ventricular ejection fraction (LVEF) 24.6±11%, 85% males, 52% idiopathic dilated cardiomyopathy (DCM), mean observation time 1.9±0.4 years] a therapy with low‐dose amiodarone (1000 mg/week) plus titrated doses of carvedilol (target 50 mg/day) was instituted. In addition, patients received a prophylactic dual chamber pacemaker (PM) in order to protect from bradycardia and for continuous holter monitoring. The devices were programed in back‐up mode with a basal rate of 40 i.p.m. with a hysteresis of 25%. Significantly, more patients were in sinus rhythm after 1 year than at study entry (85% vs. 63%, P<0.01). In 47 patients, under therapy over at least 1 year, the resting heart rate fell from 90±19 to 59±5 b.p.m. (P<0.001). Ventricular premature contractions in 24‐h holter ECGs were suppressed from 1.0±3 to 0.1±0.3%/24 h (P<0.001) as did numbers of tachycardias >167 b.p.m. detected by the pacemaker (1.2±2.8 episodes/patient/3 months vs. 0.3±0.8 episodes/patient/3 months after 1 year (P<0.01). The LVEF increased from 26±10 to 39±13% (P<0.001). NYHA class improved from 3.17±0.3 to 1.8±0.6 (P<0.001) as well as right heart catheterization data. From the total cohort, seven patients (6%) developed symptomatic documented bradycardic rhythm disturbances requiring reprograming of their pacemakers to DDD(R)/VVI(R) mode with higher basic rates. Two of these patients developed AV block, four sinu‐atrial blocks or sinus bradycardia and one patient had bradycardic atrial fibrillation. During the observation period five patients died (3 sudden, 1 due to heart failure and 1 due to mesenteric infarction). Two patients had undergone heart transplants. The 1‐year survival rate (Kaplan–Meier) without transplantation was 89%. Compared to historic control patients with amiodarone only (n=154) or without either agent (n=283) this rate was 64 and 57% (P<0.01).

Conclusions:

Heart failure patients benefit from a combined therapy with carvedilol and amiodarone resulting in a markedly improved NYHA stage, an increase in LV ejection fraction, a stabilization of sinus rhythm, a significant reduction in heart rate, a delay of electrical signal conduction and a suppression of ventricular ectopies. Approximately 6% of patients under such a regime became pacemaker‐dependent in the first year. Compared to historic controls prognosis was better and the need for heart transplantation was lower. The exact role of either agent in combination or alone should be clarified in larger randomized studies.
Continuous Cultivation of the Diatom Nitzschia laevis for Eicosapentaenoic Acid Production: Physiological Study and Process Optimization
Authors: Wen Zhi‐You , Chen Feng
Published: July 2002

The continuous cultures of the diatom Nitzschia laevis were performed at different dilution rates ( D) and feed glucose concentrations ( S0) to investigate cellular physiological responses and its production potential of eicosapentaenoic acid (EPA). Steady‐state cell dry weight, residual glucose concentration, cell growth yield, specific glucose consumption rate, and fatty acid profiles were investigated within the range of D from 0.1 to 1.0 day−1 ( S0 fixed at 20 g/L) and the range of S0 from 5 to 35 g/L ( D fixed at 0.3 day−1), respectively. The highest EPA productivity of 73 mg L‐1 day‐1 was obtained at D = 0.5 day−1 and S0 = 20 g/L. However, when the continuous culture achieved high productivities of EPA at certain dilution rates and feed glucose concentrations, glucose in the feed could not be consumed completely. Accordingly, the continuous culture was evaluated in terms of both EPA productivity ( P) and glucose assimilation efficiency ( E). The parameter η, defined as the product of P and E, was used as an overall performance index. Since η is a function of the two independent variables Dand S0, we employed a central composite design to optimize D and S0 for the highest η value. Based on the experimental results of the design, a second‐order polynomial equation was established to represent the relationship between η and D and S0. The optimal values of D and S0 were subsequently determined as 0.481 day−1 and 15.56 g/L, respectively by the empirical model. The verification experiment confirmed the validity of the model. Under the optimal conditions, η value reached 46.5 mg L‐1 day‐1, suggesting a considerably high efficiency of the continuous culture of N. laevis in terms of EPA production and glucose utilization.
High‐resolution ultrasound to diagnose melanoma metastases in patients with clinically palpable lymph nodes
Authors: Uren Roger F , Howman‐Giles Robert , Thompson John F , Shaw Helen M , Roberts John M , Bernard Elizabeth , McCarthy William H
Published: July 2002

High‐resolution ultrasound was used to determine if it could predict the presence of metastatic disease in 52 patients with melanoma who had developed newly palpable lymph nodes during clinical follow‐up. Ultrasound proved accurate in diagnosing the presence of nodal metastases; it had a sensitivity of 94%, a specificity of 87% and an accuracy of 89%. The ultrasound features which together were diagnostic of the presence of nodal metastases were a node thickness greater than two‐thirds of the node length and the presence of low‐level echoes in the node. When these two features were both present on ultrasound, node metastases were present in every case. Ultrasound can be used to evaluate newly palpable lymph nodes in patients with melanoma. A normal ultrasound finding does not exclude micrometastases, but a lymph node showing the two key ultrasound features aforementioned is highly likely to contain metastatic disease and should be treated accordingly.
Modeling the Effects of Fishing and Implications for the Design of Marine Protected Areas: Juvenile Fish Responses to Variations in Seafloor Habitat
Authors: Lindholm James B. , Auster Peter J. , Ruth Matthias , Kaufman Les
Published: July 2002

Abstract:A number of recent studies have linked post‐settlement survivorship of Atlantic cod ( Gadus morhua) with the complexity of the seafloor to which fish settle. Survivorship is greater in habitats of higher complexity (e.g., pebble‐cobble substratum with emergent epifauna> pebble‐cobble> sand), where cover provides shelter from predators. Fishing with mobile gear such as bottom trawls and dredges reduces the complexity of seafloor habitats. We used a dynamic model to (1) link patterns in habitat‐mediated survivorship of post‐settlement juvenile cod with spatial variations in habitat complexity, (2) simulate habitat change based on fishing activities, and (3) determine the role of marine protected areas in enhancing recruitment success. Density‐dependent natural mortality was specified as three alternative functional response curves to assess the influence of different predator foraging strategies on juvenile survivorship during the first 12 months of demersal existence. We applied the model to a theoretical patch of hard‐bottom substrata and to a case study based on seafloor habitat distributions at Stellwagen Bank National Marine Sanctuary (Gulf of Maine, Northwest Atlantic). Our results demonstrate that patterns in the shape of response surfaces that show the relationship between juvenile cod survivorship and density as well as movement rate were similar regardless of functional response type, that juvenile cod movement rates and post‐settlement density were critical for predicting the effects of marine protected‐area size on survivorship, and that habitat change caused by fishing has significant negative effects on juvenile cod survivorship and use of marine protected areas can ameliorate such effects.
Acoustic and acousto-optic properties of 3-methyl 4-nitropyridine 1-oxide—a Brillouin scattering study
Authors: Sapriel J. , Hierle R. , Zyss J. , Boissier M.
Published: July 2002

The complete set of elastic and photoelastic constants of 3-methyl 4-nitropyridine 1-oxide (POM) organic single crystals is measured by Brillouin scattering. The acousto-optic figures of merit are then derived and the anisotropy of the longitudinal and transverse acoustic wave velocity clearly evidenced from the knowledge of these constants. POM appears to be a promising material for acousto-optical devices as light deflectors and modulators. It is shown that a Bragg cell using POM as an interaction medium would combine several favorable technical features.
Growth of matched metallic ErP0.6As0.4 layers on GaAs in a molecular beam epitaxy system
Authors: Le Corre A. , Caulet J. , Guivarc’h A.
Published: July 2002

Metallic layers of ErP0.6As0.4 have been grown by molecular beam epitaxy on GaAs at 500 °C. The growth has been achieved by adjusting the PH3 and AsH3 flows to obtain a good lattice match to the substrate, the erbium flux remaining below the flux of the V elements. The 10–100 nm thick epitaxial layers reproducibly showed lattice mismatch below 5×10−4 and unlike the ErAs layers, they do not degrade in the atmosphere. Due to its low resistivity (ρ=80 μΩ cm), this compound is an ideal candidate for the realization of epitaxial III-V semiconductor/metal/III-V semiconductor heterostructures.
InGaAs/AlGaAs strained single quantum well diode lasers with extremely low threshold current density and high efficiency
Authors: Choi H. K. , Wang C. A.
Published: July 2002

Graded-index separate-confinement heterostructure InGaAs/AlGaAs single quantum well diode lasers emitting at 1.02 μm have been fabricated from structures grown by organometallic vapor phase epitaxy. Under pulsed operation, threshold current densities as low as 65 A/cm2, the lowest reported for InGaAs/AsGaAs lasers, have been obtained for a cavity length L of 1500 μm. Differential quantum efficiencies as high as 90% have been obtained for L=300 μm. Output powers as high as 1.6 W per facet and power conversion efficiencies as high as 47% have been obtained for continuous operation of uncoated lasers with L=1000 μm.
Very low threshold single quantum well graded-index separate confinement heterostructure InGaAs/InGaAsP lasers grown by chemical beam epitaxy
Authors: Tsang W. T. , Choa F. S. , Wu M. C. , Chen Y. K. , Sergent A. M. , Sciortino P. F.
Published: July 2002

We have succeeded in preparing 1.5 μm wavelength strained-layer graded-index separate confinement heterostructure (GRINSCH) InGaAs/InGaAsP single quantum well (SQW) injection lasers by chemical beam epitaxy (CBE). These lasers have extremely low threshold current density Jth of 170 A/cm2, internal quantum efficiency of 83%, and internal waveguide loss of 3.8 cm−1. To the best of our knowledge, these results represent the best values obtained thus far from long-wavelength InGaAs/InGaAsP quantum well injection lasers grown by any techniques. However, despite the recent rapid reduction in Jth, the threshold-temperature dependence remains poor (T0=45 K) even in these very low Jth GRINSCH SQW lasers.
Ga2Te3 and tellurium interfacial layers in ZnTe/GaSb heterostructures studied by Raman scattering
Authors: Halsall M. P. , Wolverson D. , Davies J. J. , Lunn B. , Ashenford D. E.
Published: July 2002

Raman spectroscopy of ZnTe layers grown by molecular beam epitaxy on (100) GaSb is reported. When the laser excitation is above the band gap of the ZnTe, scattering is observed only from the ZnTe LO mode and overtones. With excitation below the ZnTe band gap, a series of low frequency peaks is observed. By comparison with bulk data these peaks are identified as originating from Ga2Te3 and Te present at the GaSb/ZnTe interface. We conclude that the presence of this interface material may degrade the layer quality and give rise to the anomalously large strain previously reported for such epilayers.
Aluminum acceptor four particle bound exciton complex in 4H, 6H, and 3C SiC
Authors: Clemen L. L. , Devaty R. P. , MacMillan M. F. , Yoganathan M. , Choyke W. J. , Larkin D. J. , Powell J. A. , Edmond J. A. , Kong H. S.
Published: July 2002

New lines in the low temperature luminescence spectra of lightly aluminum doped p-type films of 3C, 6H, and 4H SiC are identified and associated with the recombination of a neutral aluminum acceptor four particle bound exciton complex.
Second order optical nonlinearities of radio frequency sputter-deposited AlN thin films
Authors: Lin W. P. , Lundquist P. M. , Wong G. K. , Rippert E. D. , Ketterson J. B.
Published: July 2002

Polarized second harmonic generation measurements were performed on AlN films deposited on (100) sapphire substrates by the reactive rf sputtering technique. The bulk effective second order nonlinearity observed in these films is typically about 6×10−9 esu at 1.06 μm, several times larger than that of quartz or KTP. The tensorial properties of the nonlinearity are consistent with the crystal symmetry of AlN and the microcrystallinity of these films.
Demonstration of Josephson effect submillimeter wave sources with increased power
Authors: Han Siyuan , Bi Baokang , Zhang Wenxing , Lukens J. E.
Published: July 2002

A submillimeter wave source based on a new design using Josephson junction arrays has been developed and tested. The maximum rf power, delivered to a 68Ω load and detected on chip, was 47 μW at 394 GHz. Significant power was detected at a number of frequencies from 300 to 500 GHz where the power was 10 μW. The observed power at the designed operating frequency near 400 GHz is consistent with all 500 junctions in the series biased array delivering current in phase to the loads. This is in agreement with simulations of smaller arrays of the same design. The linewidth, inferred from the measured resistance at the point of maximum power, with T=4.2 K, is less than 1 MHz. The minimum inferred linewidth near 400 GHz, at somewhat lower power, is about 100 kHz.
Stable secondary electron emission from chemical vapor deposited diamond films coated with alkali-halides
Authors: Mearini G. T. , Krainsky I. L. , Dayton J. A. , Wang Yaxin , Zorman Christian A. , Angus John C. , Hoffman R. W. , Anderson D. F.
Published: July 2002

Stable secondary electron emission from cesium terminated chemical vapor deposited (CVD) diamond films has been observed. Total secondary yield coefficients (σ) ranged from 25 to 50 and were stable under continuous exposure to an electron beam from targets tested for up to 170 h. Primary current densities ranged from 1.5 to 50.0 mA/cm2. Targets were coated with CsI from 10 to 100 nm thick. Auger electron spectroscopy was used to show that the emission was activated by electron beam induced iodine depletion after short beam exposures, leaving a Cs terminated diamond surface independent of the initial CsI thickness. The electron beam activated-alkali terminated surface is air stable and stable during heating in vacuum up to 120 °C. This behavior has also been observed from CVD diamond coated with CsF, KCl, and NaCl.
Low-pressure, automated, sample packing unit for diffuse reflectance infrared spectrometry
Authors: Christy Alfred A. , Tvedt Jan Erik , Karstang Terje V. , Velapoldi Rance A.
Published: July 2002

An automatic, low-pressure packing unit has been designed with control of packing time and pressure to prepare powder samples for diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). This unit also provides a polished packing surface that ensures constant measurement height of the sample in the spectrometer. Use of this unit coupled with sample rotation during measurement and control of particle size and size distribution, provides excellent precision in obtaining DRIFTS spectra. For example, repackings by a single person or by several untrained people gave coefficients of variation from 0.8% to 2.3% for each digital spectral value for a coal sample and from 1.3% to 3.7% for thymol blue, a sharp spectral featured organic, rather than the 15%–30% normally found for repackings of the same sample. Thus representative DRIFTS spectra can be obtained quickly and efficiently from a powder sample with a single spectrum using this low-pressure, mechanical packing device, control of particle parameters, and sample rotation as opposed to previous efforts requiring the repacking of several samples and averaging of the spectra.
Utilization of synchrotron radiation in the far-infrared region (invited)
Authors: Nanba Takao
Published: July 2002

A spectroscopic system for the far-infrared region is described which was constructed at beamline BL6A1 of the UVSOR facility at the Institute for Molecular Science (Okazaki) and has been used since 1986. Intensity measurements at UVSOR proved that synchrotron radiation is a very bright source compared with a blackbody source throughout the entire far-infrared region. To demonstrate the advantages of synchrotron radiation in the far-infrared region, results on a reflection measurement of a small specimen and an absorption measurement under high pressure using a diamond anvil cell are shown. From the measurement of the shift of the TO phonon energy of KI with pressure, the mode Gruneisen parameter at room temperature was determined to be 1.70.
Growth of InN films on GaAs (111) and GaP(111) substrates by microwave-excited metalorganic vapor phase epitaxy
Authors: Guo Qixin , Ogawa Hiroshi , Yamano Hirofumi , Yoshida Akira
Published: July 2002

InN films have been grown on GaAs(111) and GaP(111) substrates using microwave-excited metalorganic vapor phase epitaxy. Trimethylindium and nitrogen were used as the source materials. It is revealed that epitaxial InN films can be obtained on GaAs (111) and GaP(111) by exposing the substrate to nitrogen plasma before the growth and that the crystalline quality of the InN films is strongly dependent on exposing time. All films have a wurtzite structure and display the InN(0001)// GaAs(111), InN(0001)//GaP(111) orientation.
Acoustic wave viscometer
Authors: Hoummady M. , Bastien F.
Published: July 2002

This article presents an acoustic wave viscometer using shear bulk waves excited by interdigital transducers on quartz. The attenuation of acoustic waves at the quartz-liquid interface is associated with liquid viscosity. Good agreement is found between theoretical results and experiments. The device can be used for viscosity measurements up to 600 cP. For higher viscosity the high-frequency rigidity modulus must be taken into account.
Measurement of atomic and molecular hydrogen in a tandem magnetic multicusp H− ion source by VUV spectroscopy
Authors: Young A. T. , Stutzin G. C. , Chen P. , Kunkel W. B. , Leung K. N.
Published: July 2002

The populations of ground electronic state atomic hydrogen and ground electronic state, vibrationally–rotationally excited hydrogen molecule in a negative hydrogen ion source discharge have been measured using vacuum ultraviolet (VUV) laser absorption spectroscopy. These populations have been measured under a variety of discharge conditions in two different regions of a tandem chamber ion source. Preliminary results of the measurements in the driver region and filter region are given. It is observed that the atomic hydrogen density decreases as one goes from the driver to the filter region. This indicates that the surfaces directly adjacent to the filter region are net sinks for hydrogen atoms. In contrast, the molecular vibrational population distribution shows only a small difference between the two regions, indicating that these surfaces are not net sinks for the excited molecules.
Ultrasensitive detection of hydrogen molecules by (2+1) resonance-enhanced multiphoton ionization
Authors: Vrakking Marcus J. J. , Bracker Allan S. , Suzuki Toshinori , Lee Yuan T.
Published: July 2002

Ultrasensitive detection of molecular hydrogen is reported by using Doppler-free (2+1) resonance-enhanced multiphoton ionization through the E,F 1Σ+g state. By using an arrangement with two near-transform-limited counterpropagating laser beams, a single-shot detection efficiency of 6.8×103 molecules/cm3 has been demonstrated. Frequency scans of the two-photon transitions show that the detection efficiency is limited by ac Stark effects.
Electron cyclotron resonance plasma reactor for cryogenic etching
Authors: Aydil Eray S. , Gregus Jeffrey A. , Gottscho Richard A.
Published: July 2002

Electron cyclotron resonance (ECR) plasma reactors are being used for ultralarge scale integrated circuit fabrication to meet the stringent requirements on submicron feature etching. Three issues are critical for ECR reactor design: plasma uniformity, ion energy control, and wafer temperature control. Plasma uniformity is important for minimizing over etch times and reducing the probability of producing charging damage. Ion energy control is needed to optimize etching rate, anisotropy, and selectivity without compromising device yield. Wafer temperature control is important because large ion currents at low pressure can result in wafer heating and thereby alter the rates of surface chemical processes. An ECR plasma reactor is described that is designed to etch compound semiconductors and Si at low temperatures (−170 to 20 °C), where superior selectivity and linewidth control are achievable. By measuring dc bias, floating potential, and ion saturation current densities it is shown that ion energies in this system can be controlled by applying an rf bias to the sample. To characterize plasma uniformity, the radial ion density profile is measured using a fast injection Langmuir probe. Hollow, peaked, or uniform radial plasma density profiles can be obtained depending on microwave power, pressure, and magnetic field. Plasma density profiles are influenced by microwave absorption and refraction which, in turn, are influenced by both the magnetic field and plasma density profiles. The net result is a strong coupling between wave propagation and charge particle transport. To control wafer temperature a cryogenic electrode capable of maintaining a wafer temperature to ±2.5 °C at −170 °C is used while the wafer is exposed to an electron cyclotron resonance plasma. The sample temperature is monitored using infrared laser interferometric thermometry and the heat flux to the wafer surface in an Ar plasma is measured as a function of operating parameters by monitoring temperature transients as the discharge is gated on and off.
Microsecond pulse width, intense, light-ion beam accelerator
Authors: Rej D. J. , Bartsch R. R. , Davis H. A. , Faehl R. J. , Greenly J. B. , Waganaar W. J.
Published: July 2002

A relatively long-pulse width (0.1–1 μs) intense ion beam accelerator has been built for materials processing applications. An applied Br, magnetically insulated extraction ion diode with dielectric flashover ion source is installed directly onto the output of a 1.2 MV, 300-kJ Marx generator. The diode is designed with the aid of multidimensional particle-in-cell simulations. Initial operation of the accelerator at 0.4 MV indicates satisfactory performance without the need for additional pulse shaping. The effect of a plasma opening switch on diode behavior is considered.
A probe array for the investigation of spatio-temporal structures in drift wave turbulence
Authors: Latten A. , Klinger T. , Piel A. , Pierre Th.
Published: July 2002

A probe array with 64 azimuthally arranged Langmuir probes is presented as a new diagnostic tool for the investigation of drift waves. A parallel data acquisition system provides full spatio-temporal data of azimuthally propagating waves. For both regular and turbulent states of current-driven drift waves, the information provided by such space-time patterns is compared with results obtained from conventional two-point correlation methods. The probe array allows one to directly estimate the time-averaged wave number spectrum. In a turbulent state, the spectrum yields to a power law of S(k)∝k−3.6±0.1.
A high pressure optical cell utilizing single crystal cubic zirconia anvil windows
Authors: Russell T. P. , Piermarini G. J.
Published: July 2002

A high pressure optical cell capable of producing pressures up to 13.2 GPa using gem-cut single crystal cubic zirconia (CZ) anvils was developed. Maximum pressures obtainable were found to depend upon the particular pressure transmitting medium and gasket material employed. The cubic zirconia anvil high pressure cell (CZAC) provides advantages over the diamond anvil cell in optical and infrared spectroscopy while still maintaining a substantial pressure capability. To demonstrate these advantages, microRaman, optical fluorescence, and infrared absorption measurements were made on diamond, ruby, and 1,3,5-trinitrohexahydro-1,3,5-triazine samples, respectively, using the CZAC cell under high pressure conditions.
The resolution limit of traditional correlation functions for deep level transient spectroscopy
Authors: Istratov A. A.
Published: July 2002

The factors limiting the resolution of the traditional correlation deep level transient spectroscopy (DLTS) are revealed and analyzed. It is shown that all weighting functions proposed to date provided nonsymmetrical rate windows, effectively filtering out slow transients, but were mediocre filters for fast transients. It is argued that it was the response to fast transients which actually limited the resolution of the correlation DLTS. The resolution limit of previously published weighting functions is determined. It is shown that the limitations are inherent in the earlier approach to the devising of weighting functions rather than in the correlation procedure itself. It can be overcome using new weighting functions based on the Gaver-Stehfest algorithm for the inverse Laplace transformation.
Test function for the determination of plasma parameters by electric probes
Authors: Stamate E. , Popa G. , Ohe K.
Published: July 2002

A “test function” sensitive to the electron distribution function is used to determine the plasma parameters by Langmuir probes. It was successfully applied to determine the parameters of the hot-electron group in a multipolar, magnetically confined Ar plasma, even when the ratio of bulk to hot-electron densities is greater than 50. The method can also be used to measure the positive-ion density from a probe potential slightly below the plasma potential, and to estimate the electron and negative-ion density and temperature in an Ar/SF6 plasma. A characteristic plasma potential is also introduced and is correlated with the plasma parameters.
Optical investigations of the dynamic behavior of GaSb/GaAs quantum dots
Authors: Sun C.-K. , Wang G. , Bowers J. E. , Brar B. , Blank H.-R. , Kroemer H. , Pilkuhn M. H.
Published: July 2002

Time-resolved radiative recombination measurements on GaSb quantum dots have been performed. The GaSb quantum dots are grown by molecular beam epitaxy on (100) GaAs through a self-assembly process. Time-resolved measurements show that, after a rapid hole capture process, the photoluminescence decays with a fast and a slow component. The fast component is shortened significantly with higher excitation intensity while the slow component is roughly constant. The radiative lifetimes are much longer than the lifetimes of ordinary GaSb quantum wells with a straddling band lineup. These results support a staggered band lineup and space charge induced band-bending model.
Electrical characterization of Mg-doped GaN grown by metalorganic vapor phase epitaxy
Authors: Huang J. W. , Kuech T. F. , Lu Hongqiang , Bhat Ishwara
Published: July 2002

We have applied frequency-dependent capacitance measurements and admittance spectroscopy on GaN:Mg to study the electronic states associated with Mg doping. Metalorganic vapor phase epitaxy GaN:Mg samples with two different Mg doping levels were grown and thermally annealed in nitrogen. Lateral dot-and-ring Schottky diodes using Au/Ti were fabricated. Frequency-dependent measurements on these diodes show that the capacitance is reduced at a higher frequency, most likely due to the inability of a deep center to maintain an equilibrium ionization state under a high-frequency modulation. Admittance spectroscopy, in which the conductance is monitored as a function of temperature, verifies the existence of one impurity-related acceptor level in the higher Mg-doped sample with an activation energy of 136 meV. For the lower Mg-doped sample, two acceptor levels at 124 and 160 meV were observed. We believe these levels are most probably associated with the Mg acceptor state itself, possessing energy levels which are very close to the results previously reported in the literature.
Radiative recombination lifetime measurements of InGaN single quantum well
Authors: Sun C.-K. , Keller S. , Wang G. , Minsky M. S. , Bowers J. E. , DenBaars S. P.
Published: July 2002

We present results from a time-resolved study of radiative recombination in InGaN quantum wells. The sample was grown by atmospheric pressure metal-organic chemical-vapor deposition. Time-resolved photoluminescence measurements were performed from 7 K up to room temperature. The low temperature radiative lifetime was measured to be on the order of 250 ps at a generated carrier density of 1012 cm−2. The time-resolved measurements show a bimolecular recombination characteristic. At 300 K, we observed a lifetime of 130 ps which, to the best of our knowledge, is the longest lifetime reported for any III–V nitride at room temperature.