bluuebunny/crossref_metadata_2025 huggingface dataset:
A field study with genetically engineered alfalfa inoculated with recombinantSinorhizobium meliloti: effects on the soil ecosystem
Authors: Donegan Katherine K. , Seidler Ramon J. , Doyle Jack D. , Porteous L. Arlene , Digiovanni George , Widmer Franco , Watrud Lidia S.
Published: July 2002

1. A field study using transgenic plants with associated recombinant micro‐organisms was conducted to assess the potential effects of genetically engineered organisms on soil ecosystems. Three genotypes of alfalfa plants (parental, transgenic α‐amylase‐producing and transgenic lignin peroxidase‐producing) were planted in an agricultural field plot. Immediately prior to planting, the roots of the alfalfa plants were left uninoculated or were inoculated with a wild‐type strain (PC), a recombinant strain with antibiotic resistances (RMB7201), or a recombinant strain with antibiotic resistances and enhanced nitrogen‐fixation capability (RMBPC‐2), ofSinorhizobium meliloti.

2. Analyses of the alfalfa plants and field plot soil were made over two growing seasons and included: metabolic fingerprints and DNA fingerprints of soil bacterial communities; soil microbial respiration; population counts of indigenous soil bacteria, fungi, nematodes, protozoa and micro‐arthropods; identification of nematodes and micro‐arthropods; plant shoot weight and chemistries; and soil chemistries and enzyme activities.

3. The lignin peroxidase transgenic plants had significantly lower shoot weight, and higher nitrogen and phosphorus content, than the parental or transgenic amylase plants. Distinct metabolic fingerprints, based on patterns of substrate utilization in Biolog plates, were exhibited by the soil bacterial communities associated with the three alfalfa genotypes, and those for the lignin peroxidase plants were the most unique. Significantly higher population levels of culturable, aerobic spore‐forming and cellulose‐utilizing bacteria, lower activity of the soil enzymes dehydrogenase and alkaline phosphatase, and higher soil pH levels, were also associated with the lignin peroxidase transgenic plants. Significantly higher population levels of culturable, aerobic spore‐forming bacteria were also measured in the treatments containing the recombinant RMBPC‐2S. meliloti.

4. Population levels of protozoa, nematodes and micro‐arthropods, DNA fingerprints of indigenous soil bacteria, and rates of microbial substrate‐induced respiration were not significantly affected by the transgenic alfalfa and recombinantS. melilotitreatments.

5. These results suggest that the genetically engineered organisms caused detectable changes in some components of the soil ecosystem. The primary effects we observed were associated with the transgenic lignin peroxidase alfalfa and included alterations in plant growth and chemistry and changes in soil chemistry and microbiology.
Brazilian Páramos II. Macro‐ and mesoclimate of thecampos de altitudeand affinities with high mountain climates of the tropical Andes and Costa Rica
Authors: DeForest Safford Hugh
Published: July 2002

AimThis paper presents a basic analysis of the macro‐ and mesoclimate of the Brazilian campos de altitude, a series of cool–humid, mountaintop grasslands in southeastern Brazil, and compares results with data from other tropical as well as temperate alpine sites.

LocationBeginning at altitudes of 1800–2000 m, the campos de altitude are found atop the highest summits of the main ranges of the southeastern Brazilian Highlands, between the states of Santa Catarina and Minas Gerais/Espírito Santo.

MethodsMacro‐ and mesoclimatic parameters for the campos de altitude are derived from both original data and previously reported results. Parameters include approximate radiation budgets, temperature lapse rates, seasonal and diurnal patterns in temperature, occurrence of frost, elevational gradients in precipitation, and interannual and seasonal patterns in precipitation. Using multivariate techniques and simple numerical contrasts, the climate of the campos de altitude is compared to climates of other tropical as well as temperate alpine sites.

ResultsWith respect to patterns of seasonality and the marked influence of polar frontal activity, the macroclimate of the campos de altitude is typically tropical‐marginal. However, in reference to actual temperature and precipitation values, the length and profundity of the dry season, average humidities and cloudiness, the climate of the campus de altitude more closely corresponds to that of more inner‐tropical systems. These commonalities are best developed with respect to páramo climates of the northern Andes and, especially, Costa Rica.

Main conclusionsTheir very different latitudinal and geographic positions notwith‐ standing, the campos de altitude and high mountain formations of the N. Andean and Central American Cordillera show clear macroclimatic congruities. In these congruities reside both the environmental basis for strong Andean–southeast Brazilian biogeographic connections, and the context within which evolutionary and ecological parallelisms have developed in the biota of these two widely separate neotropical mountain systems.
EXTREMITY SOFT TISSUE SARCOMA: FACTORS PREDICTIVE OF LOCAL RECURRENCE AND SURVIVAL
Authors: Wilson R. B. , Crowe P. J. , Fisher R. , Hook C. , Donnellan M. J.
Published: July 2002

Background: To identify risk factors for local recurrence and overall survival in patients with extremity soft tissue sarcoma.

Methods: A retrospective study was performed of all patients with extremity soft tissue sarcoma treated at the Combined Surgical Oncology Clinic in the Institute of Oncology at Prince of Wales Hospital between 1972 and 1992. Variables analysed included clinical presentation, patient characteristics, tumour characteristics, treatment factors and outcome.

Results: One hundred and nineteen patients were eligible for the study. The most common type of presentation was with a painless mass, usually in the thigh. Local control rates at 5 and 10 years were 75% and 73%. Local control was higher in patients who had more radical surgery and in those who received adjuvant radiotherapy. Tumour size and high grade were independent risk factors for poorer survival. Patients over 50 had poorer survival than younger patients and those who presented with recurrent tumours also tended to have poor survival compared to patients presentingde novo. The respective 5‐ and 10‐year survival rates were 65% and 62%.

Conclusion: This study suggests that local control of extremity soft tissue sarcoma is improved by radical surgery and by the addition of radiotherapy when more conservative procedures are used. Overall survival appeared to be largely determined by patient (age, recurrent presentation) and tumour characteristics (grade, size).
Long‐term survival of patients with bladder tumours: the significance of risk factors
Authors: Zieger  , Wolf  , Olsen  , HØjgaard
Published: July 2002

Objective

 To evaluate the significance of known risk factors, accessible by simple endoscopic and histological/cytological examination, on the clinical course and long‐term survival of patients with superficial urinary bladder tumours.

Patients and methods

 The study included 584 consecutive unselected patients, primarily admitted between 1976 and 1984 for newly diagnosed bladder tumour, which was superficial (Ta, T1, Tis) in 362. The patients were followed routinely in a control programme; causes of death were obtained by autopsy (44%), from hospital files (33%) or from death certificates (8%), the remaining patients being alive at the end of the study, up to 20 years after initial diagnosis. Known risk factors, e.g. tumour size, histological grade, multiplicity and positive urine cytology, and dysplasia as assessed by random or pre‐selected site biopsies, were evaluated as predetermining factors for new occurrences and survival.

Results

 Invasion of the lamina propria was the most significant prognostic factor detected in the multivariate analysis. While 14% of patients with Ta tumours had died from cancer after 15 years, 63% of the T1 tumours were eventually fatal, reaching the mortality of those with T2 disease. Other independent significant factors were tumour size and, to a lesser extent, histological grade. Multiplicity and concomitant epithelial changes, as assayed by voided urine cytology and pre‐selected site biopsies, were relevant prognostic factors for Ta but not for T1 tumours.

Conclusion

In the therapy and surveillance of superficial urinary bladder tumours, the presence of lamina propria invasion is very important.
Milestones in understanding allergy and its diagnosis
Authors: Johansson S. G. O.
Published: July 2002

The prevalence of allergic conditions continues to increase, affecting up to 40% of the population in some countries. Our understanding of the processes of allergy began in 1869, when Blackley first connected hay fever with pollen. In 1911, Dale and Laidlaw discovered that histamine was the principal mediator of anaphylaxis. This led to the development of the first antihistamine, in 1942. In 1968 the WHO International Immunoglobulin Reference Centre officially declared the discovery of IgE based on the work of Bennich, Ishizaka and Johansson. The importance of IgE in allergy is such that the definition of allergic disease is based on the presence of allergen‐specific IgE. Access to IgE allowed experimental, immunochemical studiesin vitro. Research activity in the field of immunology increased enormously and generated more important knowledge, including the discovery and characterization of leukotrienes, cytokines and histamine receptors. The involvement of other cells in the allergy process was described. In parallel with the elucidation of the processes involved in allergy came the development of new drug treatments. The first anti‐allergy agents were the antihistamines. Later came sodium cromoglycate and corticosteroids. Immunotherapy was first used in the early 1900s but became less popular with the development of anti‐allergy drugs. Now, however, there is a resurgence of interest in the technique. The discovery that there are two subtypes of T‐helper (Th) cells, which produce different cytokines, and that the Th2 subtype appears to produce cytokines associated with allergy has opened new avenues of research that hold promise for reducing the prevalence of allergy in the population, either by preventing its development or by treatments that can drive the immune system towards a Th1 bias.
Ecological Consequences of Recent Climate Change
Authors: McCarty John P.
Published: July 2002

Abstract:Global climate change is frequently considered a major conservation threat. The Earth's climate has already warmed by 0.5° C over the past century, and recent studies show that it is possible to detect the effects of a changing climate on ecological systems. This suggests that global change may be a current and future conservation threat. Changes in recent decades are apparent at all levels of ecological organization: population and life‐history changes, shifts in geographic range, changes in species composition of communities, and changes in the structure and functioning of ecosystems. These ecological effects can be linked to recent population declines and to both local and global extinctions of species. Although it is impossible to prove that climate change is the cause of these ecological effects, these findings have important implications for conservation biology. It is no longer safe to assume that all of a species' historic range remains suitable. In drawing attention to the importance of climate change as a current threat to species, these studies emphasize the need for current conservation efforts to consider climate change in both in situ conservation and reintroduction efforts. Additional threats will emerge as climate continues to change, especially as climate interacts with other stressors such as habitat fragmentation. These studies can contribute to preparations for future challenges by providing valuable input to models and direct examples of how species respond to climate change.
The Role of Smoking and Other Modifiable Lifestyle Risk Factors in Maintaining and Restoring Lower Body Mobility in Middle‐Aged and Older Americans: Results from the HRS and AHEAD
Authors: Østbye Truls , Taylor Donald Hugh , Krause Katrina M. , Van Scoyoc Lynn
Published: July 2002

OBJECTIVES:

To analyze the effect of smoking, smoking cessation, and other modifiable risk factors on mobility in middle‐aged and older Americans.

DESIGN:

Panel study; secondary data analysis.

SETTING:

United States (national sample).

PARTICIPANTS:

The Health and Retirement Study (HRS) includes data on 12,652 Americans aged 50 to 61 in four waves (1992–1998). The Asset and Health Dynamics Among the Oldest Old (AHEAD) survey followed 8,124 community‐dwelling people aged 70 years and older in three waves (1993–1998).

MEASUREMENTS:

The relationships between the primary outcome measure, lower body mobility (ability to walk several blocks and walk up one flight of stairs without difficulty), and smoking, exercise (HRS only), body mass index (BMI), and alcohol use were estimated in bivariate and multivariate analyses.

RESULTS:

Not smoking was strongly positively related to mobility, and the relative effects were similar in both panels. Among those with impaired mobility at baseline, not smoking was also strongly related to recovery. In the middle aged, there were consistent dose‐response relationships between amount smoked and impaired mobility. Fifteen years after quitting, the risk of impaired mobility returned to that of never smokers. There was also a strong dose‐response relationship between level of exercise and mobility. Inverted U‐shaped relationships with mobility were observed for BMI and alcohol consumption.

CONCLUSIONS:

The relationships between not smoking and lower body mobility in middle‐aged and older Americans are strong and consistent. Interventions aimed at reducing smoking have the potential to preserve mobility and thereby prolong health and independence in later life. J Am Geriatr Soc 50:691–699, 2002.
Thoracoscopic mapping and cryoablation of right ventricular tachycardia
Authors: Furniss S.S. , Forty J. , Simeonidou E. , Owens A. , Cowan J.C. , Bourke J.P. , Campbell R.W.F.
Published: July 2002

A 14-year-old girl with right ventricular dysplasia and recurrent drug refractory ventricular tachycardia underwent thoracoscopic mapping cryoablation. Good access to the right ventricular free wall was obtained. We suggest this technique may have an important role in the management of patients with right ventricular tachycardia.
Molecular Phylogeny of Nepenthaceae Based on Cladistic Analysis of Plastid trnK Intron Sequence Data
Authors: Meimberg H. , Wistuba A. , Dittrich P. , Heubl G.
Published: July 2002

Abstract:Nepenthaceae are an exceptional family with regard to carnivory and the uniformity of characters. This makes it difficult to resolve phylogenetic relationships due to convergent evolution of morphological features. Using comparative sequencing of the chloroplast trnK intron, the monophyly of this complex family and hypotheses of infrageneric relationships were tested. Sequences from 71Nepenthestaxa, representing all groups and two taxa of the closely related Ancistrocladaceae and Dioncophyllaceae as outgroup, were determined and analysed using maximum parsimony methods. Results of this analysis show that the isolated taxaN. distillatoria(Sri Lanka) andN. pervillei(Seychelles) are the most basal, clearly separated from the Madagascan taxaN. madagascariensisandN. masoalensiswhich are placed in a distinct subclade. This corresponds with some plesiomorphic characters shared by these taxa.N. khasiana(North India) has an intermediate position between these relic Western species and the remaining taxa. The species of the Malay Archipelago can be referred to three distinct lineages which indicate a correlation to biogeography. Thus the recent disjunct distribution ofNepenthesis interpreted as a result of an incisive extinction of progenitors, a process of migration and a subsequent diversification on the islands of Borneo, Sumatra, Sulawesi and New Guinea.

Based on our molecular data, two interpretations concerning the origin ofNepenthesare possible: i) evolution in the Northern Tethys which is supported by fossil pollen records from the European Focene, or, ii) a Gondwanaland origin at a time when the Indian plate was separated from Madagascar. Molecular data indicate that colonization of SE Asia started from an ancient Indian stock. Subsequently, in the Malay Archipelago a new secondary centre of diversity developed. Madagascar, the Seychelles and New Caledonia were probably reached by migration via land bridges, starting from widespead common ancestors with subsequent extinction leaving the current taxa. There is no evidence for long‐distance dispersal. Current infragenic classification ofNepenthesis only partly in accordance with the phylogeny inferred from trnK intron data.
The Description of Clones ofQuercus roburL. andQ. petraea(Matt.) Liebl. with Microsatellites and AFLP in an Ancient Woodland
Authors: Bakker E. G. , Van Dam B. C. , Van Eck H. J. , Jacobsen E.
Published: July 2002

Abstract:In densely populated areas autochthonousQuercus roburL. (pedunculate oak) andQ. petraea(Matt.) Liebl. (sessile oak) (Fagaceae) populations have been maintained as ancient devastated woodlands. The continuous cutting, grazing and resprouting of such woodlands has enabled the development of clonal structures. For conservation purposes, an analysis of the actual number, size and spatial distribution of clones is necessary, especially when there is an interest in genetic variation of the population. This study describes for the first time ‐ based on microsatellite and AFLP™ analysis ‐ clones in an autochthonous mixedQ. roburandQ. petraeapopulation that has been coppiced and grazed for several centuries. Based on six microsatellite loci and 69 polymorphic AFLP markers, only 14 unique genotypes were detected in a plot that consisted of 80 trees. Clones were observed for bothQ. roburandQ. petraea.The largest clone diameters were observed forQ. robur,with distances up to 5.8 m. The observed clone sizes may indicate the age of the trees.
Optical saturation of intersubband absorption in GaAs-AlxGa1−xAs quantum wells
Authors: Julien F. H. , Lourtioz J.-M. , Herschkorn N. , Delacourt D. , Pocholle J. P. , Papuchon M. , Planel R. , Le Roux G.
Published: July 2002

We have investigated intersubband absorptions between the conduction ground state and the first excited state of two AlxGa1−xAs/GaAs/AlxGa1−xAs multiple quantum well structures with x=0.3 and 85 Å well width, and with x=0.57 and 96 Å well width. Small-signal measurements show absorption peaks at 10.45 and 10.15 μm, respectively. Under an intense resonant excitation from a pulsed CO2 laser, saturation of the intersubband absorption occurred. The saturation intensity is estimated to be 340±120 kW/cm2 for the first sample and 375±120 kW/cm2 for the second. From these values, we have deduced subband decay times of the order of 10.6±3.5 ps for the first sample and 15.5±5 ps for the second.
Intersubband optical transitions in Si-Si0.5Ge0.5 superlattices
Authors: Turton R. J. , Jaros M.
Published: July 2002

Large oscillator strengths are predicted for optical transitions between conduction subbands of Si-Si0.5 Ge0.5 strained-layer superlattices. The transition energies in question are in the infrared range (50–300 meV).
High performance AlGaInP visible light-emitting diodes
Authors: Kuo C. P. , Fletcher R. M. , Osentowski T. D. , Lardizabal M. C. , Craford M. G. , Robbins V. M.
Published: July 2002

The performance of surface-emitting visible AlGaInP light-emitting diodes (LEDs) is described. The devices have external quantum efficiencies greater than 2% and luminous efficiencies of 20 lm/A in the yellow (590 nm) spectral region. This performance is roughly ten times better than existing yellow LEDs and is comparable to the highest performance red AlGaAs LEDs currently available. The devices also perform favorably compared to existing devices in the orange and green spectral regions. Low-pressure organometallic vapor phase epitaxy (OMVPE) is used to grow the epitaxial layers. The devices consist of a double heterostructure with an AlGaInP active region grown on a GaAs substrate.
All a-axis oriented YBa2Cu3O7−y-PrBa2Cu3O7−z-YBa2Cu3O7−y Josephson devices operating at 80 K
Authors: Barner J. B. , Rogers C. T. , Inam A. , Ramesh R. , Bersey S.
Published: July 2002

We have demonstrated the controllable, reproducible fabrication of nonhysteretic Josephson devices with excess-current weak-link characteristics at temperatures up to 80 K. The devices are patterned from in situ deposited a-axis oriented YBa2Cu3O7−y-PrBa2Cu3O7−z-YBa2Cu3O7−y trilayers grown on SrTiO3(001) substrates. Control of the critical current density and resistance is achieved by varying the thickness of the PrBa2Cu3O7−z barrier layer. Critical current densities in excess of 104 A/cm2 have been reproducibly measured; good uniformity across the wafer is obtained with device parameters scaling with device area. Strong constant-voltage current steps are observed under 11.2 GHz microwave radiation at temperatures up to and above 80 K.
Blue-green laser diodes
Authors: Haase M. A. , Qiu J. , DePuydt J. M. , Cheng H.
Published: July 2002

The first laser diodes fabricated from wide-band-gap II-VI semiconductors are demonstrated. These devices emit coherent light at a wavelength of 490 nm from a ZnSe-based single-quantum-well structure under pulsed current injection at 77 K. This is the shortest wavelength ever generated by a semiconductor laser diode.
Simulating growth of Mo/Si multilayers
Authors: Morgan W. Lowell , Boercker David B.
Published: July 2002

Multilayer structures of alternating thin layers of molybdenum and silicon are of great interest as x-ray optics components and a considerable amount of effort has been expended in their development. The efficiencies of these structures depend upon both the accurate control of the layer thicknesses and the sharpness in the interface between layers. High- resolution electron microscopy reveals that the interface created by deposition of Mo on Si is much more diffuse than that produced by depositing Si on Mo. We have used molecular dynamics to simulate the deposition processes and observe significant penetration of the Si substrates by the incident Mo atoms, while incident Si atoms remain on the surface of the Mo substrate.
Mechanism for displacive excitation of coherent phonons in Sb, Bi, Te, and Ti2O3
Authors: Cheng T. K. , Vidal J. , Zeiger H. J. , Dresselhaus G. , Dresselhaus M. S. , Ippen E. P.
Published: July 2002

Coherent phonons in Sb, Bi, Te, and Ti2O3 can be generated impulsively, and detected in the time domain through reflectivity modulation using 60 fs pulses of laser light at 2 eV. Experimental data for these opaque solids suggest that a direct Raman excitation mechanism is not responsible for coherent phonon generation. Rather, the excitation is attributed to an electronically induced displacement of the ion equilibrium coordinates.
Preparation and characteristics of new reverse mode film of polymer dispersed liquid crystal type
Authors: Gotoh Tomohisa , Murai Hideya
Published: July 2002

A reverse mode operation has been achieved in a polymer dispersed liquid crystal (PDLC) film by a novel methodology. A mixture of a dual frequency addressable liquid crystal (crossover frequency (fc): 13 kHz at 298 K), an acryl monomer and an acryl oligomer was irradiated by UV light under the application of an electric field [50 V, 100 Hz(≪fc)] to give a reverse mode PDLC film. The film thus prepared shows 95% transmittance in the absence of an applied voltage (OFF state), while the transmittance decreases to 5% by applying 50 V at 50 kHz (≳fc) (ON state). Upon removal of the applied voltage, the film transmittance returns to 95%. The response time (the ON time: 24 ms and the OFF time: 74 ms) are similar to those of normal mode PDLC films.
Low-leakage thin-film superconductor-insulator-normal metal tunnel junctions on co-evaporated Ba1−xRbxBiO3 and rf-sputtered Ba1−xKxBiO3
Authors: Hou C. J. , Fink R. L. , Hilbert Claude , Kroger Harry
Published: July 2002

The oxide superconductors Ba1−xKxBiO3 and Ba1−xRbxBiO3 exhibit ideal BCS-like characteristics with Tc∼30 K. We report the deposition of thin films with zero-resistance temperatures up to 25 K and transition widths less than 1 K by thermal co-evaporation and rf sputtering. Thin-film S-I-N tunnel junctions fabricated by evaporating Ag or Au onto a native barrier exhibit low leakage over 1 mm2 junctions and near-ideal BCS-like behavior with a value of 2Δ(0)/kBTco=3.5±0.2.
Magnetic and magneto-optical properties of cobalt-platinum alloys with perpendicular magnetic anisotropy
Authors: Weller D. , Brändle H. , Gorman G. , Lin C.-J. , Notarys H.
Published: July 2002

Co1−xPtx alloys with Pt contents in the range 0.45≤x≤0.9 show sizable perpendicular magnetic anisotropy, 100% perpendicular remanence and coercivities in the range 160 kA/m. Thin films of this material are grown by electron beam evaporation onto fused silica or Si, at substrate temperatures between 150 and 350 °C. Spectroscopic investigations of the polar Kerr rotation show a significant enhancement of the Pt related UV peak. A comparison of the static signal levels R×(θk2+εk2)1/2 of Co/Pt multilayers and alloys shows an overall 50% enhancement in the case of alloys. Curie temperatures around 200 °C are observed for Co∼22Pt∼78 compositions. These properties, together with the potentially high chemical stability and ease of manufacturing make Co1−xPtx alloys very attractive materials for short wavelength magneto-optic recording.
Electron transport mechanism in gallium nitride
Authors: Molnar R. J. , Lei T. , Moustakas T. D.
Published: July 2002

The electron transport mechanism in autodoped gallium nitride films grown by electron cyclotron resonance microwave plasma-assisted molecular beam epitaxy was investigated by studying the temperature dependence of the Hall coefficient and resistivity on samples with various concentrations of autodoping centers. The Hall coefficients go through a maximum as the temperature is lowered from 300 K and then saturate at lower temperatures. The resistivities in the same temperature range initially increase exponentially and then saturate at lower temperatures. These findings are accounted for if a significant fraction of electron transport, even at room temperature, takes place in the autodoping centers and that conduction through these centers becomes dominant at lower temperatures. The activation energy of these centers was found to be on the order of 20–30 meV. When the concentration of the autodoping centers becomes smaller than that of deep compensating defects, the material becomes semi-insulating and transport by hopping in the compensating defects becomes dominant.
Features of gold having micrometer to centimeter dimensions can be formed through a combination of stamping with an elastomeric stamp and an alkanethiol ‘‘ink’’ followed by chemical etching
Authors: Kumar Amit , Whitesides George M.
Published: July 2002

This letter describes a technique that can be used to produce well-defined features of gold. The technique involves patterning of a self-assembled monolayer (SAM) on a gold substrate using an elastomer stamp (fabricated either from a phenol-formaldehyde polymer or polydimethylsiloxane), followed by selective etching in an aqueous, basic solution of cyanide ion and dissolved dioxygen (1M KOH, 0.1 M KCN). Electrically conductive structures of gold with dimensions as small as 1 μm have been produced using this procedure. Once a rubber stamp is fabricated, patterning and etching of gold substrates is straightforward. This method is convenient, does not require routine access to clean rooms and photolithographic equipment, and can be used to produce multiple copies of a pattern.
Terahertz optical rectification from 〈110〉 zinc-blende crystals
Authors: Rice A. , Jin Y. , Ma X. F. , Zhang X.-C. , Bliss D. , Larkin J. , Alexander M.
Published: July 2002

We report the study of optically induced terahertz (THz) electromagnetic radiation from 〈110〉 oriented zinc-blende crystals. This work extends our previous studies of 〈100〉 and 〈111〉 GaAs. Excellent agreement between calculated results and experimental data indicates that, under conditions of moderate optical fluence and normal incidence on the unbiased sample, second-order optical rectification is the major nonlinear process that generates THz radiation.
Detection of ultrasonic motion of a scattering surface by two-wave mixing in a photorefractive GaAs crystal
Authors: Blouin Alain , Monchalin Jean-Pierre
Published: July 2002

The performance of an interferometric system based on two-wave mixing at 1.06 μm in undoped GaAs crystal, for the remote detection of transient motion of a scattering surface, is described. In this system, the wave scattered by the surface is mixed inside the photorefractive crystal with a pump wave directly derived from the laser to provide the reference wave of the interferometer. The system shows several features appropriate to industrial applications, although its sensitivity is less than passive interferometric systems of the confocal Fabry–Perot type presently in use, except in the low frequency range (below 1 MHz).
Multilayered organic electroluminescent device using a novel starburst molecule, 4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine, as a hole transport material
Authors: Shirota Yasuhiko , Kuwabara Yoshiyuki , Inada Hiroshi , Wakimoto Takeo , Nakada Hitoshi , Yonemoto Yoshinobu , Kawami Shin , Imai Kunio
Published: July 2002

A novel π-conjugated starburst molecule, 4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine (m-MTDATA), which forms a stable amorphous glass, functions as an excellent hole transport material for organic electroluminescent devices. An electroluminescent device consisting of double hole transport layers of m-MTDATA and 4,4′-bis(3-methylphenylphenylamino)biphenyl and an emitting layer of tris(8-quinolinolato)aluminum exhibits a high luminance efficiency and significant durability.
Enhancement of second harmonic generation at 1.06 μm using a quasi-phase-matched AlGaAs/GaAs asymmetric quantum well structure
Authors: Qu Xiaohua H. , Ruda Harry , Janz Siegfried , SpringThorpe Anthony J.
Published: July 2002

We report on the observation of a significant enhancement of second harmonic generation (SHG) in reflection mode using multiple GaAs/AlxGa1−xAs asymmetric quantum wells (AQWs). The growth sequence and spacing of these AQWs were carefully designed for quasi-phase-matching of SHG using 1.06 μm fundamental wavelength pumping. The maximum SHG measured from this AQW sample is approximately twice that of an undoped semi-insulating GaAs reference sample. This represents a 2.6 times enhancement after allowing for the cap layer absorption of the SH signal from AQWs. The SH susceptibility of a single AQW is then estimated as ‖χ(2)24,QW‖=1.3×10−11 m/V and ‖χ(2)32,QW‖=1.1×10−11 m/V, which are in excellent agreement with results of our theoretical modeling.
Study of defect states in GaN films by photoconductivity measurement
Authors: Qiu C. H. , Hoggatt C. , Melton W. , Leksono M. W. , Pankove J. I.
Published: July 2002

Optical absorption by defect states in gallium nitride (GaN) films was studied by photoconductivity (PC) spectroscopy at room temperature. A number of undoped n-type and Mg-doped p-type samples were employed in the present study. The PC response per absorbed photon decreased by more than four orders of magnitude as GaN became p-type conducting. Furthermore, all the samples exhibit PC response at photon energies far below the band gap energy of GaN. The optical absorption increases with photon energy hν from 1.5 to 3.0 eV approximately as exp(hν/E0). The parameter E0 ranges from 180 to 280 meV, and is considerably smaller for the insulating p-type sample. For a p-type conducting sample, the PC response is flat between 0.7 and 1.4 eV. A model for the density of states distribution in the forbidden gap of GaN and the effect of Mg doping is proposed.
Plug-in fast electron beam chopping system
Authors: Sadorf H. , Kratz H. A.
Published: July 2002

A new type of a two-stage electron beam chopping system is proposed. It is easily adapted to a scanning electron microscope because it needs no additional lens. The system operates with primary electron energies between 0.75 and 3 keV and pulse repetition frequencies up to the microwave range. The experimental setup as well as the operational and measurement procedure are described in detail. The achieved results are: rise-time distortion less than 35 ps, electron beam pulses of 15 ps full width at half-maximum, and an extremly small drift of less than 40 ps during 10 000 s between the electron beam sampling pulse and the main trigger input.
Design and performance of a calcia-stabilized zirconia electrolytic cell as a monitor for small amounts of H2O in H2 streams
Authors: Stanchina W. E. , Whelan J. M.
Published: July 2002

Improved performance of calcia-stabilized zirconia electrolytic cells for monitoring concentrations of H2O(g) in H2(g) streams [(g)=gas phase] has been obtained through refinements in cell design and operation. These cells have been used to measure H2O(g) concentrations in flowing H2 streams from as low as 0.018 to several hundred parts per million. For the lower H2O concentrations, the cell time constants for response were in the several minute range. It appeared that the cells operated at equilibrium in the steady state but not so under transient conditions.
New apparatus to perform fast determinations of mixture vapor–liquid equilibria up to 10 MPa and 423 K
Authors: Laugier S. , Richon D.
Published: July 2002

A new apparatus to measure vapor–liquid equilibria of mixture has been designed to work up to 10 MPa and 423 K. This apparatus makes it possible to take reproducible and representative samples and inject them directly into a chromatographic circuit {the same requirements were already satisfied by another apparatus described in a previous paper [P. Figuiére, J. F. Hom, S. Laugier, H. Renon, D. Richon, and H. Szwarc, AIChE J. 26, 872 (1980)]}. The use of the new apparatus is very simple. Comparisons with data from Kay and Albert [Ind. Eng. Chem. 48, 422 (1956)] reveal a strong similarity in the whole pressure range. Measurements in the critical region do not involve significant experimental difficulty.
Wide temperature range IR spectroscopy cell for studies of adsorption and desorption on high area solids
Authors: Basu P. , Ballinger T. H. , Yates J. T.
Published: July 2002

A new design for an infrared cell useful for studies of the spectrum of surface species on high area solids is presented. The cell is well suited over a wide temperature range (100–1000 K). Other demonstrated features of the cell include ultrahigh-vacuum operation, temperature control to ±1 K, linear and rapid temperature programmability and low-temperature gradients across the powdered sample. The method of sample preparation and support minimizes both heat and mass transport effects. A detailed literature search of previous infrared cell designs is included. Results of the application of the new cell design to the high-temperature dehydroxylation of Al2O3 are given as an example of the performance.
Automatic integrating fluorometer using an Apple-II and Scope-85
Authors: Morissette J. C. , Meunier P. C. , Popovic R.
Published: July 2002

The system presented here measures the fluorescence of plant samples in in vivo and in vitro automatically, calculating the principal photosynthetic parameters of the sample (evaluation of the F0 level of fluorescence, normalization of the fluorescence curve, rate of light trapped at the PSII complex, maximum quantum yield of photochemistry, average fluorescence induction time, and evaluation of the number of PSII reaction centers) as well as measuring heat dissipation kinetics. Because this system offers higher speed, more versatility, and greater accuracy (3%) than manual methods, it is a unique and valuable tool for laboratories involved in fluorescence research in the photosynthesis field. To demonstrate the use of this system and its superior performance, this article describes classic experiments carried out with the alga Dunaliella tertiolecta.
New display-type analyzer for the energy and the angular distribution of charged particles
Authors: Daimon Hiroshi
Published: July 2002

A new principle for analyzing the kinetic energy as well as the angular distribution of charged particles has been discovered. A new display type analyzer was constructed according to theory. It consists of an inner hemispherical grid and an outer hemispherical electrode which has a radius two times larger than that of the inner grid. Charged particles with the same kinetic energy radiate from one point to all directions inside the inner grid, are repelled by the electric field between the two spheres, and converge at the point which is symmetric to the center of the hemispheres. When an aperture is put at the point, the angular distribution of the charged particles can be observed using a two-dimensional detector which is positioned out of the aperture. The characteristics of the analyzer are (1) the acceptance cone is ultimately wide, for instance, 2π sr for the charged particles emitted from a flat surface, (2) the pattern obtained is not distorted, and (3) the two electrodes are very simple and easy to construct.
Surface thermometry by laser-induced fluorescence
Authors: Goss L. P. , Smith A. A. , Post M. E.
Published: July 2002

A novel laser-induced fluorescence technique has been developed for measuring the surface temperature of reacting and nonreacting materials. The technique involves seeding the material to be examined with a temperature-sensitive phosphor (Dy:YAG) and monitoring the laser-induced fluorescence of the phosphor to determine the temperature. The Dy:YAG phosphor displays a temperature sensitivity in the range 300–1700 K. The technique has been applied to both reacting and nonreacting surfaces under laser excitation, allowing temperature and temporal-history profiles to be determined.
Effect of coherency stresses on the hardness of epitaxial Fe(001)/Pt(001) multilayers
Authors: Daniels B. J. , Nix W. D. , Clemens B. M.
Published: July 2002

The effect of coherency stresses on the hardness of epitaxial, sputter-deposited Fe(001)/Pt(001) multilayers was investigated. Coherency stresses were over 2 GPa for films with a bilayer period, Λ, of 44 Å and relaxed by more than a factor of 10 for films with Λ=76 and 121 Å. Since the hardness of these films was constant at approximately 9 GPa over this range of Λ, we conclude that the contribution of coherency stresses to the enhanced hardness is small for this system.
Design of an advanced minimumBfor electron cyclotron resonance multicharged ion sources
Authors: Ishii S. , Kato Y.
Published: July 2002

An advanced configuration of minimum-B field is designed for the electron cyclotron resonance (ECR) multicharged ion sources. The aim is to dramatically increase the efficiency of ion beam extraction by correcting the deformed magnetic flux tube containing hot plasma. The correction is performed by reversing the polarity of successive multipoles in the longitudinal direction. This method enables us to adopt the quadrupole that causes the greatest deformation. In addition, the most intense electron acceleration can be achieved with the quadrupole, since the radial field gradient is the largest of all multipoles.
Lateral, normal, and longitudinal spring constants of atomic force microscopy cantilevers
Authors: Neumeister Jonas M. , Ducker William A.
Published: July 2002

For a V-shaped atomic force microscopy cantilever beam, the spring constants in the three principal directions are given in terms of the beam geometry and material properties. For the lateral stiffness, a closed-formed expression is presented. Also, the normal and the longitudinal stiffness are obtained from a few simple equations. The results are compared with a finite element study and found to be very accurate. All spring constants depend strongly on the cantilever thickness, which is difficult to measure. In addition, the lateral and longitudinal stiffness are sensitive to the location and the height of the attached pyramid.
Magnetic manipulation instrumentation for medical physics research
Authors: Gillies G. T. , Ritter R. C. , Broaddus W. C. , Grady M. S. , Howard M. A. , McNeil R. G.
Published: July 2002

The noncontact magnetic manipulation of probe masses within the body is an area of research that has received substantial attention from the medical physics community, especially during the past three decades. The therapeutic and diagnostic possibilities arising from such technology include site-specific drug delivery within the central nervous system, advancement of techniques for navigation and selective catheterization of vessels within the cardiovascular and cerebrovascular systems, and the nonsurgical exploration of the alimentary and respiratory tracts. In this review, we examine the physical principles underlying in vivo magnetic manipulation systems, and catalog the various types of instrumentation used for such purposes to date. Thereafter, we evaluate the different methods of image-based localization used to identify the position of the probe within the body. Finally, we appraise an emerging technology known as nonlinear magnetic stereotaxis, a technique that permits minimally invasive access to difficult-to-approach parts of the brain. We close the review with a few comments on the directions for future work within this field.
Optothermal study of small single particles
Authors: Moksin M. M.
Published: July 2002

The suitability of the thermal wave detection technique to examine nonspherical particulate contaminants on products is presented. The thermal wave signal decay curves are analyzed by using two existing decay models. The goodness of fit of the models to the experimental data is also discussed.
Improved design of cusp-type electron-cyclotron resonance ion sources
Authors: Ishii S. , Kato Y.
Published: July 2002

An ion source of electron-cyclotron resonance using cusp magnetic field is designed. The field is generated with two cylindrical magnets polarized parallel to the axis of symmetry. Lines of magnetic induction are in this configuration longer than in conventional cusp machines. The plasma electrons escaping from a line cusp are repelled by applying negative potential to an electrode repeller. The repeller of low work function emits additional electrons. A whistler wave is launched through a helical antenna at a point cusp to produce overdense plasmas. An intense ion beam is formed by extracting ions at the other point cusp where the magnetic flux is focused. The repeller materials are sputtered at the line cusp and ionized in the plasma. The atomic flux from the cylindrical surface is focused at the center of plasma to give abundant ions from the solid materials.
A catalytic flow reactor for kinetic studies of multicomponent reacting mixtures on supported catalysts
Authors: Boehman A. L. , Niksa S.
Published: July 2002

Our catalytic flow reactor presents several advantages for kinetic studies of heterogeneous chemistry on supported catalysts. This experimental facility enables determinations of the reaction rates of individual species at high conversion levels under isothermal conditions with multicomponent mixtures. Reaction rates are determined simultaneously for any number of species at points along supported catalysts under typical exhaust conditions, allowing detailed characterization of selectivities and inhibition effects. Tight thermal control permits the observation of species with widely varying reactivities, a situation that is typical in exhaust aftertreatment applications. The reactor is ideally suited to studying reaction kinetics under either reducing or oxidizing conditions, as demonstrated by reactant profile data measured with both lean and rich hydrocarbon exhaust streams.
Measuring ultrashort laser pulses in the time-frequency domain using frequency-resolved optical gating
Authors: Trebino Rick , DeLong Kenneth W. , Fittinghoff David N. , Sweetser John N. , Krumbügel Marco A. , Richman Bruce A. , Kane Daniel J.
Published: July 2002

We summarize the problem of measuring an ultrashort laser pulse and describe in detail a technique that completely characterizes a pulse in time: frequency-resolved optical gating. Emphasis is placed on the choice of experimental beam geometry and the implementation of the iterative phase-retrieval algorithm that together yield an accurate measurement of the pulse time-dependent intensity and phase over a wide range of circumstances. We compare several commonly used beam geometries, displaying sample traces for each and showing where each is appropriate, and we give a detailed description of the pulse-retrieval algorithm for each of these cases.
All-optical programmable AND gate implementation in a germanium-doped silica planar waveguide
Authors: Ranon P. M. , Dajani I. , Kester J. J. , Alley T. G.
Published: July 2002

We report the results of an all-optical programmable AND logic gate. This gate consists of a germanium-doped silica planar waveguide, a laser, and the means of coupling two fundamental frequency beams into different guiding modes of the waveguide along with a second harmonic beam coupled into one guiding mode. These waves interfere in the film generating a set of semipermanent second-order susceptibility gratings which give rise to the waveguide, the film-generated second harmonic light wave made to behave as an output of a logic AND gate. The fundamental and second harmonic light were sent into the waveguide during the programming sequence, but only the fundamental light was injected to probe the logic gate to produce an output. The measured signal-to-noise ratio was 17 dB.
Low-temperature study of current and electroluminescence in InGaN/AlGaN/GaN double-heterostructure blue light-emitting diodes
Authors: Perlin Piotr , Osiński Marek , Eliseev Petr G. , Smagley Vladimir A. , Mu Jian , Banas Michael , Sartori Philippe
Published: July 2002

Electrical and optical properties of Nichia double-heterostructure blue light-emitting diodes, with In0.06Ga0.94N:Zn, Si active layer, are investigated over a wide temperature range from 10 to 300 K. Current–voltage characteristics have complex character and suggest the involvement of various tunneling mechanisms. At small voltages (and currents), the peak wavelength of the optical emission shifts with the applied bias across a large spectral range from 539 nm (2.3 eV) up to 443 nm (2.8 eV). Light emission takes place even at the lowest temperatures, indicating that a complete carrier freeze-out does not occur.
Room-temperature continuous-wave operation of InGaN multi-quantum-well structure laser diodes
Authors: Nakamura Shuji , Senoh Masayuki , Nagahama Shin-ichi , Iwasa Naruhito , Yamada Takao , Matsushita Toshio , Sugimoto Yasunobu , Kiyoku Hiroyuki
Published: July 2002

Continuous-wave (cw) operation of InGaN multi-quantum-well structure laser diodes (LDs) was demonstrated at room temperature (RT). The threshold current and voltage of the LD were 130 mA and 8 V, respectively. The threshold carrier density was 9 kA/cm2. The lifetime of the LDs under RT cw operation was 1 s due to large heat generation. Mode hopping of the emission wavelength of the LDs was observed. The average wavelength drift due to temperature increase was 0.066 nm/K between 20 and 70 °C, because of the temperature dependence of the gain profile due to band-gap narrowing of the InGaN active layer.