bluuebunny/crossref_metadata_2025 huggingface dataset:
Social and spatial organisation in colonies of a primitively eusocial wasp, Ropalidia revolutionalis (de Saussure) (Hymenoptera: Vespidae)
Authors: Robson Ska , Bean K , Hansen J , Norling K , Rowe RJ , White D
Published: July 2002

We investigated individual reproductive flexibility and the division of labour in five post‐emergence colonies of the primitively eusocial wasp Ropalidia revolutionalis, by relating behavioural observations of individuals at the nest to their ovarian development. Analysing time‐activity budgets with principal components and canonical discriminant analysis revealed three distinct groups of individuals, based on their spatial distribution relative to the nest. Individuals could be assigned to a group based on: whether they spent most of their time near or away from the nest (first principal component, 75% variance); whether they sat on or next to the comb when in the nest vicinity (second principal component, 16% variance); or whether they sat on or off the capped cells (that contain pupae) when sitting on the combs themselves (third principal component, 6% variance). Colonies had either one or two reproductive individuals, but the distinct groups they belonged to could vary. In three monogynous colonies reproductive individuals spent the majority of their time sitting on capped cells. In two polygynous colonies, primary reproductives were also located on capped cells but the secondary reproductives, with smaller oocytes, were located either next to the nest or on the capped cells of a second comb. In all colonies levels of aggressive interactions were low. These findings indicate that spatial position is an important component of social organisation and that there are multiple pathways through which an individual can achieve reproductive dominance. Finally, comparison with other Ropalidia species shows that the pattern of social organisation varies in this wasp genus.
The development of myopia in Hong Kong children between the ages of 7 and 12 years: a five‐year longitudinal study
Authors: Edwards M.H.
Published: July 2002

The purpose of this work was to characterize the development of refractive error in Hong Kong children between the ages of 7 and 12 years. A non self‐selected sample of 7‐year old children was recruited and followed for 5 years, non‐cycloplegic refractions being carried out annually. A life‐table was used to determine myopia incidence and prevalence. The mean annual change in the spherical equivalent refraction (SER) was −0.32 D; 75 out of 83 subjects followed for 5 years became less hyperopic or more myopic, the maximum progression occurring between 9 and 11 years of age. The mean change in SER over the 5 years in children who were myopic at age 12 years was significantly greater than that in children who remained non‐myopic. The incidence of myopia at age 7–8 years was 9% and at age 11–12 years was 18–20%. At age 7 years the prevalence of progressive myopia was 1.6% and 2.5% of subjects had anisometropia. Any treatment to prevent myopia should start by the age of 6 years and treatment to retard development should commence before age 9 years.
The Association of Bone Mineral Density and Depression in an Older Population
Authors: Robbins John , Hirsch Calvin , Whitmer Rachel , Cauley Jane , Harris Tamara , For The Cardiovascular Health Study
Published: July 2002

OBJECTIVE: To evaluate the association between bone mineral density (BMD) and measurements of depression in an older population.

DESIGN: Population‐based, cross‐sectional study.

SETTING: Study subjects were participants in the Cardiovascular Health Study (CHS), a longitudinal, long‐term, follow‐up study, at the University of California Davis (Sacramento, California) and the University of Pittsburgh (Pittsburgh, Pennsylvania) clinical centers.

PARTICIPANTS: A random sample of 1,566 Medicare enrollees age 65 and older enrolled in the CHS.

MEASUREMENTS: Total hip BMD, measured using dual energy x‐ray absorptiometry (DEXA), after adjustment for multiple covariates, was compared with depression evaluated with the Center for Epidemiological Studies 10‐item Depression Scale (CES‐Dm). Risk factors for osteoporosis were compared in depressed and nondepressed participants. Potential correlates were entered into a regression model. Depression scores were compared in normal, osteopenic, and osteoporotic individuals.

RESULTS: Sixteen percent of participants were clinically depressed; 9% had BMDs in the osteoporotic range. Mean BMD was 40 mg/cm2 lower in those with clinical depression. High CES‐Dm scores were associated with lower BMD (P < .001) when adjusted for body mass index (BMI), age, kilocalories of activity, estrogen use, gender, race, smoking and drinking. When stratified by race, this remained true for all Caucasians (P < .01), all African Americans (P < .05), and when stratified by race and gender the association remained only for all Caucasian women (P < .001). In women and Caucasian men there was an increase in depression scores among individuals with osteoporotic‐range BMDs.

CONCLUSIONS: A significant association was found between BMD and depressive symptoms after adjustment for osteoporosis risk factors. In Caucasians, depressive symptoms were associated with both osteoporotic and osteopenic levels of BMD. Causality cannot be ascribed, with only one measurement of BMD. We postulate that there may be an unmeasured third factor, such as an endogenous steroid, that is responsible for both low BMD and depression. J Am Geriatr Soc 49:732–736, 2001.
Influence of Aging and Other Cardiovascular Risk Factors on Baroreflex Sensitivity
Authors: Piccirillo Gianfranco , Di Giuseppe Vincenza , Nocco Marialuce , Lionetti Marco , Moisè Antonio , Naso Camilla , Tallarico Demetrio , Marigliano Vincenzo , Cacciafesta Mauro
Published: July 2002

OBJECTIVES: To examine the influence of known cardiovascular risk factors (cholesterol, blood glucose levels, arterial pressures, heart rate, and aging) on baroreflex sensitivity.

DESIGN: An observational epidemiological study.

SETTING: Geriatric Division at the Policlinico Umberto Primo, University of Rome La Sapienza.

PARTICIPANTS: Two hundred three subjects whose ages ranged from 9 to 94 years, apparently healthy and free of detectable clinical evidence of atherosclerosis.

MEASUREMENTS: All subjects underwent determination of baroreflex sensitivity by phenylephrine infusion (BSphe), and by a noninvasive method derived from spectral analysis of R‐R interval and arterial pressure variabilities (α index).

RESULTS: The population, subdivided into tertiles for each variable studied, had lower BSphe values and lower α indexes as a function of age, plasma low‐density lipoprotein (LDL) cholesterol, and systolic blood pressure. The α index was significantly lower in both groups with elevated LDL cholesterol levels than in those with lower levels (II and III vs I tertile, P < .001), whereas BSphe differed significantly only in the two groups who had extreme levels of LDL (I vs III tertile, P < .001). Multiple regression analysis identified a negative association of the α index with age (P < .001), heart rate (P < .01), area under the glucose‐response curve (P < .001), and LDL cholesterol (P < .01), but of BSphe only with age (P < .001) and heart rate (P < .01).

CONCLUSION: These findings indicate that some risk factors for coronary heart disease adversely influence baroreflex sensitivity.
Molecular beam epitaxy of layered Dy-Ba-Cu-O compounds
Authors: Schlom D. G. , Eckstein J. N. , Hellman E. S. , Streiffer S. K. , Harris J. S. , Beasley M. R. , Bravman J. C. , Geballe T. H. , Webb C. , von Dessonneck K. E. , Turner F.
Published: July 2002

Heteroepitaxial Dy-Ba-Cu-O films have been grown in situ on SrTiO3 substrates using an oxygen plasma beam and elemental source beams in a modified molecular beam epitaxy machine. By periodically shuttering the Dy and Ba beams during growth, flat surfaces of layered Dy-Ba-Cu-O compounds have been obtained. Periodic oscillations in the intensity of the in situ reflection high-energy electron diffraction pattern were observed during shuttered growths. Depending on growth conditions, the as-grown layers have ranged from insulating to superconducting with onset temperatures above 60 K.
dc and rf measurements of the kink effect in 0.2 μm gate length AlInAs/GaInAs/InP modulation-doped field-effect transistors
Authors: Palmateer L. F. , Tasker P. J. , Schaff W. J. , Nguyen L. D. , Eastman L. F.
Published: July 2002

Presented in this letter are measurements of the kink effect in 0.2 μm gate length AlInAs/GaInAs/InP modulation-doped field-effect transistors. The dc kink effect, which results in a sharp increase of the dc output conductance, has been eliminated in structures grown with a low AlInAs V:III flux ratio. The kink effect is a low-frequency mechanism that is not present at microwave frequencies and is attributed to trapping phenomena in the AlInAs.
Mechanism of picosecond ultraviolet laser sputtering of sapphire at 266 nm
Authors: Brand J. L. , Tam A. C.
Published: July 2002

Ultraviolet laser sputtering of sapphire was observed to result in droplet ejection when done in air, pressurized air, or in 20 mTorr pressure. Such droplets were collected and studied with scanning electron microscopy and optical microscopy. The collected particles were spherical and ranged in size up to 3 μm in diameter. Some particles appeared to have been molten and splattered on the collection plate. The size of the particles was independent of the ambient pressure. However, the collection efficiency of the collection plate was ∼30 times greater at 20 mTorr pressure as compared to one atmosphere. The similar result for measurements of the sputter depth under a range of background pressure indicates that the mechanism for the laser sputtering of sapphire at 266 nm with 30 ps pulses and a fluence near 10 J/cm2 is independent of the ambient pressure. Redeposition of debris onto the sputtered sample was significantly greater in one atmosphere pressure than in reduced pressure. These findings indicate that hydrodynamic sputtering is the most likely mechanism for the laser sputtering of sapphire at high sputter rates.
Lorentz force and magnetic stress in force-free configurations
Authors: Salingaros N. A.
Published: July 2002

Special current distributions that are widely assumed to have vanishing self-force in fact can have sizable magnetic forces. The Lorentz self-force is often miscomputed by ignoring part of the magnetic self-field in the traditional model of force-free configurations. Furthermore, magnetic stresses in general do not vanish when the Lorentz force does. These stresses are responsible for the observed deformation of Lorentz force-free electromagnets. Although straightforward, these results revise some long-established models in superconducting magnet design, magnetic confinement fusion, and astrophysical magnetic fields.
Electron transport properties of strained InxGa1−xAs
Authors: Thobel J. L. , Baudry L. , Cappy A. , Bourel P. , Fauquembergue R.
Published: July 2002

As a first approach to the study of strained pseudomorphic materials, we have used a Monte Carlo method to calculate the effect of strain on electron transport properties of bulk InGaAs. Strain-induced velocity reduction is found to be much more pronounced for InGaAs grown on GaAs substrate than for InGaAs grown on InP substrate.
Scaling behavior of YBa2Cu3O7−δ thin-film weak links
Authors: Russek S. E. , Lathrop D. K. , Moeckly B. H. , Buhrman R. A. , Shin D. H. , Silcox J.
Published: July 2002

The superconductive weak link properties of microbridges formed in c-axis normal YBa2Cu3O7−δ polycrystalline thin films containing a variable amount of large angle tilt boundaries have been studied. In the low critical current density limit these weak links have current-voltage (I-V) characteristics that are accurately modeled by the resistively shunted junction model. The I-V’s are found to accurately follow a simple scaling law with the product of the critical current and weak link resistance Rn varying linearly with the weak link conductance.
Field-effect transistors using alkyl substituted oligothiophenes
Authors: Akimichi H. , Waragai K. , Hotta S. , Kano H. , Sakaki H.
Published: July 2002

Field-effect transistors (FETs) have been prepared using thin films of alkyl substituted oligothiophenes. These compounds bring about a significant increase in the source-drain channel current when compared to the conventional nonsubstituted oligothiophenes. The increased channel current mostly results from the enhanced carrier mobility of the material. We report that the FETs are readily made by a single routine process of casting or evaporation.
Gettering thresholds for transition metals by oxygen-related defects in silicon
Authors: Falster R. J. , Fisher G. R. , Ferrero G.
Published: July 2002

This letter reports a qualitative study of the gettering of technologically important transition metal contaminants by a wide variety of distributions of oxygen precipitates and related defects in silicon. Various metals were diffused into specially prepared silicon wafers containing densities of oxygen precipitates ranging between 105 and 2×1010 cm−3. The precipitates were of a variety of sizes both with and without punched-out dislocation networks and associated stacking faults. Following previous work and using the Haze Test to monitor gettering activity, a threshold in precipitate density has been determined for the complete gettering of Cu and Ni (about 1×105 and 3×106 cm−3, respectively). No influence of precipitate size (above an as yet to be determined minimum) or of the presence of punched-out dislocations or stacking faults could be determined for these two metals, the fastest diffusing of the 3d group. Comments on the gettering of Fe are made.
Using light as a stencil
Authors: Prentiss M. , Timp G. , Bigelow N. , Behringer R. E. , Cunningham J. E.
Published: July 2002

A new method for laterally manipulating the morphology of a thin film is presented, which uses the force exerted by light to deflect neutral atoms in an atomic beam during deposition. We have evaluated the dependence of the thickness of a thin metal film on the frequency, intensity, and the spatial structure of the light field, and find that the stimulated component of the force is suitable for laterally organizing atoms from centimeter to submicron dimensions.
Photoinduced enhancement of superconductivity
Authors: Nieva G. , Osquiguil E. , Guimpel J. , Maenhoudt M. , Wuyts B. , Bruynseraede Y. , Maple M. B. , Schuller Ivan K.
Published: July 2002

We show clear and conclusive experimental evidence for the enhancement of superconductivity in GdBa2Cu3Ox and YBa2Cu3Ox thin films by photoexcitation. Upon laser illumination the critical temperature increases while the resistivity of the material decreases. The relaxation back to the original state is very slow, of the order of days at room temperature. The existence of this effect opens the possibility of fabricating weak-link devices with in situ tunable superconducting characteristics.
TiNCl formation during low-temperature, low-pressure chemical vapor deposition of TiN
Authors: Hegde Rama I. , Fiordalice Robert W. , Tobin Philip J.
Published: July 2002

We report for the first time the existence of the titanium nitride chloride (TiNCl) compound in low-temperature (400 °C) low-pressure chemical vapor deposition (LPCVD) TiN films deposited using TiCl4/NH3 chemistry. Thin-film x-ray diffraction and Auger electron spectroscopy was used in the film characterization. Physical, chemical, and electrical properties of the resulting low-temperature LPCVD TiN films are discussed.
Nano edge roughness in polymer resist patterns
Authors: Yoshimura Toshiyuki , Shiraishi Hiroshi , Yamamoto Jiro , Okazaki Shinji
Published: July 2002

Ultrasmall edge roughness in delineated patterns (nano edge roughness) is investigated in nanostructures made of negative-type electron beam polymer resists by atomic force microscope measurements. Very narrow isolated lines 10–20 nm wide are fabricated with a finely focused electron beam provided by a scanning electron microscope. A chemical amplification novolak resin-based resist shows nano edge roughness which cannot be neglected in nanofabrication. To investigate the origin of the roughness, conventional two-component resist systems are microscopically compared. An azide polyvinylphenol-based resist and an azide novolak resin-based resist are used. The novolak resin-based resist exhibits a rougher surface than the polyvinylphenol-based one. This result suggests that the polymer structures of the base resins cause nano edge roughness of a chemical amplification resist in connection with the acid diffusion during the post-exposure bake process.
Possibility of carbon nitride formation by low-energy nitrogen implantation into graphite: In situ electron spectroscopy studies
Authors: Hoffman A. , Gouzman I. , Brener R.
Published: July 2002

The possibility of carbon nitride formation by low-energy nitrogen ion irradiation of graphite was investigated by in situ x-ray photoelectron spectroscopy. Room-temperature and hot 500-eV N+2 implantations were performed with saturation doses for which a constant nitrogen concentration was obtained. Analysis of the N(1s) core level line indicates the existence of three different carbon–nitrogen bonding states in the room-temperature implanted layer. Annealing experiments up to 500 °C revealed a slight, gradual decrease of nitrogen concentration in the implanted layer accompanied by a partial redistribution of the nitrogen bonding states. Hot nitrogen implantations at 300 and 500 °C resulted in a predominant population of the more covalent, with higher N(1s) binding energy, nitrogen bonding state. Such a distribution of carbon–nitrogen chemical bonds could not have been obtained by annealing of the room-temperature implanted layer. These results may be of importance in finding a way to produce the elusive β-C3N4 phase by ion beam assisted deposition.
Dominant free-exciton recombination radiation in chemical vapor deposited diamonds
Authors: Kawarada Hiroshi , Tsutsumi Takahiro , Hirayama Hiroki , Yamaguchi Akira
Published: July 2002

Dominant free-exciton recombination radiation has been obtained from chemical vapor deposited diamonds. The crystals are formed in a microwave plasma using the mixtures CO and CO2 diluted with hydrogen. The concentration of CO2 and the position of the samples in the plasma affect the crystallinity of the samples. The peak emission intensity ratio between the free-exciton recombination radiation and the band A emission is more than 20 in the samples formed at the edge of discharging area and with the optimum concentration of CO2. The value is the highest ever reported in diamond.
Influence of surface defects on the electrical behavior of aluminum-porous silicon junctions
Authors: Cadet C. , Deresmes D. , Vuillaume D. , Stievenard D.
Published: July 2002

Using transient-current measurements on porous silicon layers made on p+ silicon substrate, we characterize the surface defects of the porous silicon material, i.e., the defects located at the interface between porous silicon and a thin layer of native oxide. An energy location near midgap (these defects can be efficient radiative lifetime killers) and a trap concentration in close agreement with the number of trivalent silicon defects—as measured by electron spin resonance—are deduced.
Measurement of the complex nonlinear refractive index of single crystal p-toluene sulfonate at 1064 nm
Authors: Lawrence Brian L. , Cha Myoungsik , Torruellas William E. , Stegeman George I. , Etemad Shahab , Baker Gregory , Kajzar François
Published: July 2002

Z-scan at 1064 nm was used with single, 35 ps pulses to measure the nonlinear refraction and absorption in single crystal PTS (p-toluene sulfonate). Detailed analysis of the Z-scan data based on Δn=n2I+n3I2 and Δα=α2I+α3I2 yielded n2=5(±1)×10−12 cm2/W, α2=100(±20) cm/GW, n3=−5(±1)×10−21 cm4/W2 and α3=−5(±1) cm3/GW.2 The resulting two photon figure of merit T for PTS is marginal for high throughput, all-optical waveguide switching at 1064 nm.
Generation of tunable narrow-band THz radiation from large aperture photoconducting antennas
Authors: Weling A. S. , Hu B. B. , Froberg N. M. , Auston D. H.
Published: July 2002

We report a novel technique for the generation of tunable narrow-band submillimeter wave electromagnetic radiation in free space. This is accomplished by mixing two linearly chirped optical pulses with a variable time delay on a biased large aperture GaAs photoconducting antenna. The center frequency of the THz radiation varies linearly with the delay between the two chirped pulses from dc to ∼1 THz.
Terahertz frequency response of an In0.53Ga0.47As/AlAs resonant-tunneling diode
Authors: Scott J. S. , Kaminski J. P. , Wanke M. , Allen S. J. , Chow D. H. , Lui M. , Liu T. Y.
Published: July 2002

We have measured the room-temperature, broad-band, terahertz response of a high-speed In0.53Ga0.47As/AlAs resonant-tunneling diode from 120 GHz to 3.9 THz using the free-electron lasers at UCSB. The ‘‘rectified’’ response is measured with a conventional probe station by using the tungsten probe tip as a whisker antenna. Normalizing the rectified response in the resonant-tunneling regime with the off-resonant response we remove the extrinsic frequency dependence controlled by the antenna and the RC time constant and measure an intrinsic relaxation time.
Nanoindentation hardness measurements using atomic force microscopy
Authors: Bhushan Bharat , Koinkar Vilas N.
Published: July 2002

An atomic force microscope (AFM), with a specially prepared diamond tip, has been modified to measure indentation hardness with an indentation depth as low as 1 nm. This indentation depth is much smaller than the depth of more than 20 nm that have been reported to date. The AFM indentation technique allows the hardness measurements of surface monolayers and ultrathin films in multilayered structures at very shallow depths and low loads. The nanoindentation hardness of single crystal silicon is measured using this technique. A subtraction technique is also described which allows the actual hardness measurements of rough surfaces such as magnetic thin film rigid disks.
Stress and crystallinity in 〈100〉, 〈110〉, and 〈111〉 oriented diamond films studied using Raman microscopy
Authors: Sails Stephanie R. , Gardiner Derek J. , Bowden Michael , Savage James , Haq Sajad
Published: July 2002

Stress and crystallinity variations along the growth direction in three diamond films of different preferred orientations have been investigated using Raman microscopy to monitor the change in band center and full width at half maximum (FWHM) of the first-order diamond phonon with distance along a single diamond crystal. The results showed a consistent trend for the 〈100〉 oriented film, with both the peak position and FWHM being largest close to the silicon substrate and decreasing along the direction of crystal growth. The 〈110〉 and 〈111〉 orientations showed random variation throughout.
Neutron powder diffraction at pressures beyond 25 GPa
Authors: Klotz S. , Besson J. M. , Hamel G. , Nelmes R. J. , Loveday J. S. , Marshall W. G. , Wilson R. M.
Published: July 2002

Full structural studies of condensed media under high pressure by neutron powder diffraction have been limited in practice to 2–3 GPa for several decades. This range is in general too small to allow a precise determination of the pressure dependence of atomic coordinates. As a consequence, almost no direct measurements exist, for example, of the pressure dependence of the bond lengths in H2 and the planetary ices. In this letter, a technique is presented which makes it possible to pressurize samples of 35 mm3 volume up to 30 GPa and to collect neutron diffraction patterns in a few hours by time-of-flight techniques. This method provides data which can be treated by Rietveld profile refinement methods, as demonstrated on a sample of D2O ice VII at 26 GPa. This represents a tenfold increase of the pressure range over which refinable neutron diffraction data can be obtained and should have a number of applications in such fields as fundamental physicochemistry, and geo- and planetary sciences.
Use of optimal estimation theory, in particular the Kalman filter, in data analysis and signal processing
Authors: Cooper William S.
Published: July 2002

The Kalman filter, a powerful and useful optimal estimation technique, does not seem to be widely known among physicists. Here we outline the derivation of the algorithm, and give three examples of its use: (a) in estimating the value of a constant, with both system and measurement noise, (b) in numerical differentiation of noisy data, and (c) in optimally estimating the amplitude of a signal with arbitrary but known time dependence superimposed on a noisy background.
Techniques for the growth of superconducting oxide thin films using pure ozone vapor
Authors: Berkley D. D. , Goldman A. M. , Johnson B. R. , Morton J. , Wang T.
Published: July 2002

A simple, inexpensive apparatus for the production of pure ozone vapor for use in the in situ growth of superconducting oxide thin films is described. Pure condensed ozone is distilled at 77 K from a dilute mixture of ozone in oxygen gas. The condensed ozone is subsequently heated, raising its vapor pressure to provide an adequate flow of ozone gas into the thin film growth chamber. Thin films of YBa2 Cu3 O7−x with zero resistance at temperatures as high as 85 K have been grown with a deposition chamber pressure of only 2×10−7 Torr and without a post-deposition anneal processing step. Unlike most other commonly used forms of highly reactive oxygen, ozone can be made and stored in very pure form. This makes it very useful when a well-characterized oxidizing gas is needed for systematic studies of the growth kinetics and oxidation of the films. Safety aspects of the ozone-production process are discussed.
Dual purpose pyrometer for temperature and solidification velocity measurement
Authors: Hofmeister W. H. , Bayuzick R. J. , Robinson M. B.
Published: July 2002

A dual purpose pyrometer is described that allows both accurate radiance temperature measurement and fast temporal response. The system uses two silicon photodiodes with separate optical paths derived from a common spot on the sample. The optical bandwidths and response times of each detection circuit are tailored to the function of each radiometer. The radiance temperature of electromagnetically levitated metallic samples is measured over a narrow optical bandwidth with a high-gain silicon detector. The velocity of solidification of undercooled melts can be deduced from the rise time of the second silicon detector which samples a broad optical bandwidth and has a fast response time. Results from experiments on the undercooling and solidification behavior of electromagnetically levitated pure nickel show that the solidification velocity approaches 17 m/s at high undercooling.
High-pressure dilatometer
Authors: So P. T. C. , Gruner S. M. , Shyamsunder E.
Published: July 2002

A high-pressure dilatometer capable of measuring volume changes of 2×10−6 cm3 is described. Fractional volume changes of 1 part in 104 can be measured over a temperature range of −30–90 °C, and a pressure range of 1 bar (0.1 MPa)–3 kbar (300 MPa). The dilatometer is constructed out of a commercial high-pressure valve and a compact home-built pressure sensor. The system was specially designed to study lipid-water biological systems. Preliminary studies on the lipid dioleoylphosphatidylethanolamine (DOPE) revealed the existence of phases not previously reported for this lipid.
X-ray dichroism and Faraday effect studies in ordered and disordered Fe3Pt
Authors: Alp E. E. , Ramanathan M. , Salem-Sugui S. , Oliver F. , Stojanoff V. , Siddons D. P.
Published: July 2002

The magnetic properties of Fe3Pt compound depend on the degree of disorder present in the system. We have compared a cold-rolled, disordered sample with a heat treated, ordered sample using circularly polarized synchrotron radiation at the Fe K (7112 eV) and at the Pt L3 (11 564 eV) absorption edge, as well as by Mossbauer spectroscopy, and x-ray diffraction. Fe–K edge dichroism is compared to the measurements of Faraday rotation using linearly polarized radiation. We found that the magnitude of magnetic dichroism at the Pt L3 edge is reduced when the disordered Fe3Pt is heat treated and ordered. The enhanced sensitivity of the Faraday rotation measurements compared to the magnetic dichroism measurements at the K edges of transition metals are reported on.
Vacuum desensitization of CR-39 track recording plastic
Authors: Prohaska R. , Garate E. , Papadichev V. , Fisher A. , Rostoker N.
Published: July 2002

It has been observed that prolonged (several hours) exposure to vacuum (P<10−4 Torr) renders CR-39 insensitive to the passage of 5.67 MeV alpha particles. Subsequent exposure to air results in a recovery of sensitivity.
Broadband time-domain-reflectometry dielectric spectroscopy using variable-time-scale sampling
Authors: Hager N. E.
Published: July 2002

Methods for increasing the bandwidth of time-domain-reflectometry (TDR) dielectric spectroscopy using variable-time-scale sampling are presented. Consecutive segments of the TDR transient are sampled with increasing time increments and the entire transient transformed into the frequency domain using a running Laplace transform. Instrumentation artifacts are identified and controlled by examining reflected transients for stray artifacts prior to transformation, either on individual time scales or on a composite log time scale. Transform algorithms are verified using spice simulation in both time and frequency domains. Results are presented for a conducting salt solution, showing continuous dielectric spectra from 100 kHz to 5 GHz in the frequency domain, and requiring acquisition over six decades of time in the time domain to capture the entire response.
All-optical modulation via nonlinear cascading in type II second-harmonic generation
Authors: Assanto G. , Wang Z. , Hagan D. J. , VanStryland E. W.
Published: July 2002

Utilizing a type II interaction for second-harmonic generation in a crystal of potassium titanyl phosphate, we experimentally demonstrate the all-optical action of a light modulator with both signal and output at the same optical wavelength. This modulator is controlled by the intensity of the injected signal, a characteristic that makes it a suitable candidate for all-optical transistor action and ultrafast analog processing in transparent networks for telecommunications.
An investigation of pseudovibration signals in dual beam laser vibrometry
Authors: McDevitt T. E. , Vikram C. S.
Published: July 2002

The role of speckles in generating erroneous laser vibrometer signals in the case of a beam undergoing flexural and longitudinal motion is investigated. As illustrated by experimental results, spurious signals, brought about predominantly by flexural motion in this case, can be removed by increasing the speckle size at the photodetector plane. The approach can provide a simple but effective remedy to the pseudovibration problem.
Three-dimensional displacements of a piezoelectric tube scanner
Authors: Yang Shengyuan , Huang Wenhao
Published: July 2002

This article gives the quantitative three-dimensional displacements of a piezoelectric tube scanner subject to arbitrary voltages. The results including the influences of the tip’s position and length are reported. The displacements are determined by the piezoelectric strain/charge constant d31 and the geometrical parameters of the scanner. Experiment results show the feasibility of the proposed method to calibrate the effective piezoelectric constant of a scanner. The coupling between vertical and transverse scanning displacements is discussed. Comparison of the newly developed formulas with the previous formulas and finite element calculation is carried out. The theoretical basis of the recently proposed “circular arc bending model” is found and the exact form of the model is also derived. Numerical results show that the exact form agrees with the experimental results much better than the previous form. The formulas presented here can be used for the design, calibration, and further application of piezoelectric tube scanners in scanning probe microscopes.
Measurements of the thermodynamic equation of state via the pressure dependence of thermophysical properties of air by a thermal-wave resonant cavity
Authors: Pan Guang , Mandelis Andreas
Published: July 2002

The thermodynamic equation of state for ambient air was investigated by means of a thermal-wave resonant cavity in the pressure range between 40 and 760 Torr and at ambient, or near-ambient, temperature conditions. The pressure dependencies of the thermal diffusivity, conductivity, effusivity, and thermal-wave-source infrared emissivity were measured. The experimental results were found to be consistent with the ideal gas law for air in the foregoing pressure and temperature range. It was observed that the thermal diffusivity of air increases linearly with decreasing cavity pressure. The experimental curves obtained from the four channels (amplitude, phase, in-phase, and quadrature) of the thermal-wave signal-demodulating lock-in amplifier were fitted to thermal-wave resonant cavity theory, and the thermal conductivity and effusivity of the air in the cavity were also calculated as functions of pressure. Within the experimental error range, the thermal conductivity was found to be independent of pressure and equal to (28.9±0.2)×10−3 W/m K at 309–310 K. The thermal effusivity of air exhibited a linear increase with increasing pressure at approximately constant ambient temperature. In addition, the infrared emissivity of the resistively heated Cr–Ni thermal-wave thin-film strip source (cavity wall) was measured as a function of the source rms voltage at several pressures. The obtained values, ranging from 0.094 to 0.108, showed that the emissivity decreases with decreasing cavity pressure.
Noncontact electrical resistivity measurement technique for molten metals
Authors: Rhim Won-Kyu , Ishikawa Takehiko
Published: July 2002

A noncontact technique of measuring the changes in electrical conductivity (or resistivity) of conducting liquids is reported. The technique is based on a conducting drop that is levitated by the high-temperature electrostatic levitator in a high vacuum. This technique, which utilizes the principle of the asynchronous induction motor, measures the relative changes in torque as a function of temperature by applying a rotating magnetic field to the sample. Changes in electrical resistivity are related to the changes in measured torque using the formula developed for the induction motor. Validity of this technique was demonstrated using a pure aluminum sample around its melting temperature. When the measurement results were calibrated by a literature value of resistivity at the melting point, our resistivity data around the melting point could be expressed by rliq=24.19+1.306×10−2(T−Tm) μΩ cm over Tm∼1160 K, rsolid=10.77+1.421×10−2(T−Tm) μΩ cm over 700 K∼Tm, and the thermal conductivity as determined by the Wiedemann–Franz–Lorenz law from the resistivity data was given by κliq(T)=94.61+4.41×10−2(T−Tm) W m−1 K−1, κsolid(T)=211.13−7.57×10−2(T−Tm) W m−1 K−1. Both electrical resistivity and thermal conductivity are in close agreement with the literature, confirming the validity of the present technique.
High-resolution pulsed field ionization photoelectron-photoion coincidence spectroscopy using synchrotron radiation
Authors: Jarvis G. K. , Weitzel Karl-Michael , Malow Marcus , Baer Tomas , Song Y. , Ng C. Y.
Published: July 2002

We have developed a sensitive and generally applicable scheme for performing pulsed field ionization (PFI) photoelectron (PFI-PE)-photoion coincidence (PFI-PEPICO) spectroscopy using two-bunch and multibunch synchrotron radiation at the Advanced Light Source. We show that this technique provides an ion internal state (or energy) selection limited only by the PFI-PE measurement. Employing a shaped pulse for PFI and ion extraction, a resolution of 0.6 meV [full width at half maximum (FWHM)] is observed in the PFI-PEPICO bands for Ar+(2P3/2,1/2). As demonstrated in the PFI-PEPICO study of the process, O2+hν→O2+(b 4Σg−, v+=4, N+)+e−→O+(4S)+O(3P)+e−, the dissociation of O2+(b 4Σg−, v+=4) in specific rotational N+ levels can be examined. The simulation of the experimental breakdown diagram for this reaction supports the conclusion that the threshold for the formation of O+(4S)+O(3P) from O2+(b 4Σg−, v+=4) lies at N+=9. We have also recorded the PFI-PEPICO time-of-flight (TOF) spectra of O+ formed in the dissociation of O2+(b 4Σg−, v+=4–7). The simulation of these O+ TOF spectra indicates that the PFI-PEPICO method is applicable for the determination of kinetic energy releases. Previous PFI-PE studies on O2 suggest that a high-n O2 Rydberg state [O2*(n)] with a dissociative ion core undergoes prompt dissociation to yield a high-n′ O-atom Rydberg state [O*(n′)] [Evans et al., J. Chem. Phys. 110, 315 (1999)]. The subsequent PFI of O*(n′) accounts for the formation of a PFI-PE and O+. Since the PFI-PE intensities for O+ and O2+ depend on the lifetimes of O*(n′) and O2*(n), respectively, the PFI-PE intensity enhancement observed for rotational transitions to O2+(b 4Σg−, v+=4, N+⩾9) can be attributed to the longer lifetimes for O*(n′) than those for O2*(n). The PFI-PEPICO study of the dissociation of CH3+ from CH4 also reveals the lifetime effects and dc field effects on the observed intensities for CH3+ and CH4+. The high resolution for PFI-PEPICO measurements, along with the ability to distinguish the CH3+ fragments due to the supersonically cooled CH4 beam from those formed by the thermal CH4 sample, has allowed the determination of a highly accurate dissociation threshold for CH3+ from CH4.
Form birefringence of volume gratings in photopolymers
Authors: Yang Changxi , Yeh Pochi
Published: July 2002

We investigate experimentally the form birefringence due to photoinduced one- and two-dimensional volume index gratings in DuPont photopolymers. Experimental results on the dispersion of the form birefringence versus the illumination wavelength and the grating period for one-dimensional gratings are presented. We also investigate the form birefringence due to two-dimensional volume gratings. Positive form birefringence and biaxial form birefringence can be obtained by recording two volume gratings with different grating wave vectors.
Room temperature optical gain in sol-gel derived CdS quantum dots
Authors: Butty J. , Peyghambarian N. , Kao Y. H. , Mackenzie J. D.
Published: July 2002

Under strong nanosecond excitation, we demonstrate that II–VI semiconductor quantum dots exhibit optical gain up to room temperature. The CdS nanocrystallites, fabricated by sol-gel process, are embedded in a sodium borosilicate glass matrix. The gain is spectrally broad and the crossing between absorption and gain is well above the bulk absorption band edge energy, since our nanocrystallites are in the intermediate quantum confinement regime. The gain has a long tail extending to the low energy side of the absorption edge. This tail was shown theoretically to originate from the multiple excited states involved in the recombination between two and one electron-hole pairs.
Micro-objective manipulated with optical tweezers
Authors: Sasaki Minoru , Kurosawa Tutomu , Hane Kazuhiro
Published: July 2002

A microscope is described that uses a μm-sized ball lens, which is here termed micro-objective, manipulated with optical tweezers to image the side view of the arbitrary region of a sample. Since this micro-objective is small in size, it can go into a concave region to produce a local image of the inside which the conventional microscope cannot observe. Preliminary results show good lens performance from the micro-objective when combined with optical tweezers.
Influence of pressure on photoluminescence and electroluminescence in GaN/InGaN/AlGaN quantum wells
Authors: Perlin Piotr , Iota Valentin , Weinstein Bernard A. , Wiśniewski Przemek , Suski Tadeusz , Eliseev Petr. G. , Osiński Marek
Published: July 2002

We have measured photoluminescence and electroluminescence in two different types of high-brightness single-quantum-well light emitting diodes manufactured by Nichia Chemical Industries with InxGa1−xN active layers (x=0.45 and x=0.15), under hydrostatic pressures up to 8 GPa. We discovered that the pressure shift of the primary luminescence peak in each diode is very small: 12 and 16 meV/GPa for the green and blue diodes, respectively. The observed pressure coefficients are much lower than those characteristic of the energy gap in GaN (≈40 meV/GPa) or the energy gap in InN (≈33 meV/GPa). This kind of behavior is usually associated with recombination processes involving localized states. These localized states may be associated either with band tails (arising from In fluctuations in the active layer or from high density of defects), and/or with localized excitons of various types.
Avalanche upconversion in Er3+ doped fluoroindate glass
Authors: Rakov N. , de Araújo Cid B. , Messaddeq Y. , Aegerter M. A.
Published: July 2002

Avalanche upconversion is reported for Er3+ doped fluoroindate glass pumped at 633.5 nm. Strong frequency upconversion signals and intensity dependent transmittances are observed. The results of the transient and steady-state measurements agree well with the predictions of a rate-equation model which take into account cross-relaxation processes among pairs of erbium ions.
Azimuthal surface gliding of a nematic liquid crystal
Authors: Vorflusev V. P. , Kitzerow H.-S. , Chigrinov V. G.
Published: July 2002

In-plane surface gliding of a thermotropic nematic liquid crystal is investigated at substrates with weak azimuthal anchoring energy under different external electric fields parallel to the substrates. The anchoring is a result of photoinduced anisotropy in a poly-(vinyl)-alcohol alignment layer with embedded azodye molecules. The experimentally measured time constant, which describes the gliding, is inversely proportional to the electric field strength. The surface viscosity value of the liquid crystal director at the substrates extracted from the presented model is estimated as γs⩾0.33 Js/m2.
Band gap states of Ti, V, and Cr in 4H–silicon carbide
Authors: Achtziger Norbert , Witthuhn Wolfgang
Published: July 2002

Band gap states of Ti, V, and Cr in n-type 4H–SiC were investigated by radiotracer deep level transient spectroscopy (DLTS). Doping with the radioactive isotopes V48 and Cr51 was done by recoil implantation followed by annealing (1600 K). Repeated DLTS measurements during the elemental transmutation of these isotopes to Ti48 and V51, respectively, reveal the corresponding concentration changes of band gap states. Thus, six levels are identified in the band gap: Cr levels at 0.15, 0.18, and 0.74 eV, one V level at 0.97 eV, and two Ti levels at 0.13 and 0.17 eV below the conduction band edge.
Polarization field effects on the electron-hole recombination dynamics in In0.2Ga0.8N/In1−xGaxN multiple quantum wells
Authors: Buongiorno Nardelli Marco , Rapcewicz Krzysztof , Bernholc J.
Published: July 2002

The effect of the polarization field in wurtzite In0.2Ga0.8N/In1−xGaxN (x>0.8) multiple quantum wells is studied from first principles. The pyroelectric and piezoelectric fields naturally present in the system due to its wurtzite structure are strong enough to reduce the interband recombination rate in an ideal quantum well. We suggest that composition fluctuations, observed in the active region of actual devices, provide the necessary confinement for an improved recombination rate and lasing.
Irreversible refrigerators under per-unit-time coefficient of performance optimization
Authors: Velasco S. , Roco J. M. M. , Medina A. , Calvo Hernández A.
Published: July 2002

A finite-time thermodynamics analysis is used to investigate the optimal coefficient of performance (COP) of an irreversible Carnot refrigerator using the per-unit-time COP as an objective function for optimization. The model includes finite-rate heat transfers between the refrigerant and the external heat reservoirs, heat leak between heat reservoirs, and internal dissipations of the refrigerant. Heat conductances associated with heat transfers are optimized by maximizing the cooling power per unit of capital invested in the refrigerator. The obtained results are consistent with performance data for real low-temperature refrigerators.
Gain characteristics of InGaN/GaN quantum well diode lasers
Authors: Song Y.-K. , Kuball M. , Nurmikko A. V. , Bulman G. E. , Doverspike K. , Sheppard S. T. , Weeks T. W. , Leonard M. , Kong H. S. , Dieringer H. , Edmond J.
Published: July 2002

We have investigated spectroscopically the gain characteristics of InGaN quantum well (QW) diode lasers. While the transparency condition can be reached at a moderate current density, the filling of localized band-edge states is a prerequisite for achieving lasing in this profoundly nonrandom alloy.
Effects of C or Si co-implantation on the electrical activation of B atoms implanted in 4H–SiC
Authors: Itoh Hisayoshi , Troffer Thomas , Peppermuller Christian , Pensl Gerhard
Published: July 2002

The influence of co-implantation of C or Si ions on the electrical activation of B acceptors in 4H–SiC was studied by using Hall effect and photoluminescence (PL) investigations. The free hole concentration in B-implanted layers is found to increase due to co-implantation of C and to decrease owing to Si co-implantation. Hot co-implantation of C at 800 °C gives rise to a further increase of the free hole concentration. It is found that the intensity of the PL peak at a wavelength 383.9 nm, which arises from shallow B acceptors [Sridhara et al., Mater. Sci. Forum 264–268, 461 (1998)], is enhanced by the coimplantation of C. These results demonstrate that the electrical properties of B-implanted p-type layers are improved by C co-implantation. The mechanisms, which alter the electrical activation of implanted B atoms due to co-implantation of C or Si, are discussed.
Superconductor–normal–superconductor Josephson junctions fabricated by oxygen implantation into YBa2Cu3O7−δ
Authors: Kahlmann F. , Engelhardt A. , Schubert J. , Zander W. , Buchal Ch. , Hollkott J.
Published: July 2002

We report Josephson junctions in YBa2Cu3O7−δ  films, fabricated by oxygen irradiation through a 50 nm wide slit in an implantation mask. After annealing the irradiated microbridges at 500 °C in an oxygen atmosphere, this process creates a homogeneous barrier region with a reduced but finite transition temperature, allowing Josephson coupling in a temperature window of ⩽15 K. Over the entire temperature range of Josephson coupling these junctions show resistively shunted junction behavior. The exponential dependence of the critical current on temperature is in good agreement with conventional superconductor–normal–superconductor proximity effect theory.
Highly reflective GaN/Al0.34Ga0.66N quarter-wave reflectors grown by metal organic chemical vapor deposition
Authors: Someya T. , Arakawa Y.
Published: July 2002

Quarter-wave reflectors consisting of sets of GaN and Al0.34Ga0.66N layers have been grown on sapphire substrates by atmospheric-pressure metal organic chemical vapor deposition. A periodic structure with flat interfaces was observed by high-resolution scanning electron microscopy. X-ray diffraction measurements were performed to characterize the structures, from which the Al content x in the AlxGa1−xN layers was determined to be 0.34. No cracks could be seen on the surface of the reflectors by optical microscopy. The measured peak reflectivity at 390 nm increases with the number of pairs and reaches as high as 96±2% in the 35-pair reflector.