bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimating Sliding Displacement of an Unanchored Body Subjected to Earthquake Excitation
Authors: Choi Byounghoan , Tung C. C. David
Published: November 2002

A freestanding rigid body under the action of base excitation can move in many different ways. In this study, the sliding response of a body is considered. The body is placed on a horizontal base that undergoes a one-dimensional horizontal motion. In 1965, Newmark (1965) gave a simple formula to determine the sliding distance of a freestanding body subjected to a single rectangular acceleration pulse of short duration at the base. The objective of this study is to see if this formula can be applied to estimate the sliding displacement of a body under the action of real earthquakes. Newmark's formula calls for the maximum velocity of the base which information is usually not directly available. To make use of the response spectrum commonly available to the engineers, Newmark's formula is first re-derived and expressed in terms of the maximum displacement of the base, which can be determined from the absolute displacement response spectrum in low frequency range. An ensemble of 75 real earthquakes is then employed, the equation of sliding motion is solved numerically and the average of the maximum sliding displacement of the body relative to the base is computed. The computed displacement is then compared with that obtained by Newmark's formula. This is done for a body placed on the ground as well as on the floors of a building. It is shown that Newmark's formula can be used if an adjustment factor, as suggested in this study, is applied.

Key words: earthquake, sliding, unanchored body
Design Considerations for a Base-Isolated Demonstration Building
Authors: Taniwangsa Wendy
Published: November 2002

A base-isolated demonstration building (BIDB) was built in Indonesia as part of an ongoing effort by the United Nations Industrial Development Organization to promote the use of base isolation technology for common structures in earthquake-prone developing countries. The superstructure of the demonstration building is a four-story reinforced concrete frame with masonry infill walls, designed in accordance with the Indonesian Seismic Code. A specially developed isolation system for this project consisted of 16 high-damping natural rubber bearings, which were connected to the columns and foundation using recessed-type connections at the ground level. The seismic isolation provisions from the 1994 Uniform Building Code were adapted to complement the Indonesian Seismic Code requirements for this project, and site-specific spectra were developed and used for the design of the isolation system. This paper discusses the design considerations for the base-isolated demonstration building, the design and testing of the bearings and the cost-effectiveness of the isolation system. The seismic performance of the base-isolated building is discussed in the companion paper. It is expected that this newly developed isolation system, designed specifically for low-axial pressure applications, can be adopted for the earthquake protection of a variety of smaller public buildings—such as housing, schools, and hospitals—in developing countries.
Seismic Retrofitting of R/C Shaft Support of Elevated Tanks
Authors: Rai Durgesh C.
Published: November 2002

The circular, reinforced concrete (R/C) shaft-type support for elevated tanks lacks redundancy, damping and additional strength typically present in building framing systems and, therefore, should be designed for larger seismic resistance. However, the Indian seismic code IS:1893-1984 prescribes the same basic seismic force as that for the most ductile building framing system for which the design force is the least. Furthermore, the code-specified one-mass idealization of elevated water tanks is not appropriate for large (large width to depth ratio) and partially filled tanks. The low design forces lead to a weak and slender support—a very unfavorable feature in high seismic areas, as evidenced in the failure of two water tanks in the 1997 Jabalpur earthquake and a great many in the 2001 Bhuj earthquake. It is rather difficult to enhance the ductility and energy dissipation capacity of thin-walled, R/C shaft supports. Concrete jacketing is used as a retrofit measure to enhance the lateral strength and ductility by changing the failure mode of concrete crushing to a more ductile tension yielding. This scheme requires substantial strengthening of the existing foundation.
Seismic Design Based on the Yield Displacement
Authors: Aschheim Mark
Published: November 2002

Although seismic design traditionally has focused on period as a primary design parameter, relatively simple arguments, examples, and observations discussed herein suggest that the yield displacement is a more stable and more useful parameter for seismic design. The stability of the yield displacement is illustrated with four detailed examples, consisting of moment-resistant frame buildings. Each frame is designed to limit roof drift for a specific ground motion using an “equivalent” SDOF model in conjunction with Yield Point Spectra. The effectiveness of the simple design method is established by nonlinear dynamic analysis. Yield displacements were stable and consistent while the fundamental periods of vibration (and lateral stiffness) required to meet the performance objective differed substantially.
Prediction and diagnosis of faults in hydraulic systems
Authors: Angeli C , Chatzinikolaou A
Published: November 2002

Fault prediction offers a new perspective to diagnostic engineering systems by covering a wider area of the diagnostic task. This paper presents the fault prediction and diagnosis process of a knowledge-based diagnostic system that is able to predict and diagnose faults in hydraulic systems. Expert systems technology is used cooperatively with dynamic modelling information and on-line sensor information in a suitable environment for the interaction of symbolic and numerical data. This system has been successfully implemented and tested on an actual electrohydraulic system.
Precision design and numerical control machining of tapered ball-end milling cutters
Authors: Lai H-Y , Chen W-F
Published: November 2002

The paper presents a systematic modelling approach for precision design and numerical control (NC) machining of the tapered ball-end milling (TBEM) cutter that has emerged as a powerful tool for mould-making industries. The major contribution of this work is to produce a complete cutting edge that was conventionally neglected or oversimplified near the ending portion interfacing with the tapered ball end. In order to comply suitably with the requirement for a specific rotating speed, both radial and axial cutting speeds are carefully derived by using a given helical angle defined as the angle between the cutting edge and the revolving axis. Both projected profiles, one normal to the revolving axis and the other tangential to the groove, are used to produce precision sectional profiles of the grinding wheel. In compliance with maximal sectional radius of the taper, the profile of the groove section and the feeding speed of the grinding wheel are computed in sequence. By means of a two-axis NC machine, the shape of the TBEM cutter that possesses a nearly constant helical angle can be systematically designed and produced. With a slightly remedial grinding procedure at the ball end, the dimensional accuracy of the groove and the cutting edge of the TBEM cutter can be well controlled.
Direct tool-path generation from massive point input
Authors: Chui K L , Yu K M , Lee T C
Published: November 2002

The paper presents an algorithm and methodologies for the direct numerical control (NC) cutter path generation from a point cloud. Different from the existing approach, it will generate the cutter path without any reconstruction of the surface patch. Based on the scanned data, a ball nose cutter is assumed to move over the points with a specific cutter diameter. A sphere (shape of cutter) with a specific radius is formed by two or more digitized points. The approach combines point pairs to form rows of spheres. By joining the centre of spheres with are splines, the preliminary tool path is calculated. Finally, the exact tool path is found by means of a general compensation algorithm.
Pharyngo-laryngo-oesophagectomy and gastric pull-up for post-cricoid and cervical oesophageal squamous cell carcinoma
Authors: Ullah R. , Bailie N. , Kinsella J. , Anikin V. , Primrose W. J. , Brooker D. S.
Published: November 2002

Pharyngo-laryngo-oesophagectomy and gastric pull-up (PLOGP) is a complex and relatively uncommon procedure. The aim of this study is to analyse the results of PLOGP in patients with post-cricoid and cervical oesophageal squamous cell carcinomas.

This study was a retrospective review of 26 patients (11 males + 15 females, mean age 63.5 years) who underwent PLOGP from 1988 to 1997. Eighteen (69 per cent) patients were staged as T3 and eight (31 per cent) T4. Eighteen (69 per cent) patients had N0, seven (27 per cent) N1 and one (four per cent) N2 disease. Multiple primary tumours were recorded in three (11.5 per cent) patients. Four (15 per cent) patients had pre-operative radiotherapy with poor response and two (eight per cent) required emergency tracheotomy prior to surgery. Feeding jejunostomy was performed on 19 (73 per cent) and neck lymph node dissection in eight (31 per cent) patients.

The mean duration of surgery was five hours (range 3.5 to 7.5) with a mean blood loss of 840 ml (range 160 to 1800), a mean stay in ICU of 4.2 days and hospital stay ranged from nine to 84 days (mean 34). Three (11.5 per cent) patients died (pneumonia – one, congestive heart failure – one pulmonary embolus – one) in the early post-operative period. Eight (31 per cent) patients remain alive from 30 to 136 months (mean 58 months). Two (eight per cent) patients died with no evidence of disease. Thirteen (50 per cent) patients died of their disease between two to 51 months (mean 17.3 months) post-operatively. Kaplan-Meier survival estimates for one year was 65 per cent, for three years 35 per cent and for five years 26 per cent (see Figure 1). Median survival in the whole series was 18 months.

Post-operative speech was with an electrolarynx in 16 (62 per cent). One patient (four per cent) used gastric speech and one patient (four per cent) used a Blom-Singer valve effectively. Five (19 per cent) patients had no speech post-operatively. All patients maintained oral feeding. Gastric transposition constitutes a safe and reliable method of restoring the continuity of the upper digestive tract following pharyngo-laryngo-oesophagectomy.
Evaluation of a complex intervention for changing professional behaviour: the Evidence Based Out Reach (EBOR) Trial
Authors: Nazareth Irwin , Freemantle Nick , Duggan Catherine , Mason James , Haines Andy
Published: November 2002

Objectives: To identify the effect of a complex intervention (educational outreach visits by pharmacists) designed to change general practitioners' (GPs') prescribing on each step of a hypothesised pathway of change leading to the final primary trial outcome of change in prescribing.

Method: The study was undertaken in six health authorities in the North of England and six in London. We described three steps leading to this outcome: the general practices agreeing to participate; GPs in each practice attending the outreach visit conducted by the pharmacists; and the GPs' prescribing practice being influenced by these visits. The outcomes of each step were assessed using a combination of quantitative and qualitative methods.

Results: Of the 102 practices randomly selected, 75 (73.5%) agreed to participate. The odds of all the doctors attending the outreach meeting in small practices (i.e. 1-2 partners) was 6.7 (95% CI: 4.4-23.5) compared with other practices (i.e. > 3 partners). Although the pharmacists reported that they had established a good rapport at 100 (72%) first visits and had agreed management plans for 110 (79%) of these visits, they were confident that the practice was likely to alter its prescribing in only 41% of these visits. Pharmacists' and GPs' satisfaction with the outreach visits did not necessarily lead to prescribing changes after the practice visit, and the GPs' knowledge of the guidelines promoted by the pharmacists did not necessarily translate into changes in clinical practice. The main barriers to the implementation of guidelines identified by the pharmacists at the follow-up visits were organisational difficulties, the GPs' scepticism of the evidence presented to them and the doctors' lack of interest in changing their prescribing behaviour.

Conclusions: Although our study is limited by a post hoc rather than a pre hoc design, it provides a pragmatic approach to understanding the factors influencing the pathway of change in prescribing behaviour in response to academic outreach visits.
Management or leadership?
Authors: Grint Keith
Published: November 2002

This article considers the roots of the division between management and leadership, and suggests that the division encourages individuals and organizations to displace responsibility for problems in health services onto others. Given the significant limits to the power of leaders, the difficulty of establishing a science of leadership, and the increasing complexity facing health service management, the problems might appear insurmountable. However, drawing on lessons from the different approaches of the combatants in the infinitely greater complexity of the Second World War, it is suggested that trying to 'manage' the chaos by controlling it, or relying on 'leaders' to solve our problems, or buying in yet more consultants, are deeply problematic strategies; only mass leadership and collective responsibility are likely to solve the problems.
Voltage Control Methods with Grid Connected Wind Turbines: A Tutorial Review
Authors: Slootweg J. G. , de Haan S. W. H. , Polinder H. , Kling W. L.
Published: November 2002

Within electricity grid networks it is conventional for large-scale central generators to both provide power and control grid node voltage. Therefore when wind turbines replace conventional power stations on a substantial scale, they must not only generate power, but also control grid node voltages. This paper reviews the basic principles of voltage control for tutorial benefit and then considers application of grid-connected wind turbines for voltage control. The most widely used contemporary wind turbine types are considered and further detail is given for determining the range of variables that allow control.
Cost effectiveness of guideline advice for children with asthma: A literature review
Authors: Feenstra Talitha L. , Rutten‐van Mölken Maureen P.M.H. , Jager Johannes C. , van Essen‐Zandvliet Liesbeth E.M.
Published: November 2002

Asthma is an important chronic disease among children. This study reviews the cost effectiveness of interventions in the long‐term care of asthmatic children and compares these results with treatment advice in four current guidelines. Cost‐effectiveness studies were searched for in Medline, Embase, Healthstar, Biosis, and the Office of Health Economics‐Health Economic Evaluations Database (OHE‐HEED), and the Cochrane Library was searched for meta‐analyses of clinical trials.

In the four reviewed guidelines, cost effectiveness is not explicitly used as a criterion. The cost‐effectiveness studies show sufficient evidence for the cost effectiveness of treatment with inhaled steroids and for self‐management programs for severe asthmatic patients. Inclusion of these results in the guidelines would not lead to significant changes in current treatment advice. The effectiveness of various measures for trigger avoidance is not fully proven, and hence neither is their cost effectiveness. Available information on the cost effectiveness of cromolyn could be used to focus the guidelines. Finally, evidence exists that organizational interventions, e.g., the employment of asthma nurses, can result in cost savings, but it is unclear to what extent these results can be generalized.

More cost‐effectiveness studies are needed, especially on long‐acting bronchodilators and self‐management programs for mild and moderate asthma, in order to help make the guidelines more informative and reduce the differences between them. Pediatr Pulmonol. 2002; 34:442–454. © 2002 Wiley‐Liss, Inc.
Distribution in allele frequencies of predisposition‐to‐atopy genotypes in Chinese children
Authors: Leung T.F. , Tang N.L.S. , Chan I.H.S. , Li A.M. , Ha G. , Lam C.W.K. , Fok T.F.
Published: November 2002

Asthma is one of the most common chronic diseases in childhood; it is caused by a complex interaction between genetic factors and exposure to environmental allergens and irritants. Previous studies using the candidate gene approach showed that asthma was linked to a number of susceptibility genetic loci in Caucasian subjects. There are, however, only a few studies on asthma predisposition genes in the Chinese population. We studied the distribution of allele frequencies of I50V for the interleukin‐4 receptor, two polymorphisms in intron 2 and exon 7 for the high‐affinity IgE receptor (FcεRI‐β), R16G and E27Q for the β2‐adrenoceptor ,and R275Q (824G/A) for CC chemokine receptor 3 in Chinese children.

Seventy‐six patients, with a mean age of 10.6 years, and 70 age‐ and sex‐matched controls, were studied. Significantly more subjects in the asthma group had specific IgE antibodies against environmental allergens (P < 0.0001; odds ratio, 9.82). Genotyping of the six genetic markers showed that none of the six polymorphisms was associated with asthma in this cohort. The allele frequencies of I50V, R16G, and E27Q in our population were similar to those published for Asian subjects but not Caucasians. The R275Q substitution was a rare finding in our study and in the published reports.

Our results demonstrate ethnic differences in polymorphisms of atopy candidate genes. Additional studies involving larger samples are required to investigate the association between asthma or atopy and the genotypes studied to date in Chinese children. Pediatr Pulmonol. 2002; 34:419–424. © 2002 Wiley‐Liss, Inc.
Bonding and mechanical properties of ultrathin diamond-like carbon films
Authors: Beghi M. G. , Ferrari A. C. , Teo K. B. K. , Robertson J. , Bottani C. E. , Libassi A. , Tanner B. K.
Published: November 2002

Ultrathin 2-nm-thick carbon coatings are needed to increase the storage density in magnetic hard disks. We show how x-ray reflectivity, surface Brillouin scattering, resonant Raman scattering, and electron energy loss spectroscopy can measure consistently the structural and mechanical properties of these thin films. 2 nm films retain a Young’s modulus of 100 GPa.
Red electrophosphorescence from polymer doped with iridium complex
Authors: Gong Xiong , Ostrowski Jacek C. , Bazan Guillermo C. , Moses Daniel , Heeger Alan J.
Published: November 2002

We demonstrate efficient, bright red electrophosphorescent light emitting diodes (LEDs) employing tris (2,5-bis-2′-(9′,9′-dihexylfluorene) pyridine) iridium (III), [Ir(HFP)3], doped into a blend of poly(vinylcarbazole) (PVK) with 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazol (PBD). At a current density of 2.35 mA/cm2 (brightness of 169 cd/m2), the external quantum efficiency (QEext) and luminous efficiency (LE) were 5% ph/el and 7.2 cd/A, respectively. Even at 50 mA/cm2, QEext=3.4% ph/el and LE=5.2 cd/A. The electroluminescent emission is characteristic of Ir(HFP)3, with maximum at 600 nm. The devices exhibited no emission from either PVK or PBD, even at the lowest concentration of Ir(HFP)3 (0.05 wt %). The results demonstrate that electrophosphorescence with high brightness and efficiency can be achieved from polymer-based LEDs fabricated by processing the active materials from solution.
Torsional frequency response of cantilever beams immersed in viscous fluids with applications to the atomic force microscope
Authors: Green Christopher P. , Sader John E.
Published: November 2002

The frequency response of a cantilever beam is strongly dependent on the fluid in which it is immersed. In a companion study, Sader [J. Appl. Phys. 84, 64, (1998)] presented a theoretical model for the flexural vibrational response of a cantilever beam, that is immersed in a viscous fluid, and excited by an arbitrary driving force. Due to its relevance to applications of the atomic force microscope (AFM), we extend the analysis of Sader to the related problem of torsional vibrations, and also consider the special case where the cantilever is excited by a thermal driving force. Since longitudinal deformations of AFM cantilevers are not measured normally, combination of the present theoretical model and that of the companion study enables the complete vibrational response of an AFM cantilever beam, that is immersed in a viscous fluid, to be calculated.
Model for electrical isolation of GaN by light-ion bombardment
Authors: Titov A. I. , Kucheyev S. O.
Published: November 2002

We present a model for electrical isolation of GaN by light-ion bombardment. In our model, a decrease in the concentration of free carriers responsible for isolation is assumed to be due to the formation of complexes of ion-beam-generated point defects with shallow donor or acceptor dopants. These defect interaction processes are described in terms of quasichemical reactions. Results show that our model can adequately describe experimental data for electrical isolation in the case of MeV light-ion irradiation of n-GaN.
Magnetic force microscopy of ferromagnetic nanoparticles formed in Al2O3 and SiO2 by ion implantation
Authors: Vallet C. E. , White C. W. , Withrow S. P. , Budai J. D. , Boatner L. A. , Sorge K. D. , Thompson J. R. , Beaty K. S. , Meldrum A.
Published: November 2002

Magnetic force microscopy (MFM) has been used to investigate the properties of ferromagnetic FePt nanoparticles produced by the implantation of Fe and Pt ions into single-crystal Al2O3 or fused SiO2 followed by thermal processing. The MFM results are compared to cross-section and plan view transmission electron microscopy images of the same samples. We demonstrate that MFM can detect magnetism in nanosized particles that are situated several hundred nm below the sample surface. MFM is shown to be a promising tool for studying the characteristics of magnetic nanoparticles produced by ion implantation.
Coverage dependence of hydrogen absorption into Pd(111)
Authors: Nobuhara K. , Kasai H. , Nakanishi H. , Okiji A.
Published: November 2002

We investigate the absorption of H into Pd(111). In particular, we study the coverage dependence of the H-induced relaxation of the Pd lattice and the corresponding variation in the energy barrier for H absorption. We calculate, within density functional theory, the corresponding potential energy curves for the case where the H impinges on a frozen lattice surface, and on a lattice surface that is allowed to undergo H-induced relaxation. We consider the case where the final H coverage θ=1/9 and 1/4. From the results, it can be seen that, for both coverages, the energy barrier for H absorption takes a minimum value at a face-centered-cubic hollow site on the frozen lattice surface. Furthermore, the barrier is lowered by relaxation of the Pd lattice. The H-induced relaxation of the Pd lattice when θ=1/9 is more remarkable than when θ=1/4.
Effect of structure on radiative recombination processes in amorphous silicon suboxide prepared by rf sputtering
Authors: Yoshida Ken’ichi , Umezu Ikurou , Sakamoto Naomichi , Inada Mitsuru , Sugimura Akira
Published: November 2002

We studied the relationship between the structure and photoluminescence (PL) mechanism of amorphous silicon suboxide (a-SiOx) thin films prepared by the cosputtering method. The microscopic structure of the film was estimated by x-ray photoemission spectroscopy and infrared absorption spectroscopy. Electronic states were investigated by optical absorption and photothermal deflection spectroscopy. The results indicate that the film is separated into two types of regions: Si-rich cluster regions and amorphous SiO2-rich regions. The size of the Si-rich cluster is estimated, according to the quantum confinement model in which no other effects are assumed to exist, to be less than several nm, when the oxygen fraction x is larger than 1.0. The PL peak energy increased monotonically with the x value, whereas it showed different temperature dependences between the larger x value samples and the smaller ones. The PL characteristics observed can consistently be explained by assuming that there are two origins for PL in the present samples: recombination between the tail states in a-Si-rich clusters and luminescence from localized states around the boundaries between the a-Si cluster and the a-SiO2 matrix.
Photocrystallization of amorphous ZnO
Authors: Asakuma Naoko , Hirashima Hiroshi , Imai Hiroaki , Fukui Toshimi , Maruta Ayako , Toki Motoyuki , Awazu Koichi
Published: November 2002

Structural changes stimulated by UV light irradiation for sol-gel-derived amorphous ZnO were investigated. Transformation of amorphous ZnO into the wurtzite phase was achieved by irradiation of 4.9 eV photons in air using a conventional low-pressure mercury lamp. On the other hand, the crystallization was not observed by UV irradiation in vacuum. Cleavage of the Zn–O network with electronic excitation and subsequent oxidation with activated oxygen species are deduced to be essential for the formation of the ordered structure from the amorphous phase.
Local structure of Co nanocrystals embedded in hydrogenated amorphous carbon: An x-ray absorption study
Authors: Kolobov A. V. , Tominaga J. , Zvonareva T. K. , Ivanov Omskii V. I. , Oyanagi H.
Published: November 2002

Co nanocrystals embedded into a hydrogenated amorphous carbon matrix have been studied. The formation of the nanocrystals has been detected by transmission electron microscopy. The local structure of the nanocrystals was investigated by x-ray absorption fine-structure spectroscopy. We found that in as-deposited samples, Co atoms are predominantly coordinated by carbon with the fraction of Co–Co bonds increasing with an increase in the Co content. In the annealed samples, Co nanocrystals are formed with a characteristic size of 20 nm and with the structural parameters similar to that of bulk Co. About 30% of Co atoms remain bonded to the amorphous carbon matrix in the annealed sample.
Piezoelectric properties of 3-Xperiodic Pb(ZrxTi1−x)O3–polymer composites
Authors: Smay James E. , Cesarano Joseph , Tuttle Bruce A. , Lewis Jennifer A.
Published: November 2002

The piezoelectric properties of lead zirconate titanate (PZT)–polymer composites were studied as a function of composition and phase connectivity. PZT skeletal structures were fabricated by robotic deposition, densified at 1275 °C, and subsequently infiltrated with epoxy to produce the desired PZT–polymer composites. These 3-X structures consisted of a three-dimensional lattice of PZT rods (3–3) embedded in a polymer matrix, a PZT lattice/polymer matrix capped with PZT face plates (3–2), or PZT lattice/polymer matrix capped with PZT face plates and encircled by a solid PZT ring (3–1). The PZT:polymer ratio was varied systematically by changing the lattice (rod) spacing in each composite architecture. The concentration of PZT pillars, which formed along the poling direction at the intersections between PZT rods, varied as the PZT volume fraction squared. These 3-X composites displayed enhanced hydrostatic figures of merit relative to monolithic PZT due to stress concentration in the PZT pillars and their dramatically reduced dielectric constant, with the highest values found for the 3–2 and 3–1 composites. Our experimental observations were compared to theoretical predictions based on an isostrain, unit cell model modified to account for the partial support of stress in the stiff epoxy phase.
Stability studies of ultrashallow junction formed by low energy boron implant and spike annealing
Authors: Shao Lin , Wang Xuemei , Rusakova Irene , Chen Hui , Liu Jiarui , Bennett Joe , Larson Larry , Jin Jianyue , van der Heide P. A. W. , Chu Wei-Kan
Published: November 2002

The stability of junctions formed by spike anneal remains a crucial issue for the device performance. In this study, 0.2 keV B implanted silicon was thermally spike annealed at 1100 °C. Samples were then furnace annealed under temperatures between 550 and 750 °C to study their stabilities. We have observed the anomalous diffusion of boron during the post-spike furnace annealing in nitrogen ambient. The anomalous behavior shows two features in the near-surface region and in the tail region. B diffusion in the tail region was transient, e.g., with an enhancement of 103×equilibrium at 700 °C for the first 60 s. In the near-surface region, a large number of B atoms move toward the native oxide/Si interface with a diffusion rate also transient and similar to that observed in the tail region. It is indicated that interstitials are generated due to spike annealing and will cause instability of the junction during the following thermal processes.
Measurements of atomic carbon density in processing plasmas by vacuum ultraviolet laser absorption spectroscopy
Authors: Tanaka Norifusa , Tachibana Kunihide
Published: November 2002

Measurements of the absolute C atom density in an inductively coupled plasma (ICP) source were carried out by using vacuum ultraviolet (VUV) laser absorption spectroscopy with the resonance lines of C atoms at wavelengths around 94.5 and 165.7 nm. A tunable VUV laser covering these wavelength ranges was generated by a two-photon resonance/four-wave mixing technique in Xe gas. No absorption at around 94.5 nm could be observed, but from the absorption spectra around 165.7 nm we successfully derived the absolute density of C atoms in the ICP source. The obtained values varied from 1×1010 to 1×1011 cm−3, depending on the source gas and operating conditions of the plasma source. The relatively small density values compared to other atomic species are attributed to the large loss rates, which mostly occur on the surface.
Effect of Al, Cu, Ga, and Nb additions on the magnetic properties and microstructural features of sintered NdFeB
Authors: Pandian S. , Chandrasekaran V. , Markandeyulu G. , Iyer K. J. L. , Rama Rao K. V. S.
Published: November 2002

This study describes the relative effect on the permanent magnet characteristics viz. remanence (Br), intrinsic coercivity (Hci), Curie temperature (TC), and rectangularity of the intrinsic demagnetization curve, when Al, Cu, Ga, and Nb are added individually to NdFeB. Each elemental addition causes significant improvement in Hci but the level of improvement differs from one additive element to the other. The addition of Nb is favored over other elements for realizing maximum enhancement in Hci and rectangularity of the demagnetization curve. The microstructural features of the sintered samples of NdFeB with elemental addition show the formation of a new phase, in addition to the phases (φ,η, and Nd-rich) generally found in the ternary sample. The factors influencing the permanent magnet characteristics of sintered samples are the distribution of the Nd-rich phase in the intergranular region, the size and distribution of the minor phases at the grain junctions, the formation and distribution of new phases due to alloying addition, and the solubility of the dopant element in various phases coexisting in the sample.
Optical pump and probe measurement of the thermal conductivity of low-k dielectric thin films
Authors: Daly Brian C. , Maris Humphrey J. , Ford Wayne K. , Antonelli George A. , Wong Larry , Andideh Ebrahim
Published: November 2002

We report on measurements of the thermal conductivity of a number of amorphous materials, including fluorinated silicate glass and carbon-doped oxides. These materials are of interest to the microelectronics industry for use as insulators in microprocessors. The samples measured were in the form of thin films deposited onto silicon substrates. Measurements were made using an optical technique in which the film is heated with a picosecond light pulse, and a time-delayed, probe light pulse is used to measure the temperature of the film as a function of time. We find that the thermal conductivity of these low-k dielectrics is reduced by as much as a factor of 5 with respect to amorphous SiO2. Most measurements were made at room temperature, but for two samples we additionally report on measurements for the temperature range 150–375 K. Results for the thermal conductivity for these materials are compared to theories of heat flow in amorphous solids.
Collective molecular rotation in D2O
Authors: Shelton David P.
Published: November 2002

The hyper-Rayleigh scattering (HRS) spectrum of liquid D2O was measured at 90° scattering angle with linearly polarized light (VV, HV, VH, and HH polarization geometries). The VV and HV spectral profiles are similar, but the HV and VH spectral profiles are very different. This can be accounted for by scattering from nonlocal modes of molecular reorientation. The local mode and the transverse nonlocal mode both result in Lorentzian spectral components with width increasing from 1.1 cm−1 at T=23 °C to 3.3 cm−1 at 80 °C. The spectrum due to the longitudinal nonlocal mode has width <0.3 cm−1. A relatively weak and very broad collision-induced spectral component is also observed. The relative integrated intensities of the local, transverse and longitudinal components of the VH HRS spectrum are 21%, 45%, and 34%, indicating that molecular reorientation in water is predominantly a collective effect.
Magnetic switching and magnetoresistance in nanoscale spin tunnel junctions
Authors: Urech M. , Korenivski V. , Haviland D. B.
Published: November 2002

Co/AlO x / Co magnetic tunnel junctions in both multijunction arrays and double-tunnel junction geometries have been studied. The junctions exhibit magnetoresistance (MR) and change their resistance by ∼10% depending on the relative magnetic orientation of the tunnel junction electrodes. MR measurements show a strong dependence on the device geometry. We find that it is necessary to form tunnel junctions with electrode width ∼70 nm for the magnetic switching at the tunnel junction to be clean and single domain like.
Ferromagnetism in fractal-based complexes
Authors: Ugajin Ryuichi
Published: November 2002

Ferromagnetism in fractal-based complexes, which are generated using the dielectric-breakdown model with appropriate controls of their fractal dimension, is investigated using the standard Monte Carlo simulations. The difference in the fractal dimensions of a nerve-cell-like complex creates a heterotic phase in which the spin-ordered Gibbs state of a somatic nucleus and the spin-disordered Gibbs state of dendritic portions are orchestrated. On the other hand, a nebulalike complex in which many sites are grown on a dendritic substrate behaves as a single ferromagnetic system and is characterized by a particular Curie temperature.
Effect of crystallographic orientation on grain size distribution
Authors: Valcu Bogdan , Takahashi Yoshio , Bertram H. Neal
Published: November 2002

The control of grain size statistics is essential in the manufacture of granular thin films used in high-density recording. In this article transmission electron microscope observations of perpendicular media are shown that indicate larger grain size dispersion than in typical longitudinal media. We explain this result by utilizing a simple Voronoi model that includes the crystallographic symmetry. The higher symmetry of the magnetic layer in perpendicular media increases the grain size dispersion. It is argued that out-of plane dispersion of the vertical axes of grains, important in longitudinal media, further enhances the differences between grain size distributions in these two types of media. The results are confirmed by experimental measurements.
Leakage current behavior of SrBi2Ta2O9 ferroelectric thin films on different bottom electrodes
Authors: Das Rasmi R. , Bhattacharya P. , Katiyar Ram S. , Bhalla A. S.
Published: November 2002

SrBi 2 Ta 2 O 9 thin films on various bottom electrodes/substrates such as Pt/TiO2/SiO2/Si (Pt) and LaNiO3/Pt/TiO2/SiO2/Si (LNO) were grown using the pulsed laser deposition technique. X-ray diffraction studies revealed that as-grown (at 500 °C) films were crystallized in the layered structure after annealing at 800 °C. Films grown on platinized silicon exhibited maximum value of remanent polarization (2Pr∼21.5 μC/cm2) with coercive field (Ec) of ∼67 kV/cm. The dielectric constant and dissipation factor also decreased with the introduction of a 50 nm conducting LaNiO3 oxide electrode at the interface of Pt and SBT thin films, which might be contributed by the high resistive oxide electrode layers. The dc leakage characteristics of the films were studied at elevated temperatures and the data were fitted with the Schottky emission model. The barrier heights of the films grown on Pt and LNO substrates were estimated to be 1.27 and 1.12 eV with optical dielectric constants of 6.3 and 17, respectively. The reduction in barrier height was attributed to the lower work function of the LNO electrode.
Properties of hafnium oxide films grown by atomic layer deposition from hafnium tetraiodide and oxygen
Authors: Kukli Kaupo , Ritala Mikko , Sundqvist Jonas , Aarik Jaan , Lu Jun , Sajavaara Timo , Leskelä Markku , Hårsta Anders
Published: November 2002

Polycrystalline monoclinic HfO2 films were atomic layer deposited on Si(100) substrates by a nonhydrous carbon-free process of HfI4 and O2. The oxygen to hafnium ratio corresponded to the stoichiometric dioxide within the limits of accuracy of ion beam analysis. A 1.5–2.0 nm thick SiO2 interface layer formed between the HfO2 films and Si substrates. Hysteresis of the capacitance–voltage curves was observed in Al/HfO2/p-Si(100) structures with oxide grown in the substrate temperature range of 570–755 °C. The hysteresis ceased with an increase in O2 pressure. The effective permittivity of the dielectric layers varied between 12 and 16. The breakdown voltages were found to be lower in the case of higher oxygen doses and higher HfO2 deposition temperatures.
Self-assembled quantum dots: A study of strain energy and intersubband transitions
Authors: Lin Yih-Yin , Singh Jasprit
Published: November 2002

In this article we examine the strain energy and intersubband optical transitions in self-assembled dots on GaAs and InP substrates. On the GaAs substrate, in addition to the InAs/GaAs dots we examine strain compensated InAs/GaAsP dots on GaAs substrates. We find that the strain energy configuration profile shows that there is preference for certain dot sizes and shapes. Our calculated dot sizes agree well with experimental observations. We find that the addition of phosphorus in the covering matrix reduces the total strain energy of the system with little effects on the intersubband transition strength for the vertical incident light. The reduced strain energy should allow one to incorporate a large number of dot array stacks for devices such as lasers and detectors and thus increases the optical responses. Our studies for the InAs/InP system show that due to the lower strain mismatch there is no particular preference for dot sizes. The optical response for intersubband transitions is weaker and occurs at longer wavelengths in comparison to the InAs/GaAs dots.
Ejecta particle size distributions for shock loaded Sn and Al metals
Authors: Sorenson D. S. , Minich R. W. , Romero J. L. , Tunnell T. W. , Malone R. M.
Published: November 2002

When a shock wave interacts at a metal vacuum interface “ejected particulates” (ejecta) can be emitted from the surface. The mass, size, shape, and velocity of the ejecta varies depending on the initial shock conditions and the material properties of the metal sample. To understand this phenomena, experiments have been conducted at the Pegasus Pulsed Power Facility located at Los Alamos National Laboratory. For the experiments reported in this article, the facility is used to implode a cylinder to a velocity of 3.4 mm/μs. When this cylinder impacts a smaller diameter target cylinder, shock pressures of 30 and 40 GPa can be obtained in Al and Sn metals, respectively. Ejecta formation proceeds as the shock wave in the metal sample interacts at the metal vacuum interface. The size of the ejected particles is then measured using an in-line Fraunhofer holography technique. In this report, ejecta particle size distributions will be presented for shocked Al and Sn metals. The measured particle size distributions exhibit a power law scaling with critical exponents in the same universality class as for two- or three-dimensional percolation theory. The similarity suggests that fragmentation has its origin in an instability that manifests large-scale fluctuations at breakup.
Reduced microwave losses of YBa2Cu3O7−δ thin films on electro-optic LiNbO3 crystals
Authors: Fàbrega L. , Rubı́ R. , Fontcuberta J. , Sánchez F. , Ferrater C. , Garcı́a-Cuenca M. V. , Varela M. , Collado C. , Mateu J. , Menendez O. , O’Callaghan J. M.
Published: November 2002

We report on the growth of epitaxial YBa2Cu3O7 thin films on X-cut LiNbO3 single crystals. The use of double CeO2/YSZ buffer layers allows a single in-plane orientation of YBa2Cu3O7, and results in superior superconducting properties. In particular, surface resistance Rs values of 1.4 mΩ have been measured at 8 GHz and 65 K. The attainment of such low values of Rs constitutes a key step toward the incorporation of high Tc materials as electrodes in photonic and acoustic devices.
Two-dimensional electron-gas actuation and transduction for GaAs nanoelectromechanical systems
Authors: Tang H. X. , Huang X. M. H. , Roukes M. L. , Bichler M. , Wegscheider W.
Published: November 2002

We have fabricated doubly clamped beams from GaAs/AlGaAs quantum-well heterostructures containing a high-mobility two-dimensional electron gas (2DEG). Applying an rf drive to in-plane side gates excites the beam’s mechanical resonance through a dipole–dipole mechanism. Sensitive high-frequency displacement transduction is achieved by measuring the ac emf developed across the 2DEG in the presence of a constant dc sense current. The high mobility of the incorporated 2DEG provides low-noise, low-power, and high-gain electromechanical displacement sensing through combined piezoelectric and piezoresistive mechanisms.
Predicting the permeability of sandstone from image analysis of pore structure
Authors: Lock Peter A. , Jing Xudong , Zimmerman Robert W. , Schlueter Erika M.
Published: November 2002

A model is developed that allows accurate prediction of the permeability of a core sample of sedimentary rock, based on two-dimensional image analysis of its pore structure. The pore structure is idealized as consisting of a cubic network of pore tubes, with the tubes having an arbitrary distribution of cross-sectional areas and shapes. The areas and perimeters of the individual pores are estimated from image analysis of scanning electron micrographs of thin sections, with appropriate stereological corrections introduced to account for the angle between axis of the pore tube and plane of the thin section. The individual conductances of each tube are estimated from the measured areas and perimeters, using the hydraulic radius approximation. Variations in the pore diameter along the length of the tube are accounted for with a “constriction factor” whose derivation is based on laminar flow through an irregular tube. Effective-medium theory is used to find the effective single-tube conductance, based on the measured distribution of individual conductances. This procedure is applied to several consolidated North Sea reservoir sandstones, and some outcrop sandstones, with permeabilities ranging from 20 to 1400 mD. The predicted permeabilities are typically within a factor of 2 of the measured values, with an average error in logk of only 0.168.
Weak localization and magnetoresistance of island-like thin copper films
Authors: Dai Jianbiao , Tang Jinke
Published: November 2002

We report magnetotransport and weak localization effects in island-like thin copper films. The samples show significant negative magnetoresistance (NMR) when a perpendicular magnetic field (H⊥>0.25 T) is applied. When the field is parallel to the film, the samples also show NMR for H∥>2.5 T, below which positive magnetoresistance (PMR) is found. The temperature dependence of the resistivity and NMR in both perpendicular and parallel fields are due to the weak localization effect in the two-dimensional (2D) system. The observation of NMR in the parallel field is in agreement with Altshuler and Aronov’s prediction [B. L. Altschuler and A. G. Aronov, Zh. Eksp. Teor. Fiz. Pis’ma Red. 33, 515 (1981)]. The PMR observed at low field is analyzed mainly in terms of the spin–orbit scattering, although other mechanisms may also be possible. It is suggested that the island-like geometry can significantly affect the localization and magnetotransport in 2D metallic films.
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ordering and microstructure of FePt thin films with Cu, Ag, and Au additive
Authors: Platt C. L. , Wierman K. W. , Svedberg E. B. , van de Veerdonk R. , Howard J. K. , Roy A. G. , Laughlin D. E.
Published: November 2002

The influence of Cu, Ag, and Au additives on the L10 ordering, texture, and grain size of FePt thin films has been examined. Lattice parameter data indicated that Au and Ag additives tended to segregate from FePt, but Cu alloyed with FePt. FePt films with Au or Ag additive showed 1–2 kOe higher coercivity values compared to a pure FePt film after annealing at 450 °C and above for 10 min. The addition of at least 20 vol. % Cu to FePt boosted average coercivity values and increased (001)/(002) x-ray peak intensity ratios, suggesting an accelerated L10 ordering process for annealing temperatures exceeding 350 °C. Decreasing the film thickness promoted (001) film texture in FePt+20% Cu films, but higher annealing temperatures were required to achieve large coercivity. Au and Ag limited the average grain size compared to a pure FePt film. Cu additive increased the average grain size and film roughness.
Growth and dielectric behavior of radio frequency magnetron-sputtered lead magnesium niobate thin films
Authors: Jaydeep Shreekala , Yadav S. , Malla B. P. , Kulkarni A. R. , Venkatramani N.
Published: November 2002

Lead magnesium niobate (PMN) thin films have been grown on quartz/Cr/Au substrates from a single target source by rf magnetron sputtering at room temperature. Sputtering parameters and the post-annealing temperature have been optimized to obtain phase pure PMN films. Grain sizes, obtained from atomic force microscopy and x-ray line broadening, show nanosized grains of nearly 45 nm. Dielectric response of photolithographically patterned quartz/Cr/Au/PMN/Au structures have been studied. The effect of film thickness and frequency on the dielectric constant has been examined at room temperature. The dielectric constant and remanent polarization show linear thickness dependence.
Thermoacoustic heat pumping effect in a Gifford–McMahon refrigerator
Authors: Sunahara S. , Biwa T. , Mizutani U.
Published: November 2002

The heat exchange process between the working helium gas and the regenerator materials in a Gifford–McMahon refrigerator is studied from the viewpoint of thermoacoustic phenomena, by measuring the cooling power as a function of the phase angle between pressure and displacement oscillations of the working gas. It is found that the optimum phase angle maximizing the cooling power dramatically increases when the operating temperature decreases below 20 K. This behavior represents the progress of the irreversible heat exchange process due to the reduction of the thermal diffusivity of helium gas.