bluuebunny/crossref_metadata_2025 huggingface dataset:
Midwifery Management of First Trimester Bleeding and Early Pregnancy Loss
Authors: Thorstensen Katrina Alef
Published: October 2002

As many as 25% of women experience bleeding in the first and early second trimester of pregnancy; about half of these will have a miscarriage or, more rarely, ectopic or molar pregnancy loss. This can be a difficult time for women because of the uncertainty of the outcome, lack of preventative measures, and emotional significance of early pregnancy loss. The qualities that characterize midwifery care, including providing complete information, encouraging self‐determination, and being sensitive to the emotional state, are particularly important at this time. This article reviews the epidemiology; physiologic process; signs and symptoms of first trimester bleeding; miscarriage and other early pregnancy losses; and methods of clinical, biochemical, and sonographic evaluation. A framework to guide midwifery evaluation and management, based on confirmation of an intrauterine pregnancy followed by the determination of viability, is presented. Surgical, medical, and expectant management of nonviable pregnancy, management of viable pregnancy when bleeding persists, and follow‐up care, including screening for psychological sequelae, are discussed. Case studies and specific clinical guidelines for midwifery care, consultation, collaboration, and referral are included. Understanding the emotional significance of first trimester bleeding and loss as a basis for sensitive care throughout the management process is addressed.
DEVELOPING AN EVIDENCE‐BASED PRACTICE PROTOCOL: IMPLICATIONS FOR MIDWIFERY PRACTICE
Authors: Carr Katherine Camacho
Published: October 2002

Evidence‐based practice is defined and its importance to midwifery practice is presented. Guidelines are provided for the development of an evidence‐based practice protocol. These include: identifying the clinical question, obtaining the evidence, evaluating the validity and importance of the evidence, synthesizing the evidence and applying it to the development of a protocol or clinical algorithm, and, finally, developing an evaluation plan or measurement strategy to see if the new protocol is effective.
Midwifery Co‐Management of Hyperemesis Gravidarum
Authors: Slager Joan , Lavery J. Patrick
Published: October 2002

Hyperemesis gravidarum is an infrequent, yet significant, maternal complication of pregnancy. Beginning with the frequently experienced nausea and vomiting of pregnancy, symptoms can progress to hyperemesis, a debilitating condition affecting maternal and fetal well‐being. A basic understanding of the pathophysiology of the disease process and an awareness of the therapeutic interventions that are available will facilitate midwifery planning for either the collaborative care or the potential referral to medical management, both of which may be required with this clinical entity. The diagnosis and initial management of hyperemesis is within the purview of midwifery care. As certain critical features of duration and severity evolve, medical collaboration and ultimate hospitalization may be required. For those few individuals requiring the most intense level of care, the critical support and encouragement afforded by midwifery participation will contribute to timely resolution of this debilitating condition. This article discusses the continuum from differential diagnosis to ultimate care of the woman who has excessive nausea and vomiting of pregnancy. Collaboration among health care providers will allow all to exercise their respective skills in achieving the optimum in safe therapy and support for their patients.
MEDICALLY COMPLEX PREGNANCY: A CASE REPORT ILLUSTRATING CNM/MD COLLABORATIVE MANAGEMENT
Authors: Gray Molly , D'Amato Lisa
Published: October 2002

In contemporary society, many women with complex medical conditions are attempting fertility and becoming pregnant. The patient presents with an impressive medical complication, yet many of her key educational and psychosocial needs are typical of those for any pregnant woman. Striving for “normalcy,” she may actively seek midwifery care to help her create a family‐centered birth experience. Indeed, the midwife practicing with physician colleagues may have the opportunity to collaboratively manage increasingly complex cases. This article describes the case of collaborative management during pregnancy and delivery of a patient with the cardiac syndrome Wolff‐Parkinson White syndrome (WPW). First diagnosed with WPW at the age of 13, the patient's condition was initially controlled with oral medication. Eventually, the patient's symptomology worsened and required repeated treatment by cardiac ablation of the accessory pathway. Illustrative of the possibilities for enhanced care of the medically complex pregnant patient via collaborative management, the discussion details not only the pertinent physiologic events but the benefits and process of care. A review of the cardiophysiology of WPW is also presented
ACNM ESSENTIAL DOCUMENTS: A MIDWIFE'S SUIT OF ARMOR
Authors: King Tekoa , Summers Lisa , Williams Deanne
Published: October 2002

As the oldest professional midwifery organization in the United States, The American College of Nurse Midwives (ACNM) represents the profession of midwifery in the United States and sets standards for education, certification, and practice. The ACNM has generated and revised several critical documents that provide guidance for the scope of midwifery practice, individually and collectively. This article reviews essential ACNM documents and their role in supporting professional midwifery.
THE EVOLVING SCOPE OF NURSE‐MIDWIFERY PRACTICE IN THE UNITED STATES
Authors: Burst Helen Varney , Stone Susan E.
Published: October 2002

The purpose of this article is to review the evolving scope of practice of nurse‐midwifery since its introduction in the United States in 1925. Factors that contributed to the profession's evolution in practice are identified.
Lubricated friction and volume dilatancy are coupled
Authors: Demirel A. Levent , Granick S.
Published: October 2002

Dilation (expansion of film thickness) by ∼0.1 Å, which is less than one-tenth of the width of confined fluid molecules, was observed when confined films crossed from the resting state (“static friction”) to sliding (“kinetic friction”). These measurements were based on using piezoelectric bimorph sensors possessing extremely high resolution for detecting position changes, during the course of sliding molecularly thin films of squalane, a model lubricant fluid, between atomically smooth single crystals of mica. Detailed inspection of energy balance shows that the dilation data and the friction forces satisfied energy conservation of identifiable energies at the slip point, from static to kinetic friction. This shows experimentally, for the first time to the best of our knowledge, a direct coupling between friction forces and decrease in the mean density of the intervening molecularly thin fluid.
Geometry optimization of triply charged yttrium-doped helium clusters: HenY3+
Authors: Wesendrup Ralf , Esperenza Moyano Gloria , Pernpointner Markus , Schwerdtfeger Peter
Published: October 2002

Global minima of the Coulomb-stable clusters HenY3+ were calculated using a simulated annealing procedure based on state-of-the-art two-body potentials for the He–Y3+ and He–He pair interactions, and compared with subsequent density-functional theory (DFT). Both approaches yield very similar symmetries for the global minima up to a number of 12 helium atoms when occupation of the second helium shell becomes more favorable at the DFT level. In the simulated annealing two-body approach the second shell is occupied from atom 17 onwards. Both methods predict an exceptional stability for the icosahedral cluster He12Y3+.
A combined nuclear dynamics and electronic study of the coupling between the internal rotation of the methyl group and the intramolecular proton transfer in 5-methyltropolone
Authors: Vendrell Oriol , Moreno Miquel , Lluch José M.
Published: October 2002

In this work we have theoretically studied the splittings experimentally observed in 5-methyl tropolone in the first excited singlet state, S1. Tropolone shows a vibrational level splitting due to delocalization of the wave function over the symmetric potential energy double well in the proton-transfer coordinate. This splitting dramatically decreases when asymmetry is introduced. However, a noticeable splitting is observed in 5-methyltropolone internal rotational levels indicating a coupling between methyl internal rotational and proton-transfer degrees of freedom. We have developed a reduced-dimensionality model for the potential energy surface (PES), which maintains the main characteristics of the molecule and that can be fitted to electronic structure calculations. For this PES we have calculated stationary wave functions using a full quantum method. We have performed test calculations using different energy barrier heights in order to observe the splitting behavior for this kind of molecules. In order to fit our PES to the real system surface we have also performed an extensive set of ab initio calculations in the S1 state using different methods. Finally we present a discussion about such electronic calculations, showing the present difficulties to obtain excited state potential energy surfaces with great accuracy beyond the Franck–Condon vertical excitation region.
Computer simulations of hyperbranched polymers: The influence of the Wiener index on the intrinsic viscosity and radius of gyration
Authors: Sheridan Peter F. , Adolf David B. , Lyulin Alexey V. , Neelov Igor , Davies Geoffrey R.
Published: October 2002

The influence of the Wiener index on solution properties of trifunctional hyperbranched polymers has been investigated using Brownian dynamics simulations with excluded volume and hydrodynamic interactions. A range of degrees of polymerization (N) and degrees of branching (DB) were used. For each DB and N, several molecules with different Wiener indices (W) were simulated, where W depends on the arrangement of branch points. The intrinsic viscosity and the radius of gyration (Rg) of HPs were both observed to scale with W at a constant N via a power law relationship, as found in the literature. Through their relationships to W, an expression relating intrinsic viscosity to Rg was obtained. This relationship is found to fall centrally between the predictions of Flory and Fox for linear polymers and that of Zimm and Kilb for branched polymers. Molecular shape in solution is also found to depend on W and N, as observed through the W dependence of the ratio of Rg to the hydrodynamic radius, Rh.
Potential of mean force between a spherical particle suspended in a nematic liquid crystal and a substrate
Authors: Kim Evelina B. , Faller Roland , Yan Qiliang , Abbott Nicholas L. , de Pablo Juan J.
Published: October 2002

We consider a system where a spherical particle is suspended in a nematic liquid crystal confined between two walls. We calculate the liquid-crystal-mediated potential of mean force between the sphere and a substrate by means of Monte Carlo simulations. Three methods are used: a traditional Monte Carlo approach, umbrella sampling, and a novel technique that combines canonical expanded ensemble simulations with a recently proposed density-of-states formalism. The latter method offers advantages in that it facilitates good sampling of phase space without prior knowledge of the energy landscape of the system. The resulting potential of mean force, computed as a function of the normal distance between the sphere and a surface, suggests that the sphere is attracted to the surface, even in the absence of attractive molecular interactions.
Extensivity and the contracted Schrödinger equation
Authors: Herbert John M. , Harriman John E.
Published: October 2002

We provide an extensive formulation of the contracted Schrödinger equation and other reduced eigenvalue equations. Nonextensive (unconnected) terms in these equations cancel exactly, leading to completely connected one- and two-electron equations that together are equivalent to the Schrödinger equation. We discuss how these equations can be solved for the one- and two-electron cumulants. These cumulants yield a two-electron reduced density matrix that is necessarily size consistent, even for an approximate solution. A diagram technique, introduced to aid the formal manipulations, clarifies the connection between density matrix reconstruction and solution of the CSE.
A five-dimensional quantum mechanical study of the H+CH4→H2+CH3 reaction
Authors: Szichman Henrik , Baer Roi
Published: October 2002

A quantum mechanical approach to the treatment of atom–penta-atom abstraction process of the type E+FABCD→EF+ABCD is presented. The initial 12 degrees of freedom problem is simplified to a reaction having only 7 active degrees of freedom, emulating a rotating–stretching FABCD molecule. Its internal angles are frozen at their equilibrium values as the molecule collides with an attacking E atom. This model is then applied to the study of the H+CH4→H2+CH3 reaction, predicting for the first time remarkable non-Arrhenius behavior. The dynamics was based on the Jordan and Gilbert analytical potential energy surface (JG-PES). The method employs the infinite-order-sudden-approximation (IOSA) method for the methane (CH4) rotations. Next, the coupled states (CS or jz) approximation is used to decouple the total angular momentum J from internal rotational operators. Finally, precessions are overcome by averaging the JG-PES around the out-of-plane angle in the attacking atom geometry. This treatment leads to a five-dimensional fully quantum mechanical computation for determining the total reaction probabilities, cross sections, and temperature-dependent rate constants. Comparing with experiment, the calculated rate constants show good agreement at high temperatures. At lower temperatures there are pronounced tunneling effects. A detailed comparison is made to other theoretical and experimental treatments.
Molecular dynamics simulations of the liquid–vapor interface of a molten salt. III. Size asymmetry effects and binary mixtures
Authors: Aguado Andrés , Madden Paul A.
Published: October 2002

The structure and surface tension of the liquid–vapor interface of pure LiCl and KCl molten salts and of LiCl-KCl binary mixtures of different concentrations have been studied by using molecular dynamics simulations and a slab geometry. For the surface tension and its temperature and composition dependences, good agreement with experimental determinations is achieved. A comparison of the structure of LiCl and KCl interfaces allows us to discuss the relevance of size asymmetry effects on interfacial properties. These effects are apparent in the structure of the LiCl interface, but only when a description of polarization interactions is included in the potential model. Polarization facilitates the formation of a displacement dipole moment across the interface by allowing an opposing electronic dipole moment of approximately the same magnitude, so that the total dipole moment is always small and thus not unfavorable from an electrostatic point of view. The study of the binary mixtures shows that the surface tension is relatively insensitive to the specific LiCl concentration for a broad range of compositions. This is explained by potassium segregation towards the surface. In these cases, where segregation effects are important, we have found that very long simulations (several nanoseconds long) are needed in order to obtain converged density profiles. For all the systems studied, the local ion coordination number reduces to 50% of its bulk value only when the ion density has reduced to less than 5% of its bulk value, showing the importance of clustering effects in this kind of interface.
Rotational dynamics of charged colloidal spheres: Role of particle interactions
Authors: Koenderink Gijsberta H. , Lettinga M. Pavlik , Philipse Albert P.
Published: October 2002

Time-resolved phosphorescence anisotropy (TPA) is used to measure the short-time rotational diffusion coefficient Dsr(φ) of charged tracer spheres as a function of the volume fraction φ of like-charged colloidal host spheres in nonaqueous solvents. Sphere interactions are varied from long-range repulsive to short-range attractive by changing the ionic strength and the solvent composition. It is shown that Dsr(φ) is very sensitive to details of the interaction near contact, in agreement with theory. In contrast, the low-shear viscosity ηL(φ) of the host dispersions is mostly controlled by the tail of the interaction potential. We discuss the applicability of Stokes–Einstein–Debye scaling Dsr(φ)∝1/ηL(φ), and Dsr(φ)∝1/η∞(φ), where η∞ is the high-frequency-limiting viscosity. Scaling with ηL(φ) fails at high particle and low salt concentrations, while scaling with η∞ is fairly good, in particular when an apparent nonstick boundary condition is imposed on the friction factor. We conclude that TPA is well suited for use as a microrheological technique.
Reversible charge separation through exciplex formation
Authors: Burshtein A. I.
Published: October 2002

The Unified Theory of exciplex formation by intermolecular electron transfer or straightforward light excitation of complexes is developed. It includes the reversible dissociation of exciplexes to a singlet ion pair, subjected to spin conversion and recombination to either the ground or triplet state. In the contact approximation the quantum yields of free ions, exciplexes, and triplet products of recombination are calculated analytically. The main results of previous spinless theories are reproduced and shown to be identical to those available with the Integral Encounter Theory.
New lambda integration method to compute surface free energies of disordered surfaces
Authors: Grochola Gregory , Russo Salvy P. , Snook Ian K. , Yarovsky Irene
Published: October 2002

Previously we studied a range of λ-integration paths, specifically designed for calculating surface and interfacial free energies of solids with disordered surfaces or interfaces, using molecular dynamics or Monte Carlo simulation methods. Some of these were successfully applied to the stable low index (100) and (110) Fe bcc surfaces, up to temperatures high enough (1200 K) to induce the onset of surface disorder via the formation of adatoms. Here we apply these same methods to the high energy (111) bcc Fe face, where the “ideal” surface structure was found to be metastable at low temperatures. The results showed that application of paths used in our previous study lead to irreversibility. Hence we further refine the paths with the development of a much more powerful and general path, which we termed the “blanket lambda” path. We show the newest path to be reversible and to provide “exact” surface free energy reference points for the stable and metastable surface structures of the (111) bcc Fe face. We also show this general path to be applicable to the low index (100) and (110) faces.
Semirigid vibrating rotor target model for CH4 dissociation on a Ni(111) surface
Authors: Xiang Yun , Zhang John Z. H. , Wang Dun Y.
Published: October 2002

We present a theoretical treatment of the semirigid vibrating rotor target model to study dissociative chemisorption of CH4 at the atop site on Ni(111) surface. In this treatment, the fixed-site approximation is used to study chemisorption of methane on Ni treated as a rigid and locally flat surface. This results in a four-dimensional (4D) theoretical model to treat methane dissociation on Ni. Using parameters from ab initio calculations, an empirical potential energy surface is constructed for the CH4/Ni(111) system over the atop site. A 4D quantum dynamics calculation using the time-dependent wave-packet method is carried out on this potential energy surface. Our calculation shows that the dissociation probability of methane is an increasing function of kinetic energy, and the C–H stretching vibration significantly enhances the dissociation. The dissociation probability has a strong dependence on the initial orientation of the molecule. Reasonably good agreement is found between the current theoretical calculation and experimental results.
Energetics of the manganese trimer and tetramer ions
Authors: Terasaki Akira , Minemoto Shinichirou , Kondow Tamotsu
Published: October 2002

The photodissociation processes of the manganese cluster ions Mnn+ (n=3 and 4) were investigated in the visible and near-infrared photon-energy ranges. The threshold energies were determined for the two-atom-loss channels by measurements of the spectra of the partial photodissociation cross sections. The binding energies of Mnn+ (n=3 and 4) were obtained by using these threshold energies and the known bond dissociation energy of Mn2+. The bond dissociation energies of Mn3+, D0(Mn2+⋯Mn), and Mn4+, D0(Mn3+⋯Mn), were determined to be 0.83±0.05 and 1.04±0.07 eV, respectively. Thus the binding energies (per atom) of Mn3+ and Mn4+ turned out to be 0.74±0.03 and 0.82±0.05 eV, respectively. These findings show that the interaction between manganese atoms is exceptionally weak, compared with other transition-metal cluster ions.
Space-selective precipitation of metal nanoparticles inside glasses
Authors: Qiu Jianrong , Shirai Mitsuru , Nakaya Takayuki , Si Jinhai , Jiang Xiongwei , Zhu Congshan , Hirao Kazuyuki
Published: October 2002

We report the precipitation and control of metal nanoparticles inside transparent glasses. An Ag+-doped silicate glass sample was first irradiated by using an 800 nm femtosecond laser at room temperature and then annealed at 550 °C. The area near the focal point of the laser beam became gray after laser irradiation and yellow after further annealing at 550 °C for 10 min. Absorption and electron spin resonance spectra of the glass sample showed that a portion of silver ions near the focused part of the laser beam inside the glass were reduced to silver atoms after the laser irradiation. These silver atoms aggregated to form nanoparticles after further annealing at temperatures above 500 °C. A mechanism is suggested that consists of multiphoton reduction, which is induced by the fundamental light of the laser beam and supercontinuum white light, and diffusion of silver atoms driven by heat energy to form nanoparticles. The observed phenomenon may have promising applications for the fabrication of three-dimensional multicolored images inside a transparent material and for integrative micro-optical switches.
The thermodynamics of reversible cyclization in semiflexible polymers
Authors: Dua Arti , Cherayil Binny J.
Published: October 2002

A recent model of the irreversible kinetics of ring formation in semiflexible polymers [J. Chem. Phys. 116, 399 (2002)] is generalized to the case of equilibrium cyclization, for which the rate constants for the forward and backward reaction are finite. The model is based on the diffusion-reaction formalism of Wilemski and Fixman [J. Chem. Phys. 60, 866 (1974)], and employs a path integral representation of the semiflexible chain (within a certain Gaussian approximation) to derive an expression for the steady state probability of occurrence of open configurations for given values of the chain length N, the reaction radius a, the degree of stiffness z, and the ratio of forward to backward reaction rates k/kr. The steady state probability is used to calculate the free energy changes for the open-to-close transition. Chain rigidity is found to strongly influence the standard Gibbs free energy and enthalpy for the transition. While flexible chains tend to cyclize by virtue of their entropic elasticity alone, cyclization in semiflexible chains is also governed by the change in enthalpy between the open and closed states. The results are in qualitative agreement with the experimental measurements of Libchaber and co-workers.
Second-harmonic spectroscopy of two-dimensional Si nanocrystal layers embedded in SiO2 films
Authors: Jiang Y. , Sun L. , Downer M. C.
Published: October 2002

We present observations of optical second-harmonic generation (SHG) from dense (1010 or 6×1011 cm−2) layers of 5 or 8 nm average diameter silicon nanocrystals (NCs) embedded in thin (6–15 nm) SiO2 films on silicon substrates. Time-dependent SHG monitors optically-driven electrostatic charging of the Si NC layer as well as subsequent charge leakage, and thus provides noncontact electrical characterization of Si-NC-based device structures. SHG intensity and phase spectra of Si NCs are distinguished from contributions of the Si substrate by polarization-dependent and frequency-domain interferometric SH spectroscopy, which reveal a NC-size-dependent blueshift of the E1 resonance consistent with quantum confinement.
Complete three-dimensional band gap in macroporous silicon photonic crystals
Authors: Leonard S. W.
Published: October 2002

The prospect of obtaining a complete three-dimensional band gap in macroporous silicon photonic crystals is investigated theoretically. Band structure calculations indicate that a modified form of the simple cubic lattice of air spheres in silicon exhibits a complete band gap, with a bandwidth of up to 4%. It is further shown that this quasispherical crystal may be fabricated using standard etching procedures. These results provide a practical route to obtaining large-scale, high-quality, silicon photonic crystals with a complete band gap.
Optical and structural properties of InAsP ternary self-assembled quantum dots embedded in GaAs
Authors: Ribeiro E. , Maltez R. L. , Carvalho W. , Ugarte D. , Medeiros-Ribeiro G.
Published: October 2002

We report on the growth of self-assembled ternary InAsP quantum dots embedded into GaAs. A comparison between average sizes and recombination energies for different dot species (InAs, InAsP, and InP) confirms the formation of the ternary alloy islands. By carefully changing the growth conditions, we determined a global growth map for InAs, InAsP, and InP dots, showing that it is possible to tailor the optical characteristics of the InAsP species, thus covering the energy range between InAs and InP quantum dot emission.
Piezoelectric nonlinearity of Pb(Zr,Ti)O3 thin films probed by scanning force microscopy
Authors: Shvartsman V. V. , Kholkin A. L. , Pertsev N. A.
Published: October 2002

Local piezoelectric response of Pb(Zr,Ti)O3 thin films is investigated by scanning force microscopy as a function of the amplitude of driving ac field. Thus obtained local piezoelectric nonlinearity is compared with the macroscopic behavior deduced earlier from interferometric measurements. The nanoscale piezoelectric properties are found to be remarkably different from the average macroscopic response. In particular, the local piezoelectric nonlinearity measured inside uniformly polarized areas (domains) is unexpectedly high, being qualitatively different for the as-grown domains of opposite polarities. The minority domains are often unstable and switch into the opposite polarization state under an electric field several times lower than that required for global polarization switching. This effect is explained by the presence of charged domain boundaries below the surface and by their field-induced depinning.
Phase diagram for the interaction of oxygen with SiC
Authors: Song Y. , Smith F. W.
Published: October 2002

We report on experimental studies of the interactions of oxygen with the 4H– and 6H–SiC surfaces at high temperatures. It is observed that these interactions lead to the growth of passivating SiO2 layers at high O2 pressures, etching of the surfaces at lower pressures, and enhancements of the surface segregation of carbon at still lower pressures. A pressure–temperature phase diagram for the oxidation of SiC containing these three experimentally observed regions is presented.
Dynamic characteristics of high-speed In0.4Ga0.6As/GaAs self-organized quantum dot lasers at room temperature
Authors: Ghosh S. , Pradhan S. , Bhattacharya P.
Published: October 2002

We have measured the room-temperature modulation characteristics of self-organized In0.4Ga0.6As/GaAs quantum dot lasers in which electrons are injected into the dot lasing states by tunneling. A small-signal modulation bandwidth of f−3 dB=22 GHz is measured. Values of differential gain at 288 K of dg/dn≅8.85×10−14 cm2 and gain compression factor ε=7.2×10−16 cm3 are derived from the modulation data. Extremely low values of linewidth enhancement factor α∼1 and chirp <0.6 Å were also measured in the devices.
Electron emission from GaN n–p junctions
Authors: Shaw Jonathan L. , Treece Randolph E. , Patel Dinesh , Menoni Carmen S. , Smith Jim R. , Pankove J. I.
Published: October 2002

We report on electron emission from cesiated GaN n–p junctions in forward bias. Surface electric fields ∼3 V/μm caused a fivefold increase in emission current. Initial maximum currents in excess of 200 nA degrade to 50 nA due to charge trapping but are quickly recovered at zero bias. Energy spectra confirm negative electron affinity 80 h after cesiation, indicate resistive losses limit the emission current, and reveal significant emission at energies above the Fermi level of the injecting contact.
Stressed metal probes for atomic force microscopy
Authors: Hantschel Thomas , Chow Eugene M. , Rudolph Dirk , Fork David K.
Published: October 2002

Common scanning probes with straight cantilevers and micrometer-sized tips are not suited for substrates with very high topography. Therefore, we have developed stressed metal probes that use bent cantilevers and can have a tip height of hundreds of micrometers. The use of a transparent substrate allows the laser beam light to shine through the probe chip in atomic force microscopy (AFM). This letter describes the stressed probe concept and presents first measurements on thin film samples and on the bottom of deep structures. Our probe concept extends the functionality of AFM systems and is an alternative to straight cantilever probes in many applications.
Organic light-emitting devices with extended operating lifetimes on plastic substrates
Authors: Weaver M. S. , Michalski L. A. , Rajan K. , Rothman M. A. , Silvernail J. A. , Brown J. J. , Burrows P. E. , Graff G. L. , Gross M. E. , Martin P. M. , Hall M. , Mast E. , Bonham C. , Bennett W. , Zumhoff M.
Published: October 2002

We fabricate long-lived organic light-emitting devices using a 175 μm thick polyethylene terephthalate substrate coated with an organic–inorganic multilayered barrier film and compare the rate of degradation to glass-based devices. The observed permeation rate of water vapor through the plastic substrate was estimated to be 2×10−6 g/m2/day. Driven at 2.5 mA/cm2, we measure a device lifetime of 3800 h from an initial luminance of 425 cd/m2.
GaN islanding by spontaneous rearrangement of a strained two-dimensional layer on (0001) AlN
Authors: Adelmann C. , Gogneau N. , Sarigiannidou E. , Rouvière J.-L. , Daudin B.
Published: October 2002

It is shown that a two-dimensional GaN layer grown on (0001) AlN under Ga-rich conditions remains two-dimensional while annealing under a Ga flux due to a surfactant effect of Ga. In contrast, further annealing under vacuum without the Ga flux leads to evaporation of excess Ga and to spontaneous transformation of the GaN layer into islands if the initial layer is thicker than about 2.5 monolayers. The resulting morphology is studied by atomic force microscopy and transmission electron microscopy. The latter reveals that these islands sit on top of a continuous 2.5 monolayer thick wetting layer, i.e., they represent a Stranski–Krastanow structure.
Cathodoluminescence of Cu diffusion in CdTe thin films for CdTe/CdS solar cells
Authors: Romero Manuel J. , Albin David S. , Al-Jassim Mowafak M. , Wu Xuanzhi , Moutinho Helio R. , Dhere Ramesh G.
Published: October 2002

We investigate the distribution of Cu acceptor states in CdTe thin films used in high-efficiency solar cells. These states are CuCd and Cui+–VCd− complexes, which are relatively deep and shallow acceptors, respectively. Cathodoluminescence spectroscopy and imaging show that, first, CuCd and Cui+–VCd− do not coexist and, second, the primary diffuser is represented by Cui+–VCd− complexes. Our results are used to discuss the effect of grain boundaries on Cu diffusion.
Ge–Sn semiconductors for band-gap and lattice engineering
Authors: Bauer M. , Taraci J. , Tolle J. , Chizmeshya A. V. G. , Zollner S. , Smith David J. , Menendez J. , Hu Changwu , Kouvetakis J.
Published: October 2002

We describe a class of Si-based semiconductors in the Ge1−xSnx system. Deuterium-stabilized Sn hydrides provide a low-temperature route to a broad range of highly metastable compositions and structures. Perfectly epitaxial diamond-cubic Ge1−xSnx alloys are grown directly on Si(100) and exhibit high thermal stability, superior crystallinity, and crystallographic and optical properties, such as adjustable band gaps and lattice constants. These properties are completely characterized by Rutherford backscattering, low-energy secondary ion mass spectrometry, high-resolution transmission electron microscopy, x-ray diffraction (rocking curves), as well as infrared and Raman spectroscopies and spectroscopic ellipsometry. Ab initio density functional theory simulations are also used to elucidate the structural and spectroscopic behavior.
GaAs quantum box cascade lasers
Authors: Becker C. , Sirtori C. , Drachenko O. , Rylkov V. , Smirnov D. , Leotin J.
Published: October 2002

Measurements of the light emission under strong magnetic field from quantum cascade lasers emitting at 9 and 11 μm are reported. The laser intensity shows strong oscillations as a function of the magnetic field. This effect is due to changes in the lifetime of the upper state of the laser transition, which is controlled by electron-optical phonon scattering. This process is strongly modified by the extra confinement imposed by a magnetic field applied perpendicular to the plane of the layers, which breaks the electron dispersion into discrete Landau levels. The experimental results are in remarkable agreement with our calculations of the phonon-limited lifetime. We also show that this experiment provides direct indications of the ratio of the scattering rates associated with the two nonradiative transitions in the active region.
Virtual surfaces, director domains, and the Fréedericksz transition in polymer-stabilized nematic liquid crystals
Authors: Kossyrev Pavel A. , Qi Jun , Priezjev Nikolai V. , Pelcovits Robert A. , Crawford Gregory P.
Published: October 2002

The critical field of the Fréedericksz transition and switching dynamics are investigated for polymer-stabilized nematic liquid crystals as a function of polymer concentration. A simple phenomenological model is proposed to describe the observed critical field and dynamic response time behaviors as a function of concentration. In this model, the polymer fibrils form director domains, which are bounded by “virtual surfaces” with a finite anchoring energy.
Angular rotation of magnetic hysteresis of ion-irradiated ferromagnetic thin films
Authors: Chang G. S. , Callcott T. A. , Zhang G. P. , Woods G. T. , Kim S. H. , Shin S. W. , Jeong K. , Whang C. N. , Moewes A.
Published: October 2002

The magnetization direction of a cobalt-platinum film has been manipulated by magnetic-field-assisted ion-beam mixing. A uniaxial easy magnetization axis is induced along the oscillation direction of the incident beam of 80 keV Ar+ ions. The easy axis was then rotated by 60°, when the same ion irradiation process was carried out in the presence of an external magnetic field. Magnetic force microscopy measurements show that line shaped domain structures are created with their long axis along the induced magnetization directions. It is proposed that the creation of adjacent regions with orthogonal magnetization can play a crucial role in stabilizing the magnetostatic dipolar interaction between adjacent bits of magnetic data storage devices.
Self-assembled GaAs antiwires in In0.53Ga0.47As matrix on (100) InP substrates
Authors: Lin S. D. , Lee C. P. , Hsieh W. H. , Suen Y. W.
Published: October 2002

The growth of GaAs antiwires in the In0.53Ga0.47As matrix on InP substrate has been investigated. The periodic, wire-like structure was obtained when a proper amount of GaAs was deposited. The grown antiwires have a height about 1.2–2.0 nm and a period about 23 nm. Using an In0.53Ga0.47As/In0.52Al0.48As modulation-doped structure, the effect of the GaAs antiwires on the two-dimensional electron gas mobility was investigated. For the sample with antiwires near the two-dimensional channel, a significant anisotropy in low temperature mobility was observed.
Low-temperature operation of AlGaN single-quantum-well light-emitting diodes with deep ultraviolet emission at 285 nm
Authors: Chitnis A. , Pachipulusu R. , Mandavilli V. , Shatalov M. , Kuokstis E. , Zhang J. P. , Adivarahan V. , Wu S. , Simin G. , Asif Khan M.
Published: October 2002

We present a study of the electrical and optical characteristics of 285 nm emission deep ultraviolet light-emitting diodes (LED) at temperatures from 10 to 300 K. At low bias, our data show the tunneling carrier transport to be the dominant conduction mechanism. The room-temperature performance is shown to be limited mostly by poor electron confinement in the active region and a pronounced deep level assisted recombination but not by the hole injection into the active region. At temperatures below 100 K, the electroluminescence peak intensity increases by more than one order of magnitude indicating that with a proper device design and improved material quality, milliwatt power 285 nm LED are viable.
An intelligent biological information management system
Authors: Palakal Mathew , Mukhopadhyay Snehasis , Mostafa Javed , Raje Rajeev , N'Cho Mathias , Mishra Santosh
Published: October 2002

Motivation: As biomedical researchers are amassing a plethora of information in a variety of forms resulting from the advancements in biomedical research, there is a critical need for innovative information management and knowledge discovery tools to sift through these vast volumes of heterogeneous data and analysis tools. In this paper we present a general model for an information management system that is adaptable and scalable, followed by a detailed design and implementation of one component of the model. The prototype, called BioSifter, was applied to problems in the bioinformatics area.

Results: BioSifter was tested using 500 documents obtained from PubMed database on two biological problems related to genetic polymorphism and extracorporal shockwave lithotripsy. The results indicate that BioSifter is a powerful tool for biological researchers to automatically retrieve relevant text documents from biological literature based on their interest profile. The results also indicate that the first stage of information management process, i.e. data to information transformation, significantly reduces the size of the information space. The filtered data obtained through BioSifter is relevant as well as much smaller in dimension compared to all the retrieved data. This would in turn significantly reduce the complexity associated with the next level transformation, i.e. information to knowledge.

Contact: mpalakal@cs.iupui.edu

* To whom correspondence should be addressed.
Condition specific transcription factor binding site
characterization in Saccharomyces cerevisiae
Authors: Harrison Rhonda , DeLisi Charles
Published: October 2002

Motivation: We demonstrate a computational process by which transcription factor binding sites can be elucidated using genome-wide expression and binding profiles. The profiles direct us to the intergenic locations likely to contain the promoter regions for a given factor. These sequences are multiply and locally aligned to give an anchor motif from which further characterization can take place.

Results: We present bases for and assumptions about the variability within these motifs which give rise to potentially more accurate motifs, capture complex binding sites built upon the basis motif, and eliminate the constraints of the currently employed promoter searching protocols. We also present a measure of motif quality based on the occurrence of the putative motifs in regions observed to contain the binding sites. The assumptions, motif generation, quality assessment and comparison allow the user as much control as their a priori knowledge allows.

Availability: IGRDB and the datasets mentioned herein are available at http://chipdb.wi.mit.edu/

Contact: rhonda@bu.edu

* To whom correspondence should be addressed.
Bayesian automatic relevance determination algorithms for classifying gene
expression data
Authors: Li Yi , Campbell Colin , Tipping Michael
Published: October 2002

Motivation: We investigate two new Bayesian classification algorithms incorporating feature selection. These algorithms are applied to the classification of gene expression data derived from cDNA microarrays.

Results: We demonstrate the effectiveness of the algorithms on three gene expression datasets for cancer, showing they compare well with alternative kernel-based techniques. By automatically incorporating feature selection, accurate classifiers can be constructed utilizing very few features and with minimal hand-tuning. We argue that the feature selection is meaningful and some of the highlighted genes appear to be medically important.

Contact: C.Campbell@bris.ac.uk

* To whom correspondence should be addressed.  Present address: Information and Mathematical Sciences, Genome Institute of Singapore, 1 Science Park Road, The Capricorn #05-01, Singapore 117528, Republic of Singapore
Selecting signature oligonucleotides to identify
organisms using DNA arrays
Authors: Kaderali Lars , Schliep Alexander
Published: October 2002

Motivation: DNA arrays are a very useful tool to quickly identify biological agents present in some given sample, e.g. to identify viruses causing disease, for quality control in the food industry, or to determine bacteria contaminating drinking water. The selection of specific oligos to attach to the array surface is a relevant problem in the experiment design process. Given a set S of genomic sequences (the target sequences), the task is to find at least one oligonucleotide, called probe, for each sequence in S. This probe will be attached to the array surface, and must be chosen in a way that it will not hybridize to any other sequence but the intended target. Furthermore, all probes on the array must hybridize to their intended targets under the same reaction conditions, most importantly at the temperature T at which the experiment is conducted.

Results: We present an efficient algorithm for the probe design problem. Melting temperatures are calculated for all possible probe–target interactions using an extended nearest-neighbor model, allowing for both non-Watson–Crick base-pairing and unpaired bases within a duplex. To compute temperatures efficiently, a combination of suffix trees and dynamic programming based alignment algorithms is introduced. Additional filtering steps during preprocessing increase the speed of the computation.

The practicability of the algorithms is demonstrated by two case studies: The identification of HIV-1 subtypes, and of 28S rDNA sequences from ≥400 organisms.

Availability: The software is available on request.

Contact: kaderali@zpr.uni-koeln.de

* To whom correspondence should be addressed.
Fold-recognition detects an error in the Protein Data Bank
Authors: Bujnicki Janusz , Rychlewski Leszek , Fischer Daniel
Published: October 2002

* To whom correspondence should be addressed dfischer@cs.bu.ac.il
Genquire: genome annotation browser/editor
Authors: Wilkinson M.D. , Block D. , Crosby W.L.
Published: October 2002

Summary: We present a software package, Genquire, that allows visualization, querying, hand editing, and de novo markup of complete or partially annotated genomes. The system is written in Perl/Tk and uses, where possible, existing BioPerl data models and methods for representation and manipulation of the sequence and annotation objects. An adaptor API is provided to allow Genquire to display a wide range of databases and flat files, and a plugins API provides an interface to other sequence analysis software.

Availability: Genquire v3.03 is open-source software. The code is available for download and/or contribution at http://www.bioinformatics.org/Genquire

Contact: mwilkinson@gene.pbi.nrc.ca

* To whom correspondence should be addressed.  Present address: Genomics Institute of the Novartis Research Foundation, 10675 John Jay Hopkins Drive, San Diego, CA 92121, USA
Genexp—a genetic network simulation environment
Authors: Vu Tra Thi , Vohradsky Jiri
Published: October 2002

Summary: An environment for simulation of dynamics of genetic regulatory networks is presented. The model is based on the recurrent neural network principle and allows to interactively simulate various genetic regulatory interactions under different features of the system. The results are displayed graphically.

Availability: http://proteom.biomed.cas.cz/genexp

Contact: vohr@biomed.cas.cz

* To whom correspondence should be addressed.
Effects of in situ pyrolytic-gas passivation on reliability of ultrathin silicon oxide gate films
Authors: Yamada Hiroshi
Published: October 2002

Ultradry oxidation assisted by an in situ passivation method that uses a little pyrolytic N2O gas was investigated to improve the reliability of ultrathin silicon oxide films less than 5 nm thick as gate insulators. The passivation was found to significantly improve the potential barrier height energy and time-dependent dielectric breakdown lifetimes without increasing the interface state density. It was also found that these remarkable improvements of the main electrical properties can be obtained only with a moisture content less than 1 ppb. Although the apparent existence of the N-related inclusions and the change in the binding states of the oxide cannot be confirmed, it appears that a small microscopic structural change may be brought about near the oxide–silicon substrate interface.
Application of phase-imaging tapping-mode atomic-force microscopy to investigate the grain growth and surface morphology of TiSi2
Authors: Pang C. H. , Hing P. , See A.
Published: October 2002

Phase-imaging tapping-mode atomic-force microscopy (TM AFM) has been used to study the grain size of TiSi2 films. Presently, there are few reports in the literature on the application of the phase imaging technique for grain size characterization. In this study, very clear images of TiSi2 grains have been obtained and compared to transmission electron microscopy micrographs. For the first time, both triple point C54–TiSi2 nuclei and C49-phase grains have been clearly identified with this technique. C49 and C54–TiSi2 nuclei are about 50 and 15 nm, respectively at 650 °C. The C49-to-C54 phase transformation of TiSi2 is confirmed by x-ray diffraction. This study demonstrated that TM AFM can be used for grain size characterization with high accuracy and efficiency.
Etching parylene-N using a remote oxygen microwave plasma
Authors: Callahan Russell , Raupp Gregory , Beaudoin Stephen
Published: October 2002

The etching characteristics of parylene-N in a remote microwave oxygen plasma have been studied. The etch rate was measured over a range of pressures from 0.4 to 2.0 Torr and oxygen flow rates from 25 to 125 sccm using an applied plasma power of 250 W. In order to describe the etching behavior of the polymer as a function of different process parameters, a model has been developed to predict the concentration of reactive species at the polymer surface. The model uses two different plasma physics models to predict the net molecular oxygen dissociation rate in the microwave plasma. The species concentrations at the plasma outlet are used as the inlet condition for a model of the afterglow region, which includes a delivery tube and an etching chamber. The afterglow region is modeled using momentum and mass conservation equations. The predicted atomic oxygen concentrations at the polymer surface are inserted into a simple etch rate model and an etch rate is calculated and compared to etch rate data. The best agreement between theory and experiment was found using a plasma physics model developed by the Joint Institute for Laboratory Astrophysics and an etch rate model that has a reaction order of 0.5 with respect to the oxygen atom concentration.