bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of strain variation on photoluminescence from InGaAs quantum dots in air‐bridge structures
Authors: Nakaoka T. , Kakitsuka T. , Saito T. , Kako S. , Ishida S. , Nishioka M. , Yoshikuni Y. , Arakawa Y.
Published: July 2003

We have fabricated freestanding wire (air‐bridge) structures with a bowed shape by introducing a strain layer to vary the strain around quantum dots. The photoluminescence peak energy shift following the shape change of the bridge can be observed for individual InGaAs quantum dots. We find systematic dependence of the peak shift on the dot position along the growth direction. The dependence of the peak shift is explained by strain distribution in the bridge. The strain distribution in the bridge as well as in the dot is calculated using a finite element method. Using the strain data, the electronic structures of the dots embedded in the bridge structures are calculated within the effective mass approximation. The calculated energy shifts agree well with the experimental ones.
Magnetic properties of charged excitons in self‐assembled quantum dots
Authors: Schulhauser C. , Högele A. , Warburton R. J. , Govorov A. O. , Schoenfeld W. , Garcia J. M. , Petroff P. M. , Karrai K.
Published: July 2003

We report on low temperature (4.2 K) magneto‐luminescence measurements performed on charged tuneable GaInAs self‐assembled quantum dots. We mapped the magnetic field dispersion (0–9 Tesla) of the exciton with excess electron charges set from 0 to 3. For the doubly and triply charged excitons the emission line shows a doublet corresponding to the singlet and triplet configuration of the quantum dot in the final state after photon emission. We map here for the first time the dispersion of the singlet state of the doubly charged exciton and show that the triply charged exciton undergoes a transition resulting from a magnetic field induced frustration of the Hund's rule.
Quantum dots: a source of multicolor photons with tunable statistics and correlated polarizations
Authors: Mizrahi U. , Regelman D. V. , Gershoni D. , Ehrenfreund E. , Petroff P. M.
Published: July 2003

We report on measurements of temporal and polarization correlations measurements of multi‐color photons emitted from cw optically excited single semiconductor quantum dots. We show that there are tunable intensity and polarization correlations among photons emitted at the same, and at different wavelengths due to the recombination of electron–hole pairs from different collective many‐carrier quantum states confined in the dots. The observed polarization correlations between the emitted photons are qualitatively explained in terms of long electronic spin memory.
Pattern‐effect‐free amplification and cross‐gain modulation achieved by using ultrafast gain nonlinearity in quantum‐dot semiconductor optical amplifiers
Authors: Akiyama Tomoyuki , Hatori Nobuaki , Nakata Yoshiaki , Ebe Hiroji , Sugawara Mitsuru
Published: July 2003

We demonstrate that the pattern effect of semiconductor optical amplifiers appearing in amplified signals and in cross‐gain modulated signals can be suppressed by using quantum dots as active media. This property, which originates from the ultrafast (less than 3 ps) gain nonlinearity of quantum dots dominated by spectral‐hole burning, in principle enables pattern‐effect‐free operations at up to 160 Gb/s. Experimental confirmation of this property was conducted at 40 Gb/s.
Indistinguishable single photons from a quantum dot
Authors: Fattal David , Santori Charles , Vuckovic J. , Solomon G. S. , Yamamoto Yoshihisa
Published: July 2003

We report a set of experiments designed to test the quantum indistinguishability of single photons emitted by a resonantly pumped InAs/GaAs quantum dot, embedded in a microcavity. We first performed high resolution interferometric measurements on the source to infer its coherence time. By comparison with the exciton lifetime, obtained by time‐resolved spectroscopy, we found that some quantum dots were emitting almost transform‐limited photons. The measured ratio of the coherence time to the pulse duration gives a lower bound on the dephasing time which agrees well with previous studies. We then directly measured the mean overlap between wave packets of consecutive photons emitted 2 ns apart, through a Hong–Ou–Mandel type two‐photon interference experiment. For the best dot, an overlap as high as 0.81 was inferred. This result suggests that quantum dots could be a practical single photon source to perform quantum information processing experiments. We stress the importance of the microcavity for identical photon generation.
Large spontaneous emission enhancement in InAs quantum dots coupled to microdisk whispering gallery modes
Authors: Solomon G. S. , Xie Z. , Fang W. , Xu J. Y. , Yamilov A. , Cao H. , Ma Y. , Ho S. T.
Published: July 2003

Measuring the enhancement of spontaneous emission decay rates of quantum dot emission coupled to microcavity modes is typically hampered by variable coupling of the quantum dot emission. This is particularly evident in the microdisk cavity since the whispering gallery modes are localized near the disk edge, while quantum dot emitters are typically uniformily distributed throughout the disk. The distribution of spontaneous emission decay rates under these circumstances can be determined using a distribution function for the various spontaneous decay rates, and demonstrate that large decay rate enhancement are present. To remove the spatial coupling variation, quantum dots are selectively placed near the microdisk edge. Initial photoluminescence measurements indicate that recombination processes in these quantum dots are not dominated by surface recombination.
Single quantum dot pairs with controllable interdot coupling
Authors: Welsch M. K. , Bacher G. , Schömig H. , Forchel A. , Zaitsev S. , Becker C. R. , Molenkamp L. W.
Published: July 2003

We report on a new approach for preparing single pairs of quantum dots with controllable interdot coupling. Starting from a double quantum well heterostructure, a selective intermixing technique was applied to define pairs of vertically stacked single quantum dots. The incorporation of Mn2+ ions in only one of the dots results in strongly different effective g‐factors of the dots, enabling us to control the interdot coupling simply by applying an external magnetic field.
Exciton–phonon interaction in epitaxial CdSe/ZnSe nanostructures
Authors: Kapitonov A. M. , Woggon U. , Leonardi K. , Hommel D. , Edamatsu K. , Itoh T.
Published: July 2003

The low‐temperature optical properties of submonolayer CdSe/ZnSe nanostructures have been investigated with nominal layer thickness of 0.15 ML and 0.58 ML CdSe. In photoluminescence excitation spectroscopy (PLE) we observe more than 10 equidistant peaks separated by the ZnSe LO‐phonon energy even at energies high above the ZnSe‐band edge. The peak heights and line shapes are extremely sensitive to the monolayer coverage, have strongly different intensities in emission and PLE and deviate from the Poissonian intensity distribution expected within the concept of a constant, material specific Huang–Rhys parameter S. A bound polaron model is proposed to explain the optical properties of quantum structures for which the approach of a pure electronic quantum confinement is not appropriate. Intrinsic coherence of joint exciton–phonon modes is very promising, e.g. for application in quantum information processing or coherent population transfer.
Single‐photon and photon‐pair emission from CdSe/Zn(S,Se) quantum dots
Authors: S. Strauf  , Ulrich S. M. , Sebald K. , Michler P. , Passow T. , Hommel D. , Bacher G. , Forchel A.
Published: July 2003

We report on the generation of triggered single photons and photon pairs relying on pulsed optical excitation of epitaxially grown self‐assembled CdSe quantum dots (QDs). Single‐photon emission is studied on individual CdSe/Zn(S,Se) QDs for temperatures up to 200 K. At low temperatures nearly perfect single‐photon emission is achieved whereas at higher temperatures an increasing multi‐photon emission probability due to spectrally overlapping acoustic phonon sidebands of neighboring QDs is observed. The multi‐photon emission probability of a bare QD (background subtracted) is strongly suppressed. Furthermore, the polarization cross correlation of the biexciton–exciton cascade has been investigated in a CdSe/ZnSe QD at low temperatures. A strong polarization correlation of the emitted photon pairs of ∼74% is observed in a linear detection basis.
Simple spin textures in a quantum dot
Authors: Ciorga M. , Korkusiński M. , Pioro‐Ladriere M. , Zawadzki P. , Hawrylak P. , Sachrajda A. S.
Published: July 2003

Measurements and calculations previously reported for a lateral quantum dot at magnetic fields close to the transition to the maximum density droplet provided evidence that the increase of spin polarisation of a dot with magnetic field is interrupted by spin depolarization events. The loss of spin polarisation is associated with correlated states corresponding to condensation of spin excitons into spin textures. In this paper a detailed experimental and theoretical analysis is performed of the excitation spectra at the first two spin flip events in a few electron quantum dot. In this less complicated regime we are able to identify these correlated states as spin and charge excitons and bi‐excitons. In particular we focus on a dot containing eight electrons. Coulomb blockade experiments, supported by detailed calculations, confirm the presence of these correlated states at the second spin flip.
Aharonov–Bohm effect of a quantum ring in the Kondo regime
Authors: Keyser U. F. , Fühner C. , Haug R. J. , Wegscheider W. , Bichler M. , Abstreiter G.
Published: July 2003

We investigate a small tuneable quantum ring fabricated by direct local oxidation using an atomic force microscope. The device contains very few electrons and is tuned into the Kondo regime. We study this Kondo effect by temperature dependent measurements. At finite bias voltages we observe additional peaks. These vanish with increasing temperature indicating Kondo correlations for these excited states. Additionally, the geometry of our device allows to study Aharonov–Bohm oscillations in the Kondo regime for a device containing less than ten electrons. We observe a modulation of the Kondo effect with a reduced Aharonov–Bohm period explained by electron–electron interaction in our small quantum ring.
Spin selective tunneling and blockade in two‐electron double quantum dot
Authors: Ono K. , Austing D. G. , Tokura Y. , Tarucha S.
Published: July 2003

We have studied a non‐linear transport of double quantum dots in a two‐electron regime, and found a pronounced blockade region in addition to the ordinary Coulomb blockade. This extra blockade region appears only on one polarity of the source drain voltage, and is ascribed to the selection rule of two‐electron spins for an inter‐dot tunneling as well as to an irreversible tunneling from the reservoir to the dots. In this extra blockade region the two‐electron spin stays in the triplet state even in a zero magnetic field. A small leakage current indicates that the lifetime of this triplet state is about 100 ns.
Observation of in‐plane polarized intersublevel absorption in strongly coupled InGaAs/GaAs self assembled quantum dots
Authors: Adawi A. M. , Zibik E. A. , Wilson L. R. , Lemaître A. , Sheng W.D. , Cockburn J. W. , Skolnick M. S. , Leburton J. P. , Hopkinson M. , Hill G. , Liew S. L. , Cullis A. G.
Published: July 2003

We present a mid‐infrared absorption study of an n‐i‐n structure containing two planes of strongly coupled In0.5Ga0.5As self assembled quantum dots. We find that the dominant absorption occurs for light polarized in the growth plane (TE‐polarized), contrasting with uncoupled dots which exhibit predominantly TM‐polarized absorption in the same energy range. Our measurements suggest that uncoupled dots grown under the same conditions as the coupled dots contain one bound (s‐like) electron level. By coupling the dots the confinement length in the growth direction (z) is increased, lowering the energy of the s‐like ground state and binding additional px, y‐like excited states. A significantly increased normal incidence photocurrent sinal is measured for the sample containing coupled dots, relative to samples containing up to 30 layers of uncoupled dots, confirming the enhancement of the normal incidence absorption.
Wavelength selective data storage in InGaAs–GaAs quantum dots
Authors: Kroutvar M. , Zrenner A. , Ducommun Y. , Finley J. J. , Abstreiter G.
Published: July 2003

We present the first demonstration of wavelength selective charge storage (electrons or holes) in In0.5Ga0.5As self‐assembled quantum dots with optical readout. Our results demonstrate unambiguously wavelength selective charging with long (≫25 μs) data storage lifetimes and enable us to probe directly carrier excitation processes and potentially electron spin dynamics in micro‐ensembles of quantum dots.
Open issues for lasing at 1.3 μm in MOCVD‐grown quantum dots
Authors: De Giorgi M. , Passaseo A. , Maruccio G. , De Vittorio M. , Todaro M. T. , Rinaldi R. , Cingolani R.
Published: July 2003

A study of the carrier dynamics in MOCVD‐grown InGaAs/GaAs quantum dots emitting at 1.3 μm at room temperature has been done. The PL rise time measured as a function of the temperature shows that carrier relaxation into the QD ground state occurs within a few picoseconds due to a very efficient carrier–phonon scattering process. In spite of this very efficient carrier capture in our dots and a small temperature dependence of the quantum efficiency, which are favorable for laser applications, we show that our QDs have a very strong permanent dipole moment which prevents the emission from the ground state and the lasing at 1.3 μm.
Self‐assembled quantum dots as a source of single photons and photon pairs
Authors: Shields A. J. , Stevenson R. M. , Thompson R. M. , Ward M. B. , Yuan Z. , Kardynal B. E. , See P. , Farrer I. , Lobo C. , Cooper K. , Ritchie D. A.
Published: July 2003

We investigate the emission from a single self‐organised InAs/GaAs quantum dots as a potential single or pair photon source. Single photon emission is stimulated by exciting the dot with ps laser pulses and collecting either the exciton or biexciton emission line. A more convenient and practical arrangement is to excite the quantum dot electrically by growing it inside a p–i–n structure. Photon pairs are generated through collecting both the exciton and biexciton emissions. We show a strong correlation in the emission times of the exciton and biexciton photon from the dot, as well as in their linear polarisations.
Overview of spin‐based quantum dot quantum computation
Authors: Hu Xuedong , Das Sarma S.
Published: July 2003

Here we give an overview of the research on spin‐based quantum dot quantum computation. In particular, we discuss the conditions for the Heisenberg exchange Hamiltonian to be a satisfactory description of two‐electron interaction in a GaAs double dot. We also discuss theoretical issues related to spin relaxation, spin encoding, and spin measurement. A brief account is also given to spin‐based quantum computation in SiGe quantum dots and donors in Si.
Rabi‐flopping of the ground state excitonin a single self‐assembled quantum dot
Authors: Beham E. , Zrenner A. , Findeis F. , Bichler M. , Abstreiter G.
Published: July 2003

We report Rabi‐oscillations of the ground state exciton in a single self‐assembled quantum dot (QD). Experimentally, we apply a photocurrent (PC) technique, that enables us to monitor the occupation probability of the exciton state by measuring the dc tunneling current out of the QD. Coherent PC spectrocopy was performed by resonant ps‐excitation of the ground state exciton. Rabi‐oscillations are shown to be directly reflected in the PC. In the case of π‐pulse excitation, we receive a quantitative PC given by I = f × e, with the repetition frequency of the experiment f and the elementary charge e. In our experiment we nearly reach this maximum current showing that our experiment acts as a quantitative proof for Rabi‐flopping in a single QD. In a systematic study of field‐dependence we find Rabi‐oscillations with reduced PC amplitude.
Kinetically controlled engineering of quantum dot arrays
Authors: Dubrovskii V. G.
Published: July 2003

A kinetic model for the formation of arrays of coherent strained islands is developed. The derived expressions provide a detailed characterization of quantum dot arrays in terms of island size and density as functions of substrate temperature, growth rate, exposition time and the amount of deposit. The obtained results give a guideline to the kinetically controlled engineering of quantum dot arrays with required structural properties.
Nonlinear optical susceptibilities of copper‐ and silver‐doped silicate glasses in the ultraviolet range
Authors: Ganeev R. A. , Ryasnyansky A. I. , Stepanov A. L. , Usmanov T.
Published: July 2003

Nonlinear optical response of copper and silver nanoparticles synthesized by ion implantation in silicate glasses was investigated in ultraviolet range (354.7 nm). The real and imaginary parts of the third‐order nonlinear susceptibility χ(3) of composite materials were measured. It was shown that Im χ(3) was connected with saturable absorption whereas Re χ(3) was due to self‐defocusing of laser radiation in materials.
Polarized electrons, trions, and nuclei in charged quantum dots
Authors: Bracker A. S. , Tischler J. G. , Korenev V. L. , Gammon D.
Published: July 2003

Spin polarization in GaAs quantum dots has been investigated in the article [1] featured as Editor's Choice of the present issue. Electrons are polarized through relaxation processes after photoluminescence excitation and are identified by the Hanle effect. The cover figure is a schematic diagram describing the selective removal of negatively polarized excitons by optically pumped spin down electrons, which increases exciton and decreases trion PL polarization, respectively. The corresponding author, Allan Bracker, is a member of NRL's Nanostructures Section, focusing on the physics and application of electronic structures with reduced dimensionality.

This paper is an invited presentation from the 2nd International Conference on Semiconductor Quantum Dots held in Tokyo, 30 September–3 October 2002. The full proceedings of this meeting, guest‐edited by Y. Arakawa and S. Tarucha, are published in physica status solidi (c) 0, No. 4 (2003).
Physicochemical and structural properties of bacteriostatic sulfonamides: Theoretical study
Authors: Soriano‐Correa Catalina , Esquivel Rodolfo O. , Sagar Robin P.
Published: July 2003

A theoretical study at the Hartree–Fock and density functional theory levels is performed on sulfonamide‐type bacteriostatic compounds with the aim to provide an insight into their structure–activity relationship. The basicity of the p‐amino group is analyzed by means of the proton affinities and the protonation energies, showing that molecules presenting bacteriostatic activity are less basic, i.e., they are characterized by larger protonation energies and smaller proton affinities. The acidity of the amide group is analyzed through the deprotonation energy. The results reveal that the more acidic molecules present a larger bacteriostatic activity. This result is also confirmed from a study of bond orders. A bond order analysis of the amide group suggests that the electron attracting group in these molecules is responsible for the increase in acidity. The charge of the SO2 group is also shown to be affected by the presence of the electron attracting group and consequently related to the acidity of the molecules. A geometric analysis shows that structures in which the amino group is more coplanar with respect to the benzenic ring possess larger bacteriostatic activity. A conformational analysis of these molecules illustrates that active molecules have relatively larger torsion energy barriers. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 165–172, 2003
Theory of strongly correlated electron systems: Hubbard–Anderson models from an exact Hamiltonian, and perturbation theory near the atomic limit within a nonorthogonal basis set
Authors: Sandalov Igor , Johansson Börje , Eriksson Olle
Published: July 2003

The theory of correlated electron systems is formulated in a form that allows the use as a reference point a density functional theory in the local density approximation (LDA DFT) for solids or molecules. The theory is constructed in two steps. As a first step, the total Hamiltonian is transformed into a correlated form. To elucidate the microscopic origin of the parameters of the periodic Hubbard–Anderson model (PHAM) the terms of the full Hamiltonian that have the operator structure of PHAM are separated. It is found that the matrix element of mixing interaction includes ion configuration‐ and number of particles‐dependent contributions from the Coulomb interaction. In a second step the diagram technique (DT) is developed by means of generalization of the Baym–Kadanoff method for correlated systems. The advantages of the method are that: (1) A nonorthogonal basis can be used, in particular the one generated by LDA DFT; (2) the equations for Green's functions (GFs) for the Fermi and Bose types of quasiparticles can be formulated in the form of a closed system of functional equations. The latter allows us to avoid the question of the nonunique decoupling procedure existing in previous versions of the DT and perform the expansion in terms of dressed GFs. Although the expressions for all interactions depend on the overlap matrix, it is shown that the theory is formally equivalent to one with orthogonal states with redefined interactions. When the PHAM is treated from the atomic‐limit side the vertexes are generated by kinematic interactions. The latter arise due to nontrivial commutation relations between X‐operators and come from the mixing, hopping, and overlap of states. The equations for GFs are derived within the nonorthogonal basis set in Hubbard‐I, one‐loop and random‐phase approximations with respect to kinematic interactions. The self‐consistent equation for “Hubbard Us” is derived. The technique developed is general, in particular its “bosonic” part can be used for description of spin systems with arbitrary anisotropy, systems with orbital ordering, or ordering of multipoles. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 113–143, 2003
Chemical bonding in ternary magnesium hydrides
Authors: Orgaz Emilio , Hernández‐Trujillo Jesús
Published: July 2003

The electronic structure of various alkali and alkaline–earth magnesium‐based hydrides was investigated in detail. These types of crystalline compounds show MgH4or MgH6units ordered within a light‐metal framework. We investigated the nature of the chemical bonding in these units by means of quantum chemical calculations of several related clusters. The properties of the charge density of the clusters, within the framework of the theory of atoms in molecules, was analyzed. A further set of computations of the band structure of the solid hydrides was conducted using a state‐of the‐art density functional‐based method and the mechanism of stabilization of the MgH units is discussed. It was found that the properties obtained at the molecular level correlate well with those of the solid crystals, indicating the molecular nature of the extended systems in which the units MgHx,x= 4, 6, are stabilized by means of MgH closed‐shell interactions. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 150–164, 2003
Bond length features of linear carbon chains of finite to infinite size: Visual interpretation from Pauling bond orders
Authors: Cao Zexing , Wu Wei , Zhang Qianer
Published: July 2003

Schemes for Kekulé structure counting of linear carbon chains are suggested. Mathematical formulas, which calculate the Pauling bond order P(k, N) of a chemical bond numbered by k, are given for the carbon chain with N carbon atoms. By use of the least‐squares fitting of a linearity, relationships between Pauling bond orders and bond lengths are obtained, and such correlation of the Pauling bond order–bond length can be qualitatively extended to the excited states. The relative magnitudes of Pauling bond orders in unsaturated carbon chains dominate C–C bond lengths a well as the bond length feature with the chain size increasing. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 144–149, 2003
Contortion and Formation Structures in the Mappings between Robotic Jointspaces and Workspaces
Authors: Rooney J. , Tanev T. K.
Published: July 2003

The concepts offormationin robotic workspace (WS) andcontortionin robotic jointspace (JS) are developed, based on the notions ofposeandposture,respectively. The approach focuses on the forward and reverse mappings between jointspace and workspace. It utilizes the Cartesian product spaceJS×WSto interpret these mappings, and, in particular, their singularities as determined by the Jacobians. The singularities are interpreted from the viewpoint of geometric (Clifford) algebra. Initially, systems that have 1D jointspaces and 1D workspaces are discussed before higher‐dimensional examples are examined. © 2003 Wiley Periodicals, Inc.
A Dynamic Analysis of a Spatial Manipulator to Determine Payload Weight
Authors: Crane Carl D. , Duffy Joseph
Published: July 2003

This paper presents a methodology whereby the payload weight of a serial manipulator can be determined from a minimum set of sensor data, i.e., joint angle and joint torque measurements. The particular manipulator geometry that is analyzed is a four degree‐of‐freedom serial chain that is commonly used in excavator systems. It was quite remarkable that a relatively simple solution was obtained for the payload weight considering that there are a total of nine unknown moments and cross moments of inertia of the payload together with the unknown location of the center of mass. Example calculations are presented. © 2003 Wiley Periodicals, Inc.
Kinematics of a Family of Translational Parallel Mechanisms with Three 4‐DOF Legs and Rotary Actuators
Authors: Carricato Marco , Parenti‐Castelli Vincenzo
Published: July 2003

This paper focuses on the kinematics of a family of translational parallel mechanisms equipped with three 4‐DOF legs and rotary actuators. The direct and the inverse position problems are solved in analytical form, the velocity analysis is carried out, the workspace is determined and the loci of both kinematic singularities and isotropic configurations are derived. Furthermore, the problem of singularity avoidance by means of actuator redundancy is addressed and some solutions are proposed. Two special architectures are finally considered as case studies: in the first, the three actuation axes are mutually orthogonal; in the second, two actuation axes are parallel to each other and the third is perpendicular to them. The comparison of the two architectures on the basis of kinematic considerations allows for the selection of the second one as a preferable solution. © 2003 Wiley Periodicals, Inc.
Adaptive and Nonlinear Fuzzy Force Control Techniques Applied to Robots Operating in Uncertain Environments
Authors: Burn K. , Short M. , Bicker R.
Published: July 2003

For robots to perform many complex tasks there is a need for robust and stable force control. Linear, fixed‐gain controllers can only provide adequate performance when they are tuned to specific task requirements, but if the environmental stiffness at the robot/task interface is unknown and varies significantly, performance is degraded. This paper describes the design of two nonlinear, fuzzy force controllers, developed primarily using analytical methods, which overcome the problems of conventional control. Using simulation and an experimental robot, they are shown to perform well over a wide range of stiffness and both a quantitative and qualitative assessment of their performance compared with conventional force control is presented. © 2003 Wiley Periodicals, Inc.
A Linear Algebraic Procedure in Obtaining Reciprocal Screw Systems
Authors: Dai Jian S. , Jones John Rees
Published: July 2003

This paper presents a linear algebraic procedure in obtaining (6−n) reciprocal screws from an n‐screw system of a robotic manipulator. The procedure starts by formulating the reciprocal relationship between a screw system and its reciprocal screw system in matrix form, and augmenting the screw matrix which is assembled with n screws in the screw system. Vectors of cofactors of the augmented row are then produced and the partitioning of the screw matrix is implemented to generate each of the (6−n) reciprocal screws. The theory developed in this paper provides a novel and simple procedure to obtain reciprocal screws from any screw system. The paper illustrates applications to cases with different screw systems. © 2003 Wiley Periodicals, Inc.
Review: Don't Cross‐Thread the Screw!*
Authors: Hunt Kenneth H.
Published: July 2003

The screw is a geometrical element. As Sir Robert Ball stated a century or more ago, the screw joins the company of point, plane, and line. In mechanics, especially instantaneous kinematics and statics of rigid bodies, angular and translational velocity of a body combine as a twist on a screw; precisely analogously a force and a couple combine as awrench on a screw. In three dimensions screw theory provides essential and simple insight into the behavior of systems of jointed bodies. And screw theory can also play a leading role in the systematic selection of suitable geometrical patterns that should relate to such jointed systems. Yet the mechanics of robots—the prime example today of systems of jointed bodies—has developed with little respect for the screw, even at the most elementary level. Here I focus mainly on robot performance, the study of which has, to an excessive extent, been proceeding blindly in territory where there is an abundance of screws and systems of screws, all, as it were, shouting to be taken on board to show the way. Failure to recognize the screw, and an unwillingness to use it properly, has led to the screw's being violently abused—“cross‐threaded.” There are far too many examples of “cross‐threading” that have, regrettably, appeared in recent years in several well‐known journals. Offenses have been perpetrated and yet left unchallenged. Here I try to remove any mystery that some may see surrounding, and even concealing, the screw. I then venture to deal critically with a small selection of the many instances of cross‐threading. However, this symposium has as a main objective the celebration of a Centenary. So it betokens an element of light‐heartedness that I resort to at times within the pages that follow. © 2003 Wiley Periodicals, Inc.
Describing three‐dimensional cervical spine movement in a diseased and a non‐diseased group using multilevel modelling
Authors: Jordan K. , Jones P. W. , Dziedzic K.
Published: July 2003

Clinicians often request patients to perform movements of joints as an aid to assessment and diagnosis of many diseases. However, patients may perform abnormal secondary movements where their primary movement is limited. A new measuring system, the FASTRAK, has the potential to measure movement in three dimensions, and to measure movements of the body away from the primary movement. This paper explores the use of multilevel modelling to describe the patterns of movement where subjects are measured on several occasions for both a non‐diseased group and for a group of subjects suffering from ankylosing spondylitis. Three‐level multilevel models are described with level 3 being the subjects, level 2 being the measurement occasions (up to three) and level 1 being the measurements (three) on each occasion. The models highlight which are the most important secondary movements during the primary movement and show clinically interpretable patterns of movement that can highlight differences between diseased and non‐diseased groups. Copyright © 2003 John Wiley & Sons, Ltd.
Applying the right statistics: analyses of measurement studies
Authors: Bland J. M. , Altman D. G.
Published: July 2003

The study of measurement error, observer variation and agreement between different methods of measurement are frequent topics in the imaging literature. We describe the problems of some applications of correlation and regression methods to these studies, using recent examples from this literature. We use a simulated example to show how these problems and misinterpretations arise. We describe the 95% limits of agreement approach and a similar, appropriate, regression technique. We discuss the difference vs. mean plot, and the pitfalls of plotting difference against one variable only. We stress that these are questions of estimation, not significance tests, and show how confidence intervals can be found for these estimates. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Maternal anxiety and fetal behavior at 15 weeks' gestation
Authors: Bartha J. L. , Martinez‐Del‐Fresno P. , Romero‐Carmona R. , Hunter A. , Comino‐Delgado R.
Published: July 2003

Objective

To analyze the relationship between maternal anxiety and fetal behavior at 15 weeks' gestation.

Methods

Twenty women in two groups were studied: 10 women underwent amniocentesis and 10 controls did not. Maternal anxiety was evaluated using the State Trait Anxiety Inventory questionnaire. Maternal plasma catecholamines (noradrenaline, adrenaline, dopamine) and maternal serum adrenocorticotropic hormone, cortisol, glucose, insulin, triiodothyronine, thyroxine and thyroid‐stimulating hormone were measured. Catecholamines were also measured in the amniotic fluid of women undergoing amniocentesis. Compiled actograms of 40‐min observations were done using ultrasonography.

Results

Maternal state‐anxiety was significantly increased in the amniocentesis group. Except for fetal hiccups (r = 0.49, P = 0.03) there was no significant correlation between maternal anxiety and any of the other studied fetal movements. Maternal glucose was significantly correlated with hiccups (r = −0.59, P = 0.01), isolated leg movements (r = −0.52, P = 0.03), startles (r = −0.47, P = 0.04) and the total of the studied movements (r = −0.47, P = 0.04). Amniotic fluid catecholamines were significantly correlated with hand–face contact (r = 0.71, P = 0.02 for adrenaline), startles (r = 0.75, P = 0.01 for noradrenaline and r = 0.64, P = 0.04 for dopamine) and general movements (r = 0.89, P = 0.001 for noradrenaline).

Conclusions

This study does not support a relationship between maternal anxiety and fetal behavior in early pregnancy. Maternal glucose and plasma catecholamines could be related to fetal movements at 15 weeks' gestation. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Estimation of fetal urinary bladder volume using the sum‐of‐cylinders method vs. the ellipsoid formula
Authors: Fägerquist M. , Fägerquist U. , Odén A. , Blomberg S. G.
Published: July 2003

Objectives

A changing hourly fetal urine production rate (HFUPR) has been demonstrated when fetuses are subjected to hypoxia, which is of clinical interest. Conventionally, calculations of the HFUPR have been based on repeated two‐dimensional ultrasound bladder images during the filling phase and the formula for ellipsoids. However, the bladder shape changes from the ellipsoidal to super‐ellipsoidal during filling and the volume could be underestimated. In this study the sum‐of‐cylinders method was used, a method which does not depend on the longitudinal bladder shape being an ellipse.

Methods

The volumes from 102 urinary bladder images from 34 fetuses (three per fetus) were assessed using the sum‐of‐cylinders method. These results were compared with the corresponding findings when using the ellipsoid formula on the identical material of bladder images in a previous study.

Results

When using the sum‐of‐cylinders method vs. the ellipsoid formula, the mean volume difference was +1.6 mL. Applying the sum‐of‐cylinders method for bladder volumes of 5–40 mL resulted in standard deviations of 8.8–3.5% vs. 12.9–5.5% when using the ellipsoid formula. No deviation was found when using the sum‐of‐cylinders method vs. a known volume formula for cylinders, which simulated super‐ellipsoids on the computer screen.

Conclusions

Volume calculation by the sum‐of‐cylinders method is independent of the longitudinal bladder shape when it comes to producing accurate estimations. This method demonstrated a systematically larger volume compared with the ellipsoid formula. The sum‐of‐cylinders method is therefore preferable for volume estimations of the fetal urinary bladder. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Uterine contractions increase fetal heart preload
Authors: Takahashi Y. , Iwagaki S. , Nakagawa Y. , Kawabata I. , Tamaya T.
Published: July 2003

Objective

The preload index (PLI) has been shown to increase in the recipient fetus of twin–twin transfusion syndrome in the presence of uterine contractions. The objective of this study was to determine whether there are changes in PLI in the presence of uterine contractions in normal fetuses.

Methods

Inferior vena cava blood flow was measured using Doppler sonography in 45 normal fetuses at 18–41 weeks' gestation in the presence of uterine contractions and during quiescence and the PLI was compared between groups.

Results

There was a highly significant difference (P < 0.0001) between the mean ± SD PLI in fetuses in the absence (0.235 ± 0.07) and in the presence (0.534 ± 0.183) of uterine contractions.

Conclusion

Uterine contractions appear to increase fetal preload conditions in normal pregnancy. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
A histological and radiological investigation of the nasal bone in fetuses with Down syndrome
Authors: Tuxen A. , Keeling J. W. , Reintoft I. , Fischer Hansen B. , Nolting D. , Kjær I.
Published: July 2003

Objectives

Previous studies of nasal bone development in Down syndrome have used radiographs or ultrasound for the detection of nasal bone length or nasal bone absence. The aim of this study was to investigate the presence and size of the nasal bones in postmortem Down syndrome fetuses by means of radiographs and histological examination.

Methods

Thirty‐three aborted human fetuses (gestational age 14–25 weeks) with Down syndrome were included. A mid‐sagittal tissue block was excised from the skull base to the foramen magnum and along the lateral aspect of the spine. Radiographs of the tissue block were taken in lateral, frontal and axial projections. The length of the nasal bone was measured. The tissue blocks were cut in serial sections and stained. The crown–rump length (CRL), foot length (FL) and number of ossified bones in the hand and foot (CNO) were recorded.

Results

A total of 8/33 fetuses had bilateral nasal bone absence and two had unilateral absence. In fetuses with radiographically diagnosed nasal bone absence, no nasal bone could be found histologically. The majority of the Down syndrome fetuses had CRL, FL and CNO values within the range of those for normal age‐matched fetuses. Nasal bone length was normal or reduced.

Conclusions

Absence of the nasal bone was registered by postmortem examination in one‐third of fetuses with Down syndrome. In some fetuses this could be a result of delayed maturation associated with Down syndrome. The phenotypic differences in nasal bone appearance may reflect genotypic differences in the Down syndrome group. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Prenatal diagnosis of femur–fibula–ulna complex by ultrasound examination at 20 weeks of gestation
Authors: Geipel A. , Berg C. , Germer U. , Krokowski M. , Smrcek J. , Gembruch U.
Published: July 2003

We describe the prenatal sonographic diagnosis of femur–fibula–ulna complex at 20 weeks of gestation. On targeted ultrasound examination, a severe malformation of the lower limbs was observed. Further sonographic exploration demonstrated bilateral asymmetrical femoral hypoplasia, hypoplasia of both tibiae, bilateral aplasia of the fibulae and oligosyndactyly of the right hand with absence of the 4th and 5th rays. The prenatal sonographic features and differential diagnosis are discussed. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Acoustic streaming: a new technique for assessing adnexal cysts
Authors: Edwards A. , Clarke L. , Piessens S. , Graham E. , Shekleton P.
Published: July 2003

Objectives

To determine whether acoustic streaming has clinical value in the differentiation between various ovarian and adnexal cysts.

Methods

We assessed 29 adnexal cysts, for which pathological diagnosis was available, for the presence of acoustic streaming during B‐mode and color sonographic evaluation.

Results

Acoustic streaming was detected in 15 (52%) of the cysts. The most common cyst, endometrioma (n = 7), did not exhibit acoustic streaming in any case, while of the remaining 22 cysts, 15 exhibited acoustic streaming (P = 0.0017). Dermoid cysts exhibited acoustic streaming in two of six (33%) cases. In addition acoustic streaming was noted in two of two (100%) hemorrhagic cysts, eight of ten (80%) cystadenomas, two of three (67%) malignant cysts and in the one abscess.

Conclusions

Acoustic streaming is the first sonographic feature that may be able to completely exclude endometrioma as a possible diagnosis for an adnexal cyst. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Reliability and validity of two methods of three‐dimensional cervical volume measurement
Authors: Farrell T. , Cairns M. , Leslie J.
Published: July 2003

Objectives

To determine if cervical length obtained with three‐dimensional ultrasound correlated with the ‘true cervical volume’ and to evaluate the reliability and validity of transabdominal and transvaginal three‐dimensional cervical volume measurement.

Methods

This was a prospective observational study. Three‐dimensional cervical volume measurements were made prior to hysterectomy in 28 women. Following hysterectomy the amputated cervical volume was calculated using water displacement. For the assessment of intra‐ and interobserver reliability, the intraclass correlation coefficient (ICC) was used. The index of concordance between the sonographic cervical volumes and those obtained by the reference standard (true cervical volume) was assessed with the limits of agreement method and the ICC.

Results

Transabdominal cervical length and transvaginal cervical length correlated moderately with actual cervical volume; correlation coefficients were 0.64 and 0.57 (P < 0.05), respectively. Intraobserver reliability for both transabdominal and transvaginal cervical volume assessment was good (> 0.75). Interobserver reliability for transvaginal cervical volumes was similarly good (ICC = 0.90). However, for transabdominal measurements the interobserver reliability was poor (ICC = 0.51). The validity of both methods of three‐dimensional volume assessment was poor (ICC < 0.75). This was reflected in the wide limits of agreement, which ranged from approximately − 25 mL to + 30 mL.

Conclusion

The reliability and validity of three‐dimensional cervical volume measurement are poor. Clinical introduction of cervical volume measurement should be avoided at this time. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
The nasal bone in fetuses with trisomy 21: sonographic versus pathomorphological findings
Authors: Minderer S. , Gloning K. P. , Henrich W. , Stöger H.
Published: July 2003

Objective

To compare the sonographic findings of the nasal bone in fetuses with trisomy 21 with pathomorphological findings to determine whether the bone is truly absent.

Methods

Seventeen first‐trimester fetuses with trisomy 21 were identified; the median gestational age was 12 weeks (range, 11–14) and the median maternal age was 38 (range, 27–47) years. Transabdominal ultrasound examination, preceding transabdominal chorionic villus sampling (TA‐CVS) for karyotyping, included assessment of the fetal nose. The nasal bone was determined to be ‘hypoplastic’ or ‘absent’ and its length was measured. All pregnancies underwent termination after diagnosis. Serial sagittal sectioning with hematoxylin and eosin‐staining of formalin fixed tissue was performed.

Results

Of the 17 cases, the nasal bone was sonographically evident, but with severe hypoplasia in 10 cases, absent in six, and in the remaining case it was not able to be assessed due to fetal position. Histomorphologically, in 16 cases a nasal bone was present, detectable by the evidence of an ossification center, and in one case the ossification structure was not clearly visualized. Retrospective review of ultrasound images could identify nasal bones in five of the six cases in which they were initially reported as being absent on ultrasound examination. These were visible, but less distinct and had decreased echogenicity, hence misinterpretation led to the false finding of an absent nasal bone when it was in fact present but hypoplastic.

Conclusion

Sonographic assessment of the fetal nasal bone should not distinguish between ‘present’ and ‘absent’, but instead between ‘normal’ and ‘hypoplastic’. For reproducible results it is necessary to standardize the sonographic examination. The sonographic landmarks of the fetal nose are: the nasal bone, the skin above and the cartilaginous tip of the nose. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Sonographic diagnosis of vesicouterine fistula
Authors: Park O.‐R. , Kim T.‐S. , Kim H.‐J.
Published: July 2003

Vesicouterine fistula is one of the least common types of urogenital fistula, accounting for only 1–4% of all cases. We report a case of vesicouterine fistula after vacuum delivery in a woman with a history of a previous Cesarean section. The 29‐year‐old woman was hospitalized due to continuous serosanguinous vaginal leakage and hematuria. Transvaginal sonography demonstrated the presence of a fistulous tract between the uterus and the bladder. Cystoscopy demonstrated a small opening in the posterior bladder wall and a cystogram revealed a fistulous tract between the posterior portion of the bladder and the uterine cavity. Since the patient could not tolerate her symptoms, we decided to close the fistulous tract surgically. The fistulous tract was excised and the bladder and uterus were closed primarily. The bladder was drained with a Foley catheter for 12 days and subsequent follow‐up of the patient has demonstrated urinary continence. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.
Revisiting first‐trimester fetal biometry
Authors: Salomon L. J. , Bernard J. P. , Duyme M. , Dorion A. , Ville Y.
Published: July 2003

Introduction

Although advances in ultrasound have facilitated the diagnosis of fetal abnormalities in the first trimester, fetal biometry at this stage of pregnancy remains underused in prenatal diagnosis. We hypothesized that charts which directly correlate measurements to crown–rump length (CRL) could be more accurate than those based on gestational age (GA) derived from CRL measurement. The aim of this study was to construct CRL‐based biometric charts.

Methods

Measurements of biparietal diameter (BPD), head circumference (HC) and abdominal circumference (AC) were prospectively collected from 939 normal singleton fetuses. Charts and predictive equations were constructed from data obtained from pregnancies in which the CRL was between 45 and 84 mm and for which the outcome was normal.

Results

Measurements of BPD, HC and AC from 880 fetuses who met the criteria were correlated with CRL and used to construct charts and predictive equations. The standard error of estimates using CRL was significantly lower than that using GA in all cases.

Discussion

First‐trimester growth charts and predictive equations based on CRL instead of GA are more accurate. They might have a role in quality control of first‐trimester ultrasound examination and may help in the diagnosis of fetal conditions that involve early growth abnormalities. Copyright © 2003 ISUOG. Published by John Wiley & Sons, Ltd.