bluuebunny/crossref_metadata_2025 huggingface dataset:
Embedded Atom Method Study of Pd Thin Films on Cu(001)
Authors: Bilić A. , Shen Y. G. , King B. V. , O'Connor D. J.
Published: August 2003

We have studied the structures formed by the deposition of 0.5 and 1 monolayer (ML) of Pd on a Cu(001) surface using Monte Carlo (MC) simulations and static optimizations. The energetics are given by the semiempirical embedded atom method (EAM). At 0.5 ML Pd coverage we find that a Pd–Cu c (2×2) single layer surface alloy is created, consistent with experimental observations. At 1 ML Pd coverage a double layer c (2×2) Cu–Pd surface alloy is found to be energetically favored over structures with a clock-reconstructed topmost layer. However, metastable configurations of the top layer consisting of a clock-rotated phase with the (2×2) p4g symmetry coexisting with phases with c (2×2) and p (2×2) symmetries can also be obtained, in agreement with the experimental results.
Dephasing of Local Vibrations in a Planar Lattice of Adsorbed Molecules
Authors: Rozenbaum V. M. , Kuzmenko I. V.
Published: August 2003

We investigate anharmonically coupled high- and low-frequency excitations in a planar lattice of adsorbed molecules interacting with phonons of a crystal. Dephasing of high-frequency local vibrations by low-frequency resonance modes is described in terms of the temperature Green's function. The equations obtained are solved, first, with a small ratio of the anharmonic-coupling coefficient for high- and low-frequency modes to the resonance width, and second, in the low-temperature limit. High-frequency spectral-line positions and widths depend on dispersion laws and resonance-mode lifetimes. It is shown that lateral interactions of low-frequency modes of adsorbed molecules can lead to a significant narrowing of high-frequency spectral lines, which is consistent with experimental data.
Time-Reversed Internal-Source Holography
Authors: Tong S. Y. , Huang H.
Published: August 2003

We have derived an expression for incident-beam-induced fine structures at a local site. We show that using time-reversal arguments, local incident-beam-induced fine structures are equivalent to photoelectron holography with an isotropic reference wave. We suggest that positron-beam-induced desorption or Auger fine structures offer attractive alternatives to using electron beams because the positron-atom scattering factor contains less angular anisortropy and the multiple scattering is weaker.
Thermal Desorption and Surface Diffusion Complicated by Dipole–Dipole Interaction between Adsorbed Particles
Authors: Zhdanov V. P.
Published: August 2003

General self-consistent equations are derived to describe thermal desorption and surface diffusion affected by dipole–dipole interactions between adsorbed particles. Special attention is paid to the analysis of mutual depolarization of dipoles.
Na and Cl2 Interaction on it and 2H–TaSe2(0001) Surfaces
Authors: Papageorgopoulos C. A. , Kamaratos M. , Saltas V. , Jaegermann W. , Pettenkofer C. , Tonti D.
Published: August 2003

In this paper we study the interaction of Cl 2 and Na on 1T– TaSe 2 and 2H– TaSe 2(0001) surfaces in the temperature range of 100–300 K. The experiments are performed in UHV with the use of LEED and SXPS by synchrotron radiation measurements. Deposition of Na on Cl 2-covered 1T– TaSe 2 at 100 K forms initially a [Formula: see text], which with increasing temperature to 300 K leads to NaCl formation. Adsorption of Cl 2 on Na-intercalated 1T and 2H– TaSe 2 surfaces at 100 K forms Cl 2 multilayers. The first Cl 2 layer, in contact with the substrate, interacts with the Na near the surface and forms [Formula: see text]. Warming up to 300 K leads to partial desorption of Cl 2, while the remaining chlorine interacts strongly with Na, causing the deintercalation of Na to the surface in the tendency to form NaCl. The intercalation–deintercalation process takes place across the van der Waals planes and it is much faster on 2H than on 1T– TaSe 2, which is attributed to the different crystal structure of 2H and 1T of TaSe 2.
HREEL Study of the Coadsorption of Sodium and Oxygen on Ni(111)
Authors: Chiarello G. , Lucozzi P. , Cupolillo A. , Caputi L. S. , Papagno L. , Colavita E.
Published: August 2003

The coadsorption of oxygen and sodium on Ni(111) was studied by high resolution electron energy loss spectroscopy. Measurements were performed for a definite sodium precoverage, as a function of oxygen exposure and temperature. For a coverage of two layers of sodium, the loss spectra show the vibrational features related to Na– O 2 and O–O bonds of superoxide NaO 2 molecules. The annealing up to 450 K causes the decomposition of these complexes and the reappearance of the stretching frequencies of isolated Na–O and O–Ni species. At 550 K, only the oxidation of the Ni substrate occurs. The spectra are correlated to work function measurements, and the behavior of the work function versus oxygen exposure, for high alkali coverages, is ascribed to a reionization of the metallic Na layer, rather than to a penetration of oxygen atoms underneath the Na layer.
Photoelectron-Diffraction Studies of Nb(001)
Authors: Lo W.-S. , Chien T.-S. , Fang B.-S. , Wei C. M. , Mei W. N.
Published: August 2003

Photoelectron-diffration studies of Nb(001) have been performed to determine the first-interlayer contraction using Mg Kα radiation (hν=1253.6 eV) as an excitation source. Photoemission intensities of the 3d 5/2 core level were measured as a function of the polar angle along several azimuths on the single-crystal surface. The 202.3-eV (205.O-eV) binding energy for the 3d 5/2( 3d 3/2) core level was well resolved in the photoemission spectra, where the peak intensity could be easily evaluated by curve-fitting processes. Large oscillations of the 3d 5/2 intensity as a function of the polar angle due to forward-focusing were observed. Based on multiple-scattering calculations for several first-interlayer spacings ranging from the bulk value to 16% contraction, the best agreement with experiment was obtained for a (13±5)% contraction of the first-interlayer spacing.
Bismuth on GaSb(110): Structural Determination of the 1×1 and 1×2 Phases by Surface X-Ray Diffraction
Authors: Lottermoser L. , Van Gemmeren T. , Bunk O. , Johnson R. L. , Landemark E. , Smilgies D. , Nielsen M. , Feidenhans'l R.
Published: August 2003

The surface geometry of the 1×1 and 1×2 phases of bismuth on GaSb(110) has been determined using surface X-ray diffraction with synchrotron radiation. The bismuth atoms form zigzag chains along the [Formula: see text] direction of the substrate. For the 1×1 phase four different registries of the bismuth chains with respect to the GaSb(110) substrate are possible. It was found that only the epitaxial continued layer structure was in good agreement with the experimental data. In the 1×2 reconstruction every second zigzag chain in the uppermost substrate layer is missing. The reconstructed surface is terminated with a full monolayer of Bi atoms which also form zigzag chains. The Bi atoms in the chains bond alternately to the first and second layer substrate atoms and the Bi chains are inclined at 34° to the surface. This new structural model explains the higher thermal stability of the 1×2 phase compared to that of the 1×1 phase.
Metastable Structures in the Initial Stages of Si Homoepitaxy
Authors: Borovsky Brian , Krueger Michael , Ganz Eric
Published: August 2003

We discuss the growth of the first six atoms of an epitaxial Si island on Si(001). The nucleation of a six-atom island is observed to rely on a conversion between two metastable four-atom structures. These results suggest that metastable configurations play an important role in epitaxial growth.
Structure of Prototypical Semiconductor Surfaces and Interfaces Investigated by Photoemission Extended X-Ray Absorption Fine Structure (PEXAFS)
Authors: Mangat P. S. , Soukiassian P.
Published: August 2003

Extended X-ray absorption fine structure (EXAFS) has been known for half a century. However, using synchrotron radiation, it has developed into a powerful tool for determining the atomic structure of a wide variety of surfaces and interfaces. The power of this technique lies in its sensitivity to the local environment of a particular element. Photoemission extended X-ray absorption fine structure (PEXAFS) is a new variation of electron detection surface EXAFS (SEXAFS) using photoemission spectroscopy in the constant initial state mode, Due to small escape depths, a very high surface sensitivity is achieved. Other major advantages of this new technique include (i) an improved signal/noise ratio allowing very short data collection times, which is an especially useful feature for short lifetime surfaces, and (ii) double-checking interatomic distances. Combined with core level and valence band photoemission spectroscopies. PEXAFS provides the exceptional ability to probe the atomic geometry and the electronic structure at the same time and for the same surface. It thus gives access to important issues, such as (i) surface reconstruction and/or relaxation, (ii) bonding nature, (iii) adsorption site and (iv) initial interface formation. Furthermore, it could be used to clarify photoemission core level shift origin by allowing one to discriminate structural changes from other causes as initial or final state effects. This article reviews the latest PEXAFS investigations for model elemental (silicon) and compound (indium phosphide) semiconductor surfaces and their interfaces with alkali metals, antimony, aluminum, bismuth and silver.
LEEM Phase Contrast
Authors: Altman M. S. , Chung W. F. , Liu C. H.
Published: August 2003

Contrast in low energy electron microscopy (LEEM) originating in the phase of the imaging electron wave is discussed. A wave-optical model is reviewed in which LEEM step contrast is calculated as the interference of the Fresnel diffracted waves from terrace edges which meet at a step. Model predictions which take into account instrumental resolution and beam coherence effects are compared to experimental observations of steps on the W(110) and Si(111) surfaces. Most importantly, this work allows for the routine identification of the step sense with LEEM by inspection. A quantum-mechanical Kronig–Penney model is also presented to explain the quantum size effect (QSE) in electron reflectivity from thin films, which underlies LEEM quantum size contrast. Model predictions reproduce the non-free electron dispersion which is observed in experiment for Cu films on the W(110)surface. This model also serves to demonstrate the relationship between electron reflectivity and electron band structure at a fundamental level.
LEEM Measurements of Step Energies at the (001) Surface of Heavily Boron-Doped Silicon
Authors: Hannon J. B. , Swartzentruber B. S. , Kellogg G. L. , Bartelt N. C.
Published: August 2003

We have used the low energy electron microscope (LEEM) to investigate step faceting and striped phase formation on heavily boron-doped Si(001) surfaces. Measurements of thermal fluctuations along the steps, equilibrium island shapes, and the angle of triangular facets provide quantitative information on the step formation energies. We find that a simple, systematic temperature dependence of the spatial anisotropy of the free energy of isolated steps is sufficient to account for the observed faceting of the B type steps. These results suggest that the proliferation of straight A step edges at lower temperature is caused by the energy of isolated A steps becoming vanishingly small. We show that rapid cooling of the samples leads to the nucleation and growth of a high density of vacancy islands on the surfaces. Based on these results, we propose a qualitative model for mass transport during stripe formation.
Giant Faceting of Vicinal Si(001) Induced by Au Adsorption
Authors: Heringdorf F.-J. Meyer Zu , Kähler D. , Horn-Von Hoegen M. , Schmidt Th. , Bauer E. , Copel M. , Minoda H.
Published: August 2003

4° vicinal Si(001) shows perfectly ordered terraces with a width of 4 nm which are separated by double steps. Adsorption of Au at 800°C results in a dramatic change of the step morphology: the surface decomposes into areas which are perfectly flat with a (001) orientation and (119) facets, which compensate for the macroscopic miscut. Extremely straight superterraces with a length limited only by the size of the sample (here 4 mm) and a width ranging from 400 nm to 4 μm are formed by massive Si mass transport. The extreme aspect ratio of 1:10 000 of this submicron structure is attributed to a heterogeneous nucleation process.

SPA-LEED reveals a new, Au-induced incommensurate 5×3.2 reconstruction above a critical coverage as the driving force for the formation of large elongated (001) terraces. LEEM shows the strongly anisotropic nucleation process in vivo. Dark field imaging and microspot LEED techniques have been used to determine the influence of the different 5×3.2 domain orientations on the growth behavior of the (001) superterraces. The majority of domain terraces grow with a speed of more than 10 μm per second. The width and area of the (001) terraces increase proportionally to the Au coverage. The steps of the vicinal surface are accumulated in irregular step bunches. With further increasing Au coverage the step bunches are transformed into well-defined facets with a (119) orientation, as determined by SPA-LEED.

The kinetics of the faceting process have been studied with SPA-LEED, REM, STM, and light diffraction using a HeNe laser, because the typical size of the superterraces is of the order of the wavelength of visible light: the resulting structure is visible to the bare eye. The parallel arrangement of superterraces acts as an irregular optical phase grating: illumination with white light results in stripes of all possible diffraction colors.
A New Low Energy Electron Microscope
Authors: Tromp R. M. , Mankos M. , Reuter M. C. , Ellis A. W. , Copel M.
Published: August 2003

Low energy electron microscopy (LEEM) has developed into one of the premier techniques for in situ studies of surface dynamical processes, such as epitaxial growth, phase transitions, chemisorption and strain relaxation phenomena. Over the last three years we have designed and constructed a new LEEM instrument, aimed at improved resolution, improved diffraction capabilities and greater ease of operation compared to present instruments.
Development of a Low Energy Electron Microscope with an Energy Analyzer
Authors: Sakai Y. , Kato M. , Masuda S. , Harada Y. , Ichinokawa T.
Published: August 2003

A low energy electron microscope (LEEM) with an energy analyzer of the Wien filter type was constructed for surface microanalyses and imaging by irradiating the specimen surface with several types of incident beams, e.g. low energy electrons, UV photons or metastable He * atoms. A retarding type Wien filter was used for the formation of electron energy filtered images and energy spectra of selected microareas by employing energy loss electron and Auger electron, photoelectron or Penning ionization spectroscopy. Several new designs and performances have been implemented in this instrument and are presented together with some applications.
Spin-Polarized Low Energy Electron Microscopy
Authors: Duden Th. , Bauer E.
Published: August 2003

We present the concept and recent developments of spin-polarized low energy electron microscopy. A detailed discussion addresses the questions of magnetic resolution and the image acquisition rate. Examples of recent experiments illustrating the possibilities of the present instrumental setup are given.
LEEM Investigation of Refractory Metals Grown on Insulating Substrates: Nb (110) on Sapphire $(11\bar{2}0)$
Authors: Świȩch W. , Appleton R. S. , Wiemeyer B. D. , Flynn C. P.
Published: August 2003

We summarize LEEM studies of Nb (110) single crystals grown by MBE on Al 2 O 3[Formula: see text]. At temperatures between 1300 K and 1600 K the structure relaxes to create flat terraces several μm wide, and stable subgrain boundaries, by clearly visible interfacial and surface processes. The Nb surface exhibits two mirror-equivalent variants of a reconstruction, one of which prevails at low temperatures. Upon approaching Tc at ~1480 K, the two variants alternate in extended stripes along [Formula: see text], with stripe widths that decrease smoothly as T approaches Tc. Both at low T and above Tc, variants are trapped at dislocation strain fields.
LEEM and MEM Studies of Spatiotemporal Pattern Formation
Authors: Rose K. C. , Engel W. , Meißen F. , Patchett A. J. , Bradshaw A. M. , Imbihl R.
Published: August 2003

Spatiotemporal pattern formation has been investigated with low energy electron microscopy (LEEM) and mirror electron microscopy (MEM) during the catalytic oxidation of CO on Pt{110} under both oscillatory and stationary conditions. Due to higher resolution and richer contrast than in previous PEEM studies, it has been possible to investigate the details of the nucleation and propagation of reaction–diffusion fronts which make up the patterns, Further, new and more complex patterns have been discovered which demonstrate the importance of both global coupling and reaction-induced roughening.
Element-Selective Magnetic Imaging in Exchange-Coupled Systems by Magnetic Photoemission Microscopy
Authors: Kuch W. , Frömter R. , Gilles J. , Hartmann D. , Ziethen Ch. , Schneider C. M. , Schönhense G. , Swiech W. , Kirschner J.
Published: August 2003

We have used a photoemission microscope to obtain element-resolved magnetic contrast in stacked magnetic thin film systems. Magnetic information is thereby provided by X-ray magnetic circular dichroism. Elemental sensitivity, which is crucial for studying magnetic coupling phenomena in systems with several different layers, is achieved by tuning the energy of the illuminating photons to atomic absorption edges. We present measurements of a Ni-coated Co micropattern on Cu(001), and a wedged Co/Cr/Fe(001) sample. In the former sample the Ni magnetization is seen to follow the magnetization of the Co pattern, thereby changing from an out-of-plane easy axis in areas without underlying Co to in-plane on top of the Co microstructures. In the latter a reversal of the exchange coupling of the Co layer to the Fe magnetization is observed when the Cr layer thickness exceeds approximately two monolayers. A small net magnetic moment is also observed in the Cr spacer layer, which follows in sign the Co magnetization at the reversal of the exchange coupling. This finding is discussed in terms of interface roughness or interdiffusion.
SMART: An Aberration-Corrected XPEEM/LEEM with Energy Filter
Authors: Wichtendahl R. , Fink R. , Kuhlenbeck H. , Preikszas D. , Rose H. , Spehr R. , Hartel P. , Engel W. , Schlögl R. , Freund H.-J. , Bradshaw A. M. , Lilienkamp G. , Schmidt Th. , Bauer E. , Benner G. , Umbach E.
Published: August 2003

A new UHV spectroscopic X-ray photoelectron emission and low energy electron microscope is presently under construction for the installation at the PM-6 soft X-ray undulator beamline at BESSY II. Using a combination of a sophisticated magnetic beam splitter and an electrostatic tetrode mirror, the spherical and chromatic aberrations of the objective lens are corrected and thus the lateral resolution and sensitivity of the instrument improved. In addition a corrected imaging energy filter (a so-called omega filter) allows high spectral resolution (ΔE=0.1 eV ) in the photoemission modes and back-ground suppression in LEEM and small-spot LEED modes. The theoretical prediction for the lateral resolution is 5 Å; a realistic goal is about 2 nm. Thus, a variety of electron spectroscopies (XAS, XPS, UPS, XAES) and electron diffraction (LEED, LEEM) or reflection techniques (MEM) will be available with spatial resolution unreached so far.
Imaging of Magnetic Data Bits and Ferromagnetic Domains with Photoelectron Emission Microscopy
Authors: Mundschau M. , Romanowicz J. , Wang J. Y. , Sun D. L. , Chen H. C.
Published: August 2003

Magnetic data bits recorded on a computer hard drive disk and ferromagnetic domains on a sample of neodymium–iron–boron, Nd 2 Fe 14 B , a material used in strong permanent magnets, are imaged using an electrostatic photoelectron emission microscope. Local stray magnetic fields of opposite orientation, which exist above the data bits and above ferromagnetic domains, laterally deflect photoelectrons emitted from the samples and partially split the photoelectron beam into two directions. Magnetic contrast is achieved by blocking part of the photoelectron beam with the edge of an aperture. The binary code of a magnetic storage disk is read directly. Disappearance of ferromagnetic domains is followed in real time as Nd 2 Fe 14 B is heated above its Curie temperature. The spontaneous reappearance of ferromagnetic domains is seen as Nd 2 Fe 14 B is cooled.
LEEM Basics
Authors: Bauer Ernst
Published: August 2003

The fundamental physical phenomena on which LEEM is based are discussed, with the goal of showing why LEEM works, not how it works. The subjects covered include intensity, resolution, contrast, sampling depth and combination possibilities with other techniques (particularly LEED) which make LEEM a unique surface imaging method.
SPELEEM: Combining LEEM and Spectroscopic Imaging
Authors: Schmidt Th. , Heun S. , Slezak J. , Diaz J. , Prince K. C. , Lilienkamp G. , Bauer E.
Published: August 2003

At present the only surface electron microscope which allows true characteristic XPEEM (photoemission electron microscopy using synchrotron radiation) and structural characterization is the spectroscopic LEEM developed at the Technical University Clausthal in the early nineties. This instrument has in the past been used mainly for LEEM studies of various surface and thin film phenomena, because it had very limited access to synchrotron radiation. Now the microscope is connected quasipermanently to the undulator beamline 6.2 at the storage ring ELETTRA, operating successfully since the end of 1996 under the name SPELEEM (Spectroscopic PhotoEmission and Low Energy Electron Microscope). The high brightness of the ELETTRA light source, together with an optimized instrument, results in a spatial resolution better than 25 nm and an energy resolution better than 0.5 eV in the XPEEM mode. The instrument can be used alternately for XPEEM, LEEM, LEED (low energy electron diffraction), MEM (mirror electron microscopy) and other imaging modes, depending upon the particular problem studied. The combination of these imaging modes allows a comprehensive characterization of the specimen. This is of particular importance when the chemical identification of structurar features is necessary for the understanding of a surface or thin film process. In addition, PED (photoelectron diffraction) and VPEAD (valence photoelectron angular distribution) of small selected areas give local atomic configuration and band structure information, respectively.
Principles of X-Ray Magnetic Dichroism Spectromicroscopy
Authors: Stöhr J. , Padmore H. A. , Anders S. , Stammler T. , Scheinfein M. R.
Published: August 2003

A review is given of the principles underlying X-ray magnetic circular (XMCD) and linear (XMLD) dichroism spectromicroscopies consisting of polarized X-ray absorption spectroscopy in conjunction with scanning or imaging microscopy. The techniques are shown to have many useful and important capabilities for the study of complex magnetic materials. They offer elemental specificity, chemical specificity and variable depth sensitivity, among others. XMCD microscopy is best suited for the study of ferromagnets and ferrimagnets, and it allows a quantitative determination of the size and direction of spin and orbital moments. XMLD microscopy promises to become a powerful tool for the study of antiferromagnets which are difficult to study by conventional microscopy techniques.
Stochastic processes on totally disconnected topological groups
Authors: Ludkovsky S. V.
Published: September 2003

Stochastic processes on totally disconnected topological groups
are investigated. In particular, they are considered for
diffeomorphism groups and loop groups of manifolds on
non‐Archimedean Banach spaces. Theorems about a quasi‐invariance
and a pseudodifferentiability of transition measures are proved.
Transition measures are used for the construction of strongly
continuous representations including the irreducible ones of
these groups. In addition, stochastic processes on general
Banach‐Lie groups, loop monoids, loop spaces, and path spaces of
manifolds on Banach spaces over non‐Archimedean local fields are
also investigated.
Accurate solution estimates for vector difference equations
Authors: Medina Rigoberto
Published: September 2003

Accurate estimates for the norms of the solutions of a
vector difference equation are derived. They give us
stability conditions and bounds for the region of
attraction of the stationary solution. Our approach
is based on estimates for the powers of a constant matrix.
We also discuss applications of our main results to
partial reaction‐diffusion difference equations and to a
Volterra difference equation.
On uniformly close‐to‐convex functions and uniformly quasiconvexfunctions
Authors: Subramanian K. G. , Sudharsan T. V. , Silverman Herb
Published: September 2003

Two new subclasses of uniformly convex and uniformly
close‐to‐convex functions are introduced. We obtain inclusion
relationships and coefficient bounds for these classes.
Uniqueness and radial symmetry for an inverse elliptic equation
Authors: Emamizadeh B. , Mehrabi M. H.
Published: September 2003

We consider an inverse rearrangement semilinear partial
differential equation in a 2‐dimensional ball and show that it
has a unique maximizing energy solution. The solution represents
a confined steady flow containing a vortex and passing over a
seamount. Our approach is based on a rearrangement variational
principle extensively developed by G. R. Burton.
A nonuniform bound for the approximation of Poisson binomial byPoisson distribution
Authors: Neammanee K.
Published: September 2003

It is well known that Poisson binomial distribution
can be approximated by Poisson distribution. In this paper, we
give a nonuniform bound of this
approximation by using Stein‐Chen method.
A note on asymptotic helix and quantum mechanical structure
Authors: Guha Partha
Published: September 2003

Using the formulation of a moving curve, we
demonstrate that an asymptotic helix goes over to the linear
time‐dependent Schrödinger equation as shown by Dmitriyev
(2002).
Ring homomorphisms on real Banach algebras
Authors: Miura Takeshi , Takahasi Sin-Ei
Published: September 2003

Let B be a strictly real commutative real Banach algebra with
the carrier space ΦB. If A is a commutative real Banach
algebra, then we give a representation of a ring homomorphism
ρ : A → B, which needs not be linear nor
continuous. If A is a commutative complex Banach algebra, then
ρ(A) is contained in the radical of B.
Speech Discrimination in Background Noise with the Vibrant® Soundbridge™ Middle Ear Implant
Authors: Garin P. , Thill M.P. , Gerard J.M. , Galle C. , Gersdorff M.
Published: August 2003

Objective: Evaluate speech intelligibility in competing background noise for monaural users of the Vibrant® Soundbridge™ (VSB) middle ear implant (Symphonix). Patients and Material: Nine adults with moderate to severe bilateral sensorineural hearing loss, and implanted with a unilateral VSB, were included in the study. The patients’ experience of the implant ranged from 9 to 24 months. Retrospective single-subject repeated measures of speech intelligibility in background noise were performed using 2 different test procedures, the Elbaz test and the Garin and Galle test. The patients were tested VSB aided and VSB unaided in a variety of signal-to-noise ratios. The correct-score percentage for each ratio for each condition was averaged for the group of patients and compared with normative data for each test method. Results: The VSB-aided condition showed results approaching normative data for both test methods. At a signal-to-noise ratio of zero, the Elbaz test showed a mean correct score of 55% for the VSB-unaided condition versus 85% for the VSB-aided condition. The Garin and Galle test showed a mean score of 34% for the VSB-unaided condition versus 94% for the VSB-aided condition. Conclusions: Although the unilateral VSB middle ear implant does not restore stereophony, it does improve speech intelligibility in background noise.
Herpesviren bei akuter Innenohr-schwerhörigkeit und «Vestibularisausfall»: klinische und serologische Befunde
Authors: Walther L.E. , Hentschel H. , Oehme A. , Gudziol H. , Beleites E.
Published: August 2003

Ziel: In der vorliegenden Studie erfolgte die statistische Evaluierung klinischer Befunde auf der Grundlage der spezifischen Prävalenzen von IgG-, IgM- und IgA-Antikörpern gegen Herpes-simplex-Viren (HSV) und Varicella-zoster-Viren (VZV) in Serum bei Patienten mit akuter Innenohrschwerhörigkeit und akutem isoliertem peripherem Vestibularisausfall. Patienten und Methoden: Untersucht wurden Patienten mit akuter Innenohrschwerhörigkeit (HSV: n = 150, VZV: n = 104) und Vestibularisausfall (HSV: n = 60, VZV: n = 45), die sich zwischen 1996 und 2000 in stationärer Behandlung an der Universitäts-HNO-Klinik Jena befunden hatten. Die Seroprävalenzen wurden mittels ELISA (Dade Behring Enzygnost®-anti-HSV und -anti-VZV) ermittelt. Anamnestische Angaben und klinische Befunde von seropositiven wurden denen von seronegativen Patienten gegenübergestellt und statistisch analysiert. Ergebnisse: Der Grossteil (87,3%) der Patienten mit einem «Hörsturz» hatten erhöhte IgG-Titer gegen HSV, 9,3% waren gleichzeitig IgM-positiv. Die IgG-Prävalenz für VZV betrug 98,1%. Gut 4,8% waren IgM-positiv, 24% hatten eine erhöhte IgA-Konzentration, 2,9% waren IgM- und IgA-positiv. Bei Patienten mit Vestibularisausfall waren 90% HSV-IgG-positiv und 3,3% gleichzeitig IgM-positiv. Bei 100% war das VZV-IgG erhöht; 15,6% waren VZV-IgA-positiv, darunter 2 auch IgM-positiv. Die Altersverteilung der Patienten mit serologischem Hinweis auf eine HSV- oder VZV-Reaktivierung war zweigipfelig. Patienten mit eine «Hörsturz» mit möglicher HSV-Reaktivierung zeigten signifikant öfter Rezidiverkrankungen (36 versus 12%) sowie Ohrschmerz und Ohrdruck (21 versus 7%). Bei anti-VZV-IgA-positiven Erkrankten mit Vestibularisausfall lag häufiger eine Rezidiverkrankung (14 versus 5%) sowie ein vollständiger Erregbarkeitsausfall in der kalorischen Prüfung (71 versus 45%) vor. Schlussfolgerungen: Das Vorliegen einer Rezidiverkrankung und Ohrdruck bei akuter Innenohrschwerhörigkeit können Hinweise für eine HSV-Reaktivierung sein, Kopfschmerzen und ein Rezidivereignis bei Vestibularisausfall können für eine VZV-Reaktivierung sprechen.
Saliva Flow, pH, Buffer Capacity, and Colonization by Streptococcus mutans during and after Radical Radiotherapy of Head and Neck Tumours
Authors: Beer Karl T. , Zehnder Diego , Lussi Adrian , Greiner Richard H.
Published: August 2003

Background: How does oral health (saliva pH, buffer capacity, and colonization with Streptococcus mutans) change because of reduced salivary flow during and after radical radiotherapy of head and neck carcinoma dependent on ipsilateral or bilateral parotid irradiation? Patients and Methods: 20 consecutive patients who were radically irradiated because of head and neck carcinomas were studied. They were evaluated before radiotherapy, weekly during therapy, and 6 weeks after the end of treatment. Flow rate, pH and buffer capacity of saliva, and colonization with S. mutans were tested. Results: Stimulated saliva secretion rate dropped in the first radiotherapy week in both groups (p < 0.006). This effect was more pronounced in patients with bilateral parotid gland radiation (BPR) in comparison with unilateral parotid gland radiation (UPR). Depending on dose saliva production declined exponentially up to the end of treatment. No rebound was found up to 6 weeks after the end of therapy, a trend towards a further saliva production was observed. Stimulated saliva was significantly diminished when compared to production before the start of treatment (p < 0.003 for UPR and p < 0.001 for BPR). Buffer capacity was reduced parallel to the saliva deficit. The pH of saliva decreased from a mean of 7.3 before treatment to 6.3 at the end of radiotherapy and did not recover for patients with BPR. For patients with UPR, the pH decreased from a mean of 7.8 to 7.4 and remained constant. Colonization with S. mutans increased during treatment and stayed high after the end of radiotherapy. Conclusion: Saliva production is exponentially reduced during radiotherapy, starting in the first week of treatment. Recovery is not observed up to 6 weeks after therapy. Buffer capacity and pH decline during radiotherapy in relation to saliva loss. Colonization by S. mutans increases markedly during radiotherapy and remained high afterwards.
Reoperation for Chiari Malformations
Authors: Sacco David , Scott R. Michael
Published: August 2003

Background: We undertook this study to characterize those patients who required reoperations for Chiari malformation and to determine whether modifications in surgical technique at the initial procedure might have obviated the need for repeat surgery. Methods: We reviewed the hospital records, imaging studies, operative reports, and follow-up data of those patients who were undergoing a second operation as part of a consecutive series of Chiari decompressions carried out by one neurosurgeon over a 14-year period. We wished to determine whether type of Chiari malformation, age at initial surgery, the presence of associated bony anomalies, or initial operative technique contributed to the need for reoperation. Results: Twenty-two (17%) of the surgical procedures represented reoperations (16 of 100 Chiari I and 6 of 33 Chiari II decompressions). Of the patients in the series who were operated on at age 5 years or younger, 7 (16%) were reoperations (5 of 33 Chiari I and 2 of 10 Chiari II decompressions); 15 patients (17%) of those older than 5 years at surgery were reoperations (11 of 67 Chiari I and 4 of 23 Chiari II decompressions). 8 of the 16 patients who underwent reoperations for Chiari I malformation and 4 of the 6 patients who underwent reoperations for Chiari II malformation had their initial decompression surgery at age 5 years or younger. Reoperation was required because of failure to treat adequately an associated syrinx (n = 11), because of persisting neurological symptoms or headache (n = 9), or because of a possible faulty fourth ventricular stent placement (n = 2). 5 of 9 patients in the operative series with Chiari malformations associated with craniosynostosis represented reoperations (55%), and all 3 of the patients whose syrinx persisted after reoperation had craniosynostosis syndromes. Conclusions: Approximately 17% of the patients with Chiari I and Chiari II malformations in this operative series were undergoing a second operation. Factors in this series which were associated with reoperation included a young age at initial surgery, the presence of complex bony anatomy at the foramen magnum, syndromic craniosynostosis, and failure of the surgeon at the initial operation either to assess patency of the foramen of Magendie or correctly place a fourth ventricular stent.
Language Differences in Young Children with Myelomeningocele and Shunted Hydrocephalus
Authors: Vachha Behroze , Adams Richard
Published: August 2003

Objective: This comparative cohort study examined language differences in young children (preschool to first grade) with myelomeningocele and shunted hydrocephalus (MM/SH). Method: A well-validated, standardized language test was administered to 17 children with MM/SH (age range 4–6 years) and 16 age-matched, nonaffected children. Results: Standard scores were obtained within lexical/semantic, syntactic, and pragmatic domains. An analysis of performance on individual subtests within the lexical/semantic domain was striking. Children with MM/SH performed significantly worse (p < 0.01) on a test measuring the comprehension of words representing important early learning concepts and on pragmatic tasks that measured their ability to use language functionally in social situations. Conclusions: Words representing basic precepts and concepts are commonly used in instructions to children in early childhood. Difficulty with functional pragmatic language results in suboptimal communication skills. Academic and community implications are discussed.
Nasoethmoidal Meningioma with Cytogenetic Features of Tumor Aggressiveness in a 16-Year-Old Child
Authors: Ketter Ralf , Henn Wolfram , Feiden Wolfgang , Prowald Alexandra , Sittel Christian , Steudel Wolf-Ingo , Strowitzki Martin
Published: August 2003

The case of a 16-year-old girl is presented who was admitted to our hospital because of severe frontal headache. Magnetic resonance scans revealed a nasoethmoidal tumor on the right side, with erosion of the skull base and invasion of the right orbit. A needle biopsy specimen revealed the histological diagnosis of a fibroblastic meningioma (WHO grade II), with histochemically determined partial activity loss of alkaline phosphatase. The tumor was completely resected by a combined intracranial-transbasal and transnasal approach. In this case, we found a meningioma with deletion of the short arm of chromosome 1 through a translocation between chromosomes 1 and 11 [t(1;11)] as well as additional chromosomal aberrations, including partial or complete monosomy of chromosomes 2, 6, 7, 11, 13 and 22, a cytogenetic pattern known to be associated with elevated tumor aggressiveness in meningiomas of adult patients. Accordingly, this juvenile meningioma may biologically correspond to a WHO grade II adult-type meningioma with an increased risk of recurrence. Therefore, we incorporated this patient into an intensified schedule of postoperative care.
Pathologically Proven Cavernous Angiomas of the Brain following Radiation Therapy for Pediatric Brain Tumors
Authors: Baumgartner James E. , Ater Joann L. , Ha Chul S. , Kuttesch John F. , Leeds Norman E. , Fuller Greg N. , Wilson Ronald J.
Published: August 2003

Lesions consistent with cavernous angiomas (CAs) of the brain are sometimes seen on MRI scans of the brains of patients who received radiation therapy for brain tumors as children. The lesions appear years later within brain tissue that was included in radiation fields. It is unclear whether these MRI-detected lesions are true CAs or a pathological variant. This study reports the clinical, radiographical, and pathological findings in 3 cases of radiation-induced CAs of the brain. From 1995 to 1997, 3 patients previously treated with radiation therapy (45– 55 Gy) for pediatric brain tumors (medulloblastoma, ependymoma, and a presumed midbrain astrocytoma) underwent resections of symptomatic and enlarging lesions that were consistent with a CA of the brain. All of the lesions occurred within fields of prior irradiation. None of the patients had received chemotherapy as part of their cancer treatment. CA-presenting symptoms included seizures, cranial nerve deficits, and headaches. The lesions appeared 7–19 years after radiation therapy and slowly enlarged on subsequent imaging studies. MRI scans of the lesions revealed characteristics typical of CA. The lesions became symptomatic 1–5 years after they were initially noted. Surgical resection was performed 1–2 years after symptoms began. The age at resection ranged from 15 to 23 years (10–21 years after radiation therapy). Pathological analysis of the three lesions showed typical CA characteristics. Some CAs may be caused by radiation therapy for pediatric brain tumors. They are radiologically and pathologically similar to sporadically occurring CAs of the brain and may enlarge over time and become symptomatic. CAs can be safely resected using standard microsurgical techniques.
Rapidly Calcifying and Ossifying Epidural Hematoma
Authors: Erdogan Bulent , Sen Orhan , Bal Nebil , Cekinmez Melih , Altinors Nur
Published: August 2003

Conservative treatment of an epidural hematoma is not always effective in children. We describe an 8-year-old boy who had been followed up conservatively for 10 days at a local hospital due to acute epidural hematoma. A new CT revealed an expansion of the former hematoma accompanied by a thick hyperdense layer. Because the patient presented with symptoms of elevated intracranial pressure, an immediate craniotomy was performed to evacuate the hematoma. The ossified layer, which was densely adhered to the dura mater, was also completely removed. Rapid ossification and/or calcification of an epidural hematoma appearing 10 days after a head injury have not been reported previously. Possible mechanisms of rapid ossification are also discussed in relation to the present report, and the relevant literature is reviewed.
A Rare Case of Lymphangiomatosis of the Craniocervical Spine in Conjunction with a Chiari I Malformation
Authors: Jea Andrew , McNeil Ann , Bhatia Sanjiv , Birchansky Sherri , Sotrel Ana , Ragheb John , Morrison Glenn
Published: August 2003

Lymphangiomatosis of the bone is rare. The axial as well as appendicular skeleton may be affected. Neurosurgical consultation may be called for several reasons: (1) lesions involving the calvarium and/or spine; (2) nondiagnostic biopsies from more accessible and less morbid locations, and (3) persistent CSF leak and/or recurrent meningitis. Thus, it is important for the neurosurgeon to be familiar with this disease entity and consider it in the differential diagnoses of multifocal lytic lesions of the axial skeleton. We present a case report of a 4-year-old girl with lymphangiomatosis of the skull base and upper cervical spine with concurrent Chiari I malformation and briefly review the literature.
Treatment of Pain and Limited Movement of the Shoulder in Hemiplegic Patients with Botulinum Toxin A in the Subscapular Muscle
Authors: Yelnik Alain P. , Colle Florence M.C. , Bonan Isabelle V.
Published: August 2003

Three poststroke hemiplegic patients were treated by injecting Botulinum toxin A (BtxA) into the subscapularis muscle, to reduce pain and increase the range of motion in the shoulder. According to the described procedure, 250 units of Dysport toxin were injected through a 0.8-mm diameter needle with electrostimulation guidance. In the 3 cases, injection of BtxA reduced pain and improved the range of motion, especially abduction and external rotation, of the hemiplegic shoulder. This result confirms the role of spasticity in hemiplegic shoulder pain and the beneficial effects of Botulinum toxin injection into the subscapularis muscle deserve to be confirmed in further series.
Daily Dialysis: The Long and the Short of It
Authors: Gotch Frank A. , Levin Nathan W.
Published: August 2003

There is considerable enthusiasm for daily hemodialysis despite the increased time commitment required of patients because of reported improvements in patient well-being, appetite and blood pressure control. To date, this therapy has been largely empirical and has been defined primarily by treatment time (t) and categorized as short daily hemodialysis (SDHD) with t about 2 h and long nocturnal hemodialysis (LNHD) with t 8–9 h. It is the authors’ view that studies comparing clinical outcome with SDHD and LNHD to conventional hemodialysis (CHD) must have dialysis dosage well defined if they are to provide generalizable results. There is a broad range and overlap in the magnitude of solute removal in reported studies of SDHD, LNHD and CHD, which is illustrated here through kinetic consideration of four solutes: (1) urea; (2) inorganic phosphorus (iP); (3) β2-microglobulin (β2M) and (4) Na/water. The following observations can be made: (1) Patient subjective reports of increased appetite and protein intake may correlate poorly with kinetic calculation of protein catabolic rate. (2) A model of iP mass balance was developed and indicates that iP removal with CHD is inadequate; current SDHD is also inadequate to highly excessive depending on the dose of dialysis. (3) β2M removal with SDHD is virtually the same as reported for LNHD, reflecting major differences in dialyzer membranes used. (4) The decrease in predialysis overhydration is a predictable function of the number of dialyses per week and may be one of the most important benefits of more frequent dialysis. (5) The standard Kt/V (stdKt/V) provides a uniform method of dose calculation but the therapy prescription should also include consideration of the other solutes evaluated above.
Effects of Polymyxin B-Immobilized Fiber Hemoperfusion on Amino Acid Imbalance in Septic Encephalopathy
Authors: Nakamura Tsukasa , Kawagoe Yasuhiro , Matsuda Takaharu , Ebihara Isao , Koide Hikaru
Published: August 2003

Background: Septic encephalopathy is a common term denoting the signs of progressing central nervous system dysfunction in septic patients. Metabolic alterations including amino acid imbalance are involved in the pathogenesis of septic encephalopathy. The aim of the present study was to determine whether the ratio of branched-chain amino acids to aromatic amino acids is altered in patients with septic encephalopathy and whether polymyxin B-immobilized fiber (PMX-F) hemoperfusion affects this balance. Methods: 16 septic patients with encephalopathy, 10 septic patients without encephalopathy, and 20 healthy controls were included in this study. Sepsis was diagnosed according to the ACCP/SCCM Consensus Conference criteria. Plasma endotoxin levels, interleukin-6 (IL-6) levels, and amino acid ratios were measured before and after PMX-F treatment. Results: Within 12 h of the onset of septic encephalopathy, plasma endotoxin and IL-6 levels were increased significantly in septic patients with encephalopathy in comparison to those in septic patients without encephalopathy (endotoxin, p < 0.05; IL-6, p < 0.01) and those in healthy controls (endotoxin; p < 0.001; IL-6, p < 0.001). The ratio of branched-chain amino acids to aromatic amino acids in septic patients with encephalopathy was decreased in comparison to the ratio in septic patients without encephalopathy (p < 0.05) and that in healthy controls (p < 0.01). PMX-F treatment reduced plasma endotoxin (p < 0.01) and IL-6 levels (p < 0.01) and increased the ratio of branched-chain amino acids to aromatic amino acids (p < 0.01). Conclusion: The amino acid imbalance in patients with septic encephalopathy may be a marker for the severity of the septic syndrome, and PMX-F hemoperfusion is effective in ameliorating the increased plasma endotoxin and IL-6 levels and the amino acid imbalance in these patients.
Does Monitoring of Pre-/Post-Dialyzer Pressure Difference Improve Efficiency in Intermittent Hemodialysis?
Authors: Gabutti Luca , Colucci Giuseppe , Martella Antonio , Schönholzer Carlo , Marone Claudio
Published: August 2003

Background: Continuous monitoring of pre-/post-dialyzer pressure difference (ΔP) is widely used in continuous renal replacement therapies to monitor extracorporeal circuit function. The aim of this study was to verify whether ΔP may help to identify chronic subclinical worsening of dialysis quality due to incomplete dialyzer clotting in intermittent hemodialysis. Methods: Nine chronic hemodialysis patients were enrolled in the study and dialyzed twice (high-flux polysulfone dialyzer) with ΔP and urea-clearance monitoring: the first session with a standard anticoagulation and the second without. To verify whether a visible clotting of the dialyzer precedes or follows a significant ΔP increase, we checked the dialyzers for the presence of red clots after a saline flush performed when a 50% increase in ΔP was registered. Results: In the second dialysis session after a 50% increase in ΔP (documented in 7/9 patients), all dialyzers, after saline flush, showed a visible fiber clotting but not a significant reduction (>15%) in urea clearance. In the majority of the patients (6/7), until a few minutes before complete occlusion of the extracorporeal circuit, the urea clearance did not change significantly (–8.9 ± 12.7%). Conclusions: The usual check of the presence or absence of red clots in the dialyzer at the end of the dialysis session is enough, in the absence of red clots, to ensure that dialyzer efficiency is maintained during the whole treatment. Contrary to what is applied in CRRT, a continuous monitoring of ΔP during intermittent hemodialysis would not significantly help to unmask unnoticed inefficient hemodialysis sessions.