bluuebunny/crossref_metadata_2025 huggingface dataset:
Simple homogeneous models
Authors: Buechler Steven , Lessmann Olivier
Published: November 2002

Geometrical stability theory is a powerful set of model-theoretic tools that can lead to structural results on models of a simple first-order theory. Typical results offer a characterization of the groups definable in a model of the theory. The work is carried out in a universal domain of the theory (a saturated model) in which the Stone space topology on ultrafilters of definable relations is compact. Here we operate in the more general setting of homogeneous models, which typically have noncompact Stone topologies. A structure

M
M

equipped with a class of finitary relations

R

\mathcal {R}

is strongly

λ
\lambda

-homogeneous if orbits under automorphisms of

(
M
,

R

)

(M,\mathcal {R})

have finite character in the following sense: Given

α
\alpha

an ordinal

>
λ
≤

|

M

|

>\lambda \leq |M|

and sequences

a
¯

=
{

a
i

:

i
>
α

}

\bar {a}=\{\,a_i:\:i>\alpha \,\}

,

b
¯

=
{

b
i

:

i
>
α

}

\bar {b}=\{\,b_i:\:i>\alpha \,\}

from

M
M

, if

(

a

i
1

,
…
,

a

i
n

)

(a_{i_1},\dots ,a_{i_n})

and

(

b

i
1

,
…
,

b

i
n

)

(b_{i_1},\dots ,b_{i_n})

have the same orbit, for all

n
n

and

i
1

>
⋯
>

i
n

>
α

i_1>\dots >i_n>\alpha

, then

f
(

a
¯

)
=

b
¯

f(\bar {a})=\bar {b}

for some automorphism

f
f

of

(
M
,

R

)

(M,\mathcal {R})

. In this paper strongly

λ
\lambda

-homogeneous models

(
M
,

R

)

(M,\mathcal {R})

in which the elements of

R

\mathcal {R}

induce a symmetric and transitive notion of independence with bounded character are studied. This notion of independence, defined using a combinatorial condition called “dividing”, agrees with forking independence when

(
M
,

R

)

(M,\mathcal {R})

is saturated. A concept central to the development of stability theory for saturated structures, namely parallelism, is also shown to be well-behaved in this setting. These results broaden the scope of the methods of geometrical stability theory.
The classification problem for torsion-free abelian groups of finite rank
Authors: Thomas Simon
Published: November 2002

We prove that for each

n
≥
1

n \geq 1

, the classification problem for torsion-free abelian groups of rank

n
+
1

n+1

is not Borel reducible to that for torsion-free abelian groups of rank

n
n

.
The Internet as a medium of training for picture archival and communication systems (PACS)
Authors: Majid Shaheen , Misra Ramesh Kumar
Published: November 2002

Picture archival and communication systems (PACS) are being widely used in radiology departments for the storage and archiving of medical images of patients. On‐site training for PACS users is often carried out shortly after the hardware installation. PACS users are considered proficient when the number of errors or “unspecified” examinations is minimized. Explores the potential of the Internet as a training medium for PACS applications. Three hospitals participated in this study. It was found that the rate of errors at two of the hospitals reduced considerably after the Web‐based training. The third hospital maintained its consistently low rate of errors both pre and post Web‐based training. Concludes that the Internet can be used as an effective medium for PACS applications training as well as for other similar systems.
Public relations activities in an academic library: the roles of the circulation librarian
Authors: Olabisi Babafemi Grace
Published: November 2002

Public relations activities as they relate to the roles of the circulation librarian in an academic library are discussed. The position of the circulation librarian as the public relations officer of his or her library in fulfilling the objectives of the institution and the library are also discussed. Services must be acceptable and the only way to make them acceptable is through public relations activities. The quality of the circulation librarian is highlighted for good public relations results. The services of the circulation librarian who uses public relations tools to function are also discussed as well as the ways the impact can be felt. This discussion highlights the similarity of the activities of the circulation librarian and the public relations officer of any establishment, and how they affect their organisation in positive ways.
The story of the London Library
Authors: Glasgow Eric
Published: November 2002

The circumstances of the foundation of the London Library and the influence of Thomas Carlyle are described. The nature and importance of the library and of its collections are discussed and numerous famous members throughout its history are indicated. The influence of the library on the Victorian literary scene and on books written during the twentieth century are demonstrated.
Modeling of Plastic Strain-Induced Martensitic Transformation for Cryogenic Applications
Authors: Garion C. , Skoczen B.
Published: November 2002

A simplified model of martensitic transformation in stainless steels at cryogenic temperatures is proposed. The constitutive modeling of plastic flow under cryogenic conditions is based on the assumption of small strains (⩽0.2). The hardening law for the biphase material (α′ martensite platelets embedded in the γ austenite matrix) has been obtained from the Mori-Tanaka homogenization. A mixed hardening with combined isotropic and kinematic contributions is proposed. The constitutive model, containing a reasonable number of parameters, has been numerically implemented and checked with respect to experimental data. Finally, the model is applied to compute the martensite evolution in thin-walled corrugated shells designed for cryogenic temperatures (mechanical compensation system of the Large Hadron Collider at CERN).
Mass spectrometric studies of low pressure CH4, CH4/H2, and H2 plasma beams generated by an inductively coupled radio frequency discharge
Authors: Okada Katsuyuki , Komatsu Shojiro
Published: November 2002

Low pressure CH4, CH4/H2, and H2 plasma beams were generated by a 13.56 MHz inductively coupled radio frequency (rf) plasma with a magnetic field (∼300 G) to utilize them as radical sources for the epitaxial growth of diamond. The threshold ionization technique using a quadrupole mass spectrometer has been employed to measure the absolute density of CH3 radicals (n) in CH4 and CH4/H2 plasma beams. The ions of CH4 and CH4/H2 plasma beams were composed of CHx, C2Hx, C3Hx, and Hx fragment ions, while Hx fragment ions occupied the H2 plasma beam. When the rf power and the pressure were increased, the n and the relative intensities of H3+, C2Hx, and C3Hx fragment ions were increased. This implies that both the homogeneous secondary ion–molecular reactions and the heterogeneous plasma–surface interactions take place in the plasma generation region of the low pressure plasma beams with an increase in rf power and pressure. The increase of H3+ also induces an increase of atomic hydrogen, which is essential for diamond growth. It is therefore concluded that moderate rf power and higher pressure are favorable for diamond growth.
Quantitative analysis of annealing-induced structure disordering in ion-implanted amorphous silicon
Authors: Cheng Ju-Yin , Gibson J. M. , Baldo P. M. , Kestel B. J.
Published: November 2002

We use fluctuation electron microscopy to characterize medium-range order in ion-implanted amorphous silicon. In fluctuation microscopy, intensity fluctuation in a dark-field image contains the information of high-order atomic correlations in the length scale of 1–3 nm. In this study, we heated as-implanted silicon at 500, 550, and 580 °C for various times. Our results indicate that in the beginning amorphous silicon is a disordered phase with robust medium-range order. Thermal annealing leads to disordering of the structure. Furthermore, we find that the activation energy of the disordering is about 2.7 eV, close to the activation energy for thermal relaxation (about 2.2 eV). Our finding suggests a strong correlation between structure disordering and thermal relaxation.
A biaxial rotation for depositing homogeneous large-area double-sided YBa2Cu3O7−X thin films
Authors: Tao B. W. , Li Y. R. , Liu X. Z. , He S. M. , Geerk J.
Published: November 2002

To deposit homogeneous large-area double-sided YBa2Cu3O7–X thin films simultaneously, a single inverted cylindrical target sputtering system with a simple rotation apparatus and a tubelike heater has been developed. The substrate (2 in. LaAlO3) rotated continuously in the heater so that films can be deposited on both sides simultaneously. Three different rotation modes, which are vertical in-plane rotation, out-of-plane rotation, and biaxial rotation (filed as a Chinese patent), have been tried out. The thickness distributions have been measured and compared with theoretical investigation results. While deposited with the subtle biaxial rotation mode, the film shows a much better thickness homogeneity than that with the other two single-axial rotation modes. The measurement result of critical transition temperature (TC) gives the demonstration that the biaxial rotation technique effectively improves the homogeneity of large-area thin films deposited by inverted cylindrical sputtering. Microwave surface resistance (RS), which is the key property for high-temperature superconductivity films used for fabricating microwave devices, ranged from 20 to 50 mΩ (at 75 K, 145 GHz).
Structural and luminescent properties of ZnTe film grown on silicon by metalorganic chemical vapor deposition
Authors: Shan C. X. , Fan X. W. , Zhang J. Y. , Zhang Z. Z. , Wang X. H. , Ma J. G. , Lu, Y. M. , Liu Y. C. , Shen D. Z. , Kong X. G. , Zhong G. Z.
Published: November 2002

Reported here are the structural and luminescent properties of ZnTe films grown on Si substrates by metalorganic chemical vapor deposition (MOCVD). ZnO intermediate layers annealed at different temperature are employed to buffer the thermal and chemical difference between the ZnTe epilayers and silicon substrates. With increasing the annealing temperature of ZnO buffer layer, the crystallization of ZnTe assessed by x-ray diffraction is improved. Temperature dependent photoluminescence (PL) of the ZnTe epilayer is processed to evaluate the optical properties of our samples. The PL spectra are characterized by an asymmetry line shape labeled E, and it can be dissolved into two Gaussian lines with energy discrepancy of about 18.5 meV. The origins of these two Gaussian lines are thought to be free and bound excitons emission, respectively. The dependence of luminescence on temperature indicates that the emission from bound excitons dominates the spectrum below 157 K. While above 157 K, the bound excitons are detrapped to become free excitons, and free excitons emission becomes dominant. Also, the broadening of the emission line resulting from the ionized impurity scattering cannot be neglected above 157 K. Temperature dependence of the full width at half maximum and peak energy of the spectra can be comprehended well under the framework of the two-dissociation-process theory, which, in turn, further strengthens the validity of the origin of the spectra.
Low-temperature Ar/N2 remote plasma nitridation of SiO2 thin films
Authors: Khandelwal Amit , Niimi Hiro , Lucovsky Gerald , Lamb H. Henry
Published: November 2002

Low-temperature nitridation of SiO2 thin films by Ar/N2 remote plasma processing was investigated using on-line Auger electron spectroscopy, angle-resolved x-ray photoelectron spectroscopy (ARXPS), and optical emission spectroscopy (OES). Nitridation experiments were performed at 300 °C using 30 W Ar/N2 remote plasmas at 0.1 and 0.3 Torr. Ar/N2 remote plasma exposure of 5 nm SiO2 films for 30 min results in nitrogen incorporation throughout the films, independent of process pressure and plasma reactor configuration (i.e., upstream versus downstream N2 injection). ARXPS indicates a N–Si3 local bonding configuration with second nearest neighbor oxygen atoms. Ar/N2 remote plasma exposure at 0.1 Torr results in higher nitrogen concentrations (8–10 at. %). Reactor configuration has a negligible effect at 0.1 Torr; conversely, downstream N2 injection results in higher nitrogen concentrations (5–6 at. %) than upstream injection (3–4 at. %) at 0.3 Torr. OES indicates that the Ar/N2 remote plasmas contain N2 triplet excited states and ground-state N atoms. The Ar emission intensities and the saturation N concentrations in the resultant films follow similar trends with processing pressure and reactor configuration; the N2 first positive emission intensities run counter to these trends. We infer that low-temperature SiO2 nitridation by Ar/N2 remote plasmas is a two-step process: O removal by Ar+ ion bombardment and N insertion by plasma-generated active N species. Moreover, the first step appears to be rate limiting under the conditions employed in this study. Annealing the oxynitride films in N2 at 900 °C decreases the N concentration and results in a more uniform nitrogen distribution.
Epitaxial growth of metastable δ-TaN layers on MgO(001) using low-energy, high-flux ion irradiation during ultrahigh vacuum reactive magnetron sputtering
Authors: Shin C.-S. , Kim Y.-W. , Hellgren N. , Gall D. , Petrov I. , Greene J. E.
Published: November 2002

We report on the microstructural evolution and physical properties of epitaxial δ-TaN layers grown on MgO(001) at 600 °C by ultrahigh vacuum reactive magnetron sputtering of Ta in mixed Ar/N2 discharges as a function of the N2 fraction fN2 (0.100⩽fN2⩽0.275) and the incident ion energy Ei (8.4⩽Ei⩽65 eV). The ratio of the ion-to-Ta fluxes Ji/JTa incident at the growing film was maintained at 11±0.5 with 0.100⩽fN2⩽0.200 and 15±0.3 with 0.250⩽fN2⩽0.275. High-resolution x-ray diffraction, transmission electron microscopy, and Rutherford backscattering spectrometry results show that films grown with Ei≲40 eV are single-phase δ-TaNx(001), with x increasing from 0.94 with fN2=0.100 to 1.37 with fN2=0.275, exhibiting a cube-on-cube epitaxial relationship with the substrate: (001)δ-TaN‖(001)MgO and [100]δ-TaN‖[100]MgO. However, the use of Ei≲20 eV leads to δ- TaNx(001) layers which are underdense with a self-organized array of 1-nm-wide nanopipes oriented predominantly along orthogonal 〈100〉 directions. The nanopipes, which are first observed at film thicknesses of ≃5 nm and extend to the surface, form due to the combination of low adatom surface diffusivities, leading to kinetic roughening, and atomic shadowing. Fully dense stoichiometric epitaxial δ-TaN(001) films were obtained with Ei=30 eV and fN2=0.125. Increasing Ei to 40 eV results in a high density of {111} stacking faults. Films grown with even higher ion energies, 40<Ei⩽65 eV, contain large concentrations of residual extended defects as well as hexagonal γ-Ta2N second-phase inclusions. The room-temperature resistivity, hardness, elastic modulus, and relaxed lattice constant of fully dense stoichiometric δ-TaN(001) are 185±15 μΩ cm, 32.9±0.9 GPa, 435±15 GPa, and 0.4351±0.0002 nm, respectively.
Anomalies in modeling of anisotropic etching of silicon: Facet boundary effects
Authors: Elalamy Z. , Landsberger L. M. , Pandy A. , Kahrizi M. , Stateikina I. , Michel S.
Published: November 2002

Beginning with an idealized model of anisotropic etching of silicon in which the etch behavior depends only on the crystal features presented to the etchant, this article extends the model to address certain anomalies observed in the data. The idealized model is based on profiles of underetched surfaces and underetch behavior as a function of mask-edge deviation in wagon-wheel experiments on Si{110} and Si{100} at different TMAH concentrations. Underetched surfaces are found to follow a cohesive system composed of planes defined by two types of crystal features: periodic bond chains and rows of kinks. But it is also found that the same crystal planes in the same etchant often exhibit different etch rates. These anomalies are outlined, and interactions at the boundaries between adjacent facets are proposed to explain them.
Observation of step-flow growth in femtosecond pulsed laser deposition of Si on Si(100)-2×1
Authors: Hegazy M. S. , Elsayed-Ali H. E.
Published: November 2002

Step-flow growth mode is observed for 100 fs pulsed laser deposition (fsPLD) of Si on vicinal Si(100)-2×1, while the Volmer–Weber mode is observed for fsPLD of Si on Si(100)-1×1. Reflection high-energy electron diffraction (RHEED) is used to in situ monitor the dynamics of the film growth while ex situ atomic force microscopy (AFM) is used to observe the morphology of the grown film. For Si on Si(100)-2×1, the diffraction pattern’s basic features remain unchanged during deposition, indicating step-flow growth. AFM shows smooth growth on flat terraces. However, for Si on Si(100)-1×1 two growth behaviors are observed. For a laser fluence of 1.9 J/cm2 and a substrate temperature below ∼400 °C, we observe a decay of the RHEED peaks until they completely disappear, indicating the loss of the long-range order in the grown film. Postdeposition analysis shows three-dimensional (3D) clusters associated with the Volmer–Weber growth mode. On the other hand, deposition above ∼400 °C at the same laser fluence results in the decay and eventual disappearance of the reflection diffraction peaks accompanied by the evolution of a transmission pattern instead. Transmission patterns appear when the electrons are diffracted in a transmission mode through 3D crystallites. These crystallites are observed in the AFM images.
Creation of stable, low work function surfaces on Si by implantation of 3 keV Cs+
Authors: Musket R. G. , Balooch M.
Published: November 2002

Silicon surfaces having native oxides were implanted with 3 keV Cs+ ions and annealed. Implanted doses of 1, 1.7, and 3×1016 Cs/cm2 led to room-temperature work functions with stable, reproducible values of 2.3±0.15 eV after vacuum annealing at 100–560 °C. The resulting surfaces have been characterized with regard to the amount of Cs retained, the thermal and environmental stability of the work function, and the composition and chemistry of the implanted layer. The surface layers consisted of a compound of Si–Cs–O, which is compositionally stable to temperatures of ∼400 °C in vacuum. In addition, we found that these surfaces are stable with regard to exposures to background gases and ambient air.
Plasma–surface kinetics and simulation of feature profile evolution in Cl2+HBr etching of polysilicon
Authors: Jin Weidong , Vitale Steven A. , Sawin Herbert H.
Published: November 2002

The etching of polysilicon by low energy Cl2+HBr plasma beam was studied, and the etching yield as a function of composition, ion impingement energy and ion incident angle was measured. The etching yield by HBr plasma beam is slightly lower than Cl2 plasma beam. The angular dependence of etching yield by both Cl2 and HBr beam strongly suggests the mechanism of ion induced chemical etching, with highest etching yield at normal incident angle. For Cl2 beam, the etching yield almost keeps constant until the off-normal incident angle of ions increased to 45°, while for HBr beam, the etching yield starts dropping even with small off-normal angle. The angular dependence of etching yield by Cl2+HBr plasma at different composition exhibits similar trend as pure HBr. Using x-ray photoelectron spectroscopy, the coverage of Cl and Br on polysilicon surfaces after etching in Cl2+HBr plasmas was measured. The Cl coverage after etching with pure Cl2 plasma beam is about 1.4 times higher than the Br coverage after etching with pure HBr plasma beam, due to the larger size of Br atom. The instantaneous sputtering yields of polysilicon by Ar+ ions after Cl2 and HBr plasma etching are similar, indicating that the lower Br coverage is not responsible for the lower etching rate in HBr plasma. The effect of the angular dependent etching yield difference between Cl2 and HBr on feature profile evolution, as identified with Monte Carlo simulation, might contribute to the more anisotropic etching in HBr plasma.
Photoelastic modulation-reflection absorption infrared spectroscopy of CO on Pd(111)
Authors: Stacchiola D. , Thompson A. W. , Kaltchev M. , Tysoe W. T.
Published: November 2002

The photoelastic modulation-reflection absorption infrared spectrum (PEM-RAIRS) of CO on single crystal Pd(111) is measured for CO pressures up to ∼150 Torr. The ac component of the signal, corresponding to the infrared signal of the surface, is measured using a synchronous demodulator circuit rather than using a lock-in amplifier as used in previous experiments to measure the infrared spectra of model catalysts surfaces. This allows the spectra to be collected at almost the same speed as RAIRS spectra performed in ultrahigh vacuum. A simplified synchronous demodulator circuit is described consisting of two sample-and-hold circuits operating at 100 kHz. Spectra are obtained that are in excellent agreement with previous results showing that a combination of hcp and fcc threefold sites are occupied by CO at 300 K. Atop sites become occupied as the CO pressure increases. Heating the Pd(111) sample to ∼500 K removes all adsorbed CO.
Effect of surface polymerization on plasma and process stability in polycrystalline-silicon etching
Authors: Xu Songlin , Lill Thorsten , Deshmukh Shashank , Joubert Olivier
Published: November 2002

Properties of the plasma containing Cl2, HBr, and O2 species used for polysilicon etching change when the chamber wall is coated with organic polymer, causing the etch performance to drift. In this work, the plasma instability due to surface polymerization has been characterized through the comparison of free radical densities in an etch chamber coated with fluorocarbon polymer and other materials such as silicon oxide and anodized aluminum. The results of plasma diagnostics show that chlorine, bromine, and oxygen densities decrease after a polymer film is deposited onto the chamber wall. The root cause for the decrease in halogen radical densities has been attributed to the higher surface recombination rate of these free radicals on polymer surface, while the decrease in oxygen radical density is mainly caused by the consumption of oxygen in the cleaning of the polymer deposition. The impact of the plasma property change on etch performance has also been analyzed through etch rate and critical dimension (CD) evaluation. The lower free radical density in polymer-coated chamber generally lowers the etch rate and generates CD gain but the sensitivity of the process drift to the plasma property variation depends on process conditions. Approaches to reduce the effect of surface polymerization have been discussed.
An image‐guided high intensity focused ultrasound device for uterine fibroids treatment
Authors: Chan Arthur H. , Fujimoto Victor Y. , Moore Donald E. , Martin Roy W. , Vaezy Shahram
Published: November 2002

A high intensity focused ultrasound (HIFU) device was developed for treating uterine fibroid tumors. This prototype device enables image‐guided therapy by aligning a commercially available abdominal ultrasound image probe to a vaginal HIFU transducer so the HIFU focus is in the image plane. The device was designed based on anatomical constraints of the female pelvic structures. HIFU was generated using a 3.5 MHz PZT‐8 crystal, 25.4 mm in diameter, bonded to an aluminum lens. Computer simulations were performed to ensure that effective focusing was achievable at a fixed focal depth of 40 mm. Transducer efficiency was empirically determined to be 58%, and the half pressure maximum focal dimensions were 11 mm in length and 1.2 mm in width. A water‐filled latex condom surrounding the transducer provided acoustic coupling, a stand‐off, and allowed water circulation for transducer cooling. In vitro experiments in a tissue‐mimicking gel phantom and in turkey breast demonstrated ultrasound image‐guided lesion formation, or tissue necrosis, at the focus due to HIFU induced thermal and cavitation effects. The HIFU treatment site appeared as a hyperechoic spot on the ultrasound image at intensities above 1250 The results of in vitro experiments and in vivo ergonomic testing in six human volunteers indicated that the device has the potential of providing a nonsurgical approach for uterine fibroid treatment. Future in vivo studies in large animal models and fibroids patients are planned.
Characteristics and quality assurance of a dedicated open 0.23 T MRI for radiation therapy simulation
Authors: Mah Dennis , Steckner Michael , Palacio Elizabeth , Mitra Raj , Richardson Theresa , Hanks Gerald E.
Published: November 2002

A commercially available open MRI unit is under routine use for radiation therapy simulation. The effects of a gradient distortion correction (GDC) program used to post process the images were assessed by comparison with the known geometry of a phantom. The GDC reduced the magnitude of the distortions at the periphery of the axial images from 12 mm to 2 mm horizontally along the central axis and distortions exceeding 20 mm were reduced to as little as 2 mm at the image periphery. Coronal and sagittal scans produced similar results. Coalescing these data into distortion as a function of radial distance, we found that for radial distances of <10 cm, the distortion after GDC was <2 mm and for radial distances up to 20 cm, the distortion was <5 mm. The dosimetric errors resulting from homogeneous dose calculations with this level of distortion of the external contour is <2%. A set of triangulation lasers has been added to establish a virtual isocenter for convenient setup and marking of patients and phantoms. Repeated measurements of geometric phantoms over several months showed variations in position between the virtual isocenter and the magnetic isocenter were constrained to <2 mm. Additionally, the interscan variations of 12 randomly selected points in space defined by a rectangular grid phantom was found to be within the intraobserver error of ∼1 mm in the coronal, sagittal, and transverse planes. Thus, the open MRI has sufficient geometric accuracy for most radiation therapy planning and is temporally stable.
Technical note: Sinogram merging to compensate for truncation of projection data in tomotherapy imaging
Authors: Hooper H. R. , Fallone B. G.
Published: November 2002

An advantage of helical tomotherapy radiation therapy systems is that on‐line megavoltage computed tomography (CT) images can be reconstructed to verify patient positioning. One limitation of such systems is that the field‐of‐view (FOV) of the photon fan‐beam is limited by the aperture size of the binary multileaf collimator (MLC) used to modulate treatment beams. For patients larger than the FOV the acquired sinograms will be truncated causing artifacts in the resultant megavoltage CT images. Computer simulations are used to demonstrate that such artifacts can be eliminated or at least reduced by merging appropriately acquired truncated fan‐beam sinograms to form a nontruncated parallel‐beam sinogram. The necessary fan‐beam sinograms are acquired with the patient translated to different offset locations within the gantry. The parallel‐beam sinogram is then used to reconstruct the final CT image. The increase in patient dose due to the acquisition of more than one fan‐beam sinogram can be reduced by using properly designed binary MLC fields to block redundant projection rays.
Optical measurement of human retinal macular pigment and its spatial distribution with age
Authors: Chang Yin , Lee Feng‐Lih , Chen Shih‐Jen , Chen Sheng‐Fu
Published: November 2002

The existence of macular pigment (MP) in human eyes has been found to be of importance in the prevention of age‐related macular degeneration (ARMD). A noninvasive technique of two‐wavelength imaging fundus reflectometry was developed to measure the density distribution of this yellow pigment in retina in vivo. A total of 55 healthy human subjects were recruited and divided into three groups with average ages and sample sizes of and years respectively. Only the MP distributions in the horizontal meridian of retinas are presented in this report. The results show that the average peak optical density of MP are and from young to old groups, respectively. No significant difference is shown in the statistical t‐test between the groups of the peak MP density. The half width of MP spatial distribution (HWMPD) are and from young to old groups, respectively. Mean It shows that the area of MP is increased approximately by a rate of 0.06°/yr according to the application of linear regression. However, the cause of the MP extension in the retina with age is unknown.
The effects of stereo shift angle, geometric magnification and display zoom on depth measurements in digital stereomammography
Authors: Goodsitt Mitchell M. , Chan Heang‐Ping , Darner Katie L. , Hadjiiski Lubomir M.
Published: November 2002

We are developing virtual three‐dimensional (3‐D) cursors for measuring depths in digital stereomammograms. We performed a study to investigate the effects of stereo shift angle, geometric magnification, and display zoom on the accuracy of depth measurements made with a virtual 3‐D cursor. A phantom containing 50 low contrast fibrils at depths ranging from 1 to 11 mm was imaged with a full‐field digital mammography system. Left‐ and right‐eye images were generated at stereo shift angles of ±3° and ±6°, using either contact or 1.8× geometric magnification geometry. The images were viewed on a high‐resolution stereoscopic display system in normal and 2× zoom mode. Observers viewed the images with stereo glasses and adjusted the depth of a cross‐shaped virtual cursor to best match the perceived depth of each fibril. The results for two trained observers with excellent stereo acuity were nearly identical when viewing the same images. The average root mean square errors for the two observers were 1.2 mm (±3° contact, no zoom), 1.3 mm (±3° contact zoom), 0.8 mm (±6° contact, no zoom), 0.6 mm (±6° contact, zoom), 0.8 mm (±3 magnification, no zoom), 0.7 mm (±3° magnification, zoom), and 0.2 mm (±6° magnification, no zoom). One observer repeated the entire study for two additional fibril phantom configurations. Combining all the results, we found that for the contact geometry increasing the stereo shift angle from ±3° to ±6° improved the depth measurement accuracy by factors of about 1.2–4.0. Zooming did not provide observable improvement in the depth measurement accuracy; sometimes having no effect, sometimes improving the accuracy, and other times reducing the accuracy, with no general trends. Its effect is likely within experimental errors. However, the stereo effect was more readily visualized in the zoom mode. Geometric magnification improved the depth measurement accuracy. The best accuracy among all cases was about 0.2 mm, obtained with geometric magnification using a stereo angle of ±6°. This is the mode we recommend for obtaining accurate depth measurements with virtual cursors in stereomammograms.
HIDDEN SYMMETRIES OF CONSTRAINED SYSTEMS
Authors: NEVES C. , WOTZASEK C.
Published: November 2002

In this work, constraint conversion techniques are used to disclose the role of the second-class constraints as generator of hidden symmetries. The example of the SU(2) Skyrme model is thoroughly investigated in this approach. This study is generalized to a set of second-class surfaces of arbitrary geometries resulting from the semiclassical quantization of the collective mode of nonlinear field theories. The consequences of the hidden symmetry over the physical spectrum and the ordering ambiguity problem are explored.
ON THE SUPERSYMMETRIC DIRAC EQUATION AND THE HETEROTIC SUPERSTRING THEORY
Authors: POLLOCK M. D.
Published: November 2002

The supersymmetry transformations under which the four-dimensional massless Dirac equation for a two-component, spin-1/2 fermion field ψ (the Weyl equation) remains invariant were obtained by Volkov and Akulov, who used the result to construct the action S = a-1 ∫ |W| d4x in terms of the energy-momentum tensor [Formula: see text], where Wij = δij + aTij and a is a constant. Here, we show, in the approximation [Formula: see text], that the terms linear, quadratic and quartic in Tij are contained in the bosonic sector of the dimensionally reduced, heterotic superstring action, including higher-derivative gravitational terms up to order ℛ4. By comparison of coefficients, we derive the value B r ≈ 3.5 for the radius squared of the internal space in units of the Regge slope parameter α′, slightly greater than the Hagedorn radius squared [Formula: see text]. The cubic terms are also discussed.
FLUCTUATION ANALYSIS OF THE HOURLY TIME VARIABILITY IN OBSERVATIONAL GEOELECTRICAL SIGNALS
Authors: TELESCA LUCIANO , LAPENNA VINCENZO , MACCHIATO MARIA
Published: November 2002

We investigate, by the Detrended Fluctuation Analysis (DFA), the long-range correlations in the hourly time variability of geoelectrical signals measured by the station Tramutola, located in one of the most seismic area of southern Italy. The DFA power-law exponent, characterizing the temporal fluctuations of these signals, shows significant variation, possibly related with the seismic activity of the area investigated.
MANAGING ENVIRONMENTAL INNOVATION IN THE ENERGY SECTOR: THE CASE OF PHOTOVOLTAIC AND WAVE POWER DEVELOPMENT IN NORWAY
Authors: CHRISTIANSEN ATLE CHRISTER , BUEN JØRUND
Published: November 2002

This article analyses key characteristics pertaining to the evolution of nascent technologies and enterprises. More specifically, we analyse the development of two new renewable energy technologies — solar photovoltaic (PV) and wave power (WP) — within the Norwegian energy sector. There are mainly two reasons for selecting these technologies. First, they may facilitate the transition to more sustainable energy supplies. Second, they display strikingly different development dynamics, from which important lessons can be learned for the management of innovation in the energy sector. The main causes of the Norwegian PV industry's success are its ability to exploit a global niche market, and the effective matching of technological capabilities with market opportunities into strategies for learning and legitimacy. The constrained development of WP technology, on the other hand, is not only attributed to technical difficulties, but also to the lack of niche markets, research rivalry, decreasing public support, and insufficient organisational capacity.
FACTORS ENABLING AND INHIBITING SUSTAINABLE TECHNOLOGIES IN CONSTRUCTION: THE CASE OF ACTIVE SOLAR HEATING SYSTEMS
Authors: DEWICK PAUL , MIOZZO MARCELA
Published: November 2002

The domestic building sector across Europe accounts for around 40% of total energy consumption. Mitigation strategies for greenhouse gas emissions have focused on improving the energy efficiency of buildings, both in terms of electricity use and space heating. In addition to improving the thermal properties of the building envelope and developing mechanisms to encourage energy conservation, the use of new energy technologies in new build and retro-fit residential buildings has the capacity to reduce significantly energy consumption. Active solar heating (ASH) systems are one such technology, suitable for widespread use across new and existing buildings in the housing stock, which have the potential to make a significant contribution to sustainable building and regeneration. Their generally slow adoption can be attributed to high capital cost and unknown cost effectiveness, but these factors do not adequately explain considerable differences between European countries in the take-up of new sustainable technologies in construction. This suggests that there are sets of more important factors and institutions inhibiting or facilitating their adoption. This paper examines the structural and institutional factors behind these differentials and draws implications for the management of innovation by construction firms and government policy for those countries under-exploiting the potential of ASH systems. Regulation, legislation and fiscal and financial incentives can encourage innovation and can help to promote solar technology. For countries such as the UK and France, lessons can be learned from the fixed price schemes, direct capital grant support, tax incentives and other such initiatives employed in Denmark, Germany, the Netherlands and Sweden. However, manufacturers and suppliers of ASH systems cannot be considered independently of other firms along the building chain. By raising the visibility of the adoption of this sustainable technology, construction firms can benefit their organisations from the reputation for installing this innovation, while confining the risk to this particular technology. Government can also play a role in increasing the capacity of construction firms to identify appropriate sustainable technologies and evaluate their potential costs and benefits.
Herbivore Offense
Authors: Karban Richard , Agrawal Anurag A.
Published: November 2002

▪ Abstract  Herbivore offense describes traits that allow herbivores to increase their feeding and other uses of host plants when these uses benefit the herbivores. We argue that ecological interactions and coevolution between plants and herbivores cannot be understood without an offense-defense framework. Thus far, plant defense theory and data have far outpaced knowledge of herbivore offense. Offensive tactics include feeding and oviposition choices, enzymatic metabolism of plant compounds, sequestration, morphological adaptations, symbionts, induction of plant galls, and induced plant susceptibility, trenching, and gregarious feeding. We propose that offensive tactics can be categorized usefully depending upon when they are effective and whether they are plastic or fixed traits. The advantages of offensive traits have not been adequately described in terms of herbivore fitness. Similarly, a more complete understanding of the costs and limitations of offensive traits will help put the herbivore back in plant-herbivore interactions and coevolution.
Plant Ecological Strategies: Some Leading Dimensions of Variation Between Species
Authors: Westoby Mark , Falster Daniel S. , Moles Angela T. , Vesk Peter A. , Wright Ian J.
Published: November 2002

▪ Abstract  An important aim of plant ecology is to identify leading dimensions of ecological variation among species and to understand the basis for them. Dimensions that can readily be measured would be especially useful, because they might offer a path towards improved worldwide synthesis across the thousands of field experiments and ecophysiological studies that use just a few species each. Four dimensions are reviewed here. The leaf mass per area–leaf lifespan (LMA-LL) dimension expresses slow turnover of plant parts (at high LMA and long LL), long nutrient residence times, and slow response to favorable growth conditions. The seed mass–seed output (SM-SO) dimension is an important predictor of dispersal to establishment opportunities (seed output) and of establishment success in the face of hazards (seed mass). The LMA-LL and SM-SO dimensions are each underpinned by a single, comprehensible tradeoff, and their consequences are fairly well understood. The leaf size–twig size (LS-TS) spectrum has obvious consequences for the texture of canopies, but the costs and benefits of large versus small leaf and twig size are poorly understood. The height dimension has universally been seen as ecologically important and included in ecological strategy schemes. Nevertheless, height includes several tradeoffs and adaptive elements, which ideally should be treated separately. Each of these four dimensions varies at the scales of climate zones and of site types within landscapes. This variation can be interpreted as adaptation to the physical environment. Each dimension also varies widely among coexisting species. Most likely this within-site variation arises because the ecological opportunities for each species depend strongly on which other species are present, in other words, because the set of species at a site is a stable mixture of strategies.
Gulf of Mexico Hypoxia, A.K.A. “The Dead Zone”
Authors: Rabalais Nancy N. , Turner R. Eugene , Wiseman William J.
Published: November 2002

Abstract  The second largest zone of coastal hypoxia (oxygen-depleted waters) in the world is found on the northern Gulf of Mexico continental shelf adjacent to the outflows of the Mississippi and Atchafalaya Rivers. The combination of high freshwater discharge, wind mixing, regional circulation, and summer warming controls the strength of stratification that goes through a well-defined seasonal cycle. The physical structure of the water column and high nutrient loads that enhance primary production lead to an annual formation of the hypoxic water mass that is dominant from spring through late summer. Paleoindicators in dated sediment cores indicate that hypoxic conditions likely began to appear around the turn of the last century and became more severe since the 1950s as the nitrate flux from the Mississippi River to the Gulf of Mexico tripled. Whereas increased nutrients enhance the production of some organisms, others are eliminated from water masses (they either emigrate from the area or die) where the oxygen level falls below 2 mg l−1 or lower for a prolonged period. A hypoxia-stressed benthos is typified by short-lived, smaller surface deposit-feeding polychaetes and the absence of marine invertebrates such as pericaridean crustaceans, bivalves, gastropods, and ophiuroids. The changes in benthic communities, along with the low dissolved oxygen, result in altered sediment structure and sediment biogeochemical cycles. Important fisheries are variably affected by increased or decreased food supplies, mortality, forced migration, reduction in suitable habitat, increased susceptibility to predation, and disruption of life cycles.
Bidirectional Cyclic Performance of Reinforced Concrete Bridge Column-Superstructure Subassemblies
Authors: Mosalam Khalid M. , Naito Clay J. , Khaykina Svetlana
Published: November 2002

The paper presents the methodology and findings from large-scale experiments conducted on reinforced concrete bridge subassemblies. Each subassembly consisted of the middle column/cap-beam joint of a three-column bridge bent and a large part of the monolithically cast-in-place box-girder of a typical California highway bridge. The subassemblies were subjected to constant gravity load and gradually increasing bidirectional cyclic lateral loading. One subassembly represented common practice in California and the other considered new design using headed reinforcing bars with reduced volume of transverse reinforcement to improve joint construction. When loading in the transverse direction, i.e., parallel to the cap-beam, the use of headed bars led to better global and local performances due to improved confinement of the joint region with less volume of reinforcement. On the other hand, when loading in the longitudinal direction, i.e., parallel to the box-girder, the headed bars were more engaged, as evident by their yielding, in confining the joint region than the conventional reinforcement. The effect of bidirectional loading on global damage of the box-girder slabs is presented as variation of the effective moment of inertia of the cap-beam cross section with displacement ductility indicating that Caltrans estimates are conservative up to displacement ductility of five.

Key words: bidirectional cyclic loading, box-girders, bridge joints, headed reinforcement, reinforced concrete
A Displacement-Focused Seismic Design of Mixed Building Systems
Authors: Paulay Tom
Published: November 2002

A postulated prediction of displacements in ductile reinforced concrete building systems is based on a redefinition of basic structural properties. Contrary to the ability of traditional techniques, the proposed approach permits displacement limits, relevant to ductile mixed systems, i.e., those with markedly differing components, to be established before details, such as strengths, are addressed. This should lead to significant benefits at the stage of preliminary design. Acceptable displacement limits, associated with currently introduced direct displacement-based seismic design strategies, can be readily and simply established. Similarly, limits of displacement ductility demands on components and the system, associated with current force-based approaches, can be estimated already as part of the preliminary design.
Quality of life issues in cancer of the oral cavity
Authors: Talmi Yoav P.
Published: November 2002

Quality of life issues in head and neck cancer have been portrayed increasingly in the medical literature in recent decades. Reports vary in sample size and study design but the majority are cross-sectional and suffer from inherent bias. Many of the patients’ complaints in cancer of the head and neck manifest close linkage to problems related to the oral cavity. Frequent specific problems are trismus, pain, xerostomia, and speech and swallowing disorders. Although quality of life is multifactorial and subjective, some improvement may be achieved by recognizing and addressing problems during the course of treatment. More longitudinal long-term studies are indicated in order to better define quality of life along the time axis.
Major ear surgery in a paediatric day care unit
Authors: Rowlands R. G. , Harris R. , Hern J. , Knight J. R.
Published: November 2002

Abstract Traditionally major ear surgery in children has been regarded as an in-patient procedure. Evidence from the USA for adults, however, concludes that it is both safe and effective to perform many major ear procedures as day cases. We have been carrying out major ear operations on children as day cases routinely for six years in a dedicated children’s day unit and examined our data to find out whether it was both safe and feasible to perform major ear surgery in children on a day-case basis. As our main outcome measure we used the rate of unplanned admissions.

We found that the unplanned admission rate for surgery, excluding mastoid surgery, was 6.7 per cent and that procedures such as myringoplasty, ossiculoplasty, bilateral pinnaplasty, meatoplasty and tympanotomy with excision of cholesteatoma, were eminently suitable for day surgery.
Factors that inform the career choice of medical students: implications for otolaryngology
Authors: Ranta M. , Hussain S. S. M. , Gardiner Q.
Published: November 2002

Knowledge of the factors that inform the career choice of medical students may help plan the workforce for medical specialities. To determine which factors inform the career choice of medical students we carried out a survey of medical students at the start of their educational block in Otolaryngology. Of 202 questionnaires handed out 169 were returned (84 per cent). Students were asked to rank factors according to their importance in their career choice. The single most important factor was career progression. Other factors include on-call commitment, teachers as role models, and the interest for a particular subject. At the present time progression from senior house officer grade to specialist registrar grade in Otolaryngology is delayed. If this issue is not addressed the influx of applicants into Otolaryngology training programmes will be reduced, limiting the pool from which candidates can be chosen for a career in Otolaryngology.
Fish bones in the vallecula and tongue base: removal with the rigid nasal endoscope
Authors: Savage Julian , Brookes Natalie , Lloyd Simon , Mackay Ian
Published: November 2002

The tongue base and vallecula are common anatomical sites for impaction of inadvertently swallowed fish bones. Many techniques for their removal have been described but this apparently simple procedure can still pose a surgical challenge. We describe a previously unreported technique using rigid endoscopy with the 4 mm 30 degree Hopkins’ rod as a visual aid for transoral removal of the impacted bone. The technique has proved to be very well tolerated by the patient and more acceptable in terms of morbidity, time and resources than either flexible endoscopy or rigid endoscopy under general anaesthetic.