bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of continuous light on experimental refractive errors in chicks
Authors: Guo S. S. , Sivak J. G. , Callender M. G. , Herbert K. L.
Published: July 2002

It is possible to induce ametropias in young chicks either by depriving the developing eye of clear form vision with a translucent goggle or by defocusing the retinal image with convex or concave lenses. The refractive properties of the developing chick eye are also altered by raising young birds in a continuous light environment. The effects of superimposing form deprivation or defocus treatments on chicks raised in continuous light are unclear. Newly hatched (n = 31) chicks were raised for 2 weeks under continuous light while wearing either translucent goggles or + 10 or − 10 diopter (D) lenses over one eye. Refractive states, corneal curvature and intraocular dimensions were measured periodically by retinoscopy, keratometry and A‐scan ultrasound. The birds were sacrificed after 2 weeks and the eyes removed and measured with calipers. Under continuous light, all eyes treated with translucent goggle and − 10D lens developed moderate myopia (− 2.6 ± 0.5 D and − 1.4 ± 0.3 D, respectively) by day 4. The eyes treated with a + 10 D lens developed moderate hyperopia (+ 4.8 ± 0.5 D) at day 4. Corneal curvatures of all treated eyes were slightly, but significantly, larger than contralateral control eyes by day 4. After 2 weeks of goggle or lens application, all the treated eyes were hyperopic due to corneal flattening. But the eyes treated with a goggle or a − 10 D lens still showed relative myopia compared to the fellow eyes (treated minus untreated = − 3.8 ± 0.4 D and − 2.8 ± 0.4 D, respectively), and the eyes treated with a + 10 D lens showed more hyperopia than fellow eyes (treated minus untreated = + 5.1 ± 0.6 D). Compared with the control eyes, the axial length (mainly vitreous chamber depth) was slightly, but significantly, increased in the eyes treated with a goggle or a − 10 D lens, and the axial length decreased slightly in the eyes treated with + 10 D lens. The results suggest that form deprivation and retinal defocus (induced by ± 10 D lenses) could still induce experimental refractive errors (myopia and hyperopia) in chicks kept under continuous light, but the effects of form deprivation and retinal defocus were partially suppressed by continuous light.
Night myopia and driving
Authors: Charman W. N.
Published: July 2002

Current knowledge of the refractive shifts (twilight myopia, night myopia, dark focus) that occur as the luminance is progressively lowered from photopic levels is reviewed. In complete darkness, myopic changes of the order of 1 dioptre are typical in young adult subjects. These gradually diminish as presbyopia is approached. The possible role of these refractive changes in causing visual difficulties for young drivers on the road at night is considered. It is concluded that high mesopic levels (about 1 cd/m2) of road luminance produced by street and vehicle lighting are normally too great to allow significant refractive shifts to occur, although acuity will be reduced due to light‐dependent neural changes. Under these circumstances it appears unlikely that specific night‐driving prescriptions will be beneficial: the accurate correction of normal refractive errors is, however, more important during night than day driving due to the greater blur associated with the larger night‐time pupil. Suggestions are made for further experimental work in this area.
Therapeutic contact lenses
Authors: Weed Kathryn H.
Published: July 2002

Therapeutic contact lenses are a rewarding area of optometric practice. Within Sunderland Eye Infirmary a diversity of ocular conditions present, creating a wide range of challenges. A variety of case histories will be discussed.

A prosthetic scleral shell was made for a chemical burn injury which presented with symblepharon. A traumatic cataract (caused by a flying contact lens lid) was extracted and an aphakic hydrogel contact lens with an opaque iris print and clear pupil was required to maintain vision and decrease symptoms of glare. Two cases of perforating injury resulting in opaque corneas are shown. In one case the lens was ordered from a trial set, the other prosthetic contact lens was hand‐painted to match a photograph sent to the manufacturer. A hydrogel occlusive pupil contact lens was used to cover a dense white inoperable cataract caused by recurrent chronic uveitis in rheumatoid arthritis. This type of contact lens is also used for diplopia therapy.
Accuracy of a calibrated retinoscope
Authors: Smythe K. L.
Published: July 2002

Aim: It is not always possible in clinical practice to use a trial frame. We have therefore attempted to compare the accuracy of cylinder axis determination using standard retinoscopy versus a calibrated retinoscope.

Methods: We have designed a scale, fitted to a standard retinoscope, which indicates the axis of cylinder. A single experienced retinoscopist determined, in a blind manner, the axis of cylinder using the new calibrated retinoscope and a traditional instrument with a trial frame distant from the eye. Retinoscopy was performed on a model eye using each retinoscope first in a random fashion. The axis of cylinder was set randomly at 5° intervals between 5° and 180°, retinoscopy being performed using each instrument three times at each interval.

Results: On χ2 statistical analysis we found the calibrated retinoscope was significantly more accurate to within 5° of the true cylinder axis.

Conclusions: The accuracy of the cylinder determination, when refracting without using a trial frame, can be significantly improved to within 5°C of the true axis when using a calibrated retinoscope.
Non‐compliance in contact lens wear
Authors: Claydon Bridget E. , Efron Nathan , Woods Craig
Published: July 2002

Non‐compliance in the contact lens field has been widely documented and discussed. The major areas of non‐compliance in contact lens wear have been highlighted as the lack of hand and lens case hygiene, the over‐wearing of contact lenses, the poor attendance of patients at aftercare appointments and the inadequate use of care and maintenance systems. Education is one of the factors thought to influence compliance. A prospective, randomized, controlled and double masked study was performed to assess the effect of a ‘compliance enhancement strategy’ on levels of compliance among contact lens wearers over 12 months. Eighty experienced contact lens patients were randomly allocated to two experimental groups. A standard level of contact lens instruction was applied to the first group, and in addition extra education was applied to patients in the second group. Patients were given free supplies of ReNu multipurpose solution and Medalist 38 soft contact lenses (Bausch & Lomb, Rochester, New York). Compliance levels were assessed at a 12‐month aftercare appointment by demonstration and questionnaire. The results indicate that the additional education had a significant effect on the compliance levels of the patients to whom it was applied. The population of contact lens wearers were generally very compliant and the contact lenses and care regimen were clinically successful. In this paper the results for the whole study population are compared to those reported in previous compliance studies. The results are found to be similar in many areas and suggest that practitioners should be encouraged to review the compliant behaviour of their contact lens patients at every aftercare appointment, paying particular attention to the areas of frequent non‐compliance highlighted.
Demonstration of the sodium‐hydrogen exchanger NHE‐1 in corneal endothelial cells
Authors: Rimmer Sharon J. , Wigham Chris G. , Hodson Stuart A.
Published: July 2002

Purpose: Maintenance of corneal hydration and transparency requires the presence of many membrane transporter proteins in the corneal endothelium, including, it is suggested, a sodium‐hydrogen (Na+/H+) exchanger. This study investigates the presence of the Na+/H+ exchanger (NHE) in bovine and sheep corneal endothelium.

Methods: A polyclonal antibody, specific for type 1 Na+/H+ exchanger (NHE‐1), was used to screen bovine and sheep corneal endothelial cells for the presence of NHE activity by the Western blotting technique. Using immunoassay quantification techniques (ELISA), the quantity of NHE‐1 present was measured.

Results: Western blot analysis, using the NHE‐1 antibody, recognized proteins with a mass of 70 kDa and 56 kDa in bovine and sheep corneal endothelial cells respectively. From the measured activity of NHE‐1 detected using ELISA and the previously measured cell density, an estimate of the number of NHE‐1 molecules present in each corneal endothelial cell was calculated to be 40 000 per cell.

Conclusion: Bovine and sheep corneal endothelium contain type I Na+/H+ exchanger (NHE‐1). Future immunochemical studies will confirm its precise membrane location. This data provides direct evidence of its existence and the quantitative estimate of its concentration in the membrane provides further opportunity to resolve its role in transendothelial bicarbonate ion transport.

Acknowledgement: The polyclonal antibody was a generous gift from Prof. L. Fliegel, Department of Biochemistry and Pediatrics, University of Alberta.
Infant emmetropization
Authors: Ehrlich D. L. , Anker S. , Atkinson J. , Braddick O. J. , Weeks F. , Wade J.
Published: July 2002

Aim: The Cambridge vision screening programme allows the emmetropization process to be described in a large infant population (n = 278 infants). Cycloplegic retinoscopy refraction change between 9 and 20 months of age is described for various refractive components.

Methods: Following videorefractive VPR‐1 screening at 75 cm, of over 5000 infants, groups of infants with large lags (>2.8 D) and normal lags (<2.8 D) of accommodation were longitudinally followed‐up. All were non‐strabismic. 1% cyclopentolate retinoscopy results (sphero‐cyl lens neutralized ± 0.5 D) were analysed.

Results: For all components, the emmetropization rate significantly correlated with the initial powers (difference v mean correlation R).

The relationship of hyperopia and astigmatism reduction will be discussed. Emmetropization in a subgroup of infants wearing spectacles will also be presented.

Conclusion: Analysis of infant emmetropization shows the refractive components emmetropize with their rate of reduction related to initial power.

Acknowledgement: Supported by Medical Research Council Grant G7908507.
Lectin analysis of endothelial glycoconjugates in the retina of the rat
Authors: Hayes A. J. , Lawrenson J. G. , Allt G.
Published: July 2002

The vascular endothelial glycocalyx has many important functions such as mediating cell‐cell interactions and possibly a role in permeability. The aim of this study was to investigate the expression of endothelial cell (EC) glycoconjugates in retinal microvessels. Paraffin sections of fixed adult rat retina were treated with a range of biotinylated lectins followed by an avidin‐FITC conjugate. Binding sites for the lectins Canavalia ensiformis (Con A), Ricinus communis (RCA) and Triticum vulgaris (WGA) were expressed Sambicus nigra (SNA), which labels terminal sialic acid residues (NeuNAc) in a 2–6 glycosidic linkage to β galactose (βGal), and Maakia amurensis (MAA), which labels terminal sialic acid when joined in a 2–3 linkage to β galactose, both labelled strongly. In contrast, Ulex europaeus (UEA) and Glycine max (SBA) were negative Arachis hypogaea (PNA), which labels the terminal disaccharide sequence galactose β 1–3 N‐acetylgalactosamine (GalNAc), was strongly positive only after pre‐treatment with the sialic acid digesting enzyme neuraminidase. These suggest a predominance of the oligosaccharide sequence:

NeuNAc α 2–3 Gal β 1–3 GalNAc and NeuNAc α 2–6 Gal β 1–3 Gal. These sugar sequences may be significant in the function of the glycocalyx in retinal microvessels.

Acknowledgement Supported by the Nuffield Foundation.
Early detection of changes in visual function in diabetes mellitus
Authors: Ismail G. M. , Whitaker D.
Published: July 2002

Purpose: Several measures of visual performance were used to investigate the possibility of a reliable, quick and low‐cost method of differentiating between diabetic patients with and without early retinopathy.

Methods: Four groups of patients were recruited: a normal control group (30 patients); a non‐insulin dependent diabetic group without retinopathy (30 patients); a similar group with early retinopathy (30 patients); a similar group with more advanced retinopathy (14 patients). High‐ and low‐contrast LogMAR visual acuity, Pelli‐Robson contrast sensitivity and the Farnsworth‐Munsell 100‐Hue colour vision test were performed on all patients by an experimenter who was independent of the classification stage.

Results: Comparison of mean test scores for each subject group reveals deficits in performance for all tests as a function of severity of diabetic retinal changes. However, none of the tests were successful in differentiating the subject groups with and without early retinopathy (P>>0.05). Larger differences in performance were found when comparing the non‐diabetics against diabetics without retinopathy. Both the Pelli‐Robson chart and the 100‐Hue test result in mean scores which were significantly different in these two groups (P < 0.01 and P < 0.05 respectively). QROC analysis of the results confirmed this impression, with kappa coefficients for efficiency of discriminability being generally higher for comparison between non‐diabetics and those without retinopathy (0.17 < k < 0.37) than between early diabetic groups (0.13 < k < 0.26). Discrimination between patients with pre‐clinical diabetics and those with moderate retinopathy was more efficient (0.21 < k < 0.62).

Conclusion: Tests of visual function appear to be of limited value in screening for the presence of early retinopathy. Rather, a mild decline in visual function appears to already be present in those diabetics without retinopathy.
The multi‐sensory approach to the optometric management of children with specific learning difficulties (such as dyslexia and dyspraxia)
Authors: Grounds Annette R.
Published: July 2002

In the 1920's Skeffington portrayed vision as a product of the interaction of four component subprocesses. These sub‐processes were depicted as four overlapping intertwined circles, with vision emerging as a product of their interaction. The circles represent the antigravity system, centring, identification and speech auditory processes. He postulated that if any of these sub‐processes fails to develop correctly, the emergent vision will be affected.

In children with specific learning difficulties these sub‐processes can be affected to different degrees. So as well as the more well documented problems with tracking eye movements, convergence insufficiency, reduced fusional reserves and accommodative facility, all of which can be improved with specific exercises, attention should also be given to multisensory exercises.

Visual space is a varying mix of central and peripheral vision. The attention given to each will vary with visual task, and also from person to person. For best visual performance the correct balance between the two systems is required. If a person is too centrally oriented they tend to be very “focal” in their behavior, ignoring peripheral stimuli and paying too much attention to detail and tend to process sequentially. In contrast the peripherally biased person has poor concentration, jumps from one thing to the other and is easily distracted by peripheral stimuli; a particular problem in a busy classroom environment.

The types of problems commonly found in youngsters with specific learning difficulties will be presented, with the emphasis on a multisensory exercise programme specifically designed to improve these problems.
Fixation disparity at different viewing distances and the preferred viewing distance in a laboratory near‐vision task
Authors: Jaschinski Wolfgang
Published: July 2002

Previous research has shown that subjects with normal binocular vision differ reliably in the extent to which their fixation disparity changes in the exo direction when the viewing distance is shortened from 100 to 20 cm. Since fixation disparity can lead to asthenopic complaints, the present study investigates whether an exo fixation disparity induced by proximity may cause subjects to move to a longer viewing distance during a near‐vision task in order to reduce exo fixation disparity. In two optometric sessions, fixation disparity and accommodation were tested at 60, 40, and 30 cm viewing distance. In a further session, subjects were required to begin a one‐hour near‐vision task at about 40 cm viewing distance, at which the text characters subtended a comfortable visual angle of 21 min arc. Later, the subjects were free to adopt any viewing distance. In the initial phase of the task, subjects moved back from the screen to a greater or lesser extent that was correlated with the amount of proximal exo fixation disparity: the more a subject's fixation disparity changed to exo when the viewing distance had been shortened from 60 to 30 cm the more he or she moved to longer viewing distances in the course of the near‐vision task. Further, the more distant the resting position of vergence (dark vergence), the more visual complaints the subjects indicated after the task relative to before.
Vision with disposable toric contact lenses and daily‐wear toric contact lenses
Authors: Velasco Cabrera J. , Bermúdez Rodríguez J.
Published: July 2002

The study compared the vision, the use and evaluation criteria in a group of students with corrective daily‐wear toric contact lenses and disposable toric contact lenses, in order to ascertain which of the two optical systems is more advantageous. We fitted 114 subjects with daily‐wear and disposable lenses to be worn for 12 months, one type of lens in one eye and the other type in the fellow eye. The results reveal no significant differences between the two systems in terms of visual acuity attained; both lenses centred well and were comfortable. Nevertheless, the deposits were significantly greater in the daily‐wear lenses. The ocular reactions were less with the disposable toric lenses. In conclusion, the disposable lenses led to fewer deposits and less ocular reactions, but are limited in parameters. However, both optical systems were appropriate for correcting for astigmatism, and provided good visual acuity.
Early detection of changes in visual function in diabetes mellitus
Authors: Ismail Galal M. , Whitaker David
Published: July 2002

Psychophysical measurements were performed with a view to providing an assessment of early neural functional integrity in the presence of no or minimal diabetic retinopathy (DR). The investigations were carried out on a normal group and a number of age‐ and sex‐matched non‐insulin dependent diabetic groups with different levels of DR. Results were considered in terms of the presence of functional changes relative to the severity of DR and the duration of diabetes. Significant deficits were found for visual acuity (VA), contrast sensitivity (CS) and colour vision. Both CS and colour vision measurements differentiated between non‐diabetics and those with diabetes but without DR. However, none of the tests reliably distinguished diabetics without DR from those with early retinal changes although VA and colour vision (especially along a blue‐yellow colour axis) were sensitive to more substantial retinal changes. This finding suggests such tests may be useful as screening tests for more advanced levels of background DR.
The Treatment Gap in Epilepsy: The Current Situation and Ways Forward
Authors: Meinardi H. , Scott R. A. , Reis R. , On Behalf Of The Ilae Commission on the Developing World J. W. A. S. Sander
Published: July 2002

Summary: This article is a summary of a workshop held by the ILAE concerning the issue of the epilepsy treatment gap in developing countries. The gap is defined in terms of those people with epilepsy who are not being appropriately treated and is the result of an array of medical, political, social, economic, and cultural factors. The situation regarding the treatment gap for various countries is reviewed, along with some of its causes. Although the overall gap is estimated to be large, a number of recent projects and interventions have been effective in delivering appropriate treatment to people with epilepsy in underresourced countries of the developing world. It is hoped that these may be transferable elsewhere and that, combined with the ILAE/IBE/WHO Global Campaign against Epilepsy and increased support from the worldwide epilepsy community, the treatment gap will begin to be bridged.
The Last 48 Hours of Life in Long‐Term Care: A Focused Chart Audit
Authors: Hall Pippa , Schroder Cori , Weaver Lynda
Published: July 2002

OBJECTIVES:

TAs a component of palliative care educational program development, the faculty at the University of Ottawa Institute of Palliative Care wished to assess end‐of‐life care for patients in long‐term care (LTC) settings to develop an educational strategy for physicians.

DESIGN:

A chart audit, focusing on the last 48 hours of life of residents dying in LTC facilities.

SETTING:

Five LTC facilities in a city in Canada.

PARTICIPANTS:

Residents who died in the LTC facilities in a 12‐month period. Those who died suddenly (i.e., with no palliation period) or in a hospital were excluded.

MEASUREMENTS:

Symptoms highlighted in the literature as commonly found in the terminally ill and the matching treatments were recorded on an audit form created by the authors. Included were pain, dyspnea, noisy breathing, delirium, dysphagia, fever, and myoclonus.

RESULTS:

One hundred eighty‐five charts were reviewed. A large number of patients were cognitively impaired. Cancer was the final diagnosis in 14% of cases. Respiratory symptoms were the most prevalent symptom, with dyspnea being first and noisy breathing third. Pain was second, with a prevalence similar to that found in studies of cancer patients. Dyspnea was not treated in 23% of the patients with this symptom; opioids were used in only 27% of cases with dyspnea. Ninety‐nine percent of patients who experienced pain were treated for it. Less than one‐third of patients with noisy breathing were treated. Delirium was not treated in 38% of the cases, and no antidopaminergic medications were administered. Nurses were primarily responsible for documenting end‐of‐life issues, supporting the families of the dying residents, and communicating with other team members.

CONCLUSION:

The focused chart audit identified the high prevalence of cognitive impairment in the patient population, which complicates symptom management. Respiratory symptoms predominated in the last 48 hours of life. This symptom profile differs from that of cancer patients, who, according to the literature, have more pain and less respiratory trouble. Management of symptoms was variable. Nurses played a crucial role in the care of dying residents through their documentation and communication of end‐of‐life issues. Appropriate palliative care education can provide knowledge and skills to all healthcare professionals, including physicians, and assist them in the control of symptoms and improvement of quality of life for patients dying in LTC facilities. J Am Geriatr Soc 50:501–506, 2002.
Photoprotective Responses to Winter Stress in Evergreen Mediterranean Ecosystems
Authors: García‐Plazaola J. I. , Hernández A. , Becerril J. M.
Published: July 2002

Abstract: The role of antioxidants and regulation of photosynthesis as photoprotective adaptations of Mediterranean vegetation to winter stress have been studied. These mechanisms are influenced by the degree of environmental stress (studied at different altitudes) and the taxonomic origin of each species. Thus, antioxidant composition was species‐dependent, but not apparently affected by altitude; while the reductions in photochemical efficiency, associated with the presence of zeaxanthin and a lower chlorophyll content, were common among species with increasing altitude. Three different strategies to cope with winter stress were observed in Mediterranean evergreens. First, in Buxus sempervirens antioxidant concentration was very high and the photochemical efficiency was much reduced, with a large accumulation of zeaxanthin. Second, in other Mediterranean sclerophylls, reversible reductions of PSII efficiency related to activity of the xanthophyll cycle allowed day to day adaptation of photosynthetic rates. Third, the summer semideciduous Cistus species maintained a high photochemical efficiency and accumulated little antioxidant, and this strategy could be justified by the occurrence two leaf populations with different physiological tolerances to environmental stress.
Effects of excimer laser irradiation on the transmission, index of refraction, and density of ultraviolet grade fused silica
Authors: Rothschild M. , Ehrlich D. J. , Shaver D. C.
Published: July 2002

Radiation-induced changes in high-purity fused silica during prolonged irradiation with a pulsed laser at 193 nm have been studied. Radiolytically induced UV absorption bands, an increase in index of refraction, and stress birefringence are observed. The formation mechanisms are analyzed in terms of radiolytic atomic rearrangement of a-SiO2 initiated by two-photon absorption. The quantum efficiency for the formation of E′ point defects per pair of absorbed 193 nm photons has been determined to be ∼7.5×10−4; matrix compaction, as high as a few parts in 10−5, is identified as the source of the birefringence and index change. It has been further observed that E′ centers can be photobleached.
Photoluminescence characteristics of AlGaN-GaN-AlGaN quantum wells
Authors: Khan M. A. , Skogman R. A. , Van Hove J. M. , Krishnankutty S. , Kolbas R. M.
Published: July 2002

AlxGa1−xN-GaN quantum wells were grown on basal plane sapphire by low-pressure metalorganic vapor deposition. The photoluminescence spectra of samples of different well thicknesses and x values were measured. The experimental data were compared with the calculated solutions of the finite square quantum well and the bound states involved in the optical transition were identified.
Direct observation of interfacial point defects generated by channel hot hole injection in n-channel metal oxide silicon field effect transistors
Authors: Krick J. T. , Lenahan P. M. , Dunn G. J.
Published: July 2002

Using a modified electron spin resonance technique known as spin-dependent recombination, we have found that channel hot hole injection in n channel metal oxide silicon (MOS) transistors creates the trivalent silicon dangling bond defect known as the Pbo center. This letter reports the first direct identification of the atomic structure of interfacial point defects created by channel hot carrier stressing in MOS transistors.
Correlation of electrical-resistivity anomalies and crystal structure in copper-germanium thin-film alloys
Authors: Aboelfotoh M. O. , Tawancy H. M. , Krusin-Elbaum L.
Published: July 2002

We report a nonmonotonic dependence of electrical resistivity on Ge concentration in Cu-Ge thin-film alloys containing 0–40 at.% Ge. This behavior is corrected with structural changes occurring in the alloys as the Ge concentration is increased. The resistivity is found to remain remarkably low (typically less than 10 μΩ cm) over a range of Ge concentration extending from 25 to 35 at.%.
Influence of the electric field on the quasibookshelf stripe deformation in an electroclinic liquid crystal
Authors: Crawford G. P. , Geer R. E. , Naciri J. , Shashidhar R. , Ratna B. R.
Published: July 2002

A quantitative study of the effect of electric field on the stripe domains formed by layer deformation in chiral smectic A liquid crystals is presented. X-ray diffraction studies reveal that the angle between the layer normals in adjacent stripe domains increases with increasing electric field. A simple model is presented to derive the true molecular tilt angle from optical transmission measurements. The relationship between the optical tilt angle and the tilt angle evaluated from x-ray measurements of the smectic layer thickness indicates that the molecules are tilting as rigid rods.
Tertiary fusion neutron diagnostic for density-radius product and stability of inertial confinement fusion
Authors: Welch D. R. , Kislev H. , Miley G. H.
Published: July 2002

The fluence of high-energy (>14 MeV) ‘‘secondary’’ neutrons, produced in D–T reactions involving suprathermal fuel ions created by elastic scattering with 14-MeV ‘‘primary’’ neutrons, yields information about the fuel density-radius product (ρR) and the hydrodynamic stability of inertial-confinement fusion (ICF) targets. The suprathermal ions, produced in proportion to the fuel ρR, create secondary neutrons with energies ≤30 MeV when fusing with a thermal ion. The ratio of secondary to primary neutrons determines the mean fuel ρR. Since secondary neutrons, which are mainly formed near the fuel tamper interface with energies >24 MeV, are radially directed, the detection of their angular distribution provides a unique measurement of the deviation from spherical geometry of the fuel ρR. Valid for fuel ρR>0.1 g/cm2 and D–T yield above 1014, this diagnostic would be valuable in upcoming ICF experiments.
Contactless transport measurement of metals in pulsed high magnetic fields
Authors: Sakakibara T. , Goto T. , Miura N.
Published: July 2002

A contactless method is developed for high-sensitivity magnetoresistance measurement in pulsed high fields. The resistivity is measured by observing transmission of a radio-frequency field through a thin specimen. The transmission rate is analytically given as a function of the resistivity within the classical skin-effect regime. By use of a high-frequency (0.1–100 MHz), electrical noise coming from pulsed magnetic fields can be rejected effectively and the sensitivity of the measurement is improved by at least a factor of 100 compared with that of a conventional dc four-terminal method. The present method is available for the measurements on superconductors, magnetic metals, and any other materials with short collision time in high magnetic fields. Upper critical fields and magnetoresistance of recent high Tc superconductors Y-Ba-Cu-O are measured up to 40 T.
Development of a miniaturized, light-weight magnetic sector for a field-portable mass spectrograph
Authors: Sinha M. P. , Tomassian A. D.
Published: July 2002

We have designed and fabricated a miniaturized, light-weight magnetic sector for a focal plane mass spectrograph (Mattauch–Herzog design) by using a new high-energy-product magnet material (Nd-B-Fe alloy), and a high permeability magnet yoke material (V-Co-Fe alloy). The magnetic sector weighs less than 10 kg and has a focal plane of 5.1 cm in length and covers a nominal mass range of 40–240 amu. Such a magnetic sector in conjunction with an array detector and a short microbore capillary column is eminently suited for the development of a field-portable gas chromatograph-mass spectrometer instrument of high performance.
Determination of the elliptical polarization parameters of vacuum ultraviolet radiation
Authors: Bobashev V. , Vasyutinskii O. S.
Published: July 2002

The article presents a new experimental method suitable to determine the Stokes parameters of arbitrary polarized synchrotron radiation (SR) in photon energy range E=10–100 eV. The essence of the method is the transformation of frequency of given vacuum-ultraviolet SR to a low energy spectral region by means of exciting the fluorescence of atoms to be followed by measurement of the Stokes parameters of the fluorescent light and the calculation of the Stokes parameters of the SR through the known transformation formulas.
Lens correction for the implementation of cylindrical vessels in a spectrophotometer
Authors: Spear Jonathan D. , Russo Richard E. , Andrews John E. , Grant Patrick M.
Published: July 2002

A simple optical correction system for allowing cylindrical vials to be used as sample vessels in a spectrophotometer is described. Light within the spectrophotometer enters and exits the liquid samples through the curved glass wall of the vials. Absorption spectra can be obtained conveniently without the need for solution transfer into standard rectangular spectrophotometer cuvettes.
Midinfrared beamline at the National Synchrotron Light Source port U2B
Authors: Carr G. L. , Hanfland M. , Williams G. P.
Published: July 2002

A new infrared beamline has been developed on a conventional dipole bending magnet port of the vacuum ultraviolet ring at the National Synchrotron Light Source. The port provides approximately 12 mrad horizontal and 8 mrad vertical aperture, which limits the useful spectral range to wavelengths less than 20 μm. Though the total flux across the midinfrared is less than that from a globar source, the calculated brightness is at least two orders of magnitude greater. Also, the synchrotron source delivers light in subnanosecond pulses. The developing experimental programs include studies of hydrogen and other materials at extremely high pressures, and time-resolved studies of infrared sensor materials. The measurement results presented here, characterizing the actual brightness advantage and spectroscopic performance, demonstrate the synchrotron’s remarkable advantage for microspectroscopic studies.
Neutron penumbral imaging of inertial confinement fusion targets at Phébusa)
Authors: Delage O. , Garconnet J.-P. , Schirmann D. , Rouyer A.
Published: July 2002

First 14 MeV neutron images of imploded microballoons have been obtained at the Phébus laser facility at CEL-V in 1992 [Garconnet et al. Laser Part Beams 11, 3 (1994)]. The sizes of the neutron source have been measured by using a coded-aperture imaging system and a scintillator array as a detector. The threshold of the experimental setup was typically 2×1010 neutrons/shot. 600–800 μm source sizes in direct drive experiments have been measured with a 130 μm two-point resolution. In 1993 we improved the sensitivity of the camera by increasing the light collection efficiency. It can now work at a neutron yield as small as a few 108. Thanks to this improvement some images in indirect drive experiments have been recorded in the range 3×108–5×109 with a 56 μm two-point resolution. Wiener filter, homomorphic Wiener filter, and Nugent’s ‘‘comb filter’’ methods have been used and compared to deconvolve the penumbral images. Design of the camera and numerical method performances will be discussed.
Microstructural study of Nd-doped LiTaO3
Authors: Wu Xing-Long , Zhang Zhi-Qiang , Hu An , Zhang Ming-Sheng , Jiang Shu-Sheng , Feng Duan
Published: July 2002

X-ray diffraction, infrared, and Raman spectra of Nd-doped LiTaO3 (LT:Nd) were examined. X-ray diffraction patterns of the x and y faces display the appearance of new diffraction peaks and the existence of microtwin crystals, indicating the microstructural deviation from a trigonal system of pure LT crystal. Infrared transmission spectrum shows more than seven strong vibrational bands in the high frequency region 1500–6000 cm−1. Their intensities and frequencies hardly change after annealing the sample at high temperature. We attribute these bands to the existence of defects and some metal and organic complexes in the sample. Similar results were obtained from the Raman spectra. In addition, the transmitted polarized light photomicrograph of the Z face of LT:Nd displays the occurrence of a helix dislocation. All experimental results indicate that the microstructural imperfection of LT:Nd can lead to some new optical effects.
Revision of H2 passivation of P
b interface defects in standard (111)Si/SiO2
Authors: Stesmans A.
Published: July 2002

Passivation with molecular H2 of Pb interface defects in thermal (111)Si/SiO2 (dry; 870 °C) over extended temperature (TH) and time (tH) ranges unveil nonexponential decay of [Pb] vs tH. This contrasts with previously reported exponential behavior, shown to have resulted from inadvertent incorrect monitoring of [Pb] and limited TH and tH ranges. The previous defect-H2 reaction limited model may still consistently account for the data if expanded by the revealed spread of 0.06 eV around the inferred mean activation energy Ef=1.51 eV vis-à-vis the previous single-valued Ef=1.66 eV; The inferred pre-exponential factor is now found in compliance with the model. However, results may encourage re-evaluation of other models previously discarded on the basis of their nonexponential passivation prediction.
p- and n-type carbon doping of InxGa1−xAsyP1−y alloys lattice matched to InP
Authors: Cohen G. M. , Benchimol J. L. , Le Roux G. , Legay P. , Sapriel J.
Published: July 2002

The carbon doping of InxGa1−xAsyP1−y alloys grown by chemical beam epitaxy was studied in the whole range of compositions lattice matched to InP, using carbon–tetrabromide as a source of carbon. The conductivity changed from p- to n-type when going from In0.53Ga0.47As to InP, with a transition point at a composition corresponding to a wavelength of 1.35 μm. The carbon doped n-type quaternaries were found to be very compensated even for compositions close to InP. The p-type quaternaries showed little compensation near the transition point, and almost no compensation for compositions close to In0.53Ga0.47As. Reducing the V/III ratio, while keeping all other growth parameters unchanged, increased the incorporation of the carbon atom, and reduced the compensation for p-type quaternaries. The inversion point position did not change appreciably when the quaternaries were grown with a halved V/III ratio.
Characterization of dislocations in GaN by transmission electron diffraction and microscopy techniques
Authors: Ponce F. A. , Cherns D. , Young W. T. , Steeds J. W.
Published: July 2002

A combination of transmission electron microscopy imaging and diffraction techniques is used to characterize crystal defects in homoepitaxial GaN thin films. The Burgers vectors of dislocations is established by combining large-angle convergent beam electron diffraction and conventional diffraction contrast techniques. It is shown that dislocations with Burgers vectors c, a, and c+a are present. Evidence is presented that dislocation segments lying in the interfacial plane are dissociated on a fine scale. The significance of the observations for understanding homoepitaxial growth of GaN is discussed.
Deep levels and persistent photoconductivity in GaN thin films
Authors: Qiu C. H. , Pankove J. I.
Published: July 2002

Photocurrent decay in GaN thin films was studied in the time span from a few seconds to several days. The persistent photoconductivity (PPC) behavior was observed not only in Mg-doped p-type GaN films but also in undoped n-type GaN films. The photoconductivity spectra and the photocurrent response time were measured using a weak probe light at several times after the samples had been kept in the dark. During the relaxation, the photocurrent due to the subband-gap probe light decreased more than the photocurrent due to the UV probe light. It is suggested that metastable centers at 1.1, 1.40, and 2.04 eV above the valence band edge are responsible for the PPC behavior in Mg-doped GaN, and that Ga vacancy is the candidate for PPC effect in n-type GaN.
Carrier dynamics of low-temperature-grown GaAs observed via THz spectroscopy
Authors: Prabhu S. S. , Ralph S. E. , Melloch M. R. , Harmon E. S.
Published: July 2002

Subpicosecond electron lifetimes in low-temperature-grown GaAs are unambiguously demonstrated via far infrared terahertz spectroscopy. A systematic study of low-temperature-grown GaAs, as-grown and annealed, reveal carrier lifetimes to be directly related to the excess arsenic incorporation and anneal conditions. Contrary to previous observations, electron lifetimes of 600 fs (200 fs) are found in 0.25% (0.5%) excess arsenic GaAs. We attribute the observed differences to the far infrared interaction and the use of dilute photoexcitation densities which eliminate both band-edge resonance and high carrier densities effects. A simple model is developed to determine the relative electron mobility and to interpret the results. Additionally, time resolved differential spectroscopy reveals Drude-like behavior of the free carrier conductivity within 1 ps of excitation.
Growth and characterization of phosphorous doped {111} homoepitaxial diamond thin films
Authors: Koizumi S. , Kamo M. , Sato Y. , Ozaki H. , Inuzuka T.
Published: July 2002

An n-type semiconducting diamond thin film was obtained by microwave enhanced plasma chemical vapor deposition using phosphine (PH3) as a dopant source. A homoepitaxial diamond thin film with a thickness of about 300 nm was grown on the {111} surface of a type Ib diamond with a variety of dopant concentrations. Over a wide range of dopant concentrations (PH3/CH4: 1000–20 000 ppm), the n-type conduction was confirmed by Hall-effect measurements. The activation energy of carriers was 0.43 eV. The Hall mobility of about 23 cm2/V s has been obtained at around 500 K for the 1000 ppm sample. No significant increase of hydrogen has been observed by secondary-ion-mass-spectroscopy analysis for the phosphorous doped layers.
Ion dependent interstitial generation of implanted mercury cadmium telluride
Authors: Williams B. L. , Robinson H. G. , Helms C. R.
Published: July 2002

The creation of Hg interstitials during ion implantation of mercury cadmium telluride is found to strongly depend on the preferred lattice position of the element implanted. Elements that substitute onto the cation sublattice create significantly more interstitials than elements that sit interstitially or on the anion sublattice. In particular, implants of column II elements Mg and Zn produced much larger interstitial concentrations than implants of column VI elements S and Se. Implants of B, which resides mostly as an interstitial, produced Hg interstitial concentrations intermediate between the column II and column VI ions. Recoils from implant damage also contributed to Hg interstitial formation in heavier mass implants (Zn and Se), but appear to have negligible influence on interstitial generation in implants of lighter ions.
Long range order in AlxGa1−xN films grown by molecular beam epitaxy
Authors: Korakakis D. , Ludwig K. F. , Moustakas T. D.
Published: July 2002

The first observation of atomic long range ordering in AlxGa1−xN thin films grown by electron cyclotron resonance assisted molecular beam epitaxy on sapphire and 6H-SiC substrates is reported. The phenomenon was investigated by studying the superlattice peaks (0001), (0003), and (0005) using x-ray diffraction. The relative intensity of these peaks was found to be largest for Al content in the 30%–50% range in qualitative agreement with expectations for an ordered structure of ideal Al0.5Ga0.5N stoichiometry. The average size of the ordered domains in the films was found to be within a factor of 4 of the films’ thicknesses. The degree of ordering depends on the III/V flux ratio and exhibits a weaker dependence on Si doping.
Broadband optical limiting with multiwalled carbon nanotubes
Authors: Sun X. , Yu R. Q. , Xu G. Q. , Hor T. S. A. , Ji W.
Published: July 2002

Optical limiting effects in multiwalled carbon nanotubes have been observed in the visible and infrared spectral regions with nanosecond laser pulses. The multiwalled carbon nanotubes investigated include those suspended in distilled water and embedded in polymethyl methacrylate films. Among all the samples measured, the limiting performance of the carbon nanotube suspension is the best with the limiting threshold determined to be ∼1, 5, and 13 J/cm2 at 532, 700, and 1064 nm, respectively. The possible mechanism for the observed effects is discussed.
Differences in nature of defects between SrBi2Ta2O9 and Bi4Ti3O12
Authors: Park B. H. , Hyun S. J. , Bu S. D. , Noh T. W. , Lee J. , Kim H.-D. , Kim T. H. , Jo W.
Published: July 2002

X-ray photoemission spectroscopy measurements were executed to compare the nature of defects in SrBi2Ta2O9 (SBT) and Bi4Ti3O12 (BTO) films. In the SBT film, it was found that the oxygen ions at the metal–oxygen octahedra were much more stable than those at the Bi2O2 layers. On the other hand, for the BTO film, oxygen vacancies could be induced both at the titanium–oxygen octahedra and at the Bi2O2 layers. We suggested that the difference in stability of the metal–oxygen octahedra should be related to different fatigue behaviors of the SBT and the BTO films.
Ultraviolet photon counting with GaN avalanche photodiodes
Authors: McIntosh K. A. , Molnar R. J. , Mahoney L. J. , Molvar K. M. , Efremow N. , Verghese S.
Published: July 2002

Photon counting, utilizing Geiger-mode avalanche response, has been demonstrated at 300 K in avalanche photodiodes fabricated in GaN grown by hydride vapor-phase epitaxy. Measurements have been made using both passive-quench and time-gated modes of operation. The two important figures of merit for photon-counting applications, photon detection efficiency (PDE) and dark count rate, were measured. A maximum PDE of 13% was measured at 325 nm with a dark count rate of 400 kHz. Typical mesa-etched devices exhibit a parasitic shunt leakage current of less than 20 nA at 90% of breakdown voltage.
Micromagnetism and high temperature coercivity of MnBi/Al multilayers
Authors: Rüdiger U. , Güntherodt G. , Fumagalli P. , Thomas L. , Parkin S. S. P. , Kent A. D.
Published: July 2002

The micromagnetic properties of multilayered MnBi/Al films have been investigated and compared to pure MnBi thin films. Pure MnBi films reveal an anomalous increase of the high temperature coercivity, which has been explained on the basis of a hybrid domain wall pinning model. The multilayer-type preparation of MnBi/Al thin films results in significantly reduced MnBi particle size of approximately 40 nm. The smaller particle size leads to a change of the dominant magnetization reversal process from one driven by domain wall movement toward coherent rotation. This was investigated via magnetic force microscopy imaging and micromagnetic calculations. The absence of domain walls during magnetization reversal results in a clear suppression of the increase of the high temperature coercivity observed in pure MnBi films.
Dielectric enhancement and Maxwell–Wagner effects in ferroelectric superlattice structures
Authors: O’Neill D. , Bowman R. M. , Gregg J. M.
Published: July 2002

In an attempt to reproduce the functional properties associated with relaxor electroceramics, pulsed laser deposition has been used to fabricate thin-film capacitor structures in which the dielectric layer is composed of a superlattice of Ba0.8Sr0.2TiO3 and Ba0.2Sr0.8TiO3. The properties of the capacitors were investigated as a function of superlattice periodicity. The dielectric constant was significantly enhanced at stacking periodicities of a few unit cells, consistent with relaxor behavior. However, enhancement in dielectric constant was generally associated with high dielectric loss. Analysis of the imaginary permittivity as a function of frequency shows that fine-scale superlattices conform to Maxwell–Wagner behavior. This suggests that the observed enhancement of the real part of the dielectric constant is an artifact produced by carrier migration to interfaces within the dielectric. A comparison of this data with that already published on dielectric superlattices suggests that previous claims of an enhancement in dielectric constant may also be attributed to the Maxwell–Wagner effect.
Etching of SiO2 and Si in fluorocarbon plasmas: A detailed surface model accounting for etching and deposition
Authors: Gogolides Evangelos , Vauvert Philippe , Kokkoris George , Turban Guy , Boudouvis Andreas G.
Published: July 2002

A surface model is presented for the etching of silicon (Si) and silicon dioxide (SiO2) in fluorocarbon plasmas. Etching and deposition are accounted for using a generalized concept for the “polymer surface coverage,” which is found to be equivalent to a normalized fluorocarbon film thickness covering the etched surfaces. The model coefficients are obtained from fits to available beam experimental data, while the model results are successfully compared with high-density plasma etching data.