bluuebunny/crossref_metadata_2025 huggingface dataset:
Dental school admissions in Ireland: can current selection criteria predict success?
Authors: Lynch C. D. , McConnell R. J. , Hannigan A.
Published: April 2006

Introduction:  Entry into university education in Ireland, including dental school, is based solely on academic performance in the Leaving Certificate Examination, held at the end of formal school education. The aim of this investigation was to examine the suitability of this process for the selection of dental students in Ireland.

Materials and methods:  Information for all dental students who entered the dental degree programme immediately following completion of the Leaving Certificate Examination at the National University of Ireland, Cork, during the years 1997–1999 was retrieved. Information was collected relating to gender, the number of times the student had attempted the Leaving Certificate Examination, their performance in this examination, the total number of marks awarded to each student at the end of the First and Final Dental Examinations, and their performance in individual modules.

Results:  Whilst there was a significant relationship between performance in the Leaving Certificate Examination and the First Dental Examination (correlation coefficient = 0.22, P < 0.05), this relationship could only explain 12% of the variation within the performance of students in this examination. There was no relationship between performance in the Leaving Certificate and the Final Dental Examination (correlation coefficient = 0.09, P > 0.05). There was a significant correlation between performance in the Leaving Certificate Examination and performance in seven of the 55 programme modules, all of which were pre‐clinical modules, and of which five were related to basic sciences.

Conclusions:  Based on the limitations of this study, the current selection process for dental students in Ireland seems to be of limited value.
The William Blake Archive: An Overview
Authors: Jones Steven E.
Published: April 2006

This essay offers an introduction to and summary of The William Blake Archive (WBA) as an online, multimedia, scholarly edition. It covers the history of the WBA's initial online publication in 1996 and then describes the conception and structure of the edition, its editorial principles, and “object‐centered” organization, hierarchical structure, and interface. Next the essay surveys the WBA's editorial methods and procedures, including how the resource – which aims for “virtually reunified” corpus – has been produced and managed at The University of Virginia's Institute for Advanced Technology in the Humanities (IATH), and concludes with a look at the method of publication and delivery (including the role of structural markup and the World Wide Web).
Health insurance reform and older Australians
Authors: Temple Jeromey B
Published: April 2006

Objectives:  This study aims to (i) document the changing proportions of older persons with health insurance in a period of policy change, (ii) examine why older persons do and do not purchase health insurance, and (iii) discuss these findings in relation to implications for current and future cohorts of the aged.

Method:  Data from the Private Health Insurance Administrative Council and the ABS are used to estimate cross‐sectional and cohort shifts in health insurance coverage among persons aged 55 years and over.

Results:  Prior to recent reforms, approximately 37% of persons aged 55 years and older have hospital health insurance compared with 45% in 2001, with considerable variation in coverage by age and sex.

Conclusion:  Health insurance coverage has increased among older Australians, albeit disproportionately. Affordability remains a key issue for older Australians and may become more problematic in future age cohorts.
Isolation and structural characterization of the Ndh complex from mesophyll and bundle sheath chloroplasts of Zea mays
Authors: Darie Costel C. , Biniossek Martin L. , Winter Veronika , Mutschler Bettina , Haehnel Wolfgang
Published: April 2006

Complex I (NADH: ubiquinone oxidoreductase) is the first complex in the respiratory electron transport chain. Homologs of this complex exist in bacteria, mitochondria and chloroplasts. The minimal complex I from mitochondria and bacteria contains 14 different subunits grouped into three modules: membrane, connecting, and soluble subcomplexes. The complex I homolog (NADH dehydrogenase or Ndh complex) from chloroplasts from higher plants contains genes for two out of three modules: the membrane and connecting subcomplexes. However, there is not much information about the existence of the soluble subcomplex (which is the electron input device in bacterial complex I) in the composition of the Ndh complex. Furthermore, there are contrasting reports regarding the subunit composition of the Ndh complex and its molecular mass. By using blue native (BN)/PAGE and Tricine/PAGE or colorless‐native (CN)/PAGE, BN/PAGE and Tricine/PAGE, combined with mass spectrometry, we attempted to obtain more information about the plastidal Ndh complex from maize (Zea mays). Using antibodies, we detected the expression of a new ndh gene (ndhE) in mesophyll (MS) and bundle sheath (BS) chloroplasts and in ethioplasts (ET). We determined the molecular mass of the Ndh complex (550 kDa) and observed that it splits into a 300 kDa membrane subcomplex (containing NdhE) and a 250 kDa subcomplex (containing NdhH, ‐J and ‐K). The Ndh complex forms dimers at 1000–1100 kDa in both MS and BS chloroplasts. Native/PAGE of the MS and BS chloroplasts allowed us to determine that the Ndh complex contains at least 14 different subunits. The native gel electrophoresis, western blotting and mass spectrometry allowed us to identify five of the Ndh subunits. We also provide a method that allows the purification of large amounts of Ndh complex for further structural, as well as functional studies.
Hemagglutinin‐33 of type A botulinum neurotoxin complex binds with synaptotagmin II
Authors: Zhou Yu , Foss Sean , Lindo Paul , Sarkar Hemanta , Singh Bal Ram
Published: April 2006

Botulinum neurotoxin type A (BoNT/A), the most toxic substance known to mankind, is produced by Clostridium botulinum type A as a complex with a group of neurotoxin‐associated proteins (NAPs) through polycistronic expression of a clustered group of genes. NAPs are known to protect BoNT against adverse environmental conditions and proteolytic digestion. Hemagglutinin‐33 (Hn‐33) is a 33 kDa subcomponent of NAPs that is resistant to protease digestion, a feature likely to be involved in the protection of the botulinum neurotoxin from proteolysis. However, it is not known whether Hn‐33 plays any role other than the protection of BoNT. Using immunoaffinity column chromatography and pull‐down assays, we have now discovered that Hn‐33 binds to synaptotagmin II, the putative receptor of botulinum neurotoxin. This finding provides important information relevant to the design of novel antibotulism therapeutic agents targeted to block the entry of botulinum neurotoxin into nerve cells.
Comparative analysis of carbohydrate‐binding properties of two tandem repeat‐type Jacalin‐related lectins, Castanea crenata agglutinin and Cycas revoluta leaf lectin
Authors: Nakamura Sachiko , Yagi Fumio , Totani Kiichiro , Ito Yukishige , Hirabayashi Jun
Published: April 2006

Lectins belonging to the jacalin‐related lectin family are distributed widely in the plant kingdom. Recently, two mannose‐specific lectins having tandem repeat‐type structures were discovered in Castanea crenata (angiosperm) and Cycas revoluta (gymnosperm). The occurrence of such similar molecules in taxonomically less related plants suggests their importance in the plant body. To obtain clues to understand their physiological roles, we performed detailed analysis of their sugar‐binding specificity. For this purpose, we compared the dissociation constants (Kd) of Castanea crenata agglutinin (CCA) and Cycas revoluta leaf lectin (CRLL) by using 102 pyridylaminated and 13 p‐nitrophenyl oligosaccharides with a recently developed automated system for frontal affinity chromatography. As a result, we found that the basic carbohydrate‐binding properties of CCA and CRLL were similar, but differed in their preference for larger N‐linked glycans (e.g. Man7–9 glycans). While the affinity of CCA decreased with an increase in the number of extended α1–2 mannose residues, CRLL could recognize these Man7–9 glycans with much enhanced affinity. Notably, both lectins also preserved considerable affinity for mono‐antennary, complex type N‐linked glycans, though the specificity was much broader for CCA. The information obtained here should be helpful for understanding their functions in vivo as well as for development of useful probes for animal cells. This is the first systematic approach to elucidate the fine specificities of plant lectins by means of high‐throughput, automated frontal affinity chromatography.
Molecular mechanisms in successful peripheral regeneration
Authors: Makwana Milan , Raivich Gennadij
Published: April 2006

Peripheral nerve injury is normally followed by a robust regenerative response. Here we describe the early changes associated with injury from the initial rise in intracellular calcium and the subsequent activation of transcription factors and cytokines leading to an inflammatory reaction, and the expression of growth factors, cytokines, neuropeptides, and other secreted molecules involved in cell‐to‐cell communication promoting regeneration and neurite outgrowth. The aim of this review is to summarize the molecular mechanisms that play a part in executing successful regeneration.
AcmA of Lactococcus lactis is an N‐acetylglucosaminidase with an optimal number of LysM domains for proper functioning
Authors: Steen Anton , Buist Girbe , Horsburgh Gavin J. , Venema Gerard , Kuipers Oscar P. , Foster Simon J. , Kok Jan
Published: April 2006

AcmA, the major autolysin of Lactococcus lactis MG1363 is a modular protein consisting of an N‐terminal active site domain and a C‐terminal peptidoglycan‐binding domain. The active site domain is homologous to that of muramidase‐2 of Enterococcus hirae, however, RP‐HPLC analysis of muropeptides released from Bacillus subtilis peptidoglycan, after digestion with AcmA, shows that AcmA is an N‐acetylglucosaminidase. In the C‐terminus of AcmA three highly similar repeated regions of 45 amino acid residues are present, which are separated by short nonhomologous sequences. The repeats of AcmA, which belong to the lysine motif (LysM) domain family, were consecutively deleted, removed, or, alternatively, one additional repeat was added, without destroying the cell wall‐hydrolyzing activity of the enzyme in vitro, although AcmA activity was reduced in all cases. In vivo, proteins containing no or only one repeat did not give rise to autolysis of lactococcal cells, whereas separation of the producer cells from the chains was incomplete. Exogenously added AcmA deletion derivatives carrying two repeats or four repeats bound to lactococcal cells, whereas the derivative with no or one repeat did not. In conclusion, these results show that AcmA needs three LysM domains for optimal peptidoglycan binding and biological functioning.
The small heat shock proteins and their role in human disease
Authors: Sun Yu , MacRae Thomas H.
Published: April 2006

Small heat shock proteins (sHSPs) function as molecular chaperones, preventing stress induced aggregation of partially denatured proteins and promoting their return to native conformations when favorable conditions pertain. Sequence similarity between sHSPs resides predominately in an internal stretch of residues termed the α‐crystallin domain, a region usually flanked by two extensions. The poorly conserved N‐terminal extension influences oligomer construction and chaperone activity, whereas the flexible C‐terminal extension stabilizes quaternary structure and enhances protein/substrate complex solubility. sHSP polypeptides assemble into dynamic oligomers which undergo subunit exchange and they bind a wide range of cellular substrates. As molecular chaperones, the sHSPs protect protein structure and activity, thereby preventing disease, but they may contribute to cell malfunction when perturbed. For example, sHSPs prevent cataract in the mammalian lens and guard against ischemic and reperfusion injury due to heart attack and stroke. On the other hand, mutated sHSPs are implicated in diseases such as desmin‐related myopathy and they have an uncertain relationship to neurological disorders including Parkinson's and Alzheimer's disease. This review explores the involvement of sHSPs in disease and their potential for therapeutic intervention.
The role of the SEA (sea urchin sperm protein, enterokinase and agrin) module in cleavage of membrane‐tethered mucins
Authors: Palmai‐Pallag Timea , Khodabukus Naila , Kinarsky Leo , Leir Shih‐Hsing , Sherman Simon , Hollingsworth Michael A. , Harris Ann
Published: April 2006

The membrane‐tethered mucins are cell surface‐associated dimeric or multimeric molecules with extracellular, transmembrane and cytoplasmic portions, that arise from cleavage of the primary polypeptide chain. Following the first cleavage, which may be cotranslational, the subunits remain closely associated through undefined noncovalent interactions. These mucins all share a common structural motif, the SEA module that is found in many other membrane‐associated proteins that are released from the cell surface and has been implicated in both the cleavage events and association of the subunits. Here we examine the SEA modules of three membrane‐tethered mucins, MUC1, MUC3 and MUC12, which have significant sequence homology within the SEA domain. We previously identified the primary cleavage site within the MUC1 SEA domain as FRPG/SVVV a sequence that is highly conserved in MUC3 and MUC12. We now show by site‐directed mutagenesis that the F, G and S residues are important for the efficiency of the cleavage reaction but not indispensable and that amino acids outside this motif are probably important. These data are consistent with a new model of the MUC1 SEA domain that is based on the solution structure of the MUC16 SEA module, derived by NMR spectroscopy. Further, we demonstrate that cleavage of human MUC3 and MUC12 occurs within the SEA domain. However, the SEA domains of MUC1, MUC3 and MUC12 are not interchangeable, suggesting that either these modules alone are insufficient to mediate efficient cleavage or that the 3D structure of the hybrid molecules does not adequately recreate an accessible cleavage site.
Methods of Continuing Professional Education Preferred by Irish Pediatric Nurses
Authors: Doyle Carmel
Published: April 2006

PURPOSE.  To explore the continuing professional education (CPE) of pediatric nurses in Ireland and establish if and in what ways pediatric nurses are taking part in CPE as well as factors that might assist or hinder pediatric nurses in undertaking CPE.

DESIGN AND METHODS.  A stratified random sample of 205 registered children's nurses (RCNs) completed a questionnaire.

RESULTS.  RCNs in Ireland use a variety of methods of CPE, the most popular being journal reading, while the least popular method is the use of computerized journal databases and the internet. Many RCNs appear to lack the computer skills necessary to utilize these methods of CPE.

PRACTICE IMPLICATIONS.  The favored methods of CPE by RCNs need to be utilized and promoted in the practice setting in order to ensure RCNs are up to date in the provision of quality care to pediatric patients.
Improvement of NO2 a Sensing Performances by an Additional Second Component to the Nano‐Structured NiO Sensing Electrode of a YSZ‐Based Mixed‐Potential‐Type Sensor
Authors: Plashnitsa Vladimir V. , Ueda Taro , Miura Norio
Published: April 2006

Nano‐sized NiO powder was modified by the addition of BaO, La2O3, and CuO (10 wt% each) to change its morphology and electrochemical catalytic activities. Then, the NOx‐sensing characteristics of mixed‐potential‐type YSZ‐based planar sensor attached with each of the obtained NiO‐based samples as a sensing electrode (SE) were examined at elevated temperatures. As a result, the CuO‐added NiO SE was found to give a large enhancement in the NO2 sensitivity as well as the NO2 selectivity at 800°C even under a wet condition, in comparison with the pure NiO SE.
Monitoring Delamination Progression in Thermal Barrier Coatings by Mid‐Infrared Reflectance Imaging
Authors: Eldridge Jeffrey I. , Spuckler Charles M. , Martin Richard E.
Published: April 2006

Mid‐infrared (MIR) reflectance imaging is shown to be a reliable diagnostic tool for monitoring delamination progression in thermal barrier coatings (TBCs). MIR reflectance imaging utilizes the maximum transparency of TBCs in the 3–6 μm wavelength region to probe below‐surface delamination crack propagation that is typically hidden from visible wavelength inspection. The image contrast that identifies delamination progression arises from the increased reflectance produced by a large component of total internal reflection at the TBC/buried‐crack interface. Imaging was performed at a wavelength of 4 μm to take advantage of the relatively high transmittance of plasma‐sprayed 8 wt% yttria‐stabilized zirconia (8YSZ) TBCs along with a desirable relative insensitivity to potentially interfering absorptions by atmospheric constituents at that wavelength. A key advantage of MIR reflectance imaging over competing techniques is that it is sensitive to delamination progression even at very early stages before delamination cracks start linking together; therefore, TBC health assessment can be achieved throughout the life of the TBC well before TBC failure is imminent. Examples are presented to demonstrate monitoring delamination progression by MIR reflectance imaging in 8YSZ TBC‐coated specimens subjected to furnace cycling to 1163°C. The experimental results were in good agreement with reflectance values predicted by a four‐flux Kulbelka–Munk approximation applied to the extreme cases of a completely adherent and a completely detached TBC. Practical considerations, including potential interfering effects from surface contamination, sintering, and erosion are discussed.
Effects of husbandry parameters on the life‐history traits of the apple snail, Marisa cornuarietis: effects of temperature, photoperiod, and population density
Authors: Aufderheide John , Warbritton Ryan , Pounds Nadine , File‐Emperador Sharon , Staples Charles , Caspers Norbert , Forbes Valery
Published: April 2006

Abstract. These experiments are part of a larger study designed to investigate the influence of husbandry parameters on the life history of the apple snail, Marisa cornuarietis. The overall objective of the program is to identify suitable husbandry conditions for maintaining multi‐generation populations of this species in the laboratory for use in ecotoxicological testing. In this article, we focus on the effects of photoperiod, temperature, and population density on adult fecundity and juvenile growth. Increasing photoperiod from 12 to 16 h of light per day had no effect on adult fecundity or egg hatching and relatively minor effects on juvenile growth and development. Rearing snails at temperatures between 22°C and 28°C did not influence the rates of egg production or egg clutch size. However, the rates of growth and development (of eggs and juveniles) increased with increasing temperature in this range, and when temperatures were reduced to 22°C egg‐hatching success was impaired. Juvenile growth and development were more sensitive to rearing density than adult fecundity traits. On the basis of the present results, we conclude that rearing individuals of M. cornuarietis at a temperature of 25°C, a photoperiod of 12L:12D, and a density of <0.8 snails L−1 (with lower densities for juvenile snails) should provide favorable husbandry conditions for maintaining multi‐generation populations of this species.
Changes in nuclear morphology associated with elevated DNA levels during gametogenesis in cyclopoid copepods with chromatin diminution
Authors: Rasch Ellen M. , Wyngaard Grace A.
Published: April 2006

Abstract. Most species of freshwater cyclopoid copepods follow a conventional course of DNA replication during gametogenesis, but certain species regularly undergo chromatin diminution during early embryogenesis, a process that is accompanied by the exclusion of large amounts of heterochromatic DNA from progenitor somatic cells and selective retention of this DNA by primordial germ cells after their segregation from the soma. We have used scanning microdensitometry and image analysis cytometry of individual Feulgen‐stained nuclei to determine the DNA levels of individual somatic cell nuclei, oocytes, spermatocytes, and sperm for seven species, including Acanthocyclops brevispinosus, Acanthocyclops vernalis, Ectocyclops phaleratus, Eucyclops agilis, Eucyclops ensifer, Macrocyclops albidus, and Thermocyclops decipiens. The oocyte nuclei of these species have twice the DNA content of their diploid somatic cell nuclei. In specimens of Cyclops strenuus, Mesocyclops edax, Mesocyclops longisetus, Mesocyclops longisetus curvatus, and Metacyclops mendocinus, marked increases in DNA levels were noted in both female and male germ cells before meiosis. The appearance of enlarged nuclei with densely stained chromocenters is a distinguishing feature of oocytes and spermatocytes of cyclopoid species that exhibit excessive accumulations of DNA during gametogenesis and subsequently undergo chromatin diminution. The net increase in DNA content of the prediminution nuclei is 6–10 times the DNA level of their somatic cell nuclei and is largely attributable to increases in the amount of DNA associated with their heterochromatic chromocenters. The identification of a morphologically distinctive type of germ cell and its dramatic accumulation of large amounts of DNA before meiosis are discussed in terms of the selective elimination of heterochromatin during early cleavage stages in these cyclopoid species.
Leaf Litter Decomposition and Substrate Chemistry of Early Successional Species on Landslides in Puerto Rico1
Authors: Shiels Aaron B.
Published: April 2006

Decomposition is a critical process for nutrient release and accumulation of soil organic matter in disturbed soils, such as those found on landslides. I conducted a decomposition experiment on five landslides in the Luquillo Mountains of Puerto Rico as part of an investigation of the successional roles of two of the most common plant colonists to landslides,Cecropia schreberianaMiq. (Cecropiaceae) a pioneer tree species, andCyathea arborea(L.) Sm. (Cyatheaceae) a pioneer tree fern. I compared leaf litter decomposition over one year and the initial and 1‐yr chemistry for both species. Initial litter chemistry differed between the two species, asCecropiahad slightly higher nitrogen (9.2 mg/g) thanCyathea(8.2 mg/g) and higher lignin (28.6%) thanCyathea(26.0%), but water‐soluble carbon and nonpolar extractable carbon (fats and oils, waxes, chlorophylls) were higher inCyatheathanCecropia.Total carbon, acid‐soluble carbon, total phosphorus, and pH did not differ significantly between leaf litter species. Across all five landslides,Cyathea(k= 0.93 ± 0.06) leaves decomposed significantly faster thanCecropia(k= 0.68 ± 0.06). The differences in these species leaf litter decomposition rates and chemical composition could potentially influence organic matter dynamics and nutrient cycling rates in these early successional systems.
Phenology of Ficus racemosa in Xishuangbanna, Southwest China1
Authors: Zhang Guangming , Song Qishi , Yang Darong
Published: April 2006

Leaf and fig phenology (including leafing, flowering, and fruiting) and syconium growth of Ficus racemosa were studied in Xishuangbanna, China. Leaffall and flushing of F. racemosa occurred twice yearly: in mid‐dry season (December to March) and mid‐rainy season (July to September). The adult leaf stage of the first leaf production was remarkably longer than that of the second. F. racemosa bears syconia throughout the year, producing 4.76 crops annually. Asynchronous fig production was observed at a population level. Fig production was independent of leafing. Fig production peaks were not evident, but fluctuation was clear. Diameter growth rates of syconium were normally higher in early developmental stages than in later stages, and reached a peak coinciding with the female flower phase. The mean ± SD of syconium diameter of the female flower phase was 2.19 ± 0.36 cm, and reached 3.67 ± 0.73 cm of the male flower phase. Syconium diameter and receptacle cavity quickly enlarged at the female and male flower phases. Monthly diameter increment of the syconium was primarily affected by average monthly temperature, rather than rainfall or relative humidity.
Annual Growth Ring Patterns in Brachystegia spiciformis Reveal Influence of Precipitation on Tree Growth1
Authors: Trouet Valérie , Coppin Pol , Beeckman Hans
Published: April 2006

The availability of exactly dated tree‐ring chronologies is limited in tropical regions. However, these chronologies could contribute widely to studies of the influence of natural and human‐induced factors on tropical forests. We examine the potential for building a chronology based on three sites in the miombo woodland of western Zambia. Brachystegia spiciformis Benth., a dominant species from this vegetation type, is used. Response of the chronology to several climatic factors is examined. All specimens showed very clear growth rings, and cross‐dating between radii of a tree was successful for all trees. Site chronologies could be constructed after cross‐dating of growth ring series of individual trees. The mean growth ring curves of the three sites were significantly similar, allowing for the construction of a regional chronology. Correlation function analysis between the tree‐ring chronology and regional climatic variables revealed that climate at the core of the rainy season, in December and January, has an explicit influence on tree growth. Where precipitation and relative humidity in these months influence tree growth positively, temperature correlates in a negative way. Some 20 percent of the variance in the B. spiciformis tree‐ring chronology is accounted for by wet season rainfall. The successful cross‐dating and correlation between a tree‐ring chronology and climate demonstrated in this study indicate annual ring formation in B. spiciformis trees and sensitivity to climatic conditions.
Evaluation of different models to describe egg and pupal development of Xyleborus fornicatus Eichh. (Coleoptera: Scolytidae), the shot‐hole borer of tea in Sri Lanka
Authors: WALGAMA RAVINDRA SAMPATH , ZALUCKI MYRON PHILLIP
Published: April 2006

Abstract
Development data of eggs and pupae of Xyleborus fornicatus Eichh. (Coleoptera: Scolytidae), the shot‐hole borer of tea in Sri Lanka, at constant temperatures were used to evaluate a linear and seven nonlinear models for insect development. Model evaluation was based on fit to data (residual sum of squares and coefficient of determination or coefficient of nonlinear regression), number of measurable parameters, the biological value of the fitted coefficients and accuracy in the estimation of thresholds. Of the nonlinear models, the Lactin model fitted experimental data well and along with the linear model, can be used to describe the temperature‐dependent development of this species.
EFFECT OF PHOSPHATE SALTS AND TRANSGLUTAMINASE IN PREVENTION OF FREEZE CRACKING IN FROZEN DICED BROILER BREAST
Authors: SUNGTONG P. , CHAIWANICHSIRI S. , RUANGTRAKOOL B. , SUZUKI T. , TAKAI R. , TANTRATIAN S.
Published: April 2006

Raw broiler breast meat was cooked and diced to 1.5 × 1.5 × 1.5 cm

3

then frozen under air‐blast, still‐air and cryogenic conditions. It was found that freezing with cryogenic at −70C at a rate of 37.50 cm/h produced 38.34% cracked pieces and increasing the freezing rate produced more cracked pieces. Cracking could be found on up to four sides of the dice. A small increase in the moisture of the dice drastically increased the cracking. Tumbling the meat with 1% sodium triphosphate solution prior to cooking and freezing at −70C reduced the amount of freeze cracking in the product from 47.50 to 24.17%. Tumbling the meat with 0.5% transglutaminase (TGase) reduced the cracked product to 25.84%. Increasing TGase not only increased the moisture content of the products but also reduced the number of cracked products. The TGase‐treated dices had narrower and shorter cracks than phosphate‐treated and without treatment dices.
Simulation study of junction effect on field emission from one-dimensional nanostructure grown on silicon substrate
Authors: Lan Yung-Chiang , Yan MingXun , Liu Wen-Jen , Hu Yuan , Lin Tsang-Lang
Published: April 2006

In this article, the field-emission properties of the one-dimensional nanostructure grown on doped silicon substrate have been studied via computer simulation. The classical transport equation is used to describe the carrier transport in the material and solved together with Poisson’s equation. The field emission at the emitter-vacuum interface is modeled by the Fowler-Nordheim equation. Our simulation results agree with the experimental results qualitatively. For narrow-band-gap material, the p-type Si substrate will limit the field-emission current in the high applied voltage region. This result can be ascribed to the formation of reverse-biased p-n junction. For wide-band-gap material, however, the p-type Si substrate will enhance the field-emission current, which is attributable to the lower carrier injection barrier height and the stronger driving force offered by the p-type substrate.
Quantum effect in the field emission of carbon nanotubes
Authors: Liang Shi-Dong , Huang N. Y. , Deng S. Z. , Xu N. S.
Published: April 2006

A theoretical formalism is developed to study the intrinsic properties of field emission from the single-walled carbon nanotubes (SWCNTs), including the current-voltage characteristic, the energy spectrum, and their responses to the magnetic field. The SWCNTs can be classified to two kinds, metallic and semiconducting tubes, according to field-emission properties. They have different slopes of the Fowler-Nordheim [Proc. R. Soc. London, Ser. A 119, 173 (1928)] plot, energy spectra, and different responses to the magnetic field, which originate from the energy band structure of SWCNTs.
Depth resolution studies in SiGe delta-doped multilayers using ultralow-energy O2+ secondary-ion-mass spectrometry
Authors: Chanbasha A. R. , Wee A. T. S.
Published: April 2006

Improvements in depth resolution using low primary ion energy secondary-ion-mass spectrometry have been demonstrated. This comprehensive study is done using a wide range of impact angles at ultralow energies. In this work, using Ge delta-doped Si samples, we confirm that depth resolution can be improved by lowering the primary ion impact energy at ultralow energy. By varying the angle of incidence from 0° to 70°, we noted that a better depth resolution is achievable not only at normal incidence but over a wider range of impact angles as the probe energy is reduced. The best depth resolution was observed using Ep∼250eV and θ∼0°–40° with full width at half maximum (FWHM) ∼1.5nm and λd<1nm throughout the depth profiled (120nm). Using Ep∼500eV, we observed a good depth resolution of FWHM ∼2.2nm and λd∼1.2nm throughout the depth evaluated at θ∼0°–30°. Using Ep∼1keV, a good depth resolution of FWHM ∼3.5nm and λd∼1.8nm was observed at θ∼0°–20°. The dynamic range was also evaluated, the best being achieved at θ∼50° for Ep∼250eV, θ∼40° for Ep∼500eV, and at θ∼30° for Ep∼1keV. Contributions from roughening and atomic mixing to the depth resolution of δ layers are discussed using the mixing-roughness-information depth model.
Bottom-up fill mechanisms of electroless copper plating with addition of mercapto alkyl carboxylic acid
Authors: Wang Zenglin , Liu Zhijuan , Jiang Hongyan , Wei Wang Xiu
Published: April 2006

Copper electrodeposition is used in the damascene process for the fabrication of interconnections of ultralarge-scale integrated semiconductor devices. Copper electroless plating is one of the most promising processes for the formation of a seed layer for electroplating. In this article, the effect of additives of mercapto alkyl carboxylic acid (MACA) such as 3-mercaptopropionic acid, 11-mercaptoundecanoic acid, and 16-mercaptohexadecanoic acid on bottom-up filling of electroless copper in deep submicrometer via holes was investigated. The inhibition of copper plating deposition on the plane surface was observed with an addition of MACAs, and bottom-up fill was confirmed for MACAs with alkyl chain numbers of 3, 11, and 16. The bottom-up fill tendency was enhanced with increasing alkyl chain number. This result strongly suggests that the diffusion coefficient of inhibitor molecule plays an important role for bottom-up fill mechanisms, because MACA with longer alkyl chain has smaller diffusion coefficient than that with shorter alkyl chain.
Microelectronically fabricated LiCoO2∕SiO2/polycrystalline-silicon power cells planarized by chemical mechanical polishing
Authors: Ariel Nava , Isaacson David M. , Fitzgerald Eugene A.
Published: April 2006

Monolithic integration of different electronic circuit elements onto a single chip is beneficial for the purpose of reducing overall system cost as well as improving performance and reliability. Integrating a power unit onto a silicon chip requires the implementation of a thin-film solid-state battery that is compatible with existing silicon integrated circuit technology in terms of manufacturing methods, materials, and performance. One of the materials in the battery industry, studied by us, is silicon dioxide (SiO2). The high level of process control for thin SiO2 layers which is a result of microelectronic advances, its insulating properties, and its past reported permeability to light ions have motivated us to exploit SiO2 as a solid-state electrolyte in our integrated thin-film battery. This SiO2 electrolyte layer is thermally grown from an amorphous silicon (a-Si) thin layer deposited on doped polycrystalline silicon (polysilicon) which serves as the anode against a thin-film-sputtered LiCoO2 cathode. We have fabricated and characterized ultrathin solid-state thin-film power cells consisting of LiCoO2, SiO2, and polysilicon. Cells containing an ultrathin SiO2 lithium-free electrolyte with a thickness range of 7–40nm and active-area sizes of 5×5, 2×2, 1×1, and 0.5×0.5mm2 were created using established microelectronics processing and expertise. Ultrathin cells require smooth surfaces (nanometer-scale roughness) as opposed to higher roughness encountered in bulk batteries and microbatteries. To ensure a very thin and flat electrolyte, this work demonstrates the implementation of a planarization step by using chemical mechanical polishing (CMP) in the fabrication of the integrated solid-state thin-film lithium-ion battery. Polishing the polysilicon layer reduced its 1×1μm2 root-mean-square roughness from 8.06to0.53nm and led to smoother interfaces and to higher quality of the SiO2 grown on top of it. The cells were charged and discharged using conventional microelectronic electrical testing equipment and exhibited improved performance when prepared with the additional CMP planarization step. Up to 40% of the charge was retrieved from the planarized cells compared to a maximum of 14.5% retrieved from the nonplanarized cells. The open circuit voltage (VOC) of the LiCoO2∕SiO2/polysilicon cell was estimated by comparing the initial charge voltage values obtained with different electrolyte thicknesses and was found to be 2.19±0.02V. The results presented in this work show the importance of interfacial quality in the process of moving to integrated power on a chip.
Dopant diffusion modeling for heteroepitaxial SiGe∕Si devices
Authors: Chakravarthi S. , Chidambaram P. R. , Machala C. F. , Mansoori M.
Published: April 2006

A comprehensive model to predict dopant diffusion (Sb, As, B, and P) in epitaxially strained silicon germanium (SiGe) CMOS transistors is presented. The effect of germanium is primarily comprehended as a change in point defect populations (self-interstitials and vacancies). Our analysis validates this approximation for most dopants (Sb, As, Ge, and P). With germanium concentration, the vacancy population increases much more than the interstitial concentration. Consequently, the fractional interstitial mediated diffusion decreases with increasing germanium. For boron an additional change in pair formation/migration energy is required to explain the observed experimental data. The model is used to explore heteroepitaxially grown SiGe∕Si device design options.
Growth of gallium nitride nanorods by metalorganic molecular beam epitaxy
Authors: Kuo Shou-Yi , Kei C. C. , Hsiao C. N. , Chao C. K.
Published: April 2006

Without a catalyst or template layer, high-quality GaN nanorods have been grown by rf radical source metalorganic molecular beam epitaxy on c-sapphire substrates. Scanning electron microscopy, transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDX), and x-ray diffraction were employed to characterize the GaN nanorods. These nanorods have an average diameter of 50nm, and the rod areal density can reach 1×1010cm−2 depending on the growth parameters. High-resolution TEM results indicate that the well-aligned GaN nanorods have a single-crystal hexagonal wurtzite structure with preferential [0001] orientation, and no droplet was observed at the end of the nanorods. Meanwhile, EDX analysis revealed gallium and nitrogen as the only detectable elements. These high-quality and high-density GaN nanorods might be useful for practical applications in nanoscale optoelectronic and electronic devices.
Statistical modeling of field-enhancement-factor distribution of nanostructured carbon films
Authors: Park Kyung Ho , Lee Soonil , Koh Ken Ha
Published: April 2006

We measured the field-emission properties of nanostructured carbon films (NSCFs), carbon nanotubes, and carbon nanoparticles, using a microtip and a large area phosphor-screen anode. The normal distribution of turn-on electric fields which was measured using a microtip anode from 100 square cells of 30×30μm2 for each NSCF indicated an asymmetric distribution of field-enhancement factor β with a large-β tail. The direct deduction of the field-enhancement factors via fitting of current-versus-voltage curves to the simplified Fowler-Nordheim (FN) equation with a series-resistance effect confirmed the asymmetric β distribution. Moreover, field-emission features observed using a large area phosphor screen, such as a slight curvature in the FN plots at the low voltage regime and applied-field-dependent exponential increase of emission-site densities, turned out to be consistent with the asymmetric β distribution.
Modeling of field-assisted emission from the image states of a glass substrate
Authors: Mayer A. , Chung M. S. , Kumar N. , Weiss B. L. , Miskovsky N. M. , Cutler P. H.
Published: April 2006

A device has been reported recently in which electrons transit through the image states of a negative-electron-affinity glass substrate before being emitted to the vacuum. The external field required for this emission may be as low as 10V∕cm, which is up to three orders of magnitude lower than the fields encountered with other materials. In order to address what appears to be an essential aspect of this device, we present a modeling of field-assisted emission from the image states of a dielectric substrate. The analysis includes a characterization of the image states and considers direct tunneling and thermal excitation to higher energy levels as possible mechanisms for the emission. The model turns out to provide surface charge densities and emission currents that are in excellent agreement with experiments. For the working conditions of the device, the simulations show that the emission has a dominant thermally enhanced field emission component and that the image states play a significant role in pinning the Fermi level to values that are close to the vacuum level.
Improved dc and microwave performance of heterojunction bipolar transistors by full sulfur passivation
Authors: Cheng Shiou-Ying , Fu Ssu-I , Chu Kuei-Yi , Lai Po-Hsien , Chen Li-Yang , Liu Wen-Chau , Chiang Meng-Hsueh
Published: April 2006

The temperature-dependent dc characteristics of InGaP∕GaAs heterojunction bipolar transistors with and without full sulfur passivation are systematically studied and demonstrated. The studied device with full sulfur passivation shows lower specific contact resistance ρC, lower sheet resistance Rsh, lower collector-emitter offset voltage ΔVCE, and higher dc gain βF than devices without sulfur passivation. The device with full sulfur passivation also exhibits better rf performance. In addition, the studied device with full sulfur treatment shows lower temperature variation coefficients of ρC,Rsh,ΔVCE, and βF. Thus, the device with sulfur treatment presents relatively temperature-independent characteristics that can extend the transistor action to higher temperature regimes.
Quantum size dependence of electron distribution on carbon nanotubes and its influence on field emission
Authors: Filip L. D. , Nicolaescu D. , Silva S. R. P.
Published: April 2006

A two-dimensional model of quasi-free-electrons is used to compute the electron axial distribution on a carbon nanotube and the energy distribution of the field emitted electrons. The nature of the substrate-nanotube contact is taken into account by varying the boundary condition for the electronic wave function. In qualitative agreement with the experimental results to date, regular patterns of the axial electron density and electron accumulation on the nanotube cap are obtained. The energy distribution of the field emitted electrons shows a multiple peak structure superimposed over a very fine distribution of maxima. Such a multiple peak structure is also qualitatively confirmed in experiments. The behavior of the distribution of the emitted electrons with the extraction voltage and with the operation temperature is investigated.
Constrained segment shapes in direct‐aperture optimization for step‐and‐shoot IMRT
Authors: Bedford James L. , Webb Steve
Published: April 2006

Previous studies have shown that, by optimizing segment shapes and weights directly, without explicitly optimizing fluence profiles, effective IMRT plans can be generated with fewer segments. This study proposes a method of direct‐aperture optimization with aperture shape constraints, which is designed to provide segmental IMRT plans using a minimum of simple, regular segments. The method uses a cubic function to create smoothly curving multileaf collimator shapes. Constraints on segment dimension and equivalent square are applied, and each segment can be constrained to lie within the previous one, for easy generation of fluence profiles with a single maximum. To simply optimize the segment shapes and reject any shapes which violate the constraints is too inefficient, so an innovative method of feedback optimization is used to ensure in advance that viable aperture shapes are generated. The algorithm is demonstrated using a simple cylindrical phantom consisting of a hemi‐annular planning target volume and a central cylindrical organ‐at‐risk. A simple IMRT rectum case is presented, where segments are used to replace a wedge. More complex cases of prostate and seminal vesicles and prostate and pelvic nodes are also shown. The algorithm produces effective plans in each case with three to five segments per beam. For the simple plans, the constraint that each segment should be contained within the previous one adds additional simplicity to the plan, for a small reduction in plan quality. This study confirms that direct‐aperture optimization gives efficient solutions to the segmental IMRT inverse problem and provides a method for generating simple apertures. By using such a method, the workload of IMRT verification may be reduced and simplified, as verification of fluence profiles from individual beams may be eliminated.
A semianalytic model to extract differential linear scattering coefficients of breast tissue from energy dispersive x‐ray diffraction measurements
Authors: LeClair Robert J. , Boileau Michel M. , Wang Yinkun
Published: April 2006

The goal of this work is to develop a technique to measure the x‐ray diffraction signals of breast biopsy specimens. A biomedical x‐ray diffraction technology capable of measuring such signals may prove to be of diagnostic use to the medical field. Energy dispersive x‐ray diffraction measurements coupled with a semianalytical model were used to extract the differential linear scattering coefficients of breast tissues on absolute scales. The coefficients describe the probabilities of scatter events occuring per unit length of tissue per unit solid angle of detection. They are a function of the momentum transfer argument, , where angle and wavelength. The technique was validated by using a diameter polychromatic x‐ray beam incident on a diameter thick sample of water. Water was used because good x‐ray diffraction data are available in the literature. The scatter profiles from 6° to 15° in increments of 1° were measured with a thick cadmium zinc telluride detector. A diameter Pb aperture was placed on top of the detector. The target to detector distance was and the duration of each measurement was . Ensemble averages of the results compare well with the gold standard data of A. H. Narten [“X‐ray diffraction data on liquid water in the temperature range 4°C–200°C,” ORNL Report No. 4578 (1970)]. An average 7.68% difference for which most of the discrepancies can be attributed to the background noise at low angles was obtained. The preliminary measurements of breast tissue are also encouraging.
A novel approach to accurate portal dosimetry using CCD‐camera based EPIDs
Authors: Franken E. M. , de Boer J. C. J. , Heijmen B. J. M.
Published: April 2006

A new method for portal dosimetry using CCD camera‐based electronic portal imaging devices (CEPIDs) is demonstrated. Unlike previous approaches, it is not based on a priori assumptions concerning CEPID cross‐talk characteristics. In this method, the nonsymmetrical and position‐dependent cross‐talk is determined by directly imaging a set of cross‐talk kernels generated by small fields (“pencil beams”) exploiting the high signal‐to‐noise ratio of a cooled CCD camera. Signal calibration is achieved by imaging two reference fields. Next, portal dose images (PDIs) can be derived from electronic portal dose images (EPIs), in a fast forward‐calculating iterative deconvolution. To test the accuracy of these EPI‐based PDIs, a comparison is made to PDIs obtained by scanning diode measurements. The method proved accurate to within (1 SD), for on‐axis symmetrical and asymmetrical fields with different field widths and homogeneous phantom thicknesses, off‐axis Alderson thorax fields and a strongly modulated IMRT field. Hence, the proposed method allows for fast, accurate portal dosimetry. In addition, it is demonstrated that the CEPID cross‐talk signal is not only induced by optical photon reflection and scatter within the CEPID structure, but also by high‐energy back‐scattered radiation from CEPID elements (mirror and housing) towards the fluorescent screen.