bluuebunny/crossref_metadata_2025 huggingface dataset:
The Control of Spikelet Meristem Identity by the
branched silkless1
Gene in Maize
Authors: Chuck George , Muszynski Michael , Kellogg Elizabeth , Hake Sarah , Schmidt Robert J.
Published: November 2002

Most of the world's food supply is derived from cereal grains that are borne in a unique structure called the spikelet, the fundamental unit of inflorescence architecture in all grasses.
branched silkless1
(
bd1
) is a maize mutation that alters the identity of the spikelet meristem, causing indeterminate branches to form in place of spikelets. We show that
bd1
encodes a putative ERF transcription factor that is conserved in different grasses and is expressed in a distinct domain of the spikelet meristem. Its expression pattern suggests that signaling pathways regulate meristem identity from lateral domains of the spikelet meristem.
QUINTESSENCE AND COSMIC ACCELERATION
Authors: MAK M. K. , HARKO T.
Published: November 2002

A cosmological model with perfect fluid and self-interacting quintessence field is considered in the framework of the spatially flat Friedmann–Robertson–Walker (FRW) geometry. By assuming that all physical quantities depend on the volume scale factor of the Universe, the general solution of the gravitational field equations can be expressed in an exact parametric form, with the volume taken as the parameter, and with the quintessence field as a free parameter. With an appropriate choice of the scalar field a class of exact parametric solutions is obtained, with an exponential type scalar field potential fixed via the gravitational field equations. The general physical behavior of the model is consistent with the recent cosmological scenario favored by supernova type Ia observations, indicating an accelerated expansion of the Universe.
CELLULAR AUTOMATA AND LATTICE BOLTZMANN TECHNIQUES: AN APPROACH TO MODEL AND SIMULATE COMPLEX SYSTEMS
Authors: CHOPARD BASTIEN , DUPUIS ALEXANDRE , MASSELOT ALEXANDRE , LUTHI PASCAL
Published: November 2002

We discuss the cellular automata approach and its extensions, the lattice Boltzmann and multiparticle methods. The potential of these techniques is demonstrated in the case of modeling complex systems. In particular, we consider applications taken from various fields of physics, such as reaction-diffusion systems, pattern formation phenomena, fluid flows, fracture processes and road traffic models.
Homogenization of Freshwater Faunas
Authors: Rahel Frank J.
Published: November 2002

▪ Abstract  Biotic homogenization is the increased similarity of biotas over time caused by the replacement of native species with nonindigenous species, usually as a result of introductions by humans. Homogenization is the outcome of three interacting processes: introductions of nonnative species, extirpation of native species, and habitat alterations that facilitate these two processes. A central aspect of the homogenization process is the ability of species to overcome natural biogeographic barriers either through intentional transport by humans or through colonization routes created by human activities. Habitat homogenization through reservoir construction contributes to biotic homogenization as local riverine faunas are replaced with cosmopolitan lentic species. The homogenization process has generally increased biodiversity in most freshwater faunas, as the establishment of new species has outpaced the extinction of native species. There are important exceptions, however, where the establishment of nonindigenous species has had devastating impacts on endemic species. The homogenization process appears likely to continue, although it could be slowed through reductions in the rate of invasions and extirpations and by rehabilitating aquatic habitats so as to favor native species.
Reproductive Protein Evolution
Authors: Swanson Willie J. , Vacquier Victor D.
Published: November 2002

▪ Abstract  The evolution of proteins involved in reproduction is only now beginning to be studied. A reoccurring observation is the rapid evolution of the molecules mediating reproductive events following the release of gametes. We review the examples where rapid evolution of reproductive proteins has been documented, covering taxa ranging from diatoms to humans. The selective pressures causing this divergence remain unknown, but several hypotheses are presented. The functional consequences of this rapid divergence could be involved in speciation.
Estimating Divergence Times from Molecular Data on Phylogenetic and Population Genetic Timescales
Authors: Arbogast Brian S. , Edwards Scott V. , Wakeley John , Beerli Peter , Slowinski Joseph B.
Published: November 2002

▪ Abstract  Molecular clocks have profoundly influenced modern views on the timing of important events in evolutionary history. We review recent advances in estimating divergence times from molecular data, emphasizing the continuum between processes at the phylogenetic and population genetic scales. On the phylogenetic scale, we address the complexities of DNA sequence evolution as they relate to estimating divergences, focusing on models of nucleotide substitution and problems associated with among-site and among-lineage rate variation. On the population genetic scale, we review advances in the incorporation of ancestral population processes into the estimation of divergence times between recently separated species. Throughout the review we emphasize new statistical methods and the importance of model testing during the process of divergence time estimation.
Disturbance to Marine Benthic Habitats by Trawling and Dredging: Implications for Marine Biodiversity
Authors: Thrush Simon F. , Dayton Paul K.
Published: November 2002

▪ Abstract  The direct effects of marine habitat disturbance by commercial fishing have been well documented. However, the potential ramifications to the ecological function of seafloor communities and ecosystems have yet to be considered. Soft-sediment organisms create much of their habitat's structure and also have crucial roles in many population, community, and ecosystem processes. Many of these roles are filled by species that are sensitive to habitat disturbance. Functional extinction refers to the situation in which species become so rare that they do not fulfill the ecosystem roles that have evolved in the system. This loss to the ecosystem occurs when there are restrictions in the size, density, and distribution of organisms that threaten the biodiversity, resilience, or provision of ecosystem services. Once the functionally important components of an ecosystem are missing, it is extremely difficult to identify and understand ecological thresholds. The extent and intensity of human disturbance to oceanic ecosystems is a significant threat to both structural and functional biodiversity and in many cases this has virtually eliminated natural systems that might serve as baselines to evaluate these impacts.
Nutrient Cycling by Animals in Freshwater Ecosystems
Authors: Vanni Michael J.
Published: November 2002

▪ Abstract  Animals are important in nutrient cycling in freshwater ecosystems. Via excretory processes, animals can supply nutrients (nitrogen and phosphorus) at rates comparable to major nutrient sources, and nutrient cycling by animals can support a substantial proportion of the nutrient demands of primary producers. In addition, animals may exert strong impacts on the species composition of primary producers via effects on nutrient supply rates and ratios. Animals can either recycle nutrients within a habitat, or translocate nutrients across habitats or ecosystems. Nutrient translocation by relatively large animals may be particularly important for stimulating new primary production and for increasing nutrient standing stocks in recipient habitats. Animals also have numerous indirect effects on nutrient fluxes via effects on their prey or by modification of the physical environment. Future studies must quantify how the importance of animal-mediated nutrient cycling varies among taxa and along environmental gradients such as ecosystem size and productivity.
The Early Radiations of Cetacea (Mammalia): Evolutionary Pattern and Developmental Correlations
Authors: Thewissen J. G. M. , Williams E. M.
Published: November 2002

▪ Abstract  The origin and early evolution of Cetacea (whales, dolphins, and porpoises) is one of the best examples of macroevolution as documented by fossils. Early whales are divided into six families that differ greatly in their habitats, which varied from land to freshwater, coastal waters, and fully marine. Early cetaceans lived in the Eocene (55–37 million years ago), and they show an enormous morphological diversity. Toward the end of the Eocene the modern cetacean body plan originated, and this body plan remained more or less the same in the subsequent evolution. It is possible that some aspects of this body plan are rooted in constraints that are dictated by cetacean embryol ogic development and controlled by genes that affect many organ systems at once. It may be possible to use a study of patterns of correlations among morphological traits to test hypotheses of developmental links among organ systems.
Mast Seeding in Perennial Plants: Why, How, Where?
Authors: Kelly Dave , Sork Victoria L.
Published: November 2002

▪ Abstract  For many years biologists have debated whether mast seeding (the synchronous intermittent production of large seed crops in perennial plants) results from weather conditions or is an evolved plant reproductive strategy. In this review, we analyze the evidence for the underlying causes of masting. In the absence of selection for higher or lower variability, plants will vary in tandem with the environment (resource matching). Two selective factors often favor the evolution of masting: increased pollination efficiency in wind-pollinated species, and satiation of seed predators. Other factors select against masting, including animal pollination and frugivore dispersal. A survey of 570 masting datasets shows that wind-pollinated species had higher seed production coefficients of variation (CVs) than biotically pollinated ones. Frugivore-dispersed species had low CVs whereas predator-dispersed plants had high CVs, consistent with gaining benefits from predator satiation rather than dispersal. The global pattern of masting shows highest seed crop variability at mid latitudes and in the Southern Hemisphere, which are similar to the patterns in variability of rainfall. We conclude that masting is often an adaptive reproductive trait overlaid on the direct influence of weather.
Industrial Ecosystem Development at the Metropolitan Level
Authors: Kincaid Judy , Overcash Michael
Published: November 2002

This article presents the result of a two‐year project funded by the U.S. Environmental Protection Agency to identify potential by‐products partnerships between industries in a six‐county metropolitan area in North Carolina, U.S.A. The project gathered data from 182 industries and institutions in the region regarding (1) by‐products that might be usable by other, nearby firms, and (2) the inputs they used that might be furnished from another facility's by‐products. These data, which were also linked to geographic information system maps, were used to identify potential regional partnerships for the reuse of materials, water, and energy. Of the 182 participating facilities, probable or possible partnerships were found for 48% during the limited project period. This project demonstrated the value of a local facilitator and the value of specific techniques for identifying and promoting potential by‐products partnerships.
A YORUBA TALE OF MARRIAGE, MAGIC, MISOGYNY AND LOVE
Authors: Schiltz Marc
Published: November 2002

In this paper I approach the efflorescence of witchcraft-sorcery concerns in post-colonial Africa through the personal experiences of Délé, a Nigerian friend and research assistant. At one level, the witchcraft-sorcery incidents offer illustrations of the rural-urban conflict situations that the Comaroffs and other Africanists have written about in recent years. Yet at another level I read Délé's texts for what they are, the chronicles of a real-life drama in which he plays the tragic hero's role. As a storyteller, Délé recalls events in which the actors' virtues, vices, and emotions constantly mirror our own experiences of what people can turn out to be as they progress through life. In Délé's case I perceive such a progression in his shift from a virtue-centred Catholic upbringing in rural Ìséyìn to a more prayer/power-centred aládúrà-Pentecostalism in Lagos, when recently the spectres of mágùn sorcery and witchcraft began to close in on his marriage, livelihood and health. Délé's tale compels me, as a friend and correspondent with a different view of the world, to reconsider the morally universalising aspects of what it entails to be human. I attempt this from the triple perspective of Délé's ancestral roots in traditional Yoruba religion, his attraction towards aládúrà-Pentecostalism in a failed nation-state, and his nostalgia for the missionary Catholicism through which our friendship first developed.
Comparison of asthma prevalence in the ISAAC and the ECRHS. ISAAC Steering Committee and the European Community Respiratory Health Survey. International Study of Asthma and Allergies in Childhood
Authors: Pearce N , Sunyer J , Cheng S , Chinn S , Bjorksten B , Burr M , Keil U , Anderson HR , Burney P
Published: November 2002

International and regional prevalence comparisons are required to test and generate hypotheses regarding the causes of increasing asthma prevalence in various age groups worldwide. The International Study of Asthma and Allergies in Childhood (ISAAC) is the first such study in children and the European Community Respiratory Health Survey (ECRHS) is the first such study in adults. Therefore, a comparison of the findings of these two surveys was conducted, for the 17 countries in which both surveys were undertaken. There was a strong correlation between the ISAAC and ECRHS prevalence data, with 64% of the variation at the country level, and 74% of the variation at the centre level, in the prevalence of "wheeze in the last 12 months" in the ECRHS phase I data being explained by the variation in the ISAAC phase I data. There was also generally good agreement in the international patterns observed in the two surveys for self-reported asthma (74% of country level and 36% of centre level variation explained), self-reported asthma before age 14 yrs (64 and 26%), hay fever (61 and 73%) and eczema (41 and 50%). Thus although there were differences in the absolute levels of prevalence observed in the two surveys, there is good overall agreement between the International Study of Asthma and Allergies in Childhood and European Community Respiratory Health Survey study findings with regard to international prevalence patterns. These findings, therefore, add support to the validity of the two studies, which provide a new picture of global patterns of asthma prevalence from child- to adulthood, and identify some of the key phenomena which future research must address.
The performance of coated tungsten carbide drills when machining carbon fibre-reinforced epoxy composite materials
Authors: Murphy C , Byrne G , Gilchrist M D
Published: November 2002

This paper is concerned with the effect of coatings on the performance of tungsten carbide (WC) drills in the drilling of carbon fibre-reinforced epoxy. Although composites are becoming increasing popular, there is a deficit in the existing knowledge of drilling composites, and in particular carbon fibre-reinforced epoxy resins. Two coated drills, namely titanium nitride (TiN)-coated and diamond-like carbon (DLC)-coated drills, were investigated and for comparative purposes an uncoated drill. The testing involved drilling a series of consecutive holes. During these tests the thrust forces and torques were monitored, following which the tool was inspected for flank wear and the workpiece inspected for damage in terms of hole tolerance, delamination and spalling.

For all three tool types (uncoated, TiN coated and DLC coated), only a small number of drilled holes were found to satisfy an H8 tolerance criterion. An investigation of the hole diameter through the thickness of the composite revealed that it was the outermost plies that caused the hole to fail this tolerance criterion. The effect of tool wear caused the measured thrust forces and torques to increase over the life of the tool. While the degree of measured tool wear was small by comparison with that associated with drilling conventional materials, the effects were found to result in unacceptable damage to the composite. The damage was apparent in the form of spalling, chip-out and matrix cracking. The coatings were not found to reduce either tool wear or damage to the composite.
Mathematical modelling of elliptic helicoid screw transmission systems
Authors: Wu D-S , Lai H-Y , Chen C-K
Published: November 2002

This paper presents a systematic modelling procedure for producing high precision elliptic helicoid screw transmission systems. The modelling procedure includes both the derivation of the geometric model of the helicoid screw and the construction of profile models for the revolving conjugate elements. The profile models are derived by using several techniques including the theories of differential geometry, coordinate transformation and meshing principles. Since the meshing model of the screw transmission system is constructed systematically by rigorous differential geometry and meshing theories, the lead screw model thus developed can lead to good transmission quality and high system performance. In order to verify the effectiveness of the proposed models and the modelling procedure, the performance of the proposed system is evaluated numerically by several different indices including the transmissivity index, the manipulability index and the lubrication angle. The numerical results obtained by using the proposed modelling procedure are also verified by experimental data taken directly from a sample product produced by the NC machine using the proposed theory. A comparative study is conducted. The results indicate that the proposed elliptic helicoid screw model proposed in this paper is accurate and efficient. The proposed theory and performance indices can be used to design for various screw systems of high performance.
Comparison of intra- and interpulse modulation in laser percussion drilling
Authors: Low D K Y , Li L
Published: November 2002

The effects of intra- and interpulse temporal modulation (shaping) during laser percussion drilling are investigated in terms of hole geometry characteristics and control. While intrapulse shaping involves temporally shaping within an individual laser pulse and repeatedly using the shaped pulse throughout the pulse train, interpulse shaping is carried out by temporal pulse shaping the overall delivery pattern of a pulse train required to percussion drill a hole. A fibre optic delivered neodymium-doped yttrium aluminium garnet (Nd:YAG) laser was employed to drill through-holes in stainless steel 304 plates with various combinations of intra- and interpulse shapes. The fundamental effects of intra- and interpulse shaping are also compared with percussion drilling using unshaped rectangular intrapulses and the normal delivery pattern interpulse shape. The work has shown that interpulse shaping is effective in reducing the hole taper and improving the overall hole wall parallelism during laser percussion drilling. This was chiefly attributed to the optimized laser pulse distribution as the beam propagates into the hole.
Gross dehiscence of the bone covering the facial nerve in the light of otological surgery
Authors: Bayazit Yildirim A. , Ozer Enver , Kanlikama Muzaffer
Published: November 2002

Understanding the relationship between the anatomy of the fallopian canal and a variety of ear diseases is necessary. In this study, our purpose was to identify the incidence of facial nerve dehiscence in patients undergoing surgery for a variety of chronic ear diseases.

The operative records of 219 patients were reviewed retrospectively for dehiscence of the facial canal. The diagnoses were cholesteatoma (n = 49), tympanosclerosis (n = 51), adhesive otitis media (n = 38), and chronic otitis media (n = 81). Only 17 of 219 who underwent tympanoplasty without mastoidectomy were excluded from the calculations.

Dehiscence of the facial canal was encountered in 18 (8.9 per cent) of 202 patients. The dehiscence rate was highest with cholesteatoma, followed by adhesive otis media, chronic otis media and tympanosclerosis (p<0.01). The canal dehiscence was mainly seen in the tympanic segment and second genu, and was rare in the mastoid segment. Labyrinthine fistula was the most common pathology that coexisted with the dehiscence. It was encountered in two (11.1 per cent) of 18 patients. In conclusion, the likelihood of dehiscent bone covering the tympanic segment of the fallopian canal is significantly higher in cholesteatoma than the other chronic ear diseases. The surgeon can feel somewhat more confident while performing surgery for tympanosclerosis as far as the dehiscence in the fallopian canal is concerned.
How much variation in clinical activity is there between general practitioners? A multi-level analysis of decision-making in primary care
Authors: Davis Peter , Gribben Barry , Lay-Yee Roy , Scott Alastair
Published: November 2002

Objectives: There is considerable policy interest in medical practice variation (MPV). Although the extent of MPV has been quantified for secondary care, this has not been investigated adequately in general practice. Technical obstacles to such analyses have been presented by the reliance on ecological small area variation (SAV) data, the binary nature of many clinical outcomes in primary care and by diagnostic variability. The study seeks to quantify the extent of variation in clinical activity between general practitioners by addressing these problems.

Methods: A survey of nearly 10 000 encounters drawn from a representative sample of general practitioners in the Waikato region of New Zealand was carried out in the period 1991-1992. Participating doctors recorded all details of clinical activity for a sample of encounters. Measures used in this analysis are the issuing of a prescription, the ordering of a laboratory test or radiology examination, and the recommendation of a future follow-up office visit at a specified date. An innovative statistical technique is adopted to assess the allocation of variance for binary outcomes within a multi-level analysis of decision-making.

Results: As expected, there was considerable variability between doctors in levels of prescribing, ordering of investigations and requests for follow up. These differences persisted after controlling for case-mix and patient and practitioner attributes. However, analysis of the components of variance suggested that less than 10% of remaining variability occurred at the practitioner level for any of the measures of clinical activity. Further analysis of a single diagnostic group - upper respiratory tract infection - marginally increased the practitioner contribution.

Conclusions: The amount of variability in clinical activity that can definitively be linked to the practitioner in primary care is similar to that recorded in studies of the secondary sector. With primary care doctors increasingly being grouped into larger professional organisations, we can expect application of multi-level techniques to the analysis of clinical activity in primary care at different levels of organisational complexity.
Detection and correction of endotracheal‐tube position in premature neonates
Authors: Lange Malte , Jonat Susanne , Nikischin Werner
Published: November 2002

Due to the short airways in premature children, an accurate position of the endotracheal tube (ETT) is crucial for adequate mechanical ventilation. Verification of ETT‐position is done in chest radiographs. However, ETT‐position varies substantially with head movement. When the head is flexed, the tube might appear too deeply inserted, and inadvertent extubation may occur in cases of retraction of ETT after radiography. Extension of the cervical spine will suggest an inappropriately high ETT‐position, so that intended corrections can lead to main‐stem intubation. Radiographic visible skeletal structures could serve as reference points to allow the detection of head declination and imperfect positioning of ETT. Ratios of anatomical landmarks were used to estimate head position.

In this study, 111 radiographs of 24 preterm neonates with a gestational age of 24–29 weeks and weights of 500–1,000 g were analyzed. A mathematical algorithm for the detection and correction of ETT‐positions, based on common chest radiographs, was developed. In 108 cases (97.3%), ETT‐distance from the midtracheal level was less than 2 mm after use of the proposed correction.

Thus, the suggested correction equation for head position enables verification of the actual ETT‐position without requiring a defined placement of the head during radiography. Moreover, it can be helpful for estimating the depth of ETT‐insertion in conditions when radiography is not available. Pediatr Pulmonol. 2002; 34:455–461. © 2002 Wiley‐Liss, Inc.
Ventilatory control in newborn mice prenatally exposed to cocaine
Authors: Autret Fanny , Dauger Stéphane , Renolleau Sylvain , Eng Guy Vardon , Kosofsky Barry E. , Gressens Pierre , Gaultier Claude , Gallego Jorge
Published: November 2002

Infants born to mothers who used cocaine during pregnancy are at increased risk for neonatal death and respiratory impairments. Confounding factors such as multiple substance abuse make it difficult to isolate the effects of cocaine. We used a murine model to test the hypothesis that prenatal cocaine exposure may impair ventilatory responses to chemical stimuli in newborns. Seventy‐two pregnant mice were randomly assigned to three groups: cocaine (COC), saline (SAL), and untreated (UNT). COC and SAL mice received subcutaneous injections of either 20 mg/kg of cocaine or a saline solution twice a day from gestational days 8–17. Ventilation (V′E) and tidal volume (VT), both divided by body weight, and breath duration (TTOT) were measured using whole‐body plethysmography in freely moving COC (n = 47), SAL (n = 123), and UNT (n = 93) pups on postnatal day 2.

The comparison between SAL and UNT pups showed significant differences in baseline breathing and in V′E responses to hypoxia, suggesting that maternal stress caused by injections affected the development of ventilatory control in pups. Baseline TTOT was significantly longer in COC than in SAL pups. V′E responses to hypoxia were significantly smaller in COC than in SAL pups (+27 ± 35% vs. +38 ± 25%), but V′E responses to hypercapnia were similar (29 ± 15% vs. 25 ± 23%).

Thus, breathing control was impaired by prenatal cocaine exposure, possibly because of abnormal development of neurotransmitter systems, such as the dopamine and serotonin systems. Pediatr Pulmonol. 2002; 34:434–441. © 2002 Wiley‐Liss, Inc.
Dehydroepiandrosterone (DHEA) such as 17β‐estradiol prevents MPTP‐induced dopamine depletion in mice
Authors: D'Astous Myreille , Morissette Marc , Tanguay Bastien , Callier Sophie , Di Paolo Thérèse
Published: November 2002

Previous work from our laboratory has shown prevention of 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP)‐induced striatal dopamine (DA) depletion in mice by 17β‐estradiol, progesterone, and raloxifene. Dehydroepiandrosterone (DHEA), a neurosteroid, was shown to have neuroprotective activities in various paradigms of neuronal death but its effect in vivo in mice on MPTP toxicity has not been reported. We investigated the effects of 17β‐estradiol (2 μg/day) and DHEA (3 mg/day) for 5 days before and after an acute treatment of four MPTP (10 mg/kg) injections in male C57Bl/6 mice. Striatal DA concentrations and its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were measured by HPLC. MPTP mice that received 17β‐estradiol or DHEA had striatal DA, DOPAC, and HVA concentrations comparable to intact animals and higher than striatal DA, DOPAC, and HVA levels in saline‐MPTP‐treated mice. MPTP treatment led to an increase of striatal DA turnover (assessed with the HVA/DA ratio); DHEA and 17β‐estradiol prevented this increase. 17β‐Estradiol did not affect striatal DA and metabolites concentrations in intact mice in this paradigm. Furthermore, in the substantia nigra DHEA and 17β‐estradiol prevented the MPTP‐induced dopamine transporter and tyrosine hydroxylase mRNA decreases measured by in situ hybridization. Therefore, DHEA such as 17β‐estradiol is active in preventing the catecholamine‐depleting effect of MPTP and our results suggest that this involves neuroprotection of DA neurons. Synapse 47:10–14, 2003. © 2002 Wiley‐Liss, Inc.
Interleukin‐1β abrogates long‐term depression of hippocampal CA1 synaptic transmission
Authors: Ikegaya Yuji , Delcroix Isabelle , Iwakura Yoichiro , Matsuki Norio , Nishiyama Nobuyoshi
Published: November 2002

Although interleukin‐1β (IL‐1β) is well known to modulate synaptic transmission and plasticity of the hippocampus, no study has yet evaluated how this cytokine affects long‐term depression (LTD), one of the major forms of hippocampal synaptic plasticity. Here we report that at Schaffer collateral‐CA1 synapses, bath application of IL‐1β induces a long‐lasting decrease in synaptic strength in intact slices, but not in disinhibited slices in the presence of bicuculline, a γ‐aminobutyric acid receptor antagonist. The IL‐1β‐induced synaptic depression efficiently foreclosed the subsequent induction of LTD in response to a 1‐Hz tetanus and, conversely, it was also prevented by preexisting LTD. These results suggest that IL‐1β‐induced, persistent depression of synaptic efficacy is required for GABAergic activation and shares, at least in part, a common cellular mechanism for LTD. Synapse 47:54–57, 2003. © 2002 Wiley‐Liss, Inc.
‘Vials, Ampoules and a Bucketful of Syringes’: The Experience of the Self-Administration of Hormonal Drugs in IVF
Authors: Throsby Karen
Published: November 2002

During the process of in vitro fertilization (IVF), hormonal drugs are used to stimulate the woman's ovaries to produce multiple eggs. The injecting of the drugs is often performed by the women themselves outside of the clinical context, constituting a gendered burden of work that is rendered invisible by the dominant representations of treatment as undergone by couples and performed by doctors. Based on a series of interviews with women and couples who have undergone IVF unsuccessfully and who have ended treatment at least two years previously, this paper focuses on two aspects of the self-injection of hormonal drugs that emerged from the participants accounts: firstly, the gendered ways in which the drug regimen was experienced as compromising privacy and secondly, the strategic use of images of both illicit and medical drug use in the accounts. The paper argues that in spite of the dominant representation of IVF as a couples’ technology, the IVF process is profoundly gendered, both in terms of bodily intervention and in the distribution of labour in the implementation of treatment; that the invisibility of the drug regimens from dominant representations of IVF can leave those undergoing treatment unprepared for some of the problems that the self-administration of the drugs can raise, particularly in terms of maintaining privacy; and finally, that images of the drug injection are mobilized strategically in the accounts to locate themselves within normative social reproductive standards. This highlights the extent to which the enduring ideological construction of proper womanhood as defined by motherhood continues to pose a dilemma for those who are involuntarily childless.
Optical constants of methyl-pentaphenylsilole by spectroscopic ellipsometry
Authors: Peng H. J. , Liu Z. T. , Chen H. Y , Ho Y. L. , Tang B. Z. , Wong M. , Huang H. C. , Kwok H. S.
Published: November 2002

The optical properties of 1-methyl-1,2,3,4,5-pentaphenylsilole thin films grown on silicon substrate were investigated using spectroscopic ellipsometry (SE). Accurate refractive index n and extinction coefficient k, in the wavelength range of 250 to 800 nm, were determined. Sellmeier equations, amorphous semiconductor model, and a three-oscillator classical Lorentz model were used to fit the data in different spectral ranges. A band gap of 2.78 eV and uv absorption peaks at 368 and 263 nm were derived from the SE spectrum. Additionally, the absorption spectra near the major band edges show optical properties similar to that of an amorphous semiconductor.
Atomic scale morphology of self-organized periodic elastic domains in epitaxial ferromagnetic MnAs films
Authors: Kästner M. , Herrmann C. , Däweritz L. , Ploog K. H.
Published: November 2002

The surface of epitaxial MnAs layers grown on GaAs(001) substrates by molecular beam epitaxy is studied by atomic force microscopy and scanning tunneling microscopy (STM). A periodic array of alternating ridges and grooves is observed. The periodicity ranges from 200 to 900 nm and increases with increasing layer thickness. The terrace-step morphology and the surface reconstruction on the ridges and in the grooves are imaged by STM. It is found that both are independent from the ridge-groove structure, supporting the idea that the formation of the ridge-groove structure is due to elastic distortion of the film during cooling after growth.
Dynamic charge-carrier-mobility-mediated holography in thin layers of photoconducting polymers
Authors: Bartkiewicz S. , Miniewicz A. , Sahraoui B. , Kajzar F.
Published: November 2002

The dynamic holography technique is proposed for the measurement of the charge-carrier-mobility in thin layers of a photoconducting polymer, used in optically addressed liquid-crystal spatial light modulators. The photorefractive properties of these modulators are studied under short-pulse (20 ps, 532 nm) laser illumination conditions and the charge mobility in the photoconducting polymer (μh=10−7 cm2/V s) is obtained from the temporal evolution of intensity of the first-order diffracted beam. A mechanism responsible for the grating formation is proposed and discussed.
Effective ionic charge polarization using typical supporting electrolyte and charge injection phenomena in molecularly doped polymer light-emitting diodes
Authors: Itoh Eiji , Yamashita Takanori , Miyairi Keiichi
Published: November 2002

An effective method of enhancing charge injection and electroluminescence efficiency of polymer-based light-emitting diodes is introduced. Spin-coated films of poly (N-vinylcarbazole) blended with electron-transport material (Bu–PBD), laser dye (Coumarin6), and the typical supporting electrolyte [tetraethylammonium perchlorate (TEAP)] were examined and it was found that the injection current and luminance of the light emitting diodes doped with TEAP were enhanced dramatically after heat treatment at 80 °C and appropriate biasing in an external electric field of 1.5×108 V/m at this temperature. A charge injection model based on Fowler–Nordheim tunneling is proposed, taking into account electric field distortion due to the accumulation of ionic space charges at the electrode/film interface. The relaxation time of ionic polarization is found to be related to the cation size of the electrolyte.
Transmission electron microscopy study of the InP/InGaAs and InGaAs/InP heterointerfaces grown by metalorganic vapor-phase epitaxy
Authors: Decobert Jean , Patriarche Gilles
Published: November 2002

InP/InGaAs and InGaAs/InP interfaces in heterostructures grown by metalorganic vapor-phase epitaxy (MOVPE) have been studied by transmission electron microscopy (TEM). Cross-sectional TEM 002 dark field images of the direct (InP–InGaAs) and inverted (InGaAs–InP) interfaces revealed a great difference in abruptness. Whereas the direct interface is always well defined and flat, the inverted one is compositionally graded and shows surface undulations. InP–InGaAs heterostructures were studied for different layer thicknesses and phosphine flow rates. The results indicate that this effect originates more from the substitution of arsenic by phosphorus atoms in subsurface InGaAs monolayers rather than from As carryover to the InP layer. The strong As–P exchange observed over several InGaAs monolayers is related to the large difference in chemical bond strength between Ga–As and Ga–P. This is supported by comparison with InP/InAlAs/InP and InP/In1−xGaxAsyP1−y/InP (0.1<x<0.4) heterostructures. The inverted InAlAs/InP interface is much more abrupt than the InGaAs/InP one and does not show any surface undulations. Furthermore, the In1−xGaxAsyP1−y/InP interface surface undulations increase with x composition. These results, valid for our experimental configuration, indicate that MOVPE grown InGaAs/InP interfaces can be improved by using very low hydride flow during the switching sequence.
The 212.8-nm photodissociation of formic acid: Degenerate four-wave mixing spectroscopy of the nascent OH(X 2Πi) radicals
Authors: Lee Keon Woo , Lee Kyoung-Seok , Jung Kyung-Hoon , Volpp Hans-Robert
Published: November 2002

The 212.8-nm photodissociation dynamics of formic acid was investigated utilizing degenerate four-wave mixing spectroscopy. The background-free rotational spectrum of the nascent OH radicals was obtained, and a cold rotational energy distribution peaking at N″=3 was extracted from the DFWM spectrum. The distribution was well approximated by a Boltzmann distribution with a rotational temperature of Trot∼716 K, which corresponds to an average rotational energy of ∼498 cm−1. The observation of a nonstatistical spin–orbit state distribution, with a preference for the low-energy F1 manifold, implies the absence of any interactions with nearby triplet states during dissociation. Preferential population of the Λ-doublet was observed, indicating that the ν7 H–O–C bending vibration in HCOOH(Ã) and the recoil impulse are the principal sources of the OH rotation.
Formation of carbon nanotubes by plasma enhanced chemical vapor deposition: Role of nitrogen and catalyst layer thickness
Authors: Valentini L. , Kenny J. M. , Lozzi L. , Santucci S.
Published: November 2002

The growth behavior of carbon nanotubes (CNTs), produced by radio frequency plasma enhanced chemical vapor deposition, is studied here as a function of the CH4/N2 ratio and Ni catalyst layer thickness. Scanning electron microscopy shows that by employing a suitable deposition (methane) to etching (nitrogen) gas ratio, it is possible to obtain the growth of nanotubes with a limited presence of amorphous carbon on the substrate surface. In particular a progressive transition from random to aligned CNTs is observed when nitrogen is added to the plasma atmosphere. The electronic structure was then investigated by C 1s and valence band photoemission spectroscopy. The results show a shift of the overall spectral to a higher-binding-energy side and a larger density of the states at the Fermi level indicating the formation of metallic aligned tubes with increasing nitrogen fraction in the plasma atmosphere. The electronic structure indicates the insertion of odd-member rings in the graphene network leading to an improvement of the mechanical properties. The thickness of the Ni layer has a strong influence on the CNTs growth showing maximum value for nanotube formation at 20 nm.
Exciton–phonon interaction in molecular crystals with noncorrelated couplings between excited states and lattice vibrations
Authors: Tovstenko V. I. , Sekirin I. V.
Published: November 2002

On the example of a simple model of molecular crystal with cubic symmetry and with only one molecule per elementary cell, we consider the system of interacting Frenkel singlet excitons and crystal lattice phonons. Coupling of excited states is included in the terms of the Hamiltonian which are diagonal and off-diagonal with respect to the exciton operators. The linear constant of interaction between the phonons and the quantum-mechanical current of transition of a crystal from its ground to its excited state is taken into account as well. It is shown that the joint consideration of several exciton–phonon interaction constants leads to renormalization of the exciton band and of the dipole moment of transition. Green’s function and its mass operator are obtained. The proposed calculational method and the obtained formulas can be useful for the study of energy spectrum and optical properties of specific crystalline systems, when considering the problems of transfer of excitation energy in crystals, as well as when studying the other phenomena in which the exciton–phonon interaction plays an important role.
Optical constants of In0.53Ga0.47As/InP: Experiment and modeling
Authors: Muñoz Martı́n , Holden Todd M. , Pollak Fred H. , Kahn Mathias , Ritter Dan , Kronik Leeor , Cohen Guy M.
Published: November 2002

The optical constants ε(E)=ε1(E)+iε2(E) of unintentionally doped In0.53Ga0.47As lattice matched to InP have been measured at 300 K using spectral ellipsometry in the range of 0.4 to 5.1 eV. The ε(E) spectra displayed distinct structures associated with critical points at E0 (direct gap), spin-orbit split E0+Δ0 component, spin-orbit split E1, E1+Δ1, E0′ feature, as well as E2. The experimental data over the entire measured spectral range (after oxide removal) has been fit using the Holden model dielectric function [Holden et al., Phys. Rev. B 56, 4037 (1997)], plus a Kramers–Kronig consistent correction, described in this work, that improves the fitting at low energies. This extended model is based on the electronic energy-band structure near these critical points plus excitonic and band-to-band Coulomb-enhancement effects at E0, E0+Δ0, and the E1, E1+Δ1, doublet. In addition to evaluating the energies of these various band-to-band critical points, information about the binding energy (R1) of the two-dimensional exciton related to the E1, E1+Δ1 critical points was obtained. The value of R1 was in good agreement with effective mass/k⋅p theory. The ability to evaluate R1 has important ramifications for first-principles band-structure calculations that include exciton effects at E0, E1, and E2 [M. Rohlfing and S. G. Louie, Phys. Rev. Lett. 81, 2312 (1998); S. Albrecht et al., Phys. Rev. Lett. 80, 4510 (1998)].
Blue upconversion enhancement by a factor of 200 in Tm3+-doped tellurite glass by codoping with Nd3+ ions
Authors: Rakov N. , Maciel G. S. , Sundheimer M. L. , de S. Menezes L. , Gomes A. S. L. , Messaddeq Y. , Cassanjes F. C. , Poirier G. , Ribeiro S. J. L.
Published: November 2002

We investigated near-infrared-to-blue upconversion from thulium (Tm3+) doped in tellurite glasses upon continuous wave excitation near 800 nm. We observed an enhancement of over two orders of magnitude of the upconverted emission at ∼480 nm when neodymium (Nd3+) ions were codoped with Tm3+ ions. For comparison, using a Tm3+:Nd3+ codoped fluorozirconate glass as a reference material we observed a 40-fold enhancement of the blue emission. Analysis of the blue emission for samples with different doping levels of Nd3+ ions showed that energy transfer between Nd3+ and Tm3+ is the mechanism responsible for the enhancement in upconversion.
Terahertz optically pumped Si:Sb laser
Authors: Pavlov S. G. , Hübers H.-W. , Riemann H. , Zhukavin R. Kh. , Orlova E. E. , Shastin V. N.
Published: November 2002

Far-infrared stimulated emission from optically pumped neutral Sb donors in silicon has been obtained. Lasing with a wavelength of 58.2 μm from the intracenter 2p0→1s(T2:Γ8) transition has been realized under CO2 laser pumping at liquid helium temperature. The population inversion mechanism is based on the relatively long-living excited state, 2p0, leading to an accumulation of the photoexcited electrons.
Controlling the spin of metal atoms adsorbed on oxide surfaces: Ni on regular and defective sites of the MgO(001) surface
Authors: Lopez N. , Paniagua J. C. , Illas F.
Published: November 2002

We have analyzed the relative energy of nonmagnetic and magnetic low-lying electronic states of Ni atoms adsorbed on regular and defective sites of the MgO(001) surface. To this end cluster and periodic surface models are used within density functional theory. For Ni atoms adsorbed on oxygen vacancies at low coverage, the interaction energy between the metal and the support is much larger than on regular sites. Strong bonding results in a diamagnetic adsorbed species and the energy required to reach the high-spin state increases. Moreover, a correlation appears between the low-spin to high-spin energy difference and the interaction energy hypothesizing that it is possible to prepare the surface to tune the high-spin to low-spin energy difference. Magnetic properties of adsorbed thin films obtained upon increasing coverage are more difficult to interpret. This is because the metallic bond is readily formed and dominates over the effect of the atoms directly bound to the vacancy.
Synchrotron x-ray scattering study of lattice relaxation in InN epitaxial layers on sapphire(0001) during dc sputter growth
Authors: Lee Ik Jae , Kim Jin Woo , Hwang Yoon-Hwae , Kim Hyung-Kook
Published: November 2002

We present the results of a high-resolution synchrotron x-ray scattering study of the lattice relaxation in an InN (0001) epitaxial layer grown on sapphire (0001) by a dc faced magnetron sputtering deposition method. X-ray powder diffraction, rocking curve, x-ray reflectivity, and atomic force microscopy surface morphology studies consistently suggest that films thinner than ∼170 Å should be highly strained, and be grown as two-dimensional epitaxial layers, in spite of the large mismatch of ∼29%. We deduced the condition for extended domain matching. The strain was relieved as the film thickness increased, while columnar seeds started to nucleate on parts of the film.
Phase-sensitive near-field imaging of metal nanoparticles
Authors: Prikulis J. , Xu H. , Gunnarsson L. , Käll M. , Olin H.
Published: November 2002

We report on the near-field imaging of silver nanoparticles using an aperture-type near-field microscope operated in illumination mode. The nanoparticles are imaged as interference patterns, due to far-field superposition of the optical fields emitted from the tip and elastically scattered from localized surface plasmons (SP). Aperture-type probe can thus be used to obtain information on the phase shift associated with localized SP coupling at the illumination wavelength.
Correlation between the type of threading dislocations and photoluminescence characteristics at different doping concentrations of Si in GaN films
Authors: Kim Chinkyo , Kim Sungwoo , Choi Yoonho , Leem Shi-Jong
Published: November 2002

At various doping concentrations of Si in GaN films, the correlation between the type of dislocations and photoluminescence (PL) characteristics was investigated. A different broadening behavior of symmetric and asymmetric Bragg peaks as a function of carrier concentration provided qualitative evidence that the type of threading dislocations generated in GaN layers was strongly dependent on the doping levels of Si. PL spectra in conjunction with x-ray rocking curve measurements suggested that the yellow luminescence associated with deep levels was more strongly related with edge dislocations than screw or mixed ones.