bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling rare gene variation to gain insight into the oldest biomarker in autism: construction of the serotonin transporter Gly56Ala knock-in mouse
Authors: Veenstra-VanderWeele Jeremy , Jessen Tammy N. , Thompson Brent J. , Carter Michelle , Prasad Harish C. , Steiner Jennifer A. , Sutcliffe James. S. , Blakely Randy D.
Published: June 2009

Alterations in peripheral and central indices of serotonin (5-hydroxytryptamine, 5-HT) production, storage and signaling have long been associated with autism. The 5-HT transporter gene (HTT, SERT, SLC6A4) has received considerable attention as a potential risk locus for autism-spectrum disorders, as well as disorders with overlapping symptoms, including obsessive-compulsive disorder (OCD). Here, we review our efforts to characterize rare, nonsynonymous polymorphisms in SERT derived from multiplex pedigrees carrying diagnoses of autism and OCD and present the initial stages of our effort to model one of these variants, Gly56Ala, in vivo. We generated a targeting vector to produce the Gly56Ala substitution in the Slc6a4 locus by homologous recombination. Following removal of a neomycin resistance selection cassette, animals exhibiting germline transmission of the Ala56 variant were bred to establish a breeding colony on a 129S6 background, suitable for initial evaluation of biochemical, physiological and behavioral alterations relative to SERT Gly56 (wildtype) animals. SERT Ala56 mice were achieved and exhibit a normal pattern of transmission. The initial growth and gross morphology of these animals is comparable to wildtype littermate controls. The SERT Ala56 variant can be propagated in 129S6 mice without apparent disruption of fertility and growth. We discuss both the opportunities and challenges that await the physiological/behavioral analysis of Gly56Ala transgenic mice, with particular reference to modeling autism-associated traits.
Chemical and Sensory Characteristics of Products Fried in High‐Oleic, Low‐Linolenic Rapeseed Oil
Authors: Matthäus Bertrand , Haase Norbert U. , Unbehend Günter
Published: June 2009

The effects of frying Berlin doughnuts and potato crisps in high‐oleic, low‐linolenic (HOLL) rapeseed oil were compared to other commonly used oils (i.e., palm olein, high‐oleic sunflower oil, or partially hydrogenated oils). The chemical parameters characterizing the oxidative state of the products fried in HOLL were comparable to products being fried in other commonly used oils. The sensory characteristics of potato crisps fried in HOLL rapeseed oil were satisfactory and comparable to products fried in the other oils. Potato crisps were stable under nitrogen atmosphere for 20 weeks as measured by sensory quality scores. However, a storage time of 16 weeks was achieved for products stored under normal atmosphere. The suitability of HOLL rapeseed oil to improve the storage stability of Berlin doughnuts was limited. The sensory quality decreased during storage due to the development of abnormal taste and smell. Changes in the sensory quality were comparable to the results of the partially hydrogenated oils but worse for products fried in palm olein. Nevertheless, HOLL was a good alternative to partially hydrogenated oils as a frying medium.
MAXIMAL SUBSETS OF PAIRWISE NONCOMMUTING ELEMENTS OF THREE-DIMENSIONAL GENERAL LINEAR GROUPS
Authors: AZAD AZIZOLLAH , PRAEGER CHERYL E.
Published: June 2009

Let G be a group. A subset N of G is a set of pairwise noncommuting elements if xy⁄=yx for any two distinct elements x and y in N. If ∣N∣≥∣M∣ for any other set of pairwise noncommuting elements M in G, then N is said to be a maximal subset of pairwise noncommuting elements. In this paper we determine the cardinality of a maximal subset of pairwise noncommuting elements in a three-dimensional general linear group. Moreover, we show how to modify a given maximal subset of pairwise noncommuting elements into another maximal subset of pairwise noncommuting elements that contains a given ‘generating element’ from each maximal torus.
EXTENSION ALGEBRAS OF CUNTZ ALGEBRA, II
Authors: LIU SHUDONG , FANG XIAOCHUN
Published: June 2009

In this paper, we construct the unique (up to isomorphism) extension algebra, denoted by E∞, of the Cuntz algebra 𝒪∞ by the C*-algebra of compact operators on a separable infinite-dimensional Hilbert space. We prove that two unital monomorphisms from E∞ to a unital purely infinite simple C*-algebra are approximately unitarily equivalent if and only if they induce the same homomorphisms in K-theory.
Tracking medfly predation by the wolf spider, Pardosa cribata Simon, in citrus orchards using PCR-based gut-content analysis
Authors: Monzó C. , Sabater-Muñoz B. , Urbaneja A. , Castañera P.
Published: June 2009

The Mediterranean fruit fly, Ceratitis capitata (Wiedemann), which is often controlled chemically, is a major citrus pest in Spain; however, alternative biological control strategies such as those based on the conservation of polyphagous predators should be developed. The wolf spider, Pardosa cribata Simon, is an abundant predator found in citrus orchards in eastern Spain. In this study, we have evaluated polymerase chain reaction (PCR)-based techniques as a means of detecting C. capitata DNA remains in P. cribata specimens. To do so, two pairs of C. capitata species-specific primers were designed and tested. Primer specificity was tested on species closely related to C. capitata and with other pests and natural enemies present in citrus orchards. Medfly DNA was detectable in 100% of P. cribata from 0 to 12 h post ingestion for both primer pairs, decreasing to 37% at 96 h after prey ingestion for one pair of primers. DNA detectability half-lives were of 78.25 h and 78.08 h for each pair of primers but no statistical differences were found between them. Pardosa cribata specimens were field-collected daily after sterile C. capitata pupae had been deployed in the citrus orchard. Afterwards, the wolf spiders were analyzed and DNA remains of C. capitata were detected in 5% of them, with a peak of 15% coinciding with maximum C. capitata emergence. This study is the first to reveal the potential use of DNA markers to track medfly predation by P. cribata in citrus orchards and provides a new tool to estimate the potential role of this spider in biological-control conservation programs.
History of HTA: Introduction
Authors: Banta David , Jonsson Egon
Published: June 2009

For the past several years, we have discussed the idea of producing a publication on the history of health technology assessment (HTA). It seemed important to us to develop this history now, while those who lived it can give their own accounts. An exception is Seymour Perry, the first president of ISTAHC and the Director of the first national public program in HTA, the U.S. National Center for Health Care Technology (NCHCT). See the In Memoriam in this issue.
Development of the International Network of Agencies for Health Technology Assessment
Authors: Hailey David
Published: June 2009

Objectives: To describe the development of the International Network of Agencies for Health Technology Assessment (INAHTA) and its activities.

Methods: Review of literature material and other documents produced by or relating to INAHTA.

Results: INAHTA includes organizations that provide health technology assessment (HTA) advice to governments and receive most of their funding from public sources. In early 2009, there were forty-six members from twenty-seven countries, including both national and regional agencies. Interaction with other organizations includes links to Health Technology Assessment International (HTAi), the European Union Network for Health Technology Assessment (EUnetHTA), PAHO (the Pan American Health Organization, and the World Health Organization (WHO). An important feature of INAHTA is the routine interaction of its members with public sector decision makers. Output from the network has included guidelines and frameworks on HTA, reports of surveys, and joint projects.

Conclusions: INAHTA has developed as a global point of contact and information for those with interests in HTA.
The history of health technology assessment in Australia
Authors: Hailey David
Published: June 2009

Objectives:To describe the development and application of health technology assessment (HTA) in Australia.

Methods:Review of relevant literature and other documents related to HTA in Australia.

Results:Most HTA activity in Australia has been associated with provision of advice for the two national subsidy programs, Medicare, and the Pharmaceutical Benefits Scheme (PBS). National advisory bodies established by the federal government have had a prominent role. Assessments from the advisory bodies have had a major influence on decisions related to Medicare and the PBS, and in some other areas. Technologies without links to the national subsidy schemes, and those that are widely distributed, have been less well covered by HTA. To some extent these are addressed by evaluations supported by state governments, but details of approaches taken are not readily available.

Conclusions:HTA in Australia now has a long history and is well established as a source of advice to health decision makers. Challenges remain in extending the scope of assessments, developing more transparent approaches in some areas, and consistently applying appropriate standards.
Austria: History of health technology assessment during the past 20 years
Authors: Wild Claudia
Published: June 2009

Objectives: The aim of this article is to describe and analyze the stages toward recognition and implementation of health technology assessment (HTA).

Methods: System analysis of structures and institutions and their use of HTA.

Results: Austria is a latecomer in implementing evaluations/HTA as decision support. It can to a certain degree absorb the increasing international knowledge. Austria had a long time to observe the successes and failures of HTA in other countries and to learn from other countries. The implementation of HTA within the Austrian healthcare system ran through stages of uptake: starting 1989 with a systematic review on international activities, first international networking and collaboration since 1991, proposed assessments until the late 1990s, followed by reactive assessments on demand mostly on high volume and costly technologies since then. Since 2000, HTA is used on a regular basis for investment and reimbursement decisions by several players, namely the Ministry of Health, the Social Insurance and hospital cooperations. In 2006, the Austrian HTA-institute was founded.

Conclusions: It took approximately 15 years from first research activities in HTA to an institutionalization. HTA in Austria is not only product- but also process-oriented: The actual production of assessments for decision support is as important as the structuring and accompanying of the process of decisions making. In addition, shaping the public understanding of science (characterized by the intrinsic belief that all new medical interventions provide added value to the healthcare system) is part of Austrian HTA.
History of health technology assessment in Hungary
Authors: Gulácsi László , Brodszky Valentin , Péntek Márta , Varga Szilárd , Vas Gábor , Boncz Imre
Published: June 2009

In Hungary, the history of the health technology assessment (HTA) dates back to 1993 when HTA and related activities started by professional initiatives. The legal background, institutionalization, and training capacities were created between 1998 and 2004. The main challenges for HTA in Hungary are partly similar to the ones in countries with a developed economy; no question it is time for cost-effectiveness. However, there are very important differences as well, that is why transferability and adaptability issues have to be considered. This article describes the characteristic features of the Hungarian healthcare system, the history and the current role of HTA, and the most important challenges.
Production of bovine cloned embryos with donor cells frozen at a slow cooling rate in a conventional freezer (−20 °C)
Authors: Chacón Liliana , Gómez Martha C. , Jenkins Jill A. , Leibo Stanley P. , Wirtu Gemechu , Dresser Betsy L. , Pope C. Earle
Published: June 2009

Usually, fibroblasts are frozen in dimethyl sulphoxide (DMSO, 10% v/v) at a cooling rate of 1 °C/min in a low-temperature (−80 °C) freezer (LTF) before storage in liquid nitrogen (LN2); however, a LTF is not always available. The purpose of the present study was to evaluate apoptosis and viability of bovine fibroblasts frozen in a LTF or conventional freezer (CF; −20 °C) and their subsequent ability for development to blastocyst stage after fusion with enucleated bovine oocytes. Percentages of live cells frozen in LTF (49.5%) and CF (50.6%) were similar, but significantly less than non-frozen control (88%). In both CF and LTF, percentages of live apoptotic cells exposed to LN2 after freezing were lower (4% and 5%, respectively) as compared with unexposed cells (10% and 18%, respectively). Cells frozen in a CF had fewer cell doublings/24 h (0.45) and required more days (9.1) to reach 100% confluence at the first passage (P) after thawing and plating as compared with cells frozen in a LTF (0.96 and 4.0 days, respectively). Hypoploidy at P12 was higher than at P4 in cells frozen in either a CF (37.5% vs. 19.2%) or in a LTF (30.0% vs. 15.4%). A second-generation cryo-solution reduced the incidence of necrosis (29.4%) at 0 h after thawing as compared with that of a first generation cryo-solution (DMEM + DMSO, 60.2%). The percentage of apoptosis in live cells was affected by cooling rate (CF = 1.9% vs. LFT = 0.7%). Development of bovine cloned embryos to the blastocyst stage was not affected by cooling rate or freezer type.
Exogenous hyalin and sea urchin gastrulation. Part IV: a direct adhesion assay – progress in identifying hyalin's active sites
Authors: Ghazarian Haike , Coyle-Thompson Catherine , Dalrymple William , Hutchins-Carroll Virginia , Metzenberg Stan , Razinia Ziba , Carroll Edward J. , Oppenheimer Steven B.
Published: June 2009

InStrongylocentrotus purpuratusthe hyalins are a set of three to four rather large glycoproteins (hereafter referred to as ‘hyalin’), which are the major constituents of the hyaline layer, the developing sea urchin embryo's extracellular matrix. Recent research from our laboratories has shown that hyalin is a cell adhesion molecule involved in sea urchin embryo-specific cellular interactions. Other laboratories have shown it to consist of 2–3% carbohydrate and a cloned, sequenced fragment demonstrated repeat domains (HYR) and non-repeat regions. Interest in this molecule has increased because HYR has been identified in organisms as diverse as bacteria, flies, worms, mice and humans, as well as sea urchins. Our laboratories have shown that hyalin appears to mediate a specific cellular interaction that has interested investigators for over a century, archenteron elongation/attachment to the blastocoel roof. We have shown this finding by localizing hyalin on the two components of the cellular interaction and by showing that hyalin and anti-hyalin antibody block the cellular interaction using a quantitative microplate assay. The microplate assay, however, has limitations because it does not directly assess hyalin's effects on the adhesion of the two components of the interaction. Here we have used an elegant direct assay that avoids the limitations, in which we microdissected the two components of the adhesive interaction and tested their re-adhesion to each other, thereby avoiding possible factors in the whole embryos that could confound or confuse results. Using both assays, we found that mild periodate treatment (6 h to 24 h in sodium acetate buffer with 0.2 M sodium periodate at 4 °C in the dark) of hyalin eliminates its ability to block the cellular interaction, suggesting that the carbohydrate component(s) may be involved in hyalin's specific adhesive function. This first step is important in identifying the molecular mechanisms of a well known cellular interaction in the NIH-designated sea urchin embryo model, a system that has led to the discovery of scores of physiological mechanisms, including those involved in human health and disease.
In vitrodevelopment of goat parthenogenetic and somatic cell nuclear transfer embryos derived from different activation protocols
Authors: Guo Jitong , Liu Fengjun , Guo Zekun , Li Yu , An Zhixing , Li Xuefeng , Li Yuqiang , Zhang Yong
Published: June 2009

Oocyte activation is an essential step in animal cloning to allow subsequent development of the reconstructed embryos. A special activation protocol is required for different animal species. The present study investigated low temperature, electrical pulses, ethanol, ionomycin and strontium for goat oocyte activation in order to optimize the protocols. We found, as a result, effective activation and parthenogenetic development of goat oocytes that had been derived from ionomycin, strontium and electrical pulse groups. Within each group 79.3–81.6%, 2.2–78.8% and 65.5% of the oocytes cleaved and 16.2–24.8%, 0–15.6% and 11.1% of the cleaved embryos developed into blastocysts when the oocytes were activated by ionomycin combined with 6-dimethylaminopurine, strontium plus cytochalasin B and electrical pulses combined with cytochalasin B, respectively. However, low temperature and ethanol were both unable to activate goat oocytes under our experimental conditions. When ionomycin combined with 6-dimethylaminopurine and strontium plus cytochalasin B was applied to activate somatic cell nuclear transfer embryos derived from cultured cumulus, 51.0% and 72.5% of the embryos cleaved, respectively. After transfer of 4-cell embryos into recipients, one (1/19 and 1/7) of the recipients from each group was found to be pregnant as detected by ultrasound, but both of these recipients lost the embryos between 45 and 60 days of pregnancy.
Dionysus and drama in the Buddhist art of Gandhara
Authors: Brancaccio Pia , Liu Xinru
Published: June 2009

This essay examines the relationships existing between Dionysian traditions of wine drinking and drama that reached the easternmost part of the Hellenistic world, and the Buddhist culture and art that flourished in Gandhara (Eastern Afghanistan and Northern Pakistan) under the Kushan kings between the first and third centuries CE. By piecing together archaeological, artistic and literary evidence, it appears that along with viniculture and viticulture, Dionysian rituals, Greek theatre and vernacular drama also became rooted in these eastern lands. Continuous interactions with the Graeco-Roman world strengthened these important cultural elements. At the beginning of the Common Era Dionysian traditions and drama came to be employed by the Buddhists of Gandhara to propagate their own ideas. The creation of a body of artworks representing the life of the Buddha in narrative form along with the literary work of Ashvaghosha, may be an expression of the same dramatic format that developed locally along with a strong Dionysian ritual presence.
Desirable teeth: the medieval trade in Arctic and African ivory
Authors: Seaver Kirsten A.
Published: June 2009

This article examines the Danish archaeologist Else Roesdahl’s hypothesis that, by the early fourteenth century, an abundance in Europe of elephant ivory from Africa caused a price drop that edged out walrus ivory, with a devastating economic impact on Norse Greenland that directly contributed to the colony’s collapse. While it seems clear that artisanal use of walrus ivory fell from the late fourteenth century onward, and that Greenland exports of walrus ivory decreased in the fourteenth century, evidence for a pre-1500 price drop for African elephant ivory in the European market is lacking. Nor can it be demonstrated that European demand for walrus tusks shrank prior to 1500. Roesdahl’s speculations about changes in the ivory trade and their effect on the Norse Greenland colony are therefore open to question as an explanation for the colony’s demise. An alternative view is proposed, namely that reduced export of Greenland walrus ivory was initiated by the Greenlanders themselves in response to political and economic changes in the Atlantic and North Sea region, at a time when codfish drew English fishermen and fish merchants ever farther west into the North Atlantic, and that the Greenlanders took part in that westward movement.
European colonial soldiers in the nineteenth century: their role in white global migration and patterns of colonial settlement
Authors: Bosma Ulbe
Published: June 2009

More than six million European soldiers were involved in nineteenth-century empire-building and a substantial number of them stayed behind in the colonies. Throughout history, soldiers have been priming the pump for settler colonies, being a reliable force in difficult pioneering circumstances with high mortality rates. In the age of European mass migration, however, these colonial soldiers were consistently excluded from migration statistics. This article argues that there is a nexus between the beginning of the age of mass migration and the exclusion of colonial soldiers from migration history. Their status as un-free labourers developed into an anomaly at a time when free labour and free European migration increasingly became the norm. An important implication of including these colonial soldiers in the purview of migration history would be a revisiting of nineteenth-century European emigration history. It would require a broader comparative perspective on coercive labour conditions among nineteenth-century European migrants (military and non-military). This effort could be part of an ongoing revision of the perception of the age of European mass migration as overwhelmingly free.
Influence of light and temperature on the marine iron cycle: From theoretical to global modeling
Authors: Tagliabue Alessandro , Bopp Laurent , Aumont Olivier , Arrigo Kevin R.
Published: June 2009

Iron regulates net primary production (NPP) in a number of ocean regions and exists in a variety of different forms in seawater, not all of which are bioavailable. We used a relatively complex iron cycle model to examine variability in iron speciation as a function of irradiance/temperature and parameterize its first‐order impact in a global ocean biogeochemistry model (OBM), which necessitated certain assumptions regarding the representation of iron chemistry. Overall, we find that higher irradiance (typical of shallower mixed layers) promotes the conversion of dissolved iron (dFe) into bioavailable forms (bFe) and increases bFe concentration by 5–53%, depending on parameter values. Temperature plays a secondary role in controlling bFe, with cold mixed layers increasing bFe concentrations. For a given irradiance and temperature, the presence of bioavailable Fe ligands increases bFe/dFe. When bioavailable Fe ligands are present, then reducing the photolability, increasing the log conditional stability, or increasing the concentration of such ligands all act to increase bFe/dFe. Such processes are currently not represented in global OBMs, where iron is typically parameterized as one pool, and we find that NPP can vary by >±20% regionally if the impact of temperature and irradiance on bFe is included, even under a constant circulation. Additionally, iron chemistry is important in controlling the depth over which phytoplankton iron limitation can be alleviated and the subsequent efficiency of iron‐based NPP. We also suggest organically complexed dFe must be bioavailable if distributions of phytoplankton biomass and macronutrients are to be reconciled with observations. Our results are important in understanding the role of the irradiance/mixing regime in governing the supply of iron to phytoplankton under a changing climate. New data sets on iron speciation and rate processes will aid in refining our model.
Magnetic structure of an oceanic core complex at the southernmost Central Indian Ridge: Analysis of shipboard and deep‐sea three‐component magnetometer data
Authors: Sato Taichi , Okino Kyoko , Kumagai Hidenori
Published: June 2009

We investigated the magnetic structure of an oceanic core complex (OCC) at the southernmost Central Indian Ridge (CIR) near 25°S on the basis of newly collected magnetic and bathymetric data and submersible dives. The OCC is located off‐axis on the western flank of the CIR and is characterized by typical megamullion morphology with flow line–parallel corrugations. The OCC is similar in size to those found along the Mid‐Atlantic Ridge (MAR), but the CIR OCC formed in an estimated 0.8 Ma, which is slightly shorter than the average time for the formation of OCCs along the MAR. The magnetization intensity over the CIR OCC is quite weak compared to that over adjacent seafloor of the same age. Mostly gabbroic rocks were recovered from outcrops during submersible dives. Fault rocks were also recovered from the corrugated surface, suggesting that the OCC surface represents the plane of a detachment fault. Although the magnetization intensity is rather low, we were able to identify the Brunhes‐Matuyama boundary and the Jaramillo and Olduvai subchrons on and around the OCC using vector magnetic analysis. Over the OCC, the Jaramillo subchron, which cannot be recognized from magnetic data acquired at the sea surface, was identified using data from a magnetometer attached to a submersible. The locus of this subchron is consistent with that observed over the seafloor adjacent to the OCC. Combining the results of magnetic survey and rock sampling, we would like to point out the possibility that the gabbroic rocks constituted the OCC and preserved seafloor‐spreading history, although there are several interpretations of the low magnetization.
Natural free convection in porous media: First field documentation in groundwater
Authors: Van Dam Remke L. , Simmons Craig T. , Hyndman David W. , Wood Warren W.
Published: June 2009

Natural free convection is a process of great importance in disciplines from hydrology to meteorology, oceanography, planetary sciences, and economic geology, and for applications in carbon sequestration and nuclear waste disposal. It has been studied for over a century – but almost exclusively in theoretical and laboratory settings. Despite its importance, conclusive primary evidence of free convection in porous media does not currently exist in a natural field setting. Here, we present recent electrical resistivity measurements from a sabkha aquifer near Abu Dhabi, United Arab Emirates, where large density inversions exist. The geophysical images from this site provide, for the first time, compelling field evidence of fingering associated with natural free convection in groundwater.
Obtaining vector magnetic field maps from single‐component measurements of geological samples
Authors: Lima Eduardo A. , Weiss Benjamin P.
Published: June 2009

Maxwell's equations can be used to demonstrate that the components of a static magnetic field in a region of space devoid of sources are not independent. This means that magnetometers that measure a single component of the magnetic field can potentially obtain all of three components of the field external to a source. Here we present an improved technique in the Fourier domain which can obtain the complete vector field planar map from just the planar map of one component. This technique is fast, robust, does not rely on any specific source type or configuration, and does not require the formulation of an inverse problem. An in‐depth analysis of the advantages and shortcomings of the technique is presented, demonstrating that high‐quality three‐component field maps with virtually no information loss can be obtained when proper sensor and mapping configurations are used. Several results derived from both synthetic and experimental data are presented. In particular, practical cases are shown where vector maps can assist the analysis of magnetic properties of geological samples. MATLAB® routines implementing the basic vector map calculation algorithm are available as auxiliary materials and can be readily adapted for processing magnetic data obtained from a variety of magnetic sensors.
Synoptic flow structures in the confluence region of the Kuroshio and the Ryukyu Current
Authors: Nagano Akira , Ichikawa Kaoru , Ichikawa Hiroshi , Konda Masanori , Murakami Kiyoshi
Published: June 2009

In the southeastern region of Kyushu, Japan, the Kuroshio from the East China Sea encounters the Ryukyu Current from the east of the Ryukyu Islands. By analyzing synoptic sections of water properties and geostrophic velocity in August 2004 and October 2005, we distinguished the waters in the Kuroshio southeast of Kyushu to be separated into an offshore region and a shallow onshore one. The onshore water is derived from the East China Sea, while the offshore water originates from both the east of Amami‐Oshima Island and the interior region of the North Pacific. The water mass transport from the east of Amami‐Oshima Island may become equivalent to that of the Kuroshio in the East China Sea as in October 2005. The volume transport–averaged temperature of the Kuroshio southeast of Kyushu is significantly lower than that in the East China Sea because of the confluence with the colder Ryukyu Current east of the Amami‐Oshima Island.
Influence of frequency‐dependent soil electrical parameters on the evaluation of lightning electromagnetic fields in air and underground
Authors: Delfino Federico , Procopio Renato , Rossi Mansueto , Rachidi Farhad
Published: June 2009

This paper is aimed at analyzing the influence of the frequency‐dependent behavior of the ground electrical parameters (conductivity and ground permittivity) on the electromagnetic field radiated by a cloud‐to‐ground lightning return stroke. Both radiation in air (over the conducting ground plane) and underground are considered in the analysis. The adopted method is based on the classical Sommerfeld's theory and takes advantage of an efficient ad hoc numerical procedure to face with the slow converging Sommerfeld's integrals. This feature allows the electromagnetic field to be computed without any sort of mathematical approximation and, since it is carried out in the frequency domain, can be used either if the ground permittivity and conductivity are considered constant or if they vary with the working frequency with any functional law. Simulations have been performed to identify the cases in which the approximation of constant ground permittivity and conductivity leads to satisfactory results. It is shown that for soils with water contents of 2% to 10% (ground conductivities in the order of 0.001 to 0.01 S/m), the assumption of constant electrical parameters appears to be reasonable. However, for either very poorly conducting soils (10−4 S/m or so) or highly conducting soils (10−1 S/m), the electromagnetic field components appear to be significantly affected by the frequency dependence of the ground electrical parameters.
Parameterization of cloud droplet size distributions: Comparison with parcel models and observations
Authors: Hsieh W. C. , Nenes A. , Flagan R. C. , Seinfeld J. H. , Buzorius G. , Jonsson H.
Published: June 2009

This work examines the efficacy of various physically based approaches derived from one‐dimensional adiabatic parcel model frameworks (a numerical model and a simplified parameterization) to parameterize the cloud droplet distribution characteristics for computing cloud effective radius and autoconversion rate in regional/global atmospheric models. Evaluations are carried out for integrations with single (average) and distributions of updraft velocity, assuming that (1) conditions at smax are reflective of the cloud column or (2) cloud properties vary vertically, in agreement with one‐dimensional parcel theory. The predicted droplet distributions are then compared against in situ cloud droplet observations obtained during the CRYSTAL‐FACE and CSTRIPE missions. Good agreement of droplet relative dispersion between parcel model frameworks indicates that the parameterized parcel model essentially captures one‐dimensional dynamics; the predicted distributions are overly narrow, with relative dispersion being a factor of 2 lower than observations. However, if conditions at cloud maximum supersaturation are used to predict relative dispersion and applied throughout the cloud column, better agreement is seen with observations, especially if integrations are carried out over the distribution of updraft velocity. When considering the efficiency of the method, calculating cloud droplet spectral dispersion at smax is preferred for linking aerosol with droplet distributions in large‐scale models.
An analysis of VLF electric field spectra measured in Titan's atmosphere by the Huygens probe
Authors: Morente Juan A. , Portí Jorge A. , Blanchard Cedric , Navarro Enrique A. , Salinas Alfonso
Published: June 2009

A numerical simulation of Titan's electromagnetic cavity in the VLF band is carried out using the Transmission Line Matrix (TLM) method, with the aim of assessing the VLF electric field spectra sent by the Huygens probe. In an Earth‐like model, successive peaks would be expected in the spectra, associated with multiple reflections of the electromagnetic wave on the external surfaces of Titan's electromagnetic cavity, formed by the ionosphere and a conductive ground or underground surface. However, owing to high losses conferred by the electrical conductivity to Titan's atmosphere, the direct numerical and experimental spectra are decreasing functions of the frequency without resonances or other special forms. The weak atmospheric resonances are extracted from the data measured by the Huygens's sensors after a procedure based on analysis of the late time response is applied to the experimental spectra. The new late time spectra present the appearance expected, with successive peaks and a mean between adjacent resonances of 0.67 kHz, in agreement with the late time TLM results when the Borucki et al. (2006) conductivity profile with aerosols is introduced in the numerical model. This gap in frequency between successive peaks gives an effective optical distance between the ground and the conductive ionosphere of approximately 220 km, considerably higher than the terrestrial one where this distance is around 75 km.
Glacial long period seismic events at Katla volcano, Iceland
Authors: Jónsdóttir Kristín , Roberts Roland , Pohjola Veijo , Lund Björn , Shomali Zaher Hossein , Tryggvason Ari , Böðvarsson Reynir
Published: June 2009

Repeating long‐period (lp) earthquakes are commonly observed in volcanic regions worldwide. They are usually explained in terms of a volcanic source effect or anomalous propagation through the volcano. Recently, large lp events have also been associated with the motion of massive ice streams. Our joint analysis of climatic and new seismic data shows that small lp events observed at Katla volcano, Iceland, are in fact related to ice movement in a steep outlet glacier and not, as previously thought, to volcanic intrusive activity. The over 13000 lp events recorded since 2000 are consistent in character and magnitude with seasonal changes of the glacier. As the current global warming trend could cause similar earthquake sequences at other glacier covered volcanoes, identifying them as glacial rather than eruption precursors is vital.
Improved hurricane track and intensity forecast using single field‐of‐view advanced IR sounding measurements
Authors: Li Jun , Liu Hui
Published: June 2009

Hyperspectral infrared sounders such as the AIRS and IASI provide unprecedented global atmospheric temperature and moisture soundings with high vertical resolution and accuracy. The AIRS and IASI data have been used in global numerical weather prediction models with positive impact on weather forecasts. The high spatial resolution single field‐of‐view soundings retrieved from AIRS have been applied to hurricane track and intensity assimilations and forecasts. The newly developed NCAR WRF/DART ensemble data assimilation is performed at 36 km resolution. Studies show that the track error for Hurricane Ike (2008) is reduced greatly when AIRS soundings are used compared with the control run which includes other observations such as radiosonde, satellite cloud winds, aircraft data, ship data, and land surface data, etc. The hurricane intensity forecast is also substantially improved when AIRS data are assimilated. This study demonstrates the importance of high spatial and hyperspectral IR sounding data in forecasting hurricanes.
Properties of the boundary layer potential for northward interplanetary magnetic field
Authors: Sundberg K. Å. T. , Blomberg L. G. , Cumnock J. A.
Published: June 2009

We present a method for estimating the portion of the ionospheric high‐latitude potential that maps to the magnetospheric boundary layer during steady northward IMF and global ionospheric 4‐cell convection patterns associated with lobe reconnection, together with the results of a statistical study based on DMSP F13 data from 1996–2004. In comparison with a previous study for steady southward IMF by K. Å. T. Sundberg et al. (2008), the results show significantly larger boundary layer potentials, with a mean value of 10 kV for the 271 events studied, corresponding to roughly 30–35% of the potential generated by the solar wind interaction. In a statistical analysis, the boundary layer potential is also shown to depend significantly on viscous parameters such as the solar wind velocity, density and pressure.
Intragrain defects in polycrystalline silicon layers grown by aluminum-induced crystallization and epitaxy for thin-film solar cells
Authors: Van Gestel Dries , Gordon Ivan , Bender Hugo , Saurel Damien , Vanacken Johan , Beaucarne Guy , Poortmans Jef
Published: June 2009

Polycrystalline silicon (pc-Si) thin-films with a grain size in the range of 0.1–100 μm grown on top of inexpensive substrates are economical materials for semiconductor devices such as transistors and solar cells and attract much attention nowadays. For pc-Si, grain size enlargement is thought to be an important parameter to improve material quality and therefore device performance. Aluminum-induced crystallization (AIC) of amorphous Si in combination with epitaxial growth allows achieving large-grained pc-Si layers on nonsilicon substrates. In this work, we made pc-Si layers with variable grain sizes by changing the crystallization temperature of the AIC process in order to see if larger grains indeed result in better solar cells. Solar cells based on these layers show a performance independent of the grain size. Defect etching and electron beam induced current (EBIC) measurements showed the presence of a high density of electrically active intragrain defects. We therefore consider them as the reason for the grain size independent device performance. Besides dislocations and stacking faults, also Σ3 boundaries were electrically active as shown by combining electron backscattered diffraction with EBIC measurements. The electrical activity of the defects is probably triggered by impurity decoration. Plasma hydrogenation changed the electrical behavior of the defects, as seen by photoluminescence, but the defects were not completely passivated as shown by EBIC measurements. In order to reveal the origin of the defects, cross section transmission electron microscopy measurements were done showing that the intragrain defects are already present in the AIC seed layer and get copied into the epitaxial layer during epitaxial growth. The same types of intragrain defects were found in layers made on different substrates (alumina ceramic, glass ceramic, and oxidized silicon wafer) from which we conclude that intragrain defects are not related to the relatively rough alumina ceramic substrates often used in combination with high temperature epitaxy. Further improvement of the material quality, and hence device performance, is therefore not simply achieved by increasing the grain size, but the intragrain quality of the material also needs to be taken into account. For pc-Si layers based on AIC and epitaxial growth, the seed layer has a crucial impact on the intragrain defect formation.
Size effect in magneto-optical properties of Co nanoparticle dispersed systems
Authors: Ozaki Shinsuke , Kura Hiroaki , Maki Hideyuki , Sato Tetsuya
Published: June 2009

Faraday rotation spectra of Co nanoparticles embedded in polymethylmethacrylate (PMMA) matrix were investigated by the theoretical and experimental approaches. Co nanoparticles were synthesized by means of the thermal decomposition method, which makes it possible to control the particle concentration without changing the particle size distribution. The amplitude of Faraday rotation is dependent on the particle concentration, and the Faraday rotation spectra show the blueshift accompanied by the decrease in size of Co nanoparticles. The experimental results of Faraday spectra were consistent with the calculation using the Maxwell-Garnett model which is considering the size-dependent free-electron contribution and size independent bound-electron contribution. It was found that the spectral shift was caused only by the size-dependent diagonal element in the dielectric constant tensor, which originates from the confinement of the free electrons in nanoparticles.
Electron dynamics in films made of transition metal nanograins embedded in SiO2: Infrared reflectivity and nanoplasma infrared resonance
Authors: Massa Néstor E. , Denardin Juliano C. , Socolovsky Leandro M. , Knobel Marcelo , Zhang (Xixiang Zhang) X. X.
Published: June 2009

We report on near normal infrared reflectivity spectra of ∼550 nm thick films made of cosputtered transition metal nanograins and SiO2 in a wide range of metal fractions. Co0.85(SiO2)0.15,with conductivity well above the percolation threshold has a frequency and temperature behavior according to what it is find in conducting metal oxides. The electron scattering rate displays a unique relaxation time characteristic of single type of carriers experiencing strong electron-phonon interactions. Using small polaron fits we identify those phonons as glass vibrational modes. Ni0.61(SiO2)0.39, with a metal fraction closer to the percolation threshold, undergoes a metal-nonmetal transition at ∼77 K. Here, as it is suggested by the scattering rate nearly quadratic dependence, we broadly identify two relaxation times (two carrier contributions) associated to a Drude mode and a midinfrared overdamped band, respectively. Disorder induced, the midinfrared contribution drives the phase transition by thermal electron localization. Co0.51(SiO2)0.49 has the reflectivity of an insulator with a distinctive band at ∼1450 cm−1 originating in electron promotion, localization, and defect induced polaron formation. Angle dependent oblique reflectivity of globally insulating Co0.38(SiO2)0.62, Fe0.34(SiO2)0.66, and Ni0.28(SiO2)0.72, reveals a remarkable resonance at that band threshold. We understand this as due to the excitation by normal to the film electric fields of defect localized electrons in the metallic nanoparticles. At higher oblique angles, this localized nanoplasma couples to SiO2 longitudinal optical Berreman phonons resulting in band peak softening reminiscent to the phonon behavior undergoing strong electron-phonon interactions. Singular to a globally insulating phase, we believe that this resonance might be a useful tool for tracking metal-insulator phase transitions in inhomogeneous materials.
Zero bias thermally stimulated currents in synthetic diamond
Authors: Mori R. , Miglio S. , Bruzzi M. , Bogani F. , De Sio A. , Pace E.
Published: June 2009

Zero bias thermally stimulated currents (ZBTSCs) have been observed in single crystal high pressure high temperature (HPHT) and polycrystalline chemical vapor deposited (pCVD) diamond films. The ZBTSC technique is characterized by an increased sensitivity with respect to a standard TSC analysis. Due to the absence of the thermally activated background current, new TSC peaks have been observed in both HPHT and pCVD diamond films, related to shallow activation energies usually obscured by the emission of the dominant impurities. The ZBTSC peaks are explained in terms of defect discharge in the nonequilibrium potential distribution created by a nonuniform traps filling at the metal-diamond junctions. The electric field due to the charged defects has been estimated in a quasizero bias TSC experiment by applying an external bias.
Mean free path limitation of thermoelectric properties of bismuth nanowire
Authors: Murata Masayuki , Nakamura Daiki , Hasegawa Yasuhiro , Komine Takashi , Taguchi Takashi , Nakamura Shinichiro , Jaworski Christopher M. , Jovovic Vladimir , Heremans Joseph P.
Published: June 2009

A limiting mean free path was considered in order to better understand the temperature and wire diameter dependence of the resistivity and Seebeck coefficient of bismuth microwire and nanowire samples. The mean free path limited mobility was numerically calculated from experimentally measured mobility in a bulk bismuth sample, and the electron and hole mobilities were dramatically decreased to a 10 μm mean free path. Therefore, the temperature dependence of resistivity in very thin wire was quite different from that of a bulk sample, which had a positive temperature coefficient. The calculations showed that the temperature coefficient decreased gradually with decreasing mean free path, and the coefficient became negative for a mean free path of less than 1 μm at about 150 K. The Seebeck coefficient was also calculated, but showed only a weak dependence on mean free path compared with the resistivity. Experimental comparisons were made to previous measurements of bismuth microwire or nanowire samples, and the temperature and wire diameter dependencies of the resistivity and Seebeck coefficient were qualitatively and quantitatively in very good agreement. Therefore, the temperature dependencies of nanowire samples over 850 nm in diameter were well described using the mean free path limitation.
Electronic behavior of the Zn- and O-polar ZnO surfaces studied using conductive atomic force microscopy
Authors: Moore J. C. , Kenny S. M. , Baird C. S. , Morkoç H. , Baski A. A.
Published: June 2009

We have used conducting atomic force microscopy (CAFM) to study the morphology and electronic behavior of as-received and air-annealed (0001) Zn- and (0001¯) O-polar surfaces of bulk ZnO. Both polar surfaces exhibit relatively flat morphologies prior to annealing, which rearrange to form well-defined steps upon annealing in air at 1050 °C for 1 h. Long-term exposure to air results in surface layer pitting and the destruction of steps for both the as-received and air-annealed (0001¯) surfaces, indicating its enhanced reactivity relative to the (0001) surface. CAFM I-V spectra for polar surfaces are similar and indicate Ohmic to rectifying behavior that depends on the maximum applied ramp voltage, where higher voltages result in more conducting behavior. These data and force-displacement curves suggest the presence of a physisorbed H2O layer, which is removed at higher voltages and results in higher conduction.
Achromatic reflectron compressor design for bright pulses in femtosecond electron diffraction
Authors: Kassier G. H. , Haupt K. , Erasmus N. , Rohwer E. G. , Schwoerer H.
Published: June 2009

We have designed a femtosecond electron gun suitable for ultrafast electron diffraction experiments, operating in the 30–100 kV regime. The concept is based on recompression of chirped expanding electron pulses emitted from a direct current photogun using a novel dispersion-corrected reflectron concept. We show, using detailed numerical simulations, that our design is capable of producing electron pulses containing 200 000 electrons with a full width at half maximum pulse duration of 130 fs, a root mean squared (rms) pulse radius of 140 μm, and transverse coherence length of 1.5 nm at 100 kV. Our analysis includes the bunch properties at the sample, as well as interactions of the main pulse of high charge density with diffracted electrons. Since our design employs only static electron optics, we believe that it will be easier to implement than concepts based on radio frequency compression.