bluuebunny/crossref_metadata_2025 huggingface dataset:
A socially-driven topology improvement framework with applications in content distribution and trust management
Authors: Stai Eleni , Karyotis Vasileios , Papavassiliou Symeon
Published: June 2011

Contemporary networking infrastructures are required to be capable of adapting to the increasing trends of user demands, as well as the impairments of their operational environment. In this work, by exploiting the power varying capabilities of multihop wireless networks and inspired by social structures of the higher protocol layers, we develop a distributed and dynamic physical topology modification framework for weighted and directed multihop networks. The operational robustness and effectiveness of the proposed framework is demonstrated in two highly popular application areas, namely QoS-oriented content distribution and trust management in wireless multihop networks. We focus on the emerging trade-offs of topology modification, and through analysis and simulation, we demonstrate how social features can be used in improving the physical network topology and corresponding performance.
Geochemical trends through time and lateral variability of diatom floras in the Pleistocene Olorgesailie Formation, southern Kenya Rift Valley
Authors: Owen R. B. , Renaut R. W. , Potts R. , Behrensmeyer A. K.
Published: June 2011

The Olorgesailie Formation (1.2–0.49 Ma) consists of fluvial and lacustrine rift sediments that have yielded abundant Acheulean artifacts and a fossil hominin (Homo cf. erectus). In testing prior understandings of the paleoenvironmental context, we define nine new geochemical zones. A Chemical Index of Alteration suggests increased catchment weathering during deposition of Members 1, 2, 7, 11, and 13. Biophile elements (Br, S) peak in M8–9 and lower M13 possibly reflecting increased input from soil erosion. REE data show that the Magadi Trachytes supplied most siliciclastic grains. Sixteen diatom stages indicate conductivities of 200–16,000 μS cm− 1 and pH of 7.5–9.5 for five deep-water lakes, ten shallow lakes and sixteen wetlands. These results are compared with diatom data from other sections in the basin and show aquatic spatial variability over km-scale distances. Similar floras are traceable over several kilometers for M2, M3 and M9, indicating broadly homogeneous lacustrine conditions during these times, but diatoms in other members imply variable conditions, some related to local tectonic controls. This lateral and temporal variability emphasizes the importance of carrying out stratigraphic sampling at multiple sites within a basin in efforts to define the environmental context relevant to human evolution.
Cavitation bubble dynamics in a liquid gap of variable height
Authors: GONZALEZ-AVILA SILVESTRE ROBERTO , KLASEBOER EVERT , KHOO BOO CHEONG , OHL CLAUS-DIETER
Published: June 2011

We report on an experimental study of cavitation bubble dynamics within sub-millimetre-sized narrow gaps. The gap height is varied, while the position of the cavitation event is fixed with respect to the lower gap wall. Four different sizes of laser-induced cavitation bubbles are studied using high-speed photography of up to 430,000 frames per second. We find a strong influence of the gap height, H, on the bubble dynamics, in particular on the collapse scenario. Also, similar bubble dynamics was found for the same non-dimensional gap height η = H/Rx, where Rx is the maximum radius in the horizontal direction. Three scenarios are observed: neutral collapse at the gap centre, collapse onto the lower wall and collapse onto the upper wall. For intermediate gap height the bubble obtains a conical shape 1.4 < η < 7.0. For large distances, η > 7.0, the bubble no longer feels the presence of the upper wall and collapses hemispherically. The collapse time increases with respect to the expansion time for decreasing values of η. Due to the small scales involved, the final stage of the bubble collapse could not be resolved temporally and numerical simulations were performed to elucidate the details of the flow. The simulations demonstrate high-speed jetting towards the upper and lower walls and complex bubble splitting for neutral collapses.
Up-regulation of PPARγ, heat shock protein-27 and -72 by naringin attenuates insulin resistance, β-cell dysfunction, hepatic steatosis and kidney damage in a rat model of type 2 diabetes
Authors: Kumar Sharma Ashok , Bharti Saurabh , Ojha Shreesh , Bhatia Jagriti , Kumar Narender , Ray Ruma , Kumari Santosh , Singh Arya Dharamvir
Published: June 2011

Naringin, a bioflavonoid isolated from grapefruit, is well known to possess lipid-lowering and insulin-like properties. Therefore, we assessed whether naringin treatment ameliorates insulin resistance (IR), β-cell dysfunction, hepatic steatosis and kidney damage in high-fat diet (HFD)–streptozotocin (STZ)-induced type 2 diabetic rats. Wistar albino male rats were fed a HFD (55 % energy from fat and 2 % cholesterol) to develop IR and on the 10th day injected with a low dose of streptozotocin (40 mg/kg, intraperitoneal (ip)) to induce type 2 diabetes. After confirmation of hyperglycaemia (>13·89 mmol/l) on the 14th day, different doses of naringin (25, 50 and 100 mg/kg per d) and rosiglitazone (5 mg/kg per d) were administered orally for the next 28 d while being maintained on the HFD. Naringin significantly decreased IR, hyperinsulinaemia, hyperglycaemia, dyslipidaemia, TNF-α, IL-6, C-reactive protein and concomitantly increased adiponectin and β-cell function in a dose-dependent manner. Increased thiobarbituric acid-reactive substances and decreased antioxidant enzyme activities in the serum and tissues of diabetic rats were also normalised. Moreover, naringin robustly increased PPARγ expression in liver and kidney; phosphorylated tyrosine insulin receptor substrate 1 in liver; and stress proteins heat shock protein (HSP)-27 and HSP-72 in pancreas, liver and kidney. In contrast, NF-κB expression in these tissues along with sterol regulatory element binding protein-1c and liver X receptor- expressions in liver were significantly diminished. In addition, microscopic observations validated that naringin effectively rescues β-cells, hepatocytes and kidney from HFD-STZ-mediated oxidative damage and pathological alterations. Thus, this seminal study provides cogent evidence that naringin ameliorates IR, dyslipidaemia, β-cell dysfunction, hepatic steatosis and kidney damage in type 2 diabetic rats by partly regulating oxidative stress, inflammation and dysregulated adipocytokines production through up-regulation of PPARγ, HSP-27 and HSP-72.
Bone-protective effects of bioactive fractions and ingredients in Sambucus williamsii HANCE
Authors: Xiao Hui-Hui , Dai Yi , Wan Hoi-Ying , Wong Man-Sau , Yao Xin-Sheng
Published: June 2011

Our previous study demonstrated that 60 % ethanol crude extract of Sambucus williamsii HANCE (SWH) improved bone mass, bone strength and bone micro-structure in both ovariectomised (OVX) rats and mice. The present study aims to identify the bioactive fractions and ingredients in SWH that account for its osteoprotective effects. Bilateral sham-operated mice acted as controls. OVX C57BL/6J mice, aged 12 weeks, were orally administrated daily with vehicle or 17β-oestradiol (3·2 mg/kg), SWH (60 % ethanol crude extract; 1·0 g/kg), SWA (water eluate; 0·570 g/kg), SWB (30 % ethanol eluate; 0·128 g/kg) or SWC (50 and 95 % ethanol eluates; 0·189 g/kg) for 12 weeks. The effects of the different fractions on bone properties in the OVX mice model were studied. In addition, their effects on osteoblast proliferation and differentiation were evaluated in UMR 106 cells. SWC significantly restored bone mineral density and improved bone size and bone content parameters in the femur and tibia as well as increased biomechanical strength at the tibia diaphysis in OVX mice. Similarly, SWC was the most potent fraction in stimulating cell proliferation and differentiation in UMR 106 cells. Also, SWC did not alter uterus weight in OVX mice. Nine major peaks, seven lignans and two phenolic acids, in the HPLC fingerprint of the SWC fraction were identified, isolated and characterised. In conclusion, the present study demonstrated that SWC was the most potent fraction in SWH that exerted anti-osteoporotic effects. Furthermore, lignans might be the potential bioactive components in SWC.
Tannic acid is more effective than clofibrate for the elevation of hepatic β-oxidation and the inhibition of 3-hydroxy-3-methyl-glutaryl-CoA reductase and aortic lesion formation in apo E-deficient mice
Authors: Do Gyeong-Min , Kwon Eun-Young , Ha Tae-Youl , Bok Park Yong , Kim Hye-Jin , Jeon Seon-Min , Lee Mi-Kyung , Choi Myung-Sook
Published: June 2011

The effects of tannic acid (TA) supplementation (0·02 %, wt/wt) were compared with the effects of clofibrate (CF) supplementation (0·02 %, wt/wt) in apo E-deficient (apo E− / −) mice fed a AIN-76 semi-synthetic diet (normal diet) over 20 weeks. The mice were monitored for the modulation of hepatic mRNA expression and the activities of lipid-regulating enzymes. Both TA and CF supplementation lowered hepatic 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGR) activity and prevented atherosclerotic lesion formation in comparison with the control group. Hepatic carnitine palmitoyl transferase and β-oxidation activities were significantly higher in the TA and CF groups than in the control group. Both CF and TA supplementation resulted in significant decreases in hepatic HMGR mRNA levels in association with its enzyme activity. However, in contrast to CF supplementation, TA supplementation seemed to decrease the accumulation of hepatic lipids in the apo E− / −mice without increasing liver weight. These results suggest that the overall effect of TA is more desirable than CF for the alleviation of hepatic lipogenesis and atherogenesis in apo E− / −mice.
Audiological manifestations of allergic rhinitis
Authors: Singh Satbir , Nagarkar Anu N , Bansal Sandeep , Vir Dharm , Gupta Ashok K
Published: June 2011

Background:

Allergic rhinitis is associated with excess specific immunoglobulin E. Inner ear involvement (via both cellular and humoral immunity) is poorly understood, but appears to arise from the endolymphatic sac and duct.

Aims:

To assess the otological and audiological status of patients with allergic rhinitis.

Methodology:

Thirty allergic rhinitis patients (14 men, 16 women; age 17–45 years, mean 31 years) and 20 controls (12 men, eight women; age 21–42 years, mean 27 years) underwent audiological investigation.

Results:

All study group patients had sensorineural (rather than conductive) hearing loss, worse at high frequencies. All had abnormal transient evoked otoacoustic emissions and 27 had abnormal distortion product otoacoustic emissions. All had a statistically significantly prolonged wave I latency, and shortened absolute wave I–III and I–V interpeak latencies, compared with controls.

Conclusion:

Allergic rhinitis patients had a higher prevalence of hearing loss and otoacoustic emission abnormalities than controls. The endolymphatic sac can process antigens and produce its own local antibody response; the resulting inflammatory mediators and toxic products may interfere with hair cell function. Additional research is needed to determine the clinical value of audiometry and otoacoustic emission testing in allergic rhinitis.
Jejunostomy after oesophagectomy: A review of evidence and current practice
Authors: Couper Graeme
Published: June 2011

Patients undergoing oesophagectomy often have nutritional needs at the time of diagnosis and in the post-operative period. The aim of this article is to review the current literature and report on the author's experience of routine feeding jejunostomy insertion following oesophagectomy. The records of forty-eight consecutive patients undergoing oesphagectomy under the author's care were reviewed. Although the evidence of benefit of peri-operative feeding in patients undergoing oesophagectomy is limited, there is a clear need to establish a feeding route at the time of surgery. Oesophagectomy is associated with a mortality rate of 5–10% and a morbidity rate of 30–40% even in high-volume specialist centres. Over 50% of patients developing complications will require an alternative to oral feeding beyond 30 d. The enteral route is preferred in terms of safety and cost. A surgical feeding jejunostomy is associated with a low complication rate and a mortality rate of less than 1%. In forty-eight patients undergoing oesophagectomy the average weight loss at 6 months was 8·4 kg with only 8% regaining their pre-operative weight. Large reductions in weight at 6 months post-operatively were recorded irrespective of the development of post-operative complications or early recurrent disease. Routine jejunostomy insertion is recommended to ensure adequate nutrition in patients who develop post-operative complications and for those patients with long-term reduced appetite and poor oral intake.
Acinetobacter calcoaceticus–Acinetobacter baumannii complex species in clinical specimens in Singapore
Authors: KOH T. H. , TAN T. T. , KHOO C. T. , NG S. Y. , TAN T. Y. , HSU L-Y. , OOI E. E. , VAN DER REIJDEN T. J. K. , DIJKSHOORN L.
Published: June 2011

This study was performed to determine the prevalence, distribution of specimen sources, and antimicrobial susceptibility of the Acinetobacter calcoaceticus–Acinetobacter baumannii (Acb) species complex in Singapore. One hundred and ninety-three non-replicate Acb species complex clinical isolates were collected from six hospitals over a 1-month period in 2006. Of these, 152 (78·7%) were identified as A. baumannii, 18 (9·3%) as ‘Acinetobacter pittii’ [genomic species (gen. sp.) 3], and 23 (11·9%) as ‘Acinetobacter nosocomialis’ (gen. sp. 13TU). Carbapenem resistance was highest in A. baumannii (72·4%), followed by A. pittii (38·9%), and A. nosocomialis (34·8%). Most carbapenem-resistant A. baumannii and A. nosocomialis possessed the blaOXA-23-like gene whereas carbapenem-resistant A. pittii possessed the blaOXA-58-like gene. Two imipenem-resistant strains (A. baumannii and A. pittii) had the blaIMP-like gene. Representatives of carbapenem-resistant A. baumannii were related to European clones I and II.
Reducing fuzzy answer set programming to model finding in fuzzy logics
Authors: JANSSEN JEROEN , VERMEIR DIRK , SCHOCKAERT STEVEN , DE COCK MARTINE
Published: June 2011

In recent years, answer set programming (ASP) has been extended to deal with multivalued predicates. The resulting formalismsallow for the modeling of continuous problems as elegantly as ASP allows for the modeling of discrete problems, by combining thestable model semantics underlying ASP with fuzzy logics. However, contrary to the case of classical ASP where manyefficient solvers have been constructed, to date there is no efficient fuzzy ASP solver. A well-knowntechnique for classical ASP consists of translating an ASP programPto a propositional theory whose models exactlycorrespond to the answer sets ofP. In this paper, we show how this idea can be extended to fuzzy ASP, paving the wayto implement efficient fuzzy ASP solvers that can take advantage of existing fuzzy logic reasoners.
Investment strategies in retirement: in the presence of a means-tested government pension
Authors: BUTT ADAM , DENG ZIYONG
Published: June 2011

A simulation approach is used to investigate how various investment strategies affect the ability of retirees to spend at a desired level up until death. Retirees are assumed to maintain all investment and longevity risk, and also have access to a government-sponsored and means-tested Age Pension to provide part of their desired expenditure. It is found that a 100% allocation to growth assets is optimal for large expenditure desires relative to initial balance levels, with allocations outside of this being sensitive to movements in initial balance and desired expenditure level, as well as interactions with the Age Pension.
Saddle towers and minimal k-noids in ℍ2 × ℝ
Authors: Morabito Filippo , Rodríguez M. Magdalena
Published: June 2011

Given k ≥ 2, we construct a (2k − 2)-parameter family of properly embedded minimal surfaces in ℍ2 × ℝ invariant by a vertical translation T, called saddle towers, which have total intrinsic curvature 4π(1 − k), genus zero and 2k vertical Scherk-type ends in the quotient by T. Each of those examples is obtained from the conjugate graph of a Jenkins–Serrin graph over a convex polygonal domain with 2k edges of the same (finite) length. As limits of saddle towers, we obtain properly embedded minimal surfaces, called minimal k-noids, which are symmetric with respect to a horizontal slice (in fact they are vertical bi-graphs) and have total intrinsic curvature 4π(1 − k), genus zero and k vertical planar ends.
THE SINO-VIETNAMESE DISPUTE OVER TERRITORIAL CLAIMS, 1974–1978: VIETNAMESE NATIONALISM AND ITS CONSEQUENCES
Authors: Path Kosal
Published: June 2011

Relying on Vietnamese internal government documents now available to scholars for consultation in the No. 3 Vietnam National Archive in Hanoi, this article examines the linkage between the escalated Sino-Vietnamese territorial dispute and the increased Vietnamese mistreatment of Chinese residents and experts in northern Vietnam from 1974 to 1978 owing to state-sponsored Vietnamese anti-China/irredentist nationalism. During this period, Vietnamese leaders were seeking to forge national unity, solidify popular loyalty to the state, and mobilize domestic resources to defend the Vietnamese “fatherland” against the threat of Chinese territorial expansion. Specifically, this article demonstrates how these policies encouraged mistreatment of Chinese residents and experts, and created a climate of fear and paranoia within the Chinese community which caused the widespread flight of Chinese from northern Vietnam in 1977–1978.
The naturalness of (many) social institutions: evolved cognition as their foundation
Authors: BOYER PASCAL , PETERSEN MICHAEL BANG
Published: June 2011

Most standard social science accounts only offer limited explanations of institutional design, i.e. why institutions have common features observed in many different human groups. Here we suggest that these features are best explained as the outcome of evolved human cognition, in such domains as mating, moral judgment and social exchange. As empirical illustrations, we show how this evolved psychology makes marriage systems, legal norms and commons management systems intuitively obvious and compelling, thereby ensuring their occurrence and cultural stability. We extend this to propose under what conditions institutions can become ‘natural’, compelling and legitimate, and outline probable paths for institutional change given human cognitive dispositions. Explaining institutions in terms of these exogenous factors also suggests that a general theory of institutions as such is neither necessary nor in fact possible. What are required are domain-specific accounts of institutional design in different domains of evolved cognition.
A Paleogene extensional arc flare‐up in Iran
Authors: Verdel Charles , Wernicke Brian P. , Hassanzadeh Jamshid , Guest Bernard
Published: June 2011

Arc volcanism across Iran is dominated by a Paleogene pulse, despite protracted and presumably continuous subduction along the northern margin of the Neotethyan ocean for most of Mesozoic and Cenozoic time. New U‐Pb and 40Ar/39Ar data from volcanic arcs in central and northern Iran constrain the duration of the pulse to ∼17 Myr, roughly 10% of the total duration of arc magmatism. Late Paleocene‐Eocene volcanic rocks erupted during this flare‐up have major and trace element characteristics that are typical of continental arc magmatism, whereas the chemical composition of limited Oligocene basalts in the Urumieh‐Dokhtar belt and the Alborz Mountains which were erupted after the flare‐up ended are more consistent with derivation from the asthenosphere. Together with the recent recognition of Eocene metamorphic core complexes in central and east central Iran, stratigraphic evidence of Eocene subsidence, and descriptions of Paleogene normal faulting, these geochemical and geochronological data suggest that the late Paleocene‐Eocene magmatic flare‐up was extension related. We propose a tectonic model that attributes the flare‐up to decompression melting of lithospheric mantle hydrated by slab‐derived fluids, followed by Oligocene upwelling and melting of enriched mantle that was less extensively modified by hydrous fluids. We suggest that Paleogene magmatism and extension was driven by an episode of slab retreat or slab rollback following a Cretaceous period of flat slab subduction, analogous to the Laramide and post‐Laramide evolution of the western United States.
Modified equilibrium temperature models for cold‐water streams
Authors: Herb William R. , Stefan Heinz G.
Published: June 2011

Water temperature determines the spatial distribution of fish species, including cold‐water fish such as trout, and is driven by the balance of the heat flux across the water surface and the heat flux across the sediment surface. In this study, a modified equilibrium temperature model was developed for cold‐water streams that includes the effect of groundwater inflow. The modified equilibrium temperature model gives estimates of daily average stream temperature based on climate conditions, riparian shading, stream width, and groundwater input rate and temperature. For a small tributary stream with relatively uniform riparian shading, the modified equilibrium temperature was found to be a good predictor of daily average stream temperature, with a root‐mean‐square errors (RMSE) of 1.2°C. The modified equilibrium temperature model also gave good estimates (1.4°C RMSE) of daily average stream temperature for a larger stream when riparian shading was averaged over sufficiently long distances. A sensitivity analysis using the modified equilibrium temperature model confirmed that water temperature in cold‐water streams varies strongly with riparian shading, stream width, and both groundwater inflow rate and temperature. These groundwater parameters therefore need to be taken into account when climate change impacts on stream temperature are projected. The stream temperature model developed in this study is a useful tool to characterize temperature conditions in cold‐water streams with different levels of riparian shading and groundwater inputs and to assess the impact of future land use and climate change on temperature in these streams.
Determining critical infrastructure for ocean research and societal needs in 2030
Authors: Glickson Deborah , Barron Eric , Fine Rana
Published: June 2011

The United States has jurisdiction over 3.4 million square miles of ocean—an expanse greater than the land area of all 50 states combined. This vast marine area offers researchers opportunities to investigate the ocean's role in an integrated Earth system but also presents challenges to society, including damaging tsunamis and hurricanes, industrial accidents, and outbreaks of waterborne diseases. The 2010 Gulf of Mexico Deepwater Horizon oil spill and 2011 Japanese earthquake and tsunami are vivid reminders that a broad range of infrastructure is needed to advance scientists' still incomplete understanding of the ocean. The National Research Council's (NRC) Ocean Studies Board was asked by the National Science and Technology Council's Subcommittee on Ocean Science and Technology, comprising 25 U.S. government agencies, to examine infrastructure needs for ocean research in the year 2030. This request reflects concern, among a myriad of marine issues, over the present state of aging and obsolete infrastructure, insufficient capacity, growing technological gaps, and declining national leadership in marine technological development; these issues were brought to the nation's attention in 2004 by the U.S. Commission on Ocean Policy.
Tracking global change at local scales: Phenology for science, outreach, conservation
Authors: Sharron Ed , Mitchell Brian
Published: June 2011

A Workshop Exploring the Use of Phenology Studies for Public Engagement; New Orleans, Louisiana, 14 March 2011; During a George Wright Society Conference session that was led by the USA National Phenology Network (USANPN; http://www.usanpn.org) and the National Park Service (NPS), professionals from government organizations, nonprofits, and higher‐education institutions came together to explore the possibilities of using phenology monitoring to engage the public. One of the most visible effects of global change on ecosystems is shifts in phenology: the timing of biological events such as leafing and flowering, maturation of agricultural plants, emergence of insects, and migration of birds. These shifts are already occurring and reflect biological responses to climate change at local to regional scales. Changes in phenology have important implications for species ecology and resource management and, because they are place‐based and tangible, serve as an ideal platform for education, outreach, and citizen science.
Mekonnen Gebremichael receives 2010 Early Career Hydrologic Sciences Award: Citation
Authors: Krajewski Witold
Published: June 2011

Mekonnen Gebremichael received the 2010 Early Career Hydrologic Sciences Award at the 2010 AGU Fall Meeting, held 13–17 December in San Francisco, Calif. The award is for significant early‐career contributions to hydrologic science.
Mekonnen Gebremichael receives 2010 Early Career Hydrologic Sciences Award: Response
Authors: Gebremichael Mekonnen
Published: June 2011

Mekonnen Gebremichael received the 2010 Early Career Hydrologic Sciences Award at the 2010 AGU Fall Meeting, held 13–17 December in San Francisco, Calif. The award is for significant early‐career contributions to hydrologic science.
Murugesu Sivapalan receives 2010 Hydrologic Sciences Award: Citation
Authors: Foufoula‐Georgiou Efi
Published: June 2011

Murugesu Sivapalan received the 2010 Hydrologic Sciences Award at the 2010 AGU Fall Meeting, held 13–17 December in San Francisco, Calif. The award is for outstanding contributions to the science of hydrology.
The climate crisis: An introductory guide to climate change
Authors: Trenberth Kevin E.
Published: June 2011

Human‐induced climate change, sometimes called “global warming,” has, unfortunately, become a “hot” topic, embroiled in controversy, misinformation, and claims and counterclaims. It should not be this way, because there are many scientific facts that provide solid information on which to base policy. There is a very strong observational, theoretical, and modeling base in physical science that underpins current understanding of what has happened to Earth's climate and why and what the prospects are for the future under certain assumptions. Moreover, these changes have impacts, which are apt to grow, on the environment and human society. To avoid or reduce these impacts and the economic and human effects of undesirable future climate change requires actions that are strongly opposed by those with vested interests in the status quo, some of whom have funded misinformation campaigns that have successfully confused the public and some politicians, leading to paralysis in political action. Without mitigation of climate change, one would suppose that at least society would plan sensibly for the changes already happening and projected, but such future adaptation plans are also largely in limbo. The implication is that we will suffer the consequences. All of these aspects are addressed in this informative and attractive book, which is written for a fairly general but technically informed audience. The book is strongly based upon the 2007 Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) and therefore has a solid scientific basis. Many figures, graphs, and maps come from the three IPCC working group reports, although the captions often do not explain the detail shown. Given that the IPCC reports totaled nearly 3000 pages, to distill the complex material down to 249 pages is no mean task, and the authors have succeeded quite well.
Characterizing lightning emissions that cause gamma ray flashes
Authors: Tretkoff Ernie
Published: June 2011

Terrestrial gamma ray flashes (TGFs) are bursts of high‐energy radiation released in Earth's atmosphere during thunderstorms and are believed to be associated with lightning. Progress has been made in their study, but much remains to be learned about the properties of these events and related lightning activity. To characterize the lightning processes that produce TGFs, Lu et al. analyzed 56 TGFs detected by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) satellite from 2004 to 2009. They looked at the timing and characteristics of the very low frequency (VLF) and ultralow‐frequency (ULF) emissions that occur in conjunction with TGFs. The researchers determined that the large majority of TGF‐associated lightning signals contain at least one VLF impulse superimposed on a slow ULF pulse, indicative of significant upward negative charge transfer within 2–6 milliseconds; gamma rays are emitted in the course of this slow process, suggesting that this process plays a key role in gamma ray production, the authors report. (Journal of Geophysical Research‐Space Physics, doi:10.1029/2010JA016141, 2011)
New ice core record of atmospheric methane
Authors: Tretkoff Ernie
Published: June 2011

Atmospheric concentrations of methane, an important greenhouse gas, have varied in the past on time scales ranging from seasons to hundreds of thousands of years. Understanding past variations is important to interpreting current natural and anthropogenic changes. Mitchell et al. present a new high‐precision, high‐resolution atmospheric methane record covering 1000–1800 C.E. from an ice core from the West Antarctic Ice Sheet Divide project that has confirmed the existence of multidecadal‐scale variability during this time period. The new record, which complements other existing ice core methane records, shows that multidecadal‐scale methane variability is only weakly correlated or uncorrelated with reconstructed temperature and precipitation variations. The authors also found that time periods when war or plague resulted in population declines are coincident with global atmospheric methane decreases. (Journal of Geophysical Research‐Biogeosciences, doi:10.1029/2010JG001441, 2011)
Critical role of interleukin‐17/interleukin‐17 receptor axis in mediating Con A‐induced hepatitis
Authors: Yan Shu , Wang Luman , Liu Nan , Wang Ying , Chu Yiwei
Published: June 2011

Concanavalin A (Con A)‐induced hepatitis is thought to be a T‐cell‐mediated disease with active destruction of liver cells. Interleukin (IL)‐17 is a cytokine produced principally by CD4+ T cells. However, whether IL‐17/IL‐17 receptor (IL‐17/IL‐17R)‐mediated responses are involved in T‐cell‐mediated Con A‐induced liver injury remains unclear. In this study, we found that IL‐17 expression was highly elevated in liver tissues during Con A‐induced hepatitis. The increased levels of IL‐17 were paralleled with the severity of liver injury reflected by Alanine aminotransaminase and histological assay as well as the secretion of tumor necrosis factor (TNF)‐α and IL‐6. Blockage of IL‐17 significantly ameliorated Con A‐induced hepatitis, while overexpression of IL‐17 systemically resulted in massive hepatocyte necrosis in mice. Furthermore, overexpression of an IL‐17R immunoglobulin G1 fusion protein significantly attenuated liver inflammation after acute Con A treatment. High expression of IL‐17R on Kupffer cells was also observed along with the production of cytokines including TNF‐α and IL‐6. Inhibition of Kupffer cells by gadolinium chloride completely prevented Con A‐induced liver injury and cytokine release. Finally, IL‐17‐expressing CD4+ T and natural killer T cells were greatly increased in Con A‐injected mice compared with that in controls. Overall, our results indicate that IL‐17R signaling is critically involved in the pathogenesis in Con A‐induced hepatitis, and blockade of IL‐17/IL‐17R signaling pathway may represent a novel therapeutic intervention in human autoimmune‐related hepatitis.
Efficient Nd3+→Yb3+ energy transfer processes in high phonon energy phosphate glasses for 1.0 μm Yb3+ laser
Authors: Rivera-López F. , Babu P. , Basavapoornima Ch. , Jayasankar C. K. , Lavín V.
Published: June 2011

Efficient Nd3+→Yb3+ resonant and phonon-assisted energy transfer processes have been observed in phosphate glasses and have been studied using steady-state and time-resolved optical spectroscopies. Results indicate that the energy transfer occurs via nonradiative electric dipole-dipole processes and is enhanced with the concentration of Yb3+ acceptor ions, having an efficiency higher than 75% for the glass doped with 1 mol% of Nd2O3 and 4 mol% of Yb2O3. The luminescence decay curves show a nonexponential character and the energy transfer microscopic parameter calculated with the Inokuti-Hirayama model gives a value of 240 × 10−40 cm6 s−1, being one of the highest reported in the literature for Nd3+-Yb3+ co-doped matrices. From the steady-state experimental absorption and emission cross-sections, a general expression for estimating the microscopic energy transfer parameter is proposed based upon the theoretical methods developed by Miyakawa and Dexter and Tarelho et al. This expression takes into account all the resonant mechanisms involved in an energy transfer processes together with other phonon-assisted nonvanishing overlaps. The value of the Nd3+→Yb3+ energy transfer microscopic parameter has been calculated to be 200 × 10−40 cm6 s−1, which is in good agreement with that obtained from the Inokuti-Hirayama fitting. These results show the importance of the nonresonant phonon-assisted Nd3+→Yb3+ energy transfer processes and the great potential of these glasses as active matrices in the development of multiple-pump-channel Yb3+ lasers.
Monte Carlo simulation of silicon atomic displacement and amorphization induced by ion implantation
Authors: García Luis Jou , Kawamura Yoko , Uematsu Masashi , Hernández-Mangas Jesús M. , Itoh Kohei M.
Published: June 2011

The amorphization of silicon due to atomic displacement during ion implantation has been simulated. A model based on Monte Carlo calculation reproduces very well the depth profile of atomic mixing and displacement length of host silicon atoms reported by previous experiments. The critical displacement in the depth direction for amorphization has been determined to be 5 Å. This average threshold value is shown to be universal for identification of amorphous regions in silicon for a wide range of implantation conditions involving different doping species, acceleration energies, and doses.
Characterization of freestanding semi-insulating Fe-doped GaN by photoluminescence and electromodulation spectroscopy
Authors: Dumcenco D. O. , Levcenco S. , Huang Y. S. , Reynolds C. L. , Reynolds J. G. , Tiong K. K. , Paskova T. , Evans K. R.
Published: June 2011

A detailed optical characterization of a freestanding wurtzite semi-insulating Fe-doped GaN (SI-GaN:Fe) grown by hydride-vapor-phase-epitaxy was carried out by photoluminescence (PL) and contactless electroreflectance (CER) at 10 and 300 K, respectively, and photoreflectance at 300 K. Low-temperature PL spectrum of the Ga-face consisted of the Fe3+ impurity characteristic series of IR peaks with a sharp zero-phonon line (ZPL) at 1.299 eV, yellow and blue broad emission bands, and near-band-edge (NBE) emission in the ultraviolet region. The narrow linewidth of 135 μeV of the ZPL and the measured energy difference of ∼70 meV between the ZPL and E2 (high) phonon replica, which is sensitive to the lattice strain, shows good crystal quality and a strain-free incorporation of iron. The obtained transition energies of A, B, and C excitonic features in the CER spectra and the n = 2 excited states (2s) of the A and B excitons enable the estimation of the exciton binding energies. In addition to the free excitonic recombination, the PL spectrum of the Ga-face exhibited clear donor and acceptor related features in the NBE region, while the N-face exhibited a broad emission band related to the free-to-bound recombination only. The differences were explained by the presence of impurity-induced band-tail states in the N-face SI-GaN:Fe due to an increased impurity density and the incorporation of large volume vacancy-type defects.
Dielectric properties of aluminum silver alloy thin films in optical frequency range
Authors: Yang Guang , Sun Jingbo , Zhou Ji
Published: June 2011

The dielectric properties of direct current (dc) magnetron sputtering aluminum silver alloy films in optical frequency have been quantitatively studied by variable angle spectroscopic ellipsometry. The structure and surface topography of the alloy films were characterized using scanning probe microscopy and x-ray diffraction. The Drude–Lorentz model was used to simulate the dielectric function of Al-Ag alloy films. Meanwhile, the effective medium theory has been utilized for the treatment of surface roughness. We found that the interband transition around 1.5 eV can be shifted through a variable annealing temperature and a changeable silver percentage of Al-Ag alloys.
The influence of a Si cap on self-organized SiGe islands and the underlying wetting layer
Authors: Brehm M. , Grydlik M. , Groiss H. , Hackl F. , Schäffler F. , Fromherz T. , Bauer G.
Published: June 2011

For the prototypical SiGe/Si(001) Stranski-Krastanow (SK) growth system, the influence of intermixing caused by the deposition of a Si cap layer at temperatures Tcap between 300°C and 700°C is studied both for the SiGe wetting layer (WL) and the SiGe islands. Systematic growth experiments were carried out with an ultrahigh resolution of down to 0.005 monolayers (ML) of deposited Ge. The properties of the samples were investigated via photoluminescence (PL) spectroscopy, atomic force microscopy (AFM), and transmission electron microscopy. We studied in detail the influence of Tcap in the three main coverage regions of SiGe SK growth, which are (i) the WL build-up regime, (ii) the island nucleation regime, where most of the Ge is supplied via material transfer from the WL, and (iii) the saturation regime, where the WL thickness remains initially stable. At Tcap = 300°C, we found that both the WL and the island are essentially preserved in composition and shape, whereas at 500°C the WL becomes heavily alloyed during capping, and at 700°C the islands also become alloyed. At Tcap = 500°C we found enhanced WL intermixing in the presence of dome-shaped islands, whereas at Tcap = 700°C the WL properties become dominated by the dissolution of pyramid-shaped islands upon capping. At Ge coverages above ≈6 ML, we found an unexpected thickening of the WL, almost independently of Tcap. This finding suggests that the density and the volume of the dome-shaped islands have an upper limit, beyond which excess Ge from the external source again becomes incorporated into the WL. Finally, we compared PL spectra with AFM-based evaluations of the integral island volumes in order to determine in a straightforward manner the average composition of the SiGe islands.
Relation between crystallinity and chemical nature of surface on wettability: A study on pulsed laser deposited TiO2 thin films
Authors: Shirolkar Mandar M. , Phase Deodatta , Sathe Vasant , Rodríguez-Carvajal J. , Choudhary Ram Janay , Kulkarni Sulabha K.
Published: June 2011

Pure titania (TiO2) polycrystalline thin films in rutile, anatase and mixed phase have been grown on amorphous glass substrates by pulsed laser deposition method at various oxygen gas pressure. Wettability investigations have been carried out on these films. Consistent with our previous report [J. Phys. D: Appl. Phys. 41, 155308 (2008)] it has been observed that for nearly same surface roughness large contact angle or superhydrophobicity is present when sample has a pure single phase and lower contact angle or hydrophobicity when mixed phases were present. Structural characterizations suggest that in addition to roughness, pure phase film surface associated with hydrophobic sites and mixed phase film surface show association of both hydrophobic and hydrophilic sites, which might be inducing specific wetting character. UV treatment induces superhydrophilicity in the films. It was observed that UV irradiation causes nonequilibrium state on the TiO2 surface, leading to changes in the electron density, which in turn produces decrement in the crystallinity and lattice expansion. Reversible changes in the wetting state on the pure phase surfaces were observed to be faster than those on the mixed phase surfaces. We tried to establish the possible relation between crystalline phases, chemical nature of surface on reversible wettability besides the main governing parameter viz. surface roughness.
Electronic structure studies of Fe doped CeO2 thin films by resonance photoemission spectroscopy
Authors: Khare Amit , Choudhary R. J. , Phase D. M. , Sanyal Sankar P.
Published: June 2011

We have studied the modification in the electronic properties of pulsed laser deposited CeO2 thin films due to Fe doping (2 and 6 at %), with the help of x-ray photoemission spectroscopy (XPS) and resonance photoemission spectroscopy (RPES) measurements. XPS results indicate the ionic state of Fe in the Fe doped films, ruling out the possibility of Fe metallic clusters. Valence band spectra of CeO2 show an additional feature after Fe doping, suggesting its incorporation in the CeO2 matrix. RPES studies on these films reveal the hybridization between oxygen vacancy induced Ce localized states and Fe derived states.
Study of laser beam propagation in microholes and the effect on femtosecond laser micromachining
Authors: Tao Sha , Wu Benxin , Lei Shuting
Published: June 2011

In femtosecond (fs) laser micromachining, such as microhole drilling, the hole created by previous laser pulses may act like a waveguide, whose sidewall may significantly affect the beam profile of subsequent laser pulses propagating into the hole. This effect is very important for both the fundamental study and the practical applications of fs laser micromachining, but has not been well studied in literature. The effect is investigated in this paper by numerically solving the transient Maxwell’s wave equation. The study reveals how microholes affect laser intensity profile for different laser and hole parameters, and the implied effects on fs laser micromachining. The study has provided a good fundamental physical explanation for the elliptical hole shape obtained in fs laser micromachining with linearly polarized laser beams.
Modeling magnetotransport in inhomogeneous (Ge,Mn) films
Authors: Yu I.-S. , Jamet M. , Marty A. , Devillers T. , Barski A. , Beigné C. , Bayle-Guillemaud P. , Cibert J.
Published: June 2011

We have performed numerical simulations using the finite elements method in order to investigate magnetotransport in manganese doped germanium thin films. Up to now, several groups have reported similar transport measurements on (Ge,Mn) films obtained either by low temperature molecular beam epitaxy or by manganese implantation of germanium wafers. However, different physical interpretations have been proposed, including the existence of a diluted carrier-mediated ferromagnetic phase. Here, by carefully taking into account the morphology of (Ge,Mn) films (Mn-rich ferromagnetic inclusions in a highly diluted germanium matrix), we can reproduce some experimental findings. In particular, in order to observe high positive magnetoresistance and Hall angles, there are two requirements: (i) a strong anomalous Hall effect within Mn-rich inclusions and (ii) a conductivity contrast between these inclusions and the germanium matrix. Finally, we conclude that (Ge,Mn) films behave as granular ferromagnetic systems.
Epitaxial graphene surface preparation for atomic layer deposition of Al2O3
Authors: Garces N. Y. , Wheeler V. D. , Hite J. K. , Jernigan G. G. , Tedesco J. L. , Nepal Neeraj , Eddy C. R. , Gaskill D. K.
Published: June 2011

Atomic layer deposition was employed to deposit relatively thick (∼30 nm) aluminum oxide (Al2O3) using trimethylaluminum and triply-distilled H2O precursors onto epitaxial graphene grown on the Si-face of silicon carbide. Ex situ surface conditioning by a simple wet chemistry treatment was used to render the otherwise chemically inert graphene surface more amenable to dielectric deposition. The obtained films show excellent morphology and uniformity over large (∼64 mm2) areas (i.e., the entire sample area), as determined by atomic force microscopy and scanning electron microscopy. X-ray photoelectron spectroscopy revealed a nearly stoichiometric film with reduced impurity content. Moreover, from capacitance-voltage measurements a dielectric constant of ∼7.6 was extracted and a positive Dirac voltage shift of ∼1.0 V was observed. The graphene mobility, as determined by van der Pauw Hall measurements, was not affected by the sequence of surface pretreatment and dielectric deposition.
Cluster size and exchange dispersion in perpendicular magnetic media
Authors: Peng Y. , Wu X. W. , Pressesky J. , Ju G. P. , Scholz W. , Chantrell R. W.
Published: June 2011

A computational study of the effects of the intergranular exchange field and its dispersion on the cluster size in perpendicular recording media is presented. The dispersion arises from the grain size dispersion and the dispersion of intrinsic exchange coupling between individual grains. It is found that increasing the degree of dispersion reduces the cluster size due to weakly coupled grains acting as pinning sites against the expansion of the clusters. A simple semi-analytical model is proposed which gives good agreement with the numerical calculations in the limit of the large anisotropy constant.
Oxygen incorporation effects in annealed epitaxial La(1−x)SrxMnO3 thin films
Authors: Petrisor T. , Gabor M. S. , Boulle A. , Bellouard C. , Tiusan C. , Pana O. , Petrisor T.
Published: June 2011

This paper presents our results regarding oxygen incorporation effects in epitaxial La(1-x)SrxMnO3 thin films, deposited on SrTiO3 (001) single crystal substrates, by annealing in different gas mixtures of argon and oxygen. A particular emphasis is placed on the correlation of structural properties with the magnetic properties of the films, Curie temperature, and coercive field. In this sense, we demonstrate that the evolution of the diffuse part of the ω-scans performed on the films are due to oxygen excess in the film lattice, which creates cationic vacancies within the films. Also, we show that two regimes of oxygen incorporation in the films exist, one in which the films evolve toward a single phase and oxygen stoichiometry is recovered, and a second one dominated by oxygen over-doping effects. In order to support our study, XPS measurements were performed, from which we have evaluated the Mn3+/Mn4+ ionic ratio.
A large polarization in Ce-modified bismuth ferrite thin films
Authors: Wang Yuanyu
Published: June 2011

Bi0.95Ce0.05FeO3 (BCFO) thin films were grown on SrRuO3/TiO2/SiO2/Si(100) substrates via radio frequency sputtering. The BCFO thin film has a (111) orientation with a high phase purity. Improved dielectric behavior is observed for the BCFO thin film as compared with that of pure bismuth ferrite thin film. A large remanent polarization of 2Pr ∼ 183.9 μC/cm2 is induced in the BCFO thin film, owing to the (111) orientation and the introduction of Ce. The local phase decomposition induced by larger depolarization fields and the oxygen vacancies dominates the fatigue resistance of the BCFO thin film.