| 1. |
-
- 2019
-
Tidskriftsartikel (refereegranskat)
|
|
| 2. |
- Kanoni, Stavroula, et al.
(författare)
-
Implicating genes, pleiotropy, and sexual dimorphism at blood lipid loci through multi-ancestry meta-analysis.
- 2022
-
Ingår i: Genome biology. - : Springer Science and Business Media LLC. - 1474-760X .- 1465-6906 .- 1474-7596. ; 23:1
-
Tidskriftsartikel (refereegranskat)abstract
- Genetic variants within nearly 1000 loci are known to contribute to modulation of blood lipid levels. However, the biological pathways underlying these associations are frequently unknown, limiting understanding of these findings and hindering downstream translational efforts such as drug target discovery.To expand our understanding of the underlying biological pathways and mechanisms controlling blood lipid levels, we leverage a large multi-ancestry meta-analysis (N=1,654,960) of blood lipids to prioritize putative causal genes for 2286 lipid associations using six gene prediction approaches. Using phenome-wide association (PheWAS) scans, we identify relationships of genetically predicted lipid levels to other diseases and conditions. We confirm known pleiotropic associations with cardiovascular phenotypes and determine novel associations, notably with cholelithiasis risk. We perform sex-stratified GWAS meta-analysis of lipid levels and show that 3-5% of autosomal lipid-associated loci demonstrate sex-biased effects. Finally, we report 21 novel lipid loci identified on the X chromosome. Many of the sex-biased autosomal and X chromosome lipid loci show pleiotropic associations with sex hormones, emphasizing the role of hormone regulation in lipid metabolism.Taken together, our findings provide insights into the biological mechanisms through which associated variants lead to altered lipid levels and potentially cardiovascular disease risk.
|
|
| 3. |
- Blunden, Jessica, et al.
(författare)
-
State of the Climate in 2012
- 2013
-
Ingår i: Bulletin of The American Meteorological Society - (BAMS). - 0003-0007 .- 1520-0477. ; 94:8, s. S1-S258
-
Tidskriftsartikel (refereegranskat)abstract
- For the first time in serveral years, the El Nino-Southern Oscillation did not dominate regional climate conditions around the globe. A weak La Ni a dissipated to ENSOneutral conditions by spring, and while El Nino appeared to be emerging during summer, this phase never fully developed as sea surface temperatures in the eastern conditions. Nevertheless, other large-scale climate patterns and extreme weather events impacted various regions during the year. A negative phase of the Arctic Oscillation from mid-January to early February contributed to frigid conditions in parts of northern Africa, eastern Europe, and western Asia. A lack of rain during the 2012 wet season led to the worst drought in at least the past three decades for northeastern Brazil. Central North America also experienced one of its most severe droughts on record. The Caribbean observed a very wet dry season and it was the Sahel's wettest rainy season in 50 years. Overall, the 2012 average temperature across global land and ocean surfaces ranked among the 10 warmest years on record. The global land surface temperature alone was also among the 10 warmest on record. In the upper atmosphere, the average stratospheric temperature was record or near-record cold, depending on the dataset. After a 30-year warming trend from 1970 to 1999 for global sea surface temperatures, the period 2000-12 had little further trend. This may be linked to the prevalence of La Ni a-like conditions during the 21st century. Heat content in the upper 700 m of the ocean remained near record high levels in 2012. Net increases from 2011 to 2012 were observed at 700-m to 2000-m depth and even in the abyssal ocean below. Following sharp decreases in to the effects of La Ni a, sea levels rebounded to reach records highs in 2012. The increased hydrological cycle seen in recent years continued, with more evaporation in drier locations and more precipitation in rainy areas. In a pattern that has held since 2004, salty areas of the ocean surfaces and subsurfaces were anomalously salty on average, while fresher areas were anomalously fresh. Global tropical cyclone activity during 2012 was near average, with a total of 84 storms compared with the 1981-2010 average of 89. Similar to 2010 and 2011, the North Atlantic was the only hurricane basin that experienced above-normal activity. In this basin, Sandy brought devastation to Cuba and parts of the eastern North American seaboard. All other basins experienced either near-or below-normal tropical cyclone activity. Only three tropical cyclones reached Category 5 intensity-all in Bopha became the only storm in the historical record to produce winds greater than 130 kt south of 7 N. It was also the costliest storm to affect the Philippines and killed more than 1000 residents. Minimum Arctic sea ice extent in September and Northern Hemisphere snow cover extent in June both reached new record lows. June snow cover extent is now declining at a faster rate (-17.6% per decade) than September sea ice extent (-13.0% per decade). Permafrost temperatures reached record high values in northernmost Alaska. A new melt extent record occurred on 11-12 July on the Greenland ice sheet; 97% of the ice sheet showed some form of melt, four times greater than the average melt for this time of year. The climate in Antarctica was relatively stable overall. The largest maximum sea ice extent since records begain in 1978 was observed in September 2012. In the stratosphere, warm air led to the second smallest ozone hole in the past two decades. Even so, the springtime ozone layer above Antarctica likely will not return to its early 1980s state until about 2060. Following a slight decline associated with the global 2 emissions from fossil fuel combustion and cement production reached a record 9.5 +/- 0.5 Pg C in 2011 and a new record of 9.7 +/- 0.5 Pg C is estimated for 2012. Atmospheric CO2 concentrations increased by 2.1 ppm in 2012, to 392.6 ppm. In spring 2012, 2 concentration exceeded 400 ppm at 7 of the 13 Arctic observation sites. Globally, other greenhouse gases including methane and nitrous oxide also continued to rise in concentration and the combined effect now represents a 32% increase in radiative forcing over a 1990 baseline. Concentrations of most ozone depleting substances continued to fall.
|
|
| 4. |
- Berndt, Sonja I., et al.
(författare)
-
Genome-wide meta-analysis identifies 11 new loci for anthropometric traits and provides insights into genetic architecture
- 2013
-
Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 45:5, s. 501-U69
-
Tidskriftsartikel (refereegranskat)abstract
- Approaches exploiting trait distribution extremes may be used to identify loci associated with common traits, but it is unknown whether these loci are generalizable to the broader population. In a genome-wide search for loci associated with the upper versus the lower 5th percentiles of body mass index, height and waist-to-hip ratio, as well as clinical classes of obesity, including up to 263,407 individuals of European ancestry, we identified 4 new loci (IGFBP4, H6PD, RSRC1 and PPP2R2A) influencing height detected in the distribution tails and 7 new loci (HNF4G, RPTOR, GNAT2, MRPS33P4, ADCY9, HS6ST3 and ZZZ3) for clinical classes of obesity. Further, we find a large overlap in genetic structure and the distribution of variants between traits based on extremes and the general population and little etiological heterogeneity between obesity subgroups.
|
|
| 5. |
- Speliotes, Elizabeth K., et al.
(författare)
-
Association analyses of 249,796 individuals reveal 18 new loci associated with body mass index
- 2010
-
Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 42:11, s. 937-948
-
Tidskriftsartikel (refereegranskat)abstract
- Obesity is globally prevalent and highly heritable, but its underlying genetic factors remain largely elusive. To identify genetic loci for obesity susceptibility, we examined associations between body mass index and ~2.8 million SNPs in up to 123,865 individuals with targeted follow up of 42 SNPs in up to 125,931 additional individuals. We confirmed 14 known obesity susceptibility loci and identified 18 new loci associated with body mass index (P < 5 × 10−8), one of which includes a copy number variant near GPRC5B. Some loci (at MC4R, POMC, SH2B1 and BDNF) map near key hypothalamic regulators of energy balance, and one of these loci is near GIPR, an incretin receptor. Furthermore, genes in other newly associated loci may provide new insights into human body weight regulation.
|
|
| 6. |
- Heid, Iris M, et al.
(författare)
-
Meta-analysis identifies 13 new loci associated with waist-hip ratio and reveals sexual dimorphism in the genetic basis of fat distribution
- 2010
-
Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 42:11, s. 949-960
-
Tidskriftsartikel (refereegranskat)abstract
- Waist-hip ratio (WHR) is a measure of body fat distribution and a predictor of metabolic consequences independent of overall adiposity. WHR is heritable, but few genetic variants influencing this trait have been identified. We conducted a meta-analysis of 32 genome-wide association studies for WHR adjusted for body mass index (comprising up to 77,167 participants), following up 16 loci in an additional 29 studies (comprising up to 113,636 subjects). We identified 13 new loci in or near RSPO3, VEGFA, TBX15-WARS2, NFE2L3, GRB14, DNM3-PIGC, ITPR2-SSPN, LY86, HOXC13, ADAMTS9, ZNRF3-KREMEN1, NISCH-STAB1 and CPEB4 (P = 1.9 × 10⁻⁹ to P = 1.8 × 10⁻⁴⁰) and the known signal at LYPLAL1. Seven of these loci exhibited marked sexual dimorphism, all with a stronger effect on WHR in women than men (P for sex difference = 1.9 × 10⁻³ to P = 1.2 × 10⁻¹³). These findings provide evidence for multiple loci that modulate body fat distribution independent of overall adiposity and reveal strong gene-by-sex interactions.
|
|
| 7. |
- Lango Allen, Hana, et al.
(författare)
-
Hundreds of variants clustered in genomic loci and biological pathways affect human height.
- 2010
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 1476-4687 .- 0028-0836. ; 467:7317, s. 832-8
-
Tidskriftsartikel (refereegranskat)abstract
- Most common human traits and diseases have a polygenic pattern of inheritance: DNA sequence variants at many genetic loci influence the phenotype. Genome-wide association (GWA) studies have identified more than 600 variants associated with human traits, but these typically explain small fractions of phenotypic variation, raising questions about the use of further studies. Here, using 183,727 individuals, we show that hundreds of genetic variants, in at least 180 loci, influence adult height, a highly heritable and classic polygenic trait. The large number of loci reveals patterns with important implications for genetic studies of common human diseases and traits. First, the 180 loci are not random, but instead are enriched for genes that are connected in biological pathways (P = 0.016) and that underlie skeletal growth defects (P<0.001). Second, the likely causal gene is often located near the most strongly associated variant: in 13 of 21 loci containing a known skeletal growth gene, that gene was closest to the associated variant. Third, at least 19 loci have multiple independently associated variants, suggesting that allelic heterogeneity is a frequent feature of polygenic traits, that comprehensive explorations of already-discovered loci should discover additional variants and that an appreciable fraction of associated loci may have been identified. Fourth, associated variants are enriched for likely functional effects on genes, being over-represented among variants that alter amino-acid structure of proteins and expression levels of nearby genes. Our data explain approximately 10% of the phenotypic variation in height, and we estimate that unidentified common variants of similar effect sizes would increase this figure to approximately 16% of phenotypic variation (approximately 20% of heritable variation). Although additional approaches are needed to dissect the genetic architecture of polygenic human traits fully, our findings indicate that GWA studies can identify large numbers of loci that implicate biologically relevant genes and pathways.
|
|
| 8. |
- Scott, Robert A., et al.
(författare)
-
Large-scale association analyses identify new loci influencing glycemic traits and provide insight into the underlying biological pathways
- 2012
-
Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; 44:9, s. 991-1005
-
Tidskriftsartikel (refereegranskat)abstract
- Through genome-wide association meta-analyses of up to 133,010 individuals of European ancestry without diabetes, including individuals newly genotyped using the Metabochip, we have increased the number of confirmed loci influencing glycemic traits to 53, of which 33 also increase type 2 diabetes risk (q < 0.05). Loci influencing fasting insulin concentration showed association with lipid levels and fat distribution, suggesting impact on insulin resistance. Gene-based analyses identified further biologically plausible loci, suggesting that additional loci beyond those reaching genome-wide significance are likely to represent real associations. This conclusion is supported by an excess of directionally consistent and nominally significant signals between discovery and follow-up studies. Functional analysis of these newly discovered loci will further improve our understanding of glycemic control.
|
|
| 9. |
- Palmer, Nicholette D, et al.
(författare)
-
A genome-wide association search for type 2 diabetes genes in African Americans.
- 2012
-
Ingår i: PloS one. - San Francisco : Public Library of Science (PLoS). - 1932-6203. ; 7:1, s. e29202-
-
Tidskriftsartikel (refereegranskat)abstract
- African Americans are disproportionately affected by type 2 diabetes (T2DM) yet few studies have examined T2DM using genome-wide association approaches in this ethnicity. The aim of this study was to identify genes associated with T2DM in the African American population. We performed a Genome Wide Association Study (GWAS) using the Affymetrix 6.0 array in 965 African-American cases with T2DM and end-stage renal disease (T2DM-ESRD) and 1029 population-based controls. The most significant SNPs (n = 550 independent loci) were genotyped in a replication cohort and 122 SNPs (n = 98 independent loci) were further tested through genotyping three additional validation cohorts followed by meta-analysis in all five cohorts totaling 3,132 cases and 3,317 controls. Twelve SNPs had evidence of association in the GWAS (P<0.0071), were directionally consistent in the Replication cohort and were associated with T2DM in subjects without nephropathy (P<0.05). Meta-analysis in all cases and controls revealed a single SNP reaching genome-wide significance (P<2.5×10(-8)). SNP rs7560163 (P = 7.0×10(-9), OR (95% CI) = 0.75 (0.67-0.84)) is located intergenically between RND3 and RBM43. Four additional loci (rs7542900, rs4659485, rs2722769 and rs7107217) were associated with T2DM (P<0.05) and reached more nominal levels of significance (P<2.5×10(-5)) in the overall analysis and may represent novel loci that contribute to T2DM. We have identified novel T2DM-susceptibility variants in the African-American population. Notably, T2DM risk was associated with the major allele and implies an interesting genetic architecture in this population. These results suggest that multiple loci underlie T2DM susceptibility in the African-American population and that these loci are distinct from those identified in other ethnic populations.
|
|
| 10. |
- Wheeler, Eleanor, et al.
(författare)
-
Impact of common genetic determinants of Hemoglobin A1c on type 2 diabetes risk and diagnosis in ancestrally diverse populations : A transethnic genome-wide meta-analysis
- 2017
-
Ingår i: PLoS Medicine. - : PUBLIC LIBRARY SCIENCE. - 1549-1277 .- 1549-1676. ; 14:9
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Glycated hemoglobin (HbA1c) is used to diagnose type 2 diabetes (T2D) and assess glycemic control in patients with diabetes. Previous genome-wide association studies (GWAS) have identified 18 HbA1c-associated genetic variants. These variants proved to be classifiable by their likely biological action as erythrocytic (also associated with erythrocyte traits) or glycemic (associated with other glucose-related traits). In this study, we tested the hypotheses that, in a very large scale GWAS, we would identify more genetic variants associated with HbA1c and that HbA1c variants implicated in erythrocytic biology would affect the diagnostic accuracy of HbA1c. We therefore expanded the number of HbA1c-associated loci and tested the effect of genetic risk-scores comprised of erythrocytic or glycemic variants on incident diabetes prediction and on prevalent diabetes screening performance. Throughout this multiancestry study, we kept a focus on interancestry differences in HbA1c genetics performance that might influence race-ancestry differences in health outcomes.Methods & findings: Using genome-wide association meta-analyses in up to 159,940 individuals from 82 cohorts of European, African, East Asian, and South Asian ancestry, we identified 60 common genetic variants associated with HbA1c. We classified variants as implicated in glycemic, erythrocytic, or unclassified biology and tested whether additive genetic scores of erythrocytic variants (GS-E) or glycemic variants (GS-G) were associated with higher T2D incidence in multiethnic longitudinal cohorts (N = 33,241). Nineteen glycemic and 22 erythrocytic variants were associated with HbA1c at genome-wide significance. GS-G was associated with higher T2D risk (incidence OR = 1.05, 95% CI 1.04-1.06, per HbA1c-raising allele, p = 3 x 10-29); whereas GS-E was not (OR = 1.00, 95% CI 0.99-1.01, p = 0.60). In Europeans and Asians, erythrocytic variants in aggregate had only modest effects on the diagnostic accuracy of HbA1c. Yet, in African Americans, the X-linked G6PD G202A variant (T-allele frequency 11%) was associated with an absolute decrease in HbA1c of 0.81%-units (95% CI 0.66-0.96) per allele in hemizygous men, and 0.68%-units (95% CI 0.38-0.97) in homozygous women. The G6PD variant may cause approximately 2% (N = 0.65 million, 95% CI0.55-0.74) of African American adults with T2Dto remain undiagnosed when screened with HbA1c. Limitations include the smaller sample sizes for non-European ancestries and the inability to classify approximately one-third of the variants. Further studies in large multiethnic cohorts with HbA1c, glycemic, and erythrocytic traits are required to better determine the biological action of the unclassified variants.Conclusions: As G6PD deficiency can be clinically silent until illness strikes, we recommend investigation of the possible benefits of screening for the G6PD genotype along with using HbA1c to diagnose T2D in populations of African ancestry or groups where G6PD deficiency is common. Screening with direct glucose measurements, or genetically-informed HbA1c diagnostic thresholds in people with G6PD deficiency, may be required to avoid missed or delayed diagnoses.
|
|
| 11. |
- Beal, Jacob, et al.
(författare)
-
Robust estimation of bacterial cell count from optical density
- 2020
-
Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
-
Tidskriftsartikel (refereegranskat)abstract
- Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
|
|
| 12. |
- Bull, Caroline J., et al.
(författare)
-
Adiposity, metabolites, and colorectal cancer risk : Mendelian randomization study
- 2020
-
Ingår i: BMC Medicine. - : BMC. - 1741-7015. ; 18:1
-
Tidskriftsartikel (refereegranskat)abstract
- Background Higher adiposity increases the risk of colorectal cancer (CRC), but whether this relationship varies by anatomical sub-site or by sex is unclear. Further, the metabolic alterations mediating the effects of adiposity on CRC are not fully understood. Methods We examined sex- and site-specific associations of adiposity with CRC risk and whether adiposity-associated metabolites explain the associations of adiposity with CRC. Genetic variants from genome-wide association studies of body mass index (BMI) and waist-to-hip ratio (WHR, unadjusted for BMI; N = 806,810), and 123 metabolites from targeted nuclear magnetic resonance metabolomics (N = 24,925), were used as instruments. Sex-combined and sex-specific Mendelian randomization (MR) was conducted for BMI and WHR with CRC risk (58,221 cases and 67,694 controls in the Genetics and Epidemiology of Colorectal Cancer Consortium, Colorectal Cancer Transdisciplinary Study, and Colon Cancer Family Registry). Sex-combined MR was conducted for BMI and WHR with metabolites, for metabolites with CRC, and for BMI and WHR with CRC adjusted for metabolite classes in multivariable models. Results In sex-specific MR analyses, higher BMI (per 4.2 kg/m(2)) was associated with 1.23 (95% confidence interval (CI) = 1.08, 1.38) times higher CRC odds among men (inverse-variance-weighted (IVW) model); among women, higher BMI (per 5.2 kg/m(2)) was associated with 1.09 (95% CI = 0.97, 1.22) times higher CRC odds. WHR (per 0.07 higher) was more strongly associated with CRC risk among women (IVW OR = 1.25, 95% CI = 1.08, 1.43) than men (IVW OR = 1.05, 95% CI = 0.81, 1.36). BMI or WHR was associated with 104/123 metabolites at false discovery rate-corrected P <= 0.05; several metabolites were associated with CRC, but not in directions that were consistent with the mediation of positive adiposity-CRC relations. In multivariable MR analyses, associations of BMI and WHR with CRC were not attenuated following adjustment for representative metabolite classes, e.g., the univariable IVW OR for BMI with CRC was 1.12 (95% CI = 1.00, 1.26), and this became 1.11 (95% CI = 0.99, 1.26) when adjusting for cholesterol in low-density lipoprotein particles. Conclusions Our results suggest that higher BMI more greatly raises CRC risk among men, whereas higher WHR more greatly raises CRC risk among women. Adiposity was associated with numerous metabolic alterations, but none of these explained associations between adiposity and CRC. More detailed metabolomic measures are likely needed to clarify the mechanistic pathways.
|
|
| 13. |
- Kabir, Mohammad, 1974, et al.
(författare)
-
Fabrication of individual, vertically aligned carbon nanofibres on metal substrates from prefabricated catalyst dots
- 2006
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 17:3, s. 790-794
-
Tidskriftsartikel (refereegranskat)abstract
- Carbon nanofibres (CNFs) of controlled diameter and length were grown on different metal substrates using plasma-enhanced chemical vapour deposition (PECVD). The diameter control of catalyst dots (and hence CNF diameter) was obtained by using the shot modulation technique in electron beam lithography. Catalyst dots of different sizes within arrays of different pitch were prepared and the dependence of the growth of vertically aligned CNFs on these parameters was studied for different metal underlayers. Good quality vertically aligned CNFs with a narrow length distribution were grown on Mo and W substrates. The structures grown on Nb substrates were significantly shorter for identical growth conditions and showed a lower nucleation rate. We demonstrate that through the shot modulation technique it is possible to control the diameter variation of CNFs from a single design geometry for the catalyst deposition. Individual VACNFs can be grown down to a pitch within the range 100–500 nm.
|
|
| 14. |
- Kim, B., et al.
(författare)
-
Electrical transport measurement of molecular device fabricated by electrochemical deposition of platinum electrode
- 2006
-
Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090. ; 499, s. 196-200
-
Tidskriftsartikel (refereegranskat)abstract
- Electrical properties of 1,4-benzenedimethanethiol are measured using the electrochemically deposited platinum electrode as one of contact lead to the molecule. Temperature dependence of current-voltage characteristics were measured from room temperature to 27 K. Fowler–Nordheim type tunneling conduction below 40 K and current fluctuation at low temperature were observed. The fluctuating behavior can be understood as electromigration and/or thermal vibration of platinum atoms at the contact between the molecule and the platinum electrode.
|
|
| 15. |
|
|
| 16. |
- Lee, SangWook, et al.
(författare)
-
Fabrication and mechanical properties of suspended one-dimensional polymer nanostructures: polypyrrole nanotube and helical polyacetylene nanofibre
- 2006
-
Ingår i: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 17, s. 992-996
-
Tidskriftsartikel (refereegranskat)abstract
- Mechanical properties of suspended quasi-one-dimensional polymer nanostructures were investigated using atomic force microscopy (AFM). A recently developed new acid-free etch method combined with electron beam lithography was used to fabricate suspended polypyrrole (PPy) nanotubes and helical polyacetylene (HPA) nanofibres. The elastic modulus of each suspended structure was obtained by AFM force–distance measurements. The estimated modulus value of the PPy nanotube (HPA nanofibre) was 0.96 GPa (0.5 GPa). Using this acid-free method, all-organic flexible NEMS devices can be fabricated in the future.
|
|
| 17. |
|
|
| 18. |
|
|
| 19. |
- Yao, Yiming, 1957, et al.
(författare)
-
Nucleation and aligned growth of multi-wall carbon nanotube films during thermal CVD
- 2007
-
Ingår i: Carbon. - : Elsevier BV. - 0008-6223. ; 45, s. 2065-2071
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The development during early growth of a multi-wall carbon nanotube film by thermal CVD with acetylene (C2H2) and hydrogen at 750 °C has been characterized in detail by cross-section transmission electron microscopy. The studies provide information on the nanotube growth mechanisms and the complex catalyst transformations that are essential for the onset of different growth stages. An initial random growth catalysed by supported particles is followed by aerosol growth of aligned tubes. This results in a two-layered film structure, where a film of aligned nanotubes is lifting up an initially formed nanotube network from the substrate.
|
|
| 20. |
|
|
| 21. |
- Yu, H.Y., et al.
(författare)
-
Current enhancement with alternating gate voltage in the Coulomb blockade regime of a single wall carbon nanotube
- 2004
-
Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 79, s. 1613-1615
-
Tidskriftsartikel (refereegranskat)abstract
- We investigated the current–voltage characteristics of a carbon nanotube in a single electron transistor structure with alternating gate voltage. A continuous current enhancement effect with increasing frequency of the applied gate voltage up to 13 MHz is reported. Assuming that I=nef, more than 1000 electrons are driven to flow across the source–drain channel at VDS=100 mV, 13 MHz of gate voltage (Vp-p=2 V) and T=1.8 K. The continuous current enhancement is explained by the broadening effect of the discrete energy levels of the finite-length carbon nanotube.
|
|
| 22. |
- Axelsson, S., et al.
(författare)
-
Theoretical and experimental investigations of three-terminal carbon nanotube nanorelays
- 2005
-
Ingår i: New J. Phys. - : IOP Publishing. - 1367-2630. ; 7
-
Tidskriftsartikel (refereegranskat)abstract
- We present theoretical and experimental investigations of three-terminal nanoelectromechanical relays based on suspended carbon nanotubes. A charge is induced in the nanotube by applying a voltage to an underlying gate electrode thus inducing the nanotube to bend and make contact with a drain electrode. Such devices have potential applications as fast switches, logic devices, memory elements and pulse generators. We describe two modes of operation: a contact mode where the nanotube makes physical contact with the drain electrode and a non-contact mode where electrical contact between the nanotube and the drain electrode is made via a field emission current.
|
|
| 23. |
- Bengtsson, Stefan, 1961, et al.
(författare)
-
Carbon-based nanoelectromechanical devices
- 2011
-
Ingår i: International Journal of High Speed Electronics and Systems. - 1793-6438. ; 20:1, s. 195-204
-
Tidskriftsartikel (refereegranskat)abstract
- Carbon-based nanoelectromechanical devices are approaching applications in electronics. Switches based on individual carbon nanotubes deliver record low off-state leakage currents. Arrays of vertically aligned carbon nanotubes or nanofibers can be fabricated to constitute varactors. Very porous, low density arrays of quasi-vertically aligned arrays of carbon nanotubes behave mechanically as a single unit with very unusual material properties.
|
|
| 24. |
|
|
| 25. |
- Boyle, Mark, et al.
(författare)
-
Excitation dynamics of Rydberg states in C60
- 2005
-
Ingår i: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 36, s. 339-351
-
Tidskriftsartikel (refereegranskat)abstract
- The electron and nuclear dynamics of C60 fullerenes irradiated with femtosecond laser pulses are investigated with photoelectron and photoion spectroscopy. The focus of this work is the detailed exploration of the population mechanism of Rydberg levels within the excitation process of neutral C60. The effect of excitation wavelength, intensity, chirp, and polarization on the kinetic energy distribution of photoelectrons in single-pulse experiments gives first insight into the underlying processes. In combination with time-resolved two-color pump-probe spectroscopy depending on either pump, or probe pulse intensity, a more complete picture of the interaction can be drawn. The results point towards a very interesting but nevertheless complex behavior including four steps: (i) non-adiabatic multielectron excitation of the HOMO (hu) → LUMO+1 (t1g) transition; (ii) thermalization within the hot electron cloud on a time scale below 100fs, followed by a coupling of energy to vibrational modes of the molecule via doorway state(s); (iii) population of electronically excited Rydberg states by multiphoton absorption, and (iv) single photon ionization from the excited Rydberg states. This excitation process results in a characteristic sequence of photoelectron lines in the photoemission spectra. The comparison of the experimental results with recent theoretical work gives convincing evidence that non-adiabatic multielectron dynamics (NMED) plays a key role for the understanding of the response of C60 to short-pulse laser radiation.
|
|
| 26. |
- Boyle, Mark, et al.
(författare)
-
Two colour pump-probe study and internal energy dependence of Rydberg state excitation
- 2004
-
Ingår i: Physical Review A. - 1050-2947. ; 70
-
Tidskriftsartikel (refereegranskat)abstract
- Excitation of Rydberg states in isolated C60 is studied by time-resolved photoelectron spectroscopy in a femtosecond two-color pump-probe experiment. The relaxation time for electron-electron interaction is determined to be approximately 100 fs with the t1g(LUMO + 1) orbital being considered to define the doorway state in a nonadiabatic multielectron excitation process. The internal energy stored in vibrational modes of the C60 at 770 K is found to support the excitation process very efficiently while in "cold" C60 (80 K), no significant Rydberg population is detected.
|
|
| 27. |
- Bulgakov, Alexander, 1956, et al.
(författare)
-
Phosphorus cluster production by laser ablation
- 2004
-
Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 79, s. 1369-1372
-
Tidskriftsartikel (refereegranskat)abstract
- Neutral and charged phosphorus clusters of a wide size range have been produced by pulsed laser ablation (PLA) in vacuum at 532, 337, and 193 nm ablating wavelengths and investigated by time-of-flight mass spectrometry. The neutral Pn clusters are even-numbered with local abundance maxima at n=10 and 14, while the cationic and anionic clusters are preferentially odd-numbered with P7+, P21+, and P17- being the most abundant ions. The dominance of the magic clusters is more pronounced at 337-nm ablation that is explained by efficient direct ejection of their building blocks under these conditions. Nanocrystalline phosphorus films have been produced by PLA in ambient helium gas.
|
|
| 28. |
|
|
| 29. |
- Bulgakova, Nadya, 1956, et al.
(författare)
-
A general continuum approach to describe fast electronic transport in pulsed laser irradiated materials: the problem of Coulomb explosion
- 2005
-
Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 81, s. 345-356
-
Tidskriftsartikel (refereegranskat)abstract
- We present a continuum model, based on a drift-diffusion approach, aimed at describing the dynamics of electronic excitation, heating, and charge-carrier transport in different materials (metals, semiconductors, and dielectrics) under femtosecond and nanosecond pulsed laser irradiation. The laser-induced charging of the targets is investigated at laser intensities above the material removal threshold. It is demonstrated that, for near-infrared femtosecond irradiation, charging of dielectric surfaces causes a sub-picosecond electrostatic rupture of the superficial layers, alternatively called Coulomb explosion (CE), while this effect is strongly inhibited for metals and semiconductors as a consequence of superior carrier transport properties. On the other hand, application of the model to UV nanosecond pulsed laser interaction with bulk silicon has pointed out the possibility of Coulomb explosion in semiconductors. For such regimes a simple analytical theory for the threshold laser fluence of CE has been developed, showing results in agreement with the experimental observations. Various related aspects concerning the possibility of CE depending on different irradiation parameters (fluence, wavelength and pulse duration) and material properties are discussed. This includes the temporal and spatial dynamics of charge-carrier generation in non-metallic targets and evolution of the reflection and absorption characteristics.
|
|
| 30. |
- Bulgakova, Nadya, 1956, et al.
(författare)
-
Electronic transport and consequences for material removal in ultrafst pulsed laser ablation of materials
- 2004
-
Ingår i: Physical Review B. - 1098-0121. ; 69
-
Tidskriftsartikel (refereegranskat)abstract
- Fast electronic transport is investigated theoretically based on a drift-diffusion approach for different classes of materials (metals, semiconductors, and dielectrics) under ultrafast, pulsed laser irradiation. The simulations are performed at intensities above the material removal threshold, characteristic for the ablation regime. The laser-induced charging of dielectric surfaces causes a subpicosecond electrostatic rupture of the superficial layers, an effect which, in comparison, is strongly inhibited for metals and semiconductors as a consequence of superior carrier transport properties.
|
|
| 31. |
- Bulgakova, Nadya, 1956, et al.
(författare)
-
Model description of surface charging during ultrafast pulsed laser ablationof materials
- 2004
-
Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 79, s. 1153-1155
-
Tidskriftsartikel (refereegranskat)abstract
- We present a model describing the dynamical mechanisms responsible for generating fast ion ejection under ultra-short pulsed laser irradiation. The model is based on a simplified drift–diffusion approach describing the evolution of the laser-generated charge carriers, their transport, and the electric field generated as a result of quasi-neutrality breaking in the irradiated target. The importance of different processes in generating the non-thermal material-ejection mechanisms is discussed. A common frame is applied to dielectrics, semiconductors, and metals and different dynamical behaviour is observed. The modelling results are in good agreement with fs pump–probe studies and measurements of the velocity distributions of the emitted ions.
|
|
| 32. |
- Bulgakova, Nadya, 1956, et al.
(författare)
-
Possible role of charge transport in enhanced carbon nanotube growth
- 2006
-
Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 85, s. 109-116
-
Tidskriftsartikel (refereegranskat)abstract
- We consider the role of electric fields during metal-catalysed thermal chemical vapour deposition growth of carbon nanotubes and show that enhanced growth occurs from a negatively biased electrode. An electric field, applied externally to the growing tubes and/or generated as a result of electron emission or self-biasing, may strongly affect the carbon supply through the catalyst nanoparticle, enhancing the growth rate. Different aspects of the growth process are analysed: the nature of the nanoparticle catalysis, carbon dissolution kinetics, electron emission from the nanotube tips, charge transport in the nanotube-catalytic nanoparticle system and carbon drift and diffusion through the catalyst under the action of the electric field. A fundamental tenet for modelling of charge-transport dynamics during the nanotube growth process is proposed.
|
|
| 33. |
- Bulgakova, Nadya, 1956, et al.
(författare)
-
Surface charging under pulsed laser ablation of solids and its consequences: studies with a continuum approach
- 2005
-
Ingår i: SPIE Proceedings. - : SPIE. - 0277-786X. ; 5714, s. 9-23
-
Tidskriftsartikel (refereegranskat)abstract
- Dynamics of electronic excitation, heating and charge-carrier transport in different materials (metals, semiconductors, and dielectrics) under femtosecond pulsed laser irradiation is studied based on a unified continuum model. A simplified drift-diffusion approach is used to model the energy flow into the sample in the first hundreds of femtoseconds of the interaction. The laser-induced charging of the targets is investigated at laser intensities slightly above the material removal threshold. It is demonstrated that, under near-infrared femtosecond irradiation regimes, charging of dielectric surfaces causes a sub-picosecond electrostatic rupture of the superficial layers, alternatively called Coulomb explosion (CE), while this effect is strongly inhibited for metals and semiconductors as a consequence of superior carrier transport properties. Various related aspects concerning the possibility of CE for different irradiation parameters (fluence, wavelength and pulse duration) as well as the limitations of the model are discussed. These include the temporal and spatial dynamics of charge-carrier generation in non-metallic targets and evolution of the optical (reflection and absorption) characteristics. A controversial topic concerning CE probability in laser irradiated semiconductor targets is also a subject of this work.
|
|
| 34. |
- Campbell, Eleanor E B, 1960, et al.
(författare)
-
Ionisation of Fullerenes and Fullerene Clusters using Ultrashort Laser Pulses
- 2006
-
Ingår i: Photochem. Photobiol. Sci.. - : Springer Science and Business Media LLC. - 1474-905X. ; 5, s. 1183-1189
-
Tidskriftsartikel (refereegranskat)abstract
- We give a brief review of the literature concerning the ultra-short pulse ionisation of fullerenes in the gas phase. Emphasis is placed on the excitation time dependence of different ionisation regimes as manifested by photoelectron spectroscopy. The ionisation rates are modelled for the intermediate situation where the excitation energy is equilibrated between electronic degrees of freedom but not yet coupled to vibrational degrees of freedom. The model is shown to describe many aspects of the experiments. New results are presented on the intra-cluster molecular fusion of fullerene molecules when van der Waals bound clusters of fullerenes are exposed to ultra-short laser pulses. Pump–probe measurements give a decay time constant for the intra-cluster fusion reaction of 520 ± 55 fs. A comparison with monomer ionisation results suggests that the time window for the fusion reaction is influenced by the coupling of the electronic excitation energy to vibrational degrees of freedom of the molecules in the cluster.
|
|
| 35. |
- Campbell, Eleanor E B, 1960
(författare)
-
Nanotuben - elektronikens hopp
- 2004
-
Ingår i: Forskning och Framsteg. - 0015-7937. ; :7, s. 20-23
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
|
|
| 36. |
- Ding, Feng, 1970, et al.
(författare)
-
Graphitic encapsulation of catalyst particles in carbon nanotube production
- 2006
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 110:15, s. 7666-7670
-
Tidskriftsartikel (refereegranskat)abstract
- A new model is proposed for the encapsulation of catalyst metal particles by graphite layers that are obtained, for example, in low-temperature chemical vapor deposition production of carbon nanotubes (CNTs). In this model graphite layers are primarily formed from the dissolved carbon atoms in the metal-carbide particle when the particle cools. This mechanism is in good agreement with molecular dynamics simulations (which show that precipitated carbon atoms preferentially form graphite sheets instead of CNTs at low temperatures) and experimental results (e.g., encapsulated metal particles are found in low-temperature zones and CNTs in high-temperature regions of production apparatus, very small catalyst particles are generally not encapsulated, and the ratio of the number of graphitic layers to the diameter of the catalyst particle is typically 0.25 nm(-1)).
|
|
| 37. |
- Dittmer, Staffan, 1970, et al.
(författare)
-
Electric field aligned growth of single-walled nanotubes
- 2004
-
Ingår i: Current Applied Physics. - : Elsevier BV. - 1567-1739. ; 4, s. 595-598
-
Tidskriftsartikel (refereegranskat)abstract
- Electric field aligned, single-walled carbon nanotubes are grown between electrodes using thermal chemical vapour deposition (CVD) of methane. The growth occurs on a thin film layered catalyst of aluminium, iron and molybdenum patterned on top of electrodes. The nanotubes bridge 10 μm sized electrode gaps and have a typical diameter of less than 2 nm as measured by Raman spectroscopy and atomic force microscopy. We present electrical transport measurements on a directly grown nanotube which shows p-type semiconducting behaviour.
|
|
| 38. |
|
|
| 39. |
- Dittmer, Staffan, 1970, et al.
(författare)
-
In situ Raman studies of single-walled carbon nanotubes grown by local
- 2008
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 457
-
Tidskriftsartikel (refereegranskat)abstract
- Using in situ Raman spectroscopy we investigate single wall carbon nanotube growth on Mo electrodes, using a highly localized resistive heating technique. Small diameter semiconducting single wall nanotubes grow very rapidly when the catalyst support is heated to a temperature of 800 C. The G/D ratio shows an interesting time-dependent behaviour. It first decreases, indicating the presence of amorphous carbon and then significantly increases again after ca. 5 min growth while retaining the position and shape expected for predominantly semiconducting carbon nanotubes.
|
|
| 40. |
- Dittmer, Staffan, 1970, et al.
(författare)
-
Local heating method for growth of aligned carbon nanotubes at low ambient temperature
- 2008
-
Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 34:10, s. 834-838
-
Tidskriftsartikel (refereegranskat)abstract
- We use a highly localised resistive heating technique to grow vertically aligned multiwalled nanotube films and aligned single-walled nanotubes on substrates with an average temperature of less than 100oC. The temperature at the catalyst can easily be as high as 1000 oC but an extremely high temperature gradient ensures that the surrounding chip is held at much lower temperatures, even as close as 1μm away from the local heater. We demonstrate the influence of temperature on the height of multi-walled nanotube films, illustrate the feasibility of sequential growth of single-walled nanotubes by switching between local heaters and also show that nanotubes can be grown over temperature sensitive materials such as resist polymer.
|
|
| 41. |
- Dittmer, Staffan, 1970, et al.
(författare)
-
Low ambient temperature CVD growth of carbon nanotubes
- 2006
-
Ingår i: Applied Physics A. - : Springer Science and Business Media LLC. - 0947-8396 .- 1432-0630. ; 84, s. 243-246
-
Tidskriftsartikel (refereegranskat)abstract
- We show that good quality single-walled and multi-walled carbon nanotubes can be grown on CMOS-compatible metal electrodes at ambient room temperature using highly localised catalyst heating at nanostructured electrodes. The method is relatively straightforward and allows considerable flexibility in the kinds of devices that can be fabricated as well as allowing CVD nanotube growth to take place in the close vicinity of temperature-sensitive materials and devices.
|
|
| 42. |
- Dong Su, Lee, et al.
(författare)
-
Quantum dot manipulation in a single-walled carbon nanotube using a carbon nanotube gate
- 2006
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 89:23, s. 233107-1
-
Tidskriftsartikel (refereegranskat)abstract
- Cross junctions of carbon nanotubes (CNTs) separated by thin oxide layers have been fabricated, in which the top CNT is used as a local gate to control the electron transport through the lower CNT. Coulomb oscillation was observed in the lower CNTs at low temperatures. The gating field from the upper CNTs is seen to modulate the band structure in the lower CNTs, producing double quantum dot systems. The ability to modulate the electronic structure of CNTs in such a way opens up many possibilities for future electronic and logical nanodevices
|
|
| 43. |
- Eriksson, Anders, 1975, et al.
(författare)
-
Direct Transmission Detection of Tunable Mechanical Resonance in an Individual Carbon Nanofiber Relay
- 2008
-
Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- A direct on-chip transmission measurement of the resonance frequency of an individual singly clamped carbon nanofiber relay is reported. The experimental results are in good agreement with a small signal model and show the expected tuning of the resonance frequency with changing bias voltage.
|
|
| 44. |
- Gromov, Andrei, 1959, et al.
(författare)
-
Covalent Amino functionalisation of single walled carbon nanotubes
- 2005
-
Ingår i: J. Materials Chem. - : Royal Society of Chemistry (RSC). - 0959-9428 .- 1364-5501. ; 15, s. 3334-3339
-
Tidskriftsartikel (refereegranskat)abstract
- Chemical transformation of single-wall carbon nanotubes (SWNT), edge-terminated with carboxylic groups, to SWNT species with amino groups directly attached to the tube open ends has been performed. Different synthetic approaches have been investigated. The reaction products were characterised by FTIR, Raman spectroscopy, XPS and SEM.
|
|
| 45. |
- Hansen, Klavs, 1958, et al.
(författare)
-
Competition between fusion and intra-cluster fusion in highly excited fullerene clusters
- 2007
-
Ingår i: Israel Journal of Chemistry. - 0021-2148. ; 47
-
Tidskriftsartikel (refereegranskat)abstract
- The occurrence of intra-cluster fusion of fullerene molecules inside van der Waals bound fullerene clusters can be observed following femtosecond laser excitation. We show that the fusion reaction competes with the fission of multiply charged clusters. Energetic barriers to the reaction of at least 85 eV have to be overcome, similar to the energetic barriers to molecular fusion observed in fullerene ion–neutral fullerene collision experiments.
|
|
| 46. |
- Hansen, Klavs, 1958, et al.
(författare)
-
Do we know the value of the Gspann parameter?
- 2004
-
Ingår i: Int.J.Mass Spectrom.. - : Elsevier BV. - 1387-3806. ; 233, s. 215-221
-
Tidskriftsartikel (refereegranskat)abstract
- We reanalyze some of the data used by Klots to establish an experimental basis for the claim by Gspann that clusters have a highest temperature in molecular beams. The value of this temperature is given by the evaporative activation energy and a dimensionless parameter called the Gspann parameter. The value of the Gspann parameter we derive from the data is higher than the value found by Klots, and is consistent with the predictions from detailed balance theory, although a number of uncertainties persist. More recent data on oxygen clusters are analyzed with the same methods and the model dependent uncertainties are shown to be fairly large.
|
|
| 47. |
- Hansen, Klavs, 1958, et al.
(författare)
-
ISSPIC13 proceedings - Preface
- 2007
-
Ingår i: Eur.Phys.J D. - 1434-6060. ; 43
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
|
|
| 48. |
- Hansen, Klavs, 1958, et al.
(författare)
-
Laser power dependence in femtosecond ionization of fullerenes
- 2005
-
Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 42, s. 282-285
-
Tidskriftsartikel (refereegranskat)abstract
- Fullerene ionization can under some circumstances be modelled as thermal emission of electrons from a transiently hot electron gas. Application of this idea to experiments involving femtosecond lasers gave theoretical evidence for ion yields that would vary with the pulse energy of the laser to some power, identical to the behavior seen in multi-photon experiments. The reason for this behavior is investigated here. The crucial component is identified as the Poisson statistics for photon absorption and a strong variation of the ion yield with energy.
|
|
| 49. |
- Hansen, Klavs, 1958, et al.
(författare)
-
The frequency factor in statistical fullerene decay
- 2006
-
Ingår i: Int. J. Mass Spec.. - : Elsevier BV. - 1387-3806. ; 252, s. 79-95
-
Tidskriftsartikel (refereegranskat)abstract
- Experiments on fullerene decay are reviewed and the frequency factor for C2 emission is extracted. The value is also calculated theoretically. Inclusion of a number of previously disregarded degrees of freedom for the products increase the theoretical estimate for C60 to above 1020 s−1, in good agreement with experimental results.
|
|
| 50. |
- Hedén, Martin, 1976, et al.
(författare)
-
Determination of the triplet state lifetime of vibrationally excited C-60
- 2003
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 118:16, s. 7161-7164
-
Tidskriftsartikel (refereegranskat)abstract
- The lifetime of the ground triplet state of vibrationally excited C-60 has been determined in a two-color pump-probe experiment. An intense pump pulse (337 nm, 4 ns) was used to excite the neutral molecules. The triplet state was probed via single photon ionization with a weak probe pulse (193 nm). The lifetime was found to be on the order of 1 mus. This is rather low to explain recent delayed ionization results but higher than expected from an extrapolation of earlier measurements at lower temperatures. (C) 2003 American Institute of Physics.
|
|
