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Determination of the Bending Rigidity of Graphene via Electrostatic Actuation of Buckled Membranes
Lindahl, Niklas,Midtvedt, Daniel,Svensson, Johannes,Nerushev, Oleg A.,Lindvall, Niclas,Isacsson, Andreas,Campbell, Eleanor E. B. American Chemical Society 2012 Nano letters Vol.12 No.7
<P>Classical continuum mechanics is used extensively to predict the properties of nanoscale materials such as graphene. The bending rigidity, κ, is an important parameter that is used, for example, to predict the performance of graphene nanoelectromechanical devices and also ripple formation. Despite its importance, there is a large spread in the theoretical predictions of κ for few-layer graphene. We have used the snap-through behavior of convex buckled graphene membranes under the application of electrostatic pressure to determine experimentally values of κ for double-layer graphene membranes. We demonstrate how to prepare convex-buckled suspended graphene ribbons and fully clamped suspended membranes and show how the determination of the curvature of the membranes and the critical snap-through voltage, using AFM, allows us to extract κ. The bending rigidity of bilayer graphene membranes under ambient conditions was determined to be 35.5<SUB>–15.0</SUB><SUP>+20.0</SUP> eV. Monolayers are shown to have significantly lower κ than bilayers.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2012/nalefd.2012.12.issue-7/nl301080v/production/images/medium/nl-2012-01080v_0001.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl301080v'>ACS Electronic Supporting Info</A></P>
Spatial and temporal distribution of Pu in the Northwest Pacific Ocean using modern coral archives
Lindahl, Patric,Andersen, Morten B.,Keith-Roach, Miranda,Worsfold, Paul,Hyeong, Kiseong,Choi, Min-Seok,Lee, Sang-Hoon Elsevier 2012 Environment international Vol.40 No.-
<P><B>Abstract</B></P> <P>Historical <SUP>239</SUP>Pu activity concentrations and <SUP>240</SUP>Pu/<SUP>239</SUP>Pu atom ratios were determined in skeletons of dated modern corals collected from three locations (Chuuk Lagoon, Ishigaki Island and Iki Island) to identify spatial and temporal variations in Pu inputs to the Northwest Pacific Ocean. The main Pu source in the Northwest Pacific is fallout from atmospheric nuclear weapons testing which consists of global fallout and close-in fallout from the former US Pacific Proving Grounds (PPG) in the Marshall Islands. PPG close-in fallout dominated the Pu input in the 1950s, as was observed with higher <SUP>240</SUP>Pu/<SUP>239</SUP>Pu atom ratios (>0.30) at the Ishigaki site. Specific fallout Pu contamination from the Nagasaki atomic bomb and the Ivy Mike thermonuclear detonation at the PPG were identified at Ishigaki Island from the <SUP>240</SUP>Pu/<SUP>239</SUP>Pu atom ratios of 0.07 and 0.46, respectively. During the 1960s and 1970s, global fallout was the major Pu source to the Northwest Pacific with over 60% contribution to the total Pu. After the cessation of the atmospheric nuclear tests, the PPG again dominated the Pu input due to the continuous transport of remobilised Pu from the Marshall Islands along the North Equatorial Current and the subsequent Kuroshio Current. The Pu contributions from the PPG in recent coral bands (1984 onwards) varied over time with average estimated PPG contributions between 54% and 72% depending on location.</P> <P><B>Highlights</B></P> <P>► Low levels of Pu isotopes determined in dated NW Pacific coral samples. ► Contribution from different Pu sources estimated. ► Unusual high <SUP>240</SUP>Pu/<SUP>239</SUP>Pu ratio of 0.46 is attributed to 1952 Ivy Mike detonation. ► Identified Pu contribution from the Nagasaki atomic bomb.</P>
Lindahl, P.,Asami, R.,Iryu, Y.,Worsfold, P.,Keith-Roach, M.,Choi, M.S. Pergamon Press ; Elsevier Science Ltd 2011 Geochimica et cosmochimica acta Vol.75 No.5
The Pu isotopes, <SUP>239</SUP>Pu and <SUP>240</SUP>Pu, were determined in annually-banded skeletons of an accurately dated (1943-1999) modern coral (Porites lobata) from Guam Island to identify historical Pu sources to the tropical Northwest Pacific Ocean. Activity concentrations of <SUP>239+240</SUP>Pu and <SUP>240</SUP>Pu/<SUP>239</SUP>Pu atom ratios were determined in the dated coral bands using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Close-in fallout from the former US Pacific Proving Grounds (PPG) in the Marshall Islands and global fallout were identified as the two main sources. The Guam site was dominated by PPG close-in fallout in the 1950s, with an average <SUP>240</SUP>Pu/<SUP>239</SUP>Pu atom ratio of 0.315+/-0.005. In addition, a higher <SUP>240</SUP>Pu/<SUP>239</SUP>Pu atom ratio (0.456+/-0.020) was observed that could be attributed to fallout from the ''Ivy Mike'' thermonuclear detonation in 1952. The atom ratio decreased in the 1960s and 1970s due to increase in the global fallout with a low <SUP>240</SUP>Pu/<SUP>239</SUP>Pu atom ratio (∼0.18). Recent coral bands (1981-1999) are dominated by the transport of remobilised Pu, with high <SUP>240</SUP>Pu/<SUP>239</SUP>Pu atom ratios, from the Marshall Islands to Guam Island along the North Equatorial Current (NEC). This remobilised Pu was estimated to comprise 69% of the total Pu in the recent coral bands, although its contribution was variable over time.
EPR Studies of the Active Sites of Carbon Monoxide Dehydrogenase from Clostridium thermoaceticum
Shin, Woonsup,Lindahl, Paul A. 한국분석과학회 1995 분석과학 Vol.8 No.4
The active sites of the nickel and iron-containing enzyme, carbon monoxide dehydrogenase (CODH) from clostridium thermoaceticum were investigated using Electron Paramagnetic Resonance (EPR) technique. CODH exhibits several spectral features called NiFeC, $g_{ave}=1.82$, $g_{ave}=1.86$. FCII signals which are originated from different clusters in this enzyme. CODH is know to catalyze two different kinds of reactions - acetyl-CoA synthesis and CO oxidation. The acetyl-CoA synthesis activity can be followed by monitoring CO/acetyl-CoA exchange. The addition of 1,10-phenanthroline (phen) to CODH selectively destroyed the CO/acetyl-CoA exchange activity and eliminated the NiFeC signal completely. CO oxidation activity and other EPR signals were unaffected. Such behavior demonstrates that CODH has two distinct active sites and that the NiFe complex is only responsible for the CO/acctyl-CoA exchange activity. Phen caused the removal of only 30% of Ni in the NiFe complex ($0.3Ni/{\alpha}{\beta}$) as shown by the quantitative metal analysis. The phen-treated CODH could be reactivated fully by incubation In $Ni^{2+}$ solution. Radioactive $^{63}Ni^{2+}$ was used to quantitate the amount of the $Ni^{2+}$ incorporated into phen-treated enzyme and showed that the amount was the same as the removed by the phen treatment. i.e. $0.3Ni/{\alpha}{\beta}$. This indicates that only 30% of NiFe complexes are labile and responsible for the CO/acctyl-CoA exchange activity, the other 70% are non-labile and have no exchange activity. This is the first clear evidence that the NiFe complex is heterogencous and labile and non-labile Ni sites arc interacting differently with substrates and chelating agents like phen.
Carbon nanotube field effect transistors with suspended graphene gates.
Svensson, Johannes,Lindahl, Niklas,Yun, Hoyeol,Seo, Miri,Midtvedt, Daniel,Tarakanov, Yury,Lindvall, Niclas,Nerushev, Oleg,Kinaret, Jari,Lee, Sangwook,Campbell, Eleanor E B American Chemical Society 2011 Nano letters Vol.11 No.9
<P>Novel field effect transistors with suspended graphene gates are demonstrated. By incorporating mechanical motion of the gate electrode, it is possible to improve the switching characteristics compared to a static gate, as shown by a combination of experimental measurements and numerical simulations. The mechanical motion of the graphene gate is confirmed by using atomic force microscopy to directly measure the electrostatic deflection. The device geometry investigated here can also provide a sensitive measurement technique for detecting high-frequency motion of suspended membranes as required, e.g., for mass sensing.</P>
Free-Standing 3D-Sponged Nanofiber Electrodes for Ultrahigh-Rate Energy-Storage Devices
Agostini, Marco,Lim, Du Hyun,Brutti, Sergio,Lindahl, Niklas,Ahn, Jou Hyeon,Scrosati, Bruno,Matic, Aleksandar American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.40
<P>We have designed a self-standing anode built-up from highly conductive 3D-sponged nanofibers, that is, with no current collectors, binders, or additional conductive agents. The small diameter of the fibers combined with an internal spongelike porosity results in short distances for lithium-ion diffusion and 3D pathways that facilitate the electronic conduction. Moreover, functional groups at the fiber surfaces lead to the formation of a stable solid-electrolyte interphase. We demonstrate that this anode enables the operation of Li-cells at specific currents as high as 20 A g<SUP>-1</SUP> (approx. 50C) with excellent cycling stability and an energy density which is >50% higher than what is obtained with a commercial graphite anode.</P> [FIG OMISSION]</BR>
Wofford, J.,Park, J.,McCormick, S.,Chakrabarti, M.,Lindahl, P. ROYAL SOCIETY OF CHEMISTRY 2016 Metallomics Vol.8 No.7
<P>Mossbauer and EPR spectra of fermenting yeast cells before and after cell wall (CW) digestion revealed that CWs accumulated iron as cells transitioned from exponential to post-exponential growth. Most CW iron was mononuclear nonheme high-spin (NHHS) Fe-III, some was diamagnetic and some was superparamagnetic. A significant portion of CW Fe was removable by EDTA. Simulations using an ordinary-differential-equations-based model suggested that cells accumulate Fe as they become metabolically inactive. When dormant Fe-loaded cells were metabolically reactivated in Fe-deficient bathophenanthroline disulfonate (BPS)-treated medium, they grew using Fe that had been mobilized from their CWs AND using trace amounts of Fe in the Fe-deficient medium. When grown in Fe-deficient medium, Fe-starved cells contained the lowest cellular Fe concentrations reported for a eukaryotic cell. During metabolic reactivation of Fe-loaded dormant cells, Fe-III ions in the CWs of these cells were mobilized by reduction to Fe-II, followed by release from the CW and reimport into the cell. BPS short-circuited this process by chelating mobilized and released Fe-II ions before reimport; the resulting Fe-II(BPS) 3 complex adsorbed on the cell surface. NHHS Fe-II ions appeared transiently during mobilization, suggesting that these ions were intermediates in this process. In the presence of chelators and at high pH, metabolically inactive cells leached CW Fe; this phenomenon probably differs from metabolic mobilization. The iron regulon, as reported by Fet3p levels, was not expressed during post-exponential conditions; Fet3p was maximally expressed in exponentially growing cells. Decreased expression of the iron regulon and metabolic decline combine to promote CW Fe accumulation.</P>