Organic memory using [6,6]-phenyl-C(61) butyric acid methyl ester: morphology, thickness and concentration dependence studies

We report a simple memory device in which the fullerene-derivative [6,6]-phenyl-C(61) butyric acid methyl ester (PCBM) mixed with inert polystyrene (PS) matrix is sandwiched between two aluminum (Al) electrodes. Transmission electron microscopy (TEM) images of PCBM:PS films showed well controlled morphology without forming any aggregates at low weight percentages (<10?wt%) of PCBM in PS. Energy dispersive x-ray spectroscopy (EDX) analysis of the device cross-sections indicated that the thermal evaporation of the Al electrodes did not lead to the inclusion of Al metal nanoparticles into the active PCBM:PS film. Above a threshold voltage of <3?V, independent of thickness, a consistent negative differential resistance (NDR) is observed in devices in the thickness range from 200 to 350?nm made from solutions with 4-10?wt% of PCBM in PS. We found that the threshold voltage (V(th)) for switching from the high-impedance state to the low-impedance state, the voltage at maximum current density (V(max)) and the voltage at minimum current density (V(min)) in the NDR regime are constant within this thickness range. The current density ratio at V(max) and V(min) is more than or equal to 10, increasing with thickness. Furthermore, the current density is exponentially dependent on the longest tunneling jump between two PCBM molecules, suggesting a tunneling mechanism between individual PCBM molecules. This is further supported with temperature independent NDR down to 240?K.     

Signaled Step Size for Downlink Power Control of Dedicated Channels in UTRA TDD

This paper discusses downlink inner loop power control of dedicated channels in UTRA TDD. The current UTRA TDD downlink power control is similar to one in UTRA FDD mode, that comprises of closed inner loop and quality based outer loop. However, due to the time division feature and associated fexibility with asymmetry of TDD, the inner loop can not react as fast as in FDD and it is affected by rapid changes in environment. Therefore, the effect of the inner loop algorithm to the performance of UTRA TDD network is studied in this paper. Especially, the use of asymmetric step sizes for power up and power down commands is evaluated in contrast to the conventional symmetric power adjustment. Since it would be beneficial for the downlink inner loop power control to reach the target SIR as fast as possible, the power control step size based on the difference between the UE measured SIR and target SIR would be the most desirable power adjustment. Since the effectiveness of this type of an algorithm depends on available signaling bandwidth that is used, a study is carried out to find the tradeoff between the signaling bandwidth and related network performance.Janne Kurjenniemi was born in Jyväskylä, Finland, in March 1974. He received the M.Sc. in telecommunications in 2001 from the University of Jyväskylä, Jyväskyl, Finland. He is working as a Researcher at the Department of Mathematical Information Technology, University of Jyväskylä. His research interests include radio resource management for wireless communication systems.Otto-Aleksanteri Lehtinen was born in Tampere, Finland, in September 1971. He received the Master of Science in Technology in 1999 from the Helsinki University of Technology, Department of Electrical engineering (major in radio technology, minor signal processing and computer devices). His research interests include radio resource management for wireless communication systems.Tapani Ristaniemi was born in Kauhava, Finland, in 1971. He received the M.Sc. in mathematics in 1995, Ph.Lic. in applied mathematics in 1997, and Ph.D. in telecommunications in 2000 from the University of Jyväskylä, Jyväskylä, Finland. During 2001–2003 he was a professor of telecommunications at the Department of Mathematical Information Technology, University of Jyväskylä. In 2003 he joined the Institute of Communications Engineering in the Tampere University of Technology, Finland, where he has been a professor of wireless data communications. His research interests include signal processing for communications and radio resource management for wireless networks.     

Unruly Representation: Materiality,indexicality and agency of the photographic trace

This article examines photographic representation as a material and indexical trace caused by photons reflected and/or emitted from the photographed objects. It argues that the contested idea of indexicality remains relevant to the photograph despite the digitalization of the photographic process. It also suggests that the trace works as an affordance which renders ambiguous the photographic representation as re-presentation. The material trace provides an anchorage point for the presence of the photographed objects. However, the very same presence destabilizes the photograph’s function as a representation and renders its status controversial. Therefore, the photograph both is and is not a representation. As a much-celebrated guarantee of photographic truth, the trace works, in fact, as an element of perpetual epistemological controversy and also as an affordance for philosophical, ontological and poetic analysis.     

Carbon nanotube micropillars trigger guided growth of complex human neural stem cells networks

Nano Research - New strategies for spatially controlled growth of human neurons may provide viable solutions to treat and recover peripheral or spinal cord injuries. While topography cues are known...     

Properties and Stability of Mining-Induced Meromixis in Two Small Boreal Lakes in Eastern Finland

Mine waters are a significant point source stressor for aquatic environments, not only due to their acidity and high metal concentrations, but also because of their high electrolyte concentrations. Ion-rich mine waters can disturb the seasonal mixing of lake waters, even leading to permanent stratification, i.e. meromixis. In this study, we investigated two small natural lakes receiving waters from closed Ni-Cu mines. To characterize the present chemical and physical conditions of these two boreal lakes, we collected water samples and in-situ water column measurements seasonally in 2017 and 2018. We modelled the stability of meromixis in the lakes under varying physico-chemical and meteorological conditions with the MATLAB-based open-source model code, MyLake. Chemical analyses and water column measurements show that both lakes are currently meromictic with a chemocline separating the circulating, well-oxygenated upper water from the non-circulating, hypoxic bottom water. The main anion was SO₄ in both lakes, while the main cations were Ca, Mg, Na, and K. Elevated concentrations of conservative elements flowing from the mine areas are crucial in maintaining the meromixis. Modelling scenarios suggest that the meromixis would be sustained for several decades even if the external load ceased completely. Lake morphology and sheltered surroundings also seem to contribute to maintaining the meromixis in these lakes. Consequently, our results indicate that small headwaters are sensitive to persistent meromixis even when external loading is mild.

     

Oxidation of accident tolerant fuel candidates

In this study, the oxidation of various accident tolerant fuel candidates produced under different conditions have been evaluated and compared relative to the reference standard – UO₂. The candidates considered in this study were UN, U₃Si₂, U₃Si₅, and a composite material composed of UN–U₃Si₂. With the spark plasma sintering (SPS) method, it was possible to fabricate samples of UN with varying porosity, as well as a high-density composite of UN–U₃Si₂?(10%). Using thermogravimetry in air, the oxidation behaviors of each material and the various microstructures of UN were assessed. These results reveal that it is possible to fabricate UN to very high densities using the SPS method, such that its resistance to oxidation can be improved compared to U₃Si₅ and UO₂, and compete favorably with the principal ATF candidates, U₃Si₂, which shows a particularly violent reaction under the conditions of this study, and the UN–U₃Si₂?(10%) composite.     

On TiN-particle fuel based helium-cooled transmutation systems

We have designed a sub-critical helium-cooled core with TiN-coated particle fuel, dedicated to the transmutation of minor actinides. The excellent neutronic properties of helium allows for a low plutonium fraction in the fuel, which yields a low reactivity swing, Δk = 2600 pcm, for a burnup of 31.2%. Further the neutron spectrum is hard, limiting the buildup of Cm and Cf. The high burnup combined with a minor actinide burning rate of 355 kg/GWth year makes the present design an attractive transmutation system.     

Supplemental safety? Exploring experienced safety in relation to other qualities of successful public spaces

ABSTRACT

Combining insights from the urban design and criminological literature, this paper explores the degree to which conviviality, feeling welcome, and feeling at home are related to peoples’ experiences of safety. A questionnaire was distributed on four squares in the city of Utrecht, the Netherlands. While participants valued the positive qualities of the squares differently, feeling safe was connected to a wider, positive evaluation of the quality of space and especially to feeling at home. By investing primarily in public spaces that are ‘homely’ or ‘domesticated’, a ‘supplemental safety’ might therefore be nurtured. This poses important insights for safety management.