54 research outputs found
Current-voltage characteristics of asymmetric double-barrier Josephson junctions
We develop a theory for the current-voltage characteristics of diffusive
superconductor-normal metal-superconductor Josephson junctions with resistive
interfaces and the distance between the electrodes smaller than the
superconducting coherence length. The theory allows for a quantitative
analytical and numerical analysis in the whole range of the interface
transparencies and asymmetry. We focus on the regime of large interface
resistance compared to the resistance of the normal region, when the
electron-hole dephasing in the normal region is significant and the finite
length of the junction plays a role. In the limit of strong asymmetry we find
pronounced current structures at the combination subharmonics of
, where is the proximity minigap in the normal
region, in addition to the subharmonics of the energy gap in the
electrodes. In the limit of rather transparent interfaces, our theory recovers
a known formula for the current in a short mesoscopic connector - a convolution
of the current through a single-channel point contact with the transparency
distribution for an asymmetric double-barrier potential.Comment: 10 pages, 3 figure
Proceedings of the International RILEM Conference Materials, Systems and Structures in Civil Engineering segment on Service Life of Cement-Based Materials and Structures
Vol. 1O volume II encontra-se disponĂvel em: http://hdl.handle.net/1822/4390
International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Service Life of Cement-Based Materials and Structures
Vol. 2O volume I encontra-se disponĂvel em: http://hdl.handle.net/1822/4341
Synthetic, spectroscopic, and electrochemical studies on complexes of ruthernium an osmium
CHAPTER 1
Reviews triply halide bridged binuclear ruthenium
systems of the type [Lâââââ ClâRuClâ RuClᔧLâââᔧâ] in
oxidation states ranging from Ruâ(II/II) to Ruâ(III/III).
In the present work, organo-soluble salts of [RuâXâ]Âłâ»
(X = CI,Br) are described and their electrochemical,
magnetic and spectroscopic properties investigated.
Electrosynthesis of the oxidised derivatives [RuâXâ]ÂČâ» and
[RuâXâ]â», and their characterisation by electronic
absorption spectroscopy and magnetic susceptibility
measurements have helped to elucidate their electronic
nature, leading to a greater understanding of the nature
of ruthenium triple halide-bridged complexes in general.
CHAPTER 2
Mixed-valence triple chloro bridged binuclear
complexes of ruthenium bearing NHâ or Hâ0 terminal ligands
such as [RuâClâ(NHâ)â]ÂČâș and [RuâClâ(HâO)â]ÂČâș are
discussed. A comprehensive examination of the redox
properties of [RuâClâ(NHâ)â]ÂČâș achieved in non-aqueous
media, and of optical spectra in differing oxidation
states, are reported. The underlying metal metal
interactions are discussed in relation to the influence of
terminal ligand basicity.
CHAPTER 3
A sequence of binuclear complexes of the type
[Ruâ Brâ(AsRâ) (âââ)] (x = 5,6)] have been synthesised and
previous suggestions regarding their structure as
indicated by esr studies and their electrochemical
behaviour, have been enhanced and reinforced.
CHAPTER 4
Electroreduction of mer [OsClâ (PMeâPh)â ] in a variety
of coordinating media has produced a range of 6-coordinate
Os(II) monomeric complexes in two separable isomeric
forms. In non-coordinating solvents the Os(III) complex is
found to expel chloride under most conditions, to give a
detectable 5-coordinate intermediate, which can react
under favourable conditions to produce doubly- and
triply-bridged binuclear species. This series of
electro-initiated reactions has so far yielded many
separate complexes, identified by both spectroscopic
methods and voltammetric data.
APPENDIX 1
Voltammetric measurements establish a reversible
one-electron oxidation for the complex [RuClâ
NO]ÂČâ». Bulk
electrogeneration of the resulting oxidised species has
allowed i.r, esr and magnetic susceptibility measurements
to confirm its existance as the low-spin [RuClâ
NO]â» ion,
in contrast to previous reports.
APPENDIX 2
Electrochemical studies on [Osâ(OCOR)âClâ] (R = Et,
âżPr) and [Osâ(hp)â CIâ] (hp = hydroxypyridinate anion)
establish a reversible one-electron reduction for these
complexes, producing the first examples of species
containing the Osââ”âș core. These derivatives have been
characterised by voltammetry, electronic absorption
spectroscopy, esr spectroscopy and magnetic susceptibility
measurements
Miniaturized Electron Optics based on Self-Assembled Micro Coils
Zahlreiche GerĂ€te, die in den Naturwissenschaen, in der Industrie und im Gesundheitswesen unverzichtbar sind, basieren auf Strahlen schneller geladener Teilchen. Dazu zĂ€hlen unter anderem Elektronen- und Ionenmikroskope, entsprechende Lithographiestrahlanlagen und Röntgenstrahlungsquellen. Magnetische Optiken, die Strahlen geladener Teilchen ablenken, formen und fokussieren, sind das RĂŒckgrat aller GerĂ€te die mit hochenergetischen Teilchen arbeiten, da sie im Vergleich zu Optiken, die auf elektrischen Feldern basieren, bei hohen Teilchengeschwindigkeiten eine ĂŒberlegene optische Leistung aufweisen. Konventionelle makroskopische magnetische Optiken sind jedoch groĂ, teuer und platzraubend, nicht hochfrequenzfĂ€hig und erfordern aktive (Wasser-)KĂŒhlung zur WĂ€rmeabfuhr. Sie sind daher fĂŒr Mehrstrahlinstrumente, miniaturisierte Anwendungen und schnelle Strahlmanipulation ungeeignet, die fĂŒr zukĂŒnftige Fortschritte in der Nanofabrikation und -analyse gebraucht werden. Im Rahmen dieser Arbeit wurden die ersten magnetischen selbst-assemblierenden Mikro-Origami-Elektronenoptiken entwickelt, hergestellt und charakterisiert. Mit dem verwendeten Miniaturisierungsansatz können, bei Ă€hnlicher optischer Leistung, alle oben genannten Nachteile von konventionellen magnetischen Optiken ĂŒberwunden werden. Die auĂergewöhnlichen Eigenschaften dieser optischen Elemente werden durch die einzigartigen Merkmale der Mikrospulen ermöglicht: geringe GröĂe, geringe InduktivitĂ€t und geringer Widerstand. Im Rahmen dieser Arbeit wurden unter anderem adaptive Phasenplaen hergestellt, die Elektronenvortexstrahlen mit einem bislang unerreichten Bahndrehimpuls von bis zu mehreren 1000 Ìh erzeugen. Des Weiteren wurden schnelle Elektronenstrahldeflektoren zur Strahlablenkung, zum zweidimensionalen Rastern und fĂŒr stroboskopische Experimente gefertigt. Sie besitzen eine Ablenkleistung im mrad-Bereich fĂŒr 300 kV Elektronen und einen Frequenzdurchgang bis zu 100 MHz. DarĂŒber hinaus wurden miniaturisierte adrupollinsen mit Brennweiten kleiner als 46 mm fĂŒr 300 kV Elektronen entwickelt. Diese drei Arten elektronenoptischer Elemente sind von groĂem Interesse fĂŒr verschiedenste Anwendungen in der Nanofabrikation und -analyse, da sie unter anderem als integrale Bestandteile von zu entwickelnden Mehrstrahlinstrumenten, miniaturisierten GerĂ€ten und stroboskopischen Messaufbauten dienen können.:1 Introduction
1.1 Charged Particle Optics
1.2 Miniaturized Charged Particle Optics
1.3 Phase Plates for Transmission Electron Microscopy
2 Charged Particle Optics
2.1 Hamiltonian Formalism
2.2 Gaussian Matrix Optics
2.3 Transfer Matrices of Magnetic Elements
2.3.1 Single Quadrupole
2.3.2 Quadrupole Multiplets
2.3.2.1 Quadrupole Doublet
2.3.2.2 Quadrupole Triplet
2.3.2.3 Higher Order Quadrupole Multiplets
2.4 Scaling Laws for Charged Particle Optics
2.4.1 Thin Film
2.4.2 Electrostatic Scaling Laws
2.4.3 Magnetic Scaling Laws
3 Design and Fabrication of Miniaturized Electron Optics
3.1 Basics of Polymer-Based Self-Assembly Technology
3.2 Basic Coil Design and Magnetic Field Simulations
3.3 CoFeSiB-Pyrex Core-Shell Micro Wires
3.4 Fabrication of Self-Assembled Micro Coil Devices
4 Optical Properties of Self-Assembled Miniaturized Electron Optics
4.1 Electron Vortex Phase Plate
4.1.1 Projected Magnetic Fields
4.1.2 Vortex Beam Characteristics
4.2 Miniaturized Deflector
4.3 Quadrupole Focusing Optic
4.4 High Frequency Characteristics of Self-Assembled Electron Optics
5 Summary and Outlook
5.1 Applications of Electron Vortex Beams with Large OAM
5.2 Optics of Large Optical Power for Pulsed Instruments
5.3 Stroboscopic TEM Measurements
5.4 Miniaturized Wigglers, Undulators and Free Electron Lasers
5.5 Towards Integrated Electron Optical SystemsBeams of highly accelerated charged particles are essential for numerous indispensable devices used throughout natural sciences, industry and the healthcare sector, e.g., electron and ion microscopes, charged particle lithography machines and X-ray radiation sources. Magnetic charged particle optics that deflect, shape and focus high-energy charged particles are the backbone of all such devices, because of their superior optical power compared to electric field optics at large particle velocities. Conventional macroscopic magnetic optics, however, are large, costly and bulky, not high frequency capable and require active cooling for heat dissipation. They are therefore unsuitable for fast beam manipulation, multibeam instrumentation, and miniaturized applications, much desired for future advances in nanofabrication and analysis. The first on-chip micro-sized magnetic charged particle optics realized via a self-assembling micro-origami process were designed, fabricated and characterized within the frame of this work. The utilized micro-miniaturization approach overcomes all the aforementioned obstacles for conventional magnetic optics, while maintaining similar optical power. The exceptional properties of these optical elements are rendered possible by the unique features of strain-engineered micro-coils: small size, small inductance and small resistivity. Within the frame of this work, adaptive phase plates were fabricated, which generate electron vortex beams with an unprecedented orbital angular momentum of up to several 1000 Ìh. Furthermore, fast electron beam deflectors for beam blanking, two-dimensional scanning and stroboscopic experiments were manufactured. They possess a deflection power in the mrad regime for 300 kV electrons and a high frequency passband up to 100 MHz. Additionally, miniaturized strong quadrupole lenses with focal lengths down to 46 mm for 300 kV electrons have been developed. These three types of electron optical elements are of great interest for a wide range of applications in nanofabrication and analysis, as they serve as integral components of future multibeam instruments, miniaturized devices, and stroboscopic measurement setups to be developed.:1 Introduction
1.1 Charged Particle Optics
1.2 Miniaturized Charged Particle Optics
1.3 Phase Plates for Transmission Electron Microscopy
2 Charged Particle Optics
2.1 Hamiltonian Formalism
2.2 Gaussian Matrix Optics
2.3 Transfer Matrices of Magnetic Elements
2.3.1 Single Quadrupole
2.3.2 Quadrupole Multiplets
2.3.2.1 Quadrupole Doublet
2.3.2.2 Quadrupole Triplet
2.3.2.3 Higher Order Quadrupole Multiplets
2.4 Scaling Laws for Charged Particle Optics
2.4.1 Thin Film
2.4.2 Electrostatic Scaling Laws
2.4.3 Magnetic Scaling Laws
3 Design and Fabrication of Miniaturized Electron Optics
3.1 Basics of Polymer-Based Self-Assembly Technology
3.2 Basic Coil Design and Magnetic Field Simulations
3.3 CoFeSiB-Pyrex Core-Shell Micro Wires
3.4 Fabrication of Self-Assembled Micro Coil Devices
4 Optical Properties of Self-Assembled Miniaturized Electron Optics
4.1 Electron Vortex Phase Plate
4.1.1 Projected Magnetic Fields
4.1.2 Vortex Beam Characteristics
4.2 Miniaturized Deflector
4.3 Quadrupole Focusing Optic
4.4 High Frequency Characteristics of Self-Assembled Electron Optics
5 Summary and Outlook
5.1 Applications of Electron Vortex Beams with Large OAM
5.2 Optics of Large Optical Power for Pulsed Instruments
5.3 Stroboscopic TEM Measurements
5.4 Miniaturized Wigglers, Undulators and Free Electron Lasers
5.5 Towards Integrated Electron Optical System
Development and modelling of a versatile active micro-electrode array for high density in-vivo and in-vitro neural signal investigation
The electrophysiological observation of neurological cells has allowed much knowledge to be gathered regarding how living organisms are believed to acquire and process sensation. Although much has been learned about neurons in isolation, there is much more to be discovered in how these neurons communicate within large networks. The challenges of measuring neurological networks at the scale, density and chronic level of non invasiveness required to observe neurological processing and decision making are manifold, however methods have been suggested that have allowed small scale networks to be observed using arrays of micro-fabricated electrodes. These arrays transduce ionic perturbations local to the cell membrane in the extracellular fluid into small electrical signals within the metal that may be measured.
A device was designed for optimal electrical matching to the electrode interface and maximal signal preservation of the received extracellular neural signals. Design parameters were developed from electrophysiological computer simulations and experimentally obtained empirical models of the electrode-electrolyte interface. From this information, a novel interface based signal filtering method was developed that enabled high density amplifier interface circuitry to be realised.
A novel prototype monolithic active electrode was developed using CMOS microfabrication technology. The device uses the top metallization of a selected process to form the electrode substrate and compact amplification circuitry fabricated directly beneath the electrode to amplify and separate the neural signal from the baseline offsets and noise of the electrode interface. The signal is then buffered for high speed sampling and switched signal routing. Prototype 16 and 256 active electrode array with custom support circuitry is presented at the layout stage for a 20 ÎŒm diameter 100 ÎŒm pitch electrode array. Each device consumes 26.4 ÎŒW of power and contributes 4.509 ÎŒV (rms) of noise to the received signal over a controlled bandwidth of 10 Hz - 5 kHz.
The research has provided a fundamental insight into the challenges of high density neural network observation, both in the passive and the active manner. The thesis concludes that power consumption is the fundamental limiting factor of high density integrated MEA circuitry; low power dissipation being crucial for the existence of the surface adhered cells under measurement. With transistor sizing, noise and signal slewing each being inversely proportional to the dc supply current and the large power requirements of desirable ancillary circuitry such as analogue-to-digital converters, a situation of compromise is approached that must be carefully considered for specific application design
MODELLING AND SIMULATION OF HIGH VOLTAGE DIRECT CURRENT TRANSMISSION SYSTEM
High voltage direct current (HVDC) is one of the technologies in electrical
transmission system. It is established as an alternative to AC transmission system.
The main purpose ofthis project is to model and simulate the HVDC system by using
software. The scope of this project is to cover the concepts about transmission
system, specifically HVDC.In fact, familiarization with softwaresuch as ATPwill be
covered too as it will assist in the modeling and simulation stage. The systematic
approaches such as research, modeling, simulation, validation and troubleshooting in
accomplishing this project are discussed in the chapter of methodology. Assessments
on several softwares were conducted in order to identify the best software in studying
the behavior of HVDC system. Besides that, data taken from real HVDC project,
which is EGAT/TNB HVDC Interconnection Project, will be discussed too.
Comparison between the simulated results and the real data were carried out in order
to validate the findings from the simulation. Based on the evaluation made on the
relevant software, it is found that ATP is the best software to be utilized in this
project. Subsequently, simulations were conducted by using ATP and desired
waveforms were obtained since they managed to resemble the real data and consistent
with the theoretical concept
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