Bistable organic materials in optoelectrical switches: Two-electrode devices vs. organic field effect transistors

The paper presents a short overview of research into properties of organic materials and structures that could be used in optoelectrical switches, i.e., switches in which changes in electrical properties are triggered by light of appropriate wavelengths. In particular, described are the structures acting by virtue of reversible photochemical reactions occurring in photochromic molecular materials

Correctness of multi-core processors with operating system support

Im Zuge der Unterstützung von Hypervisoren verifizieren wir einen realistischen Pipeline-Multi-Core-Prozessor mit integriertem Mechanismus für die zweiphasige (verschachtelte) Adressübersetzung. Das verschachtelte Übersetzungsschema wird benötigt, damit Gäste des Hypervisors (typischerweise Betriebssysteme) ihre Programme im übersetzten Modus ausführen können. Wir betrachten das Setup, in dem die Betriebssysteme als Prozesse (im übersetzten Modus) des Hypervisors laufen, 'auf der bloßen Hardware', d.h. ohne Adressübersetzung. Die geschachtelte Übersetzung wird von der geschachtelten Memory Management Unit (MMU) durchgeführt, wobei beide Übersetzungsphasen in Hardware ausgeführt werden. Sowohl die Spezifikation als auch die Implementierung der geschachtelten MMU werden ausführlich dargestellt. Es wird bewiesen, dass die geschachtelte MMU eine allgemeinere Hilfsspezifikation, die die geschachtelte MMU vom Rest der Maschine isoliert, korrekt implementiert. Letzteres erlaubt es uns, die Argumente für die Korrektheit der MMU-Implementierung in jeder Maschine auf eine einfache Simulation zwischen zwei Softwaremodellen zu reduzieren.Der Hauptbeitrag dieser Arbeit ist der vollständige Korrektheitsbeweis auf Papier für die Pipeline-Multi-Core-Implementierung des MIPS-86 ISA, der zur Unterstützung der verschachtelten Übersetzung zusätzlich erweitert wurde. Wie der Name schon vermuten lässt, kombiniert MIPS-86 den Befehlssatz von MIPS mit dem Speichermodell von x86. Zuerst betrachten wir diese erweiterte MIPS-86-Spezifikation in der sequentiellen Implementierung, die dazu dient, die Integration der verschachtelten MMUs in den MIPS-Prozessor zu demonstrieren und der Einfachheit halber auf einen einzelnen Prozessorkern beschränkt ist. Im Beweis unseres Hauptergebnisses - Korrektheit der Pipeline-Implementierung - verweisen wir auf den sequentiellen Fall, um die Korrektheit der MMU-Operation zu zeigen. Dies erlaubt uns, den Fokus auf die Probleme des Pipelinings der Maschine mit spekulativer Ausführung und Unterbrechungen zu verlagern, die bei vorhandener Adressübersetzung zu berücksichtigen sind.In the course of adding support for hypervisors, we verify a realistic pipelined multi-core processor with integrated mechanism for two-phase (nested) address translation. The nested translation scheme is required to allow guests of the hypervisor (typically operating systems) to execute their programs in translated mode. We consider the setup in which the operating systems are running as processes (in translated mode) of the hypervisor, running 'on the bare hardware', i.e., without address translation. The nested translation is performed by the nested memory management unit (MMU), with both phases of translation performed in hardware. Both the specification and the implementation of the nested MMU are presented in full detail. The nested MMU is proven to correctly implement an auxiliary, more general specification which isolates the nested MMU from the rest of the machine. The latter allows us to reduce arguments on correctness of the MMU implementation in any machine to a simple simulation between a pair of software models. The main contribution of this thesis is the complete paper and pencil correctness proof for the pipelined multi-core implementation of the MIPS-86 ISA, additionally extended to support the nested translation. As the name suggests, MIPS-86 combines the instruction set of MIPS with the memory model of x86. First, we consider this extended MIPS-86 specification in the sequential implementation, which serves to demonstrate integration of the nested MMUs into the MIPS processor and for simplicity is restricted to have a single processor core. In the proof of our main result - correctness of the pipelined implementation - we refer to the sequential case to show correctness of the MMU operation. This allows us to shift the focus towards the problems of pipelining the machine with speculative execution and interrupts, which are necessary to consider in the presence of address translation

Unsymmetrical Relaxation Paths of the Excited States in Cyanine Dyes Detected by Time-Resolved Fluorescence:Polymethinic and Polyenic Forms

Novel applications of organic dyes and vast opportunities for their molecular tailoring keep focus of scientific community on the issues of symmetry breaking in the systems having different location of uncompensated charge, which has tremendous impact on photoluminescent properties of the dyes. In this paper, we provide distinctive experimental evidences of three relaxation paths (one symmetrical and two unsymmetrical) of excited states by analysis of lifetime and spectra of time-resolved fluorescence at low temperature with strong support of quantum-chemical modeling. Importantly, the studied cyanine dye (astraphloxin) in aqueous solution has two different unsymmetrical relaxation paths of excites states in the polymethinic and donor-acceptor polyenic forms, where the last form strongly diminishes in less polar media. The experimental and computational results provide essential fundamental knowledge of molecular electronic relaxations substantially affected by matrix rigidity and polarity for design and photonic applications of elongated π-electronic systems

A dioxaborine cyanine dye as a photoluminescence probe for sensing carbon nanotubes

The unique properties of carbon nanotubes have made them the material of choice for many current and future industrial applications. As a consequence of the increasing development of nanotechnology, carbon nanotubes show potential threat to health and environment. Therefore, development of efficient method for detection of carbon nanotubes is required. In this work, we have studied the interaction of indopentamethinedioxaborine dye (DOB-719) and single-walled carbon nanotubes (SWNTs) using absorption and photoluminescence (PL) spectroscopy. In the mixture of the dye and the SWNTs we have revealed new optical features in the spectral range of the intrinsic excitation of the dye due to resonance energy transfer from DOB-719 to SWNTs. Specifically, we have observed an emergence of new PL peaks at the excitation wavelength of 735 nm and a redshift of the intrinsic PL peaks of SWNT emission (up to 40 nm) in the near-infrared range. The possible mechanism of the interaction between DOB-719 and SWNTs has been proposed. Thus, it can be concluded that DOB-719 dye has promising applications for designing efficient and tailorable optical probes for the detection of SWNTs

Enzyme-functionalized thin-cladding long-period fiber grating in transition mode at dispersion turning point for sugar-level and glucose detection

Enzyme-functionalized dual-peak long-period fiber grating (LPFG) inscribed in 80-μm-cladding B/Ge codoped single-mode fiber is presented for sugar-level and specific glucose detection. Before enzyme functionalization, the dual-peak LPFG was employed for refractive index sensing and sugar-level detection and high sensitivities of ∼4298.20  nm/RIU and 4.6696  nm/% were obtained, respectively. Glucose detection probe was attained by surface functionalization of the dual-peak LPFG via covalent binding with aminopropyl triethoxysilane used as a binding site. Optical micrographs confirmed the presence of enzyme. The surface-functionalized dual-peak LPFG was tested with D-(+)-glucose solution of different concentrations. While the peak 2 at the longer wavelength was suitable only to measure lower glucose concentration (0.1 to 1.6  mg/ml) recording a high sensitivity of 12.21±0.19  nm/(mg/ml), the peak 1 at the shorter wavelength was able to measure a wider range of glucose concentrations (0.1 to 3.2  mg/ml) exhibiting a maximum resonance wavelength shift of 7.12±0.12  nm/mg/ml. The enzyme-functionalized dual-peak LPFG has the advantage of direct inscription of highly sensitive grating structures in thin-cladding fibre without etching, and most significantly, its sensitivity improvement of approximately one order of magnitude higher than previously reported LPFG and excessively tilted fibre grating (Ex-TFG) for glucose detection

Low-loss saturable absorbers based on tapered fibers embedded in carbon nanotube/polymer composites

The emergence of low-dimensional materials has opened new opportunities in the fabrication of compact nonlinear photonic devices. Single-walled carbon nanotubes were among the first of those materials to attract the attention of the photonics community owing to their high third order susceptibility, broadband operation, and ultrafast response. Saturable absorption, in particular, has become a widespread application for nanotubes in the mode-locking of a fiber laser where they are used as nonlinear passive amplitude modulators to initiate pulsed operation. Numerous approaches have been proposed for the integration of nanotubes in fiber systems; these can be divided into those that rely on direct interaction (where the nanotubes are sandwiched between fiber connectors) and those that rely on lateral interaction with the evanescence field of the propagating wave. Tapered fibers, in particular, offer excellent flexibility to adjust the nonlinearity of nanotube-based devices but suffer from high losses (typically exceeding 50%) and poor saturable to non-saturable absorption ratios (typically above 1:5). In this paper, we propose a method to fabricate carbon nanotube saturable absorbers with controllable saturation power, low-losses (as low as 15%), and large saturable to non-saturable loss ratios approaching 1:1. This is achieved by optimizing the procedure of embedding tapered fibers in low-refractive index polymers. In addition, this study sheds light in the operation of these devices, highlighting a trade-off between losses and saturation power and providing guidelines for the design of saturable absorbers according to their application

Mixing of Excitons in Nanostructures Based on a Perylene Dye with CdTe Quantum Dots

Semiconductor quantum dots of the A2B6 group and organic semiconductors have been widely studied and applied in optoelectronics. This study aims to combine CdTe quantum dots and perylene-based dye molecules into advanced nanostructure system targeting to improve their functional properties. In such systems, new electronic states, a mixture of Wannier–Mott excitons with charge-transfer excitons, have appeared at the interface of CdTe quantum dots and the perylene dye. The nature of such new states has been analyzed by absorption and photoluminescence spectroscopy with picosecond time resolution. Furthermore, aggregation of perylene dye on the CdTe has been elucidated, and contribution of Förster resonant energy transfer has been observed between aggregated forms of the dye and CdTe quantum dots in the hybrid CdTe-perylene nanostructures. The studied nanostructures have strongly quenched emission of quantum dots enabling potential application of such systems in dissociative sensing

Emergence of additional visible range photoluminescence due to aggregation of cyanine dye:astraphloxin on carbon nanotubes dispersed with anionic surfactant

Self-organization of organic molecules with carbon nanomaterials leads to formation of functionalized molecular nano-complexes with advanced features. We present a study of physical and chemical properties of carbon nanotube-surfactant-indocarbocyanine dye (astraphloxin) in water focusing on aggregation of the dye and resonant energy transfer from the dye to the nanotubes. Self-assembly of astraphloxin is evidenced in absorbance and photoluminescence depending dramatically on the concentrations of both the dye and surfactant in the mixtures. We observed an appearance of new photoluminescence peaks in visible range from the dye aggregates. The aggregates characterized with red shifted photoluminescence peaks at 595, 635 and 675 nm are formed mainly due to the presence of surfactant at the premicellar concentration. The energy transfer from the dye to the nanotubes amplifying near-infrared photoluminescence from the nanotubes is not affected by the aggregation of astraphloxin molecules providing important knowledge for further development of advanced molecular nano-complexes. The aggregation with the turned-on peaks and the energy transfer with amplified photoluminescence create powerful tools of visualization and/or detection of the nanotubes in visible and near-infrared spectral range, respectively, boosting its possible applications in sensors, energy generation/storage, and healthcare

Effect of the charge state on the photoluminescence spectra of melanin

Steady-state and time-resolved photoluminescence (PL) spectra of natural and synthetic melanin, as well as melanin composites with surfactant, sodium dodecylbenzenesulfonate, and polymethine dye, astraphloxin, have been studied. The melanin molecules having differently charged peripheral groups with terminal O atoms and OH groups mixed with the negatively charged surfactant or positively charged astraphloxin dye feature new PL spectral bands. The kinetics of PL and time-resolved emission spectra for the melanin and the composites were also investigated and discussed in terms of intermolecular complexation, nano-aggregation and formation of chargetransfer states. The studies are aiming to understand the electronic properties of various melanins, particularly natural ones

Моделювання методом скінчених елементів механічної поведінки сплавів з пам’яттю форми

Методом скінчених елементів змодельовано й експериментально досліджено псевдопружну поведінку нікель-титанового сплаву за змінної амплітуди навантаження. Зразки з нікель-титанового сплаву (Ni – 55,8%, Ti – 44,2%) діаметром d = 1,5 мм і довжиною робочої ділянки L = 30 мм досліджували за одновісного розтягу на випробувальній машині FP-100 при кімнатній температурі на повітрі. Експериментально визначено механічні характеристики матеріалу та напруження старту й фінішу прямих і зворотних фазових перетворень, використаних при моделюванні. Створено скінченоелементну тривимірну модель, здатну відтворювати псевдопружну поведінку за статичного й повторно-статичного навантаження розтягом та розвантаження. За результатами моделювання методом скінчених елементів у середовищі ПК ANSYS Workbench 17.1 отримано залежності напружень від деформації в кожному циклі за змінної амплітуди навантаження. Виявлено, що за змінної амплітуди навантаження напруження початку та закінчення прямих і зворотних фазових перетворень змінюються у кожному циклі, а розрахункові залежності напружень від деформацій задовільно узгоджуються з експериментальними. Похибка напружень, обчислених методом скінчених елементів упродовж усіх циклів навантаження не перевищує 10,1%, а деформацій – 6,1%. У точках, які відповідають напруженням прямих і зворотних перетворень, обчислена енергія пружної деформації та енергія дисипації. Похибка енергії пружної деформації при чисельному моделюванні не перевищує 10,9%, а енергії розсіювання (дисипації) – 10,8% порівняно з експериментальними даними. Отримані результати мають теоретичне й прикладне значення для моделювання псевдопружної поведінки, міцності й витривалості конструкцій з сплавів з пам’яттю форми за сталої та змінної амплітуди навантаження.Superelastic behaviour of Ni-Ti alloy wire under variable amplitude loading was simulated and experimentally studied. Mechanical properties and phase transformation stresses (, , , ) of the material were obtained in uniaxial tensile test. The wire of 55,8% Ni – 44,2% Ti alloy with a diameter of 1,5 mm and a working length of 30 mm was tested at room temperature (+ 16°C) on the air. On the base of finite elements method, using ANSYS the stress-strain dependencies on each loading cycle were calculated. The stress-phase transformation are changes under a variable amplitude loading. The simulated stress-strain dependencies were compared with the experimental ones. The maximum error, being compared with experimental data, does not exceed 10,9%. The calculated dependences of elastic strain and dissipated energies on the amplitude stress are well agreed with experimental data. The obtained results are of theoretical and applied interest for modelling the superelastic behaviour of SMA under variable amplitude loading