112 research outputs found
Research on the combination of translucent Glass Fiber Reinforced Polymers (G.F.R.P.) and Phase Change Materials (P.C.M.), for applications in architecture
No full textThis thesis is a scouting on the possibilities of combining P.C.M.s and G.F.R.P.s into one transparent element, which could upgrade the aesthetical values of a non-transparent P.C.M.-G.F.R.P. system. The contribution of this research is twofold, providing: 1) An analysis framework for further exploration on the combination of a P.C.M. and a G.F.R.P., in respect to their basic properties and focusing on their optical properties. The framework occurs from the qualitative and quantitative findings collected via literature study, calculations and experimentation. 2) A guideline and recommendations for synthesizing the above findings into design parameters and typologies for potential architectural applications.Facade DesignBuilding TechnologyArchitectur
A roadmap for the sustainable growth of DoorMeal
No full textEmergence: In April, 2016, DoorMeal celebrated its first-year anniversary. It all started when Hannah Vreugdenhil drastically changed her unhealthy lifestyle, trading it in for a mindful and healthy lifestyle with a focus on fitness and nutrition. She shared her experiences on Instagram and people showed interest in what she was eating. Consequently, she decided to share her passion for delicious and healthy food, and DoorMeal B.V. was born. Since its inception, DoorMeal B.V. is part of Changing Life, a mother brand of various other brands that support living a fit lifestyle. Since then, DoorMeal has grown in employees, delivery area, meal variants and online followers (24.5K on Instagram and 8,000 likes on Facebook). DoorMeal uses mainly Instagram as its promotion channel to interact with its customers and prospects. Challenge: So far, the DoorMeal’ brand awareness has been driven by the power of Instagram. So, if someone is not actively involved on Instagram, that person will not likely know DoorMeal. That is why DoorMeal wants to explore the possibilities of using other channels to gain more brand awareness. While doing so, it is important to build a strong brand for DoorMeal to enhance its competitive advantage. Therefore, DoorMeal’s brand values need to be made explicit and further developed to be relevant to a larger target audience. Finally, it is important to have a shared mental model within the company to communicate a coherent message. This coherent communication will create a favourable impression and motivate DoorMeal’s customer segments to purchase a DoorMeal. Assignment: DoorMeal wants to know whether it should focus on the customers in the Netherlands or Amsterdam for market expansion. Therefore DoorMeal’s prospects should be fully understood in order to create a relevant value proposition. Branding guidelines are needed to translate these values and build a strong brand, distinguishing itself from its competition. Finally DoorMeal will receive a roadmap of actions to boost their brand awareness and branding guidelines for further development of the brand. Accordingly, the challenge can be stated as follows: “How can a strong brand be created for DoorMeal to foster competitive advantage and generate sustainable growth?” Process & results: First, the company was researched through participatory research in the preparation and delivery process and daily conversations with the founder and CEO of the company. In that way, the processes, strengths and weakness of the company were identified. Second, several studies were done to understand and analyse the external environment of the relevant users, competitors, trends, and developments to identify opportunities and threats for the company. This contextual analysis resulted in an explicitly modified brand strategy with branding guidelines, new positioning and the identification of customer segments. Finally, an action plan based on two detailed concepts was set out to create a stronger brand for DoorMeal, with a greater competitive advantage and steps to grow the company in a sustainable way.Industrial Design EngineeringProduct Innovation ManagementStrategic Product Desig
Spectra van puls code gemoduleerde signalen
No full textSommige vormen van P.C.M.-signalen, zoals bijvoorbeeld de tweede orde bipolaire code hebben een vermogensdichtheidsspectrum met spectrale nullen, terwijl in de onmiddellijke omgeving van een dergelijke "nul" slechts een zeer gering vermogen getransporteerd wordt. Nagegaan is wat de invloed op het oogdiagram van het P.C.M.- signaal is indien dit frequentiegebiedje niet meegezonden wordt. Om het informatie transporterende P.C.M.-signaal na te bootsen is een elektronische kruis-of-munt werper gebouwd die een tempo van twee miljoen "worpen" per seconde kan bereiken.Applied SciencesElectrotechniekTransmissie van Informati
Het ontwerp van een schakeling voor het genereren van 1/2T impulsen, waarvan de hoogte een stochastische variabele is met een normale verdeling: Verslag 60 middagentaak
No full textBij onderzoekingen naar de eigenschappen van pulscodemodulatie (P.C.M.) systemen blijkt behoefte te ontstaan aan een signaal dat gevormd wordt door impulsen met een herhalingsfrekwentie en impulsduur gelijk aan die van het P.C.M.-signaal en waarvan de impulshoogte een stochastische variabele is met een normale ( Gausze ) verdeling. De opdracht omvatte het ontwikkelen van een schakeling die het hierboven omschreven signaal kan leveren, waarbij nog als eis gesteld is dat de schakeling zowel unipolaire als bipolaire impulsreeksen moet kunnen leveren…Applied SciencesElectrotechniekTransmissie van Informati
Availability of organic contaminants in lake Ketelmeer sediment. Understanding sorption kinetics and distribution of in-situ contaminants
No full textElectric field, Magnetic field and Magnetization: THz time-domain spectroscopy studies
No full textTerahertz radiation is electromagnetic waves with frequencies from 0.1-10 THz. THz radiation can pass through cardboard, paper, plastics, ceramics and many other materials. Hence, it can be used for non-destructive imaging. Another important application of THz radiation is spectroscopy. Many organic molecules absorb light at THz frequencies and these absorption lines can be used for the identification of the molecules. This spectroscopic technique is called terahertz time domain spectroscopy (THz-TDS). It is a valuable tool for studying the properties of the material. In THz-TDS we measure the amplitude and phase of the THz pulse in the time domain using coherent detection techniques. Usually, in THz-TDS technique we measure the THz electric field using electro-optic detention technique. However, in thesis, the main goal is to focus on the magnetic aspect of THz generation and detection using THz-TDS. This thesis is divided into three research problems, in which THz-TDS plays the key role. In the first part, the THz-TDS setup is used for characterising the metamaterial elements. Metamaterials are artificially structured materials that are used to control and manipulate light. A split-ring resonator is one of the most common metamaterial elements. Usually these split-ring resonators are studied in far-field but near-field interactions are important to understand the properties of metamaterials. In the past electric near-field of SRRs are already studied. For the first time, we have directly measured the magnetic near-field of SRRs. The second research problem investigated in the thesis is generation of THz radiation from ferromagnetic cobalt thin film. When femtosecond laser pulses are incident on ferromagnetic metals prepared on a glass substrate, THz pulses are emitted via ultrafast demagnetization. It is often forgotten that nonmagnetic metals are also capable of emitting THz light and that such a contribution to the emitted THz field cannot a priori be excluded for magnetic metals. Our work clearly establishes a strong correlation between the magnetization and the emission of THz light following the excitation of cobalt with a femtosecond laser pulse. It does this by highlighting the role of the orientation of the magnetization in the terahertz emission from ferromagnetic thin films. We find that as we increase the cobalt film thickness, the polarisation direction of the emitted THz pulse changes, correlating with the transition from a predominantly in-plane to a predominantly out-plane magnetisation, as measured with magnetic force microscopy. When femtosecond laser light is incident on a semiconductor thin film, emission of THz radiation is observed. The emission can be enhanced if semiconductor materials are deposited on metal surfaces. In the last research problem of this thesis, in chapter 5, THz spectroscopy was used for studying the BiVO4/Au inter- faces. BiVO4 is a semiconductor material which is widely used for water splitting. When a BiVO4/Au interface is illuminated with ultrashort laser pulses, due to reflection from various interfaces, a standing wave pattern is observed. As a result, a difference in carrier concentration builds up which gives rise to THz emitting dipole. In short, this thesis discusses the possibilities of using terahertz time domain spectroscopy for studying the generation of THz radiation and using it for imaging and material characterization.Imaging PhysicsApplied Science
Grating-coupled surface plasmons for enhanced terahertz emission
No full textImPhys/Imaging PhysicsApplied Science
Een data reducerende codering voor "schrijfsignalen”
No full textVoor broncodering van "schrijfsignalen" worden enige digitale coderingsmogelijkheden, P.C.M., D.P.C.M., A.D.P.C.M., vergeleken. Onderzocht wordt welke voorspelling van de plaats van de pen op het schrijftableau uit voorafgaande plaatsen van de pen, de gemiddelde kleinste fout in de voorspelling maakt en welke codering deze voorspellingsfout met zo weinig mogelijk binaire symbolen per tijdseenheid beschrijft. Gebleken is dat bij een codering, waarbij afhankelijk van de grootte van de fout D.P.C.M. of P.C.M. gecodeerd wordt (dus eigenlijk A.D.P.C.M.) een minimum aantal binaire symbolen per tijdseenheid nodig zijn om de plaats van de pen bij de ontvanger exact te reconstrueren.Electrical Engineering, Mathematics and Computer ScienceTransmissie van Informati
Quasi-near field terahertz spectroscopy
No full textEveryday we see around us many materials that are different from one another. We identify them on the basis of their shape, texture, smell, taste, color, etc with the help of our senses. Many times it is almost impossible to identify materials only with our senses. Then, one has to look into more fundamental aspects of the materials such as their atomic or molecular constituents. Different techniques exist to identify and characterize materials. Spectroscopy is one such technique. Spectroscopy relies on the frequency selective emission or absorption of electromagnetic radiation by the materials to get information about their physical/chemical properties. There are different spectroscopic techniques to study materials and their interaction with electromagnetic radiation. Terahertz (THz) radiation is the part of electromagnetic spectrum, which lies between the microwave and infrared regions of the electromagnetic spectrum. It is loosely defined as the frequency range from 0.1 to 10 THz. Terahertz radiation can penetrate a wide range of materials: paper, wood, plastics, fabric, ceramics, semiconductors, and many others that are often opaque to visible and near-infrared (NIR) radiation. Many materials have characteristic absorption bands in the THz region. Thus, in THz imaging applications, apart from getting a THz image, the measurement can also give spectroscopic information on the samples under study, which can be used to identify the materials. In principle, this spectroscopic imaging makes it possible to identify the contents inside a package without even opening it. There exist various techniques to generate terahertz (THz) radiation. In photo-conductive antennas (PCAs), a time-dependent polarization is formed when charge carriers, created by a femtosecond laser pulse, are accelerated in an externally applied electric field. PCAs are capable of generating broadband pulses with a fairly high power. The THz generation and detection setup with the photo-conductive antenna as the THz source and electro-optic sampling as the THz detector as described in Chapter 2 gives a very high SNR of ?15000 in a measurement time of 10 ms. Even though our femtosecond laser pulses have a very high peak power, the generated THz power could not be increased further with increasing laser pump power on the emitter, because of emitter saturation. Increasing the laser spot size on the emitter gives a higher THz peak power than in the case of a tightly focused pump beam. Among the different techniques to generate THz radiation, the technique using the optical conversion of extremely short pulses of light into THz pulses at a high repetition rate is very popular. These short laser pulses are partially converted into THz light in certain non-linear optical media. By using coherent detection techniques, the amplitude and phase of the THz pulse can be detected in the time domain. This spectroscopic technique is called terahertz time domain spectroscopy (THz-TDS). A typical THz-TDS setup has a long THz beam path. Atmospheric water vapor, present also in the beam path, has many strong absorption bands in the THz region, which makes it difficult to perform spectroscopy on samples. Such a setup should therefore be flushed with dry N2 gas to reduce absorption of the THz radiation by water vapor molecules in the atmosphere. Typically, a THz-TDS setup also requires parabolic mirrors to collimate, steer and focus the THz radiation onto the detection crystal which is complicated by the fact that THz radiation is invisible. Furthermore, the THz beam diffraction and absorption at the reflecting surfaces in the THz beam path will lead to reduction of the THz power. One way to overcome all these problems is by placing the THz source and detector very close to each other. Apart from its simplicity, the advantage of such a quasi-near field terahertz spectrometer is that it can also provide a broad bandwidth (0.5-7 THz) and a good signal-to-noise ratio even without the use of lock-in detection. THz radiation is generated by optical rectication of 50 fs, 800 nm pulses from a Ti:sapphire oscillator in suitable nonlinear optical crystals such as GaP. The shape and bandwidth of the spectra of the THz pulses generated in this way, are explained with a simple model, which takes into account the effects of phase-matching and absorption of THz radiation in the generation and detection crystals. If one wants to increase the generated bandwidth to frequencies above the phonon resonance frequency, then very short laser pulses (?10 fs) and very thin crystals (?50 ?m) should be used. An important point to note is that the probe and the THz pulses are initially counter propagating and, after reflecting, co-propagating in the detection crystal. Both the calculations and the experimental results show that the effect of counter propagation of the THz pulse and the probe pulse in the detection crystal is negligible at higher frequencies, above a few hundred GHz. Samples can be inserted between the generation and detection crystals, and their absorption spectra can be measured. As the THz beam propagates, it is expected to show a frequency-dependent divergence. This changes when a sample is placed between the generation and detection crystals, making it more difficult to obtain the absolute absorption coefficient. However, this has no effect on the ability of the setup to identify materials by their spectral fingerprint. This is shown in Chapter 4, which contains measured absorption spectra of, D-tartaric acid, certain amino acids, sugars and metal oxides, in the frequency range of 0.5-7 THz. Another exciting application of THz-TDS, as described in this thesis, is the identification of polymorphs in freeze dried mannitol. Freeze drying is very commonly used in the pharmaceutical industry to increase the shelf life and dry state stabilization of the therapeutic agents, where polymorphism is identified as a serious problem. These polymorphs often can have unique physical and chemical characteristics that can influence their stability, solubility and other performance characteristics. It is important for the pharmaceutical industry to know which polymorph is formed during the freeze drying process. The measured THz absorption spectra of the ? and ? polymorphs of mannitol from 0.5 THz to 7 THz, have distinct THz absorption spectra as shown in Chapter 5, especially between 2.5 and 6 THz. Because THz-TDS can be used to identify the polymorphs of mannitol, we have subsequently used this technique to study the effect of various freeze drying techniques on the formation of these polymorphs. The results show that, for mannitol, changes in the way the material is frozen can result in the formation of different polymorphs or a mixture of polymorphs, as supported by X-ray diffraction measurements performed on these samples. The THz-TDS has the added advantage that it may be relatively easy to employ as an in-line and, almost, real time monitoring tool, unlike X-ray diffraction analysis.ISTApplied Science
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