128 research outputs found
A Field Ion Microscope Study of Interfaces
Get PDFTitle: A Field Ion Microscope Study of Interfaces, Author: Ramesh Rajagopal, Location: ThodeThis investigation is concerned with the observation of interfaces between f.c.c. and b.c.c. crystals in the field ion microscope. A high vacuum field ion microscope was designed and constructed to operate under liquid nitrogen cooling and helium gas imaging, with facilities for vapour deposition. Platinum and iridium were deposited on tungsten field ion emitters by shadow vapour deposition. The nature and contrast of deposits obtained under various experimental conditions are examined. The atomic matching observed at interfaces is discussed within the limitations of the existing interfacial contrast theory.ThesisMaster of Engineering (ME
Holographic Jet Shapes and their Evolution in Strongly Coupled Plasma
No full text© 2017 The Author(s) Recently our group analyzed how the probability distribution for the jet opening angle is modified in an ensemble of jets that has propagated through an expanding cooling droplet of plasma [K. Rajagopal, A. V. Sadofyev, W. van der Schee, Phys. Rev. Lett. 116 (2016) 211603]. Each jet in the ensemble is represented holographically by a string in the dual 4+1- dimensional gravitational theory with the distribution of initial energies and opening angles in the ensemble given by perturbative QCD. In [K. Rajagopal, A. V. Sadofyev, W. van der Schee, Phys. Rev. Lett. 116 (2016) 211603], the full string dynamics were approximated by assuming that the string moves at the speed of light. We are now able to analyze the full string dynamics for a range of possible initial conditions, giving us access to the dynamics of holographic jets just after their creation. The nullification timescale and the features of the string when it has nullified are all results of the string evolution. This emboldens us to analyze the full jet shape modification, rather than just the opening angle modification of each jet in the ensemble as in [K. Rajagopal, A. V. Sadofyev, W. van der Schee, Phys. Rev. Lett. 116 (2016) 211603]. We find the result that the jet shape scales with the opening angle at any particular energy. We construct an ensemble of dijets with energies and energy asymmetry distributions taken from events in proton-proton collisions, opening angle distribution as in [K. Rajagopal, A. V. Sadofyev, W. van der Schee, Phys. Rev. Lett. 116 (2016) 211603], and jet shape taken from proton-proton collisions and scaled according to our result. We study how these observables are modified after we send the ensemble of dijets through the strongly-coupled plasma
Finding the Scatterers in Hot Quark Soup
Get PDF© Copyright owned by the author(s) under the terms of the Creative Commons. We present a brief report on a thought experiment in which an incident energetic parton traverses a brick of quark-gluon plasma (QGP), see Ref. [1] for the full report. We calculate the probability of detecting a parton showing up at a large angle with respect to its initial direction due to scattering with the constituents of QGP, using leading order perturbative QCD. We include all relevant channels, including the Rutherford-like channel as considered in early works, and those that are not Rutherford-like but become important at a large angle. The resulting probability distributions contain information about the short distance structure of QGP. Our results provide key theoretical input toward finding the scatterers within the QGP liquid, which in turn is the necessary first step toward using precise, high-statistics, suitably differential measurements of jet modification in heavy ion collisions to study the evolution of the properties of QGP with changing resolution scale
UPEI-400, a conjugate of lipoic acid and scopoletin, mediates neuroprotection in a rat model of ischemia/reperfusion
No full textAlteration of proteins and pigments influence the function of photosystem I under iron deficiency from Chlamydomonas reinhardtii.
Get PDFBACKGROUND: Iron is an essential micronutrient for all organisms because it is a component of enzyme cofactors that catalyze redox reactions in fundamental metabolic processes. Even though iron is abundant on earth, it is often present in the insoluble ferric [Fe (III)] state, leaving many surface environments Fe-limited. The haploid green alga Chlamydomonas reinhardtii is used as a model organism for studying eukaryotic photosynthesis. This study explores structural and functional changes in PSI-LHCI supercomplexes under Fe deficiency as the eukaryotic photosynthetic apparatus adapts to Fe deficiency. RESULTS: 77K emission spectra and sucrose density gradient data show that PSI and LHCI subunits are affected under iron deficiency conditions. The visible circular dichroism (CD) spectra associated with strongly-coupled chlorophyll dimers increases in intensity. The change in CD signals of pigments originates from the modification of interactions between pigment molecules. Evidence from sucrose gradients and non-denaturing (green) gels indicates that PSI-LHCI levels were reduced after cells were grown for 72 h in Fe-deficient medium. Ultrafast fluorescence spectroscopy suggests that red-shifted pigments in the PSI-LHCI antenna were lost during Fe stress. Further, denaturing gel electrophoresis and immunoblot analysis reveals that levels of the PSI subunits PsaC and PsaD decreased, while PsaE was completely absent after Fe stress. The light harvesting complexes were also susceptible to iron deficiency, with Lhca1 and Lhca9 showing the most dramatic decreases. These changes in the number and composition of PSI-LHCI supercomplexes may be caused by reactive oxygen species, which increase under Fe deficiency conditions. CONCLUSIONS: Fe deficiency induces rapid reduction of the levels of photosynthetic pigments due to a decrease in chlorophyll synthesis. Chlorophyll is important not only as a light-harvesting pigment, but also has a structural role, particularly in the pigment-rich LHCI subunits. The reduced level of chlorophyll molecules inhibits the formation of large PSI-LHCI supercomplexes, further decreasing the photosynthetic efficiency
Small-x evolution of jet quenching parameter
No full textAbstractConcept of transverse deflection probability of a parton that travels through strongly interacting medium, recently introduced by D'Eramo, Liu and Rajagopal, has been used to derive high energy evolution equation for the jet quenching parameter in stochastic multiple scatterings regime. Jet quenching parameter, qˆ(x), appears to evolve with x, with an exponent 0.9α¯s, which is slightly less than that of xG(x) where G(x) is the gluon distribution function
Design of Human Computer Interface for blind children to learn programming languages
No full textAs the modern world progressing towards digital technologies, there is an increasing need for school students to learn programming skills so that they fit into the labor market now and in the future. Tangible programming toys and block-based languages are popular among younger children to learn to code. Students in middle and high school in several countries have begun to learn textual programming education as a step towards successful careers and educational opportunities. However, due to the visual nature of these materials and tools, they are inaccessible to blind students. Also, the accessibility aids used for interacting with computers in the first place are not accessible when it comes to programming. Braille displays are not accessible by most blind users as the braille literacy rates are falling, while screen readers do not read source code. Also, attempts to teach code using screen readers despite challenges kills the student’s enthusiasm. The project proposes a design approach to multi-modal human-computer interaction to reduce sensory and cognitive overload to enhance learning outcomes for this user group. The design goal was to develop an affordable audio-tactile interface, to help blind high school students to learn textual programming languages. Research insights were gathered from literature research, surveys, interviews, observation studies, and co-creation sessions with blind students. The insights were synthesized to form ideas, and concepts were explored. The final concept was then taken to a level of functional prototype and was validated in simulated tests. A sustainable business model was also developed to take the project forward as an open-source hardware venture.Integrated Product Desig
Identification of Probe of an Atomic Force Microscope Using Curve Fitting
No full textIn recent years the Tapping Mode-Atomic Force Microscope (TM-AFM) has become one of the most important tools for imaging on the nanometer scale. In comparison with other contemporary technologies, the AFMs have been able to obtain atomic resolution both in high vacuum and liquid environments thus affirming their supremacy. The AFM can be perceived as a combination of a mechanical profilometer, where mechanical springs are used to sense the forces, and a Scanning tunneling microscope, where piezo-electric transducers are used for scanning. The AFM is widely used to generate a topographical image of the sample surface and also to study certain characteristics of the sample. The latter is aided by measuring the forces between the sample surface and the tip of the probe.The non-linear, rapidly changing and hysteretic behavior of the tip-sample forces makes their accurate estimation extremely difficult in dynamic AFM. Moreover, the cantilever probe responds to an average of the different forces acting on the probe tip. Since several permutations of different forces can give the same periodic average, the accurate estimation of each of these forces has been evidently impossible. However, some probes exist for which the motion of the cantilever consists of super harmonic components of the tip-sample forces which provide more information about the tip-sample forces. Nevertheless the construction of these cantilevers is challenging and time consuming. Knowledge of the dynamic properties of the cantilever facilitates one to study its behaviour to a particular input. Since different forces act at different tip sample distances, a more mathematical approach towards tip-sample force estimation which includes the dynamic characteristics of the cantilever is necessary. The accurate knowledge of the cantilever dynamics is extremely important for precise estimation of tip-sample forces, deduction of mechanical properties, controller synthesis etc. Therefore in this research, the techniques to identify the state space matrices is explored. One, rather old but an immensely useful identification method are the black box identification techniques. These techniques can be used to accurately estimate the fully parameterized state space matrices of the system. The main difficulty arises in estimating these parameters specially in the absence of one of the inputs (tip-sample interactions). In this thesis research, an algorithm is developed to identify the fully parameterized state space matrices. A secondary cantilever of very high fundamental resonance frequency is used as a force sensor. This force sensor set up along with the periodic property of the tip-sample forces during TM-AFM is used to reconstruct the tip-sample interaction forces. Using the estimated tip-sample forces, a transfer function between the cantilever deflection and the estimated force is identified using a curve fitting technique. The curve fitting technique uses iterative least squares to reduce the two norm between the experimental frequency response and the frequency response estimated using the identified transfer function.Mechanical Engineering | Systems and Contro
Modulated surface texturing on temporary aluminium substrate for flexible thin-film solar cells
No full textThin-film photovoltaic technologies are gaining momentum over the currently dominated crystalline silicon technologies. In addition to the competitive prices, flexible thin-film technology especially has the added advantage such as in building integrated photovoltaics (BIPV) due to its flexibility and light weight. HyET Solar B.V. is a company based in the Netherlands which state-of-the-art Roll to Roll (R2R) technology to produce such flexible solar cells. A temporary aluminum foil is used as substrate on to which FTO/p-i-n solar cell stack is deposited. The temporary foil is etched away, and the layers are encapsulated in low cost polymer foils. This thesis is part of the on-going FlamingoPV (Flexible Lightweight Advanced Materials In Next Generation of PV) project in collaboration between HyET Solar and TU Delft, to develop single, tandem and triple junction cells with 12, 13 and 14% efficiencies and a lifetime longer than 35 years. This thesis is inspired by the work of Tan et. al [8] where record efficiency cells were achieved on solar cells deposited on ‘Modulated Surface Textured’ (MST) glass substrates. In MST, increased light scattering is obtained by superposition of various scattering mechanisms which is achieved by introducing different textures at different interfaces and stacking them together. The requirements of the MST are two-fold: to provide efficient light trapping and to aid in the growth of high-quality layers. The aim is to introduce MST in the R2R process by developing micro sized crater-shaped features on the temporary Al foil on to which naturally nano sized V-shaped textures of FTO is deposited. The crater-shaped features are developed on the Al foil (~110 um) using wet chemical etching techniques. Various acid and alkaline based etchants are experimented. The etching parameters- concentration and temperature of the etchant and the etching time are varied to achieve the optimum recipe. These parameters should be varied such that the features have a correlation length (an estimate of how wide the feature is) 3-4 um and an aspect ratio (ratio of RMS roughness to correlation length) of 12-14%. These features are characterized using SEM and AFM to measure the aforesaid parameters and reflectance and angular intensity distribution measurements to measure its effectiveness of scattering. Alkaline based etchants (KOH and NaOH) resulted in crater-shaped features unlike acid etchants which resulted in pyramidal features. It was observed that there is an initial ‘induction period’ before which the etching started. For lower temperature, time and concentration, the induction period is longer. To ensure mechanical stability during deposition stages, the foil needs to be thicker than 70 um on lab-scale. The above-mentioned etching parameters were varied, and the best recipe was found to be 1.78M KOH at 70°C for an etching time of 2 minutes, 1.78M KOH at 60°C for 3 minutes and 1.42M NaOH at 70°C for 2.5 minutes. These samples displayed a correlation length 4-4.6 um and aspect ratios from 12-14% which is close to the targeted values and are higher than the existing texturing at HyET (‘factory baseline’) which had correlation length and aspect ratios of 500 nm and 5.7% respectively. These samples also showed higher scattering compared to the factory baseline. The nc-Si:H and a-Si:H/nc-Si:H layers deposited on to these samples resulted in dense high-quality layers. The TCO/p-i-n layers deposited also adapted the texturing pattern of the Al foil, unlike the factory baseline where the Al surface morphology was not adapted by the other layers as the features were significantly smaller. Further, to enhance the uniformity of texturing, various ‘chelating agents’ and ‘surfactants’ such as gluconic acids and glycols as well as varying the speed of etching to ensure homogenous contact of etchant with the foil was carried out. Both these techniques resulted in in an increased etch rate as well as an increase in the density of the craters on the foil. Considering the limitations of the R2R process, the best lab recipes were adapted (50°C, 1.42M NaOH, 1.8 minutes) to implement on the R2R etching machine. The resulting Al foil had higher surface morphology parameters and scattering compared to the factory baseline. The cells deposited on this texturing adapted the morphology of the Al foil. Optical simulations were done using GenPro4 where the AFM data of the textures were given as the input. The best lab samples as well as the R2R testing recipe showed larger absorption in the higher wavelengths in both nc-Si:H single junction and a-Si:H/nc-Si:H tandem cells, compared to the standard factory baseline texturing.Flamingo PVElectrical Engineering | Electrical Power Engineerin
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