This work focuses on studying two types of structure: homogeneous and double-diffused emitter silicon solar cells. The emitter collection efficiencies and the recombination current densities were studied for a wide range of surface dopant concentrations and thicknesses. The frontal metal-grid was optimized for each emitter, considering the dependence on the metal-semiconductor contact resistivity and on the emitter sheet resistance. The best efficiency for n+p structures, η≈ 25.5%, is found for emitters with thicknesses between (0.5-3) µm and surface doping concentrations in the range 2 x 10(19) cm-3- 4 x 10(18) cm-3; while the n++n+p structure a maximum efficiency of η≈ 26.0% was identified for an even wider range of emitter profiles.; CNPq
The study was conducted at the Research Laboratory of Hydraulic and Irrigation Group in the Rural Engineering Department, Technical University of Madrid (Universidad Politecnica de Madrid), Madrid, Spain. Water temperatures of 20, 30, 40 degrees C and system pressures often encountered in irrigation practices of 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190 and 200 k Pa were applied to determine the effects of different water temperatures and pressures on emitter discharge. Non-pressure compensating in-line emitter which has turbulent flow regime with a long-path (labyrinth), emitter discharge was 4 L h(-1) at system pressure of 100 kPa according to the manufacturer recommended, was used. Emitters were spaced 20 cm along the drip laterals with 16 mm diameter. Discharge equations and coefficients of variation related to temperatures of 20, 30 and 40 degrees C were obtained as q = 0.375H(0.51), q = 0.358H(0.52), q = 0.346H(0.53) and 2.68, 2.09, 3.65, respectively. Discharge of the emitter was affected by different system pressures and increased as potentially (R = 0993-0996). In general. the emitter discharge increased with increasing temperature. However, especially in the common system pressures of 90-120 k Pa, differences of obtained emitter discharges between the different water temperatures were not significant (1%).; Turkish Higher Education Council
The study was conducted at the Research Laboratory of Hydraulic and Irrigation Group in the Rural Engineering Department, Technical University of Madrid (Universidad Politecnica de Madrid), Madrid, Spain. Water temperatures of 20, 30, 40 degrees C and system pressures often encountered in irrigation practices of 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190 and 200 k Pa were applied to determine the effects of different water temperatures and pressures on emitter discharge. Non-pressure compensating in-line emitter which has turbulent flow regime with a long-path (labyrinth), emitter discharge was 4 L h(-1) at system pressure of 100 kPa according to the manufacturer recommended, was used. Emitters were spaced 20 cm along the drip laterals with 16 mm diameter. Discharge equations and coefficients of variation related to temperatures of 20, 30 and 40 degrees C were obtained as q = 0.375H(0.51), q = 0.358H(0.52), q = 0.346H(0.53) and 2.68, 2.09, 3.65, respectively. Discharge of the emitter was affected by different system pressures and increased as potentially (R = 0993-0996). In general. the emitter discharge increased with increasing temperature. However, especially in the common system pressures of 90-120 k Pa, differences of obtained emitter discharges between the different water temperatures were not significant (1%).
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq); Pós-graduação em Agronomia (Irrigação e Drenagem) - FCA; O objetivo do trabalho foi comparar linhas laterais convencionais de irrigação por gotejamento com espaçamento único entre gotejadores em relação a laterais compostas por dois segmentos, cada segmento utilizando espaçamento entre emissores diferente, utilizando como indicadores os parâmetros físicos, químicos e físico-químicos da cultura de rabanete e a formação dos bulbos molhados no solo. Linhas laterais convencionais com espaçamento entre emissores de 20 cm foram comparadas às linhas laterais propostas tendo espaçamento entre emissores de 24 cm no segmento inicial e espaçamento de 20 cm no segmento final; linhas laterais convencionais com espaçamento entre emissores de 30 cm foram comparadas às linhas laterais propostas, com espaçamento entre emissores de 36 cm no segmento inicial e espaçamento de 30 cm no segmento final. Em todas as linhas, utilizou-se pressão de 100 kPa no segmento inicial e 70 kPa no segmento final, de modo que as vazões por metro de linha lateral foram as mesmas em todos os tratamentos. O experimento foi conduzido em ambiente protegido na Fazenda Experimental São Manuel...
Ultrasound transducers are typically based on piezoelectric materials, due to their good response at high frequencies. Depending on the application, ceramics, polymers and composite materials can be used. In this work, an optimization study of ultrasound transducers for underwater communications is addressed, focusing on a piston type emitter transducer operating in thickness mode (d33). The piston is constituted by an active element disk with optimized dimensions. It is discussed how the acoustic impedance, thickness, resonance frequency and structure affect the transducer performance. This work allows a better understanding of the emitter transducer characteristics allowing reaching the optimum point of operation for specific applications. Focusing on underwater communication, the acoustic channel is defined and the transducer is optimized by finite element computer simulations. The results were compared with experimental tests, which show that four-layer structures increase up to 16 dB in performance versus single-layer.
Considering recent modifications on n-type highly doped silicon parameters, an emitter optimization was made based on one-dimensional models with analytical solutions. In order to get good accuracy, a fifth order approximation has been considered. Two kinds of emitters, homogeneous and non-homogeneous, with phosphorus Gaussian profile emitter solar cells were optimized. According to our results: homogeneous emitter solar cells show their maximum efficiencies (h @ 21.60-21.74%)with doping levelsnus = 1x10(19) - 5x10(18) (cm-3) and (1.2-2.0) mum emitter thickness range. Non-homogeneous emitter solar cells provide a slightly higher efficiency (eta = 21.82-21.92%), with Ns = 1x10(20) (cm-3) with 2.0 mum thickness under metal-contacted surface and Ns = 1x10(19) - 5x10(18) (cm-3) with (1.2-2.0) mum thickness range, (sheet resistance range 90-100 W/ ) under passivated surface. Although non-homogeneous emitter solar cells have a higher efficiency than homogeneous emitter ones, the required technology is more complex and their overall interest for practical applications is questionable.
This work focuses on studying two types of structure: homogeneous and double-diffused emitter silicon solar cells. The emitter collection efficiencies and the recombination current densities were studied for a wide range of surface dopant concentrations and thicknesses. The frontal metal-grid was optimized for each emitter, considering the dependence on the metal-semiconductor contact resistivity and on the emitter sheet resistance. The best efficiency for n+p structures, η≈ 25.5%, is found for emitters with thicknesses between (0.5-3) µm and surface doping concentrations in the range 2 x 10(19) cm-3- 4 x 10(18) cm-3; while the n++n+p structure a maximum efficiency of η≈ 26.0% was identified for an even wider range of emitter profiles.
Fonte: Sociedade Brasileira de Microondas e Optoeletrônica e Sociedade Brasileira de EletromagnetismoPublicador: Sociedade Brasileira de Microondas e Optoeletrônica e Sociedade Brasileira de Eletromagnetismo
Tipo: Artigo de Revista CientíficaFormato: text/html
An analytical study to quantify the substrate parasitic effects on SiGe HBT amplifiers in both common-base and common-emitter configuration is presented. The power gain relations and stability factors are derived from the modelled S-parameters which are computed at a fixed bias point from the small-signal hybrid-∏ model of SiGe HBT in both configurations. It has been shown that the power gains of SiGe HBT amplifiers in both configurations are degraded when extrinsic and substrate parasitics are taken into account. The degradation in power gains is found to be more pronounced for CB configuration, which makes the design of HBT amplifiers, particularly in the CB mode, difficult. Close matching of the modelled data with the reported experimental results validates the proposed methodology.
Arrays of electrospray ionization (ESI) emitters have been reported previously as a means of enhancing ionization efficiency or signal intensity. A key challenge when working with multiple, closely spaced ESI emitters is overcoming the deleterious effects caused by electrical interference among neighboring emitters. Individual emitters can experience different electric fields depending on their relative position in the array, such that it becomes difficult to operate all of the emitters optimally for a given applied potential. In this work, we have developed multi-nanoESI emitters arranged with a circular pattern, which enable the constituent emitters to experience a uniform electric field. The performance of the circular emitter array was compared to a single emitter and to a previously developed linear emitter array, which verified that improved electric field uniformity was achieved with the circular arrangement. The circular arrays were also interfaced with a mass spectrometer via a matching multi-capillary inlet, and the results were compared with those obtained using a single emitter. By minimizing inter-emitter electric field inhomogeneities, much larger arrays having closer emitter spacing should be feasible.
An integrated poly(dimethylsiloxane) (PDMS) membrane-based microfluidic emitter for high performance nanoelectrospray ionization-mass spectrometry (nanoESI-MS) has been fabricated and evaluated. The ~100-μm-thick emitter was created by cutting a PDMS membrane that protrudes beyond the bulk substrate. The reduced surface area at the emitter enhances the electric field and reduces wetting of the surface by the electrospray solvent. As such, the emitter enables highly stable electrosprays at flow rates as low as 10 nL/min, and is compatible with electrospray solvents containing a large organic component (e.g., 90% methanol). This approach enables facile emitter construction, and provides excellent stability, reproducibility and sensitivity, as well as compatibility with multilayer soft lithography.
Arrays of chemically etched emitters with individualized sheath gas capillaries were developed to enhance electrospray ionization (ESI) efficiency at subambient pressures. By incorporating the new emitter array in a subambient pressure ionization with nanoelectrospray (SPIN) source, both ionization efficiency and ion transmission efficiency were significantly increased, providing enhanced sensitivity in mass spectrometric analyses. The SPIN source eliminates the major ion losses of conventional ESI-mass spectrometry (MS) interfaces by placing the emitter in the first reduced pressure region of the instrument. The new ESI emitter array design developed in this study allows individualized sheath gas around each emitter in the array making it possible to generate an array of uniform and stable electrosprays in the subambient pressure (10 to 30 Torr) environment for the first time. The utility of the new emitter arrays was demonstrated by coupling the emitter array/SPIN source with a time of flight (TOF) mass spectrometer. The instrument sensitivity was compared under different ESI source and interface configurations including a standard atmospheric pressure single ESI emitter/heated capillary, single emitter/SPIN and multi-emitter/SPIN configurations using an equimolar solution of 9 peptides. The highest instrument sensitivity was observed using the multi-emitter/SPIN configuration in which the sensitivity increased with the number of emitters in the array. Over an order of magnitude MS sensitivity improvement was achieved using multi-emitter/SPIN as compared to using the standard atmospheric pressure single ESI emitter/heated capillary interface.
Nano-ESI mass spectrometry is an attractive analytical technique due to its high sensitivity and small sample consumption, which is especially important for research areas such as proteomics. However, current nano-ESI emitters become a bottleneck for nano-ESI to be widely applied because of problems such as clogging, poor robustness, large flow resistance, and poor spray efficiency for highly aqueous solutions. The objective of this thesis study is to address the problems associated with tapered emitters and provide alternative solutions by developing advanced nano-ESI emitters. Two strategies that were explored to improve the clogging resistance and robustness while maintaining comparable electrospray performances include the development of emitters with larger apertures and multiple channels.
Following these strategies, five types of emitters were fabricated without tapering either internal or external diameters, which include a roughened open tubular emitter, a porous membrane-assisted emitter, a microstructured multiple channel photonic crystal fiber (MSF) emitter, a packed ODS bead emitter, and an entrapped ODS bead emitter. The successful transformation of MSF fibers to nanoelectrospray emitters demonstrates a new practical approach to expand the application of nano-ESI because of its availability...
Electrospray ionization (ESI) has been an invaluable technique to mass spectrometry (MS) especially for analyzing large bio-molecules with unparalleled sensitivity, robustness, and simplicity. Great effort in the development of ESI technique has been devoted in the emitter design, as its shape and geometry have proved pivotal to the electrospray performance and further MS detection. Intrinsic problems for the traditional single-hole emitters including clogging and low throughput limit the applicability of the technique. To address this issue, the current project is focused on developing multiple electrospray (MES) emitters for improved ESI-MS analysis.
In this thesis, joint work of both computational fluid dynamic (CFD) simulations for electrospray and offline electrospray experiments for spray current measurement were performed. Numerical simulations were used to test the effect of various emitter designs on electrospray performance and the laboratory results serve as a guide and validation. The CFD code was based on Taylor-Melcher leaky dielectric model (LDM) and the transient electrospray process was successfully simulated. The method was first validated via a 750 μm inner diameter (i.d.) emitter and further applied to a 20 μm i.d. model. Different stages of the electrospray process were visually demonstrated and the quantitative investigations for the change of spray current under various applied electric fields and flow rates share good agreement with previous simulations and measurements. Based on the single-aperture prototype...
A hybrid white organic light-emitting diode (WOLED) with an external quantum efficiency above 20% was developed using a new blue thermally activated delayed fluorescent material, 4,6-di(9H-carbazol-9-yl)isophthalonitrile (DCzIPN), both as a blue emitter and a host for a yellow phosphorescent emitter. DCzIPN showed high quantum efficiency of 16.4% as a blue emitter and 24.9% as a host for a yellow phosphorescent emitter. The hybrid WOLEDs with the DCzIPN host based yellow emitting layer sandwiched between DCzIPN emitter based blue emitting layers exhibited high external quantum efficiency of 22.9% with a warm white color coordinate of (0.39, 0.43) and quantum efficiency of 21.0% with a cool white color coordinate of (0.31, 0.33) by managing the thickness of the yellow emitting layer.
Field emission formulae, current-voltage characteristics and energy
distribution of emitted electrons, are derived analytically for a nonplanar
(hyperboloidal) metallic emitter model. The traditional Fowler-Nordheim
formulae, which are derived from a planar emitter model, are modified, and the
assumption of the planar emitter in the F-N model is reconsidered. Our
analytical calculation also reveals the backgrounds of the previous numerical
discussion by He et al. on the effect of the geometry of emitter on field
emission. The new formulae contain a parameter which characterizes the
sharpness of the hyperboloidal emitter, and experimental data of field
emissions from clean tungsten emitters and nanotip emitters are analyzed by
making use of this feature.; Comment: 9 pages, 8 figures
We develop a Ly-alpha radiative transfer (RT) Monte Carlo code for
cosmological simulations.High resolution,along with appropriately treated
cooling can result in simulated environments with very high optical
depths.Thus,solving the Ly-alpha RT problem in cosmological simulations can
take an unrealistically long time.For this reason,we develop methods to speed
up the Ly-alpha RT.With these accelerating methods,along with the
parallelization of the code,we make the problem of Ly-alpha RT in the complex
environments of cosmological simulations tractable.We test the RT code against
simple Ly-alpha emitter models,and then we apply it to the brightest Ly-alpha
emitter of a gasdynamics+N-body Adaptive Refinement Tree (ART) simulation at
z~8.We find that recombination rather than cooling radiation Ly-alpha photons
is the dominant contribution to the intrinsic Ly-alpha luminosity of the
emitter,which is ~4.8x10e43 ergs/s.The size of the emitter is pretty
small,making it unresolved for currently available instruments.Its spectrum
before adding the Ly-alpha Gunn-Peterson absorption (GP) resembles that of
static media,despite some net inward radial peculiar motion.This is because for
such high optical depths as those in ART simulations,velocities of order some
hundreds km/s are not important.We add the GP in two ways.First we assume no
We report a novel method to reduce the collector-emitter offset-voltage of
the wide bandgap SiC-P-emitter lateral HBTs using a dual-bandgap emitter. In
our approach, the collector-emitter offset-voltage VCE(offset) is reduced
drastically by eliminating the built-in potential difference between the
emitter-base (EB) junction and collector-base (CB) junction by using a
SiC-on-Si P-emitter. We demonstrate that the proposed dualbandgap P-emitter HBT
together with the SiGe base and Schottky collector, not only has a very low
VCE(offset) but also exhibits high current gain, reduced Kirk effect, excellent
transient response and high cutoff frequency. We evaluated the performance of
the proposed device in detail using two dimensional device simulation and a
possible BiCMOS compatible fabrication procedure is also suggested.; Comment: http://web.iitd.ac.in/~mamidala/
We develop a wavefunction approach to describe the scattering of two photons
on a quantum emitter embedded in a one-dimensional waveguide. Our method allows
us to calculate the exact dynamics of the complete system at all times, as well
as the transmission properties of the emitter. We show that the non-linearity
of the emitter with respect to incoming photons depends strongly on the emitter
excitation and the spectral shape of the incoming pulses, resulting in
transmission of the photons which depends crucially on their separation and
width. In addition, for counter-propagating pulses, we analyze the induced
level of quantum correlations in the scattered state, and we show that the
emitter behaves as a non-linear beam-splitter when the spectral width of the
photon pulses is similar to the emitter decay rate.; Comment: 15 pages, 7 figures
We study the photon blockade phenomenon in a nanocavity containing a single
four-level quantum emitter. By numerically simulating the second-order
autocorrelation function of the intra-cavity field with realistic parameters
achievable in a state-of-the-art photonic-crystal nanocavity, we show that in
the strongly coupled regime the resulting photon blockade is significantly
better than that achievable with a two-level emitter. We introduce an intuitive
picture of the photon blockade with a four-level emitter that explains the
performance difference between the two-level and the four-level emitter
schemes, as well as why -- in contrast to a cavity containing a two-level atom
-- signatures of photon blockade appear and should be experimentally observable
even outside the strong coupling regime when a four-level emitter is used.
Finally, we show that the emitter-cavity coupling achievable in a nanocavity
can overcome the non-ideal spacing of optical transitions in realistic
four-level emitters that has so far prevented experimental realization of this
photon blockade scheme.; Comment: 8 pages, 7 figures
There have been many trials to employ nano-carbon materials, such as carbon-nano-tubes and nano-diamond films, as electron-emitter. Several reasons exist why the nano-carbon materials are good for the emitter. They are, in addition to (a) unique morphological shapes of the materials good for the emitter- the high aspect ratio of the carbon-nano-tube is a good example-, (b) sturdiness(they can even be formed in a plasma), (c) high thermal conductivity (current density in the electron-emitting-nano-structure is high, thus it is vital to provide effective Joule-heat dissipation), and (d) easiness of the fabrication of the electron-emitting carbon materials. In order to fabricate good electron emitters, we have long been trying to employ a variety of fabrication CVD methods and fabricating conditions (starting CVD gas, pressure, temperature, substrate materials and so on).Then recently our emitters have shown a world-top-ranking property: very low turn-on- voltage(0.5V/µm induce 10µA/cm² of emission current) and high current at low applied voltage with gap distance of 1mm(1mA/cm² at 1.1V/µm and 100/ at 2V/µm). This excellent property comes from a carbon-nano-structure which we call CNX(Carbon-Nano-eXit). In addition, these emitter can be formed on a variety of substrates(Ni...