Search results for "AF"
showing 10 items of 23539 documents
Energy transfer in LH2 of Rhodospirillum Molischianum, studied by subpicosecond spectroscopy and configuration interaction exciton calculations.
2001
Two color transient absorption measurements were performed on a LH2 complex from Rhodospirillum molischianum by using several excitation wavelengths (790, 800, 810, and 830 nm) and probing in the spectral region from 790 to 870 nm at room temperature. The observed energy transfer time of ∼1.0 ps from B800 to B850 at room temperature is longer than the corresponding rates in Rhodopseudomonas acidophila and Rhodobacter sphaeroides. We observed variations (0.9-1.2 ps) of B800-850 energy transfer times at different B800 excitation wavelengths, the fastest time (0.9 ps) was obtained with 800 nm excitation. At 830 nm excitation the energy transfer to the B850 ring takes place within 0.5 ps. The m…
Injection and ultrafast regeneration in dye-sensitized solar cells
2014
Injection of an electron from the excited dye molecule to the semiconductor is the initial charge separation step in dye-sensitized solar cells (DSC's). Though the dynamics of the forward injection process has been widely studied, the results reported so far are controversial, especially for complete DSC's. In this work, the electron injection in titanium dioxide (TiO2) films sensitized with ruthenium bipyridyl dyes N3 and N719 was studied both in neat solvent and in a typical iodide/triiodide (I-/I3 -) DSC electrolyte. Transient absorption (TA) spectroscopy was used to monitor both the formation of the oxidized dye and the arrival of injected electrons to the conduction band of TiO2. Emiss…
The effects of environment on Arctica islandica shell formation and architecture
2017
Mollusks record valuable information in their hard parts that reflect ambient environmental conditions. For this reason, shells can serve as excellent archives to reconstruct past climate and environmental variability. However, animal physiology and biomineralization, which are often poorly un- derstood, can make the decoding of environmental signals a challenging task. Many of the routinely used shell-based proxies are sensitive to multiple different environmental and physiological variables. Therefore, the identification and in- terpretation of individual environmental signals (e.g., water temperature) often is particularly difficult. Additional prox- ies not influenced by multiple enviro…
p −1-Linear Maps in Algebra and Geometry
2012
At least since Habousch’s proof of Kempf’s vanishing theorem, Frobenius splitting techniques have played a crucial role in geometric representation theory and algebraic geometry over a field of positive characteristic. In this article we survey some recent developments which grew out of the confluence of Frobenius splitting techniques and tight closure theory and which provide a framework for higher dimension geometry in positive characteristic. We focus on local properties, i.e. singularities, test ideals, and local cohomology on the one hand and global geometric applicatioms to vanishing theorems and lifting of sections on the other.
Photoluminescence-Based Spatially Resolved Temperature Coefficient Maps of Silicon Wafers and Solar Cells
2020
In this article, we present a method to obtain implied open-circuit voltage images of silicon wafers and cells at different temperatures. The proposed method is then demonstrated by investigating the temperature coefficients of various regions across multicrystalline silicon wafers and cells from different heights of two bricks with different dislocation densities. Interestingly, both low and high temperature coefficients are found in dislocated regions on the wafers. A large spread of temperature coefficient is observed at regions with similar performance at 298 K. Reduced temperature sensitivity is found to be correlated with the increasing brick height and is exhibited by both wafers and…
A Novel Method for Characterizing Temperature Sensitivity of Silicon Wafers and Cells
2019
In this paper, we present a novel method to obtain temperature dependent lifetime and implied-open-circuit voltage (iV OC ) images of silicon wafers and solar cells. First, the method is validated by comparing the obtained values with global values acquired from lifetime measurements (for wafers) and current-voltage measurements (for cells). The method is then extended to acquire spatially resolved images of iV OC temperature coefficients of silicon wafers and cells. Potential applications of the proposed method are demonstrated by investigating the temperature coefficients of various regions across multi-crystalline silicon wafers and cells from different heights of two bricks with differe…
A study of the optical effect of plasma sheath in a negative ion source using IBSIMU code
2020
A plasma sheath inside an ion source has a strong focusing effect on the formation of an ion beam from the plasma. Properties of the beam depend on the shape and location of the plasma sheath inside the source. The most accessible experimental data dependent on the plasma sheath are the beam phase space distribution. Variation of beam emittance is a reflection of the properties of the plasma sheath, with minimum emittance for the optimal shape of the plasma sheath. The location and shape of the plasma sheath are governed by complex physics and can be understood by simulations using plasma models in particle tracking codes like IBSimu. In the current study, a model of the D-Pace’s TRIUMF lic…
Temperature Coefficients of Crystal Defects in Multicrystalline Silicon Wafers
2020
This article investigates the influence of crystallographic defects on the temperature sensitivity of multicrystalline silicon wafers. The thermal characteristics of the implied open-circuit voltage is assessed since it determines most of the total temperature sensitivity of the material. Spatially resolved temperature-dependent analysis is performed on wafers from various brick positions; intragrain regions, grain boundaries, and dislocation clusters are examined. The crystal regions are studied before and after subjecting the wafers to phosphorus gettering, aiming to alter the metallic impurity concentration in various regions across the wafers. Most intragrain regions and grain boundarie…
Anomalies of dielectric properties and conductivity in single domain LiNbO3:Zn crystals
2016
ABSTRACTA study of the temperature dependence of dielectric constant, conductivity, and piezoelectric modulus in the single-domain state of LiNbO3 crystals modified by Zn admixture at threshold concentration is reported. Unipolarity of the LiNbO3:Zn crystals is observed to increase after treatment of brand-new samples by high-temperature electro-diffusion annealing and by subsequent high-temperature annealing of short-circuited samples. The observed effects are explained as a result of meta-stable residual domains collapsing at high temperature the collapse being assisted by disintegration of charged clusters stabilizing domain walls. The rise of unipolarity is accompanied by anomalies on t…
The effect of plasma instabilities on the background impurities in charge breeder ECRIS
2017
International audience; Experimental observations of plasma instabilities in the 14.5 GHz PHOENIX charge breeder ECRIS are summarized. It has been found that the injection of 133Cs+ or 85Rb+ into oxygen discharge of the CB-ECRIS can trigger electron cyclotron instabilities, which results to sputtering of the surfaces exposed to the plasma, followed by up to an order of magnitude increase of impurity currents in the extracted n+ charge state distribution. The transition from stable to unstable plasma regime is caused by gradual accumulation and ionization of Cs/Rb altering the discharge parameters in 10 - 100 ms time scale, not by a prompt interaction between the incident ion beam and the EC…