914 research outputs found
Lymphocyte Defect in Plasmacytoma-bearing Mice
Multiple myeloma is often associated with humoral immunodepression in both man and mouse. When mice bearing the humorally immunodepressive plasmacytomas TEPC-183 and SPQC-11 were injected with SRBC, the rise of serum haemolysins was significantly less than that of non-tumour-bearing mice. Mice with the plasmacytomas MPC-11 and MOPC-315 have an antibody response similar to normal mice when injected with SRBC. Following immunization, normal mice and those bearing MPC-11 showed a 2- to 3-fold increase in total spleen lymphocytes. Mice bearing TEPC-183 or SPQC-11, the plasmacytomas causing an impaired antibody response, has significant increase in spleen lymphocytes under the same conditions. Mice bearing MOPC-315 had a very high initial count of spleen lymphocytes, which did not further increase upon immune stimulation
Growth of sulphuric acid nanoparticles under wet and dry conditions
New particle formation, which greatly influences the number concentrations
and size distributions of an atmospheric aerosol, is often followed by a
rapid growth of freshly formed particles. The initial growth of newly
formed aerosol is the crucial process determining the fraction of nucleated
particles growing to cloud condensation nuclei sizes, which have a
significant influence on climate. In this study, we report the laboratory
observations of the growth of nanoparticles produced by nucleation of
H<sub>2</sub>SO<sub>4</sub> and water in a laminar flow tube at temperatures of 283, 293
and 303 K, under dry (a relative humidity of 1%) and wet conditions
(relative humidity of 30%) and residence times of 30, 45, 60 and 90 s.
The initial H<sub>2</sub>SO<sub>4</sub> concentration spans the range from 2 × 10<sup>8</sup>
to 1.4 × 10<sup>10</sup> molecule cm<sup>−3</sup> and the calculated
wall losses of H<sub>2</sub>SO<sub>4</sub> were assumed to be diffusion limited. The
detected particle number concentrations, measured by the Ultrafine
Condensation Particle Counter (UCPC) and Differential Mobility Particle
Sizer (DMPS), were found to depend strongly on the residence time.
Hygroscopic particle growth, presented by growth factors, was found to be in
good agreement with the previously reported studies. The experimental growth
rates ranged from 20 nm h<sup>−1</sup> to 890 nm h<sup>−1</sup> at relative humidity (RH) 1% and from
7 nm h<sup>−1</sup> to 980 nm h<sup>−1</sup> at RH 30% and were found to increase
significantly with the increasing concentration of H<sub>2</sub>SO<sub>4</sub>.
Increases in the nucleation temperature had a slight enhancing effect on the
growth rates under dry conditions. The influence of relative humidity on
growth was not consistent – at lower H<sub>2</sub>SO<sub>4</sub> concentrations, the
growth rates were higher under dry conditions while at H<sub>2</sub>SO<sub>4</sub>
concentrations greater than 1 × 10<sup>10</sup> molecule cm<sup>−3</sup>, the
growth rates were higher under wet conditions. The growth rates show only a
weak dependence on the residence time. The experimental observations were
compared with predictions made using a numerical model, which investigates
the growth of particles with three different extents of neutralization by
ammonia, NH<sub>3</sub>: (1) pure H<sub>2</sub>SO<sub>4</sub> – H<sub>2</sub>O particles; (2)
particles formed by ammonium bisulphate, (NH<sub>4</sub>)HSO<sub>4</sub>; (3) particles
formed by ammonium sulphate, (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>. The highest growth
rates were found for ammonium sulphate particles. Since the model accounting
for the initial H<sub>2</sub>SO<sub>4</sub> concentration predicted the experimental
growth rates correctly, our results suggest that the commonly presumed
diffusional wall losses of H<sub>2</sub>SO<sub>4</sub> in case of long-lasting
experiments are not so significant. We therefore assume that there are not
only losses of H<sub>2</sub>SO<sub>4</sub> on the wall, but also a flux of
H<sub>2</sub>SO<sub>4</sub> molecules from the wall into the flow tube, the effect being
more profound under dry conditions and at higher temperatures of the tube
wall. Based on a comparison with the atmospheric observations, our results
indicate that sulphuric acid alone cannot explain the growth rates of
particles formed in the atmosphere
A REVIEW ON THE MATERIALS SCIENCE AND DEVICE PHYSICS OF SEMITRANSPARENT ORGANIC PHOTOVOLTAICS
In this review, the current state of materials science and the device physics of semitransparent organic solar cells is summarized. Relevant synthetic strategies to narrow the band gap of organic semiconducting molecules are outlined, and recent developments in the polymer donor and near-infrared absorbing acceptor materials are discussed. Next, an overview of transparent electrodes is given, including oxides, multi-stacks, thin metal, and solution processed electrodes, as well as considerations that are unique to ST-OPVs. The remainder of this review focuses on the device engineering of ST-OPVs. The figures of merit and the theoretical limitations of ST-OPVs are covered, as well as strategies to improve the light utilization efficiency. Lastly, the importance of creating an in-depth understanding of the device physics of ST-OPVs is emphasized and the existing works that answer fundamental questions about the inherent changes in the optoelectronic processes in transparent devices are presented in a condensed way. This last part outlines the changes that are unique for devices with increased transparency and the resulting implications, serving as a point of reference for the systematic development of next-generation ST-OPVs
Photodiode based on epitaxial silicon with high sensitivity at the wavelength 254 nm
A mathematical model of the construction of silicon photodiode based on
epitaxial structure enabling to regulate the absorption edge of silicon in the long-wave
spectral range is presented. The suggested model allows calculating the construction that
possesses low sensitivity for the wavelengths larger than 600 nm and maximal values
near the wavelength 254 nm
Characterization of the neuroactive compound profle in organic, conventional and processed tomatoes
Imaging Stacking Order in Few-Layer Graphene
Few-layer graphene (FLG) has been predicted to exist in various
crystallographic stacking sequences, which can strongly influence the
electronic properties of FLG. We demonstrate an accurate and efficient method
to characterize stacking order in FLG using the distinctive features of the
Raman 2D-mode. Raman imaging allows us to visualize directly the spatial
distribution of Bernal (ABA) and rhombohedral (ABC) stacking in tri- and
tetra-layer graphene. We find that 15% of exfoliated graphene tri- and
tetra-layers is comprised of micron-sized domains of rhombohedral stacking,
rather than of usual Bernal stacking. These domains are stable and remain
unchanged for temperatures exceeding C.Comment: submitted to Nano Letters; supplementary information about infrared
spectroscopy of ABA and ABC graphene trilayers are included
Theory of Luminescent Emission in Nanocrystal ZnS:Mn with an Extra Electron
We consider the effect of an extra electron injected into a doped quantum dot
. The Coulomb interaction and the exchange interaction between the
extra electron and the states of the Mn ion will mix the wavefunctions, split
the impurity energy levels, break the previous selection rules and change the
transition probabilities. Using this model of an extra electron in the doped
quantum dot, we calculated the energy and the wavefunctions, the luminescence
probability and the transition lifetime and compare with the experiments. Our
calculation shows that two orders of magnitudes of lifetime shortening can
occur in the transition when an extra electron is present.Comment: 15 pages, 2 Figs No change in Fig
Synthesis of CdS and CdSe nanocrystallites using a novel single-molecule precursors approach
The synthesis of CdS and CdSe nanocrystallites using the thermolysis of several dithioor
diselenocarbamato complexes of cadmium in trioctylphosphine oxide (TOPO) is reported.
The nanodispersed materials obtained show quantum size effects in their optical spectra
and exhibit near band-edge luminescence. The influence of experimental parameters on
the properties of the nanocrystallites is discussed. HRTEM images of these materials show
well-defined, crystalline nanosized particles. Standard size fractionation procedures can
be performed in order to narrow the size dispersion of the samples. The TOPO-capped CdS
and CdSe nanocrystallites and simple organic bridging ligands, such as 2,2¢-bipyrimidine,
are used as the starting materials for the preparation of novel nanocomposites. The optical
properties shown by these new nanocomposites are compared with those of the starting
nanodispersed materials
Magnetic phase transition in V2O3 nanocrystals
V2O3 nanocrystals can be synthesized through hydrothermal reduction of
VO(OH)2 using hydrazine as a reducing agent. Addition of different ligands to
the reaction produces nanoparticles, nanorods and nanoplatelets of different
sizes. Small nanoparticles synthesized in this manner show suppression of the
magnetic phase transition to lower temperatures. Using muon spin relaxation
spectroscopy and synchrotron x-ray diffraction, it is determined that the
volume fraction of the high-temperature phase, characterized by a rhombohedral
structure and paramagnetism, gradually declines with decreasing temperature, in
contrast to the sharp transition observed in bulk V2O3.Comment: 6 pages, 6 figure
DETERMINATION OF THE CHARGE CARRIER DENSITY IN ORGANIC SOLAR CELLS: A TUTORIAL
The increase in the performance of organic solar cells observed over the past few years has reinvigorated the search for a deeper understanding of the loss and extraction processes in this class of device. A detailed knowledge of the density of free charge carriers under different operating conditions and illumination intensities is a prerequisite to quantify the recombination and extraction dynamics. Differential charging techniques are a promising approach to experimentally obtain the charge carrier density under the aforementioned conditions. In particular, the combination of transient photovoltage and photocurrent as well as impedance and capacitance spectroscopy have been successfully used in past studies to determine the charge carrier density of organic solar cells. In this Tutorial, these experimental techniques will be discussed in detail, highlighting fundamental principles, practical considerations, necessary corrections, advantages, drawbacks, and ultimately their limitations. Relevant references introducing more advanced concepts will be provided as well. Therefore, the present Tutorial might act as an introduction and guideline aimed at new prospective users of these techniques as well as a point of reference for more experienced researcher
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