3,410 research outputs found
Theory of Melting and the Optical Properties of Gold/DNA Nanocomposites
We describe a simple model for the melting and optical properties of a
DNA/gold nanoparticle aggregate. The optical properties at fixed wavelength
change dramatically at the melting transition, which is found to be higher and
narrower in temperature for larger particles, and much sharper than that of an
isolated DNA link. All these features are in agreement with available
experiments. The aggregate is modeled as a cluster of gold nanoparticles on a
periodic lattice connected by DNA bonds, and the extinction coefficient is
computed using the discrete dipole approximation. Melting takes place as an
increasing number of these bonds break with increasing temperature. The melting
temperature corresponds approximately to the bond percolation threshold.Comment: 5 pages, 4 figure. To be published in Phys. Rev.
Structure Formation, Melting, and the Optical Properties of Gold/DNA Nanocomposites: Effects of Relaxation Time
We present a model for structure formation, melting, and optical properties
of gold/DNA nanocomposites. These composites consist of a collection of gold
nanoparticles (of radius 50 nm or less) which are bound together by links made
up of DNA strands. In our structural model, the nanocomposite forms from a
series of Monte Carlo steps, each involving reaction-limited cluster-cluster
aggregation (RLCA) followed by dehybridization of the DNA links. These links
form with a probability which depends on temperature and particle
radius . The final structure depends on the number of monomers (i. e. gold
nanoparticles) , , and the relaxation time. At low temperature, the
model results in an RLCA cluster. But after a long enough relaxation time, the
nanocomposite reduces to a compact, non-fractal cluster. We calculate the
optical properties of the resulting aggregates using the Discrete Dipole
Approximation. Despite the restructuring, the melting transition (as seen in
the extinction coefficient at wavelength 520 nm) remains sharp, and the melting
temperature increases with increasing as found in our previous
percolation model. However, restructuring increases the corresponding link
fraction at melting to a value well above the percolation threshold. Our
calculated extinction cross section agrees qualitatively with experiments on
gold/DNA composites. It also shows a characteristic ``rebound effect,''
resulting from incomplete relaxation, which has also been seen in some
experiments. We discuss briefly how our results relate to a possible sol-gel
transition in these aggregates.Comment: 12 pages, 10 figure
High-resolution Ce 3d-edge resonant photoemission study of CeNi_2
Resonant photoemission (RPES) at the Ce 3d -> 4f threshold has been performed
for alpha-like compound CeNi_2 with extremely high energy resolution (full
width at half maximum < 0.2 eV) to obtain bulk-sensitive 4f spectral weight.
The on-resonance spectrum shows a sharp resolution-limited peak near the Fermi
energy which can be assigned to the tail of the Kondo resonance. However, the
spin-orbit side band around 0.3 eV binding energy corresponding to the f_{7/2}
peak is washed out, in contrast to the RPES spectrum at the Ce 3d -> 4f RPES
threshold. This is interpreted as due to the different surface sensitivity, and
the bulk-sensitive Ce 3d -> 4f RPES spectra are found to be consistent with
other electron spectroscopy and low energy properties for alpha-like
Ce-transition metal compounds, thus resolves controversy on the interpretation
of Ce compound photoemission. The 4f spectral weight over the whole valence
band can also be fitted fairly well with the Gunnarsson-Schoenhammer
calculation of the single impurity Anderson model, although the detailed
features show some dependence on the hybridization band shape and (possibly) Ce
5d emissions.Comment: 4 pages, 3 figur
Structures for Interacting Composite Fermions: Stripes, Bubbles, and Fractional Quantum Hall Effect
Much of the present day qualitative phenomenology of the fractional quantum
Hall effect can be understood by neglecting the interactions between composite
fermions altogether. For example the fractional quantum Hall effect at
corresponds to filled composite-fermion Landau levels,and
the compressible state at to the Fermi sea of composite fermions.
Away from these filling factors, the residual interactions between composite
fermions will determine the nature of the ground state. In this article, a
model is constructed for the residual interaction between composite fermions,
and various possible states are considered in a variational approach. Our study
suggests formation of composite-fermion stripes, bubble crystals, as well as
fractional quantum Hall states for appropriate situations.Comment: 16 pages, 7 figure
Dual stem cell therapy synergistically improves cardiac function and vascular regeneration following myocardial infarction
Since both myocardium and vasculature in the heart are excessively damaged following myocardial infarction (MI), therapeutic strategies for treating MI hearts should concurrently target both so as to achieve true cardiac repair. Here we demonstrate a concomitant method that exploits the advantages of cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CMs) and human mesenchymal stem cell-loaded patch (hMSC-PA) to amplify cardiac repair in a rat MI model. Epicardially implanted hMSC-PA provide a complimentary microenvironment which enhances vascular regeneration through prolonged secretion of paracrine factors, but more importantly it significantly improves the retention and engraftment of intramyocardially injected hiPSC-CMs which ultimately restore the cardiac function. Notably, the majority of injected hiPSC-CMs display adult CMs like morphology suggesting that the secretomic milieu of hMSC-PA constitutes pleiotropic effects in vivo. We provide compelling evidence that this dual approach can be a promising means to enhance cardiac repair on MI hearts.11Ysciescopu
Effects of different needles and substrates on CuInS2 deposited by electrostatic spray deposition
Copper indium disulphide (CuInS2) thin films were deposited using the electrostatic spray deposition method. The effects of applied voltage and solution flow rate on the aerosol cone shape, film composition, surface morphology and current conversion were investigated. The effect of aluminium substrates and transparent fluorine doped tin oxide (SnO2:F) coated glass substrates on the properties of as-deposited CuInS2 films were analysed. An oxidation process occurs during the deposition onto the metallic substrates which forms an insulating layer between the photoactive film and substrate. The effects of two different spray needles on the properties of the as-deposited films were also studied. The results reveal that the use of a stainless steel needle results in contamination of the film due to the transfer of metal impurities through the spray whilst this is not seen for the glass needle. The films were characterised using a number of different analytical techniques such as X-ray diffraction, scanning electron microscopy, Rutherford back-scattering and secondary ion mass spectroscopy and opto-electronic measurements
Temperature-Dependent Pseudogaps in Colossal Magnetoresistive Oxides
Direct electronic structure measurements of a variety of the colossal
magnetoresistive oxides show the presence of a pseudogap at the Fermi energy
E_F which drastically suppresses the electron spectral function at E_F. The
pseudogap is a strong function of the layer number of the samples (sample
dimensionality) and is strongly temperature dependent, with the changes
beginning at the ferromagnetic transition temperature T_c. These trends are
consistent with the major transport trends of the CMR oxides, implying a direct
relationship between the pseudogap and transport, including the "colossal"
conductivity changes which occur across T_c. The k-dependence of the
temperature-dependent effects indicate that the pseudogap observed in these
compounds is not due to the extrinsic effects proposed by Joynt.Comment: 5 pages, 6 figures, submitted to Phys. Rev.
Fractional Quantum Hall States of Clustered Composite Fermions
The energy spectra and wavefunctions of up to 14 interacting quasielectrons
(QE's) in the Laughlin nu=1/3 fractional quantum Hall (FQH) state are
investigated using exact numerical diagonalization. It is shown that at
sufficiently high density the QE's form pairs or larger clusters. This
behavior, opposite to Laughlin correlations, invalidates the (sometimes
invoked) reapplication of the composite fermion picture to the individual QE's.
The series of finite-size incompressible ground states are identified at the QE
filling factors nu_QE=1/2, 1/3, 2/3, corresponding to the electron fillings
nu=3/8, 4/11, 5/13. The equivalent quasihole (QH) states occur at nu_QH=1/4,
1/5, 2/7, corresponding to nu=3/10, 4/13, 5/17. All these six novel FQH states
were recently discovered experimentally. Detailed analysis indicates that QE or
QH correlations in these states are different from those of well-known FQH
electron states (e.g., Laughlin or Moore-Read states), leaving the origin of
their incompressibility uncertain. Halperin's idea of Laughlin states of QP
pairs is also explored, but is does not seem adequate.Comment: 14 pages, 9 figures; revision: 1 new figure, some new references,
some new data, title chang
Absorption cross section in the topologically massive gravity at the critical point
The absorption cross section for the the warped AdS black hole background
shows that it is larger than the area even if the s-wave limit is considered.
It raises some question whether the deviation from the areal cross section is
due to the warped configuration of the geometry or the rotating coordinate
system, where these two effects are mixed up in the warped AdS black hole.
So, we study the low-frequency scattering dynamics of propagating scalar fields
under the warped AdS background at the critical point which reduces to the
BTZ black hole in the rotating frame without the warped factor, which shows
that the deformation effect at the critical point does not appear.Comment: 12 pages, LaTe
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