739 research outputs found
Prediction of infrared light emission from pi-conjugated polymers: a diagrammatic exciton basis valence bond theory
There is currently a great need for solid state lasers that emit in the
infrared, as this is the operating wavelength regime for applications in
telecommunications. Existing --conjugated polymers all emit in the visible
or ultraviolet, and whether or not --conjugated polymers that emit in the
infrared can be designed is an interesting challenge. On the one hand, the
excited state ordering in trans-polyacetylene, the --conjugated polymer
with relatively small optical gap, is not conducive to light emission because
of electron-electron interaction effects. On the other hand, excited state
ordering opposite to that in trans-polyacetylene is usually obtained by
chemical modification that increases the effective bond-alternation, which in
turn increases the optical gap. We develop a theory of electron correlation
effects in a model -conjugated polymer that is obtained by replacing the
hydrogen atoms of trans-polyacetylene with transverse conjugated groups, and
show that the effective on-site correlation in this system is smaller than the
bare correlation in the unsubstituted system. An optical gap in the infrared as
well as excited state ordering conducive to light emission is thereby predicted
upon similar structural modifications.Comment: 15 pages, 15 figures, 1 tabl
Immunological relationships between receptors for insulin and insulin-like growth factor I. Evidence for structural heterogeneity of insulin-like growth factor I receptors involving hybrids with insulin receptors
CX3CR1+ interstitial dendritic cells form a contiguous network throughout the entire kidney
Dendritic cells (DCs) interface innate and adaptive immunity in nonlymphoid organs; however, the exact distribution and types of DC within the kidney are not known. We utilized CX3CR1GFP/+ mice to characterize the anatomy and phenotype of tissue-resident CX3CR1+ DCs within normal kidney. Laser-scanning confocal microscopy revealed an extensive, contiguous network of stellate-shaped CX3CR1+ DCs throughout the interstitial and mesangial spaces of the entire kidney. Intravital microscopy of the superficial cortex showed stationary interstitial CX3CR1+ DCs that continually probe the surrounding tissue environment through dendrite extensions. Flow cytometry of renal CX3CR1+ DCs showed significant coexpression of CD11c and F4/80, high major histocompatibility complex class II and FcR expression, and immature costimulatory but competent phagocytic ability indicative of tissue-resident, immature DCs ready to respond to environment cues. Thus, within the renal parenchyma, there exists little immunological privilege from the surveillance provided by renal CX3CR1+ DCs, a major constituent of the heterogeneous mononuclear phagocyte system populating normal kidney
X-Band ESR Determination of Dzyaloshinsky-Moriya Interaction in 2D SrCu(BO) System
X-band ESR measurements on a single crystal of SrCu(BO) system in
a temperature range between 10 K and 580 K are presented. The temperature and
angular dependence of unusually broad ESR spectra can be explained by the
inclusion of antisymmetric Dzyaloshinsky-Moriya (DM) interaction, which yields
by far the largest contribution to the linewidth. However, the well-accepted
picture of only out-of-plane interdimer DM vectors is not sufficient for
explanation of the observed angular dependence. In order to account for the
experimental linewidth anisotropy we had to include sizable in-plane components
of interdimer as well as intradimer DM interaction in addition to the
out-of-plane interdimer one. The nearest-neighbor DM vectors lie perpendicular
to crystal anisotropy c-axis due to crystal symmetry. We also emphasize that
above the structural phase transition occurring at 395 K dynamical mechanism
should be present allowing for instantaneous DM interactions. Moreover, the
linewidth at an arbitrary temperature can be divided into two contributions;
namely, the first part arising from spin dynamics governed by the spin
Hamiltonian of the system and the second part due to significant spin-phonon
coupling. The nature of the latter mechanism is attributed to phonon-modulation
of the antisymmetric interaction, which is responsible for the observed linear
increase of the linewidth at high temperatures.Comment: 17 pages, 4 figures, submitted to PR
Giant infrared intensity of the Peierls mode at the neutral-ionic phase transition
We present exact diagonalization results on a modified Peierls-Hubbard model
for the neutral-ionic phase transition. The ground state potential energy
surface and the infrared intensity of the Peierls mode point to a strong,
non-linear electron-phonon coupling, with effects that are dominated by the
proximity to the electronic instability rather than by electronic correlations.
The huge infrared intensity of the Peierls mode at the ferroelectric
transition is related to the temperature dependence of the dielectric constant
of mixed-stack organic crystals.Comment: 4 pages, 4 figure
Global Waste Management Outlook
The Global Waste Management Outlook, a collective effort of the United Nations Environment Programme and the International Waste Management Association, is a pioneering scientific global assessment on the state of waste management and a call for action to the international community. Prepared as a follow up to the Rio+20 Summit and as a response to UNEP Governing Council decision GC 27/12, the document establishes the rationale and the tools for taking a holistic approach towards waste management and recognizing waste and resource management as a significant contributor to sustainable development and climate change mitigation. To complement the Sustainable Development Goals of the Post-2015 Development Agenda, the Outlook sets forth Global Waste Management Goals and a Global Call to Action to achieve those goals
LADA type diabetes, celiac diasease, cerebellar ataxia and stiff person syndrome. A rare association of autoimmune disorders.
Celiac disease--in its typical form--is a chronic immune-mediated enteropathy with typical clinical symptoms that develops against gliadin content of cereal grains, and is often associated with other autoimmune diseases. In cases of atypical manifestation classic symptoms may be absent or mild, and extra-intestinal symptoms or associated syndromes dominate clinical picture. The authors present a longitudinal follow-up of such a case. A 63-years old woman was diagnosed with epilepsy at the age of 19, and with progressive limb ataxia at the age of 36, which was initially thought to be caused by cerebellar atrophy, later probably by stiff person syndrome. At the age 59, her diabetes mellitus manifested with type 2 diabetic phenotype, but based on GAD positivity later was reclassified as type 1 diabetes. Only the last check-up discovered the celiac disease, retrospectively explaining the entire disease course and neurological symptoms. By presenting this case, the authors would like to draw attention to the fact that one should think of the possibility of celiac disease when cerebellar ataxia, progressive neurological symptoms and diabetes are present at the same time. An early diagnosis may help to delay the progression of disease and help better treatment
Nonlinear optical response and spin-charge separation in one-dimensional Mott insulators
We theoretically study the nonlinear optical response and photoexcited states
of the Mott insulators. The nonlinear optical susceptibility \chi^(3) is
calculated by using the exact diagonalization technique on small clusters. From
the systematic study of the dependence of \chi^(3) on dimensionality, we find
that the spin-charge separation plays a crucial role in enhancing \chi^(3) in
the one-dimensional (1D) Mott insulators. Based on this result, we propose a
holon-doublon model, which describes the nonlinear response in the 1D Mott
insulators. These findings show that the spin-charge separation will become a
key concept of optoelectronic devices.Comment: 5 pages with 3 figures, to appear in PRB RC, 15 August 200
Structural and Electronic Instabilities in Polyacenes: Density Matrix Renormalization Group Study of a Long--Range Interacting Model
We have carried out Density Matrix Renormalization Group (DMRG) calculations
on the ground state of long polyacene oligomers within a Pariser-Parr-Pople
(PPP) Hamiltonian. The PPP model includes long-range electron correlations
which are required for physically realistic modeling of conjugated polymers. We
have obtained the ground state energy as a function of the dimerization
and various correlation functions and structure factors for
. From energetics, we find that while the nature of the Peierls'
instabilityin polyacene is conditional and strong electron correlations enhance
the dimerization. The {\it cis} form of the distortion is favoured over the
{\it trans} form. However, from the analysis of correlation functions and
associated structure factors, we find that polyacene is not susceptible to the
formation of a bond order wave (BOW), spin density wave (SDW) or a charge
density wave (CDW) in the ground state.Comment: 31 pages, latex, 13 figure
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