84 research outputs found
Upper bounds on absorption and scattering
A general framework for determining fundamental bounds in nanophotonics is
introduced in this paper. The theory is based on convex optimization of dual
problems constructed from operators generated by electromagnetic integral
equations. The optimized variable is a contrast current defined within a
prescribed region of a given material constitutive relations. Two power
conservation constraints analogous to optical theorem are utilized to tighten
the bounds and to prescribe either losses or material properties. Thanks to the
utilization of matrix rank-1 updates, modal decompositions, and model order
reduction techniques, the optimization procedure is computationally efficient
even for complicated scenarios. No dual gaps are observed. The method is
well-suited to accommodate material anisotropy and inhomogeneity. To
demonstrate the validity of the method, bounds on scattering, absorption, and
extinction cross sections are derived first and evaluated for several canonical
regions. The tightness of the bounds is verified by comparison to optimized
spherical nanoparticles and shells. The next metric investigated is
bi-directional scattering studied closely on a particular example of an
electrically thin slab. Finally, the bounds are established for Purcell's
factor and local field enhancement where a dimer is used as a practical
example.Comment: 38 pages, 16 figure
Two-photon-induced birefringence in azo-dye bearing polyimide; the birefringence changes versus the writing power
Ultra-short high-intensity light pulses were utilized
to induce the optical birefringence in a polyimide material
possessing the azo-dye covalently bonded to the main
chain. The obtained results showed that a two-photon absorption
process was involved in a creation of the sample
birefringence which, to the best of our knowledge, was not
previously reported for polyimide materials. The growths
and decays of birefringence were examined as functions of
the pulse intensities. No damage to the material during the
illumination process was detected in a wide range of optical
powers applied. High birefringence level of the order of
0.005 was measured
Conversion Matrix Method of Moments for Time-Varying Electromagnetic Analysis
A conversion matrix approach to solving network problems involving
time-varying circuit components is applied to the method of moments for
electromagnetic scattering analysis. Detailed formulations of this technique's
application to the scattering analysis of structures loaded with time-varying
circuit networks or constructed from general time-varying media are presented.
The computational cost of the method is discussed, along with an analysis of
compression techniques capable of significantly reducing computational cost for
partially loaded systems. Several numerical examples demonstrate the
capabilities of the technique along with its validation against conventional
methods of modeling time-varying electromagnetic systems, such as finite
difference time domain and transient circuit co-simulation.Comment: 11 pages, 11 figure
(Photo)physical properties of new molecular glasses end-capped with thiophene rings composed of diimide and imine units
New symmetrical arylene bisimide derivatives formed by using electron-donating-electron-accepting systems were synthesized. They consist of a phthalic diimide or naphthalenediimide core and imine linkages and are end-capped with thiophene, bithiophene, and (ethylenedioxy)thiophene units. Moreover, polymers were obtained from a new diamine, N,N′-bis(5- aminonaphthalenyl)naphthalene-1,4,5,8-dicarboximide and 2,5- thiophenedicarboxaldehyde or 2,2′-bithiophene-5,5′-dicarboxaldehyde. The prepared azomethine diimides exhibited glass-forming properties. The obtained compounds emitted blue light with the emission maximum at 470 nm. The value of the absorption coefficient was determined as a function of the photon energy using spectroscopic ellipsometry. All compounds are electrochemically active and undergo reversible electrochemical reduction and irreversible oxidation processes as was found in cyclic voltammetry and differential pulse voltammetry (DPV) studies. They exhibited a low electrochemically (DPV) calculated energy band gap (Eg) from 1.14 to 1.70 eV. The highest occupied molecular orbital and lowest unoccupied molecular orbital levels and Eg were additionally calculated theoretically by density functional theory at the B3LYP/6-31G(d,p) level. The photovoltaic properties of two model compounds as the active layer in organic solar cells in the configuration indium tin oxide/poly(3,4-(ethylenedioxy)thiophene):poly(styrenesulfonate)/active layer/Al under an illumination of 1.3 mW/cm2 were studied. The device comprising poly(3-hexylthiophene) with the compound end-capped with bithiophene rings showed the highest value of Voc (above 1 V). The conversion efficiency of the fabricated solar cell was in the range of 0.69-0.90%
Olfactory discrimination predicts cognitive decline among community-dwelling older adults
The presence of olfactory dysfunction in individuals at higher risk of Alzheimer's disease has significant diagnostic and screening implications for preventive and ameliorative drug trials. Olfactory threshold, discrimination and identification can be reliably recorded in the early stages of neurodegenerative diseases. The current study has examined the ability of various olfactory functions in predicting cognitive decline in a community-dwelling sample. A group of 308 participants, aged 46–86 years old, were recruited for this study. After 3 years of follow-up, participants were divided into cognitively declined and non-declined groups based on their performance on a neuropsychological battery. Assessment of olfactory functions using the Sniffin' Sticks battery indicated that, contrary to previous findings, olfactory discrimination, but not olfactory identification, significantly predicted subsequent cognitive decline (odds ratio=0.869; P<0.05; 95% confidence interval=0.764−0.988). The current study findings confirm previously reported associations between olfactory and cognitive functions, and indicate that impairment in olfactory discrimination can predict future cognitive decline. These findings further our current understanding of the association between cognition and olfaction, and support olfactory assessment in screening those at higher risk of dementia
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