91 research outputs found
Kinetic Inductance and Penetration Depth of Thin Superconducting Films Measured by THz Pulse Spectroscopy
We measure the transmission of THz pulses through thin films of YBCO at
temperatures between 10K and 300K. The pulses possess a useable bandwidth
extending from 0.1 -- 1.5 THz (3.3 cm^-1 -- 50 cm^-1). Below T_c we observe
pulse reshaping caused by the kinetic inductance of the superconducting charge
carriers. From transmission data, we extract values of the London penetration
depth as a function of temperature, and find that it agrees well with a
functional form (\lambda(0)/\lambda(T))^2 = 1 - (T/T_c)^{\alpha}, where
\lambda(0) = 148 nm, and \alpha = 2. *****Figures available upon request*****Comment: 7 Pages, LaTe
Anomalous Behavior Of The Complex Conductivity Of Y_{1-x}Pr_xBa_2Cu_3O_7 Observed With THz Spectroscopy
We have measured the electrodynamic properties of Y_{1-x}Pr_xBa_2Cu_3O_7
single crystal thin films as a function of temperature using coherent
THz-time-domain spectroscopy. We obtain directly the complex conductivity
, the London penetration depth , the
plasma frequency , and the quasiparticle scattering rate . We
find that drops exponentially rapidly with below the critical
temperature in {\em all} the superconducting samples, implying that this
behavior is a {\em signature} of high- superconductivity. The plasma
frequency decreases with increasing Pr content, providing evidence that Pr
depletes carriers, leaving the CuO planes {\em underdoped}. Both the
conductivity in the THz region and the dc resistivity yield evidence for the
opening of a spin gap {\em above} .Comment: 9 pages, REVTEX 3.
Localization by disorder in the infrared conductivity of (Y,Pr)Ba2Cu3O7 films
The ab-plane reflectivity of (Y{1-x}Prx)Ba2Cu3O7 thin films was measured in
the 30-30000 cm-1 range for samples with x = 0 (Tc = 90 K), x = 0.4 (Tc = 35 K)
and x = 0.5 (Tc = 19 K) as a function of temperature in the normal state. The
effective charge density obtained from the integrated spectral weight decreases
with increasing x. The variation is consistent with the higher dc resistivity
for x = 0.4, but is one order of magnitude smaller than what would be expected
for x = 0.5. In the latter sample, the conductivity is dominated at all
temperatures by a large localization peak. Its magnitude increases as the
temperature decreases. We relate this peak to the dc resistivity enhancement. A
simple localization-by-disorder model accounts for the optical conductivity of
the x = 0.5 sample.Comment: 7 pages with (4) figures include
Synthesis of macrocyclic receptors with intrinsic fluorescence featuring quinizarin moieties
An unprecedented class of macrocycles with intrinsic fluorescence consisting of phenolic trimers and quinizarin is developed. Though they are lacking strong hydrogen bonds as observed in calixarenes, the two examples introduced here each adopt a vase-like conformation with all four aromatic units pointing in one direction (syn orientation). This âconeâ conformation has been confirmed by NMR spectroscopy, molecular modeling, and X-ray crystallography. The laminar, electron-rich fluorophore as part of the macrocycle allows additional contacts to enclosed guest molecules
Dendrimer-Encapsulated Metal Nanoparticles: Synthesis, Characterization, and Applications to Catalysis
Dendrimers as anti-inflammatory agents
Dendrimers constitute an intriguing class of macromolecules which find applications in a variety of areas including biology. These hyperbranched macromolecules with tailored backbone and surface groups have been extensively investigated as nanocarriers for gene and drug delivery, by molecular encapsulation or covalent conjugation. Dendrimers have provided an excellent platform to develop multivalent and multifunctional nanoconjugates incorporating a variety of functional groups including drugs which are known to be anti-inflammatory agents. Recently, dendrimers have been shown to possess anti-inflammatory properties themselves. This unexpected and intriguing discovery has provided an additional impetus in designing novel active pharmaceutical agents. In this review, we highlight some of the recent developments in the field of dendrimers as nanoscale anti-inflammatory agents
Pushing the Limits for ThiolâEne and CuAAC Reactions: Synthesis of a 6th Generation Dendrimer in a Single Day
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