217 research outputs found
Optical characteristics of single wavelength-tunable InAs/InGaAsP/InP(100) quantum dots emitting at 1.55 um
We have studied the emission properties of individual InAs quantum dots (QDs)
grown in an InGaAsP matrix on InP(100) by metal-organic vapor-phase epitaxy.
Low-temperature microphotoluminescence spectroscopy shows emission from single
QDs around 1550 nm with characteristic exciton-biexciton behavior, and a
biexciton antibinding energy of more than 2 meV. Temperature-dependent
measurements reveal negligible optical-phonon induced broadening of the exciton
line up to 50 K, and emission from the exciton state clearly persists above 70
K. Furthermore, we find no measurable polarized fine structure splitting of the
exciton state within the experimental precision. These results are encouraging
for the development of a controllable photon source for fiber-based quantum
information and cryptography systems.Comment: 3 pages, 4 figures, submitted AP
XMAP215 is a Processive Microtubule Polymerase
Fast growth of microtubules is essential for rapid assembly of the microtubule cytoskeleton during cell proliferation and differentiation. XMAP215 belongs to a conserved family of proteins that promote microtubule growth. To determine how XMAP215 accelerates growth, we developed a single-molecule assay to visualize directly XMAP215-GFP interacting with dynamic microtubules. XMAP215 binds free tubulin in a 1:1 complex that interacts with the microtubule lattice and targets the ends by a diffusion-facilitated mechanism. XMAP215 persists at the plus end for many rounds of tubulin subunit addition in a form of “tip-tracking.” These results show that XMAP215 is a processive polymerase that directly catalyzes the addition of up to 25 tubulin dimers to the growing plus end. Under some circumstances XMAP215 can also catalyze the reverse reaction, namely microtubule shrinkage. The similarities between XMAP215 and formins, actin polymerases, suggest that processive tip-tracking is a common mechanism for stimulating the growth of cytoskeletal polymers.Molecular and Cellular Biolog
All-optical switching due to state-filling in quantum dots
We report all-optical switching due to state-filling in quantum dots (QDs)
within a Mach-Zehnder Interferometric (MZI) switch. The MZI was fabricated
using InGaAsP/InP waveguides containing a single layer of InAs/InP QDs. A
1530-1570 nm probe beam is switched by optical excitation of one MZI-arm from
the top. By exciting below the InGaAsP bandgap, we prove that the refractive
index nonlinearity is only due to the QDs. The switching efficiency is 2
rad/(microW absorbed power). Probe wavelength insensitivity was obtained using
a broad distribution of QDs.Comment: 12 page
Tips for profitable small grain production
1 online resource (PDF, 4 pages)This archival publication may not reflect current scientific knowledge or recommendations. Current information available from the University of Minnesota Extension: https://www.extension.umn.edu
Panspermia, Past and Present: Astrophysical and Biophysical Conditions for the Dissemination of Life in Space
Astronomically, there are viable mechanisms for distributing organic material
throughout the Milky Way. Biologically, the destructive effects of ultraviolet
light and cosmic rays means that the majority of organisms arrive broken and
dead on a new world. The likelihood of conventional forms of panspermia must
therefore be considered low. However, the information content of dam-aged
biological molecules might serve to seed new life (necropanspermia).Comment: Accepted for publication in Space Science Review
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