Tens of thousands of Palestinians took to the streets today to commemorate the “nakba,” or “catastrophe,” when they fled or were expelled from their homes during the creation of the state of Israel in 1948. Palestinians clashed with Israeli security forces in the West Bank and East Jerusalem, and a shell was fired into Israel from Gaza, though it landed in an open field.
Today, almost half of the world’s Palestinian population are refugees, according to a recent report. While most Palestinians cling to the right of return to their ancestral lands as a fundamental tenant of any peace deal, a resolution remains elusive.
For more background on this issue, the editors of The I Files have put together a playlist highlighting some of the best reporting about the Israeli-Palestinian conflict.
Pima County, Arizona, is the only county in the United States that tracks migrant deaths. Here’s every one since 2001.
Triple-Decker Motif for Red-Shifted Fluorescent Protein Mutants
Bella L. Grigorenko, Alexander V. Nemukhin, Igor V. Polyakov, and Anna I. Krylov
Abstract: Among fluorescent proteins (FPs) used as genetically encoded fluorescent tags, the red-emitting FPs are of particular importance as suitable markers for deep tissue imaging. Using electronic structure calculations, we predict a new structural motif for achieving red-shifted absorption and emission in FPs from the GFP family. By introducing four point mutations, we arrive to the structure with the conventional anionic GFP chromophore sandwiched between two tyrosine residues. Contrary to the existing red FPs in which the red shift is due to extended conjugation of the chromophore, in the triple-decker motif, the chromophore is unmodified and the red shift is due to π-stacking interactions. The absorption/emission energies of the triple-decker FP are 2.25/2.16 eV, respectively, which amounts to shifts of 40 (absorption) and 25 nm (emission) relative to the parent species, the I form of wtGFP. Using a different structural motif based on a smaller chromophore may help to improve optical output of red FPs by reducing losses due to radiationless relaxation and photobleaching.
A dye laser is a laser which uses an organic dye as the lasing medium, usually as a liquid solution. Compared to gases and most solid state lasing media, a dye can usually be used for a much wider range of wavelengths. The wide bandwidth makes them particularly suitable for tunable lasers and pulsed lasers. Moreover, the dye can be replaced by another type in order to generate different wavelengths with the same laser, although this usually requires replacing other optical components in the laser as well.
The dyes used in these lasers contain rather large organic molecules which fluoresce. The incoming light excites the dye molecules into the state of being ready to emit stimulated radiation, the singlet state. In this state, the molecules emit light via fluorescence, and the dye is transparent to the lasing wavelength. Within a microsecond, or less, the molecules will change to their triplet state. In the triplet state, light is emitted via phosphorescence, and the molecules absorb the lasing wavelength, making the dye opaque. Liquid dyes also have an extremely high lasing threshold. Flashlamp pumped lasers need a flash with an extremely short duration, to deliver the large amounts of energy necessary to bring the dye past threshold before triplet absorption overcomes singlet emission. Dye lasers with an external pump laser can direct enough energy of the proper wavelength into the dye with a relatively small amount of input energy, but the dye must be circulated at high speeds to keep the triplet molecules out of the beam path.
In laser medicine these lasers are applied in several areas, including dermatology where they are used to make skin tone more even. The wide range of wavelengths possible allows very close matching to the absorption lines of certain tissues, such as melanin or hemoglobin, while the narrow bandwidth obtainable helps reduce the possibility of damage to the surrounding tissue. They are used to treat port-wine stains and other blood vessel disorders, scars and kidney stones. They can be matched to a variety of inks for tattoo removal, as well as a number of other applications.
In spectroscopy, dye lasers can be used to study the absorption and emission spectra of various materials. Their tunability, (from the near-infrared to the near-ultraviolet), narrow bandwidth, and high intensity allows a much greater diversity than other light sources. The variety of pulse widths, from ultra-short, femto-second pulses to continuous-wave operation, makes them suitable for a wide range of applications, from the study of fluorescent lifetimes and semiconductor properties to lunar laser ranging experiments.
Image Credit: Warsash Scientific