15 research outputs found
Probing Intergalactic Magnetic Fields in the GLAST Era through Pair Echo Emission from TeV Blazars
More than a dozen blazars are known to be emitters of multi-TeV gamma rays,
often with strong and rapid flaring activity. By interacting with photons of
the cosmic microwave and infrared backgrounds, these gamma rays inevitably
produce electron-positron pairs, which in turn radiate secondary inverse
Compton gamma rays in the GeV-TeV range with a characteristic time delay that
depends on the properties of the intergalactic magnetic field (IGMF). For
sufficiently weak IGMF, such "pair echo" emission may be detectable by the
Gamma-ray Large Area Space Telescope (GLAST), providing valuable information on
the IGMF. We perform detailed calculations of the time-dependent spectra of
pair echos from flaring TeV blazars such as Mrk 501 and PKS 2155-304, taking
proper account of the echo geometry and other crucial effects. In some cases,
the presence of a weak but non-zero IGMF may enhance the detectability of
echos. We discuss the quantitative constraints that can be imposed on the IGMF
from GLAST observations, including the case of non-detections.Comment: 4 pages, 3 figures, minor revisions, accepted for publication in APJ
Joint Observation of the Galactic Center with MAGIC and CTA-LST-1
MAGIC is a system of two Imaging Atmospheric Cherenkov Telescopes (IACTs), designed to detect very-high-energy gamma rays, and is operating in stereoscopic mode since 2009 at the Observatorio del Roque de Los Muchachos in La Palma, Spain. In 2018, the prototype IACT of the Large-Sized Telescope (LST-1) for the Cherenkov Telescope Array, a next-generation ground-based gamma-ray observatory, was inaugurated at the same site, at a distance of approximately 100 meters from the MAGIC telescopes. Using joint observations between MAGIC and LST-1, we developed a dedicated analysis pipeline and established the threefold telescope system via software, achieving the highest sensitivity in the northern hemisphere. Based on this enhanced performance, MAGIC and LST-1 have been jointly and regularly observing the Galactic Center, a region of paramount importance and complexity for IACTs. In particular, the gamma-ray emission from the dynamical center of the Milky Way is under debate. Although previous measurements suggested that a supermassive black hole Sagittarius A* plays a primary role, its radiation mechanism remains unclear, mainly due to limited angular resolution and sensitivity. The enhanced sensitivity in our novel approach is thus expected to provide new insights into the question. We here present the current status of the data analysis for the Galactic Center joint MAGIC and LST-1 observations
A facile synthesis of azido-terminated heterobifunctional poly(ethylene glycol)s for “click” conjugation
New azido-terminated heterobifunctional poly(ethylene glycol) (PEG) derivatives having primary amine and carboxyl end groups, (Azide-PEG-NH2 and Azide-PEG-COOH, respectively) were synthesized with high efficiency. An α-allyl-ω-hydroxyl PEG was prepared as the first step to Azide-PEG-X (X = NH2 and COOH) through the ring-opening polymerization of ethylene oxide (EO) with allyl alcohol as an initiator, followed by two-step modification of the hydroxyl end to an azido group. To introduce primary amino or carboxyl functional groups, amination and carboxylation reactions of the allyl terminal ends was then conducted by a radical addition of thiol compounds. Molecular functionalities of both ends of the PEG derivatives thus prepared were characterized by 1H, 13C NMR, and MALDI-TOF MS spectra, validating that the reaction proceeded quantitatively. The terminal azido functionality is available to conjugate various ligands with an alkyne group through the 1,3-dipolar cycloaddition reaction condition (“click chemistry”)
Polyplex Micelles with Double-Protective Compartments of Hydrophilic Shell and Thermoswitchable Palisade of Poly(oxazoline)-Based Block Copolymers for Promoted Gene Transfection
Improving the stability of polyplex
micelles under physiological
conditions is a critical issue for promoting gene transfection efficiencies.
To this end, hydrophobic palisade was installed between the inner
core of packaged plasmid DNA (pDNA) and the hydrophilic shell of polyplex
micelles using a triblock copolymer consisting of hydrophilic poly(2-ethyl-2-oxazoline),
thermoswitchable amphiphilic poly(2-<i>n</i>-propyl-2-oxazoline)
(PnPrOx) and cationic poly(l-lysine). The two-step preparation
procedure, mixing the triblock copolymer with pDNA below the lower
critical solution temperature (LCST) of PnPrOx, followed by incubation
above the LCST to form a hydrophobic palisade of the collapsed PnPrOx
segment, induced the formation of spatially aligned hydrophilic–hydrophobic
double-protected polyplex micelles. The prepared polyplex micelles
exhibited significant tolerance against attacks from nuclease and
polyanions compared to those without hydrophobic palisades, thereby
promoting gene transfection. These results corroborated the utility
of amphiphilic poly(oxazoline) as a molecular thermal switch to improve
the stability of polyplex gene carriers relevant for physiological
applications
The anti-tumor effect of trifluridine via induction of aberrant mitosis is unaffected by mutations modulating p53 activity
Abstract The fluorinated thymidine analog trifluridine (FTD) is a chemotherapeutic drug commonly used to treat cancer; however, the mechanism by which FTD induces cytotoxicity is not fully understood. In addition, the effect of gain-of-function (GOF) missense mutations of the TP53 gene (encoding p53), which promote cancer progression and chemotherapeutic drug resistance, on the chemotherapeutic efficacy of FTD is unclear. Here, we revealed the mechanisms by which FTD-induced aberrant mitosis and contributed to cytotoxicity in both p53-null and p53-GOF missense mutant cells. In p53-null mutant cells, FTD-induced DNA double-stranded breaks, single-stranded DNA accumulation, and the associated DNA damage responses during the G2 phase. Nevertheless, FTD-induced DNA damage and the related responses were not sufficient to trigger strict G2/M checkpoint arrest. Thus, these features were carried over into mitosis, resulting in chromosome breaks and bridges, and subsequent cytokinesis failure. Improper mitotic exit eventually led to cell apoptosis, caused by the accumulation of extensive DNA damage and the presence of micronuclei encapsulated in the disrupted nuclear envelope. Upon FTD treatment, the behavior of the p53-GOF-missense mutant, isogenic cell lines, generated by CRISPR/Cas9 genome editing, was similar to that of p53-null mutant cells. Thus, our data suggest that FTD treatment overrode the effect on gene expression induced by p53-GOF mutants and exerted its anti-tumor activity in a manner that was independent of the p53 function