2,716 research outputs found
Moisture interaction and stability of ZOT (Zinc Orthotitanate) thermal control spacecraft coating
Two of the many performance requirements of the zinc orthotitanate (ZOT) ceramic thermal control paint covering parts of the Jupiter-bound Galileo spacecraft are that it be sufficiently electrically conductive so as to prevent electrostatic discharge (ESD) damage to onboard electronics and that it adhere to and protect the substrate from corrosion in terrestrial environments. The bulk electrical resistivity of ZOT on an aluminum substrate was measured over the ranges 22 C to 90 C and 0 percent RH to 100 percent RH, and also in soft (10 (minus 2) Torr) and hard (10 (minus 7) Torr) vacuums. No significant temperature dependence was evident, but measured resistivity values ranged over 9 orders of magnitude: 10 to the 5th power ohm-cm at 100 percent RH greater than 10 to the 12th power ohm-cm in a hard vacuum. The latter value violates the ESD criterion for a typical 0.019 cm thick coating. The corrosion study involved exposing typical ZOT substrate combinations to two moisture environments - 30 C/85 percent RH and 85 C/85 percent RH - for 2000 hours, during which time the samples were periodically removed for front-to-back electrical resistance and scratch/peel test measurements. It was determined that the ZOT/Al and ZOT/Mg systems are stable (no ZOT delamination), although some corrosion (oxide formation) and resistivity increases observed among the ZOT/Mg samples warrant that exposure of some parts to humid environments be minimized
Security of distributed-phase-reference quantum key distribution
Distributed-phase-reference quantum key distribution stands out for its easy
implementation with present day technology. Since many years, a full security
proof of these schemes in a realistic setting has been elusive. For the first
time, we solve this long standing problem and present a generic method to prove
the security of such protocols against general attacks. To illustrate our
result we provide lower bounds on the key generation rate of a variant of the
coherent-one-way quantum key distribution protocol. In contrast to standard
predictions, it appears to scale quadratically with the system transmittance.Comment: 4 pages + appendix, 4 figure
Endurance of SN 2005ip after a decade: X-rays, radio, and H-alpha like SN 1988Z require long-lived pre-supernova mass loss
SN2005ip was a TypeIIn event notable for its sustained strong interaction
with circumstellar material (CSM), coronal emission lines, and IR excess,
interpreted as shock interaction with the very dense and clumpy wind of an
extreme red supergiant. We present a series of late-time spectra of SN2005ip
and a first radio detection of this SN, plus late-time X-rays, all of which
indicate that its CSM interaction is still strong a decade post-explosion. We
also present and discuss new spectra of geriatric SNe with continued CSM
interaction: SN1988Z, SN1993J, and SN1998S. From 3-10 yr post-explosion,
SN2005ip's H-alpha luminosity and other observed characteristics were nearly
identical to those of the radio-luminous SN1988Z, and much more luminous than
SNe1993J and 1998S. At 10 yr after explosion, SN2005ip showed a drop in
H luminosity, followed by a quick resurgence over several months. We
interpret this variability as ejecta crashing into a dense shell located at
around 0.05 pc from the star, which may be the same shell that caused the IR
echo at earlier epochs. The extreme H-alpha luminosities in SN2005ip and
SN1988Z are still dominated by the forward shock at 10 yr post-explosion,
whereas SN1993J and SN1998S are dominated by the reverse shock at a similar
age. Continuous strong CSM interaction in SNe~2005ip and 1988Z is indicative of
enhanced mass loss for about 1e3 yr before core collapse, longer than Ne, O, or
Si burning phases. Instead, the episodic mass loss must extend back through C
burning and perhaps even part of He burning.Comment: 14 pages, 8 figs. accepted in MNRA
Detector dead-time effects and paralyzability in high-speed quantum key distribution
Recent advances in quantum key distribution (QKD) have given rise to systems
that operate at transmission periods significantly shorter than the dead times
of their component single-photon detectors. As systems continue to increase in
transmission rate, security concerns associated with detector dead times can
limit the production rate of sifted bits. We present a model of high-speed QKD
in this limit that identifies an optimum transmission rate for a system with
given link loss and detector response characteristics
Assessment of Mucin 13 (MUC13) as an Imaging Target for Guiding Colorectal Cancer Treatment: A Pathway Towards Theranostic Development
Background: A theranostic strategy combining diagnostic imaging and targeted therapy in a single regimen is proposed for improved management and treatment of colorectal cancer (CRC). Increased specificity in detection by the noninvasive imaging technique positron emission tomography (PET) can be achieved by radiolabeling antibodies (Abs) designed to target tumor-associated antigens with increased expression post-translational modifications present in cancer cells. In this study, an Ab designed to target the transmembrane glycoprotein mucin 13 (MUC13) was radiolabeled with the positron-emitting radionuclide zirconium-89 (89Zr) for PET imaging of a xenograft mouse model of CRC. Specified uptake of this radioimmunoconjugate was observed in the presence of increased MUC13 expression was observed through imaging along with in vitro and ex vivo analyses.
Methods:
Radiochemistry: The MUC13-targeting Ab C14 conjugated with desferrioxamine (DFO) was radiolabeled with 89Zr alongside isotype control Ab MOPC-21 (IgG) at a 59 kBq/µg (1.6 µCi/µg) ratio, producing [89Zr]Zr-DFO-C14 and [89Zr]Zr-DFO-IgG. Radiochemical purity (RCP) was determined using radio-iTLC and radio-SEC. Radiochemical yield (RCY) was determined with a well-type dose calibrator.
Cellular Binding and Internalization: Cultured human CRC cell lines T84 (MUC13+) and SW480 (MUC13-) were incubated with either [89Zr]Zr-DFO-C14 or [89Zr]Zr-DFO-IgG. At 2 and 24h, cell membranes were separated and radioactivity measured to compare membrane-bound and cell-internalized activity. To determine binding specificity of radiolabeled C14, cells were co-incubated with excess unmodified Ab.
µPET/CT Imaging: T84 and SW480 cells were introduced subcutaneously in athymic nude mice. Once palpable tumors were detected, mice were placed in the following treatment groups for 1.9 MBq (50 µCi) injection: T84+[89Zr]Zr-DFO-C14 (n=5), T84+[89Zr]Zr-DFO-C14 with 350 µg C14 (n=2), SW480+[89Zr]Zr-DFO-C14 (n=5), and T84+[89Zr]Zr-DFO-IgG (n=4). PET imaging was performed 24, 48, and 120h post-injection (p.i.) alongside computational tomography (CT) imaging to provide anatomical context. After 120h, mice were euthanized and blood, organs, and tissues were collected to measure radioactivity biodistribution and radioimmunoconjugate distribution in tumor tissue.
Results: Radiolabeled C14 and IgG were successfully produced with RCY\u3e83% (n.d.c.) and RCP\u3e95%. Reflecting rapid internalization observed in vitro (57.9±13% [89Zr]Zr-DFO-C14 uptake in T84 at 2h compared to 6.57±0.6% uptake in SW480 (p89Zr]Zr-DFO-IgG uptake (p89Zr]Zr-DFO-C14 at 24h p.i. through 120h p.i. compared to that measured in SW480 xenografts (5.5±0.7% ID/cc vs. 2.8±0.5% ID/cc at 24h p.i., p89Zr]Zr-DFO-IgG (1.9±0.2% ID/cc at 24h p.i., p89Zr]Zr-DFO-C14 within the tumor. Furthermore, co-injection with excess C14 resulted in reduced PET signal (2.7±0.1% ID/cc, p=0.0002), supporting the targeting specificity of [89Zr]Zr-DFO-C14. Ex vivo biodistribution comparison confirmed high, persistent [89Zr]Zr-DFO-C14 uptake in T84-derived tumor (18.5% ID/g at 120h p.i.).
Conclusion: MUC13 expression was clearly represented by PET/CT imaging in a xenograft mouse model of CRC using a 89Zr-labeled MUC13-targeting Ab, which also demonstrated target specificity both in vitro and ex vivo. These promising results justify further exploration into developing a theranostic platform for CRC treatment. Future work will test the therapeutic efficacy of the MUC13-targeting Ab radiolabeled with a beta particle-emitting radionuclide
SN2013fs and SN2013fr: Exploring the circumstellar-material diversity in Type II supernovae
We present photometry and spectroscopy of SN2013fs and SN2013fr in the first
100 days post-explosion. Both objects showed transient, relatively narrow
H emission lines characteristic of SNeIIn, but later resembled normal
SNeII-P or SNeII-L, indicative of fleeting interaction with circumstellar
material (CSM). SN2013fs was discovered within 8hr of explosion. Its light
curve exhibits a plateau, with spectra revealing strong CSM interaction at
early times. It is a less luminous version of the transitional SNIIn PTF11iqb,
further demonstrating a continuum of CSM interaction intensity between SNeII-P
and IIn. It requires dense CSM within 6.510~cm of the
progenitor, from a phase of advanced pre-SN mass loss shortly before explosion.
Spectropolarimetry of SN2013fs shows little continuum polarization, but
noticeable line polarization during the plateau phase. SN2013fr morphed from a
SNIIn at early times to a SNII-L. After the first epoch its narrow lines
probably arose from host-galaxy emission, but the bright, narrow H
emission at early times may be intrinsic. As for SN2013fs, this would point to
a short-lived phase of strong CSM interaction if proven to be intrinsic,
suggesting a continuum between SNeIIn and II-L. It is a low-velocity SNII-L,
like SN2009kr but more luminous. SN2013fr also developed an IR excess at later
times, due to warm CSM dust that require a more sustained phase of strong
pre-SN mass loss.Comment: MNRAS accepted. 28 pages, 23 figures, 8 table
Brain-Specific Phosphorylation of MeCP2 Regulates Activity-Dependent Bdnf Transcription, Dendritic Growth, and Spine Maturation
Mutations or duplications in MECP2 cause Rett and Rett-like syndromes, neurodevelopmental disorders characterized by mental retardation, motor dysfunction, and autistic behaviors. MeCP2 is expressed in many mammalian tissues and functions as a global repressor of transcription; however, the molecular mechanisms by which MeCP2 dysfunction leads to the neural-specific phenotypes of RTT remain poorly understood. Here, we show that neuronal activity and subsequent calcium influx trigger the de novo phosphorylation of MeCP2 at serine 421 (S421) by a CaMKII-dependent mechanism. MeCP2 S421 phosphorylation is induced selectively in the brain in response to physiological stimuli. Significantly, we find that S421 phosphorylation controls the ability of MeCP2 to regulate dendritic patterning, spine morphogenesis, and the activity-dependent induction of Bdnf transcription. These findings suggest that, by triggering MeCP2 phosphorylation, neuronal activity regulates a program of gene expression that mediates nervous system maturation and that disruption of this process in individuals with mutations in MeCP2 may underlie the neural-specific pathology of RTT
Quantum key distribution with 1.25 Gbps clock synchronization
We have demonstrated the exchange of sifted quantum cryptographic key over a
730 meter free-space link at rates of up to 1.0 Mbps, two orders of magnitude
faster than previously reported results. A classical channel at 1550 nm
operates in parallel with a quantum channel at 845 nm. Clock recovery
techniques on the classical channel at 1.25 Gbps enable quantum transmission at
up to the clock rate. System performance is currently limited by the timing
resolution of our silicon avalanche photodiode detectors. With improved
detector resolution, our technique will yield another order of magnitude
increase in performance, with existing technology.Comment: 6 pages, 3 figures, 99 kB .pdf documen
A Study of Interstellar Gas and Stars in the Gravitationally Lensed Galaxy `The Cosmic Eye' from Rest-Frame Ultraviolet Spectroscopy
We report the results of a study of the rest-frame UV spectrum of the Cosmic
Eye, a luminous Lyman break galaxy at z=3.07331 gravitationally lensed by a
factor of 25. The spectrum, recorded with the ESI spectrograph on the Keck II
telescope, is rich in absorption features from the gas and massive stars in
this galaxy. The interstellar absorption lines are resolved into two components
of approximately equal strength and each spanning several hundred km/s in
velocity. One component has a net blueshift of -70 km/s relative to the stars
and H II regions and presumably arises in a galaxy-scale outflow similar to
those seen in most star-forming galaxies at z = 2-3. The other is more unusual
in showing a mean redshift of +350 km/s relative to the systemic redshift;
possible interpretations include a merging clump, or material ejected by a
previous star formation episode and now falling back onto the galaxy, or more
simply a chance alignment with a foreground galaxy. In the metal absorption
lines, both components only partially cover the OB stars against which they are
being viewed. We tentatively associate the redshifted component with the strong
damped Lyman alpha line, indicative of a column density N(H I) = (3.0 +/- 0.8)
x 10(21) atoms/cm2, and propose that it provides the dust `foreground screen'
responsible for the low ratio of far-infrared to UV luminosities of the Cosmic
Eye. Compared to other well-studied examples of strongly lensed galaxies, we
find that the young stellar population of the Cosmic Eye is essentially
indistinguishable from those of the Cosmic Horseshoe and MS 1512-cB58, while
the interstellar spectra of all three galaxies are markedly different,
attesting to the real complexity of the interplay between starbursts and
ambient interstellar matter in young galaxies (abridged).Comment: 14 pages, 6 Figures, Accepted for publication in Monthly Notices of
the Royal Astronomical Society after minor revision
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