695 research outputs found
Methods and compositions for X-ray induced release from pH sensitive liposomes
Compositions including pH sensitive lipid vesicles comprised of a lipid layer, an agent, and an organic halogen such that the agent is released from the vesicles after exposure to ionizing radiation. Methods of delivering the agent to a target in a subject using the compositions provided herein are also described. The methods allow for controlled release of the agent. The timing of release of the agent from the lipid vesicle may be controlled as well as the location of release by timing and localizing the exposure to ionizing radiation exposure
Methods and compositions for X-ray induced release from pH sensitive liposomes
Compositions including pH sensitive lipid vesicles comprised of a lipid layer, an agent, and an organic halogen such that the agent is released from the vesicles after exposure to ionizing radiation. Methods of delivering the agent to a target in a subject using the compositions provided herein are also described. The methods allow for controlled release of the agent. The timing of release of the agent from the lipid vesicle may be controlled as well as the location of release by timing and localizing the exposure to ionizing radiation exposure
Quantitative FDG-PET/CT predicts local recurrence and survival for squamous cell carcinoma of the anus
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Comparison of Structure and Properties of Femtosecond and Nanosecond Laser-Structured Silicon
We compare the optical properties, chemical composition, and crystallinity of silicon microstructures formed in the presence of SF6 by femtosecond laser irradiation and by nanosecond laser irradiation. In spite of very different morphology and crystallinity, the optical properties and chemical composition of the two types of microstructures are very similar. The structures formed with femtosecond (fs) pulses are covered with a disordered nanocrystalline surface layer less than 1 um thick, while those formed with nanosecond (ns) pulses have very little disorder. Both ns-laser-formed and fs-laser-formed structures absorb near-infrared (1.1 – 2.5 um) radiation strongly and have roughly 0.5% sulfur impurities.Engineering and Applied Science
The first cosmic ray albedo proton map of the Moon
[1] Neutrons emitted from the Moon are produced by the impact of galactic cosmic rays (GCRs) within the regolith. GCRs are high-energy particles capable of smashing atomic nuclei in the lunar regolith and producing a shower of energetic protons, neutrons and other subatomic particles. Secondary particles that are ejected out of the regolith become “albedo” particles. The neutron albedo has been used to study the hydrogen content of the lunar regolith, which motivates our study of albedo protons. In principle, the albedo protons should vary as a function of the input GCR source and possibly as a result of surface composition and properties. During the LRO mission, the total detection rate of albedo protons between 60 MeV and 150 MeV has been declining since 2009 in parallel with the decline in the galactic cosmic ray flux, which validates the concept of an albedo proton source. On the other hand, the average yield of albedo protons has been increasing as the galactic cosmic ray spectrum has been hardening, consistent with a disproportionately stronger modulation of lower energy GCRs as solar activity increases. We construct the first map of the normalized albedo proton emission rate from the lunar surface to look for any albedo variation that correlates with surface features. The map is consistent with a spatially uniform albedo proton yield to within statistical uncertainties
Insulator-to-metal transition in sulfur-doped silicon
We observe an insulator-to-metal (I-M) transition in crystalline silicon
doped with sulfur to non- equilibrium concentrations using ion implantation
followed by pulsed laser melting and rapid resolidification. This I-M
transition is due to a dopant known to produce only deep levels at equilibrium
concentrations. Temperature-dependent conductivity and Hall effect measurements
for temperatures T > 1.7 K both indicate that a transition from insulating to
metallic conduction occurs at a sulfur concentration between 1.8 and 4.3 x
10^20 cm-3. Conduction in insulating samples is consistent with variable range
hopping with a Coulomb gap. The capacity for deep states to effect metallic
conduction by delocalization is the only known route to bulk intermediate band
photovoltaics in silicon.Comment: Submission formatting; 4 journal pages equivalen
Spatial and Temporal Variability of the Gamma Radiation from Earth's Atmosphere during a Solar Cycle
The Solar Maximum Mission satellite's Gamma Ray Spectrometer observed Earth's
atmosphere for most of the period 1980-1989. Its 28deg orbit ensured that a
range of geomagnetic latitudes (geomagnetic cutoff rigidities) was sampled. We
measured the variation with time and rigidity of albedo gamma-ray lines at 1.6
MeV, 2.3 MeV and 4.4 MeV which are diagnostic of Galactic cosmic radiation
penetrating the cutoff and of the secondary neutrons produced in the
atmosphere. We found that the gamma-ray line intensities varied inversely with
solar activity and cutoff rigidity, as expected. The line ratio (1.6 MeV + 2.3
MeV)/4.4 MeV was remarkably constant (close to 0.39) at all times and
rigidities; the former two lines are produced by 5-10 MeV secondary neutrons
causing excitation and de-excitation of 14N, while the latter is produced by
more energetic (>20 MeV) neutrons inducing spallation. We infer that the shape
of the secondary neutron energy spectrum is virtually constant everywhere and
at all times. We also measured the intensity of the 0.511 MeV electron-positron
annihilation line. This line too varies with solar cycle and cutoff rigidity,
but its fall-off from low to high rigidity is less marked than that of the
nuclear lines. This results from the energy dependences of the cross sections
for positron production and for the hadronic processes which which produce
secondary neutrons.Comment: 11 pages, 12 figs., J. Geophys. Res. in pres
Iordanskii Force and the Gravitational Aharonov-Bohm effect for a Moving Vortex
I discuss the scattering of phonons by a vortex moving with respect to a
superfluid condensate. This allows us to test the compatibility of the
scattering-theory derivation of the Iordanskii force with the galilean
invariance of the underlying fluid dynamics. In order to obtain the correct
result we must retain terms in the sound-wave equation, and this
reinforces the interpretation, due to Volovik, of the Iordanskii force as an
analogue of the gravitational Bohm-Aharonov effect.Comment: 20 pages, LaTe
Precision measurements of radar transverse scattering speeds from meteor phase characteristics
We describe an improved technique for using the backscattered phase from
meteor radar echo measurements just prior to the specular point () to
calculate meteor speeds and their uncertainty. Our method, which builds on
earlier work of Cervera et al (1997), scans possible speeds in the Fresnel
distance - time domain with a dynamic, sliding window and derives a best-speed
estimate from the resultant speed distribution. We test the performance of our
method, called pre- speeds by sliding-slopes technique (PSSST), on
transverse scattered meteor echoes observed by the Middle Atmosphere Alomar
Radar System (MAARSY) and the Canadian Meteor Orbit Radar (CMOR), and compare
the results to time-of-flight and Fresnel transform speed estimates. Our novel
technique is shown to produce good results when compared to both model and
speed measurements using other techniques. We show that our speed precision is
5 at speeds less than 40 km/s and we find that more than 90 of all
CMOR multi-station echoes have PSSST solutions. For CMOR data, PSSST is robust
against the selection of critical phase value and poor phase unwrapping. Pick
errors of up to 6 pulses for meteor speeds less than about 50 km/s produce
errors of less than 5 of the meteoroid speed. In addition, the width
of the PSSST speed Kernel density estimate (KDE) is used as a natural measure
of uncertainty that captures both noise and pick uncertainties.Comment: Accepted for publication to Radio Science on 2020-06-2
International cooperation for Mars exploration and sample return
The National Research Council's Space Studies Board has previously recommended that the next major phase of Mars exploration for the United States involve detailed in situ investigations of the surface of Mars and the return to earth for laboratory analysis of selected Martian surface samples. More recently, the European space science community has expressed general interest in the concept of cooperative Mars exploration and sample return. The USSR has now announced plans for a program of Mars exploration incorporating international cooperation. If the opportunity becomes available to participate in Mars exploration, interest is likely to emerge on the part of a number of other countries, such as Japan and Canada. The Space Studies Board's Committee on Cooperative Mars Exploration and Sample Return was asked by the National Aeronautics and Space Administration (NASA) to examine and report on the question of how Mars sample return missions might best be structured for effective implementation by NASA along with international partners. The committee examined alternatives ranging from scientific missions in which the United States would take a substantial lead, with international participation playing only an ancillary role, to missions in which international cooperation would be a basic part of the approach, with the international partners taking on comparably large mission responsibilities. On the basis of scientific strategies developed earlier by the Space Studies Board, the committee considered the scientific and technical basis of such collaboration and the most mutually beneficial arrangements for constructing successful cooperative missions, particularly with the USSR
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