1,497 research outputs found
Breaking down the Barrier: Topical Liposomes as Nanocarriers for Drug Delivery into the Posterior Segment of the Eyeball
Topical instillation is the most widely preferred noninvasive route of drug administration to treat diseases affecting the anterior segment of the eye. Nonetheless, the ocular bioavailability for deeper ocular tissues is very low. Different routes of administration, such as intravitreal injections, periocular injections, and systemic administration, have been used to deliver drugs into the posterior segment ocular tissues. However, the presence of blood-retinal barriers (BRBs) makes systemic administration an impractical approach, whereas the drug delivery with the periocular administration route is compromised by ocular static and dynamic barriers. On the other hand, intravitreal injection, the most common and widely recommended route for drug administration to treat posterior ocular diseases, is related to several side effects such as endophthalmitis, hemorrhage, retinal detachment, and poor patient tolerance. Diverse strategies to overcome ocular barriers have been explored for topical drop formulations in order to deliver drugs into the posterior segment ocular tissues. In this chapter, we will review the promising topical nanocarriers for drug delivery into the posterior segment of the eye, emphasizing the use of liposomes for topical ophthalmic formulations targeting the vitreous cavity and the retina
New considerations for PM, black carbon and particle number concentration for air quality monitoring across different European cities
In many large cities of Europe standard air quality limit values of particulate matter (PM) are exceeded. Emissions from road traffic and biomass burning are frequently reported to be the major causes. As a consequence of these exceedances a large number of air quality plans, most of them focusing on traffic emissions reductions, have been implemented in the last decade. In spite of this implementation, a number of cities did not record a decrease of PM levels. Thus, is the efficiency of air quality plans overestimated? Do the road traffic emissions contribute less than expected to ambient air PM levels in urban areas? Or do we need a more specific metric to evaluate the impact of the above emissions on the levels of urban aerosols? This study shows the results of the interpretation of the variability of levels of PM, Black Carbon (BC), aerosol number concentration (N) and a number of gaseous pollutants in seven selected urban areas covering road traffic, urban background, urban-industrial, and urban-shipping environments from southern, central and northern Europe. The results showed that variations of PM and N levels do not always reflect the variation of the impact of road traffic emissions on urban aerosols. However, BC levels vary proportionally with those of traffic related gaseous pollutants, such as CO, NO₂ and NO. Due to this high correlation, one may suppose that monitoring the levels of these gaseous pollutants would be enough to extrapolate exposure to traffic-derived BC levels. However, the BC/CO, BC/NO₂ and BC/NO ratios vary widely among the cities studied, as a function of distance to traffic emissions, vehicle fleet composition and the influence of other emission sources such as biomass burning. Thus, levels of BC should be measured at air quality monitoring sites. During morning traffic rush hours, a narrow variation in the N/BC ratio was evidenced, but a wide variation of this ratio was determined for the noon period. Although in central and northern Europe N and BC levels tend to vary simultaneously, not only during the traffic rush hours but also during the whole day, in urban background stations in southern Europe maximum N levels coinciding with minimum BC levels are recorded at midday in all seasons. These N maxima recorded in southern European urban background environments are attributed to midday nucleation episodes occurring when gaseous pollutants are diluted and maximum insolation and O₃ levels occur. The occurrence of SO₂ peaks may also contribute to the occurrence of midday nucleation bursts in specific industrial or shipping-influenced areas, although at several central European sites similar levels of SO₂ are recorded without yielding nucleation episodes. Accordingly, it is clearly evidenced that N variability in different European urban environments is not equally influenced by the same emission sources and atmospheric processes. We conclude that N variability does not always reflect the impact of road traffic on air quality, whereas BC is a more consistent tracer of such an influence. However, N should be measured since ultrafine particles (<100 nm) may have large impacts on human health. The combination of PM₁₀ and BC monitoring in urban areas potentially constitutes a useful approach for air quality monitoring. BC is mostly governed by vehicle exhaust emissions, while PM₁₀ concentrations at these sites are also governed by non-exhaust particulate emissions resuspended by traffic, by midday atmospheric dilution and by other nontraffic emissions
New considerations for PM, Black Carbon and particle number concentration for air quality monitoring across different European cities
In many large cities of Europe standard air quality limit values of particulate matter (PM) are exceeded. Emissions from road traffic and biomass burning are frequently reported to be the major causes. As a consequence of these exceedances a large number of air quality plans, most of them focusing on traffic emissions reductions, have been implemented in the last decade. In spite of this implementation, a number of cities did not record a decrease of PM levels. Thus, is the efficiency of air quality plans overestimated? Do the road traffic emissions contribute less than expected to ambient air PM levels in urban areas? Or do we need a more specific metric to evaluate the impact of the above emissions on the levels of urban aerosols?
This study shows the results of the interpretation of the 2009 variability of levels of PM, Black Carbon (BC), aerosol number concentration (N) and a number of gaseous pollutants in seven selected urban areas covering road traffic, urban background, urban-industrial, and urban-shipping environments from southern, central and northern Europe.
The results showed that variations of PM and N levels do not always reflect the variation of the impact of road traffic emissions on urban aerosols. However, BC levels vary proportionally with those of traffic related gaseous pollutants, such as CO, NO2 and NO. Due to this high correlation, one may suppose that monitoring the levels of these gaseous pollutants would be enough to extrapolate exposure to traffic-derived BC levels. However, the BC/CO, BC/NO2 and BC/NO ratios vary widely among the cities studied, as a function of distance to traffic emissions, vehicle fleet composition and the influence of other emission sources such as biomass burning. Thus, levels of BC should be measured at air quality monitoring sites.
During morning traffic rush hours, a narrow variation in the N/BC ratio was evidenced, but a wide variation of this ratio was determined for the noon period. Although in central and northern Europe N and BC levels tend to vary simultaneously, not only during the traffic rush hours but also during the whole day, in urban background stations in southern Europe maximum N levels coinciding with minimum BC levels are recorded at midday in all seasons. These N maxima recorded in southern European urban background environments are attributed to midday nucleation episodes occurring when gaseous pollutants are diluted and maximum insolation and O3 levels occur. The occurrence of SO2 peaks may also contribute to the occurrence of midday nucleation bursts in specific industrial or shipping-influenced areas, although at several central European sites similar levels of SO2 are recorded without yielding nucleation episodes.
Accordingly, it is clearly evidenced that N variability in different European urban environments is not equally influenced by the same emission sources and atmospheric processes. We conclude that N variability does not always reflect the impact of road traffic on air quality, whereas BC is a more consistent tracer of such an influence. However, N should be measured since ultrafine particles (<100 nm) may have large impacts on human health.
The combination of PM10 and BC monitoring in urban areas potentially constitutes a useful approach for air quality monitoring. BC is mostly governed by vehicle exhaust emissions, while PM10 concentrations at these sites are also governed by non-exhaust particulate emissions resuspended by traffic, by midday atmospheric dilution and by other non-traffic emissions
Very high energy particle acceleration powered by the jets of the microquasar SS 433
SS 433 is a binary system containing a supergiant star that is overflowing
its Roche lobe with matter accreting onto a compact object (either a black hole
or neutron star). Two jets of ionized matter with a bulk velocity of
extend from the binary, perpendicular to the line of sight, and
terminate inside W50, a supernova remnant that is being distorted by the jets.
SS 433 differs from other microquasars in that the accretion is believed to be
super-Eddington, and the luminosity of the system is erg
s. The lobes of W50 in which the jets terminate, about 40 pc from the
central source, are expected to accelerate charged particles, and indeed radio
and X-ray emission consistent with electron synchrotron emission in a magnetic
field have been observed. At higher energies (>100 GeV), the particle fluxes of
rays from X-ray hotspots around SS 433 have been reported as flux
upper limits. In this energy regime, it has been unclear whether the emission
is dominated by electrons that are interacting with photons from the cosmic
microwave background through inverse-Compton scattering or by protons
interacting with the ambient gas. Here we report TeV -ray observations
of the SS 433/W50 system where the lobes are spatially resolved. The TeV
emission is localized to structures in the lobes, far from the center of the
system where the jets are formed. We have measured photon energies of at least
25 TeV, and these are certainly not Doppler boosted, because of the viewing
geometry. We conclude that the emission from radio to TeV energies is
consistent with a single population of electrons with energies extending to at
least hundreds of TeV in a magnetic field of ~micro-Gauss.Comment: Preprint version of Nature paper. Contacts: S. BenZvi, B. Dingus, K.
Fang, C.D. Rho , H. Zhang, H. Zho
All-particle cosmic ray energy spectrum measured by the HAWC experiment from 10 to 500 TeV
We report on the measurement of the all-particle cosmic ray energy spectrum
with the High Altitude Water Cherenkov (HAWC) Observatory in the energy range
10 to 500 TeV. HAWC is a ground based air-shower array deployed on the slopes
of Volcan Sierra Negra in the state of Puebla, Mexico, and is sensitive to
gamma rays and cosmic rays at TeV energies. The data used in this work were
taken from 234 days between June 2016 to February 2017. The primary cosmic-ray
energy is determined with a maximum likelihood approach using the particle
density as a function of distance to the shower core. Introducing quality cuts
to isolate events with shower cores landing on the array, the reconstructed
energy distribution is unfolded iteratively. The measured all-particle spectrum
is consistent with a broken power law with an index of prior to
a break at ) TeV, followed by an index of . The
spectrum also respresents a single measurement that spans the energy range
between direct detection and ground based experiments. As a verification of the
detector response, the energy scale and angular resolution are validated by
observation of the cosmic ray Moon shadow's dependence on energy.Comment: 16 pages, 11 figures, 4 tables, submission to Physical Review
Constraining the Ratio in TeV Cosmic Rays with Observations of the Moon Shadow by HAWC
An indirect measurement of the antiproton flux in cosmic rays is possible as
the particles undergo deflection by the geomagnetic field. This effect can be
measured by studying the deficit in the flux, or shadow, created by the Moon as
it absorbs cosmic rays that are headed towards the Earth. The shadow is
displaced from the actual position of the Moon due to geomagnetic deflection,
which is a function of the energy and charge of the cosmic rays. The
displacement provides a natural tool for momentum/charge discrimination that
can be used to study the composition of cosmic rays. Using 33 months of data
comprising more than 80 billion cosmic rays measured by the High Altitude Water
Cherenkov (HAWC) observatory, we have analyzed the Moon shadow to search for
TeV antiprotons in cosmic rays. We present our first upper limits on the
fraction, which in the absence of any direct measurements, provide
the tightest available constraints of on the antiproton fraction for
energies between 1 and 10 TeV.Comment: 10 pages, 5 figures. Accepted by Physical Review
Search for very-high-energy emission from Gamma-ray Bursts using the first 18 months of data from the HAWC Gamma-ray Observatory
The High Altitude Water Cherenkov (HAWC) Gamma-ray Observatory is an
extensive air shower detector operating in central Mexico, which has recently
completed its first two years of full operations. If for a burst like GRB
130427A at a redshift of 0.34 and a high-energy component following a power law
with index -1.66, the high-energy component is extended to higher energies with
no cut-off other than from extragalactic background light attenuation, HAWC
would observe gamma rays with a peak energy of 300 GeV. This paper
reports the results of HAWC observations of 64 gamma-ray bursts (GRBs) detected
by and , including three GRBs that were also
detected by the Large Area Telescope (-LAT). An ON/OFF analysis
method is employed, searching on the time scale given by the observed light
curve at keV-MeV energies and also on extended time scales. For all GRBs and
time scales, no statistically significant excess of counts is found and upper
limits on the number of gamma rays and the gamma-ray flux are calculated. GRB
170206A, the third brightest short GRB detected by the Gamma-ray Burst Monitor
on board the satellite (-GBM) and also
detected by the LAT, occurred very close to zenith. The LAT measurements can
neither exclude the presence of a synchrotron self-Compton (SSC) component nor
constrain its spectrum. Instead, the HAWC upper limits constrain the expected
cut-off in an additional high-energy component to be less than
for reasonable assumptions about the energetics and redshift of the burst.Comment: 19 pages, 6 figures, published in Ap
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