3,192 research outputs found
Wakefulness affects synaptic and network activity by increasing extracellular astrocyte-derived adenosine
Loss of sleep causes an increase in sleep drive and deficits in hippocampal-dependent memory. Both of these responses are thought to require activation of adenosine A1 receptors (adorA1Rs) and release of transmitter molecules including ATP, which is rapidly converted to adenosine in the extracellular space, from astrocytes in a process termed gliotransmission. Although it is increasingly clear that astrocyte-derived adenosine plays an important role in driving the homeostatic sleep response and the effects of sleep loss on memory (Halassa et al., 2009; Florian et al., 2011), previous studies have not determined whether the concentration of this signaling molecule increases in response to wakefulness. Here, we show that the level of adorA1R activation increases in response to wakefulness in mice (Mus musculus). We found that this increase affected synaptic transmission in the hippocampus and modulated network activity in the cortex. Direct biosensor-based measurement of adenosine showed that the net extracellular concentration of this transmitter increased in response to normal wakefulness and sleep deprivation. Genetic inhibition of gliotransmission prevented this increase and attenuated the wakefulness-dependent changes in synaptic and network regulation by adorA1R. Consequently, we conclude that wakefulness increases the level of extracellular adenosine in the hippocampus and that this increase requires the release of transmitters from astroctyes
Lognormal scale invariant random measures
In this article, we consider the continuous analog of the celebrated
Mandelbrot star equation with lognormal weights. Mandelbrot introduced this
equation to characterize the law of multiplicative cascades. We show existence
and uniqueness of measures satisfying the aforementioned continuous equation;
these measures fall under the scope of the Gaussian multiplicative chaos theory
developed by J.P. Kahane in 1985 (or possibly extensions of this theory). As a
by product, we also obtain an explicit characterization of the covariance
structure of these measures. We also prove that qualitative properties such as
long-range independence or isotropy can be read off the equation.Comment: 31 pages; Probability Theory and Related Fields (2012) electronic
versio
Results of search for magnetized quark-nugget dark matter from radial impacts on Earth
Magnetized Quark Nuggets (MQNs) are a recently proposed dark-matter candidate
consistent with the Standard Model and with Tatsumi's theory of quark-nugget
cores in magnetars. Previous publications have covered their formation in the
early universe, aggregation into a broad mass distribution before they can
decay by the weak force, interaction with normal matter through their
magnetopause, and first observation consistent MQNs, i.e. a nearly tangential
impact limiting their surface-magnetic-field parameter B_o from Tatsumi's
values of 0.1 to 10.0 TT to new value of 1.65 TT +/- 21%. The MQN mass
distribution and interaction cross section depend strongly on B_o. Their
magnetopause is much larger than their geometric dimensions and can cause
sufficient energy deposition to form non-meteorite craters, which are reported
approximately annually. We report computer simulations of the MQN energy
deposition in water-saturated peat, soft sediments, and granite and report
results from excavating such a crater. Five points of agreement between
observations and hydrodynamic simulations of an MQN impact support this second
observation consistent with MQN dark matter and suggest a method for qualifying
additional MQN events. The results also redundantly constrain B_o to greater
than 0.4 TT.Comment: 30 pages, 13 figures, submitted to Univers
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Mechanical Response and Decomposition of Thermally Degraded Energetic Materials: Experiments and Model Simulations
We report progress of a continuing effort to characterize and simulate the response of energetic materials (EMs), primarily HMX-based, under conditions leading to cookoff. Our experiments include mechanical-effects testing of HMX and FIMX with binder at temperatures nearing decomposition thresholds. Additional experiments have focused on decomposition of these EMs under confinement, measuring evolution of gas products and observing the effect of pressurization on the solid. Real-time measurements on HMX show abrupt changes that maybe due to sudden void collapse under increasing load. Postmortem examination shows significant internal damage to the pellets, including voids and cracks. These experiments have been used to help develop a constitutive model for pure HMX. Unconfined uniaxial compression tests were performed on HMX and LX-14 to examine the effect of binders on the deviatoric strength of EM pellets, and to assess the need of including deviatoric terms in the model. A scale-up experiment will be described that is being developed to validate the model and provide additional diagnostics
The Effects of Home Computers on Educational Outcomes: Evidence from a Field Experiment with Schoolchildren
Are home computers are an important input in the educational production
function? To address this question, we conduct a field experiment
involving the provision of free computers to schoolchildren for home
use. Low-income children attending middle and high schools in 15 schools
in California were randomly selected to receive free computers and
followed over the school year. The results indicate that the experiment
substantially increased computer ownership and total computer use among
the schoolchildren with no substitution away from use at school or other
locations outside the home. We find no evidence that the home computers
improved educational outcomes for the treatment group. From detailed
administrative data provided by the schools and a follow-up survey, we
find no evidence of positive effects on a comprehensive set of outcomes
such as grades, test scores, credits, attendance, school enrollment,
computer skills, and college aspirations. The estimates also do not
indicate that the effects of home computers on educational outcomes are
instead negative. Our estimates are precise enough to rule out even
modestly-sized positive or negative impacts. The lack of a positive net
effect on educational outcomes may be due to displacement from
non-educational uses such as for games, social networking, and
entertainment. We find evidence that total hours of computer use for
games and social networking increases substantially with having a home
computer, and increases more than total hours of computer use for schoolwork
Cloud chamber experiments on the origin of ice crystal complexity in cirrus clouds
This is an open access article, made available under the terms of the Creative Commons attribution license CC BY 3.0 https://creativecommons.org/licenses/by/3.0/This study reports on the origin of ice crystal complexity and its influence on the angular light scattering properties of cirrus clouds. Cloud simulation experiments were conducted at the AIDA (Aerosol Interactions and Dynamics in the Atmosphere) cloud chamber of the Karlsruhe Institute of Technology (KIT). A new experimental procedure was applied to grow and sublimate ice particles at defined super- and subsaturated ice conditions and for temperatures in the −40 to −60 °C range. The experiments were performed for ice clouds generated via homogeneous and heterogeneous initial nucleation. Ice crystal complexity was deduced from measurements of spatially resolved single particle light scattering patterns by the latest version of the Small Ice Detector (SID-3). It was found that a high ice crystal complexity is dominating the microphysics of the simulated clouds and the degree of this complexity is dependent on the available water vapour during the crystal growth. Indications were found that the crystal complexity is influenced by unfrozen H2SO4/H2O residuals in the case of homogeneous initial ice nucleation. Angular light scattering functions of the simulated ice clouds were measured by the two currently available airborne polar nephelometers; the Polar Nephelometer (PN) probe of LaMP and the Particle Habit Imaging and Polar Scattering (PHIPS-HALO) probe of KIT. The measured scattering functions are featureless and flat in the side- and backward scattering directions resulting in low asymmetry parameters g around 0.78. It was found that these functions have a rather low sensitivity to the crystal complexity for ice clouds that were grown under typical atmospheric conditions. These results have implications for the microphysical properties of cirrus clouds and for the radiative transfer through these clouds.Peer reviewedFinal Published versio
ANALISIS BANJIR RANCANGAN DENGAN METODE HSS NAKAYASU PADA BENDUNGAN GINTUNG
Jebolnya Situ Gintung merupakan akibat dari perubahan debit banjir yang terus bertambah. Hal
tersebut perlu diana/isis terhadap debit banjir rancangan yang selanjutnya dapat digunakan
untuk merencanakan Bendungan Gintung yang baru. Berdasarkan permasalahan di atas, maka
perlu dikembangkan perhitungan banjir rancangan dengan metode HSS Nakayasu. Perhitungan
dengan menggunaan data hujan. Pada penelitian ini digunakan 18 Pos stasiun penangkar hujan
yang diseleksi menurut kelayakan data menjadi 9 pos stasiun hujan dengan memasukan nilai
hujan harian maksimum tahunan. Data curah hujan yang disaring memilki tingkat kepercayaan
yang rendah, namun masih masuk ke dalam data aman. Dalam penentuan debit banjir rencana
terlebih dahulu dilakukan ana/isa frekuensi dan penetapan sebaran data curah hujan kemudian
diuji dengan chi-kuadrat. Distribusi yang sesuai adalah distribusi Log Pearson Type III. Dari
hasil ana/isa debit banjir rancangan, untuk merencanakan bendungan digunakan debit banjir
kala ulang Ql000 = 289,348 m3/dt
Mesoporous silica formation mechanisms probed using combined Spin-Echo Modulated Small Angle Neutron Scattering (SEMSANS) and Small Angle Neutron Scattering (SANS)
International audienceThe initial formation stages of surfactant-templated silica thin films which grow at the air−water interface were studied using combined spin−echo modulated small-angle neutron scattering (SEMSANS) and small-angle neutron scattering (SANS). The films are formed from either a cationic surfactant or nonionic surfactant (C16EO8) in a dilute acidic solution by the addition of tetramethoxysilane. Previous work has suggested a twostage formation mechanism with mesostructured particle formation in the bulk solution driving film formation at the solution surface. From the SEMSANS data, it is possible to pinpoint accurately the time associated with the formation of large particles in solution that go on to form the film and to show their emergence is concomitant with the appearance of Bragg peaks in the SANS pattern, associated with the two-dimensional hexagonal order. The combination of SANS and SEMSANS allows a complete depiction of the steps of the synthesis that occur in the subphase
A Comparison of Radio Axis with Host Galaxy Plane Axis in Seyfert Galaxies
We use the radio axis as an indicator of the orientation of the obscuring
torus in Seyfert galaxies, and analyze the difference between the position
angles of extended radio structures and host galaxy major axis of Seyfert 1 and
Seyfert 2 galaxies. We find that Seyfert 1's are less likely to have extended
radio structures along the host galaxy major axis, while Seyfert 2's have these
structures distributed in most directions. We also find a zone of avoidance in
the distribution of position angles; both Seyfert 1's and Seyfert 2's seem to
avoid close alignment between the radio axis and the host galaxy plane axis.
These results are analyzed from the point of view of a model in which Seyfert
1's have their obscuring torus axis aligned preferentially along the host
galaxy disk axis, and Seyfert 2's have their torus axis laying at an
intermediate angle between the galaxy disk and its axis.Comment: 9 pages of text, 10 figures and 1 table. Accepted for publication in
the Ap
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