2,289 research outputs found
Broadband Infrasound Signal of a Collapsing Hanging Glacier
A major ice collapse ((Formula presented.) 10,000 (Formula presented.)) from a hanging glacier on Mount Eiger, Switzerland was recorded by a small aperture array as a broadband (0.1–10 Hz) infrasound signal. Array analysis reveals that the high ((Formula presented.) 3 Hz) frequency signal is infrasound produced by the moving ice mass, and its back azimuth variation with time tracks the ice mass trajectory and provides a mean velocity estimate. Infrasound frequency is used to estimate a radius, that despite overestimating the volume, provides quantitative analysis in near-real time. The low ((Formula presented.) 0.1 Hz) frequency oscillation is modeled in terms of the velocity field (wind), which the moving ice mass induces on the surrounding air, producing pressure variations at the different elements. These results show how infrasound array observations may provide quantitative information of glacier collapse and ice avalanche trajectories, and possibly, volume.ISSN:0094-8276ISSN:1944-800
Spiking neurons with short-term synaptic plasticity form superior generative networks
Spiking networks that perform probabilistic inference have been proposed both
as models of cortical computation and as candidates for solving problems in
machine learning. However, the evidence for spike-based computation being in
any way superior to non-spiking alternatives remains scarce. We propose that
short-term plasticity can provide spiking networks with distinct computational
advantages compared to their classical counterparts. In this work, we use
networks of leaky integrate-and-fire neurons that are trained to perform both
discriminative and generative tasks in their forward and backward information
processing paths, respectively. During training, the energy landscape
associated with their dynamics becomes highly diverse, with deep attractor
basins separated by high barriers. Classical algorithms solve this problem by
employing various tempering techniques, which are both computationally
demanding and require global state updates. We demonstrate how similar results
can be achieved in spiking networks endowed with local short-term synaptic
plasticity. Additionally, we discuss how these networks can even outperform
tempering-based approaches when the training data is imbalanced. We thereby
show how biologically inspired, local, spike-triggered synaptic dynamics based
simply on a limited pool of synaptic resources can allow spiking networks to
outperform their non-spiking relatives.Comment: corrected typo in abstrac
First Views of a Nearby LIRG: Star Formation and Molecular Gas in IRAS 04296+2923
We present a first look at the local LIRG, IRAS04296+2923. This barred
spiral, overlooked because of its location in the Galactic plane, is among the
half dozen closest LIRGs. More IR-luminous than either M82 or the Antennae, it
may be the best local example of a nuclear starburst caused by bar-mediated
secular evolution. We present Palomar J and Pa beta images, VLA maps from
20-1.3cm, a Keck LWS image at 11.7mic and OVRO CO(1-0) and ^13CO(1-0), and 2.7
mm continuum images. The J-band image shows a symmetric barred spiral. Two
bright, compact mid-IR/radio sources in the nucleus comprise a starburst that
is equivalent to 10^5 O7 stars, probably a pair of young super star clusters
separated by 30pc. The nuclear starburst is forming stars at the rate of
~12Msun/yr, half of the total star formation rate for the galaxy of ~25Msun/yr.
IRAS04296 is bright in CO, and among the most gas-rich galaxies in the local
universe. The CO luminosity of the inner half kpc is equivalent to that of the
entire Milky Way. While the most intense CO emission extends over a 15"(2 kpc)
region, the nuclear starburst is confined to ~1-2"(150-250 pc) of the dynamical
center. From ^13CO, we find that the CO conversion factor in the nucleus is
higher than the Galactic value by a factor 3-4, typical of gas-rich spiral
nuclei. The nuclear star formation efficiency is M_gas/SFR^nuc = 2.7x10^-8
yr^-1, corresponding to gas consumption timescale, tau_SF^nuc~4x10^7 yrs. The
star formation efficiency is ten times lower in the disk, tau_SF^disk~3.3x10^8
yrs. The low absolute star formation efficiency in the disk implies that the
molecular gas is not completely consumed before it drifts into the nucleus, and
is capable of fueling a sustained nuclear starburst. IRAS04296 is beginning a
100Myr period as a LIRG, during which it will turn much of its 6x10^9Msun of
molecular gas into a nuclear cluster of stars. (abridged)Comment: Accepted, Astronomical Journa
A New Normal for the Sea Ice Index
The NSIDC Sea Ice Index is a popular data product that shows users how ice extent and concentration have changed since the beginning of the passive microwave satellite record in 1978. It shows time series of monthly ice extent anomalies rather than actual extent values, in order to emphasize the information the data are carrying. Along with the time series, an image of average extent for the previous month is shown as a white field, with a pink line showing the median extent for that month. These are updated monthly; corresponding daily products are updated daily
Stochasticity from function -- why the Bayesian brain may need no noise
An increasing body of evidence suggests that the trial-to-trial variability
of spiking activity in the brain is not mere noise, but rather the reflection
of a sampling-based encoding scheme for probabilistic computing. Since the
precise statistical properties of neural activity are important in this
context, many models assume an ad-hoc source of well-behaved, explicit noise,
either on the input or on the output side of single neuron dynamics, most often
assuming an independent Poisson process in either case. However, these
assumptions are somewhat problematic: neighboring neurons tend to share
receptive fields, rendering both their input and their output correlated; at
the same time, neurons are known to behave largely deterministically, as a
function of their membrane potential and conductance. We suggest that spiking
neural networks may, in fact, have no need for noise to perform sampling-based
Bayesian inference. We study analytically the effect of auto- and
cross-correlations in functionally Bayesian spiking networks and demonstrate
how their effect translates to synaptic interaction strengths, rendering them
controllable through synaptic plasticity. This allows even small ensembles of
interconnected deterministic spiking networks to simultaneously and
co-dependently shape their output activity through learning, enabling them to
perform complex Bayesian computation without any need for noise, which we
demonstrate in silico, both in classical simulation and in neuromorphic
emulation. These results close a gap between the abstract models and the
biology of functionally Bayesian spiking networks, effectively reducing the
architectural constraints imposed on physical neural substrates required to
perform probabilistic computing, be they biological or artificial
Verification of a New NOAA/NSIDC Passive Microwave Sea-Ice Concentration Climate Record
A new satellite-based passive microwave sea-ice concentration product developed for the National Oceanic and Atmospheric Administration (NOAA)Climate Data Record (CDR) programme is evaluated via comparison with other passive microwave-derived estimates. The new product leverages two well-established concentration algorithms, known as the NASA Team and Bootstrap, both developed at and produced by the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC). The sea ice estimates compare well with similar GSFC products while also fulfilling all NOAA CDR initial operation capability (IOC) requirements, including (1) self describing file format, (2) ISO 19115-2 compliant collection-level metadata,(3) Climate and Forecast (CF) compliant file-level metadata, (4) grid-cell level metadata (data quality fields), (5) fully automated and reproducible processing and (6) open online access to full documentation with version control, including source code and an algorithm theoretical basic document. The primary limitations of the GSFC products are lack of metadata and use of untracked manual corrections to the output fields. Smaller differences occur from minor variations in processing methods by the National Snow and Ice Data Center (for the CDR fields) and NASA (for the GSFC fields). The CDR concentrations do have some differences from the constituent GSFC concentrations, but trends and variability are not substantially different
Anomalous Variability in Antarctic Sea Ice Extents During the 1960s With the Use of Nimbus Data
The Nimbus I, II, and III satellites provide a new opportunity for climate studies in the 1960s. The rescue of the visible and infrared imager data resulted in the utilization of the early Nimbus data to determine sea ice extent. A qualitative analysis of the early NASA Nimbus missions has revealed Antarctic sea ice extents that are signicant larger and smaller than the historic 1979-2012 passive microwave record. The September 1964 ice mean area is 19.7x10 km +/- 0.3x10 km. This is more the 250,000 km greater than the 19.44x10 km seen in the new 2012 historic maximum. However, in August 1966 the maximum sea ice extent fell to 15.9x10 km +/- 0.3x10 km. This is more than 1.5x10 km below the passive microwave record of 17.5x10 km set in September of 1986. This variation between 1964 and 1966 represents a change of maximum sea ice of over 3x10 km in just two years. These inter-annual variations while large, are small when compared to the Antarctic seasonal cycle
Anomalous Variability in Antarctic Sea Ice Extents During the 1960s With the Use of Nimbus Data
The Nimbus I, II, and III satellites provide a new opportunity for climate studies in the 1960s. The rescue of the visible and infrared imager data resulted in the utilization of the early Nimbus data to determine sea ice extent. A qualitative analysis of the early NASA Nimbus missions has revealed Antarctic sea ice extents that are significant larger and smaller than the historic 1979-2012 passive microwave record. The September 1964 ice mean area is 19.7x10(exp 6) sq. km +/- 0.3x10(exp 6) sq. km. This is more the 250,000 sq. km greater than the 19.44x10(exp 6) sq. km seen in the new 2012 historic maximum. However, in August 1966 the maximum sea ice extent fell to 15.9x10(exp 6) sq. km +/- 0.3x10(exp 6) sq. km. This is more than 1.5x10(exp 6) sq. km below the passive microwave record of 17.5x10(exp 6) sq. km set in September of 1986. This variation between 1964 and 1966 represents a change of maximum sea ice of over 3x10(exp 6) sq. km in just two years. These inter-annual variations while large, are small when compared to the Antarctic seasonal cycle
Bewegung im Nuklearstreit mit dem Iran: nach den Genfer Gesprächen herrscht vorsichtiger Optimismus
Nach sechs Monaten Verhandlungspause nahmen die Vertreter der E3+3 (Deutschland, Frankreich, Großbritannien sowie China, Russland, Vereinigte Staaten) und des Iran am 15. und 16. Oktober 2013 in Genf die Gespräche über das iranische Nuklearprogramm wieder auf. Die Voraussetzungen für den Einstieg in eine diplomatische Lösung sind so gut wie lange nicht mehr. Der im Juni gewählte neue Präsident Hasan Feridon-Ruhani hat ein klares Mandat für eine Politik der Verständigung mit dem Westen. Zwar gibt es weiterhin viele Differenzen über die Kontrolle und Begrenzung des iranischen Atomprogramms. Aber bei den besonders drängenden Problemen sind Kompromisslinien erkennbar. Auch wenn die Hoffnung auf schnelle Fortschritte groß ist: Verlorengegangenes Vertrauen kann nur in einem längeren Prozess neu aufgebaut werden. Beide Seiten sollten daher einen realistischen Fahrplan für Gespräche vereinbaren und gleichzeitig Verhandlungen darüber führen, wie eine langfristige Lösung im Nuklearkonflikt aussehen kann. (Autorenreferat
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