: In aged skin, decreased levels of stratum corneum ceramides have been described. Epidermal ceramides are generated by sphingomyelin hydrolysis or synthesis from sphingosin and fatty acids and are ...degraded by ceramidase. We recently showed that epidermal acid sphingomyelinase (A‐SMase) generates ceramides with structural function in the stratum corneum lipid bilayers, which provide for the permeability barrier function of the skin. Here, we examined the activities of epidermal A‐SMase, ceramide synthase, and ceramidase in chronologically aged versus young hairless mouse skin. We found reduced A‐SMase and ceramide synthase activities in the epidermis of aged mice. However, studies on enzyme localization revealed unchanged, ongoing high A‐SMase activity in the outer epidermis, which correlated with reported normal barrier function found in aged skin under basal conditions. Reduced A‐SMase and ceramide synthase activity was noted in the inner epidermis, correlating with reduced capacity for permeability barrier repair in aging. Ceramidase activity was not age dependent. In summary, we found reduced activities of ceramide‐generating SMase and ceramide synthase in the inner epidermis of aged skin, explaining its reduced capacity in barrier repair. In contrast, A‐SMase activity in the outer epidermis was unchanged, indicating that this enzyme is crucially involved in basal permeability barrier homeostasis.
We present new results of searches for neutrino point sources in the northern sky, using data recorded in 2007-2008 with 22 strings of the IceCube detector (approximately one-fourth of the planned ...total) and 275.7 days of live time. The final sample of 5114 neutrino candidate events agrees well with the expected background of atmospheric muon neutrinos and a small component of atmospheric muons. No evidence of a point source is found, with the most significant excess of events in the sky at 2.2 sigma after accounting for all trials. The average upper limit over the northern sky for point sources of muon-neutrinos with E -2 spectrum is , in the energy range from 3 TeV to 3 PeV, improving the previous best average upper limit by the AMANDA-II detector by a factor of 2.
Point source searches with the IceCube neutrino telescope have been restricted to one hemisphere, due to the exclusive selection of upward going events as a way of rejecting the atmospheric muon ...background. We show that the region above the horizon can be included by suppressing the background through energy-sensitive cuts. This improves the sensitivity above PeV energies, previously not accessible for declinations of more than a few degrees below the horizon due to the absorption of neutrinos in Earth. We present results based on data collected with 22 strings of IceCube, extending its field of view and energy reach for point source searches. No significant excess above the atmospheric background is observed in a sky scan and in tests of source candidates. Upper limits are reported, which for the first time cover point sources in the southern sky up to EeV energies.
Using the South Pole Acoustic Test Setup (SPATS) and a retrievable transmitter deployed in holes drilled for the IceCube experiment, we have measured the attenuation of acoustic signals by South Pole ...ice at depths between 190
m and 500
m. Three data sets, using different acoustic sources, have been analyzed and give consistent results. The method with the smallest systematic uncertainties yields an amplitude attenuation coefficient
α
=
3.20
±
0.57
km
−1 between 10 and 30
kHz, considerably larger than previous theoretical estimates. Expressed as an attenuation length, the analyses give a consistent result for
λ
≡
1/
α of ∼300
m with 20% uncertainty. No significant depth or frequency dependence has been found.
► We have measured the cosmic-ray energy spectrum from 1 to 100PeV. ► Five months of data from the 26-station configuration of IceTop were used. ► Zenith angle dependences put constraints on the mass ...composition. ► In addition to the ‘knee’ feature the spectrum exhibits a hardening above 22PeV.
We report on a measurement of the cosmic ray energy spectrum with the IceTop air shower array, the surface component of the IceCube Neutrino Observatory at the South Pole. The data used in this analysis were taken between June and October, 2007, with 26 surface stations operational at that time, corresponding to about one third of the final array. The fiducial area used in this analysis was 0.122km2. The analysis investigated the energy spectrum from 1 to 100PeV measured for three different zenith angle ranges between 0° and 46°. Because of the isotropy of cosmic rays in this energy range the spectra from all zenith angle intervals have to agree. The cosmic-ray energy spectrum was determined under different assumptions on the primary mass composition. Good agreement of spectra in the three zenith angle ranges was found for the assumption of pure proton and a simple two-component model. For zenith angles θ<30°, where the mass dependence is smallest, the knee in the cosmic ray energy spectrum was observed at about 4PeV, with a spectral index above the knee of about −3.1. Moreover, an indication of a flattening of the spectrum above 22PeV was observed.
In this paper, we present the results of searches for periodic neutrino emission from a catalog of binary systems. Such modulation, observed in the photon flux, would be caused by the geometry of ...these systems. In the analysis, the period is fixed by these photon observations, while the phase and duration of the neutrino emission are treated as free parameters to be fit with the data. If the emission occurs during ~20% or less of the total period, this analysis achieves better sensitivity than a time-integrated analysis. We use the IceCube data taken from 2007 May 31 to 2008 April 5 with its 22 string configuration and from 2008 April 5 to 2009 May 20 with its 40 string configuration. No evidence for neutrino emission is found, with the strongest excess occurring for Cygnus X-3 at 2.1sigma significance after accounting for trials. Neutrino flux upper limits for both periodic and time-integrated emission are provided.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted) We present the results of a search for high-energy muon neutrinos with the IceCube detector in coincidence with the Crab Nebula flare ...reported on 2010 September by various experiments. Due to the unusual flaring state of the otherwise steady source we performed a prompt analysis of the 79-string configuration data to search for neutrinos that might be emitted along with the observed gamma -rays. We performed two different and complementary data selections of neutrino events in the time window of 10 days around the flare. One event selection is optimized for discovery of ... neutrino spectrum typical of first-order Fermi acceleration. A similar event selection has also been applied to the 40-string data to derive the time-integrated limits to the neutrino emission from the Crab. The other event selection was optimized for discovery of neutrino spectra with softer spectral index and TeV energy cutoffs as observed for various Galactic sources in gamma -rays. The 90% confidence level (CL) best upper limits on the Crab flux during the 10 day flare are 4.73 x 10 super(-11) cm super(-2) s super(-1) TeV super(-1) for an ... neutrino spectrum and 2.50 x 10 super(-10) cm super(-2) s super(-1) TeV super(-1) for a softer neutrino spectra of ..., as indicated by Fermi measurements during the flare. In this paper, we also illustrate the impact of the time-integrated limit on the Crab neutrino steady emission. The limit obtained using 375.5 days of the 40-string configuration is compared to existing models of neutrino production from the Crab and its impact on astrophysical parameters is discussed. The most optimistic predictions of some models are already rejected by the IceCube neutrino telescope with more than 90% CL.
We present the search for Cherenkov signatures from relativistic magnetic monopoles in data taken with the AMANDA-II detector, a neutrino telescope deployed in the Antarctic ice cap at the Geographic ...South Pole. The non-observation of a monopole signal in data collected during the year 2000 improves present experimental limits on the flux of relativistic magnetic monopoles: Our flux limit varies between 3.8×10
−17
cm
−2
s
−1
sr
−1
(for monopoles moving at the vacuum speed of light) and 8.8×10
−16
cm
−2
s
−1
sr
−1
(for monopoles moving at a speed
β
=
v
/
c
=0.76, just above the Cherenkov threshold in ice). These limits apply to monopoles that are energetic enough to penetrate the Earth and enter the detector from below the horizon. The limit obtained for monopoles reaching the detector from above the horizon is less stringent by roughly an order of magnitude, due to the much larger background from down-going atmospheric muons. This looser limit is however valid for a larger class of magnetic monopoles, since the monopoles are not required to pass through the Earth.
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