15,707 research outputs found
Tolerable versus actual soil erosion rates in Europe
Erosion is a major threat to soil resources in Europe, and may impair their ability to deliver a range of ecosystem goods and services. This is reflected by the European Commission's Thematic Strategy for Soil Protection, which recommends an indicator-based approach for monitoring soil erosion. Defined baseline and threshold values are essential for the evaluation of soil monitoring data. Therefore, accurate spatial data on both soil loss and soil genesis are required, especially in the light of predicted changes in climate patterns, notably frequency, seasonal distribution and intensity of precipitation. Rates of soil loss are reported that have been measured, modelled or inferred for most types of soil erosion in a variety of landscapes, by studies across the spectrum of the Earth sciences. Natural rates of soil formation can be used as a basis for setting tolerable soil erosion rates, with soil formation consisting of mineral weathering as well as dust deposition. This paper reviews the concept of tolerable soil erosion and summarises current knowledge on rates of soil formation, which are then compared to rates of soil erosion by known erosion types, for assessment of soil erosion monitoring at the European scale
A Performance Assessment of an Airborne Separation Assistance System Using Realistic Complex Traffic Flows
This paper presents the results from a study that investigates the performance of a tactical Airborne Separation Assistance System (ASAS) in en route airspace, under varying demand levels, with realistic traffic flows. The ASAS concept studied here allows flight crews of equipped aircraft to perform separation from other air traffic autonomously. This study addresses the tactical aspects of an ASAS using aircraft state data (i.e. position and velocity) to detect and resolve projected conflicts. In addition, use of a conflict prevention system helps ASAS-equipped aircraft avoid maneuvers that may cause new conflicts. ASAS-capable aircraft are equipped with satellite-based navigation and Automatic Dependent Surveillance Broadcast (ADS-B) for transmission and receipt of aircraft state data. In addition to tactical conflict detection and resolution (CD&R), a complete, integrated ASAS is likely to incorporate a strategic CD&R component with a longer look-ahead time, using trajectory intent information. A system-wide traffic flow management (TFM) component, located at the FAA command center helps aircraft to avoid regions of excessive traffic density and complexity. A Traffic Alert and Collision Avoidance System (TCAS), as used today is the system of last resort. This integrated approach avoids sole reliance on the use of the tactical CD&R studied here, but the tactical component remains a critical element of the complete ASAS. The focus of this paper is to determine to what extent the proposed tactical component of ASAS alone can maintain aircraft separation at demand levels up to three times that of current traffic. The study also investigates the effect of mixing ASAS-equipped aircraft with unequipped aircraft (i.e. current day) that do not have the capability to self-separate. Position and velocity data for unequipped aircraft needs to be available to ASASequipped. Most likely, for this future concept, state data would be available from instrument flight rules (IFR) aircraft, equipped with at least ADS-B transmission capability. The objective is to reduce the number of losses of separation to a minimum and investigate the limits of tactical-only CD&R. Thus, the objective is not, expressly, to achieve zero losses of separation with tactical ASAS because this is one component of an integrated ASAS
High-resolution Elemental Mapping of the Lunar Surface
New instruments and missions are being proposed to study the lunar surface as a result of the resurgence of interest in returning to the Moon. One instrument recently proposed is similar in concept to the x-ray fluorescence detectors flown on Apollo, but utilizes fluorescence from the L- and M-shells rather than the K-shell. This soft X-Ray Flourescence Imager (XRFI) is discussed
Cumulative Fatigue Damage of Axially Loaded Alclad 75S-T6 and Alclad 24S-T3 Aluminum-alloy Sheet
Global auroral responses to magnetospheric compressions by shocks in the solar wind: Two case studies
The global auroral responses to shocks in the solar wind at Earth were studied. The z-component of the interplanetary magnetic field, Bz, is negative ahead and behind the first shock and positive for the second case. A sudden-commencement geomagnetic storm develops in each case, with maximum D sub st 190 nT. An immediate auroral response is detected at all longitudes around the auroral oval, in which auroral luminosities increase by a factor of 2 to 3 with the first samples after each sudden commencement. The time delay in obtaining the first sample varies with local time from approx. 1 to 18 mins. No other significant variations in the aurora are associated with the immediate response. Beginning approx. 30 mins after each sudden commencement, the aurora becomes active and displays significant variations in its luminosity and spatial distribution. For Bz 0 an intense substorm develops. A sun-aligned transpolar arc forms when Bz 0, appearing first at local midnight as a polar arc and then lengthening sunward from the auroral oval across the polar cap to noon at an average speed of approx. 1 km/sec
Calculation and Measurement of Normal Modes of Vibration of an Aluminum-alloy Box Beam with and Without Large Discontinuities
Turning to art as a positive way of living with cancer: A qualitative study of personal motives and contextual influences
Why do some women turn to creative art-making after a diagnosis of cancer? Eleven women provided qualitative accounts that were analyzed following guidelines for interpretative phenomenological analysis (IPA). Some described taking up artistic leisure activities initially in order to manage emotional distress. Others emphasized their need for positive well-being, taking up art to experience achievement and satisfaction, to regain a positive identity, and to normalize family dynamics in the context of living with cancer. Participants’ turn to art-making was facilitated by biographical and contextual factors, including pre-existing craft skills, long-standing personal values and coping philosophies, family role models for managing adversity, and the supportive encouragement of family and friends. Other research has acknowledged that positive lifestyle change and post-traumatic growth can occur after a cancer diagnosis, and this study reveals a multi-faceted process. The findings suggest a need for further research into the experiences that facilitate positive lifestyle change and subjective well-being among people who are living with cancer
Revisiting 2D Numerical Models for the 19th century outbursts of Carinae
We present here new results of two-dimensional hydrodynamical simulations of
the eruptive events of the 1840s (the great) and the 1890s (the minor)
eruptions suffered by the massive star Car. The two bipolar nebulae
commonly known as the Homunculus and the little Homunculus were formed from the
interaction of these eruptive events with the underlying stellar wind. As in
previous work (Gonzalez et al. 2004a, 2004b), we assume here an interacting,
nonspherical multiple-phase wind scenario to explain the shape and the
kinematics of both Homunculi, but adopt a more realistic parametrization of the
phases of the wind. During the 1890s eruptive event, the outflow speed {\it
decreased} for a short period of time. This fact suggests that the little
Homunculus is formed when the eruption ends, from the impact of the
post-outburst Car wind (that follows the 1890s event) with the eruptive
flow (rather than by the collision of the eruptive flow with the pre-outburst
wind, as claimed in previous models; Gonzalez et al. 2004a, 2004b). Our
simulations reproduce quite well the shape and the observed expansion speed of
the large Homunculus. The little Homunculus (which is embedded within the large
Homunculus) becomes Rayleigh-Taylor unstable and develop filamentary structures
that resembles the spatial features observed in the polar caps. In addition, we
find that the interior cavity between the two Homunculi is partially filled by
material that is expelled during the decades following the great eruption. This
result may be connected with the observed double-shell structure in the polar
lobes of the Car nebula. Finally, as in previous work, we find the
formation of tenuous, equatorial, high-speed features that seem to be related
to the observed equatorial skirt of Car.Comment: accepted for publication in MNRA
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