3,240 research outputs found
Spectral properties of near-Earth and Mars-crossing asteroids using Sloan photometry
The nature and origin of the asteroids orbiting in near-Earth space,
including those on a potentially hazardous trajectory, is of both scientific
interest and practical importance. We aim here at determining the taxonomy of a
large sample of near-Earth (NEA) and Mars-crosser (MC) asteroids and analyze
the distribution of these classes with orbit. We use this distribution to
identify their source regions and to study the strength of planetary encounters
to refresh asteroid surfaces. We measure the photometry of these asteroids over
four filters at visible wavelengths on images taken by the SDSS. These colors
are used to classify the asteroids into a taxonomy consistent with the widely
used Bus-DeMeo taxonomy based on spectroscopy. We report here on the taxonomic
classification of 206 NEAs and 776 MCs determined from SDSS photometry,
representing an increase of 40% and 663% of known taxonomy classifications in
these populations. Using the source region mapper by Greenstreet et al. (2012),
we compare the taxonomic distribution among NEAs and main-belt asteroids of
similar diameters. Both distributions agree at the few percent level for the
inner part of the Main Belt and we confirm this region as a main source of
near-Earth objects. The effect of planetary encounters on asteroid surfaces are
also studied by developing a simple model of forces acting on a surface grain
during planetary encounter, which provides the minimum distance at which a
close approach should occur to trigger resurfacing events. By integrating
numerically the orbit of the 519 S-type and 46 Q-type asteroids back in time
and monitoring their encounter distance with planets, we seek to understand the
conditions for resurfacing events. The population of Q-type is found to present
statistically more encounters with Venus and the Earth than S-types, although
both types present the same amount of encounters with Mars.Comment: Accepted for publication in Icarus. 45 pages, 11 figures, 4 tables, 2
tables in appendix (supplementary material
How to Make E Learning Courses in Curricula of Natural Resources Management More Sustainable?
The Internet may be the means of realizing a forestry lecturer’s dream. Imagine being able to discuss, for example, different timber harvesting systems used internationally with a group of motivated students from different regions of the globe in one virtual classroom. (Längin, Ackerman & Lewark, 2004). The huge potential of e‐learning has not yet been fully recognized let alone realized in higher education. Over the last ten to fifteen years many e‐learning courses in the fields of natural resources management, forestry and wood sciences emerged, have been used – and often disappeared again. Much effort and money has gone into development of e‐learning courses, but sustainable examples are few in these fields – the exceptions mostly being parts of bigger e‐learning units in some universities. Reasons for short‐lived success seem to be in the first place that these courses have often been add‐ons, elective courses or self‐standing courses with little institutional and curricular anchoring. They often started with great ideas and relevant contents, but with limited long term commitment on the side of the organizers as well as of the students. As time and money needed for e‐learning courses may be a limiting factor for successful development and running them sustainably options of courses must be examined for which input is lower or at least not higher than for traditional face‐to‐face courses. This could include using share‐ ware e‐learning platforms as well as technological minimalism (Fillip, in GTZ 2005). At the same time learner oriented and activating didactical concepts should be developed, which would make the courses attractive and work against early drop‐out. Experiences and considerations will be presented. In order to make better use of the potential of e‐learning for improvement of higher education, following these ideas, the concept of WELAN has been developed by higher education specialists from IUFRO, IPFE and faculties of forestry and environmental sciences of six universities as a worldwide e‐learning academy. WELAN will explore approaches of open learning resources, i.e. courses available without tuition fees. Activities of WELAN will start with the development of recommendations for administrative regulations including course formats, course delivery, credit recognition, accreditation, tuition fees in order to allow students from different universities as well as companies to have access to e‐ learning course information and to the courses of the collaborating universities and get their credits gained easily recognized independent their affiliation. Following this the development and offering of courses and course package under the umbrella of WELAN is aimed at, for organization and funding to be divided in separate projects with defined course packages. Thus in a growing and comprehensive system essential parts of Natural Resources, Forestry and Wood Science will be covered
Southern Corn Rootworm (Coleoptera: Chrysomelidae) Adult Emergence and Population Growth Assessment After Selection With Vacuolar ATPase-A double-stranded RNA Over Multiple Generations
The southern corn rootworm, Diabrotica undecimpunctata howardi Barber (Coleoptera: Chrysomelidae), was exposed over multiple generations to vacuolar (v)ATPase-A double-stranded (ds)RNA, first as adults and later, as neonate larvae. During adult selection, high mortality and lower fecundity were observed in the RNAi-selected cages after beetles were exposed to sublethal dsRNA concentrations that varied between LC40 and LC75. During larval selection, a delay in adult emergence and effects on population growth parameters were observed after neonates were exposed to sublethal dsRNA concentrations that varied between LC50 and LC70. Some of the parameters measured for adult emergence such as time to reach maximum linear adult emergence, time elapsed before attaining linear emergence, termination point of the linear emergence, and total days of linear emergence increase, were significantly different between RNAi-selected and control colonies for at least one generation. Significant differences were also observed in population growth parameters such as growth rate, net reproductive rate, doubling time, and generation time. After seven generations of selection, there was no indication that resistance evolved. The sublethal effects caused by exposures of southern corn rootworm to dsRNAs can affect important life history traits and fitness especially through delays in adult emergence and reduction in population growth. Although changes in susceptibility did not occur, the observation of sublethal effects suggests important responses to potential selection pressure. Assuming resistance involves a recessive trait, random mating between susceptible and resistant individuals is an important factor that allows sustainable use of transgenic plants, and delays in adult emergence observed in our studies could potentially compromise this assumption
Do Undergraduate Majors or Ph.D. Students Affect Faculty Size?
Regression analysis using panel data for 42 colleges and universities over 14 years suggests that the economics faculty size of universities offering a Ph.D. in economics is determined primarily by the long-run average number of Ph.D. degrees awarded annually; the number of full-time faculty increases at almost a one-for-one pace as the average number of Ph.D.s grows. Faculty size at Ph.D. granting universities is largely unresponsive to changes in the contemporaneous number of undergraduate economics degrees awarded at those institutions. Similarly, faculty size at colleges where a bachelor’s is the highest degree awarded is responsive to the long and short term average number of economics degrees awarded but not the annual changes in BS and BA degrees awarded in economics.faculty size, student body, Ph.D. degrees, bachelor degrees
Does Teaching Load Affect Faculty Size?
Random effects estimates using panel data for 42 colleges and universities over 16 years reveal that the economics faculty size of universities offering a Ph.D. in economics is determined primarily by the long-run average number of Ph.D. degrees awarded annually; the number of full-time faculty increases at almost a one-for-one pace as the average number of Ph.D.s grows. Faculty size at Ph.D. granting universities is largely unresponsive to changes in the number of undergraduate economics degrees awarded at those institutions. In contrast, faculty size at colleges where a bachelor's is the highest degree awarded is responsive to the average number of economics degrees awarded annually, growing by about one for each additional eleven graduating economics majors.student body, faculty size, Ph.D. degrees, bachelor degrees
Efficient integration of the variational equations of multi-dimensional Hamiltonian systems: Application to the Fermi-Pasta-Ulam lattice
We study the problem of efficient integration of variational equations in
multi-dimensional Hamiltonian systems. For this purpose, we consider a
Runge-Kutta-type integrator, a Taylor series expansion method and the so-called
`Tangent Map' (TM) technique based on symplectic integration schemes, and apply
them to the Fermi-Pasta-Ulam (FPU-) lattice of nonlinearly
coupled oscillators, with ranging from 4 to 20. The fast and accurate
reproduction of well-known behaviors of the Generalized Alignment Index (GALI)
chaos detection technique is used as an indicator for the efficiency of the
tested integration schemes. Implementing the TM technique--which shows the best
performance among the tested algorithms--and exploiting the advantages of the
GALI method, we successfully trace the location of low-dimensional tori.Comment: 14 pages, 6 figure
Effects of salinity, pH and growth phase on the protein productivity by Dunaliella salina
BACKGROUND
Microalgae have long been adopted for use as human food, animal feed and high‐value products. For carotenogenesis, Dunaliella salina is one of the most studied microalgae, yet its protein synthesis has been limitedly reported. In this study, D. salina was cultivated at different NaCl and pH levels to optimize its protein productivity.
RESULTS
The biomass protein content followed an increase–decrease pattern throughout the growth phases, with a maximum in the exponential phase (60–80% over ash‐free dry weight). Adversely, the biomass pigment contents were at relatively stable levels (around 0.5% carotenoids, 1.3% chlorophyll a and 0.5% chlorophyll b over ash‐free dry weight). Among the tested conditions (1–3 mol L−1 salinity, pH 7.5–9.5), the highest protein productivity (43.5 mg L−1 day−1) was achieved at 2 mol L−1 salinity and pH 7.5 during the exponential phase, which surpassed others by 16–97%. Additionally, table salts were tested to be equivalent and cost‐efficient salt sources for the growth medium.
CONCLUSION
This study highlighted the suitability of D. salina as a protein source, providing guidelines for 70% cheaper medium formulation in the lab and for maximum protein productivity at larger scale
Blow Flies (Calliphoridae) in Alaska
Several blow fly collections were made in the vicinity of Fairbanks between May 28 and June 14, 1948, and one large collection at Anchorage on August 9, 1948. All flies were caught in screen-wire fly traps baited with liver or dead salmon. The material was identified by D. G. Hall, Bureau of Entomology and Plant Quarantine, who also generously provided information concerning the possible importance of the various species of Alaskan blow flie
Hidden quantum phase transition in MnFeGe: evidence brought by small-angle neutron scattering
The magnetic system of the MnFeGe solid solution is ordered in
a spiral spin structure in the whole concentration range of .
The close inspection of the small-angle neutron scattering data reveals the
quantum phase transition from the long-range ordered (LRO) to short range
ordered (SRO) helical structure upon increase of Fe-concentration at . The SRO of the helical structure is identified as a
Lorentzian contribution, while LRO is associated with the Gaussian contribution
into the scattering profile function. The scenario of the quantum phase
transition with as a driving parameter is similar to the thermal phase
transition in pure MnGe. The quantum nature of the SRO is proved by the
temperature independent correlation length of the helical structure at low and
intermediate temperature ranges with remarkable decrease above certain
temperature . We suggest the -dependent modification of the effective
Ruderman-Kittel-Kasuya-Yosida exchange interaction within the Heisenberg model
of magnetism to explain the quantum critical regime in MnFeGe.Comment: 6 pages, 4 figure
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