3,621 research outputs found
Biosynthesis of sideramines in fungi. Rhodotorulic acid synthetase from extracts of Rhodotorula glutinis
Structure and diffusion in amorphous aluminium silicate: A molecular dynamics computer simulation
The amorphous aluminium silicate (Al2O3)2(SiO2) [AS2] is investigated by
means of large scale molecular dynamics computer simulations. We consider fully
equilibrated melts in the temperature range 6100K >= T >= 2300K as well as
glass configurations that were obtained from cooling runs from T=2300K to 300K
with a cooling rate of about 10^12K/s. Already at temperatures as high as
4000K, most of the Al and Si atoms are four-fold coordinated by oxygen atoms.
Thus, the structure of AS2 is that of a disordered tetrahedral network. The
packing of AlO4 tetrahedra is very different from that of SiO4 tetrahedra in
that Al is involved with a relatively high probability in small-membered rings
and in triclusters in which an O atom is surrounded by four cations. We find as
typical configurations two-membered rings with two Al atoms in which the shared
O atoms form a tricluster. On larger length scales, the system shows a
microphase separation in which the Al-rich network structure percolates through
the SiO2 network. The latter structure gives rise to a prepeak in the static
structure factor at a wavenumber q=0.5\AA^{-1}. The comparison of experimental
X-ray data with the results from the simulation shows a good agreement for the
structure function. The diffusion dynamics in AS2 is found to be much faster
than in SiO2. We show that the self-diffusion constants for O and Al are very
similar and that they are by a factor of 2-3 larger than the one for Si.Comment: 30 pages of Latex, 13 figure
On object selection in gaze controlled environments
In the past twenty years, gaze control has become a reliable alternative input method not only for handicapped users. The selection of objects, however, which is of highest importance and of highest frequency in computer control, requires explicit control not inherent in eye movements. Objects have been therefore usually selected via prolonged fixations (dwell times). Dwell times seemed to be for many years the unique reliable method for selection. In this paper, we review pros and cons of classical selection methods and novel metaphors, which are based on pies and gestures. The focus is on the effectiveness and efficiency of selections. In order to estimate the potential of current suggestions for selection, a basic empirical comparison is recommended
On the structure of the Nx phase of symmetric dimers: inferences from NMR
NMR measurements on a selectively deuterated liquid crystal dimer CB-C9-CB, exhibiting two nematic phases, show that the molecules in the lower temperature nematic phase, NX, experience a chiral environment and are ordered about a uniformly oriented director throughout the macroscopic sample. The results are contrasted with previous interpretations that suggested a twist-bend spatial variation of the director. A structural picture is proposed wherein the molecules are packed into highly correlated chiral assemblies
Seebeck coefficients of half-metallic ferromagnets
In this report the Co2 based Heusler compounds are discussed as potential
materials for spin voltage generation. The compounds were synthesized by
arcmelting and consequent annealing. Band structure calculations were performed
and revealed the compounds to be half-metallic ferromagnets. Magnetometry was
performed on the samples and the Curie temperatures and the magnetic moments
were determined. The Seebeck coefficients were measured from low to ambient
temperatures for all compounds. For selected compounds high temperature
measurements up to 900 K were performed.Comment: accepted contribution o the Special Issue "Spin Caloritronics" of
Solid State Communication
Reheating in a Brane Monodromy Inflation Model
We study reheating in a recently proposed brane "monodromy inflation" model
in which the inflaton is the position of a D4 brane on a "twisted torus".
Specifically, we study the repeated collisions between the D4 brane and a D6
brane (on which the Standard Model fields are assumed to be localized) at a
fixed position along the monodromy direction as the D4 brane rolls down its
potential. We find that there is no trapping of the rolling D4 brane until it
reaches the bottom of its potential, and that reheating is entirely described
by the last brane encounter. Previous collisions have negligible effect on the
brane velocity and hence on the reheat temperature. In the context of our
setup, reheating is efficient and the reheat temperature is therefore high.Comment: 13 pages, reference adde
Recent advances in the assessment and treatment of falls in Parkinson's disease
Falls are among the most incapacitating features of Parkinson's disease. Prevention of falls requires a systematic assessment of all contributing factors (with emphasis on freezing of gait and frontal executive dysfunction), and a multidisciplinary treatment approach tailored to the specific pathophysiology of falls for each individual patient
Nanostructured Nb-substituted CaMnO3 n-type thermoelectric material prepared in a continuous process by ultrasonic spray combustion
One way to further optimize the thermoelectric properties toward a higher ZT is a temperature stable nanoengineering of materials, where the thermal conductivity is reduced by increasing the phonon scattering at the grain boundaries. To study this, Nb-substituted CaMnO3 perovskite-type material was synthesized by ultrasonic spray combustion (USC). The grain growth has been characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Finally, the thermoelectric properties of compacted and sintered bulk samples from powder prepared by a continuous scalable USC process were measured up to 1050 K. The thermoelectric legs were prepared by an adapted sintering process. Here, a compromise between enhanced porosity to reduce the thermal conductivity and securing of mechanical stability and low resistivity should be obtained. Based on the grain growth mechanisms, an advanced sintering process for additional interconnection of the particles without particle growth is needed to further increase the thermoelectric performanc
Unraveling the bidirectional associations between parental knowledge and children’s externalizing behavior
Although within- and between-family bidirectional associations between parental knowledge and children’s externalizing behavior have been theoretically proposed, studies that unravel these associations simultaneously remain scarce. This study examined these bidirectional associations within and between German families. 3611 families participated across one-year intervals between children ages 8 to 15 (50.6% boys, 34.5% fathers, 89.0% German-born, Mwaves = 3.63, SDwaves = 2.00). Random intercept cross-lagged panel models (RI-CLPM) with linear slopes revealed negative between-family associations between parental knowledge and children’s externalizing behavior, and a negative association between the random linear slopes. Generally, no within-family cross-lagged effects were found, but there were some correlated slopes across families. When teasing apart paternal and maternal knowledge, father-driven but not mother-driven lagged effects of increased knowledge predicting decreased externalizing behavior were found. The findings illustrate the importance of fathers’ knowledge and new directions for within-family studies of parent-child interactions
The potential of increasing man-made air pollution to reduce rainfall over southern West Africa
Southern West Africa has one of the fastest-growing populations worldwide. This has led to a higher water demand and lower air quality. Over the last 3 decades, most of the region has experienced decreasing rainfall during the little dry season (LDS; mid-July to end of August) and more recently also during the second rainy season (SRS; September-October), while trends during the first rainy season (FRS; mid-May to mid-July) are insignificant. Here we analyse spatio-temporal variations in precipitation, aerosol, radiation, cloud, and visibility observations from surface stations and from space to find indications for a potential contribution of anthropogenic air pollution to these rainfall trends. The proposed mechanism is that the dimming of incoming solar radiation by aerosol extinction contributes to reducing vertical instability and thus convective precipitation. To separate a potential aerosol influence from large-scale climatic drivers, a multilinear-regression model based on sea-surface temperature (SST) indices is used. During both LDS and SRS, weakly statistically significant but accelerating negative rainfall trends unrelated to known climatic factors are found. These are accompanied by a strong increase in pollution over the upstream tropical Atlantic caused by fire aerosol from Central Africa, particularly during the LDS. Over southern West Africa, no long-term aerosol records are available, inhibiting a direct quantification of the local manmade effect. However, significant decreases in horizontal visibility and incoming surface solar radiation are strong indicators for an increasing aerosol burden, in line with the hypothesized pollution impact on rainfall. The radiation trend is further enhanced by an increase in low-level cloudiness. The large spatial extent of potentially aerosol-related trends during the LDS is consistent with the stronger monsoon flow and less wet deposition during this season. Negligible aerosol impacts during the FRS are likely due to the high degree of convective organization, which makes rainfall less sensitive to surface radiation. The overall coherent picture and the accelerating trends - some of which are concealed by SST effects - should alarm policymakers in West Africa to prevent a further increase in air pollution as this could endanger water supply and food and energy production for a large and growing population
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