15,426 research outputs found
The Martian crustal dichotomy: Product of accretion and not a specific event?
Attempts to explain the fundamental crustal dichotomy on Mars range from purely endogenic to extreme exogenic processes, but to date no satisfactory theory has evolved. What is accepted is: (1) the dichotomy is an ancient feature of the Martian crust, and (2) the boundary between the cratered highlands and northern plains which marks the dichotomy in parts of Mars has undergone significant and variable modification during the observable parts of Martian history. Some ascribe it to a single mega-impact event, essentially an instantaneous rearrangement of the crustal structures (topography and lithospheric thickness). Others prefer an internal mechanism: a period of vigorous convection subcrustally erodes the northern one third of Mars, causing foundering and isostatic lowering of that part of Mars. The evidence for each theory is reviewed, with the conclusion that there is little to recommend either. An alternative is suggested: the formation of the crustal dichotomy on Mars was not a specific tectonic event but a byproduct of the accretionary process and therefore a primordial characteristic of the Martian crust, predating the oldest recognizable landforms
Photo-heterolysis and -homolysis of substituted diphenylmethyl halides, acetates, and phenyl ethers in acetonitrile: characterization of diphenylmethyl cations and radicals generated by 248-nm laser flash photolysis
Sticky physics of joy: On the dissolution of spherical candies
Assuming a constant mass-decrease per unit-surface and -time we provide a
very simplistic model for the dissolution process of spherical candies. The aim
is to investigate the quantitative behavior of the dissolution process
throughout the act of eating the candy. In our model we do not take any
microscopic mechanism of the dissolution process into account, but rather
provide an estimate which is based on easy-to-follow calculations. Having
obtained a description based on this calculation, we confirm the assumed
behavior by providing experimental data of the dissolution process. Besides a
deviation from our prediction caused by the production process of the candies
below a diameter of 2 mm, we find good agreement with our model-based
expectations. Serious questions on the optimal strategy of enjoying a candy
will be addressed, like whether it is wise to split the candy by breaking it
with the teeth or not
Fluctuation Induced Instabilities in Front Propagation up a Co-Moving Reaction Gradient in Two Dimensions
We study 2D fronts propagating up a co-moving reaction rate gradient in
finite number reaction-diffusion systems. We show that in a 2D rectangular
channel, planar solutions to the deterministic mean-field equation are stable
with respect to deviations from planarity. We argue that planar fronts in the
corresponding stochastic system, on the other hand, are unstable if the channel
width exceeds a critical value. Furthermore, the velocity of the stochastic
fronts is shown to depend on the channel width in a simple and interesting way,
in contrast to fronts in the deterministic MFE. Thus, fluctuations alter the
behavior of these fronts in an essential way. These affects are shown to be
partially captured by introducing a density cutoff in the reaction rate. Some
of the predictions of the cutoff mean-field approach are shown to be in
quantitative accord with the stochastic results
Carbanions. 3. Nuclear magnetic resonance spectroscopic and theoretical study of homoaromaticity in cyclohexadienyl anions
Next generation keyboards: The importance of cognitive compatibility
The computer keyboard of today is essentially the same as it has been for many years. Few advances have been made in keyboard design even though computer systems in general have made remarkable progress in improvements. This paper discusses the future of keyboards, their competition and compatibility with voice input systems, and possible special-application intelligent keyboards for controlling complex systems
Gallium Arsenide solar cell radiation damage experiment
Gallium arsenide (GaAs) solar cells for space applications from three different manufactures were irradiated with 10 MeV protons or 1 MeV electrons. The electrical performance of the cells was measured at several fluence levels and compared. Silicon cells were included for reference and comparison. All the GaAs cell types performed similarly throughout the testing and showed a 36 to 56 percent power areal density advantage over the silicon cells. Thinner (8-mil versus 12-mil) GaAs cells provide a significant weight reduction. The use of germanium (Ge) substrates to improve mechanical integrity can be implemented with little impact on end of life performance in a radiation environment
Technology needs of advanced Earth observation spacecraft
Remote sensing missions were synthesized which could contribute significantly to the understanding of global environmental parameters. Instruments capable of sensing important land and sea parameters are combined with a large antenna designed to passively quantify surface emitted radiation at several wavelengths. A conceptual design for this large deployable antenna was developed. All subsystems required to make the antenna an autonomous spacecraft were conceptually designed. The entire package, including necessary orbit transfer propulsion, is folded to package within the Space Transportation System (STS) cargo bay. After separation, the antenna, its integral feed mast, radiometer receivers, power system, and other instruments are automatically deployed and transferred to the operational orbit. The design resulted in an antenna with a major antenna dimension of 120 meters, weighing 7650 kilograms, and operating at an altitude of 700 kilometers
Hindrance of ^{16}O+^{208}Pb fusion at extreme sub-barrier energies
We analyze the fusion data for O+Pb using coupled-channels
calculations. We include couplings to the low-lying surface excitations of the
projectile and target and study the effect of the (O,O)
one-neutron pickup. The hindrance of the fusion data that is observed at
energies far below the Coulomb barrier cannot be explained by a conventional
ion-ion potential and defining the fusion in terms of ingoing-wave boundary
conditions (IWBC). We show that the hindrance can be explained fairly well by
applying the M3Y double-folding potential which has been corrected with a
calibrated, repulsive term that simulates the effect of nuclear
incompressibility.
We show that the coupling to one-neutron transfer channels plays a crucial
role in improving the fit to the data. The best fit is achieved by increasing
the transfer strength by 25% relative to the strength that is required to
reproduce the one-neutron transfer data. The larger strength is not unrealistic
because the calculated inelastic plus transfer cross section is in good
agreement with the measured quasielastic cross section. We finally discuss the
problem of reproducing the fusion data at energies far above the Coulomb
barrier. Here we do not account for the data when we apply the IWBC but the
discrepancy is essentially eliminated by applying the M3Y+repulsion potential
and a weak, short-ranged imaginary potential.Comment: text and 8 fifure
Association between MAPT polymorphism but not APOE promoter and elite rugby athlete status
INTRODUCTION: Incidence and outcomes of concussions have been hypothesised to be genetically influenced. The APOE Promoter G219T (rs405509) polymorphism has been associated with differential promoter activity and unfavourable outcomes after traumatic brain injury. The TT genotype is associated with a 3-fold greater risk of multiple concussions. The TT genotype of MAPT (rs10445337) has also been associated with poorer outcomes after concussion. Rugby has one of the highest incidences of concussion in sport, so it was hypothesised that APOE Promoter TT and MAPT TT genotypes would be less prevalent in elite rugby athletes because those genotypes, previously associated with increased risk, would be less compatible with achieving elite athlete status. METHODS: Participants were from the RugbyGene project, comprising elite Caucasian male rugby athletes (n = 528; mean (standard deviation) height 1.85 (0.07) m, mass 101 (14) kg, age 29 (7) yr), including 420 rugby union (RU) athletes that for some analyses were divided into forwards and backs and 108 rugby league (RL) athletes. Non-athletes were 592 Caucasian men and women (57% male, height 1.72 (0.10) m, mass 74 (14) kg, age 31 (7) yr). PCR of genomic DNA was used to determine genotypes using TaqMan probes, then groups were compared using χ2 and odds ratio (OR) statistics. RESULTS: All genotype data were in Hardy-Weinberg equilibrium. For MAPT (rs10445337), the risk genotype (TT) was underrepresented in rugby athletes (60%) compared to non-athletes (66%), CT more common in rugby athletes (34%) than non-athletes (29%) and little difference in CC genotype frequencies (χ2 = 7.092, P = 0.029; TT genotype frequency OR = 0.80, 95% confidence intervals (CI) = 0.62-1.02). There were no differences in MAPT (rs10445337) genotype frequencies between RU forwards and backs. For APOE Promoter G219T (rs405509), there were no differences in genotype frequencies between all athletes (RU and RL) and non-athletes (27% TT genotype in players and non-athletes), nor between RU forwards and backs. CONCLUSION: The MAPT (rs10445337) TT genotype is 6% less common in elite rugby athletes than non-athletes. Therefore, carrying at least one rs10445337 C allele appears to increase the probability of sustained career success in the high-risk concussion environment of elite rugby, perhaps via a greater ability to recover from concussions.Peer reviewe
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