9,944 research outputs found
Investigation of compounds essential for the origin of life
Nucleic acid sequencing as a technique to determine the chemical and biological evolution of certain prokaryotic metabolic pathways is discussed. Protein in data and a microbiological organization of the prokaryotes is included
The contribution of planetary period oscillations towards circulation and mass loss in Saturn’s magnetosphere
Magnetic reconnection is a process during which magnetic energy is released as kinetic energy. It is considered a crucial driver of energy transport and mass loss within Saturn's magnetosphere. On long-term timescales, is thought to be predominantly driven by the rapid rotation of equatorially mass-loaded flux tubes (i.e., the Vasyliunas cycle), but there is some non-negligible driving from the solar wind as well (i.e., the Dungey cycle). In this study, we investigate an atmospheric driven phenomenon that modulates Saturn's magnetosphere every ∼10.6–10.8 hr, known as planetary period oscillations (PPOs), as an additional driver of magnetic reconnection at Saturn. Using an empirical model of PPO dynamics and Cassini magnetic field and plasma measurements, we find that PPO-driven magnetic reconnection is likely to occur in Saturn's magnetosphere, however, the occurrence of the phenomenon depends on temporally variable characteristics of the PPO systems and spatial asymmetries within Saturn's equatorial magnetosphere. Thus, it is not expected to be an on-going process. On year-long timescales, we find that PPOs are expected to be on par with the Dungey Cycle in driving circulation within Saturn's magnetosphere. However, on ∼1–2 weeks-long timescales, under specific conditions where PPO-driven reconnection is expected to be active, this phenomenon can become more significant than the Vasyliunas cycle, and thus dominate circulation within Saturn's magnetosphere. On year-long timescales, this process is estimated to remove upwards of ∼20% of the mass loaded into the magnetosphere by Enceladus
The onset of synchronization in large networks of coupled oscillators
We study the transition from incoherence to coherence in large networks of
coupled phase oscillators. We present various approximations that describe the
behavior of an appropriately defined order parameter past the transition, and
generalize recent results for the critical coupling strength. We find that,
under appropriate conditions, the coupling strength at which the transition
occurs is determined by the largest eigenvalue of the adjacency matrix. We show
how, with an additional assumption, a mean field approximation recently
proposed is recovered from our results. We test our theory with numerical
simulations, and find that it describes the transition when our assumptions are
satisfied. We find that our theory describes the transition well in situations
in which the mean field approximation fails. We study the finite size effects
caused by nodes with small degree and find that they cause the critical
coupling strength to increase.Comment: To appear in PRE; Added an Appendix, a reference, modified two
figures and improved the discussion of the range of validity of perturbative
approache
First time determination of the microscopic structure of a stripe phase: Low temperature NMR in La2NiO4.17
The experimental observations of stripes in superconducting cuprates and
insulating nickelates clearly show the modulation in charge and spin density.
However, these have proven to be rather insensitive to the harmonic structure
and (site or bond) ordering. Using 139La NMR in La2NiO4.17, we show that in the
1/3 hole doped nickelate below the freezing temperature the stripes are
strongly solitonic and site ordered with Ni3+ ions carrying S=1/2 in the domain
walls and Ni2+ ions with S=1 in the domains.Comment: 4 pages including 4 figure
On the structure of the energy distribution function in the hopping regime
The impact of the dispersion of the transport coefficients on the structure
of the energy distribution function for charge carriers far from equilibrium
has been investigated in effective-medium approximation for model densities of
states. The investigations show that two regimes can be observed in energy
relaxation processes. Below a characteristic temperature the structure of the
energy distribution function is determined by the dispersion of the transport
coefficients. Thermal energy diffusion is irrelevant in this regime. Above the
characteristic temperature the structure of the energy distribution function is
determined by energy diffusion. The characteristic temperature depends on the
degree of disorder and increases with increasing disorder. Explicit expressions
for the energy distribution function in both regimes are derived for a constant
and an exponential density of states.Comment: 16 page
The LMT Galaxies' 3 mm Spectroscopic Survey: First Results
The molecular phase of the interstellar medium (ISM) in galaxies offers
fundamental insight for understanding star-formation processes and how stellar
feedback affects the nuclear activity of certain galaxies. We present here
Large Millimeter Telescope spectra obtained with the Redshift Search Receiver,
a spectrograph that cover simultaneously the 3 mm band from 74 to 111 GHz with
a spectral resolution of around 100 km/s. The observed galaxies that have been
detected previously in HCN, have different degrees of nuclear activity, one
normal galaxy (NGC 6946), the starburst prototype (M 82) and two ultraluminous
infrared galaxies (ULIRGs, IRAS 17208-0014 and Mrk 231). We plotted our data in
the HCO+/HCN vs. HCN/13CO diagnostic diagram finding that NGC 6946 and M 82 are
located close to other normal galaxies; and that both IRAS 17208-0014 and Mrk
231 are close to the position of the well known ULIRG Arp 220 reported by Snell
et al. (2011). We found that in Mrk 231 -- a galaxy with a well known active
galactic nucleus -- the HCO+/HCN ratio is similar to the ratio observed in
other normal galaxies.Comment: Proceedings to appear in "Massive Young Star Clusters Near and Far:
From the Milky Way to Reionization", 2013 Guillermo Haro Conference. Eds. Y.
D. Mayya, D. Rosa-Gonzalez, & E. Terlevich, INAOE and AMC. 5 pages, 1 figur
Covalent organic frameworks
The first members of covalent organic frameworks (COF) have been designed and successfully synthesized by
condensation reactions of phenyl diboronic acid C6H4[B(OH)2]2 and hexahydroxytriphenylene C18H6(OH)6. The
high crystallinity of the products (C3H2BO)6 (C9H12)1 (COF-1) and C9H4BO2 (COF-5) has allowed definitive
resolution of their structure by powder X-ray diffraction methods which reveal expanded porous graphitic layers that
are either staggered (COF-1, P63/mmc) or eclipsed (COF-5, P6/mmm). They exhibit high thermal stability (to
temperatures up to 500- to 600-C), permanent porosity, and high surface areas (711 and 1590 m2/g, respectively)
surpassing those of related inorganic frameworks. A similar approach has been used for the design of other extended
structures
17O NMR study of q=0 spin excitations in a nearly ideal S=1/2 1D Heisenberg antiferromagnet, Sr2CuO3, up to 800 K
We used 17O NMR to probe the uniform (wavevector q=0) electron spin
excitations up to 800 K in Sr2CuO3 and separate the q=0 from the q=\pm\pi/a
staggered components. Our results support the logarithmic decrease of the
uniform spin susceptibility below T ~ 0.015J, where J=2200 K. From measurement
of the dynamical spin susceptibility for q=0 by the spin-lattice relaxation
rate 1/T_{1}, we demonstrate that the q=0 mode of spin transport is ballistic
at the T=0 limit, but has a diffusion-like contribution at finite temperatures
even for T << J.Comment: Submitted to Phys. Rev. Lett. 4 pages, 4 figure
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