1,939 research outputs found
Formation of Lava Samples Collected by Three Alvin Submersible Dives at 14°N on the Mid-Atlantic Ridge
In 2018, a research cruise investigated the Mid-Atlantic Ridge at 14°N. During this expedition the seafloor was mapped using the AUV Sentry and basaltic lavas were collected using the HOV Alvin. To better understand the origin of these lavas, major element compositions of 40 basaltic glasses from three Alvin dives were measured using the BSU SXFive Electron Microprobe and trace element contents were measured on 33 samples using solution ICP-MS. Trace element ratios and patterns are important tools for investigating magmatic processes because they can be used to evaluate different magmatic processes; such as the amount of melting of the Earth\u27s mantle that produces the magma and the extents of crystallization prior to eruption. Lavas collected on dives AL4953 and AL4954 have similar Rare Earth Element patterns, but variable elemental abundances, suggesting fractional crystallization was an important process in their formation. By contrast, lavas collected on dive AL4955 have variable trace element patterns and ratios, indicating a change in the extents of mantle melting. To further investigate the differences in these compositions, we will use numerical models to quantify the percent of mantle melting and extents of crystallization that led to the formation of lavas erupted in this region
Universal Conductance and Conductivity at Critical Points in Integer Quantum Hall Systems
The sample averaged longitudinal two-terminal conductance and the respective
Kubo-conductivity are calculated at quantum critical points in the integer
quantum Hall regime. In the limit of large system size, both transport
quantities are found to be the same within numerical uncertainty in the lowest
Landau band, and , respectively. In
the 2nd lowest Landau band, a critical conductance is
obtained which indeed supports the notion of universality. However, these
numbers are significantly at variance with the hitherto commonly believed value
. We argue that this difference is due to the multifractal structure
of critical wavefunctions, a property that should generically show up in the
conductance at quantum critical points.Comment: 4 pages, 3 figure
Radial excitations of Q-balls, and their D-term
We study the structure of the energy-momentum tensor of radial excitations of
Q-balls in scalar field theories with U(1) symmetry. The obtained numerical
results for the excitations allow us to study in detail
patterns how the solutions behave with N. We show that although the fields and
energy-momentum tensor densities exhibit a remarkable degree of complexity, the
properties of the solutions scale with N with great regularity. This is to best
of our knowledge the first study of the D-term d1 for excited states, and we
demonstrate that it is negative --- in agreement with results from literature
on the d1 of ground state particles.Comment: 11 pages, 12 figure
Pressure-dependent optical investigations of -(BEDT-TTF)I: tuning charge order and narrow gap towards a Dirac semimetal
Infrared optical investigations of -(BEDT-TTF)I have been
performed in the spectral range from 80 to 8000~cm down to temperatures
as low as 10~K by applying hydrostatic pressure. In the metallic state, ~K, we observe a 50\% increase in the Drude contribution as well as the
mid-infrared band due to the growing intermolecular orbital overlap with
pressure up to 11~kbar. In the ordered state, , we extract how
the electronic charge per molecule varies with temperature and pressure:
Transport and optical studies demonstrate that charge order and metal-insulator
transition coincide and consistently yield a linear decrease of the transition
temperature by ~K/kbar. The charge disproportionation
diminishes by /kbar and the optical gap between
the bands decreases with pressure by -47~cm/kbar. In our high-pressure
and low-temperature experiments, we do observe contributions from the massive
charge carriers as well as from massless Dirac electrons to the low-frequency
optical conductivity, however, without being able to disentangle them
unambiguously.Comment: 13 pages, 17 figures, submitted to Phys. Rev.
Are there approximate relations among transverse momentum dependent distribution functions?
Certain exact relations among transverse momentum dependent parton
distribution functions due to QCD equations of motion turn into approximate
ones upon the neglect of pure twist-3 terms. On the basis of available data
from HERMES we test the practical usefulness of one such
``Wandzura-Wilczek-type approximation'', namely of that connecting
h_{1L}^{\perp(1)a}(x) to h_L^a(x), and discuss how it can be further tested by
future CLAS and COMPASS data.Comment: 9 pages, 3 figure
Statistical Mechanics of Canonical-Dissipative Systems and Applications to Swarm Dynamics
We develop the theory of canonical-dissipative systems, based on the
assumption that both the conservative and the dissipative elements of the
dynamics are determined by invariants of motion. In this case, known solutions
for conservative systems can be used for an extension of the dynamics, which
also includes elements such as the take-up/dissipation of energy. This way, a
rather complex dynamics can be mapped to an analytically tractable model, while
still covering important features of non-equilibrium systems. In our paper,
this approach is used to derive a rather general swarm model that considers (a)
the energetic conditions of swarming, i.e. for active motion, (b) interactions
between the particles based on global couplings. We derive analytical
expressions for the non-equilibrium velocity distribution and the mean squared
displacement of the swarm. Further, we investigate the influence of different
global couplings on the overall behavior of the swarm by means of
particle-based computer simulations and compare them with the analytical
estimations.Comment: 14 pages incl. 13 figures. v2: misprints in Eq. (40) corrected, ref.
updated. For related work see also:
http://summa.physik.hu-berlin.de/~frank/active.htm
Conductivity in a symmetry broken phase: Spinless fermions with corrections
The dynamic conductivity of strongly correlated electrons in
a symmetry broken phase is investigated in the present work. The model
considered consists of spinless fermions with repulsive interaction on a simple
cubic lattice. The investigated symmetry broken phase is the charge density
wave (CDW) with wave vector which occurs at
half-filling. The calculations are based on the high dimensional approach, i.e.
an expansion in the inverse dimension is used. The finite dimensionality
is accounted for by the inclusion of linear terms in and the true finite
dimensional DOS. Special care is paid to the setup of a conserving
approximation in the sense of Baym/Kadanoff without inconsistencies. The
resulting Bethe-Salpeter equation is solved for the dynamic conductivity in the
non symmetry broken and in the symmetry broken phase (AB-CDW). The
dc-conductivity is reduced drastically in the CDW. Yet it does not vanish in
the limit due to a subtle cancellation of diverging mobility and
vanishing DOS. In the dynamic conductivity the energy gap
induced by the symmetry breaking is clearly discernible. In addition, the
vertex corrections of order lead to an excitonic resonance lying within
the gap.Comment: 23 pages, 19 figures included with psfig, Revtex; Physical Review
B15, in press (October/November 1996) depending on the printer/screen driver,
it might be necessary to comment out figures 3,4,5,10,11,12,19 and have them
printed separatel
Heterogeneity shapes groups growth in social online communities
Many complex systems are characterized by broad distributions capturing, for
example, the size of firms, the population of cities or the degree distribution
of complex networks. Typically this feature is explained by means of a
preferential growth mechanism. Although heterogeneity is expected to play a
role in the evolution it is usually not considered in the modeling probably due
to a lack of empirical evidence on how it is distributed. We characterize the
intrinsic heterogeneity of groups in an online community and then show that
together with a simple linear growth and an inhomogeneous birth rate it
explains the broad distribution of group members.Comment: 5 pages, 3 figure panel
Ab initio study of alanine polypeptide chains twisting
We have investigated the potential energy surfaces for alanine chains
consisting of three and six amino acids. For these molecules we have calculated
potential energy surfaces as a function of the Ramachandran angles Phi and Psi,
which are widely used for the characterization of the polypeptide chains. These
particular degrees of freedom are essential for the characterization of
proteins folding process. Calculations have been carried out within ab initio
theoretical framework based on the density functional theory and accounting for
all the electrons in the system. We have determined stable conformations and
calculated the energy barriers for transitions between them. Using a
thermodynamic approach, we have estimated the times of characteristic
transitions between these conformations. The results of our calculations have
been compared with those obtained by other theoretical methods and with the
available experimental data extracted from the Protein Data Base. This
comparison demonstrates a reasonable correspondence of the most prominent
minima on the calculated potential energy surfaces to the experimentally
measured angles Phi and Psi for alanine chains appearing in native proteins. We
have also investigated the influence of the secondary structure of polypeptide
chains on the formation of the potential energy landscape. This analysis has
been performed for the sheet and the helix conformations of chains of six amino
acids.Comment: 24 pages, 10 figure
Property (RD) for Hecke pairs
As the first step towards developing noncommutative geometry over Hecke
C*-algebras, we study property (RD) (Rapid Decay) for Hecke pairs. When the
subgroup H in a Hecke pair (G,H) is finite, we show that the Hecke pair (G,H)
has (RD) if and only if G has (RD). This provides us with a family of examples
of Hecke pairs with property (RD). We also adapt Paul Jolissant's works in 1989
to the setting of Hecke C*-algebras and show that when a Hecke pair (G,H) has
property (RD), the algebra of rapidly decreasing functions on the set of double
cosets is closed under holomorphic functional calculus of the associated
(reduced) Hecke C*-algebra. Hence they have the same K_0-groups.Comment: A short note added explaining other methods to prove that the
subalgebra of rapidly decreasing functions is smooth. This is the final
version as published. The published version is available at: springer.co
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