5,538 research outputs found
Earlier green-up and spring warming amplification over Europe
The onset of green-up of plants has advanced in response to climate change. This advance has the potential to affect heat waves via biogeochemical and biophysical processes. Here a climate model was used to investigate only the biophysical feedbacks of earlier green-up on climate as the biogeochemical feedbacks have been well addressed. Earlier green-up by 5 to 30 days amplifies spring warming in Europe, especially heat waves, but makes few differences to heat waves in summer. This spring warming is most noticeable within 30 days of advanced green-up and is associated with a decrease in low- and middle-layer clouds and associated increases of downward short wave and net radiation. We find negligible differences in the Southern Hemisphere and low latitudes of the Northern Hemisphere. Our results provide an estimate of the level of skill necessary in phenology models to avoid introducing biases in climate simulations
The Kaidun Breccia Material Variety: New Clasts and Updated Hypothesis on a Space Trawl Origin
The Kaidun meteorite is a breccia containing a wide variety of different material types [1-5]. It contains lithologies of CI, CM1 and CM2, CR chondrites [6], CAIs of Types A and B [7, 8], enstatite chondrite materials (EH and EL) [3, 4], including altered enstatite clasts [9], ordinary chondrites [10], and possible R chondrite
material [11] as well as glass fragments and altered shock melt veins [4]. It also contains different achondritic clasts (including alkaline rocks) with unusual oxygen isotopic compositions representing unknown differentiated parent bodies [2, 12]. Based on Fe/Mn and Fe/Mg ratios these clasts correspond to the SNC and HED meteorites and confirm their origin from differentiated parent bodies that experienced impact events and aqueous alteration, and not represented by known meteorites. We continue studying Kaidun and report results on investigation of newly discovered objects and discuss processes of their formation, and the origin of the Kaidun microbreccia as a whole.
Results and Discussion: Clast #d7.2-68 was found in Kaidun section #7.2d. It consists of pyroxene and SiO_(2-)phases. Pyroxene is pigeonite (Fs_(63-67), Wo_(10-14), Fe/Mn – 40.1) with augite lamellae (Fs_(44-57), Wo_(20-34), Fe/Mn – 40.4) (up to 10 µm width). Equilibrium temperature of coexisting pyroxenes is close to 900°C at 5 Kbar [13]. The observed smooth shape of the CaO profile across the pyroxene lamellae could correspond to mild metamorphism after exsolution. On a plot of Fe/Mn vs. Fe/Mg, the clast falls at the far Fe-rich end of the HED pyroxenes cluster. The SiO_(2)-phase
is enriched in Al_2O_3 and FeO and possibly is tridymite. The exsolution textures of pyroxenes require annealing for a long period of time and are typical features of achondrites, especially eucrites. This clast could represent a fragment of differentiated material of a body size of which is similar to the HED parent body
Exact Equal Time Statistics of Orszag-McLaughlin Dynamics By The Hopf Characteristic Functional Approach
By employing Hopf's functional method, we find the exact characteristic
functional for a simple nonlinear dynamical system introduced by Orszag.
Steady-state equal-time statistics thus obtained are compared to direct
numerical simulation. The solution is both non-trivial and strongly
non-Gaussian.Comment: 6 pages and 2 figure
Astrophysical Fluid Dynamics via Direct Statistical Simulation
In this paper we introduce the concept of Direct Statistical Simulation (DSS)
for astrophysical flows. This technique may be appropriate for problems in
astrophysical fluids where the instantaneous dynamics of the flows are of
secondary importance to their statistical properties. We give examples of such
problems including mixing and transport in planets, stars and disks. The method
is described for a general set of evolution equations, before we consider the
specific case of a spectral method optimised for problems on a spherical
surface. The method is illustrated for the simplest non-trivial example of
hydrodynamics and MHD on a rotating spherical surface. We then discuss possible
extensions of the method both in terms of computational methods and the range
of astrophysical problems that are of interest.Comment: 26 pages, 11 figures, added clarifying remarks and references, and
corrected typos. This version is accepted for publication in The
Astrophysical Journa
Statistics of an Unstable Barotropic Jet from a Cumulant Expansion
Low-order equal-time statistics of a barotropic flow on a rotating sphere are
investigated. The flow is driven by linear relaxation toward an unstable zonal
jet. For relatively short relaxation times, the flow is dominated by
critical-layer waves. For sufficiently long relaxation times, the flow is
turbulent. Statistics obtained from a second-order cumulant expansion are
compared to those accumulated in direct numerical simulations, revealing the
strengths and limitations of the expansion for different relaxation times.Comment: 23 pages, 8 figures. Version to appear in J. Atmos. Sc
Weak ferromagnetism and internal magnetoelectric effect in LiFePO
The magnetic, thermodynamic, and pyroelectric properties of LiFePO
single crystals are investigated with emphasis on the magnetoelectric
interaction of the electrical polarization with the magnetic order parameter.
The magnetic order below T 27 K is found to be a canted
antiferromagnet with a weak ferromagnetic component along the axis. A sharp
peak of the pyroelectric current at T proves the strong internal
magnetoelectric interaction resulting in a sizable polarization decrease at the
onset of magnetic order. The magnetoelectric effect in external magnetic fields
combines a linear and a quadratic field dependence below T. Thermal
expansion data show a large uniaxial magnetoelastic response and prove the
existence of strong spin lattice coupling. LiFePO is a polar compound
with a strong interaction of the magnetic order parameter with the electric
polarization and the lattice.Comment: 8 pages, 9 figures, to be published in Phys. Rev.
Universal geometrical factor of protein conformations as a consequence of energy minimization
The biological activity and functional specificity of proteins depend on
their native three-dimensional structures determined by inter- and
intra-molecular interactions. In this paper, we investigate the geometrical
factor of protein conformation as a consequence of energy minimization in
protein folding. Folding simulations of 10 polypeptides with chain length
ranging from 183 to 548 residues manifest that the dimensionless ratio
(V/(A)) of the van der Waals volume V to the surface area A and average
atomic radius of the folded structures, calculated with atomic radii
setting used in SMMP [Eisenmenger F., et. al., Comput. Phys. Commun., 138
(2001) 192], approach 0.49 quickly during the course of energy minimization. A
large scale analysis of protein structures show that the ratio for real and
well-designed proteins is universal and equal to 0.491\pm0.005. The fractional
composition of hydrophobic and hydrophilic residues does not affect the ratio
substantially. The ratio also holds for intrinsically disordered proteins,
while it ceases to be universal for polypeptides with bad folding properties.Comment: 6 pages, 1 table, 4 figure
Dynamic scaling in the vicinity of the Luttinger liquid fixed point
We calculate the single-particle spectral function A (k, omega) of a
one-dimensional Luttinger liquid by means of a functional renormalization group
(RG) approach. Given an infrared energy cutoff Lambda = Lambda_0 e^{- l}, our
approach yields the spectral function in the scaling form, A_{\Lambda} (k_F +
p, omega) = tau Z_l tilde{A}_l (p xi, omega tau), where k_F is the Fermi
momentum, Z_l is the wave-function renormalization factor, tau = 1 / \Lambda is
the time scale and xi = v_F / \Lambda is the length scale associated with
Lambda. At the Luttinger liquid fixed point (l rightarrow infty) our RG result
for A (k, omega) exhibits the correct anomalous scaling properties, and for k =
\pm k_F agrees exactly with the well-known bosonization result at weak
coupling. Our calculation demonstrates that the field rescaling is essential
for obtaining the crossover from Fermi liquid behavior to Luttinger liquid
behavior from a truncation of the hierarchy of exact RG flow equations as the
infrared cutoff is reduced.Comment: 15 pages, 5 figure
Sensorless speed control of five-phase PMSM drives with low current distortion
This paper introduces a design for a sensorless control of a five-phase PMSM drive working at low and zero speeds with low current distortion. The rotor position is obtained through tracking the saturation saliency by measuring the dynamic currents responses of the motor due to the IGBTs switching actions. It uses the fundamental PWM waveform obtained using the multi-phase space vector pulse width modulation only. The saliency tracking algorithm used in this paper doesn’t only improve the quality of the estimated position signals but also guarantees a minimum current distortion through reducing the modifications introduced on the PWM waveform. Simulation results are provided to verify the effectiveness of the proposed strategy for saliency tracking and current distortion minimizing of a five-phase PMSM motor drive over a wide speed ranges under different load conditions
- …