What is the climate system able to do ‘on its own’?

The climate of the Earth, like planetary climates in general, is broadly controlled by solar irradiation, planetary albedo and emissivity as well as its rotation rate and distribution of land (with its orography) and oceans. However, the majority of climate fluctuations that affect mankind are internal modes of the general circulation of the atmosphere and the oceans. Some of these modes, such as El Nino-Southern Oscillation (ENSO), are quasi-regular and have some longer-term predictive skill; others like the Arctic and Antarctic Oscillation are chaotic and generally unpredictable beyond a few weeks. Studies using general circulation models indicate that internal processes dominate the regional climate and that some like ENSO events have even distinct global signatures. This is one of the reasons why it is so difficult to separate internal climate processes from external ones caused, for example, by changes in greenhouse gases and solar irradiation. However, the accumulation of the warmest seasons during the latest two decades is lending strong support to the forcing of the greenhouse gases. As models are getting more comprehensive, they show a gradually broader range of internal processes including those on longer time scales, challenging the interpretation of the causes of past and present climate events further

Enhanced Detection of Emotional Facial Expressions in Borderline Personality Disorder

Background: Borderline personality disorder (BPD) is commonly proposed to be characterized by an enhanced sensitivity for emotional stimuli. In the present study, we investigated whether BPD patients show a superior detection of emotional facial expressions relative to healthy controls. The detection of emotional information in the environment represents an important facet of emotional sensitivity. Sampling and Methods: Twenty patients with BPD were compared with 25 healthy controls. The participants were presented a rapid, continuous stream of neutral and randomly inserted emotional facial expressions and were asked to report the presentation of an emotional facial stimulus after each trial. Availability of cognitive resources was manipulated via two different task demands. Results: The participants with BPD performed significantly better in the detection of positive and negative facial expressions compared to the healthy controls. False alarm rates did not differ significantly between the two groups. Conclusions: The BPD participants showed an enhanced detection of emotional expressions that might be related to the emotional disturbances they experience. In particular, we will discuss the role of this superior emotion detection (in combination with previously reported deficits in the labeling of emotional states) for the understanding of emotional instability in BPD

NaV_2O_5 as an Anisotropic t-J Ladder at Quarter Filling

Based on recent experimental evidences that the electronic charge degrees of freedom plays an essential role in the spin-Peierls--like phase transition of NaV$_2$O$_5$, we first make the mapping of low-energy electronic states of the $d$$-$$p$ model for NaV$_2$O$_5$ to the quarter-filled $t$$-$$J$ ladder with anisotropic parameter values between legs and rungs, and then show that this anisotropic $t$$-$$J$ ladder is in the Mott insulating state, of which lowest-energy states can be modeled by the one-dimensional Heisenberg antiferromagnet with the effective exchange interaction $J_{eff}$ whose value is consistent with experimental estimates. We furthermore examine the coupling between the ladders as the trellis lattice model and show that the nearest-neighbor Coulomb repulsion on the zigzag-chain bonds can lead to the instability in the charge degrees of freedom of the ladders.Comment: 4 pages, 5 gif figures. Fig.3 corrected. Hardcopies of figures (or the entire manuscript) can be obtained by e-mail request to [email protected]

A Model Study of the Low-Energy Charge Dynamics of NaV_2O_5

An exact-diagonalization technique on small clusters is used to calculate the dynamical density correlation functions of the dimerized t-J chain and coupled anisotropic t-J ladders (trellis lattice) at quarter filling, i.e., the systems regarded as a network of pairs (dimers or rungs) of sites coupled weakly via the hopping and exchange interactions. We thereby demonstrate that the intersite Coulomb repulsions between the pairs induce a low-energy collective mode in the charge excitations of the systems where the internal charge degrees of freedom of the pairs play an essential role. Implications to the electronic states of NaV_2O_5, i.e., fluctuations of the valence state of V ions and phase transition as a charge ordering, are discussed.Comment: 4 pages, 4 gif figures. Hardcopies of figures (or the entire manuscript) can be obtained by e-mail request to [email protected]

The effect of clouds in a galactic wind on the evolution of gas-rich dwarf galaxies

(Abridged) We study the effects of interstellar clouds on the dynamical and chemical evolution of gas-rich dwarf galaxies. In particular, we focus on two model galaxies similar to IZw18 and NGC1569 in comparison to models in which a smooth initial distribution of gas is assumed. We use a 2-D hydrodynamical code coupled with a series of routines able to trace the chemical products of SNeII, SNeIa and intermediate-mass stars. Clouds are simulated by adding overdense regions in the computational grid, whose locations are chosen randomly and whose density profiles match observed ones. The clouds are inherently dynamically coupled to the diffuse gas, and they experience heat conduction from a hot surrounding gas. Due to dynamical processes and thermal evaporation, the clouds survive only a few tens of Myr. Due to the additional cooling agent, the internal energy of cloudy models is typically reduced by 20 - 40% compared with models of diffuse gas alone. The clouds delay the development of large-scale outflows by mass loading, therefore helping to retain a larger amount of gas inside the galaxy. However, their bullet effect can pierce the expanding supershell and create holes through which the superbubble can vent freshly produced metals. Moreover, assuming a pristine chemical composition for the clouds, their interaction with the superbubble dilutes the gas, reducing the metallicity. The resulting final metallicity is therefore generally lower (by ~ 0.2 - 0.4 dex) than the one attained by diffuse models.Comment: 13 pages, 11 figures, A&A accepte

Zigzag Charge Ordering in alpha'-NaV2O5

23Na NMR spectrum measurements in alpha'-NaV2O5 with a single- crystalline sample are reported. In the charge-ordered phase, the number of inequivalent Na sites observed is more than that expected from the low-temperature structures of space group Fmm2 reported so far. This disagreement indicates that the real structure including both atomic displacement and charge disproportionation is of lower symmetry. It is suggested that zigzag ordering is the most probable. The temperature variation of the NMR spectra near the transition temperature is incompatible with that of second-order transitions. It is thus concluded that the charge ordering transition is first-order.Comment: 4 pages, 5 eps figures, submitted to J. Phys. Soc. Jp

Using electronic structure changes to map the H-T phase diagram of alpha'-NaV2O5

We report polarized optical reflectance studies of \alpha'-NaV2O5 as a function of temperature (4-45 K) and magnetic field (0-60 T). Rung directed electronic structure changes, as measured by near-infrared reflectance ratios \Delta R(H)=R(H)/R(H=0 T), are especially sensitive to the phase boundaries. We employ these changes to map out an H-T phase diagram. Topological highlights include the observation of two phase boundaries slightly below T_{SG}, enhanced curvature of the 34 K phase boundary above 35 T, and, surprisingly, strong hysteresis effects of both transitions with applied field.Comment: 4 pages, 3 figures, PRB accepte

Low-Temperature Structure of the Quarter-Filled Ladder Compound alpha'-NaV2O5

The low-temperature (LT) superstructure of $\alpha'$-NaV$_2$O$_5$ was determined by synchrotron radiation x-ray diffraction. Below the phase transition temperature associated with atomic displacement and charge ordering at 34K, we observed the Bragg peak splittings, which evidence that the LT structure is monoclinic. It was determined that the LT structure is $(a-b)\times 2b \times 4c$ with the space group $A112$ where $a, b$ and $c$ represent the high temperature orthorhombic unit cell. The valence estimation of V ions according to the bond valence sum method shows that the V sites are clearly separated into two groups of V$^{4+}$ and V$^{5+}$ with a $zigzag$ charge ordering pattern. This LT structure is consistent with resonant x-ray and NMR measurements, and strikingly contrasts to the LT structure previously reported, which includes V$^{4.5+}$ sites.Comment: 4 pages, 3 figures, 1 tabl