Stochastic Paleoclimatology: Modeling the EPICA Ice Core Climate Records

We analyze and model the stochastic behavior of paleoclimate time series and assess the implications for the coupling of climate variables during the Pleistocene glacial cycles. We examine 800 kyr of carbon dioxide, methane, nitrous oxide, and temperature proxy data from the EPICA Dome-C ice core, which are characterized by 100~kyr glacial cycles overlain by fluctuations across a wide range of time scales. We quantify this behavior through multifractal time-weighted detrended fluctuation analysis, which distinguishes near red-noise and white-noise behavior below and above the 100~kyr glacial cycle respectively in all records. This allows us to model each time series as a one-dimensional periodic non-autonomous stochastic dynamical system, and assess the stability of physical processes and the fidelity of model-simulated time series. We extend this approach to a four-variable model with linear coupling terms, which we interpret in terms of the interrelationships between the time series. Methane and nitrous oxide are found to have significant destabilizing influences, while carbon dioxide and temperature have smaller stabilizing influences. We draw conclusions about causal relationships in glacial transitions and the climate processes that may have facilitated these couplings, and highlight opportunities to further develop stochastic modeling approaches.Comment: 14 pages, 6 figure

Heterogeneous Dynamics, Marginal Stability and Soft Modes in Hard Sphere Glasses

In a recent publication we established an analogy between the free energy of a hard sphere system and the energy of an elastic network [1]. This result enables one to study the free energy landscape of hard spheres, in particular to define normal modes. In this Letter we use these tools to analyze the activated transitions between meta-bassins, both in the aging regime deep in the glass phase and near the glass transition. We observe numerically that structural relaxation occurs mostly along a very small number of nearly-unstable extended modes. This number decays for denser packing and is significantly lowered as the system undergoes the glass transition. This observation supports that structural relaxation and marginal modes share common properties. In particular theoretical results [2, 3] show that these modes extend at least on some length scale $l^*\sim (\phi_c-\phi)^{-1/2}$ where $\phi_c$ corresponds to the maximum packing fraction, i.e. the jamming transition. This prediction is consistent with very recent numerical observations of sheared systems near the jamming threshold [4], where a similar exponent is found, and with the commonly observed growth of the rearranging regions with compression near the glass transition.Comment: 6 pages, improved versio

Neural Potential of a Stem Cell Population in the Hair Follicle

The bulge region of the hair follicle serves as a repository for epithelial stem cells that can regenerate the follicle in each hair growth cycle and contribute to epidermis regeneration upon injury. Here we describe a population of multipotential stem cells in the hair follicle bulge region; these cells can be identified by fluorescence in transgenic nestin-GFP mice. The morphological features of these cells suggest that they maintain close associations with each other and with the surrounding niche. Upon explantation, these cells can give rise to neurosphere-like structures in vitro. When these cells are permitted to differentiate, they produce several cell types, including cells with neuronal, astrocytic, oligodendrocytic, smooth muscle, adipocytic, and other phenotypes. Furthermore, upon implantation into the developing nervous system of chick, these cells generate neuronal cells in vivo. We used transcriptional profiling to assess the relationship between these cells and embryonic and postnatal neural stem cells and to compare them with other stem cell populations of the bulge. Our results show that nestin-expressing cells in the bulge region of the hair follicle have stem cell-like properties, are multipotent, and can effectively generate cells of neural lineage in vitro and in vivo

Direct Numerical Simulation Of Turbulent Pressure Fluctuations Over A Cone At Mach 8

Direct numerical simulations (DNS) were conducted to characterize the pressure fluctuations under the turbulent portion of the boundary layer over a sharp 7◦ half-angle cone at a nominal freestream Mach number of 8 and a unit Reynolds number of Reunit = 13.4 x 106/m. The axisymmetric cone geometry and the flow conditions of the DNS matched those measured in the Sandia Hypersonic Wind Tunnel at Mach 8 (Sandia HWT-8). The DNS-predicted wall pressure statistics, including the root-mean-square (r.m.s.) fluctuations and the power spectral density (PSD), were compared with those measured in the Sandia HWT-8. A good comparison between the DNS and the experiment was shown for the r.m.s. and PSD of wall-pressure fluctuations after spatial averaging was applied to the DNS data over an area similar to the sensing area of the transducer. The finite size of the PCB132 transducer, with a finite sensing area of d+ ≈ 50, caused significant spectral attenuation at high frequencies in the experimentally measured PSD, and the loss in sensor resolution resulted in an approximately 27% reduction in r.m.s. pressure fluctuations. The attenuation due to finite sensor sizes has only a small influence on wall-pressure coherence, as indicated by the good comparisons between the DNS without spatial filtering and the experiment for transducers with either streamwise or spanwise separations. The characteristics of turbulent pressure fluctuations at the cone surface were also compared with those over a flat plate and at the wind-tunnel nozzle wall to assess the effect of flow configurations on the scaling relations of turbulent pressure fluctuations. The inner scale was found to successfully collapse wall-pressure PSD of the cone with those over a nozzle wall and on a flat plate at a similar freestream Mach number. For all the three flow configurations, the Corcos model was found to deliver good predictions of wall pressure coherence over intermediate and high frequencies, and the Corcos parameters for the streamwise and spanwise coherence at Mach 8 were found to be similar to those reported in the literature at lower supersonic Mach numbers

Lifetime determination of excited states in Cd-106

Two separate experiments using the Differential Decay Curve Method have been performed to extract mean lifetimes of excited states in 106 Cd. The inedium-spin states of interest were populated by the Mo-98(C-12, 4n) Cd-106 reaction performed at the Wright Nuclear Structure Lab., Yale University. From this experiment, two isomeric state mean lifetimes have been deduced. The low-lying states were populated by the Mo-96(C-13, 3n)Cd-106 reaction performed at the Institut fur Kernphysik, Universitat zu Koln. The mean lifetime of the I-pi = 2(1)(+) state was deduced, tentatively, as 16.4(9) ps. This value differs from the previously accepted literature value from Coulomb excitation of 10.43(9) ps

REDD+ on the rocks? Conflict over forest and politics of justice in Vietnam

In Vietnam, villagers involved in a REDD+ (reduced emissions from deforestation and forest degradation) pilot protect areas with rocks which have barely a tree on them. The apparent paradox indicates how actual practices differ from general ideas about REDD+ due to ongoing conflict over forest, and how contestations over the meaning of justice are a core element in negotiations over REDD+. We explore these politics of justice by examining how the actors involved in the REDD+ pilot negotiate the particular subjects, dimensions, and authority of justice considered relevant, and show how politics of justice are implicit to practical decisions in project implementation. Contestations over the meaning of justice are an important element in the practices and processes constituting REDD+ at global, national and local levels, challenging uniform definitions of forest justice and how forests ought to be managed

Geometric approach to the dynamic glass transition

We numerically study the potential energy landscape of a fragile glassy system and find that the dynamic crossover corresponding to the glass transition is actually the effect of an underlying geometric transition caused by a qualitative change in the topological properties of the landscape. Furthermore, we show that the potential energy barriers connecting local glassy minima increase with decreasing energy of the minima, and we relate this behaviour to the fragility of the system. Finally, we analyze the real space structure of activated processes by studying the distribution of particle displacements for local minima connected by simple saddles

Type 2 diabetes prevention focused on normalization of glycemia: A two-year pilot study

The purpose of this study is to assess the effects of an alternative approach to type 2 diabetes prevention. Ninety-six patients with prediabetes (age 52 (10) years; 80% female; BMI 39.2 (7.1) kg/

Light scattering spectra of supercooled molecular liquids

The light scattering spectra of molecular liquids are derived within a generalized hydrodynamics. The wave vector and scattering angle dependences are given in the most general case and the change of the spectral features from liquid to solidlike is discussed without phenomenological model assumptions for (general) dielectric systems without long-ranged order. Exact microscopic expressions are derived for the frequency-dependent transport kernels, generalized thermodynamic derivatives and the background spectra.Comment: 12 page