1,764 research outputs found
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
Mean-atom-trajectory model for the velocity autocorrelation function of monatomic liquids
We present a model for the motion of an average atom in a liquid or
supercooled liquid state and apply it to calculations of the velocity
autocorrelation function and diffusion coefficient . The model
trajectory consists of oscillations at a distribution of frequencies
characteristic of the normal modes of a single potential valley, interspersed
with position- and velocity-conserving transits to similar adjacent valleys.
The resulting predictions for and agree remarkably well with MD
simulations of Na at up to almost three times its melting temperature. Two
independent processes in the model relax velocity autocorrelations: (a)
dephasing due to the presence of many frequency components, which operates at
all temperatures but which produces no diffusion, and (b) the transit process,
which increases with increasing temperature and which produces diffusion.
Because the model provides a single-atom trajectory in real space and time,
including transits, it may be used to calculate all single-atom correlation
functions.Comment: LaTeX, 8 figs. This is an updated version of cond-mat/0002057 and
cond-mat/0002058 combined Minor changes made to coincide with published
versio
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
Multiple-Point and Multiple-Time Correlations Functions in a Hard-Sphere Fluid
A recent mode coupling theory of higher-order correlation functions is tested
on a simple hard-sphere fluid system at intermediate densities. Multi-point and
multi-time correlation functions of the densities of conserved variables are
calculated in the hydrodynamic limit and compared to results obtained from
event-based molecular dynamics simulations. It is demonstrated that the mode
coupling theory results are in excellent agreement with the simulation results
provided that dissipative couplings are included in the vertices appearing in
the theory. In contrast, simplified mode coupling theories in which the
densities obey Gaussian statistics neglect important contributions to both the
multi-point and multi-time correlation functions on all time scales.Comment: Second one in a sequence of two (in the first, the formalism was
developed). 12 pages REVTeX. 5 figures (eps). Submitted to Phys.Rev.
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
Dephasing of Electrons by Two-Level Defects in Quantum Dots
The electron dephasing time in a diffusive quantum dot is
calculated by considering the interaction between the electron and dynamical
defects, modelled as two-level system. Using the standard tunneling model of
glasses, we obtain a linear temperature dependence of ,
consistent with the experimental observation. However, we find that, in order
to obtain dephasing times on the order of nanoseconds, the number of two-level
defects needs to be substantially larger than the typical concentration in
glasses. We also find a finite system-size dependence of , which
can be used to probe the effectiveness of surface-aggregated defects.Comment: two-column 9 page
Thermodynamics of glasses: a first principle computation
We propose a first principle computation of the thermodynamics of simple
fragile glasses starting from the two body interatomic potential.
A replica formulation translates this problem into that of a gas of
interacting molecules, each molecule being built of atoms, and having a
gyration radius (related to the cage size) which vanishes at zero temperature.
We use a small cage expansion, valid at low temperatures, which allows to
compute the cage size, the specific heat (which follows the Dulong and Petit
law), and the configurational entropy.Comment: Latex, 13 pages, 4 figure
Incorporating mindfulness: questioning capitalism
This paper engages with Buddhist critiques of capitalism and consumerism; and it challenges the capitalist appropriations of Buddhist techniques. We show how Buddhist modernism and Marxism/socialism can align, and how Engaged Buddhism spawns communalism and socially revolutionary impulses for sustainability and ecological responsibility within the framework of Buddhist thought and mindfulness traditions. Our case study of the Thai Asoke community exemplifies Buddhist communal mindfulness-in-action, explores successes and idiosyncrasies, and shows how communal principles can operate in such work-based communities
Borderline personality disorder co-morbidity: Relationship to the internalizingâexternalizing structure of common mental disorders
Background. Borderline personality disorder (BPD) shows high levels of co-morbidity with an array of psychiatric disorders. The meaning and causes of this co-morbidity are not fully understood. Our objective was to investigate and clarify the complex co-morbidity of BPD by integrating it into the structure of common mental disorders. Method. We conducted exploratory and confirmatory factor analyses on diagnostic interview data from a representative US population-based sample of 34 653 civilian, non-institutionalized individuals aged o18 years. We modeled the structure of lifetime DSM-IV diagnoses of BPD and antisocial personality disorder (ASPD), major depressive disorder, dysthymic disorder, panic disorder with agoraphobia, social phobia, specific phobia, generalized anxiety disorder, post-traumatic stress disorder, alcohol dependence, nicotine dependence, marijuana dependence, and any other drug dependence. Results. In both women and men, the internalizing-externalizing structure of common mental disorders captured the co-morbidity among all disorders including BPD. Although BPD was unidimensional in terms of its symptoms, BPD as a disorder showed associations with both the distress subfactor of the internalizing dimension and the externalizing dimension. Conclusions. The complex patterns of co-morbidity observed with BPD represent connections to other disorders at the level of latent internalizing and externalizing dimensions. BPD is meaningfully connected with liabilities shared with common mental disorders, and these liability dimensions provide a beneficial focus for understanding the co-morbidity, etiology and treatment of BPD
Reconstructing âthe Alcoholicâ: Recovering from Alcohol Addiction and the Stigma this Entails
Public perception of alcohol addiction is frequently negative, whilst an important part of recovery is the construction of a positive sense of self. In order to explore how this might be achieved, we investigated how those who self-identify as in recovery from alcohol problems view themselves and their difficulties with alcohol and how they make sense of othersâ responses to their addiction. Semi-structured interviews with six individuals who had been in recovery between 5 and 35 years and in contact with Alcoholics Anonymous were analysed using Interpretative Phenomenological Analysis. The participants were acutely aware of stigmatising images of âalcoholicsâ and described having struggled with a considerable dilemma in accepting this identity themselves. However, to some extent they were able to resist stigma by conceiving of an âaware alcoholic selfâ which was divorced from their previously unaware self and formed the basis for a new more knowing and valued identity
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