9,230 research outputs found
Thermodynamics of Quantum Jump Trajectories
We apply the large-deviation method to study trajectories in dissipative
quantum systems. We show that in the long time limit the statistics of quantum
jumps can be understood from thermodynamic arguments by exploiting the analogy
between large-deviation and free-energy functions. This approach is
particularly useful for uncovering properties of rare dissipative trajectories.
We also prove, via an explicit quantum mapping, that rare trajectories of one
system can be realized as typical trajectories of an alternative system.Comment: 5 pages, 3 figure
The Most Detailed Picture Yet of an Embedded High-mass YSO
High-mass star formation is not well understood chiefly because examples are
deeply embedded, relatively distant, and crowded with sources of emission.
Using VLA and VLBA observations of water and SiO maser emission, we have mapped
in detail the structure and proper motion of material 20-500 AU from the
closest high-mass YSO, radio source-I in the Orion KL region. We observe
streams of material driven in a rotating, wide angle, bipolar wind from the
surface of an edge-on accretion disk. The example of source-I provides strong
evidence that high-mass star formation proceeds via accretionComment: typo corrected and word added to abstract 6 pages including 4 B&W
figures. To appear in the Proceeding of IAU Symposium 221, Star Formation at
High Angular Resolution, Editors M. Burton, R. Jayawardhana & T. Bourke,
Astronomical Society of the Pacifi
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The use of the Continuously Regenerating Trap (CRT<sup>TM</sup>) and SCRT<sup>TM</sup> Systems to meet future emissions legislation
The progressive tightening of particulate matter (PM) legislation presents challenges to the engine development and aftertreatment communities. The Continuously Regenerating Trap (CRTTM) has been developed to enable diesel engines to meet the proposed future legislation. This passive filter system combines an oxidation catalyst with a Diesel Particulate Filter (DPF); the filter traps the PM and the oxidation catalyst generates NO2 which combusts the trapped PM at substantially lower temperatures than is possible using oxygen.
This paper outlines the operating principle of the CRTTM, and describes the performance of the system. It has been shown that the very high PM conversions obtained with the CRTTM can enable even Euro 1 engines to meet the PM limits proposed for introduction in Europe in 2005. In addition, the system removes PM across the whole particle size range, including ultrafine particulates. These results will be discussed, as will in-field durability studies which have shown that the system is still capable of converting 90% of PM after very high mileage operation (up to 600,000 km).
In addition to requiring very high PM conversion, the proposed future legislation requires substantial reductions in NOx emissions form heavy duty diesel vehicles. To meet these challenges the SCRTTM has been developed. This combines the CRTTM with SCR (Selective Catalytic Reduction) technology, and enables very high simultaneous conversions of CO, HC, PM and NOx to be achieved. The SCRTTM system is described, and its operating characteristics are discussed. It has been shown that the SCRTTM can potentially meet the legislative limits proposed for introduction in Europe in 2008
Quantum trajectory phase transitions in the micromaser
We study the dynamics of the single atom maser, or micromaser, by means of
the recently introduced method of thermodynamics of quantum jump trajectories.
We find that the dynamics of the micromaser displays multiple space-time phase
transitions, i.e., phase transitions in ensembles of quantum jump trajectories.
This rich dynamical phase structure becomes apparent when trajectories are
classified by dynamical observables that quantify dynamical activity, such as
the number of atoms that have changed state while traversing the cavity. The
space-time transitions can be either first-order or continuous, and are
controlled not just by standard parameters of the micromaser but also by
non-equilibrium "counting" fields. We discuss how the dynamical phase behavior
relates to the better known stationary state properties of the micromaser.Comment: 7 pages, 5 figure
Entropy and Temperature of a Static Granular Assembly
Granular matter is comprised of a large number of particles whose collective
behavior determines macroscopic properties such as flow and mechanical
strength. A comprehensive theory of the properties of granular matter,
therefore, requires a statistical framework. In molecular matter, equilibrium
statistical mechanics, which is founded on the principle of conservation of
energy, provides this framework. Grains, however, are small but macroscopic
objects whose interactions are dissipative since energy can be lost through
excitations of the internal degrees of freedom. In this work, we construct a
statistical framework for static, mechanically stable packings of grains, which
parallels that of equilibrium statistical mechanics but with conservation of
energy replaced by the conservation of a function related to the mechanical
stress tensor. Our analysis demonstrates the existence of a state function that
has all the attributes of entropy. In particular, maximizing this state
function leads to a well-defined granular temperature for these systems.
Predictions of the ensemble are verified against simulated packings of
frictionless, deformable disks. Our demonstration that a statistical ensemble
can be constructed through the identification of conserved quantities other
than energy is a new approach that is expected to open up avenues for
statistical descriptions of other non-equilibrium systems.Comment: 5 pages, 4 figure
Isomorphic classical molecular dynamics model for an excess electron in a supercritical fluid
Ring polymer molecular dynamics (RPMD) is used to directly simulate the
dynamics of an excess electron in a supercritical fluid over a broad range of
densities. The accuracy of the RPMD model is tested against numerically exact
path integral statistics through the use of analytical continuation techniques.
At low fluid densities, the RPMD model substantially underestimates the
contribution of delocalized states to the dynamics of the excess electron.
However, with increasing solvent density, the RPMD model improves, nearly
satisfying analytical continuation constraints at densities approaching those
of typical liquids. In the high density regime, quantum dispersion
substantially decreases the self-diffusion of the solvated electron.
In this regime where the dynamics of the electron is strongly coupled to the
dynamics of the atoms in the fluid, trajectories that can reveal diffusive
motion of the electron are long in comparison to .Comment: 24 pages, 4 figure
Fragile X (CGG)(n )repeats induce a transcriptional repression in cis upon a linked promoter: Evidence for a chromatin mediated effect
BACKGROUND: Expansion of an unstable (CGG)(n )repeat to over 200 triplets within the promoter region of the human FMR1 gene leads to extensive local methylation and transcription silencing, resulting in the loss of FMRP protein and the development of the clinical features of fragile X syndrome. The causative link between (CGG)(n )expansion, methylation and gene silencing is unknown, although gene silencing is associated with extensive changes to local chromatin architecture. RESULTS: In order to determine the direct effects of increased repeat length on gene transcription in a chromatin context, we have examined the influence of FMR1 (CGG)(n )repeats upon transcription from the HSV thymidine kinase promoter in the Xenopus laevis oocyte. We observe a reduction in mRNA production directly associated with increasing repeat length, with a 90% reduction in mRNA production from arrays over 100 repeats in length. Using a kinetic approach, we show that this transcriptional repression is concomitant with chromatin maturation and, using in vitro transcription, we show that chromatin formation is a fundamental part of the repressive pathway mediated by (CGG)(n )repeats. Using Trichostatin A, a histone deacetylase inhibitor, we show reactivation of the silenced promoter. CONCLUSIONS: Thus, isolated fragile X associated (CGG)(n )repeat arrays can exert a modifying and transcriptionally repressive influence over adjacent promoters and this repressive phenomenon is, in part, mediated by histone deacetylation
cr sn: the significance of macroconidiation for mutant hunts
cr sn: significance of macroconidiation for mutant hunt
VLA Survey of Dense Gas in Extended Green Objects: Prevalence of 25 GHz Methanol Masers
We present resolution Very Large Array (VLA) observations of four
CHOH - 25~GHz transitions (=3, 5, 8, 10) along with 1.3~cm
continuum toward 20 regions of active massive star formation containing
Extended Green Objects (EGOs), 14 of which we have previously studied with the
VLA in the Class~I 44~GHz and Class~II 6.7~GHz maser lines (Cyganowski et al.
2009). Sixteen regions are detected in at least one 25~GHz line (=5), with
13 of 16 exhibiting maser emission. In total, we report 34 new sites of
CHOH maser emission and ten new sites of thermal CHOH emission,
significantly increasing the number of 25~GHz Class I CHOH masers observed
at high angular resolution. We identify probable or likely maser counterparts
at 44~GHz for all 15 of the 25~GHz masers for which we have complementary data,
providing further evidence that these masers trace similar physical conditions
despite uncorrelated flux densities. The sites of thermal and maser emission of
CHOH are both predominantly associated with the 4.5 m emission from
the EGO, and the presence of thermal CHOH emission is accompanied by 1.3~cm
continuum emission in 9 out of 10 cases. Of the 19 regions that exhibit 1.3~cm
continuum emission, it is associated with the EGO in 16 cases (out of a total
of 20 sites), 13 of which are new detections at 1.3~cm. Twelve of the 1.3~cm
continuum sources are associated with 6.7~GHz maser emission and likely trace
deeply-embedded massive protostars
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