4,113 research outputs found
The pion quasiparticle in the low-temperature phase of QCD
We investigate the properties of the pion quasiparticle in the
low-temperature phase of two-flavor QCD on the lattice with support from chiral
effective theory. We find that the pion quasiparticle mass is significantly
reduced compared to its value in the vacuum, by contrast with the static
screening mass, which increases with temperature. By a simple argument, near
the chiral limit the two masses are expected to determine the quasiparticle
dispersion relation. Analyzing two-point functions of the axial charge density
at non-vanishing spatial momentum, we find that the predicted dispersion
relation and the residue of the pion pole are simultaneously consistent with
the lattice data at low momentum. The test, based on fits to the correlation
functions, is confirmed by a second analysis using the Backus-Gilbert method.Comment: 22 pages, 8 figure
Chiral dynamics in the low-temperature phase of QCD
We investigate the low-temperature phase of QCD and the crossover region with
two light flavors of quarks. The chiral expansion around the point in the temperature vs. quark-mass plane indicates that a sharp real-time
excitation exists with the quantum numbers of the pion. We determine its
dispersion relation and test the applicability of the chiral expansion. The
time-dependent correlators are also analyzed using the Maximum Entropy Method
(MEM), yielding consistent results. Finally, we test the predictions of
ordinary chiral perturbation theory around the point for the
temperature dependence of static observables. Around the crossover temperature,
we find that all quantities considered depend only mildly on the quark mass in
the considered range 8MeV 15MeV.Comment: 7 pages, 5 figures, talk presented at the 32nd International
Symposium on Lattice Field Theory (Lattice 2014), 23 - 28 June, 2014 Columbia
University New York, NY, US
A comparative history of Department of Defense Management reform from 1947 to 2005
MBA Professional ReportThe purpose of this MBA Project is to document and analyze the history of management reform within the Department of Defense from 1947 through the present day based on the annual reports of the Secretaries of Defense to the Congress. Since its inception in 1947, the Department of Defense has undergone nearly constant management reforms. It appears that each administration attempts to introduce some type of management reform agenda to improve the Department of Defense business processes and incorporate recent management ideas from the business community. Some of the changes are real and significant; others are changes in name only. Through analysis of annual reports of the Secretaries of Defense, a compilation of significant management reforms was created for each secretary. These reforms were analyzed and compared to one another to identify both general trends and truly unique changes in management practices. Ultimately, this analysis will help distinguish the relative significance in the management reform effort of both the individual secretaries and the specific reform initiatives.http://archive.org/details/acomparativehist1094510068US Marine Corps (USMC) authors.Approved for public release; distribution is unlimited
A novel chromosome segregation mechanism during female meiosis.
In a wide range of eukaryotes, chromosome segregation occurs through anaphase A, in which chromosomes move toward stationary spindle poles, anaphase B, in which chromosomes move at the same velocity as outwardly moving spindle poles, or both. In contrast, Caenorhabditis elegans female meiotic spindles initially shorten in the pole-to-pole axis such that spindle poles contact the outer kinetochore before the start of anaphase chromosome separation. Once the spindle pole-to-kinetochore contact has been made, the homologues of a 4-μm-long bivalent begin to separate. The spindle shortens an additional 0.5 μm until the chromosomes are embedded in the spindle poles. Chromosomes then separate at the same velocity as the spindle poles in an anaphase B-like movement. We conclude that the majority of meiotic chromosome movement is caused by shortening of the spindle to bring poles in contact with the chromosomes, followed by separation of chromosome-bound poles by outward sliding
Biocomplexity in Pacific herring (Clupea pallasii) of Puget Sound, USA
Small-scale genetic and demographic diversity can stabilize populations on a larger scale. However, subpopulations of pelagic fish species can be difficult to distinguish. Here, we examine demographic diversity in 21 stocks of Pacific herring (Clupea pallasii) in Puget Sound, USA using a multivariate auto-regressive state-space (MARSS) model, and data from both acoustic surveys paired with trawls, and subtidal egg surveys to estimate population growth trends. Herring populations associated with individual spawning beaches are asynchronous, but share a common negative growth rate across the Puget Sound estuary. We found that both survey techniques observe the same underlying demographic processes, and that egg surveys are a more accurate estimator of total spawning biomass. We used states obtained from MARSS analysis to measure portfolio effects in Puget Sound herring, and found that the Puget Sound population as a whole is stabilized by the presence of several separate spawning subpopulations. Available environmental data was not sufficient to explain variations in spawning biomass; however, herring may respond to spawning site conditions that aren’t currently measured
Displacement of transport processes on networked topologies
Consider a particle whose position evolves along the edges of a network. One
definition for the displacement of a particle is the length of the shortest
path on the network between the current and initial positions of the particle.
Such a definition fails to incorporate information of the actual path the
particle traversed. In this work we consider another definition for the
displacement of a particle on networked topologies. Using this definition,
which we term the winding distance, we demonstrate that for Brownian particles,
confinement to a network can induce a transition in the mean squared
displacement from diffusive to ballistic behaviour, for long times. A multiple scales approach is used to derive a
macroscopic evolution equation for the displacement of a particle and uncover a
topological condition for whether this transition in the mean squared
displacement will occur. Furthermore, for networks satisfying this topological
condition, we identify a prediction of the timescale upon which the
displacement transitions to long-time behaviour. Finally, we extend the
investigation of displacement on networks to a class of anomalously diffusive
transport processes, where we find that the mean squared displacement at long
times is affected by both network topology and the character of the transport
process.Comment: 22 pages, 8 figure
The pion quasiparticle in the low-temperature phase of QCD
We extend our previous studies [PhysRevD.90.054509, PhysRevD.92.094510] of
the pion quasiparticle in the low-temperature phase of two-flavor QCD with
support from chiral effective theory. This includes the analysis performed on a
finite temperature ensemble of size at MeV and a
lighter zero-temperature pion mass MeV. Furthermore, we
investigate the Gell-Mann--Oakes-Renner relation at finite temperature and the
Dey-Eletsky-Ioffe mixing theorem at finite quark mass.Comment: 8 pages, 5 figures, talk presented at 35th annual International
Symposium on Lattice Field Theory, 18-24 June 2017, Granada, Spai
Low-volume, fast response-time hollow silica waveguide gas cells for mid-IR spectroscopy
Hollow silica waveguides (HSWs) are used to produce long path length, low-volume gas cells, and are demonstrated with quantum cascade laser spectroscopy. Absorption measurements are made using the intrapulse technique, which allows measurements to be made across a single laser pulse. Simultaneous laser light and gas coupling is achieved through the modification of commercially available gas fittings with low dead volume. Three HSW gas cell configurations with different path lengths and internal diameters are analyzed and compared with a 30 m path length astigmatic Herriott cell. Limit of detection measurements are made for the gas cells using methane at a wavelength 7.82 μm. The lowest limit of detection was provided by HSW with a bore diameter of 1000 μm and a path length of 5 m and was measured to be 0.26 ppm, with a noise equivalent absorbance of 4.1×10 −4 . The long-term stability of the HSW and Herriott cells is compared through analysis of the Allan–Werle variance of data collected over a 24 h period. The response times of the HSW and Herriott cells are measured to be 0.8 s and 36 s, respectively
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