964 research outputs found
On the Solutions of the Lorentz-Dirac Equation
We discuss the unstable character of the solutions of the Lorentz-Dirac
equation and stress the need of methods like order reduction to derive a
physically acceptable equation of motion. The discussion is illustrated with
the paradigmatic example of the non-relativistic harmonic oscillator with
radiation reaction. We also illustrate removal of the noncasual
pre-acceleration with the introduction of a small correction in the
Lorentz-Dirac equation.Comment: 4 eps figs. to be published in GR
Interplay of Strain Relaxation and Chemically Induced Diffusion Barriers: Nanostructure Formation in 2D Alloys
We study the formation of nanostructures with alternating stripes composed of
bulk-immiscible adsorbates during submonolayer heteroepitaxy. We evaluate the
influence of two mechanisms considered in the literature: (i) strain relaxation
by alternating arrangement of the adsorbate species, and (ii) kinetic
segregation due to chemically induced diffusion barriers. A model ternary
system of two adsorbates with opposite misfit relative to the substrate, and
symmetric binding is investigated by off-lattice as well as lattice kinetic
Monte Carlo simulations. We find that neither of the mechanisms (i) or (ii)
alone can account for known experimental observations. Rather, a combination of
both is needed. We present an off-lattice model which allows for a qualitative
reproduction of stripe patterns as well as island ramification in agreement
with recent experimental observations for CoAg/Ru(0001) [R. Q. Hwang, Phys.
Rev. Lett. 76, 4757 (1996)]. The quantitative dependencies of stripe width and
degree of island ramification on the misfit and interaction strength between
the two adsorbate types are presented. Attempts to capture essential features
in a simplified lattice gas model show that a detailed incorporation of
non-local effects is required.Comment: 24 pages, 12 figure
Aspects of electrostatics in a weak gravitational field
Several features of electrostatics of point charged particles in a weak,
homogeneous, gravitational field are discussed using the Rindler metric to
model the gravitational field. Some previously known results are obtained by
simpler and more transparent procedures and are interpreted in an intuitive
manner. Specifically: (i) We show that the electrostatic potential of a charge
at rest in the Rindler frame is expressible as A_0=(q/l) where l is the affine
parameter distance along the null geodesic from the charge to the field point.
(ii) We obtain the sum of the electrostatic forces exerted by one charge on
another in the Rindler frame and discuss its interpretation. (iii) We show how
a purely electrostatic term in the Rindler frame appears as a radiation term in
the inertial frame. (In part, this arises because charges at rest in a weak
gravitational field possess additional weight due to their electrostatic
energy. This weight is proportional to the acceleration and falls inversely
with distance -- which are the usual characteristics of a radiation field.)
(iv) We also interpret the origin of the radiation reaction term by extending
our approach to include a slowly varying acceleration. Many of these results
might have possible extensions for the case of electrostatics in an arbitrary
static geometry. [Abridged Abstract]Comment: 26 pages; accepted for publication in Gen.Rel.Gra
Dissipative Field Theory with Caldeira-Leggett Method and its Application to Disoriented Chiral Condensation
The effective field theory including the dissipative effect is developed
based on the Caldeira-Leggett theory at the classical level. After the
integration of the small field fluctuations considered as the field radiation,
the integro-differential field equation is given and shown to include the
dissipative effects. In that derivation, special cares should be taken for the
boundary condition of the integration. Application to the linear sigma model is
given, and the decay process of the chiral condensate is calculated with it,
both analytically in the linear approximation and numerically. With these
results, we discuss the stability of chiral condensates within the quenched
approximation.Comment: 16pages, ReV-Te
Schottky mass measurements of heavy neutron-rich nuclides in the element range 70\leZ \le79 at the ESR
Storage-ring mass spectrometry was applied to neutron-rich Au
projectile fragments. Masses of Lu, Hf, Ta,
W, and Re nuclei were measured for the first time. The
uncertainty of previously known masses of W and Os nuclei
was improved. Observed irregularities on the smooth two-neutron separation
energies for Hf and W isotopes are linked to the collectivity phenomena in the
corresponding nuclei.Comment: 10 pages, 9 figures, 2 table
PIWIL4 Acts as a piRNA Binding, Epigenetically Active and Growth Regulatory Protein in Human Acute Myeloid Leukemia
Piwi proteins are critically important for maintaining the self-renewing stem cell population in lower organisms through epigenetic silencing of transposable elements via DNA methylation and H3K9me3 marks, in close interaction with a novel class of non-coding RNA called piwi interacting RNA (piRNA)
Mining Methylation for Early Detection of Common Cancers
A single method that detects multiple common cancer types at an early stage would have the biggest payoff for cancer control, say Brena and colleagues
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A statistical proxy for sulphuric acid concentration
Gaseous sulphuric acid is a key precursor for new particle formation in the atmosphere. Previous experimental studies have confirmed a strong correlation between the number concentrations of freshly formed particles and the ambient concentrations of sulphuric acid. This study evaluates a body of experimental gas phase sulphuric acid concentrations, as measured by Chemical Ionization Mass Spectrometry (CIMS) during six intensive measurement campaigns and one long-term observational period. The campaign datasets were measured in HyytiÀlÀ, Finland, in 2003 and 2007, in San Pietro Capofiume, Italy, in 2009, in Melpitz, Germany, in 2008, in Atlanta, Georgia, USA, in 2002, and in Niwot Ridge, Colorado, USA, in 2007. The long term data were obtained in Hohenpeissenberg, Germany, during 1998 to 2000. The measured time series were used to construct proximity measures ("proxies") for sulphuric acid concentration by using statistical analysis methods. The objective of this study is to find a proxy for sulfuric acid that is valid in as many different atmospheric environments as possible. Our most accurate and universal formulation of the sulphuric acid concentration proxy uses global solar radiation, SO2 concentration, condensation sink and relative humidity as predictor variables, yielding a correlation measure (R) of 0.87 between observed concentration and the proxy predictions. Interestingly, the role of the condensation sink in the proxy was only minor, since similarly accurate proxies could be constructed with global solar radiation and SO2 concentration alone. This could be attributed to SO2 being an indicator for anthropogenic pollution, including particulate and gaseous emissions which represent sinks for the OH radical that, in turn, is needed for the formation of sulphuric acid
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