976 research outputs found
Nonlinear force-free field modelling of solar coronal jets in theoretical configurations
Coronal jets occur frequently on the Sun, and may contribute significantly to the solar wind. With the suite of instruments available now, we can observe these phenomena in greater detail than ever before. Modeling and simulations can assist further in understanding the dynamic processes involved, but previous studies tend to consider only one mechanism (e.g. emergence or rotation) for the origin of the jet. In this study we model a series of idealised archetypal jet configurations and follow the evolution of the coronal magnetic field. This is a step towards understanding these idealised situations before considering their observational counterparts. Several simple situations are set up for the evolution of the photospheric magnetic field: a single parasitic polarity rotating or moving in a circular path; as well as opposite polarity pairs involved in flyby (shearing), cancellation or emergence; all in the presence of a uniform, open background magnetic field. The coronal magnetic field is evolved in time using a magnetofrictional relaxation method. While magnetofriction cannot accurately reproduce the dynamics of an eruptive phase, the structure of the coronal magnetic field, as well as the build up of electric currents and free magnetic energy are instructive. Certain configurations and motions produce a flux rope and allow the significant build up of free energy, reminiscent of the progenitors of so-called blowout jets, whereas other, simpler configurations are more comparable to the standard jet model. The next stage is a comparison with observed coronal jet structures and their corresponding photospheric evolution
Relationship among concentrations of milk urea nitrogen and plasma urea nitrogen and feeding time
Eight Holstein cows were used to determine the relationship among milk urea nitrogen (MUN), plasma urea nitrogen (PUN), and feeding time. We first established that MUN concentrations were similar in concentration among quarters by comparing milk samples from each quarter just before milking. In order to determine if collecting a sample of milk from a quarter influenced the MUN in samples taken later, samples were obtained from the right front quarter (RF) at 2, 4, 6, and 8 hr after the AM milking and from the left front quarter (LF), right rear (RR), and left rear (LR) at 4, 6, and 8 h after the AM milking, respectively. The MUN in samples obtained from RF at 4 hr was lower (P\u3c0.01) than corresponding samples taken from LF, but samples from RF at 6 and 8 hr did not differ from corresponding samples obtained from RR and LR. We concluded that by 6 hr, the effect of previous milking on MUN concentration disappeared because of dilution. To determine the influence of feeding time on MUN concentrations, cows were fed half of their normal PM feeding, injected with oxytocin at the subsequent AM milking to reduce residual milk, and offered surplus feed after the AM milking. Milk samples were collected at 2, 4, 6, 8, 10, and 12 hr after feeding from RF, LF, RR, LR, RF, and LF quarters, respectively. Blood samples were obtained from the coccygeal vein at hourly intervals after feeding with the last sample collected 12 hr after feeding. The MUN concentrations at 2, 4, 6, and 8 hr were similar. The MUN at 10 hr was similar to those at 2 and 8 hr, less than that at 4 and 6 hr, and greater than that for the 12 hr sample. Concentrations of PUN peaked at 2 hr postfeeding, then gradually declined through 12 hr postfeeding. The MUN peaked at 6 hr postfeeding and then declined. Time after feeding significantly influenced PUN and MUN concentrations.; Dairy Day, 2000, Kansas State University, Manhattan, KS, 2000
Nucleation versus Spinodal decomposition in a first order quark hadron phase transition
We investigate the scenario of homogeneous nucleation for a first order
quark-hadron phase transition in a rapidly expanding background of quark gluon
plasma. Using an improved preexponential factor for homogeneous nucleation
rate, we solve a set of coupled equations to study the hadronization and the
hydrodynamical evolution of the matter. It is found that significant
supercooling is possible before hadronization begins. This study also suggests
that spinodal decomposition competes with nucleation and may provide an
alternative mechanism for phase conversion particularly if the transition is
strong enough and the medium is nonviscous. For weak enough transition, the
phase conversion may still proceed via homogeneous nucleation.Comment: LaTeX, 10 pages with 7 Postscript figures, more discussions and
referencese added, typos correcte
Partially Annealed Disorder and Collapse of Like-Charged Macroions
Charged systems with partially annealed charge disorder are investigated
using field-theoretic and replica methods. Charge disorder is assumed to be
confined to macroion surfaces surrounded by a cloud of mobile neutralizing
counterions in an aqueous solvent. A general formalism is developed by assuming
that the disorder is partially annealed (with purely annealed and purely
quenched disorder included as special cases), i.e., we assume in general that
the disorder undergoes a slow dynamics relative to fast-relaxing counterions
making it possible thus to study the stationary-state properties of the system
using methods similar to those available in equilibrium statistical mechanics.
By focusing on the specific case of two planar surfaces of equal mean surface
charge and disorder variance, it is shown that partial annealing of the
quenched disorder leads to renormalization of the mean surface charge density
and thus a reduction of the inter-plate repulsion on the mean-field or
weak-coupling level. In the strong-coupling limit, charge disorder induces a
long-range attraction resulting in a continuous disorder-driven collapse
transition for the two surfaces as the disorder variance exceeds a threshold
value. Disorder annealing further enhances the attraction and, in the limit of
low screening, leads to a global attractive instability in the system.Comment: 21 pages, 2 figure
The new IOC and IAAF policies on female eligibility: old Emperor, new clothes?
The Caster Semenya debacle touched off by the 2009 Berlin World Athletics Championships resulted finally in IOC and IAAF abandonment of sex testing, which gave way to procedures that make female competition eligibility dependent upon the level of serum testosterone, which must be below the male range or instrumentally countered by androgen resistance. We argue that the new policy is unsustainable because (i) the testosterone-performance connection it posits is uncompelling; (ii) testosterone-induced female advantage is not ipso facto unfair advantage; (iii) the new policy reflects the gender policing impulses endemic to sport as well as the broader cultural impulses to monstrify women and to doctor women who have nothing wrong with them; (iv) female–male performance disparities are not the only reason for sex-segregated sport, but co-exist with respectable cultural and practical reasons, which (v) provide a powerful case for allowing athletes to compete in the sex category congruent with their gender identity
Sample-to-sample torque fluctuations in a system of coaxial randomly charged surfaces
Polarizable randomly charged dielectric objects have been recently shown to
exhibit long-range lateral and normal interaction forces even when they are
effectively net neutral. These forces stem from an interplay between the
quenched statistics of random charges and the induced dielectric image charges.
This type of interaction has recently been evoked to interpret measurements of
Casimir forces in vacuo, where a precise analysis of such disorder-induced
effects appears to be necessary. Here we consider the torque acting on a
randomly charged dielectric surface (or a sphere) mounted on a central axle
next to another randomly charged surface and show that although the resultant
mean torque is zero, its sample-to-sample fluctuation exhibits a long-range
behavior with the separation distance between the juxtaposed surfaces and that,
in particular, its root-mean-square value scales with the total area of the
surfaces. Therefore, the disorder-induced torque between two randomly charged
surfaces is expected to be much more pronounced than the disorder-induced
lateral force and may provide an effective way to determine possible disorder
effects in experiments, in a manner that is independent of the usual normal
force measurement.Comment: 7 pages, 3 fig
Electromagnetic form factors of the nucleon in a covariant diquark model
We present a simple covariant constituent diquark-quark model for the
nucleon. The nucleon is assumed to be composed of a scalar diquark and a quark
which interact via a quark exchange. Starting from the Bethe-Salpeter equation,
the instantaneous approximation leads to a diquark-quark Salpeter equation. In
the Mandelstam formalism, the electromagnetic form factors of the nucleon are
calculated for momentum transfers up to q^2 = - 3 \; (\mbox{GeV/c})^2. A
remarkable description of the experimental data is obtained. Especially, the
model gives nearly the right values for the proton and (negative) neutron
charge radii, and a qualitative description of the magnetic form factors.Comment: 17 pages, revtex, 8 figures in additional fil
A covariant diquark-quark model of the nucleon in the Salpeter approach
We develop a rather simple, formally covariant quark-diquark model of the
nucleon. The nucleon is treated as a bound state of a constituent quark and a
diquark interacting via a quark exchange. We include both scalar and
axial-vector diquarks. The underlying Bethe-Salpeter equation is transformed
into a pair of coupled Salpeter equations. The electromagnetic form factors of
the nucleon are calculated in the Mandelstam formalism. We obtain a very good
description of all electromagnetic form factors for momentum transfers up to -3
(GeV/c)^2.Comment: 17 pages, REVTeX, 10 figures (ps and eps) include
Designing spin-spin interactions with one and two dimensional ion crystals in planar micro traps
We discuss the experimental feasibility of quantum simulation with trapped
ion crystals, using magnetic field gradients. We describe a micro structured
planar ion trap, which contains a central wire loop generating a strong
magnetic gradient of about 20 T/m in an ion crystal held about 160 \mu m above
the surface. On the theoretical side, we extend a proposal about spin-spin
interactions via magnetic gradient induced coupling (MAGIC) [Johanning, et al,
J. Phys. B: At. Mol. Opt. Phys. 42 (2009) 154009]. We describe aspects where
planar ion traps promise novel physics: Spin-spin coupling strengths of
transversal eigenmodes exhibit significant advantages over the coupling schemes
in longitudinal direction that have been previously investigated. With a chip
device and a magnetic field coil with small inductance, a resonant enhancement
of magnetic spin forces through the application of alternating magnetic field
gradients is proposed. Such resonantly enhanced spin-spin coupling may be used,
for instance, to create Schr\"odinger cat states. Finally we investigate
magnetic gradient interactions in two-dimensional ion crystals, and discuss
frustration effects in such two-dimensional arrangements.Comment: 20 pages, 13 figure
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Family-Friendly Management, Organizational Performance and Social Legitimacy
Research on family-friendly practices has concentrated on the predictors of their use, particularly from the perspective of either institutional theory or the high involvement or commitment management vogue. This paper first shows how such perspectives can be used to generate hypotheses about the link between family-friendly management and organizational performance. Second, the paper reports research designed to test these, using data from a national representative sample of workplaces across the British economy, the Workplace Employment Relations Survey of 2004 (WERS2004). The results support the high commitment thesis that family-friendly management will strengthen the relationship between commitment and key economic outcomes, as the relationships between workforce commitment and productivity or quality are stronger in organizations when friendly management is high, which is consistent with social exchange theory. Family-friendly management is not, however, related to the human resource outcomes of labour turnover and absenteeism. Nor does the study find support for the argument that its use in conjunction with high involvement management enhances the performance effects of both. Equally, there is no support for the hypothesis from the institutional thesis that family-friendly management has positive effects on the legitimacy of the organization
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