6,114 research outputs found
Precession of the Isolated Neutron Star PSR B1828-11
Stairs, Lyne & Shemar have found that arrival time residuals from PSR
B1828-11 vary periodically with a period of 500 days. This behavior can be
accounted for by precession of the radiopulsar, an interpretation that is
reinforced by the detection of variations in its pulse profile on the same
timescale. Here, we model the period residuals from PSR B1828-11 in terms of
precession of a triaxial rigid body. We include two contributions to the
residuals: (i) the geometric effect, which arises because the times at which
the pulsar emission beam points toward the observer varies with precession
phase; (ii) the spindown contribution, which arises from any dependence of the
spindown torque acting on the pulsar on the angle between its spin and magnetic
axes. We use the data to probe numerous properties of the pulsar, most notably
its shape, and the dependence of its spindown torque on the angle between its
spin and magnetic axes, for which we assume a sum of a spin-aligned component
(with a weight 1-a) and a dipolar component perpendicular to the magnetic beam
axis (weight a), rather than the vacuum dipole torque (a=1). We find that a
variety of shapes are consistent with the residuals, with a slight statistical
preference for a prolate star. Moreover, a range of torque possibilities fit
the data equally well, with no strong preference for the vacuum model. In the
case of a prolate star we find evidence for an angle-dependent spindown torque.
Our results show that the combination of geometrical and spin-down effects
associated with precession can account for the principal features of PSR
B1828-11's timing behavior, without fine tuning of the parameters.Comment: 22 pages, 14 figures, submitted to MNRAS; added references, corrected
typo
Hohenberg-Kohn theorem for the lowest-energy resonance of unbound systems
We show that under well-defined conditions the Hohenberg-Kohn theorem (HKT)
can be extended to the lowest-energy resonance of unbound systems. Using the
Gel'fand Levitan theorem, the extended version of the HKT can also be applied
to systems that support a finite number of bound states. The extended version
of the HKT provides an adequate framework to carry out DFT calculations of
negative electron affinities.Comment: 4 pages, 3 figure
UPDRAFT FORCING MECHANISMS IN DEEP MARINE CONVECTION DRIVEN BY COLD POOLS
Aircraft and rawinsonde data collected during the CALifornia Investigation of Convection over Ocean (CALICO) field experiment between February and March of 2022 were analyzed to detail the size and magnitude of in-cloud cumuliform updrafts. Sampled convection generally occurred following wintertime cold-front passages off the central California coast, with much of the convection growing to the 6 km high tropopause and organizing into “arcs” driven by cold pools. Large-eddy simulations using Cloud Model 1 (CM1) were conducted to augment observations and characterize the three-dimensional cloud properties within cold-pool-driven convection to subsequently investigate what processes (both thermodynamic and dynamic) within the atmospheric boundary layer and free troposphere control the upward acceleration of negatively buoyant updrafts located behind a cold pool boundary. The effect of vertical wind shear on isolated and organized mesoscale convection is simulated. Organized convection is able to reach the tropopause despite the presence of strong vertical wind shear that inhibits isolated convection. Within the cold pool, the presence of negative buoyant but ascending updrafts was due to the presence of small pockets of strong upward acceleration caused by an upward-oriented pressure gradient force associated with the dynamic perturbation pressure.Distribution Statement A. Approved for public release: Distribution is unlimited.Lieutenant Commander, United States NavyOffice of Naval Researc
How training and testing histories affect generalization: a test of simple neural networks
We show that a simple network model of associative learning can\ud
reproduce three findings that arise from particular training and\ud
testing procedures in generalization experiments: the effect of 1)\ud
``errorless learning'' and 2) extinction testing on peak shift, and\ud
3) the central tendency effect. These findings provide a true test\ud
of the network model, which was developed to account for other\ud
penhomena, and highlight the potential of neural networks to study\ud
phenomena that depend on sequences of experiences with many stimuli.\ud
Our results suggest that at least some such phenomena, e.g.,\ud
stimulus range effects, may derive from basic mechanisms of\ud
associative memory rather than from more complex memory processes
Recommended from our members
Bombardier Enables Delivery of Short-Form Bomanins in the Drosophila Toll Response.
Toll mediates a robust and effective innate immune response across vertebrates and invertebrates. In Drosophila melanogaster, activation of Toll by systemic infection drives the accumulation of a rich repertoire of immune effectors in hemolymph, including the recently characterized Bomanins, as well as the classical antimicrobial peptides (AMPs). Here we report the functional characterization of a Toll-induced hemolymph protein encoded by the bombardier (CG18067) gene. Using the CRISPR/Cas9 system to generate a precise deletion of the bombardier transcriptional unit, we found that Bombardier is required for Toll-mediated defense against fungi and Gram-positive bacteria. Assaying cell-free hemolymph, we found that the Bomanin-dependent candidacidal activity is also dependent on Bombardier, but is independent of the antifungal AMPs Drosomycin and Metchnikowin. Using mass spectrometry, we demonstrated that deletion of bombardier results in the specific absence of short-form Bomanins from hemolymph. In addition, flies lacking Bombardier exhibited a defect in pathogen tolerance that we trace to an aberrant condition triggered by Toll activation. These results lead us to a model in which the presence of Bombardier in wild-type flies enables the proper folding, secretion, or intermolecular associations of short-form Bomanins, and the absence of Bombardier disrupts one or more of these steps, resulting in defects in both immune resistance and tolerance
Statistical Mechanics of Community Detection
Starting from a general \textit{ansatz}, we show how community detection can
be interpreted as finding the ground state of an infinite range spin glass. Our
approach applies to weighted and directed networks alike. It contains the
\textit{at hoc} introduced quality function from \cite{ReichardtPRL} and the
modularity as defined by Newman and Girvan \cite{Girvan03} as special
cases. The community structure of the network is interpreted as the spin
configuration that minimizes the energy of the spin glass with the spin states
being the community indices. We elucidate the properties of the ground state
configuration to give a concise definition of communities as cohesive subgroups
in networks that is adaptive to the specific class of network under study.
Further we show, how hierarchies and overlap in the community structure can be
detected. Computationally effective local update rules for optimization
procedures to find the ground state are given. We show how the \textit{ansatz}
may be used to discover the community around a given node without detecting all
communities in the full network and we give benchmarks for the performance of
this extension. Finally, we give expectation values for the modularity of
random graphs, which can be used in the assessment of statistical significance
of community structure
Recommended from our members
On the effectiveness of run-time checks
Run-time checks are often assumed to be a cost-effective way of improving the dependability of software components, by checking required properties of their outputs and flagging an output as incorrect if it fails the check. However, evaluating how effective they are going to be in a future application is difficult, since the effectiveness of a check depends on the unknown faults of the program to which it is applied. A programming contest, providing thousands of programs written to the same specifications, gives us the opportunity to systematically test run-time checks to observe statistics of their effects on actual programs. In these examples, run-time checks turn out to be most effective for unreliable programs. For more reliable programs, the benefit is relatively low as compared to the gain that can be achieved by other (more expensive) measures, most notably multiple-version diversity
A Will Before There\u27s a Way: Preschoolers And Books
Many children already possess a strong desire to master the written word. What is the key to their eagerness? What factors exist in the home and/or cultural environment that directs a child\u27s natural curiosity of the world around him/her into the arduous task of tearing apart and rebuilding language to allow written as well as vocal communication
- …