2,005 research outputs found
General pairing interactions and pair truncation approximations for fermions in a single-j shell
We investigate Hamiltonians with attractive interactions between pairs of
fermions coupled to angular momentum J. We show that pairs with spin J are
reasonable building blocks for the low-lying states. For systems with only a J
= Jmax pairing interaction, eigenvalues are found to be approximately integers
for a large array of states, in particular for those with total angular momenta
I le 2j. For I=0 eigenstates of four fermions in a single-j shell we show that
there is only one non-zero eigenvalue. We address these observations using the
nucleon pair approximation of the shell model and relate our results with a
number of currently interesting problems.Comment: a latex text file and 2 figures, to be publishe
Temporal and causal reasoning in deaf and hearing novice readers
Temporal and causal information in text are crucial in helping the reader form a coherent representation of a narrative. Deaf novice readers are generally poor at processing linguistic markers of causal/temporal information (i.e., connectives), but what is unclear is whether this is indicative of a more general deficit in reasoning about temporal/causal information. In Study 1, 10 deaf and 63 hearing children, matched for comprehension ability and age, were compared on a range of tasks tapping temporal/causal reasoning skills. In Study 2, 20 deaf and 32 hearing children, matched for age but not reading comprehension ability, were compared on revised versions of the tasks. The pattern of performance of the deaf was different from that of the hearing; they had difficulties when temporal and causal reasoning was text-based, but not when it was nonverbal, indicating that their global temporal/causal reasoning skills are comparable with those of their hearing counterparts
Polarity patterns of stress fibers
Stress fibers are contractile actomyosin bundles commonly observed in the
cytoskeleton of metazoan cells. The spatial profile of the polarity of actin
filaments inside contractile actomyosin bundles is either monotonic (graded) or
periodic (alternating). In the framework of linear irreversible thermodynamics,
we write the constitutive equations for a polar, active, elastic
one-dimensional medium. An analysis of the resulting equations for the dynamics
of polarity shows that the transition from graded to alternating polarity
patterns is a nonequilibrium Lifshitz point. Active contractility is a
necessary condition for the emergence of sarcomeric, alternating polarity
patterns.Comment: 5 pages, 3 figure
Classification of states of single- fermions with -pairing interaction
In this paper we show that a system of three fermions is exactly solvable for
the case of a single- in the presence of an angular momentum- pairing
interaction. On the basis of the solutions for this system, we obtain new sum
rules for six- symbols. It is also found that the "non-integer" eigenvalues
of three fermions with angular momentum around the maximum appear as
"non-integer" eigenvalues of four fermions when is around (or larger than)
and the Hamiltonian contains only an interaction between pairs of
fermions coupled to spin . This pattern is also found in
five and six fermion systems. A boson system with spin exhibits a similar
pattern.Comment: to be published in Physical Review
Contraction of cross-linked actomyosin bundles
Cross-linked actomyosin bundles retract when severed in vivo by laser
ablation, or when isolated from the cell and micromanipulated in vitro in the
presence of ATP. We identify the time scale for contraction as a viscoelastic
time tau, where the viscosity is due to (internal) protein friction. We obtain
an estimate of the order of magnitude of the contraction time tau ~ 10-100 s,
consistent with available experimental data for circumferential microfilament
bundles and stress fibers. Our results are supported by an exactly solvable,
hydrodynamic model of a retracting bundle as a cylinder of isotropic, active
matter, from which the order of magnitude of the active stress is estimated.Comment: To be published in Physical Biolog
The Influence of Word Characteristics on the Vocabulary of Children with Cochlear Implants
This is the author's accepted manuscript. The original publication is available at http://jdsde.oxfordjournals.org/search?fulltext=The+Influence+of+Word+Characteristics+on+the+Vocabulary+or+Children+With+Cochlear+Implants&submit=yes&x=9&y=4The goal of this study was to explore the effects of phonotactic probability, word length, word frequency, and neighborhood density on the words known by children with cochlear implants (CIs) varying in vocabulary outcomes in a retrospective analysis of a subset of data from a longitudinal study of hearing loss. Generalized linear mixed modeling was used to examine the effects of these word characteristics at three time points: pre-implant, post-implant, and longitudinal follow-up. Results showed a robust effect of neighborhood density across group and time, whereas the effect of frequency varied by time. Significant effects of phonotactic probability or word length were not detected. Taken together, these findings suggest that children with CIs may be able to use spoken language structure in a manner similar to their normal hearing counterparts, despite the differences in the quality of the input. The differences in the effects of phonotactic probability and word length imply a difficulty in initiating word learning and limited working memory ability in children with CIs
Swimming depth of migrating silver eels Anguilla japonica released at seamounts of the West Mariana Ridge, their estimated spawning sites
Five hormone-treated female Japanese silver eels Anguilla japonica were tagged with ultrasonic transmitters and released by submersible in the West Pacific at seamounts of the West Mariana Ridge, their supposed spawning grounds. Four eels were tracked for 60 to 423 min in the vicinity of the seamounts. They did not settle at the seamounts but swam at a mean speed of 0.37 m s-1 into open water above deep ground. Their mean swimming depth ranged from 81 to 172 m. Experiments suggest that pre-matured A. japonica migrate to their spawning grounds in temperate warm water and at shallow depths
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Reciprocal knock-in mice to investigate the functional redundancy of lamin B1 and lamin B2.
Lamins B1 and B2 (B-type lamins) have very similar sequences and are expressed ubiquitously. In addition, both Lmnb1- and Lmnb2-deficient mice die soon after birth with neuronal layering abnormalities in the cerebral cortex, a consequence of defective neuronal migration. The similarities in amino acid sequences, expression patterns, and knockout phenotypes raise the question of whether the two proteins have redundant functions. To investigate this topic, we generated "reciprocal knock-in mice"-mice that make lamin B2 from the Lmnb1 locus (Lmnb1(B2/B2)) and mice that make lamin B1 from the Lmnb2 locus (Lmnb2(B1/B1)). Lmnb1(B2/B2) mice produced increased amounts of lamin B2 but no lamin B1; they died soon after birth with neuronal layering abnormalities in the cerebral cortex. However, the defects in Lmnb1(B2/B2) mice were less severe than those in Lmnb1-knockout mice, indicating that increased amounts of lamin B2 partially ameliorate the abnormalities associated with lamin B1 deficiency. Similarly, increased amounts of lamin B1 in Lmnb2(B1/B1) mice did not prevent the neurodevelopmental defects elicited by lamin B2 deficiency. We conclude that lamins B1 and B2 have unique roles in the developing brain and that increased production of one B-type lamin does not fully complement loss of the other
Lowest Eigenvalues of Random Hamiltonians
In this paper we present results of the lowest eigenvalues of random
Hamiltonians for both fermion and boson systems. We show that an empirical
formula of evaluating the lowest eigenvalues of random Hamiltonians in terms of
energy centroids and widths of eigenvalues are applicable to many different
systems (except for boson systems). We improve the accuracy of the formula
by adding moments higher than two. We suggest another new formula to evaluate
the lowest eigenvalues for random matrices with large dimensions (20-5000).
These empirical formulas are shown to be applicable not only to the evaluation
of the lowest energy but also to the evaluation of excited energies of systems
under random two-body interactions
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