4,824 research outputs found
A Critique of Current Magnetic-Accretion Models for Classical T-Tauri Stars
Current magnetic-accretion models for classical T-Tauri stars rely on a
strong, dipolar magnetic field of stellar origin to funnel the disk material
onto the star, and assume a steady-state. In this paper, I critically examine
the physical basis of these models in light of the observational evidence and
our knowledge of magnetic fields in low-mass stars, and find it lacking.
I also argue that magnetic accretion onto these stars is inherently a
time-dependent problem, and that a steady-state is not warranted.
Finally, directions for future work towards fully-consistent models are
pointed out.Comment: 2 figure
Concordant cues in faces and voices: testing the backup signal hypothesis
Information from faces and voices combines to provide multimodal signals about a person. Faces and voices may offer redundant, overlapping (backup signals), or complementary information (multiple messages). This article reports two experiments which investigated the extent to which faces and voices deliver concordant information about dimensions of fitness and quality. In Experiment 1, participants rated faces and voices on scales for masculinity/femininity, age, health, height, and weight. The results showed that people make similar judgments from faces and voices, with particularly strong correlations for masculinity/femininity, health, and height. If, as these results suggest, faces and voices constitute backup signals for various dimensions, it is hypothetically possible that people would be able to accurately match novel faces and voices for identity. However, previous investigations into novel face–voice matching offer contradictory results. In Experiment 2, participants saw a face and heard a voice and were required to decide whether the face and voice belonged to the same person. Matching accuracy was significantly above chance level, suggesting that judgments made independently from faces and voices are sufficiently similar that people can match the two. Both sets of results were analyzed using multilevel modeling and are interpreted as being consistent with the backup signal hypothesis
High-Dimensional Inference with the generalized Hopfield Model: Principal Component Analysis and Corrections
We consider the problem of inferring the interactions between a set of N
binary variables from the knowledge of their frequencies and pairwise
correlations. The inference framework is based on the Hopfield model, a special
case of the Ising model where the interaction matrix is defined through a set
of patterns in the variable space, and is of rank much smaller than N. We show
that Maximum Lik elihood inference is deeply related to Principal Component
Analysis when the amp litude of the pattern components, xi, is negligible
compared to N^1/2. Using techniques from statistical mechanics, we calculate
the corrections to the patterns to the first order in xi/N^1/2. We stress that
it is important to generalize the Hopfield model and include both attractive
and repulsive patterns, to correctly infer networks with sparse and strong
interactions. We present a simple geometrical criterion to decide how many
attractive and repulsive patterns should be considered as a function of the
sampling noise. We moreover discuss how many sampled configurations are
required for a good inference, as a function of the system size, N and of the
amplitude, xi. The inference approach is illustrated on synthetic and
biological data.Comment: Physical Review E: Statistical, Nonlinear, and Soft Matter Physics
(2011) to appea
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Results of an aqueous source term model for a radiological risk assessment of the Drigg LLW Site, U.K.
A radionuclide source term model has been developed which simulates the biogeochemical evolution of the Drigg low level waste (LLW) disposal site. The DRINK (DRIgg Near field Kinetic) model provides data regarding radionuclide concentrations in groundwater over a period of 100,000 years, which are used as input to assessment calculations for a groundwater pathway. The DRINK model also provides input to human intrusion and gaseous assessment calculations through simulation of the solid radionuclide inventory. These calculations are being used to support the Drigg post closure safety case. The DRINK model considers the coupled interaction of the effects of fluid flow, microbiology, corrosion, chemical reaction, sorption and radioactive decay. It represents the first direct use of a mechanistic reaction-transport model in risk assessment calculations
IR upgrade with quadrupoles first and dipoles first
We review recent work on the LHC IR upgrades by the US-LARP collaboration. There are several optics designs under consideration – each design differs in the potential luminosity reach, accelerator physics, operational and technical challenges etc. Here we consider two main issues: (i) the likely benefits of moving the IR magnets closer to the IP for both quadrupole first and dipole first designs and (ii) the impact of beam-beam interactions in the two designs. We conclude with a summary of accelerator physics parameters for the two designs
4-(3-Azaniumylpropyl)morpholin-4-ium chloride hydrogen oxalate: An unusual example of a dication with different counter-anions
© 2014 International Union of Crystallography. The mixed organic-inorganic title salt, C7H18N2O2+·C2HO4-·Cl-, forms an assembly of ionic components which are stabilized through a series of hydrogen bonds and charge-assisted intermolecular interactions. The title assembly crystallizes in the monoclinic C2/c space group with Z = 8. The asymmetric unit consists of a 4-(3-azaniumylpropyl)morpholin-4-ium dication, a hydrogen oxalate counter-anion and an inorganic chloride counter-anion. The organic cations and anions are connected through a network of N - H⋯O, O - H⋯O and C - H⋯O hydrogen bonds, forming several intermolecular rings that can be described by the graph-set notations R33(13), R21(5), R12(5), R21(6), R23(6), R22(8) and R33(9). The 4-(3-azaniumylpropyl)morpholin-4-ium dications are interconnected through N - H⋯O hydrogen bonds, forming C(9) chains that run diagonally along the ab face. Furthermore, the hydrogen oxalate anions are interconnected via O - H⋯O hydrogen bonds, forming head-to-tail C(5) chains along the crystallographic b axis. The two types of chains are linked through additional N - H⋯O and O - H⋯O hydrogen bonds, and the hydrogen oxalate chains are sandwiched by the 4-(3-azaniumylpropyl)morpholin-4-ium chains, forming organic layers that are separated by the chloride anions. Finally, the layered three-dimensional structure is stabilized via intermolecular N - H⋯Cl and C - H⋯Cl interactions
The Large and Small Scale Structures of Dust in the Star-Forming Perseus Molecular Cloud
We present an analysis of ~3.5 square degrees of submillimetre continuum and
extinction data of the Perseus molecular cloud. We identify 58 clumps in the
submillimetre map and we identify 39 structures (`cores') and 11 associations
of structures (`super cores') in the extinction map. The cumulative mass
distributions of the submillimetre clumps and extinction cores have steep
slopes (alpha ~ 2 and 1.5 - 2 respectively), steeper than the Salpeter IMF
(alpha = 1.35), while the distribution of extinction super cores has a shallow
slope (alpha ~ 1). Most of the submillimetre clumps are well fit by stable
Bonnor-Ebert spheres with 10K < T < 19K and 5.5 < log_10(P_ext/k) < 6.0. The
clumps are found only in the highest column density regions (A_V > 5 - 7 mag),
although Bonnor-Ebert models suggest that we should have been able to detect
them at lower column densities if they exist. These observations provide a
stronger case for an extinction threshold than that found in analysis of less
sensitive observations of the Ophiuchus molecular cloud. The relationship
between submillimetre clumps and their parent extinction core has been
analyzed. The submillimetre clumps tend to lie offset from the larger
extinction peaks, suggesting the clumps formed via an external triggering
event, consistent with previous observations.Comment: 38 pages, 12 figures, accepted by Astrophysical Journal slight
changes to original due to a slight 3" error in the coordinates of the SCUBA
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Conceptual design of a nonscaling fixed field alternating gradient accelerator for protons and carbon ions for charged particle therapy
Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.The conceptual design for a nonscaling fixed field alternating gradient accelerator suitable for charged particle therapy (the use of protons and other light ions to treat some forms of cancer) is described.EPSR
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