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On Nonregularized Estimation of Psychological Networks.
An important goal for psychological science is developing methods to characterize relationships between variables. Customary approaches use structural equation models to connect latent factors to a number of observed measurements, or test causal hypotheses between observed variables. More recently, regularized partial correlation networks have been proposed as an alternative approach for characterizing relationships among variables through off-diagonal elements in the precision matrix. While the graphical Lasso (glasso) has emerged as the default network estimation method, it was optimized in fields outside of psychology with very different needs, such as high dimensional data where the number of variables (p) exceeds the number of observations (n). In this article, we describe the glasso method in the context of the fields where it was developed, and then we demonstrate that the advantages of regularization diminish in settings where psychological networks are often fitted ( p≪n ). We first show that improved properties of the precision matrix, such as eigenvalue estimation, and predictive accuracy with cross-validation are not always appreciable. We then introduce nonregularized methods based on multiple regression and a nonparametric bootstrap strategy, after which we characterize performance with extensive simulations. Our results demonstrate that the nonregularized methods can be used to reduce the false-positive rate, compared to glasso, and they appear to provide consistent performance across sparsity levels, sample composition (p/n), and partial correlation size. We end by reviewing recent findings in the statistics literature that suggest alternative methods often have superior performance than glasso, as well as suggesting areas for future research in psychology. The nonregularized methods have been implemented in the R package GGMnonreg
First-principles analysis of spin-disorder resistivity of Fe and Ni
Spin-disorder resistivity of Fe and Ni and its temperature dependence are
analyzed using noncollinear density functional calculations within the
supercell method. Different models of thermal spin disorder are considered,
including the mean-field approximation and the nearest-neighbor Heisenberg
model. Spin-disorder resistivity is found to depend weakly on magnetic
short-range order. If the local moments are kept frozen at their
zero-temperature values, very good agreement with experiment is obtained for
Fe, but for Ni the resistivity at elevated temperatures is significantly
overestimated. Agreement with experiment for Fe is improved if the local
moments are iterated to self-consistency. The overestimation of the resistivity
for paramagnetic Ni is attributed to the reduction of the local moments down to
0.35 Bohr magnetons. Overall, the results suggest that low-energy spin
fluctuations in Fe and Ni are better viewed as classical rotations of local
moments rather than quantized spin fluctuations that would require an (S+1)/S
correction.Comment: 10 pages (RevTeX), 6 eps figure
"In this chambered tumulus were found cleft skulls ...": an assessment of the evidence for cranial trauma in the British Neolithic
Interpersonal violence is a powerful expression of human social interaction. Yet a consideration of violence in the past has done relatively little to inform our discussions of the British Neolithic. Here, we present the results of an examination of some 350 earlier Neolithic crania from mainly southern Britain. Of these, 31 show healed or unhealed injuries suggestive of interpersonal violence. We suggest a conservative estimate of 2% fatal cranial injuries, and 4 or 5% healed injuries. These data are used as a platform to discuss possible contexts for, and consequences of, violence. We argue that, regardless of its actual prevalance, the reality or the threat of interpersonal violence can have an important affect on both the behaviour of individuals and the structure of society
Explaining LIGO's observations via isolated binary evolution with natal kicks
We compare binary evolution models with different assumptions about
black-hole natal kicks to the first gravitational-wave observations performed
by the LIGO detectors. Our comparisons attempt to reconcile merger rate,
masses, spins, and spin-orbit misalignments of all current observations with
state-of-the-art formation scenarios of binary black holes formed in isolation.
We estimate that black holes (BHs) should receive natal kicks at birth of the
order of (50) km/s if tidal processes do (not) realign
stellar spins. Our estimate is driven by two simple factors. The natal kick
dispersion is bounded from above because large kicks disrupt too many
binaries (reducing the merger rate below the observed value). Conversely, the
natal kick distribution is bounded from below because modest kicks are needed
to produce a range of spin-orbit misalignments. A distribution of misalignments
increases our models' compatibility with LIGO's observations, if all BHs are
likely to have natal spins. Unlike related work which adopts a concrete BH
natal spin prescription, we explore a range of possible BH natal spin
distributions. Within the context of our models, for all of the choices of
used here and within the context of one simple fiducial parameterized
spin distribution, observations favor low BH natal spin.Comment: 19 pages, 14 figures, as published in PR
Accelerated Aging System for Prognostics of Power Semiconductor Devices
Prognostics is an engineering discipline that focuses on estimation of the health state of a component and the prediction of its remaining useful life (RUL) before failure. Health state estimation is based on actual conditions and it is fundamental for the prediction of RUL under anticipated future usage. Failure of electronic devices is of great concern as future aircraft will see an increase of electronics to drive and control safety-critical equipment throughout the aircraft. Therefore, development of prognostics solutions for electronics is of key importance. This paper presents an accelerated aging system for gate-controlled power transistors. This system allows for the understanding of the effects of failure mechanisms, and the identification of leading indicators of failure which are essential in the development of physics-based degradation models and RUL prediction. In particular, this system isolates electrical overstress from thermal overstress. Also, this system allows for a precise control of internal temperatures, enabling the exploration of intrinsic failure mechanisms not related to the device packaging. By controlling the temperature within safe operation levels of the device, accelerated aging is induced by electrical overstress only, avoiding the generation of thermal cycles. The temperature is controlled by active thermal-electric units. Several electrical and thermal signals are measured in-situ and recorded for further analysis in the identification of leading indicators of failures. This system, therefore, provides a unique capability in the exploration of different failure mechanisms and the identification of precursors of failure that can be used to provide a health management solution for electronic devices
Secure authorization, access control and data integrity in Bluetooth
The Bluetooth standard has a provision for mutual authentication of connecting devices but not their actual users and allows access control during connection setup only. We propose a user authorization and pairing (UAP) application, that has the ability to perform authentication and authorization of users using role based model. The pairing procedure, which exchanges link key between devices, is also performed as a part of the user authorization process. The integrity of the message is guaranteed by using message authentication codes. We also extend an attack on a short PIN during the pairing procedure for devices compliant with the Bluetooth specification version 1.1
PHENIX first measurement of the J/psi elliptic flow parameter v2 in Au+Au collisions at sqrt(sNN) = 200 GeV
Recent results indicate that the J/psi suppression pattern differs with
rapidity showing a larger suppression at forward rapidity. J/psi suppression
mechanisms based on energy density (such as color screening, interaction with
co-movers, etc.) predict the opposite trend. On the other hand, it is expected
that more c\bar{c} pairs should be available to form quarkonia at mid-rapidity
via recombination. Some models provide a way to differentiate J/psi production
from initially produced c\bar{c} pairs and final state recombination of
uncorrelated pairs, via the rapidity and transverse momentum dependence of the
elliptic flow (v2).
During 2007 data taking at RHIC, a large sample of Au+Au collisions at
sqrt(sNN)=200 GeV was collected. The statistics has been increased compared to
previous 2004 data set, thus allowing a more precise measurement of the J/psi
production at both mid and forward rapidity. Furthermore, the PHENIX experiment
benefited from the addition of a new detector, which improves the reaction
plane resolution and allows us to measure the J/psi v2. Comparing this
measurement to the positive D-mesons v2 (through non-photonic electron decays)
will help constraining the J/psi production mechanisms and getting a more
precise picture of the proportion of J/psi coming from direct production or
charm quark coalescence.
Details on how the J/psi v2 is measured at both rapidities are presented. The
J/psi v2 as a function of transverse momentum are compared to existing models.Comment: 4 pages, 3 figures, Quark Matter 2008 proceeding
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