119 research outputs found
Testosterone Fluctuations in Young Men: The Difference Between Interacting With Like and Not-Like Others
The current study investigated young men\u27s testosterone level changes as a result of interacting with other men. Male participants (n = 84) were led to believe that a group they would be interacting with was either similar to them or not similar. The interaction was then one of two types: the other group members were inclusive, or the others excluded the participant during the group interaction. Participants provided saliva samples before and after the interaction. Results suggest that interacting with highly similar men increases circulating testosterone whereas interacting with highly dissimilar men actually lowers testosterone. The nature of the interaction was less important than similarity. Considering that testosterone surges may relate to attempts to gain status within one\u27s group, the results are interpreted as consistent with viewing hormonal changes as a mechanism to alter current behavioral propensities in ways that are likely to be most adaptive. Exploratory analyses suggest a methodologically interesting suppressor effect of the self-report items in predicting testosterone changes
On the Relationship Between the Critical Temperature and the London Penetration Depth in Layered Organic Superconductors
We present an analysis of previously published measurements of the London
penetration depth of layered organic superconductors. The predictions of the
BCS theory of superconductivity are shown to disagree with the measured zero
temperature, in plane, London penetration depth by up to two orders of
magnitude. We find that fluctuations in the phase of the superconducting order
parameter do not determine the superconducting critical temperature as the
critical temperature predicted for a Kosterlitz--Thouless transition is more
than an order of magnitude greater than is found experimentally for some
materials. This places constraints on theories of superconductivity in these
materials.Comment: 5 pages, 1 figur
Evidence for structural and electronic instabilities at intermediate temperatures in -(BEDT-TTF)X for X=Cu[N(CN)]Cl, Cu[N(CN)]Br and Cu(NCS): Implications for the phase diagram of these quasi-2D organic superconductors
We present high-resolution measurements of the coefficient of thermal
expansion of the quasi-twodimensional
(quasi-2D) salts -(BEDT-TTF)X with X = Cu(NCS), Cu[N(CN)]Br
and Cu[N(CN)]Cl. At intermediate temperatures (B), distinct anomalies
reminiscent of second-order phase transitions have been found at
K and 45 K for the superconducting X = Cu(NCS) and Cu[N(CN)]Br salts,
respectively. Most interestingly, we find that the signs of the uniaxial
pressure coefficients of are strictly anticorrelated with those of
. We propose that marks the transition to a spin-density-wave
(SDW) state forming on minor, quasi-1D parts of the Fermi surface. Our results
are compatible with two competing order parameters that form on disjunct
portions of the Fermi surface. At elevated temperatures (C), all compounds show
anomalies that can be identified with a kinetic, glass-like
transition where, below a characteristic temperature , disorder in the
orientational degrees of freedom of the terminal ethylene groups becomes frozen
in. We argue that the degree of disorder increases on going from the X =
Cu(NCS) to Cu[N(CN)]Br and the Cu[N(CN)]Cl salt. Our results
provide a natural explanation for the unusual time- and cooling-rate
dependencies of the ground-state properties in the hydrogenated and deuterated
Cu[N(CN)]Br salts reported in the literature.Comment: 22 pages, 7 figure
The Dependence of the Superconducting Transition Temperature of Organic Molecular Crystals on Intrinsically Non-Magnetic Disorder: a Signature of either Unconventional Superconductivity or Novel Local Magnetic Moment Formation
We give a theoretical analysis of published experimental studies of the
effects of impurities and disorder on the superconducting transition
temperature, T_c, of the organic molecular crystals kappa-ET_2X and beta-ET_2X
(where ET is bis(ethylenedithio)tetrathiafulvalene and X is an anion eg I_3).
The Abrikosov-Gorkov (AG) formula describes the suppression of T_c both by
magnetic impurities in singlet superconductors, including s-wave
superconductors and by non-magnetic impurities in a non-s-wave superconductor.
We show that various sources of disorder lead to the suppression of T_c as
described by the AG formula. This is confirmed by the excellent fit to the
data, the fact that these materials are in the clean limit and the excellent
agreement between the value of the interlayer hopping integral, t_perp,
calculated from this fit and the value of t_perp found from angular-dependant
magnetoresistance and quantum oscillation experiments. If the disorder is, as
seems most likely, non-magnetic then the pairing state cannot be s-wave. We
show that the cooling rate dependence of the magnetisation is inconsistent with
paramagnetic impurities. Triplet pairing is ruled out by several experiments.
If the disorder is non-magnetic then this implies that l>=2, in which case
Occam's razor suggests that d-wave pairing is realised. Given the proximity of
these materials to an antiferromagnetic Mott transition, it is possible that
the disorder leads to the formation of local magnetic moments via some novel
mechanism. Thus we conclude that either kappa-ET_2X and beta-ET_2X are d-wave
superconductors or else they display a novel mechanism for the formation of
localised moments. We suggest systematic experiments to differentiate between
these scenarios.Comment: 18 pages, 5 figure
Deciding what to replicate: a decision model for replication study selection under resource and knowledge constraints
Robust scientific knowledge is contingent upon replication of original findings. However, replicating researchers are constrained by resources, and will almost always have to choose one replication effort to focus on from a set of potential candidates. To select a candidate efficiently in these cases, we need methods for deciding which out of all candidates considered would be the most useful to replicate, given some overall goal researchers wish to achieve. In this article we assume that the overall goal researchers wish to achieve is to maximize the utility gained by conducting the replication study. We then propose a general rule for study selection in replication research based on the replication value of the set of claims considered for replication. The replication value of a claim is defined as the maximum expected utility we could gain by conducting a replication of the claim, and is a function of (a) the value of being certain about the claim, and (b) uncertainty about the claim based on current evidence. We formalize this definition in terms of a causal decision model, utilizing concepts from decision theory and causal graph modeling. We discuss the validity of using replication value as a measure of expected utility gain, and we suggest approaches for deriving quantitative estimates of replication value. Our goal in this article is not to define concrete guidelines for study selection, but to provide the necessary theoretical foundations on which such concrete guidelines could be built.Translational Abstract Replication-redoing a study using the same procedures-is an important part of checking the robustness of claims in the psychological literature. The practice of replicating original studies has been woefully devalued for many years, but this is now changing. Recent calls for improving the quality of research in psychology has generated a surge of interest in funding, conducting, and publishing replication studies. Because many studies have never been replicated, and researchers have limited time and money to perform replication studies, researchers must decide which studies are the most important to replicate. This way scientists learn the most, given limited resources. In this article, we lay out what it means to think about what is the most important thing to replicate, and we propose a general decision rule for picking a study to replicate. That rule depends on a concept we call replication value. Replication value is a function of the importance of the study, and how uncertain we are about the findings. In this article we explain how researchers can think precisely about the value of replication studies. We then discuss when and how it makes sense to use replication value as a measure of how valuable a replication study would be, and we discuss factors that funders, journals, or scientists could consider when determining how valuable a replication study is.Multivariate analysis of psychological dat
Low Temperature Penetration depth of \kappa-(ET)_2Cu[N(CN)_2]Br and \kappa-(ET)_2Cu(NCS)_2
We present high precision measurements of the penetration depth \lambda of
single crystals of \kappa-(ET)_2Cu[N(CN)2]Br and \kappa-(ET)_2Cu(NCS)_2 at
temperature down to 0.4 K. We find that, at low temperatures, the in-plane
penetration depth varies as a fractional power law, \lambda\sim T^1.5. W hilst
this may be taken as evidence for novel bose excitation processes, we show that
the data are also consistent with a quasi-linear variation of the superfluid
density, as is expected for a d-wave superconductor with impurities. Our data
for the interplane penetration depth show similar features and give a direct
measurement of the absolute value, \lambda(0)=100\pm 20 \mu m.Comment: 4 pages, 4 postscript figure
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