1,719 research outputs found
Violation of critical universality at the antiferromagnetic phase transition of YbRh2Si2
We report on precise low-temperature specific-heat measurements, C(T), of
YbRh2Si2 in the vicinity of the antiferromagnetic phase transition on a single
crystal of superior quality (RRR 150). We observe a very sharp peak at T_N=72mK
with absolute values as high as C/T=8J/molK^2. A detailed analysis of the
critical exponent \alpha around T_N reveals \alpha=0.38 which differs
significantly from those of the conventional universality classes in the
Ginzburg-Landau theory, where \alpha<0.11. Thermal-expansion measurements
corroborate this large positive critical exponent. These results provide
insight into the nature of the critical magnetic fluctuations at a
temperature-driven phase transition close to a quantum critical point.Comment: Accepted for PR
Effect of chemical disorder on NiMnSb investigated by Appearance Potential Spectroscopy: a theoretical study
The half-Heusler alloy NiMnSb is one of the local-moment ferromagnets with
unique properties for future applications. Band structure calculations predict
exclusively majority bands at the Fermi level, thus indicating {100%} spin
polarization there. As one thinks about applications and the design of
functional materials, the influence of chemical disorder in these materials
must be considered. The magnetization, spin polarization, and electronic
structure are expected to be sensitive to structural and stoichiometric
changes. In this contribution, we report on an investigation of the
spin-dependent electronic structure of NiMnSb. We studied the influence of
chemical disorder on the unoccupied electronic density of states by use of the
ab-initio Coherent Potential Approximation method. The theoretical analysis is
discussed along with corresponding spin-resolved Appearance Potential
Spectroscopy measurements. Our theoretical approach describes the spectra as
the fully-relativistic self-convolution of the matrix-element weighted,
orbitally resolved density of states.Comment: JPD submitte
Trolling in asynchronous computer-mediated communication: From user discussions to academic definitions
Whilst computer-mediated communication (CMC) can benefit users by providing quick and easy communication between those separated by time and space, it can also provide varying degrees of anonymity that may encourage a sense of impunity and freedom from being held accountable for
inappropriate online behaviour. As such, CMC is a fertile ground for studying impoliteness, whether it occurs in response to perceived threat (flaming), or as an end in its own right (trolling). Currently, first and secondorder
definitions of terms such as im/politeness (Brown and Levinson 1987; Bousfield 2008; Culpeper 2008; Terkourafi 2008), in-civility (Lakoff 2005), rudeness (Beebe 1995, Kienpointner 1997, 2008), and etiquette (Coulmas 1992), are subject to much discussion and debate, yet the CMC
phenomenon of trolling is not adequately captured by any of these terms. Following Bousfield (in press), Culpeper (2010) and others, this paper suggests that a definition of trolling should be informed first and foremost
by user discussions. Taking examples from a 172-million-word, asynchronous CMC corpus, four interrelated conditions of aggression, deception, disruption, and success are discussed. Finally, a working definition of trolling
is presented
Study protocol: asking questions about alcohol in pregnancy (AQUA): a longitudinal cohort study of fetal effects of low to moderate alcohol exposure
Despite extensive research, a direct correlation between low to moderate prenatal alcohol exposure (PAE) and Fetal Alcohol Spectrum Disorders has been elusive. Conflicting results are attributed to a lack of accurate and detailed data on PAE and incomplete information on contributing factors. The public health effectiveness of policies recommending complete abstinence from alcohol during pregnancy is challenged by the high frequency of unplanned pregnancies, where many women consumed some alcohol prior to pregnancy recognition. There is a need for research evidence emphasizing timing and dosage of PAE and its effects on child development
Electron-correlation effects in appearance-potential spectra of Ni
Spin-resolved and temperature-dependent appearance-potential spectra of
ferromagnetic Nickel are measured and analyzed theoretically. The Lander
self-convolution model which relates the line shape to the unoccupied part of
the local density of states turns out to be insufficient. Electron correlations
and orbitally resolved transition-matrix elements are shown to be essential for
a quantitative agreement between experiment and theory.Comment: LaTeX, 6 pages, 2 eps figures included, Phys. Rev. B (in press
Offering fragile X syndrome carrier screening: a prospective mixed-methods observational study comparing carrier screening of pregnant and non-pregnant women in the general population
Article focus▪ This article is a protocol of a study that involves offering fragile X syndrome carrier screening to pregnant and non-pregnant women in the general population. We are undertaking a programme evaluation approach using mixed methods to collect data about informed decisionmaking and predictors of test uptake, with a focus on psychosocial measures. We are also undertaking an economic appraisal.Key messages▪ Carrier screening for fragile X syndrome is the subject of debate because of concerns around education and counselling for this complex conditionand the potential for psychosocial harms. ▪ This study will inform policy and practice in the area of population carrier screening by examining psychosocial aspects of screening, including informed decision-making; models of screening, through antenatal care or other access points and health economics of carrier screening for fragile X syndrome.Strengths and limitations of this study▪ This study seeks to recruit 1000 women in total. This large sample size will give us sufficient power to address the aims of the study.▪ Collecting quantitative and qualitative data will provide a more in-depth picture of screening for fragile X syndrome.▪ A limitation of the study is that the data on models of screening may not be applicable to other countries that have different healthcare systems.</div
Behavior of the Quantum Critical Point and the Fermi-liquid Domain in the Heavy Fermion Superconductor CeCoIn5 studied by resistivity
We report detailed very low temperature resistivity measurements on the heavy
fermion compounds Ce_{1-x}La_{x}CoIn5 (x=0 and x=0.01), with current applied in
two crystallographic directions [100] (basal plane) and [001] (perpendicular to
the basal plane) under magnetic field applied in the [001] or [011] direction.
We found a Fermi liquid (\rho \propto T^{2}) ground state, in all cases, for
fields above the superconducting upper critical field. We discuss the possible
location of a field induced quantum critical point with respect to Hc2(0), and
compare our measurements with the previous reports in order to give a clear
picture of the experimental status on this long debated issue.Comment: 17 pages, 7 figures accepted for publication in JPS
Phase behavior and material properties of hollow nanoparticles
Effective pair potentials for hollow nanoparticles like the ones made from
carbon (fullerenes) or metal dichalcogenides (inorganic fullerenes) consist of
a hard core repulsion and a deep, but short-ranged, van der Waals attraction.
We investigate them for single- and multi-walled nanoparticles and show that in
both cases, in the limit of large radii the interaction range scales inversely
with the radius, , while the well depth scales linearly with . We predict
the values of the radius and the wall thickness at which the gas-liquid
coexistence disappears from the phase diagram. We also discuss unusual material
properties of the solid, which include a large heat of sublimation and a small
surface energy.Comment: Revtex, 13 pages with 8 Postscript files included, submitted to Phys.
Rev.
Family memories in the home: contrasting physical and digital mementos
We carried out fieldwork to characterise and compare physical and digital mementos in the home. Physical mementos are highly valued, heterogeneous and support different types of recollection. Contrary to expectations, we found physical mementos are not purely representational, and can involve appropriating common objects and more idiosyncratic forms. In contrast, digital mementos were initially perceived as less valuable, although participants later reconsidered this. Digital mementos were somewhat limited in function and expression, largely involving representational photos and videos, and infrequently accessed. We explain these digital limitations and conclude with design guidelines for digital mementos, including better techniques for accessing and integrating these into everyday life, allowing them to acquire the symbolic associations and lasting value that characterise their physical counterparts
Evolution of Quantum Criticality in CeNi_{9-x}Cu_xGe_4
Crystal structure, specific heat, thermal expansion, magnetic susceptibility
and electrical resistivity studies of the heavy fermion system
CeNi_{9-x}Cu_xGe_4 (0 <= x <= 1) reveal a continuous tuning of the ground state
by Ni/Cu substitution from an effectively fourfold degenerate non-magnetic
Kondo ground state of CeNi_9Ge_4 (with pronounced non-Fermi-liquid features)
towards a magnetically ordered, effectively twofold degenerate ground state in
CeNi_8CuGe_4 with T_N = 175 +- 5 mK. Quantum critical behavior, C/T ~ \chi ~
-ln(T), is observed for x about 0.4. Hitherto, CeNi_{9-x}Cu_xGe_4 represents
the first system where a substitution-driven quantum phase transition is
connected not only with changes of the relative strength of Kondo effect and
RKKY interaction, but also with a reduction of the effective crystal field
ground state degeneracy.Comment: 15 pages, 9 figure
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