10,496 research outputs found
Heat transport study of the spin liquid candidate 1T-TaS2
We present the ultra-low-temperature thermal conductivity measurements on
single crystals of the prototypical charge-density-wave material 1-TaS,
which was recently argued to be a candidate for quantum spin liquid. Our
experiments show that the residual linear term of thermal conductivity at zero
field is essentially zero, within the experimental accuracy. Furthermore, the
thermal conductivity is found to be insensitive to the magnetic field up to 9
T. These results clearly demonstrate the absence of itinerant magnetic
excitations with fermionic statistics in bulk 1-TaS and, thus, put a
strong constraint on the theories of the ground state of this material.Comment: 5 pages, 3 figure
The Effect of Social Support on Social Media on Asian College Students\u27 Intention to Participate in Physical Activity in the United States
Background: College students who identified themselves as Asians in the United States (i.e., Asian college students) are facing health inequalities and engaging in increasingly low levels of physical activity (PA). Although social support was found to be effective in increasing college students\u27 PA and social media is an important channel for social support for Asian students, few studies have explored how to provide social support through social media interventions to promote Asian students\u27 PA level. Thus, this study aimed to explore the effects of social support on social media on Asian college students\u27 intention to participate in PA based on the theory of planned behavior.
Methods: We conducted an online Qualtrics survey among all undergraduate students at a university on the West Coast of the United States. Among 936 respondents, 337 (36%) were Asian college students. Descriptive analysis, regression models, and mediating effect tests were performed using SPSS 28.
Results: For Asian students, social support on social media has both direct effects and indirect effects through perceived behavioral control (PBC) on their intention to participate in PA.
Conclusion: Future interventions could consider encouraging Asian students to provide support to each other and form support groups using social media to increase their PBC
Synthesis and evaluation of a novel pyrenyl-appended triazole-based thiacalix[4]arene as a fluorescent sensor for Ag+ ion
New fluorescent chemosensors 1,3-alternate-1 and 2 with pyrenyl-appended triazole-based on thiacalix[4]arene were synthesized. The fluorescence spectra changes suggested that chemosensors 1 and 2 are highly selective for Ag+ over other metal ions by enhancing the monomer emission of pyrene in neutral solution. However, other heavy metal ions, such as Cu2+, and Hg2+ quench both the monomer and excimer emission of pyrene acutely. The 1H NMR results indicated that Ag+ can be selectively recognized by the triazole moieties on the receptors 1 and 2 together with the ionophoricity cavity formed by the two inverted benzene rings and sulfur atoms of the thiacalix[4]arene
Probabilistic reconstruction of Dark Matter fields from biased tracers using diffusion models
Galaxies are biased tracers of the underlying cosmic web, which is dominated
by dark matter components that cannot be directly observed. The relationship
between dark matter density fields and galaxy distributions can be sensitive to
assumptions in cosmology and astrophysical processes embedded in the galaxy
formation models, that remain uncertain in many aspects. Based on
state-of-the-art galaxy formation simulation suites with varied cosmological
parameters and sub-grid astrophysics, we develop a diffusion generative model
to predict the unbiased posterior distribution of the underlying dark matter
fields from the given stellar mass fields, while being able to marginalize over
the uncertainties in cosmology and galaxy formation
CO2 Laser-Induced Growth of Epitaxial Graphene on 6H-SiC(0001)
The thermal decomposition of SiC surface provides, perhaps, the most
promising method for the epitaxial growth of graphene on a material useful in
the electronics platform. Currently, efforts are focused on a reliable method
for the growth of large-area, low-strain epitaxial graphene that is still
lacking. We report here a novel method for the fast, single-step epitaxial
growth of large-area homogeneous graphene film on the surface of SiC(0001)
using an infrared CO2 laser (10.6 {\mu}m) as the heating source. Apart from
enabling extreme heating and cooling rates, which can control the stacking
order of epitaxial graphene, this method is cost-effective in that it does not
necessitate SiC pre-treatment and/or high vacuum, it operates at low
temperature and proceeds in the second time scale, thus providing a green
solution to EG fabrication and a means to engineering graphene patterns on SiC
by focused laser beams. Uniform, low-strain graphene film is demonstrated by
scanning electron microscopy and x-ray photoelectron, secondary ion mass, and
Raman spectroscopies. Scalability to industrial level of the method described
here appears to be realistic, in view of the high rate of CO2-laser induced
graphene growth and the lack of strict sample-environment conditions.Comment: 32 pages, 5 figures, includes Supporting Informatio
Critical change in the Fermi surface of iron arsenic superconductors at the onset of superconductivity
The phase diagram of a correlated material is the result of a complex
interplay between several degrees of freedom, providing a map of the material's
behavior. One can understand (and ultimately control) the material's ground
state by associating features and regions of the phase diagram, with specific
physical events or underlying quantum mechanical properties. The phase diagram
of the newly discovered iron arsenic high temperature superconductors is
particularly rich and interesting. In the AE(Fe1-xTx)2As2 class (AE being Ca,
Sr, Ba, T being transition metals), the simultaneous structural/magnetic phase
transition that occurs at elevated temperature in the undoped material, splits
and is suppressed by carrier doping, the suppression being complete around
optimal doping. A dome of superconductivity exists with apparent equal ease in
the orthorhombic / antiferromagnetic (AFM) state as well as in the tetragonal
state with no long range magnetic order. The question then is what determines
the critical doping at which superconductivity emerges, if the AFM order is
fully suppressed only at higher doping values. Here we report evidence from
angle resolved photoemission spectroscopy (ARPES) that critical changes in the
Fermi surface (FS) occur at the doping level that marks the onset of
superconductivity. The presence of the AFM order leads to a reconstruction of
the electronic structure, most significantly the appearance of the small hole
pockets at the Fermi level. These hole pockets vanish, i. e. undergo a Lifshitz
transition, at the onset of superconductivity. Superconductivity and magnetism
are competing states in the iron arsenic superconductors. In the presence of
the hole pockets superconductivity is fully suppressed, while in their absence
the two states can coexist.Comment: Updated version accepted in Nature Physic
Abrupt Emergence of Pressure-Induced Superconductivity of 34 K in SrFe2As2: A Resistivity Study under Pressure
We report resistivity measurement under pressure in single crystals of
SrFe_2As_2, which is one of the parent materials of Fe-based superconductors.
The structural and antiferromagnetic (AFM) transition of T_0 = 198 K at ambient
pressure is suppressed under pressure, and the ordered phase disappears above
P_c ~ 3.6-3.7 GPa. Superconductivity with a sharp transition appears
accompanied by the suppression of the AFM state. T_c exhibits a maximum of 34.1
K, which is realized close to the phase boundary at P_c. This T_c is the
highest among those of the stoichiometric Fe-based superconductors.Comment: 4 pages, 4 figures, to be published in J. Phys. Soc. Jpn. 78 No.1
(2009
Recognition-mediated hydrogel swelling controlled by interaction with a negative thermoresponsive LCST polymer
Most polymeric thermoresponsive hydrogels contract upon heating beyond the lower critical solution temperature (LCST) of the polymers used. Herein, we report a supramolecular hydrogel system that shows the opposite temperature dependence. When the non-thermosesponsive hydrogel NaphtGel, containing dialkoxynaphthalene guest molecules, becomes complexed with the tetra cationic macrocyclic host CBPQT4+, swelling occurred as a result of host–guest complex formation leading to charge repulsion between the host units, as well as an osmotic contribution of chloride counter-ions embedded in the network. The immersion of NaphtGel in a solution of poly(N-isopropylacrylamide) with tetrathiafulvalene (TTF) end groups complexed with CBPQT4+ induced positive thermoresponsive behaviour. The LCST-induced dethreading of the polymer-based pseudorotaxane upon heating led to transfer of the CBPQT4+ host and a concomitant swelling of NaphtGel. Subsequent cooling led to reformation of the TTF-based host–guest complexes in solution and contraction of the hydrogel
Resonant dipolar collisions of ultracold molecules induced by microwave dressing
We demonstrate microwave dressing on ultracold, fermionic
NaK ground-state molecules and observe resonant dipolar
collisions with cross sections exceeding three times the -wave unitarity
limit. The origin of these collisions is the resonant alignment of the
approaching molecules' dipoles along the intermolecular axis, which leads to
strong attraction. We explain our observations with a conceptually simple
two-state picture based on the Condon approximation. Furthermore, we perform
coupled-channels calculations that agree well with the experimentally observed
collision rates. While collisions are observed here as laser-induced loss,
microwave dressing on chemically stable molecules trapped in box potentials may
enable the creation of strongly interacting dipolar gases of molecules.Comment: 6 pages, 4 figure
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