8,628 research outputs found
Cosmological Constraints on Late-time Entropy Production
We investigate cosmological effects concerning the late-time entropy
production due to the decay of non-relativistic massive particles. The
thermalization process of neutrinos after the entropy production is properly
solved by using the Boltzmann equation. If a large entropy production takes
place at late time t 1 sec, it is found that a large fraction of
neutrinos cannot be thermalized. This fact loosens the tight constraint on the
reheating temperature T_R from the big bang nucleosynthesis and T_R could be as
low as 0.5 MeV. The influence on the large scale structure formation and cosmic
microwave background anisotropies is also discussed.Comment: 4 pages, using RevTeX and five postscript figures, comments added, to
appear in Phys. Rev. Let
Evidence for Uniform Coexistence of Ferromagnetism and Unconventional Superconductivity in UGe_2: A ^73Ge-NQR Study under Pressure
We report on the itinerant ferromagnetic superconductor UGe_2 through
^73Ge-NQR measurements under pressure (P). The P dependence of the NQR spectrum
signals a first-order transition from the low-temperature (T) and low-P
ferromagnetic phase (FM2) to high-T and high-P one (FM1) around a critical
pressure of P_x ~ 1.2 GPa. The superconductivity exhibiting a maximum value of
T_sc=0.7 K at P_x ~ 1.2 GPa, was found to take place in connection with the
P-induced first-order transition. The nuclear spin-lattice relaxation rate
1/T_1 has probed the ferromagnetic transition, exhibiting a peak at the Curie
temperature as well as a decrease without the coherence peak below T_sc. These
results reveal the uniformly coexistent phase of ferromagnetism and
unconventional superconductivity with a line-node gap. We remark on an intimate
interplay between the onset of superconductivity and the underlying electronic
state for the ferromagnetic phases.Comment: 8 pages, 9 figures. to appear in J. Phys. Soc. JPN, 74 No.2 (2005
Gapless Magnetic and Quasiparticle Excitations due to the Coexistence of Antiferromagnetism and Superconductivity in CeRhIn : A study of In-NQR under Pressure
We report systematic measurements of ac-susceptibility,
nuclear-quadrupole-resonance spectrum, and nuclear-spin-lattice-relaxation time
() on the pressure ()- induced heavy-fermion (HF) superconductor
CeRhIn. The temperature () dependence of at = 1.6 GPa has
revealed that antiferromagnetism (AFM) and superconductivity (SC) coexist
microscopically, exhibiting the respective transition at K and
= 0.9 K. It is demonstrated that SC does not yield any trace of gap
opening in low-lying excitations below K, but K, followed by a = const law. These results point to the
unconventional characteristics of SC coexisting with AFM. We highlight that
both of the results deserve theoretical work on the gapless nature in low-lying
excitation spectrum due to the coexistence of AFM and SC and the lack of the
mean-field regime below K.Comment: 4pages,5figures,revised versio
A Study of Gaussianity in CMB band maps
The detection of non-Gaussianity in the CMB data would rule out a number of
inflationary models. A null detection of non-Gaussianity, instead, would
exclude alternative models for the early universe. Thus, a detection or
non-detection of primordial non-Gaussianity in the CMB data is crucial to
discriminate among inflationary models, and to test alternative scenarios.
However, there are various non-cosmological sources of non-Gaussianity. This
makes important to employ different indicators in order to detect distinct
forms of non-Gaussianity in CMB data. Recently, we proposed two new indicators
to measure deviation from Gaussianity on large angular scales, and used them to
study the Gaussianity of the raw band WMAP maps with and without the KQ75 mask.
Here we extend this work by using these indicators to perform similar analyses
of deviation from Gaussianity of the foreground-reduced Q, V, and W band maps.
We show that there is a significant deviation from Gaussianity in the
considered full-sky maps, which is reduced to a level consistent with
Gaussianity when the KQ75 mask is employed.Comment: 5 pages, 2 PS figures, uses ws-ijmpd.cls ; to be published in the
International Journal of Modern Physics
Evolution in Surface Morphology of Epitaxial Graphene Layers on SiC Induced by Controlled Structural Strain
The evolution in the surface morphology of epitaxial graphene films and
6H-SiC(0001) substrates is studied by electron channeling contrast imaging.
Whereas film thickness is determined by growth temperature only, increasing
growth times at constant temperature affect both internal stress and film
morphology. Annealing times in excess of 8-10 minutes lead to an increase in
the mean square roughness of SiC step edges to which graphene films are pinned,
resulting in compressively stressed films at room temperature. Shorter
annealing times produce minimal changes in the morphology of the terrace edges
and result in nearly stress-free films upon cooling to room temperature.Comment: 3 pages, 2 figures. Applied Physics Letters 93 (2008), 19191
New Superconducting and Magnetic Phases Emerge on the Verge of Antiferromagnetism in CeIn
We report the discovery of new superconducting and novel magnetic phases in
CeIn on the verge of antiferromagnetism (AFM) under pressure () through
the In-nuclear quadrupole resonance (NQR) measurements. We have found a
-induced phase separation of AFM and paramagnetism (PM) without any trace
for a quantum phase transition in CeIn. A new type of superconductivity
(SC) was found in GPa to coexist with AFM that is magnetically
separated from PM where the heavy fermion SC takes place. We propose that the
magnetic excitations such as spin-density fluctuations induced by the
first-order magnetic phase transition might mediate attractive interaction to
form Cooper pairs.Comment: 4 pages, 4 EPS figures, submitted to J. Phys. Soc. Jp
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A Genetic Analysis of Cichlid Scale Morphology
Epidermal appendages are found on every vertebrate this world has to offer. In fish, these are commonly represented by scales. While we have a solid grasp of how scales develop, little is known about the underlying genetic mechanisms behind these phenotypic changes. Using two species of African cichlids (Labeotropheus fuelleborni and Tropheops “red cheek”) with varying scale phenotypes, we sought to examine their F2 hybrid offspring and statistically link the responsible genetic elements to their respective parental phenotypes through Quantitative Loci Trait (QTL) analysis.
Scales were removed from six different locations across the midline of each individual. Then, numerous traits on each scale were measured, and these values were used in the QTL analysis. 42 significant QTL were identified, with multiple QTL intervals possessing promising candidate genes. These genes include: fgfr1b, efna5a, TGIF1, eIF6, and col1a1a. Previous studies have implicated these particular genes and gene families to play important roles in scale and placode development. However, they represent the minority of QTL intervals discovered, providing direction for future research towards the other QTL intervals represented by this study
Non-destructive imaging of an individual protein
The mode of action of proteins is to a large extent given by their ability to
adopt different conformations. This is why imaging single biomolecules at
atomic resolution is one of the ultimate goals of biophysics and structural
biology. The existing protein database has emerged from X-ray crystallography,
NMR or cryo-TEM investigations. However, these tools all require averaging over
a large number of proteins and thus over different conformations. This of
course results in the loss of structural information. Likewise it has been
shown that even the emergent X-FEL technique will not get away without
averaging over a large quantity of molecules. Here we report the first
recordings of a protein at sub-nanometer resolution obtained from one
individual ferritin by means of low-energy electron holography. One single
protein could be imaged for an extended period of time without any sign of
radiation damage. Since ferritin exhibits an iron core, the holographic
reconstructions could also be cross-validated against TEM images of the very
same molecule by imaging the iron cluster inside the molecule while the protein
shell is decomposed
Coexistence of Superconductivity and Antiferromagnetism in Heavy-Fermion Superconductor CeCu_{2}(Si_{1-x}Ge_{x})_{2} Probed by Cu-NQR --A Test Case for the SO(5) Theory--
We report on the basis of Cu-NQR measurements that superconductivity (SC) and
antiferromagnetism (AF) coexist on a microscopic level in
CeCu_{2}(Si_{1-x}Ge_{x})_{2}, once a tiny amount of 1%Ge (x = 0.01) is
substituted for Si. This coexistence arises because Ge substitution expands the
unit-cell volume in nearly homogeneous CeCu2Si2 where the SC coexists with
slowly fluctuating magnetic waves. We propose that the underlying exotic phases
of SC and AF in either nearly homogeneous or slightly Ge substituted CeCu2Si2
are accountable based on the SO(5) theory that unifies the SC and AF. We
suggest that the mechanism of the SC and AF is common in CeCu2Si2.Comment: 7 pages with 6 figures embedded in the text. To be published in J.
Phys. Condens. Matter, 200
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