685 research outputs found
Gamow-Teller sum rule in relativistic nuclear models
Relativistic corrections are investigated to the Gamow-Teller(GT) sum rule
with respect to the difference between the and transition
strengths in nuclei. Since the sum rule requires the complete set of the
nuclear states, the relativistic corrections come from the anti-nucleon degrees
of freedom. In the relativistic mean field approximation, the total GT
strengths carried by the nucleon sector is quenched by about 12% in nuclear
matter, while by about 8% in finite nuclei, compared to the sum rule value. The
coupling between the particle-hole states with the nucleon-antinucleon states
is also discussed with the relativistic random phase approximation, where the
divergence of the response function is renormalized with use of the counter
terms in the Lagrangian. It is shown that the approximation to neglect the
divergence, like the no-sea approximation extensively used so far, is
unphysical, from the sum-rule point of view.Comment: 12 pages, Brief review for Mod. Phys. Lett. A, using ws-mpla.cl
Magnetic reconnection during collisionless, stressed, X-point collapse using Particle-in-Cell simulation
Two cases of weakly and strongly stressed X-point collapse were considered.
Here descriptors weakly and strongly refer to 20 % and 124 % unidirectional
spatial compression of the X-point, respectively. In the weakly stressed case,
the reconnection rate, defined as the out-of-plane electric field in the
X-point (the magnetic null) normalised by the product of external magnetic
field and Alfv\'en speeds, peaks at 0.11, with its average over 1.25 Alfv\'en
times being 0.04. Electron energy distribution in the current sheet, at the
high energy end of the spectrum, shows a power law distribution with the index
varying in time, attaining a maximal value of -4.1 at the final simulation time
step (1.25 Alfv\'en times). In the strongly stressed case, magnetic
reconnection peak occurs 3.4 times faster and is more efficient. The peak
reconnection rate now attains value 2.5, with the average reconnection rate
over 1.25 Alfv\'en times being 0.5. The power law energy spectrum for the
electrons in the current sheet attains now a steeper index of -5.5, a value
close to the ones observed in the vicinity of X-type region in the Earth's
magneto-tail. Within about one Alfv\'en time, 2% and 20% of the initial
magnteic energy is converted into heat and accelerated particle energy in the
case of weak and strong stress, respectively. In the both cases, during the
peak of the reconnection, the quadruple out-of-plane magnetic field is
generated, hinting possibly to the Hall regime of the reconnection. These
results strongly suggest the importance of the collionless, stressed X-point
collapse as a possible contributing factor to the solution of the solar coronal
heating problem or more generally, as an efficient mechanism of converting
magnetic energy into heat and super-thermal particle energy.Comment: Final Accepted Version (Physics of Plasmas in Press 2007
The Gamow-Teller States in Relativistic Nuclear Models
The Gamow-Teller(GT) states are investigated in relativistic models. The
Landau-Migdal(LM) parameter is introduced in the Lagrangian as a contact term
with the pseudo-vector coupling. In the relativistic model the total GT
strength in the nucleon space is quenched by about 12% in nuclear matter and by
about 6% in finite nuclei, compared with the one of the Ikeda-Fujii-Fujita sum
rule. The quenched amount is taken by nucleon-antinucleon excitations in the
time-like region. Because of the quenching, the relativistic model requires a
larger value of the LM parameter than non-relativistic models in describing the
excitation energy of the GT state. The Pauli blocking terms are not important
for the description of the GT states.Comment: REVTeX4, no figure
Spontaneous breaking of continuous translational invariance
Unbroken continuous translational invariance is often taken as a basic
assumption in discussions of spontaneous symmetry breaking (SSB), which singles
out SSB of translational invariance itself as an exceptional case. We present a
framework which allows us to treat translational invariance on the same footing
as other symmetries. It is shown that existing theorems on SSB can be
straightforwardly extended to this general case. As a concrete application, we
analyze the Nambu-Goldstone modes in a (ferromagnetic) supersolid. We prove on
the ground of the general theorems that the Bogoliubov mode stemming from a
spontaneously broken internal U(1) symmetry and the longitudinal phonon due to
a crystalline order are distinct physical modes.Comment: 14 pages, 4 pdf/jpg figures, REVTeX 4.1; v2: section IV expanded, new
appendix and references added, numerous other minor modifications throughout
the tex
Polymorphism of Plasmodium Falciparum Dihydrofolate Reductase and Dihydropteroate Synthase Genes Among Pregnant Women with Falciparum Malaria in Banjar District, South Kalimantan Province, Indonesia
Pregnant women are highly vulnerable to malaria infection in its endemic areas, particularly infection by Plasmodium falciparum that can cause premature, low birth weight, severe anemia in pregnant women, and death. Sulfadoxine-pyrimethamine (SP) for Intermittent Preventive Treatment for pregnant (IPTp) is used for malaria control in pregnancy recommended by the World Health Organization that has already been implemented in Africa. The P. falciparum resistance to SP has been reported in several malarial endemic areas, and mutations in the genes of Plasmodium falciparum Dihydrofolate Reductase (Pfdhfr) and Dihydropteroate Synthase (Pfdhps) are shown to be associated with parasite resistance to SP treatment. Genetic analysis of Pfdhfr and Pfdhps genes in pregnant women infected with P. falciparum has not yet been examined in Indonesia. The cross-sectional study was conducted at two subdistricts, Sungai Pinang and Peramasan, in Banjar district of South Kalimantan Province, where 127 pregnant women were recruited from 2008 to April 2010. Two important mutations in Pfdhfr gene (amino acid positions at N51 and S108) and three in Pfdhps gene (A437, K540 and A581) were analyzed by nested PCR-RFLP method. All of the seven pregnant women samples infected with P. falciparum presented PfDHFR 108N and PfDHPS 437G mutations. One of the samples had the additional mutation at PfDHPS 540, in which Lys is substituted by Glu. These results suggested that P. falciparum might present only some resistance to SP at Sungai Pinang and Peramasan subdistricts, Banjar District, South Kalimantan province, Indonesia. Although there were limited number of samples, this study showed only few mutations of Pfdhfr and Pfdhps genes in P. falciparum at Banjar district, South Kalimantan Province, that suggests SP might be effective for IPTp in this area. Thus, further analysis of the other mutation sites in Pfdhfr and Pfdhps genes and in vivo efficacy study of SP with more sufficient sample numbers will be necessary to confirm this preliminarily result
Effects of the Neutron Spin-Orbit Density on Nuclear Charge Density in Relativistic Models
The neutron spin-orbit density contributes to the nuclear charge density as a
relativistic effect. The contribution is enhanced by the effective mass
stemming from the Lorentz-scalar potential in relativistic models. This
enhancement explains well the difference between the cross sections of elastic
electron scattering off Ca and Ca which was not reproduced in
non-relativistic models. The spin-orbit density will be examined in more detail
in electron scattering off unstable nuclei which would be available in the
future.Comment: 4 pages with 3 eps figures, revte
Supramolecular copolymerization driven by integrative self-sorting of hydrogen-bonded rosettes.
Molecular recognition to preorganize noncovalently polymerizable supramolecular complexes is a characteristic process of natural supramolecular polymers, and such recognition processes allow for dynamic self-alteration, yielding complex polymer systems with extraordinarily high efficiency in their targeted function. We herein show an example of such molecular recognition-controlled kinetic assembly/disassembly processes within artificial supramolecular polymer systems using six-membered hydrogen-bonded supramolecular complexes (rosettes). Electron-rich and poor monomers are prepared that kinetically coassemble through a temperature-controlled protocol into amorphous coaggregates comprising a diverse mixture of rosettes. Over days, the electrostatic interaction between two monomers induces an integrative self-sorting of rosettes. While the electron-rich monomer inherently forms toroidal homopolymers, the additional electrostatic interaction that can also guide rosette association allows helicoidal growth of supramolecular copolymers that are comprised of an alternating array of two monomers. Upon heating, the helicoidal copolymers undergo a catastrophic transition into amorphous coaggregates via entropy-driven randomization of the monomers in the rosette
Self-folding of supramolecular polymers into bioinspired topology.
Folding one-dimensional polymer chains into well-defined topologies represents an important organization process for proteins, but replicating this process for supramolecular polymers remains a challenging task. We report supramolecular polymers that can fold into protein-like topologies. Our approach is based on curvature-forming supramolecular rosettes, which affords kinetic control over the extent of helical folding in the resulting supramolecular fibers by changing the cooling rate for polymerization. When using a slow cooling rate, we obtained misfolded fibers containing a minor amount of helical domains that folded on a time scale of days into unique topologies reminiscent of the protein tertiary structures. Thermodynamic analysis of fibers with varying degrees of folding revealed that the folding is accompanied by a large enthalpic gain. The self-folding proceeds via ordering of misfolded domains in the main chain using helical domains as templates, as fully misfolded fibers prepared by a fast cooling rate do not self-fold
Non-uniform Photoinduced Unfolding of Supramolecular Polymers Leading to Topological Block Nanofibers
Synthesis of one-dimensional nanofibers with distinct topological (higher-order structural) domains in the same main chain is one of the challenging topics in modern supramolecular polymer chemistry. Non-uniform structural transformation of supramolecular polymer chains by external stimuli may enable preparation of such nanofibers. To demonstrate feasibility of this post-polymerization strategy, we prepared a photoresponsive helically folded supramolecular polymers from a barbiturate monomer containing an azobenzene-embedded rigid π-conjugated scaffold. In contrast to previous helically folded supramolecular polymers composed of a more flexible azobenzene monomer, UV-light induced unfolding of the newly prepared helically folded supramolecular polymers occurred nonuniformly, affording topological block copolymers consisting of folded and unfolded domains. The formation of such blocky copolymers indicates that the photoinduced unfolding of the helically folded structures initiates from relatively flexible parts such as termini or defects. Spontaneous refolding of the unfolded domains was observed after visible-light irradiation followed by aging to restore fully folded structures
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