1,768 research outputs found
Nitrogen defects and ferromagnetism of Cr-doped AlN diluted magnetic semiconductor from first principles
High Curie temperature of 900 K has been reported in Cr-doped AlN diluted
magnetic semiconductors prepared by various methods, which is exciting for
spintronic applications. It is believed that N defects play important roles in
achieving the high temperature ferromagnetism in good samples. Motivated by
these experimental advances, we use a full-potential density-functional-theory
method and supercell approach to investigate N defects and their effects on
ferromagnetism of (Al,Cr)N with N vacancies (V_N). Calculated results are in
agreement with experimental observations and facts of real Cr-doped AlN samples
and their synthesis. Our first-principles results are useful to elucidating the
mechanism for the ferromagnetism and exploring high-performance Cr-doped AlN
diluted magnetic semiconductors.Comment: 8 pages with figures include
On String Field Theory and Effective Actions
A truncation of string field theory is compared with the duality invariant
effective action of heterotic strings to cubic order. The three
string vertex must satisfy a set of compatibility conditions. Any cyclic three
string vertex is compatible with the effective field theory. The
effective actions may be useful in understanding the non--polynomial structure
and the underlying symmetry of covariant closed string field theory, and in
addressing issues of background independence. We also discuss the effective
action and string field theory of the string.Comment: 33 pages, IASSNS-HEP-92/3
Loop Variables and Gauge Invariant Exact Renormalization Group Equations for (Open) String Theory
An exact renormalization group equation is written down for the world sheet
theory describing the bosonic open string in general backgrounds. Loop variable
techniques are used to make the equation gauge invariant. This is worked out
explicitly up to level 3. The equation is quadratic in the fields and can be
viewed as a proposal for a string field theory equation. As in the earlier loop
variable approach, the theory has one extra space dimension and mass is
obtained by dimensional reduction. Being based on the sigma model RG, it is
background independent.
It is intriguing that in contrast to BRST string field theory, the gauge
transformations are not modified by the interactions up to the level
calculated. The interactions can be written in terms of gauge invariant field
strengths for the massive higher spin fields and the non zero mass is essential
for this. This is reminiscent of Abelian Born-Infeld action (along with
derivative corrections) for the massless vector field, which is also written in
terms of the field strength.Comment: Latex file, 40 pages.Some typos corrected and cosmetic change
catena-Poly[[diaquadichloridomanganese(II)]-μ-1,1′-bis(1H-1,2,4-triazol-1-ylmethyl)ferrocene]
In the title complex, [FeMn(C8H8N3)2Cl2(H2O)2]n, the MnII atom, located on an inversion center, is octahedrally coordinated by two N atoms from two adjacent 1,1′-bis(1H-1,2,4-triazol-1-ylmethyl)ferrocene (btmf) ligands and two Cl atoms forming the equatorial plane, with the axial positions occupied by two O atoms of coordinated water molecules. The btmf ligands link adjoining MnII atoms into a zigzag chain along the a axis. The crystal structure is stabilized by intermolecular O—H⋯N hydrogen bonds, which link the chains, forming a two-dimensional layer parallel to (10); O—H⋯Cl interactions link the layers, forming a three-dimensional network
A survey of the parameter space of the compressible liquid drop model as applied to the neutron star inner crust
We present a systematic survey the range of predictions of the neutron star
inner crust composition, crust-core transition densities and pressures, and
density range of the nuclear `pasta' phases at the bottom of the crust provided
by the compressible liquid drop model in the light of current experimental and
theoretical constraints on model parameters. Using a Skyrme-like model for
nuclear matter, we construct baseline sequences of crust models by consistently
varying the density dependence of the bulk symmetry energy at nuclear
saturation density, , under two conditions: (i) that the magnitude of the
symmetry energy at saturation density is held constant, and (ii)
correlates with under the constraint that the pure neutron matter (PNM) EoS
satisfies the results of ab-initio calculations at low densities. Such baseline
crust models facilitate consistent exploration of the dependence of crustal
properties. The remaining surface energy and symmetric nuclear matter
parameters are systematically varied around the baseline, and different
functional forms of the PNM EoS at sub-saturation densities implemented, to
estimate theoretical `error bars' for the baseline predictions. Inner crust
composition and transition densities are shown to be most sensitive to the
surface energy at very low proton fractions and to the behavior of the
sub-saturation PNM EoS. Recent calculations of the energies of neutron drops
suggest that the low-proton-fraction surface energy might be higher than
predicted in Skyrme-like models, which our study suggests may result in a
greatly reduced volume of pasta in the crust than conventionally predicted.Comment: 37 Pages, 16 figures, accepted for publication in Astrophysical
Journal Supplement Serie
Hepatitis E Virus Transmission from Wild Boar Meat
We investigated a case of hepatitis E acquired after persons ate wild boar meat. Genotype 3 hepatitis E virus (HEV) RNA was detected in both patient serum and wild boar meat. These findings provided direct evidence of zoonotic foodborne transmission of HEV from a wild boar to a human
Characteristics of DNA-binding proteins determine the biological sensitivity to high-linear energy transfer radiation
Non-homologous end-joining (NHEJ) and homologous recombination repair (HRR), contribute to repair ionizing radiation (IR)-induced DNA double-strand breaks (DSBs). Mre11 binding to DNA is the first step for activating HRR and Ku binding to DNA is the first step for initiating NHEJ. High-linear energy transfer (LET) IR (such as high energy charged particles) killing more cells at the same dose as compared with low-LET IR (such as X or γ rays) is due to inefficient NHEJ. However, these phenomena have not been demonstrated at the animal level and the mechanism by which high-LET IR does not affect the efficiency of HRR remains unclear. In this study, we showed that although wild-type and HRR-deficient mice or DT40 cells are more sensitive to high-LET IR than to low-LET IR, NHEJ deficient mice or DT40 cells are equally sensitive to high- and low-LET IR. We also showed that Mre11 and Ku respond differently to shorter DNA fragments in vitro and to the DNA from high-LET irradiated cells in vivo. These findings provide strong evidence that the different DNA DSB binding properties of Mre11 and Ku determine the different efficiencies of HRR and NHEJ to repair high-LET radiation induced DSBs
Observation of a ppb mass threshoud enhancement in \psi^\prime\to\pi^+\pi^-J/\psi(J/\psi\to\gamma p\bar{p}) decay
The decay channel
is studied using a sample of events collected
by the BESIII experiment at BEPCII. A strong enhancement at threshold is
observed in the invariant mass spectrum. The enhancement can be fit
with an -wave Breit-Wigner resonance function with a resulting peak mass of
and a
narrow width that is at the 90% confidence level.
These results are consistent with published BESII results. These mass and width
values do not match with those of any known meson resonance.Comment: 5 pages, 3 figures, submitted to Chinese Physics
Nuclear receptors in vascular biology
Nuclear receptors sense a wide range of steroids and hormones (estrogens, progesterone, androgens, glucocorticoid, and mineralocorticoid), vitamins (A and D), lipid metabolites, carbohydrates, and xenobiotics. In response to these diverse but critically important mediators, nuclear receptors regulate the homeostatic control of lipids, carbohydrate, cholesterol, and xenobiotic drug metabolism, inflammation, cell differentiation and development, including vascular development. The nuclear receptor family is one of the most important groups of signaling molecules in the body and as such represent some of the most important established and emerging clinical and therapeutic targets. This review will highlight some of the recent trends in nuclear receptor biology related to vascular biology
DNA polymerase zeta is required for proliferation of normal mammalian cells
Unique among translesion synthesis (TLS) DNA polymerases, pol ζ is essential during embryogenesis. To determine whether pol ζ is necessary for proliferation of normal cells, primary mouse fibroblasts were established in which Rev3L could be conditionally inactivated by Cre recombinase. Cells were grown in 2% O2 to prevent oxidative stress-induced senescence. Cells rapidly became senescent or apoptotic and ceased growth within 3–4 population doublings. Within one population doubling following Rev3L deletion, DNA double-strand breaks and chromatid aberrations were found in 30–50% of cells. These breaks were replication dependent, and found in G1 and G2 phase cells. Double-strand breaks were reduced when cells were treated with the reactive oxygen species scavenger N-acetyl-cysteine, but this did not rescue the cell proliferation defect, indicating that several classes of endogenously formed DNA lesions require Rev3L for tolerance or repair. T-antigen immortalization of cells allowed cell growth. In summary, even in the absence of external challenges to DNA, pol ζ is essential for preventing replication-dependent DNA breaks in every division of normal mammalian cells. Loss of pol ζ in slowly proliferating mouse cells in vivo may allow accumulation of chromosomal aberrations that could lead to tumorigenesis. Pol ζ is unique amongst TLS polymerases for its essential role in cell proliferation
- …