4,644 research outputs found
Density and Spin Linear Response of Atomic Fermi Superfluids with Population Imbalance in BCS-BEC Crossover
We present a theoretical study of the density and spin (representing the two
components) linear response of Fermi superfluids with tunable attractive
interactions and population imbalance. In both linear response theories, we
find that the fluctuations of the order parameter must be treated on equal
footing with the gauge transformations associated with the symmetries of the
Hamiltonian so that important constraints including various sum rules can be
satisfied. Both theories can be applied to the whole BCS-Bose-Einstein
condensation crossover. The spin linear responses are qualitatively different
with and without population imbalance because collective-mode effects from the
fluctuations of the order parameter survive in the presence of population
imbalance, even though the associated symmetry is not broken by the order
parameter. Since a polarized superfluid becomes unstable at low temperatures in
the weak and intermediate coupling regimes, we found that the density and spin
susceptibilities diverge as the system approaches the unstable regime, but the
emergence of phase separation preempts the divergence.Comment: 15 pages, 5 figure
BCS thermal vacuum of fermionic superfluids and its perturbation theory
The thermal field theory is applied to fermionic superfluids by doubling the
degrees of freedom of the BCS theory. We construct the two-mode states and the
corresponding Bogoliubov transformation to obtain the BCS thermal vacuum. The
expectation values with respect to the BCS thermal vacuum produce the
statistical average of the thermodynamic quantities. The BCS thermal vacuum
allows a quantum-mechanical perturbation theory with the BCS theory serving as
the unperturbed state. We evaluate the leading-order corrections to the order
parameter and other physical quantities from the perturbation theory. A direct
evaluation of the pairing correlation as a function of temperature shows the
pseudogap phenomenon results from the perturbation theory. The BCS thermal
vacuum is shown to be a generalized coherent and squeezed state. The
correspondence between the thermal vacuum and purification of the density
matrix allows a unitary transformation, and we found the geometric phase in the
parameter space associated with the transformation.Comment: 14 pages, 2 figure
Chemicals having estrogenic activity can be released from some bisphenol a-free, hard and clear, thermoplastic resins
Background: Chemicals that have estrogenic activity (EA) can potentially cause adverse health effects in mammals
including humans, sometimes at low doses in fetal through juvenile stages with effects detected in adults.
Polycarbonate (PC) thermoplastic resins made from bisphenol A (BPA), a chemical that has EA, are now often
avoided in products used by babies. Other BPA-free thermoplastic resins, some hypothesized or advertised to be
EA-free, are replacing PC resins used to make reusable hard and clear thermoplastic products such as baby bottles.
Methods: We used two very sensitive and accurate in vitro assays (MCF-7 and BG1Luc human cell lines) to quantify
the EA of chemicals leached into ethanol or water/saline extracts of fourteen unstressed or stressed (autoclaving,
microwaving, UV radiation) thermoplastic resins. Estrogen receptor (ER)-dependent agonist responses were confirmed
by their inhibition with the ER antagonist ICI 182,780.
Results: Our data showed that some (4/14) unstressed and stressed BPA-free thermoplastic resins leached chemicals
having significant levels of EA, including one polystyrene (PS), and three Tritan™ resins, the latter reportedly
EA-free. Exposure to UV radiation in natural sunlight resulted in an increased release of EA from Tritan™ resins.
Triphenyl-phosphate (TPP), an additive used to manufacture some thermoplastic resins such as Tritan™, exhibited
EA in both MCF-7 and BG1Luc assays. Ten unstressed or stressed glycol-modified polyethylene terephthalate
(PETG), cyclic olefin polymer (COP) or copolymer (COC) thermoplastic resins did not release chemicals with detectable
EA under any test condition.
Conclusions: This hazard survey study assessed the release of chemicals exhibiting EA as detected by two sensitive,
widely used and accepted, human cell line in vitro assays. Four PC replacement resins (Tritan™ and PS) released
chemicals having EA. However, ten other PC-replacement resins did not leach chemicals having EA (EA-free-resins).
These results indicate that PC-replacement plastic products could be made from EA-free resins (if appropriate EA-free
additives are chosen) that maintain advantages of re-usable plastic items (price, weight, shatter resistance) without
releasing chemicals having EA that potentially produce adverse health effects on current or future generations.This work was supported by the following NIH/NIEHS grants: R44 ES011469, 01–03 (CZY);
1R43/44 ES014806, 01–03 (CZY); subcontract (CZY, PI) on an NIH Grant 01–03
43/44ES018083-01. This work was also supported by NIH grants to MSD (P42
ES004699), and DJK and SIY (1R43ES018083-01-03, NIEHS 1R44ES019442-01-03
and NIEHS 2R44ES016964-01-03).Neuroscienc
Visible-light promoted atom transfer radical addition-elimination (ATRE) reaction for the synthesis of fluoroalkylated alkenes using DMA as electron-donor
Here, we describe a mild, catalyst-free and operationally-simple strategy for the direct fluoroalkylation of olefins driven by the photochemical activity of an electron donor-acceptor (EDA) complex between DMA and fluoroalkyl iodides. The significant advantages of this photochemical transformation are high efficiency, excellent functional group tolerance, and synthetic simplicity, thus providing a facile route for further application in pharmaceuticals and life sciences
PULL-DOWN INSTABILITY OF THE QUADRATIC NONLINEAR OSCILLATORS
A nonlinear vibration system, over a span of convincing periodic motion, might break out abruptly a catastrophic instability, but the lack of a theoretical tool has obscured the prediction of the outbreak. This paper deploys the amplitude-frequency formulation for nonlinear oscillators to reveal the critically important mechanism of the pseudo-periodic motion, and finds the quadratic nonlinear force contributes to the pull-down phenomenon in each cycle of the periodic motion, when the force reaches a threshold value, the pull-down instability occurs. A criterion for prediction of the pull-down instability is proposed and verified numerically
Viscosity modeling for ionic liquid solutions by Eyring-Wilson equation
A semi-theoretical model based on the classical Eyring’s mixture viscosity equation and the Wilson activity coefficient equation is presented for correlating the viscosity of ionic liquids with solvent systems. The accuracy of the proposed model was verified by comparing calculated and experimental viscosity values from literatures for 49mixtures with total 1560 data points. The results show that the equation similar to the Wilson activity coefficient equation can be well applied to describe the non-ideal term in the Eyring’s mixture viscosity equation. The model has a relatively simple mathematical form and can be easily incorporated into process simulation software
Characterization of a Novel ArsR-Like Regulator Encoded by Rv2034 in Mycobacterium tuberculosis
The genome of Mycobacterium tuberculosis, the causative agent of tuberculosis, encodes a large number of putative transcriptional regulators. However, the identity and target genes of only a few of them have been clearly identified to date. In a recent study, the ArsR family regulator Rv2034 was characterized as a novel positive regulator of phoP. In the current study, we characterized the auto-repressive capabilities of Rv2034 and identified several residues in the protein critical for its DNA binding activities. We also provide evidence that Rv2034 forms dimers in vitro. Furthermore, by using DNaseI footprinting assays, a palindromic sequence was identified as its binding site. Notably, we found that the dosR promoter region contains the binding motif for Rv2034, and that Rv2034 positively regulates the expression of the dosR gene. The potential roles of Rv2034 in the regulation of lipid metabolism and hypoxic adaptation are discussed
Mutant spectrum of dengue type 1 virus in the plasma of patients from the 2006 epidemic in South China
SummaryThe aim of the present study was to explore the mutant spectrum of dengue type 1 virus (DENV-1) within individuals during the 2006 dengue epidemic in South China. A 513-bp fragment including most of domain III of the envelope (E) gene was amplified directly from clinical samples, then cloned and sequenced. A total of 89 clones from six patients (range 11–17 clones per patient) were sequenced. Genetic diversity was calculated using MEGA 4 package. The total number of nucleotide mutations was 113 (3.7%) within the sequenced 513-bp E gene, with a range of 15 (3%) to 24 (4.7%) within individual viral populations, harboring more non-synonymous than synonymous mutations. The extent of sequence diversity varied among patients, with the mean diversity ranging from 0.19% to 0.32%, and the mean pairwise p-distance ranging from 0.34% to 0.65%. No genome-defective virus was detected in any clone in this study. Purifying selection may be the main driving force for the intrahost evolution: the mean dN/dS ratio was 0.532. Our findings contribute to the understanding of the genetic variation of DENV-1 in South China
- …