Superfluid phase transition and strong-coupling effects in an ultracold Fermi gas with mass imbalance

We investigate the superfluid phase transition and effects of mass imbalance in the BCS (Bardeen-Cooper-Schrieffer)-BEC (Bose-Einstein condensation) crossover regime of an cold Fermi gas. We point out that the Gaussian fluctuation theory developed by Nozi\`eres and Schmitt-Rink and the $T$-matrix theory, that are now widely used to study strong-coupling physics of cold Fermi gases, give unphysical results in the presence of mass imbalance. To overcome this problem, we extend the $T$-matrix theory to include higher-order pairing fluctuations. Using this, we examine how the mass imbalance affects the superfluid phase transition. Since the mass imbalance is an important key in various Fermi superfluids, such as $^{40}$K-$^6$Li Fermi gas mixture, exciton condensate, and color superconductivity in a dense quark matter, our results would be useful for the study of these recently developing superfluid systems.Comment: 7 pages, 4 figures, Proceedings of QFS-201

Stability of additive-free water-in-oil emulsions

We calculate ion distributions near a planar oil-water interface within non-linear Poisson-Boltzmann theory, taking into account the Born self-energy of the ions in the two media. For unequal self-energies of cations and anions, a spontaneous charge separation is found such that the water and oil phase become oppositely charged, in slabs with a typical thickness of the Debye screening length in the two media. From the analytical solutions, the corresponding interfacial charge density and the contribution to the interfacial tension is derived, together with an estimate for the Yukawa-potential between two spherical water droplets in oil. The parameter regime is explored where the plasma coupling parameter exceeds the crystallization threshold, i.e. where the droplets are expected to form crystalline structures due to a strong Yukawa repulsion, as recently observed experimentally. Extensions of the theory that we discuss briefly include numerical calculations on spherical water droplets in oil, and analytical calculations of the linear PB-equation for a finite oil-water interfacial width.Comment: 9 pages, 4 figures, accepted by JPCM for proceedings of LMC

Anticipatie op kartel- en concentratietoezicht

De Nederlandse Mededingingsautoriteit handhaaft de Mededingingswet. Op grond van de Mededingingswet is het onder meer verboden om afspraken te maken of om fusies door te voeren die de mededinging beperken. In welke mate houden bedrijven en hun adviseurs rekening met dit toezicht door de NMa? Wat is met andere woorden het anticipatie-effect van mededingingstoezicht? Wanneer mededingingsbeperkend gedrag vanwege het toezicht niet plaatsvindt, is er sprake van een anticipatie-effect. SEO Economisch Onderzoek heeft dit effect voor concentraties en kartels onderzocht door middel van enquêtes met ondernemingen en adviseurs en econometrische analyse. Uit enquêtes onder ondernemingen blijkt dat 5% van de gemelde fusies zijn aangepast voor melding om mogelijke mededingingsbezwaren weg te nemen. Naast elke 100 fusiemeldingen zijn er 13 voornemens die vanwege het toezicht op concentraties niet worden doorgezet tot een melding. Ondernemingen houden ook rekening met de Mededingingswet wanneer zij contracten vormgeven, bijeenkomsten bezoeken of overleggen. Uit de enquête onder advocaten en andere adviseurs blijkt dat tegenover elk sanctiebesluit van de NMa bijna 5 bij de NMa onbekende gevallen staan waarin een verboden gedraging is stopgezet of aangepast op grond van mededingingsrechtelijk advies. Welke factoren beïnvloeden de omvang van het anticipatie-effect? Met econometrische analyse is het effect van het marktaandeel, remedies, kosten van de melding en de doorlooptijd van de meldingsfase onderzocht. Voor karteltoezicht is het effect van de NMa-Agenda, de clementieregeling, de persoonlijke boete, de boete voor de onderneming en negatieve publiciteit onderzocht

Dependence of interface conductivity on relevant physical parameters in polarized Fermi mixtures

We consider a mass-asymmetric polarized Fermi system in the presence of Hartree-Fock (HF) potentials. We concentrate on the BCS regime with various interaction strengths and numerically obtain the allowed values of the chemical and HF potentials, as well as the mass ratio. The functional dependence of the heat conductivity of the N-SF interface on relevant physical parameters, namely the temperature, the mass ratio, and the interaction strength, is obtained. In particular, we show that the interface conductivity starts to drop with decreasing temperature at the temperature, $T_{\text{m}}$, where the mean kinetic energy of the particles is just sufficient to overcome the SF gap. We obtain $T_{\text{m}}$ as a function of the mass ratio and the interaction strength. The variation of the heat conductivity, at fixed temperature, with the HF potentials and the imbalance chemical potential is also obtained. Finally, because the range of relevant temperatures increases for larger values of the mass ratio, we consider the $^6\text{Li}$-$^{40}\text{K}$ mixture separately by taking the temperature dependence of the pair potential into account.Comment: To appear in Physica C (2012

Disruption of AKAP-PKA Interaction Induces Hypercontractility With Concomitant Increase in Proliferation Markers in Human Airway Smooth Muscle

With the ability to switch between proliferative and contractile phenotype, airway smooth muscle (ASM) cells can contribute to the progression of airway diseases such as asthma and chronic obstructive pulmonary disease (COPD), in which airway obstruction is associated with ASM hypertrophy and hypercontractility. A-kinase anchoring proteins (AKAPs) have emerged as important regulatory molecules in various tissues, including ASM cells. AKAPs can anchor the regulatory subunits of protein kinase A (PKA), and guide cellular localization via various targeting domains. Here we investigated whether disruption of the AKAP-PKA interaction, by the cell permeable peptide stearated (st)-Ht31, alters human ASM proliferation and contractility. Treatment of human ASM with st-Ht31 enhanced the expression of protein markers associated with cell proliferation in both cultured cells and intact tissue, although this was not accompanied by an increase in cell viability or cell-cycle progression, suggesting that disruption of AKAP-PKA interaction on its own is not sufficient to drive ASM cell proliferation. Strikingly, st-Ht31 enhanced contractile force generation in human ASM tissue with concomitant upregulation of the contractile protein α-sm-actin. This upregulation of α-sm-actin was independent of mRNA stability, transcription or translation, but was dependent on proteasome function, as the proteasome inhibitor MG-132 prevented the st-Ht31 effect. Collectively, the AKAP-PKA interaction appears to regulate markers of the multi-functional capabilities of ASM, and this alter the physiological function, such as contractility, suggesting potential to contribute to the pathophysiology of airway diseases

Activation of WNT/beta-Catenin Signaling in Pulmonary Fibroblasts by TGF-beta(1) Is Increased in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is characterized by abnormal extracellular matrix (ECM) turnover. Recently, activation of the WNT/β-catenin pathway has been associated with abnormal ECM turnover in various chronic diseases. We determined WNT-pathway gene expression in pulmonary fibroblasts of individuals with and without COPD and disentangled the role of β-catenin in fibroblast phenotype and function.We assessed the expression of WNT-pathway genes and the functional role of β-catenin, using MRC-5 human lung fibroblasts and primary pulmonary fibroblasts of individuals with and without COPD.Pulmonary fibroblasts expressed mRNA of genes required for WNT signaling. Stimulation of fibroblasts with TGF-β₁, a growth factor important in COPD pathogenesis, induced WNT-5B, FZD₈, DVL3 and β-catenin mRNA expression. The induction of WNT-5B, FZD₆, FZD₈ and DVL3 mRNA by TGF-β₁ was higher in fibroblasts of individuals with COPD than without COPD, whilst basal expression was similar. Accordingly, TGF-β₁ activated β-catenin signaling, as shown by an increase in transcriptionally active and total β-catenin protein expression. Furthermore, TGF-β₁induced the expression of collagen1α1, α-sm-actin and fibronectin, which was attenuated by β-catenin specific siRNA and by pharmacological inhibition of β-catenin, whereas the TGF-β₁-induced expression of PAI-1 was not affected. The induction of transcriptionally active β-catenin and subsequent fibronectin deposition induced by TGF-β₁ were enhanced in pulmonary fibroblasts from individuals with COPD.β-catenin signaling contributes to ECM production by pulmonary fibroblasts and contributes to myofibroblasts differentiation. WNT/β-catenin pathway expression and activation by TGF-β₁ is enhanced in pulmonary fibroblasts from individuals with COPD. This suggests an important role of the WNT/β-catenin pathway in regulating fibroblast phenotype and function in COPD

Ground states and dynamics of population-imbalanced Fermi condensates in one dimension

By using the numerically exact density-matrix renormalization group (DMRG) approach, we investigate the ground states of harmonically trapped one-dimensional (1D) fermions with population imbalance and find that the Larkin-Ovchinnikov (LO) state, which is a condensed state of fermion pairs with nonzero center-of-mass momentum, is realized for a wide range of parameters. The phase diagram comprising the two phases of i) an LO state at the trap center and a balanced condensate at the periphery and ii) an LO state at the trap center and a pure majority component at the periphery, is obtained. The reduced two-body density matrix indicates that most of the minority atoms contribute to the LO-type quasi-condensate. With the time-dependent DMRG, we also investigate the real-time dynamics of a system of 1D fermions in response to a spin-flip excitation.Comment: 20 pages, 15 figures, accepted for publication in New Journal of Physic