Hydrodynamic Limit of the Boltzmann Equation with Contact Discontinuities

The hydrodynamic limit for the Boltzmann equation is studied in the case when the limit system, that is, the system of Euler equations contains contact discontinuities. When suitable initial data is chosen to avoid the initial layer, we prove that there exists a unique solution to the Boltzmann equation globally in time for any given Knudsen number. And this family of solutions converge to the local Maxwellian defined by the contact discontinuity of the Euler equations uniformly away from the discontinuity as the Knudsen number $\varepsilon$ tends to zero. The proof is obtained by an appropriately chosen scaling and the energy method through the micro-macro decomposition.Comment: 34 pages. submitte

CP violation in Bd,s→l+l−B_{d,s} \to l^+l^- in the model III 2HDM

We have calculated the Wilson coefficients $C_{10}, C_{Q_i}$ (i=1,2) in the $\bar{MS}$ renormalization scheme in the model III 2HDM. Using the obtained Wilson coefficients, we have analyzed the CP violation in decays $B^0_q\to l^+l^-$ (q=d,s) in the model. The CP asymmetry, $A_{CP}$, depends on the parameters of models and $A_{CP}$ in $B_d\to l^+l^-$ can be as large as 40% and 35% for $l=\tau$ and $l=\mu$ respectively. It can reach 4% for $B^0_s$ decays. Because in SM CP violation is smaller than or equal to O($10^{-3}$) which is unobservably small, an observation of CP asymmetry in the decays $B^0_q \to l^+l^- (q=d,s)$ would unambiguously signal the existence of new physics.Comment: revtex4, 16 pages, 7 figure

Chain Length Dependence of the Photovoltaic Properties of Monodisperse Donor-Acceptor Oligomers as Model Compounds of Polydisperse Low Band Gap Polymers

Well-defined conjugated oligomers (Sn) containing from 1 to 8 units of a tricyclic building block involving a dioctyloxybenzothiadiazole unit with two thienyl side rings (S1) are synthesized by a bottom-up approach. UV–Vis absorption data of solutions show that chain extension produces a narrowing of the HOMO–LUMO gap (ΔE) to values slightly smaller than that of the parent polymer (P1). Plots of ΔE and of the band gap of films (E g) versus the reciprocal chain length show that ΔE and E g converge towards a limit corresponding to an effective conjugation length (ECL) of 7–8 S1 units. UV–Vis absorption and photoluminescence data of solutions and solid films show that chain extension enhances the propensity to inter-chain aggregation. This conclusion is confirmed by GIXD analyses which reveal that the edge-on orientation of short-chain systems evolves toward a face-on orientation as chain length increases while the π-stacking distance decreases beyond 7 units. The results obtained on solution-processed BHJ solar cells show a progressive improvement of power conversion efficiency (PCE) with chain extension; however, the convergence limit of PCE remains inferior to that obtained with the polymer. These results are discussed with regard to the role of mono/polydispersity and chain aggregation

Stability of Transonic Shock Solutions for One-Dimensional Euler-Poisson Equations

In this paper, both structural and dynamical stabilities of steady transonic shock solutions for one-dimensional Euler-Poission system are investigated. First, a steady transonic shock solution with supersonic backgroumd charge is shown to be structurally stable with respect to small perturbations of the background charge, provided that the electric field is positive at the shock location. Second, any steady transonic shock solution with the supersonic background charge is proved to be dynamically and exponentially stable with respect to small perturbation of the initial data, provided the electric field is not too negative at the shock location. The proof of the first stability result relies on a monotonicity argument for the shock position and the downstream density, and a stability analysis for subsonic and supersonic solutions. The dynamical stability of the steady transonic shock for the Euler-Poisson equations can be transformed to the global well-posedness of a free boundary problem for a quasilinear second order equation with nonlinear boundary conditions. The analysis for the associated linearized problem plays an essential role

Detailed balance condition and ultraviolet stability of scalar field in Horava-Lifshitz gravity

Detailed balance and projectability conditions are two main assumptions when Horava recently formulated his theory of quantum gravity - the Horava-Lifshitz (HL) theory. While the latter represents an important ingredient, the former often believed needs to be abandoned, in order to obtain an ultraviolet stable scalar field, among other things. In this paper, because of several attractive features of this condition, we revisit it, and show that the scalar field can be stabilized, if the detailed balance condition is allowed to be softly broken. Although this is done explicitly in the non-relativistic general covariant setup of Horava-Melby-Thompson with an arbitrary coupling constant $\lambda$, generalized lately by da Silva, it is also true in other versions of the HL theory. With the detailed balance condition softly breaking, the number of independent coupling constants can be still significantly reduced. It is remarkable to note that, unlike other setups, in this da Silva generalization, there exists a master equation for the linear perturbations of the scalar field in the flat Friedmann-Robertson-Walker background.Comment: Some typos are corrected. To appear in JCA

Rational design of a (S)-selective-transaminase for asymmetric synthesis of (1S)-1-(1,1′-biphenyl-2-yl)ethanamine

Amine transaminases offer an environmentally sustainable synthesis route for the production of pure chiral amines. However, their catalytic efficiency toward bulky ketone substrates is greatly limited by steric hindrance and therefore presents a great challenge for industrial synthetic applications. We hereby report an example of rational transaminase enzyme design to help alleviate these challenges. Starting from the Vibrio fluvialis amine transaminase that has no detectable catalytic activity toward the bulky aromatic ketone 2-acetylbiphenyl, we employed a rational design strategy combining in silico and in vitro studies to engineer the transaminase enzyme with a minimal number of mutations, achieving an high catalytic activity and high enantioselectivity. We found that, by introducing two mutations W57G/R415A, detectable enzyme activity was achieved. The rationally designed variant, W57F/R88H/V153S/K163F/I259M/R415A/V422A, showed an improvement in reaction rate by more than 1716-fold toward the bulky ketone under study, producing the corresponding enantiomeric pure (S)-amine (enantiomeric excess (ee) value of >99%)

Singlet Charge 2/32/3 Quark hiding the Top: Tevatron and LEP Implications

If $c$ and $t$ quarks are strongly mixed with a weak singlet charge $2/3$ quark, $BR(t\to \ell\nu + X)$ could be suppressed via the $t\to cH^0$ mode, thereby the top quark could still hide below $M_W$, whereas the heavy quark signal observed at the Tevatron is due to the dominantly singlet quark $Q$. This may occur without affecting the small $m_c$ value. Demanding $m_Q \simeq 175$ GeV and m_t \ltap M_W, we find that $BR(t\to \ell\nu + X)$ cannot be too suppressed. The heavy quark $Q$ decays via $W,\ H$, and $Z$ bosons. The latter can lead to $b$-tagged $Z + 4$ jet events, while the strong $c$--$Q$ mixing is reflected in sizable $Q\to sW$ fraction. $Z\to t\bar c$ decay occurs at tree level and may be at the $10^{-3}$ order, leading to the signature of $Z\to \ell\nu b\bar c$, all isolated and with large $p_T$, at $10^{-5}$ order.Comment: 10 pages + 3 Figures (not included), ReVTeX, NTUTH-94-1

Raman light scattering study and microstructural analysis of epitaxial films of the electron-doped superconductor La_{2-x}Ce_{x}CuO_{4}

We present a detailed temperature-dependent Raman light scattering study of optical phonons in molecular-beam-epitaxy-grown films of the electron-doped superconductor La_{2-x}Ce_{x}CuO_{4} close to optimal doping (x ~ 0.08, T_c = 29 K and x ~ 0.1, T_c = 27 K). The main focus of this work is a detailed characterization and microstructural analysis of the films. Based on micro-Raman spectroscopy in combination with x-ray diffraction, energy-dispersive x-ray analysis, and scanning electron microscopy, some of the observed phonon modes can be attributed to micron-sized inclusions of Cu_{2}O. In the slightly underdoped film (x ~ 0.08), both the Cu_{2}O modes and others that can be assigned to the La_{2-x}Ce_{x}CuO_{4} matrix show pronounced softening and narrowing upon cooling below T ~ T_c. Based on control measurements on commercial Cu_{2}O powders and on a comparison to prior Raman scattering studies of other high-temperature superconductors, we speculate that proximity effects at La_{2-x}Ce_{x}CuO_{4}/Cu_{2}O interfaces may be responsible for these anomalies. Experiments on the slightly overdoped La_{2-x}Ce_{x}CuO_{4} film (x ~ 0.1) did not reveal comparable phonon anomalies.Comment: 7 pages, 8 figure

Differential roles of extracellular histidine residues of GPR68 for proton-sensing and allosteric modulation by divalent metal ions

GPR68, an orphan G-protein coupled receptor, senses protons, couples to multiple G-proteins, and is also activated or inhibited by divalent metal ions. It has seven extracellular histidine residues, although it is not clear how these histidine residues play a role in both proton-sensing and metal ion modulation. Here we demonstrate that divalent metal ions are allosteric modulators that can activate or inhibit proton activity in a concentration- and pH-dependent manner. We then show that single histidine mutants have differential and varying degrees of effects on proton-sensing and metal ion modulation. Some histidine residues play dual roles in proton-sensing and metal ion modulation, while others are important in one or the other but not both. Two extracellular disulfide bonds are predicted to constrain histidine residues to be spatially close to each other. Combining histidine mutations leads to reduced proton activity and resistance to metal ion modulation, while breaking the less conserved disulfide bond results in a more severe reduction in proton-sensing over metal modulation. The small-molecule positive allosteric modulators (PAMs) ogerin and lorazepam are not affected by these mutations and remain active at mutants with severely reduced proton activity or are resistant to metal ion modulation. These results suggest GPR68 possesses two independent allosteric modulation systems, one through interaction with divalent metal ions at the extracellular surface and another through small-molecule PAMs in the transmembrane domains. A new GPR68 model is developed to accommodate the findings which could serve as a template for further studies and ligand discovery by virtual ligand docking