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We have investigated crystalline AlGaAs/GaAs optical coatings with three ultra-stable cavities operating at 4 K, 16 K, 124 K and 297 K. The response of the resonance frequencies of cavities to variations in optical power indicates effects beyond the photo-thermo-optic effect observed in dielectric coatings. These effects are strongly dependent on the intensity of the intracavity light at 1.5~\textmu m. When the rear side of the mirrors is illuminated with external light, we observe a prominent photo-modified birefringence for photon energies above the GaAs bandgap, which points to a possible mechanism relating our observations to the semiconductor properties of the coatings. Separately, we also present a low maintenance evolution of our 124 K silicon cavity system where the liquid nitrogen based cooling system is replaced with closed cycle cooling from a pulse-tube cryo-cooler.

Similarity analysis of microalgae growth is crucial for understanding microalgae cultivation, such analysis has not been considered before in previous studies. This letter considers the natural features of the microalgae growth phenomenon that are different from the inanimate process. Accordingly, the similarity of light transfer within microalgae suspensions was comprehensively studied. The characteristic number of microalgae growth and the temporal scaling function were considered to represent the growth relate characteristics. Subsequently, a group of dimensionless numbers were derived to characterize the time-dependent similarity of light within microalgae suspensions. For growth similarity, the newly introduced characteristic number of microalgae growth and the temporal scaling function of extinction, absorption and scattering were considered identical. The similarity relations of the time-dependent optical constants of microalgae were also provided for similar growth. The similarity analysis of the microalgae growth will be useful in designing and guiding experiments on microalgae cultivation., Comment: The characteristic number of microalgae growth and temporal scaling function were considered to represent the similarity growth relate characteristics

The established microalgae growth models are semi-empirical or considerable fitting coefficients exist currently. Therefore, the ability of the model prediction is reduced by the numerous fitting coefficients. Furthermore, the predicted results of the established models are dependent on the size of the photobioreactor (PBR), light intensity, flow and concentration field. The growth mechanism of microalgae has not clearly understood in PBR cultivation. It is difficult to predict the microalgae growth by theoretical methods, owing to the aforementioned factors. We developed an exploratory bridging microalgae growth model to predict the microalgae growth rate in PBRs by using the nondimensional method which is effectively in fluid dynamics and heat transfer. The analytical solution of the growth rate was obtained for the parallel flow. The nondimensional growth rate expressed as function of Reynolds number and Schmidt number, which can be used for arbitrary parallel flow due to the solution was expressed as nondimensional quantities. The theoretically predicted growth rate is compared with the experimentally measured microalgae growth rate on the order of magnitude. The nondimensional method successfully applied to the microalgae growth problem for the first time. The general nondimensional solution can unify the numerous experimental data for different laboratory conditions, and give a direction for the disorder of the microalgae growth problem. The nondimensional solution may be useful to explain the growth mechanism of microalgae and design large-scale PBRs for microalgae biofuel production. The significance of the work is to give a theoretical foundation and methodology of biological theory of microalgae growth., Comment: 24 pages, 4 figures, 1 table

The radiative properties of microalgae are basic parameters for analyzing light field distribution in photobioreactors (PBRs). With the growth of microalgae cell, their radiative properties will vary with growth time due to accumulation of pigment and lipid, cell division and metabolism. In this work, we report both experimental and theoretical evidence of temporal scaling behavior of the growth dependent radiative properties of microalgae cell suspensions. A new concept, the temporal scaling function (TSF), defined as the ratio of absorption or scattering cross-sections at growth phase to that at stationary phase, is introduced to characterize the temporal scaling. The temporal evolution and temporal scaling characteristics of the absoroption and scattering cross-sections of three example microalgae species, Chlorella vulgaris, Chlorella pyrenoidosa, and Chlorella protothecoides, were experimentally studied at spectral range 380 to 850 nm. It is shown that the TSFs of the absorption and scattering cross-sections for different microalgae species are approximately constant at different wavelength, which confirms theoretical predictions very well. With the aid of the temporal scaling relation, the radiative properties of microalgae at any growth time can be calculated based on those measured at stationary phase. The findings of this work will help the understanding of time dependent radiative properties of microalgae and facilitate their applications in light field analysis in PBRs design., Comment: 24 pages, 9 figures, submitted to JQSRT on Dec 28, 2017

Double-perovskite A2BB'O6 oxides with magnetic B and B' ions and E*-type antiferromagnetic order (E*-AFM, i.e. the ++-- structure) are believed to exhibit promising multiferroic properties, and Y2CoMnO6 (YCMO) is one candidate in this category. However, the microscopic origins for magnetically induced ferroelectricity in YCMO remain unclear. In this work, we perform detailed symmetry analysis on the exchange striction effect and lattice distortion, plus the first-principles calculations on YCMO. The E*-AFM state as the ground state with other competing states such as ferromagnetic and A-antiferromagnetic orders is confirmed. It is revealed that the ferroelectricity is generated by the exchange striction associated with the E*-AFM order and chemically rdered Mn/Co occupation. Both the lattice symmetry consideration and first-principles calculations predict that the electric polarization aligns along the b-axis. The calculated polarization reaches up to 0.4682 uC/cm2, mainly from the ionic displacement contribution. The present work presents a comprehensive understanding of the multiferroic mechanisms in YCMO and is of general significance for predicting emergent multiferroicity in other double-perovskite magnetic oxides., Comment: 9 pages,8 figures, 2 tables

Charge dipole moment and spin moment rarely coexist in single-phase bulk materials except in some multiferroics. Despite the progress in the past decade, for most multiferroics their magnetoelectric performance remains poor due to the intrinsic exclusion between charge dipole and spin moment. As an alternative approach, the oxide heterostructures may evade the intrinsic limits in bulk materials and provide more attractive potential to realize the magnetoelectric functions. Here we perform a first-principles study on LaAlO$_3$/PbTiO$_3$ superlattices. Although neither of the components is magnetic, magnetic moments emerge at the ferroelectric domain walls of PbTiO$_3$ in these superlattices. Such a twist between ferroelectric domain and local magnetic moment, not only manifests an interesting type of multiferroicity, but also is possible useful to pursuit the electrical-control of magnetism in nanoscale heterostructures., Comment: 27 pages, 4 figures

The Standard Model predicts a very small CP violation phase $\sin2\Phi^{\rm SM}_{B_s} \simeq -0.04$%= \arg M_{12} \simeq \arg\,(V^*_{ts}V_{tb})^2$ in $B_s$--$\bar B_s$ mixing. %, i.e. of order $\lambda^2\eta$. Any finite value of $\Phi_{B_s}$ measured at the Tevatron would imply New Physics. With recent hints for finite $\sin2\Phi_{B_s}$, % have appeared from CDF and D\O\, experiments at the Tevatron, we reconsider the possibility of a 4th generation. As recent direct search bounds have become considerably heavier than 300 GeV, we take the $t'$ mass to be near the unitarity bound of 500 GeV. Combining the measured values of $\Delta m_{B_s}$ with ${\cal B}(B \to X_s\ell^+\ell^-)$, together with typical $f_{B_s}$ values, we find a sizable $\sin2\Phi^{\rm SM4}_{B_s} \sim -0.33$. Using %a typical value of $m_{b'} = 480$ GeV, we extract the range % a range of values, $0.06 < |V_{t'b}| < 0.13$ from the constraints of $\Gamma(Z\to b\bar b)$, $\Delta m_{D}$ and ${\cal B}(K^+\to\pi^+\nu\bar\nu)$. A future measurement of ${\cal B}(K_L\to\pi^0\nu\bar\nu)$ will determine $V_{t'd}$., Comment: 8 pages, 11 figures

We explore the possibility of detecting flavor changing neutral Higgs couplings at the Next Linear Collider (NLC) through $e^+e^-\to \nu_e\bar{\nu_e} t\bar{c}$. In the framework of a general two-Higgs doublet model, we perform a complete calculation and find that $\sigma (e^+e^-\to \nu_e\nu_e t\bar{c}, \nu_e\bar{\nu_e} {\bar t}c)$ could reach $\sim 9$ fb for $\sqrt{s}=2 TeV$. This amounts to an annual production of 500 $t\bar{c}$ plus $\bar{t}c$ pairs at the NLC with an integrated luminosity of 50 fb$^{-1}$. The dependence of $tc$-production rate on the neutral scalar mixing angle is mild except when $\sin^2\alpha \to 0 or 1$. The $\nu\nu W^+W^-$ background should be manageable after $b$-tagging, while $\nu\nu t\bar t$ background should not be a problem when the signal event rate is still interesting. The process, together with $e^+e^-\to \nu_e\bar{\nu_e} W^+W^-, \nu_e\bar{\nu_e} ZZ$ studies, offer the chance of measuring the $t$-$c$-Higgs coupling., Comment: REVTEX, 18 pages, 7 figures; Report number changed