Sophorose Lipids From Torulopsis Bombicola

Sophorose lipids are a class of biosurfactants which have several industrial applications, such as in lubricants, humectants, personal care products, soaps and detergents. Environmental considerations are the driving force behind the use of biosurfactants because of their perceived advantages such as lower toxicity, biodegradability and ecological acceptability over chemical surfactants. The key factors that will determine the usage of a given biosurfactant include the development of an economic process for its production, the use of low-cost raw materials and high product yields. The objective of this study was to develop a fermentation process to produce high value biosurfactants from low- or negative cost sugars, fat and oil substrates with the yeast Torulopsis bombicola. A wide variety of sugar, nitrogen, fat and oil substrates were examined as potential feedstocks to obtain very effective carbon sources for sophorose lipids production. Experiments were carried out in shake flasks, 1-L Bellco stirred reactors and 20-L fermenter at 450 rpm and 30{dollar}\sp\circ{dollar}C using batch and fed-batch experiments. The results showed that sugar, nitrogen, fat and oil were interactive control parameters which influenced the structure, yield, growth-phase, and also the metabolic pathways leading to glycolipid production. It was found that the production of sophorose lipids increased with increasing concentrations of both oil and sugar, and was profoundly influenced by the sources and concentration of nitrogen. Corn steep liquor, yeast extract and peptone were shown to be very effective nitrogen sources for sophorose lipids production. It was found that optimal production of sophorose lipids occurred when nitrogen sources became limited. The maximal production of sophorose lipids could reach 150-160 g/L in the optimal medium consisting of 10% glucose, 10.5% canola oil, 0.1% urea, and 0.4% yeast extract in a 1-L Bellco fermenter stirred at 450 rpm, an air flow rate of 2 vvm and 30{dollar}\sp\circ{dollar}C. Similar yields of sophorose lipids were also obtained in a 20-L bioreactor. About 73% of the apolar sophorose lipid, which has been described as 17-L-((2{dollar}\sp\prime{dollar}-O-{dollar}\beta{dollar}-D-glucopyranosyl-{dollar}\beta{dollar}-D-glucopyranosyl) -oxy)-octadecanoic acid 1{dollar}\sp\prime{dollar}-4{dollar}\sp{lcub}\prime\prime{rcub}{dollar}-lactone 6{dollar}\sp\prime{dollar},6{dollar}\sp{lcub}\prime\prime{rcub}{dollar}-diacetate (SL-1) group, was found in the mixture of sophorose lipids produced under the above conditions. When only lactose was present as the sugar source in the medium, the yeast Torulopsis bombicola did not grow. However, in the presence of both lactose and olive oil intra- and extracellular lipids were synthesized. By fed-batch cultivation, it could be seen that the maximization of yields, productivity and the minimization of production costs of sophorose lipids were obtained because the production phase was extended and substrates and enzymes were utilized very effectively. Sets of kinetics models for batch and fed-batch fermentation processes for the growth and sophorose lipids by Torulopsis bombicola were proposed, which could successfully describe, control and predict the kinetics of cell growth and sophorose lipids production

The valley filter efficiency of monolayer graphene and bilayer graphene line defect model

In addition to electron charge and spin, novel materials host another degree of freedom, the valley. For a junction composed of valley filter sandwiched by two normal terminals, we focus on the valley efficiency under disorder with two valley filter models based on monolayer and bilayer graphene. Applying the transfer matrix method, valley resolved transmission coefficients are obtained. We find that: i) under weak disorder, when the line defect length is over about $15\rm nm$, it functions as a perfect channel (quantized conductance) and valley filter (totally polarized); ii) in the diffusive regime, combination effects of backscattering and bulk states assisted intervalley transmission enhance the conductance and suppress the valley polarization; iii) for very long line defect, though the conductance is small, polarization is indifferent to length. Under perpendicular magnetics field, the characters of charge and valley transport are only slightly affected. Finally we discuss the efficiency of transport valley polarized current in a hybrid system.Comment: 6 figure

Pion condensation in dense QCD, the dilute Bose gas, and speedy Goldstone bosons

We consider pion condensation in cold and dense QCD using chiral perturbation theory ($\chi$PT). Thermodynamic quantities are calculated at next-to-leading order in the low-energy expansion. In the nonrelatistivtic limit, we recover the classic result by Lee and Yang for the energy density of a dilute Bose gas with an $s$-wave scattering length that includes loop corrections from $\chi$PT. In the chiral limit, we calculate the thermodynamic functions to next-to-leading order in the low-energy expansion. We use Son's prescription to write down an effective field theory for the massless Goldstone boson that results from the spontaneous breakdown of the global internal symmetry $U(1)_{I_3}$ at finite isospin density $n_I$. In the ultrarelativistic limit, the phonons propagate with the speed of light up to renormalization effects. The damping rate of the phonons behaves as $p^5$ for small momenta in agreement with Beliaev's old result for a weakly interacting Bose gas.Comment: 11 pages, one figure. V2: few typos fixed and added reference

Anti-Hyperon polarization in high energy pp collisions with polarized beams

We study the longitudinal polarization of the Sigma_bar and Xi_bar anti-hyperons in polarized high energy pp collisions at large transverse momenta, extending a recent study for the Lambda_bar anti-hyperon. We make predictions by using different parametrizations of the polarized parton densities and models for the polarized fragmentation functions. Similar to the Lambda_bar polarization, the Xi_bar0 and Xi_bar+ polarizations are found to be sensitive to the polarized anti-strange sea in the nucleon. The Sigma_bar- and Sigma_bar+ polarizations show sensitivity to the light sea quark polarizations, \Delta \bar u(x) and \Delta \bar d(x), and their asymmetry.Comment: 17 pages, 9 figures,version to appear in PR

An updated determination of the pion-photon transition form factor

In this paper, we study the properties of the pion-photon transition form factor (TFF), $\gamma\gamma^{\ast} \rightarrow \pi^{0}$, by using the principle of maximum commonality (PMC) to deal with its perturbative QCD contribution up to next-to-next-to-leading order (NNLO) QCD corrections. Applying the PMC, we achieve precise pQCD approximant for the TFF in large $Q^2$-region without conventional renormalization scale ambiguity. We also discuss the power suppressed non-valence quark contribution to the TFF, which is important for a sound prediction in low and intermediate $Q^2$-region, e.g. the non-valence quark components affect the TFF by about $1\%$ to $23\%$ when $Q^{2}$ changes down from $40~{\rm GeV^{2}}$ to $4~{\rm GeV^{2}}$. The resultant pion-photon TFF shows a better agreement with previous Belle data. It is hoped that previous discrepancies between the experimental measurements and theoretical predictions could be clarified by the forth-coming precise data on the Belle II measurements.Comment: 7 pages, 6 figure

The Third Order Scalar Induced Gravitational Waves

Since the gravitational waves were detected by LIGO and Virgo, it has been promising that lots of information about the primordial Universe could be learned by further observations on stochastic gravitational waves background. The studies on gravitational waves induced by primordial curvature perturbations are of great interest. The aim of this paper is to investigate the third order induced gravitational waves. Based on the theory of cosmological perturbations, the first order scalar induces the second order scalar, vector and tensor perturbations. At the next iteration, the first order scalar, the second order scalar, vector and tensor perturbations all induce the third order tensor perturbations. We present the energy density spectrum of the third order gravitational waves for a monochromatic primordial power spectrum. The shape of the energy density spectrum of the third order gravitational waves is different from that of the second order scalar induced gravitational waves. And it is found that the third order gravitational waves sourced by the second order scalar perturbations dominate the energy density spectrum.Comment: 33 pages, 4 figure

A theory of multiple vehicle type dynamic marginal cost considering departure time choices

The analysis of single vehicle type dynamic marginal cost is extended to multiple vehicle type dynamic one based on time‐dependent multiple vehicle type queue analysis at a bottleneck. First, a dynamic link model to rep‐ resent the interactions between cars and trucks is provided. Then, the analytic expression of a multiple vehicle type dynamic marginal cost function considering departure time choices is deduced under congested and un‐congested conditions and consequently, a dynamic toll function is given. A heuristic algorithm is introduced to solve multiple vehicle type dynamic queues and toll under system optimum and user equilibrium conditions taking into account traveler's departure time. A numerical example shows that a dynamic congestion toll can diminish queues and improve system conditions when traffic demand is not changed. First published online: 10 Feb 201