The Effect of Light And Dark Periods on the Growth of Chlorella Sorokiniana: Modeling & Experimentation

Microalgae are abundant unicellular photosynthetic organisms with more than 200,000 species. They are more efficient in harvesting solar energy than land-based plants with green microalgae having more than ten times higher biodiesel productivity than the next best land-based crop. Their ability to grow in harsh environments, non-agricultural lands, and make use of wastewater, and the diversity of the products that can be extracted from them, which include cosmetics, pharmaceuticals, food supplements, biofuels, and many others, gives them the potential to replace fossil fuels and revolutionize the biotech industry. In order to move onto large scale production, first, the growth rate of the cell culture must be increased, which requires screening of promising species, studying their growth kinetics, and selecting their most suitable environment. Second, microalgae use their internal energy reservoirs (lipid bodies) during dark periods; nighttime biomass loss must be prevented. In this study, we analyzed the effect of light intensity on the growth of Chlorella sorokiniana, a promising species for biofuel production. We constructed a growth model that accurately predicts the growth response of the cell culture to varying irradiance conditions and photoperiods. We incorporated the concept of Monod kinetics into our model and quantified the effect of light intensity on biomass accumulation under lightlimiting conditions. We determined that the empirically measured maximum growth rate v parameter has a value of 0.20 h-1 which is limited by the maximum photosynthetic rate. Additionally, we determined the Monod saturation constant to be 238 |imol s-1 m-2. We found that biomass loss rate due to respiration and other metabolic activities peaked during the day (8.7x10-3 h-1), and was constant during nighttime (1.8x10-3 h-1). We determined that 5% of the biomass gained during the 16-hour day period was lost during the following 8-hour dark period, which lead to a 16% lower biomass yield when compared to a continuously illuminated culture after nine days of cultivation at a constant temperature of 30°C in a well-mixed five-liter photobioreactor. Finally, we illustrated that illuminating the dark period with low-consumption red LEDs will prevent biomass loss and enhance cell replication

Optimal Generation of Pulsed Entangled Photon Pairs

We experimentally investigate a double-pass parametric down-conversion scheme for producing pulsed, polarization-entangled photon pairs with high visibility. The amplitudes for creating photon pairs on each pass interfere to compensate for distinguishing characteristics that normally degrade two-photon visibility. The result is a high-flux source of polarization-entangled photon pulses that does not require spectral filtering. We observe quantum interference visibility of over 95% without the use of spectral filters for 200 femtosecond pulses, and up to 98.1% with 5 nm bandwidth filters.Comment: 8 pages, 6 figure

Fading Gravity and Self-Inflation

We study the cosmology of a toy modified theory of gravity in which gravity shuts off at short distances, as in the fat graviton scenario of Sundrum. In the weak-field limit, the theory is perturbatively local, ghost-free and unitary, although likely suffers from non-perturbative instabilities. We derive novel self-inflationary solutions from the vacuum equations of the theory, without invoking scalar fields or other forms of stress energy. The modified perturbation equation expressed in terms of the Newtonian potential closely resembles its counterpart for inflaton fluctuations. The resulting scalar spectrum is therefore slightly red, akin to the simplest scalar-driven inflationary models. A key difference, however, is that the gravitational wave spectrum is generically not scale invariant. In particular the tensor spectrum can have a blue tilt, a distinguishing feature from standard inflation.Comment: 35 pages, 4 figures. v3: version to appear in Phys. Rev.

Multiphoton path entanglement by non-local bunching

Multiphoton path entanglement is created without applying post-selection, by manipulating the state of stimulated parametric down-conversion. A specific measurement on one of the two output spatial modes leads to the non-local bunching of the photons of the other mode, forming the desired multiphoton path entangled state. We present experimental results for the case of a heralded two-photon path entangled state and show how to extend this scheme to higher photon numbers.Comment: 4 pages, 5 figures, published versio

New Ekpyrotic Cosmology

In this paper, we present a new scenario of the early Universe that contains a pre big bang Ekpyrotic phase. By combining this with a ghost condensate, the theory explicitly violates the null energy condition without developing any ghost-like instabilities. Thus the contracting universe goes through a non-singular bounce and evolves smoothly into the expanding post big bang phase. The curvature perturbation acquires a scale-invariant spectrum well before the bounce in this scenario. It is sourced by the scale-invariant entropy perturbation engendered by two ekpyrotic scalar fields, a mechanism recently proposed by Lehners et al. Since the background geometry is non-singular at all times, the curvature perturbation remains nearly constant on super horizon scales. It emerges from the bounce unscathed and imprints a scale-invariant spectrum of density fluctuations in the matter-radiation fluid at the onset of the hot big bang phase. The ekpyrotic potential can be chosen so that the spectrum has a ``red'' tilt, in accordance with the recent data from WMAP. As in the original Ekpyrotic scenario, the model predicts a negligible gravity wave signal on all observable scales. As such ``New Ekpyrotic Cosmology" provides a consistent and distinguishable alternative to inflation to account for the origin of the seeds of large scale structure.Comment: 41 pages, 4 figures. v2: minor corrections, references added. v3: small modifications in bounce section, references added. v4: version published in PR

Spin-orbit mode transfer via a classical analog of quantum teleportation

We translate the quantum teleportation protocol into a sequence of coherent operations involving three degrees of freedom of a classical laser beam. The protocol, which we demonstrate experimentally, transfers the polarisation state of the input beam to the transverse mode of the output beam. The role of quantum entanglement is played by a non-separable mode describing the path and transverse degrees of freedom. Our protocol illustrates the possibility of new optical applications based on this intriguing classical analogue of quantum entanglement.Comment: 5 pages, 7 figure