Size distributions in irreversible particle aggregation

The aggregation of particles in the free molecular regime pertaining to cluster growth is determined approximately for kernels describing frequently occurring physical situations. The mean particle sizes develop close to linearly in time. Scaling relations are used to derive a linear partial differential equation which is solved to show that the size distributions are close to log-normal size distributions asymptotically in time.Comment: 6 pages, 3 figure

The Largest Fullerene

Fullerenes are lowest energy structures for gas phase all-carbon particles for a range of sizes, but graphite remains the lowest energy allotrope of bulk carbon. This implies that the lowest energy structure changes nature from fullerenes to graphite or graphene at some size and therefore, in turn, implies a limit on the size of free fullerenes as ground state structures. We calculate this largest stable single shell fullerene to be of size $N=1\times10^4$, using the AIREBO effective potential. Above this size fullerene onions are more stable, with an energy per atom that approaches graphite structures. Onions and graphite have very similar ground state energies, raising the intriguing possibility that fullerene onions could be the lowest free energy states of large carbon particles in some temperature range

Cascade infrared thermal photon emission

The time development of the excitation energy of molecules and clusters cooling by emission of thermal vibrational infrared radiation has been studied. The energy distributions and the photon emission rates develop into near-universal functions that can be characterized with only a few parameters, irrespective of the precise vibrational spectra and oscillator strengths of the systems. The photon emission constant and emitted power averaged over all thermally populated states vary linearly with total excitation energy with a small offset. The time developments of ensemble internal energy distributions are calculated with respect to their first two moments. For the derived linear dependence of the emission rate constant, these results are exact

Evolutionary-conserved telomere-linked helicase genes of fission yeast are repressed by silencing factors, RNAi components and the telomere-binding protein Taz1

In Schizosaccharomyces pombe the RNAi machinery and proteins mediating heterochromatin formation regulate the transcription of non-coding centromeric repeats. These repeats share a high sequence similarity with telomere-linked helicase (tlh) genes, implying an ancestral relationship between the two types of elements and suggesting that transcription of the tlh genes might be regulated by the same factors as centromeric repeats. Indeed, we found that mutants lacking the histone methyltransferase Clr4, the Pcu4 cullin, Clr7 or Clr8, accumulate high levels of tlh forward and reverse transcripts. Mutations and conditions perturbing histone acetylation had similar effects further demonstrating that the tlh genes are normally repressed by heterochromatin. In contrast, mutations in the RNAi factors Dcr1, Ago1 or Rdp1 led only to a modest derepression of the tlh genes indicating an alternate pathway recruits heterochromatin components to telomeres. The telomere-binding protein Taz1 might be part of such a redundant pathway, tlh transcripts being present at low levels in Δtaz1 mutants and at higher levels in Δtaz1 Δdcr1 double mutants. Surprisingly, the chromodomain protein Chp1, a component of the Ago1-containing RITS complex, contributes more to tlh repression than Ago1, indicating the repressive effects of Chp1 are partially independent of RITS. The tlh genes are found in the subtelomeric regions of several other fungi raising the intriguing possibility of conserved regulation and function

Metabolic engineering of Saccharomyces cerevisiae to harness natures valuable compounds

Nature contains a treasure trove of small molecule ingredients that can improve health, wellness and nutrition. However, most of these ingredients have “issues”: the organism that makes the compound of interest is too rare, too hard to grow or does not make enough of it. Hence, the ingredient is not available at the right quality, the right price nor the necessary amount. These issues need to be solved in order to allow a larger society having access to these valuable ingredients in a sustainable manner at low costs. Evolva is leader in metabolic engineering of yeast for the production by fermentation of a diverse array of small molecule ingredients. The small molecule ingredients introduced to the market by Evolva include Resveratrol, Nootkatone, Valencene and Vanillin. Evolva and its commercial partner will launch the next-generation stevia sweetener EverSweetTM in 2018. All of these molecules are produced in a sustainable, reliable, cost-effective production at consistent quality by fermentation of engineered yeast strains, using abundant, inexpensive raw materials. Of particular interest to Evolva are the terpenes, which are known to work in a wide range of high value applications including sweeteners, flavors and fragrances, personal care, as well as human and animal health products. In spite of proven efficacy, there has been relatively little commercial development of terpene-based ingredients, mostly due to their high production cost. Here, we will present a number of terpene-based Evolva ingredient projects such as e.g. the stevia pathway, which use Evolva’s technology platforms, allowing us to produce these ingredients in an efficient and sustainable way. Please click Additional Files below to see the full abstract