Signatures of dark excitons in exciton-polariton optics of transition metal dichalcogenides

Integrating 2D materials into high-quality optical microcavities opens the door to fascinating many-particle phenomena including the formation of exciton-polaritons. These are hybrid quasi-particles inheriting properties of both the constituent photons and excitons. In this work, we investigate the so-far overlooked impact of dark excitons on the momentum-resolved absorption spectra of hBN-encapsulated WSe$_2$ and MoSe$_2$ monolayers in the strong-coupling regime. In particular, thanks to the efficient phonon-mediated scattering of polaritons into energetically lower dark exciton states, the absorption of the lower polariton branch in WSe$_2$ is much higher than in MoSe$_2$. It shows unique step-like increases in the momentum-resolved profile indicating opening of specific scattering channels. We study how different externally accessible quantities, such as temperature or mirror reflectance, change the optical response of polaritons. Our study contributes to an improved microscopic understanding of exciton-polaritons and their interaction with phonons, potentially suggesting experiments that could determine the energy of dark exciton states via momentum-resolved polariton absorption.Comment: 10 pages, 5 figure

Exciton optics, dynamics, and transport in atomically thin semiconductors

Atomically thin semiconductors such as transition metal dichalcogenide (TMD) monolayers exhibit a very strong Coulomb interaction, giving rise to a rich exciton landscape. This makes these materials highly attractive for efficient and tunable optoelectronic devices. In this Research Update, we review the recent progress in the understanding of exciton optics, dynamics, and transport, which crucially govern the operation of TMD-based devices. We highlight the impact of hexagonal boron nitride-encapsulation, which reveals a plethora of many-particle states in optical spectra, and we outline the most novel breakthroughs in the field of exciton-polaritonics. Moreover, we underline the direct observation of exciton formation and thermalization in TMD monolayers and heterostructures in recent time-resolved, angle-resolved photoemission spectroscopy studies. We also show the impact of exciton density, strain, and dielectric environment on exciton diffusion and funneling. Finally, we put forward relevant research directions in the field of atomically thin semiconductors for the near future

Methanosarcina play an important role in anaerobic co-digestion of the seaweed Ulva lactuca: metagenomics structure and predicted metabolism of functional microbial communities.

Macro-algae represent an ideal resource of third generation biofuels, but their use necessitates a refinement of commonly used anaerobic digestion processes. In a previous study, contrasting mixes of dairy slurry and the macro-alga Ulva lactuca were anaerobically digested in mesophilic continuously stirred tank reactors for 40 weeks. Higher proportions of U. lactuca in the feedstock led to inhibited digestion and rapid accumulation of volatile fatty acids, requiring a reduced organic loading rate. In this study, 16S pyrosequencing was employed to characterise the microbial communities of both the weakest (R1) and strongest (R6) performing reactors from the previous work as they developed over a 39 and 27-week period respectively. Comparing the reactor communities revealed clear differences in taxonomy, predicted metabolic orientation and mechanisms of inhibition, while constrained canonical analysis (CCA) showed ammonia and biogas yield to be the strongest factors differentiating the two reactor communities. Significant biomarker taxa and predicted metabolic activities were identified for viable and failing anaerobic digestion of U. lactuca. Acetoclastic methanogens were inhibited early in R1 operation, followed by a gradual decline of hydrogenotrophic methanogens. Near-total loss of methanogens led to an accumulation of acetic acid that reduced performance of R1, while a slow decline in biogas yield in R6 could be attributed to inhibition of acetogenic rather than methanogenic activity. The improved performance of R6 is likely to have been as a result of the large Methanosarcina population, which enabled rapid removal of acetic acid, providing favourable conditions for substrate degradation

Dwarf koa (Desmanthus virgatus)

This is the final version. It was first published by BioMed Central at http://www.biomedcentral.com/1471-2164/16/473.Background: Mobile elements are active in the human genome, both in the germline and cancers, where they can\ud mutate driver genes.\ud Results: While analysing whole genome paired-end sequencing of oesophageal adenocarcinomas to find genomic\ud rearrangements, we identified three ways in which new mobile element insertions appear in the data, resembling\ud translocation or insertion junctions: inserts where unique sequence has been transduced by an L1 (Long interspersed\ud element 1) mobile element; novel inserts that are confidently, but often incorrectly, mapped by alignment software to\ud L1s or polyA tracts in the reference sequence; and a combination of these two ways, where different sequences within\ud one insert are mapped to different loci. We identified nine unique sequences that were transduced by neighbouring\ud L1s, both L1s in the reference genome and L1s not present in the reference. Many of the resulting inserts were small\ud fragments that include little or no recognisable mobile element sequence. We found 6 loci in the reference genome to\ud which sequence reads from inserts were frequently mapped, probably erroneously, by alignment software: these were\ud either L1 sequence or particularly long polyA runs. Inserts identified from such apparent rearrangement junctions\ud averaged 16 inserts/tumour, range 0?153 insertions in 43 tumours. However, many inserts would not be detected by\ud mapping the sequences to the reference genome, because they do not include sufficient mappable sequence. To\ud estimate total somatic inserts we searched for polyA sequences that were not present in the matched normal or other\ud normals from the same tumour batch, and were not associated with known polymorphisms. Samples of these candidate\ud inserts were verified by sequencing across them or manual inspection of surrounding reads: at least 85 % were somatic\ud and resembled L1-mediated events, most including L1Hs sequence. Approximately 100 such inserts were detected per\ud tumour on average (range zero to approximately 700).\ud Conclusions: Somatic mobile elements insertions are abundant in these tumours, with over 75 % of cases having a\ud number of novel inserts detected. The inserts create a variety of problems for the interpretation of paired-end\ud sequencing data.Funding\ud was primarily from Cancer Research UK program grants to RCF and ST\ud (C14478/A15874 and C14303/A17197), with additional support awarded to\ud RCF from UK Medical Research Council, NHS National Institute for Health\ud Research (NIHR), the Experimental Cancer Medicine Centre Network and\ud the NIHR Cambridge Biomedical Research Centre, and Cancer Research UK\ud Project grant C1023/A14545 to PAWE. JMJW was funded by a Wellcome\ud Trust Translational Medicine and Therapeutics grant

Suspended photonic crystal membranes in AlGaAs heterostructures for integrated multi-element optomechanics

We present high-reflectivity mechanical resonators fabricated from AlGaAs heterostructures for use in free-space optical cavities operating in the telecom wavelength regime. The mechanical resonators are fabricated in slabs of GaAs and patterned with a photonic crystal to increase their out-of-plane reflectivity. Characterization of the mechanical modes reveals residual tensile stress in the GaAs device layer. This stress results in higher mechanical frequencies than in unstressed GaAs and can be used for strain engineering of mechanical dissipation. Simultaneously, we find that the finite waist of the incident optical beam leads to a dip in the reflectance spectrum. This feature originates from coupling to a guided resonance of the photonic crystal, an effect that must be taken into account when designing slabs of finite size. The single- and sub-\upmum-spaced double-layer slabs demonstrated here can be directly fabricated on top of a distributed Bragg reflector mirror in the same material platform. Such a platform opens a route for realizing integrated multi-element cavity optomechanical devices and optomechanical microcavities on chip.Comment: close to published version, 4+9 pages, 6+11 figure

Rearrangement processes and structural variations show evidence of selection in oesophageal adenocarcinomas

Oesophageal adenocarcinoma (OAC) provides an ideal case study to characterize large-scale rearrangements. Using whole genome short-read sequencing of 383 cases, for which 214 had matched whole transcriptomes, we observed structural variations (SV) with a predominance of deletions, tandem duplications and inter-chromosome junctions that could be identified as LINE-1 mobile element (ME) insertions. Complex clusters of rearrangements resembling breakage-fusion-bridge cycles or extrachromosomal circular DNA accounted for 22% of complex SVs affecting known oncogenes. Counting SV events affecting known driver genes substantially increased the recurrence rates of these drivers. After excluding fragile sites, we identified 51 candidate new drivers in genomic regions disrupted by SVs, including ETV5, KAT6B and CLTC. RUNX1 was the most recurrently altered gene (24%), with many deletions inactivating the RUNT domain but preserved the reading frame, suggesting an altered protein product. These findings underscore the importance of identification of SV events in OAC with implications for targeted therapies.</p

Rearrangement processes and structural variations show evidence of selection in oesophageal adenocarcinomas

Oesophageal adenocarcinoma (OAC) provides an ideal case study to characterize large-scale rearrangements. Using whole genome short-read sequencing of 383 cases, for which 214 had matched whole transcriptomes, we observed structural variations (SV) with a predominance of deletions, tandem duplications and inter-chromosome junctions that could be identified as LINE-1 mobile element (ME) insertions. Complex clusters of rearrangements resembling breakage-fusion-bridge cycles or extrachromosomal circular DNA accounted for 22% of complex SVs affecting known oncogenes. Counting SV events affecting known driver genes substantially increased the recurrence rates of these drivers. After excluding fragile sites, we identified 51 candidate new drivers in genomic regions disrupted by SVs, including ETV5, KAT6B and CLTC. RUNX1 was the most recurrently altered gene (24%), with many deletions inactivating the RUNT domain but preserved the reading frame, suggesting an altered protein product. These findings underscore the importance of identification of SV events in OAC with implications for targeted therapies.</p

The Grizzly, February 14, 2002

Salt Lake City Says Hello to the 2002 Winter Olympics • Black History Month at Ursinus: How Diverse is the Campus? • Lorelei: Blast or Bust? • All About Enron: Latest in the Scandal • Parking on Campus: Will There be Enough? • Opinions: Is the Bookstore Slighting Us?; New Dance Studio Missing One Thing: Dancers; Women Drinking While Pregnant: Is That Acceptable? • Exclusive Interview with Jamie Kennedy, Host of The Jamie Kennedy Experiment • The Silver-Brown Dance Company Stomps the Night Away • Is Digital TV Coming to Your House? • Introducing the Wellness Center • Black History Month at Ursinus: The Truth • What the Class of 2002 can Expect in the Real World • UC Women\u27s B-Ball Chops Down Washington on Friday, but Kneels to Swarthmore on Sunday • Ursinus Seeks Women\u27s Golf Coach and Prospective Players • UC Invitational Huge Success for Bears • Men\u27s Basketball Clinches Play-off Berth With Two Dominating Wins! • UC Bears Make a Splash in the Pool, Being Out-Touched by a Strong Bryn Mawr Teamhttps://digitalcommons.ursinus.edu/grizzlynews/1507/thumbnail.jp