The trion: two electrons plus one hole versus one electron plus one exciton

We first show that, for problems dealing with trions, it is totally hopeless to use the standard many-body description in terms of electrons and holes and its associated Feynman diagrams. We then show how, by using the description of a trion as an electron interacting with an exciton, we can obtain the trion absorption through far simpler diagrams, written with electrons and \emph{excitons}. These diagrams are quite novel because, for excitons being not exact bosons, we cannot use standard procedures designed to deal with interacting true fermions or true bosons. A new many-body formalism is necessary to establish the validity of these electron-exciton diagrams and to derive their specific rules. It relies on the ``commutation technique'' we recently developed to treat interacting close-to-bosons. This technique generates a scattering associated to direct Coulomb processes between electrons and excitons and a dimensionless ``scattering'' associated to electron exchange inside the electron-exciton pairs -- this ``scattering'' being the original part of our many-body theory. It turns out that, although exchange is crucial to differentiate singlet from triplet trions, this ``scattering'' enters the absorption explicitly when the photocreated electron and the initial electron have the same spin -- \emph{i}. \emph{e}., when triplet trions are the only ones created -- \emph{but not} when the two spins are different, although triplet trions are also created in this case. The physical reason for this rather surprising result will be given

How to Fail College

“How to Fail College” is a collection of short stories which explore both the physical college setting and the related feelings of aimlessness, anxiety, and guilt. This depiction of college aims to be serious, without sounding serious—to be funny without turning into parody. This is not technically an instruction manual, but all five stories should give a clear indication of how and why each character fails out of college

Linear Oligopeptides .245. Crystal and Molecular-structures of 2 N-carboxy Anhydrides of C-alpha,alpha-disubstituted Glycines

The crystal and molecular structures of 4,4-diethyl-oxazolidine-2,5-dione (1) and 3-(2'-nitrophenylsulfenyl)-4,4-di-n-propyl-oxazolidine-2,5-dione (2) have been determined by X-ray diffraction. The compounds possess the following parameters: (1) monoclinic, space group P2(1)/n (No. 14), a = 8.931(1) angstrom, b = 11.749(2) angstrom, c = 7.867(1) angstrom, beta = 98.0(2)-degrees, and Z = 4; (2) triclinic, space group P1BAR (No. 2), a = 12.187(2) angstrom, b = 9.588(1) angstrom, c = 7.681(1) angstrom, alpha = 72.9(2)-degrees, beta = 73.0(2)-degrees, gamma = 84.9(2)-degrees, Z = 2. The crystal structures were solved by direct methods. The least-squares refinements led to R values of 0.040 and 0.039 for 1144 and 2068 reflections with F greater-than-or-equal-to 7-sigma(F) for (1) and (2), respectively. The molecules of (1) are linked by intermolecular N1-H1...O2 = C2 hydrogen bonds along the y direction. The difference observed between the C1-O1 and C2-O1 distances within the heterocyclic moiety of (1) is not found in (2)

DataSheet_1_Seed sourcing strategies for ecological restoration under climate change: A review of the current literature.docx

Climate change continues to alter the seasonal timing and extremes of global temperature and precipitation patterns. These departures from historic conditions along with the predicted variability of future climates present a challenge to seed sourcing, or provenance strategy decisions, within the practice of ecological restoration. The “local is best” for seed sourcing paradigm is predicated upon the assumption that ecotypes are genetically adapted to their local environment. However, local adaptations are potentially being outpaced by climate change, and the ability of plant populations to naturally migrate or shift their distribution accordingly may be limited by habitat fragmentation. Restoration practitioners and natural area managers have a general understanding of the importance of matching the inherent adaptations of source populations with the current and/or future site conditions where those seeds or propagules are planted. However, for many species used in seed-based restoration, there is a lack of empirical evidence to guide seed sourcing decisions, which are critical for the longevity and ecological function of restored natural communities. With the goal of characterizing, synthesizing, and applying experimental research to guide restoration practice, we conducted a systematic review of the literature on provenance testing of taxa undertaken to inform seed sourcing strategies for climate resiliency. We found a strong bias in the choice of study organism: most studies have been conducted on tree species. We also found a strong bias regarding where this research has been conducted, with North America (52%) and Europe (31%) overrepresented. Experiments were designed to assess how propagule origin influences performance across both climatic (26%) and geographic (15%) distance, with some studies focused on determining how climate normal conditions (39%) impacted performance related to survivorship, growth and other parameters. We describe the patterns and gaps our review identified, highlight specific topics which require further research, and provide practical suggestions of immediate and longer-term tools that restoration practitioners can use to guide and build resilient natural communities under future climate scenarios.</p

Table_2_Seed sourcing strategies for ecological restoration under climate change: A review of the current literature.xlsx

Climate change continues to alter the seasonal timing and extremes of global temperature and precipitation patterns. These departures from historic conditions along with the predicted variability of future climates present a challenge to seed sourcing, or provenance strategy decisions, within the practice of ecological restoration. The “local is best” for seed sourcing paradigm is predicated upon the assumption that ecotypes are genetically adapted to their local environment. However, local adaptations are potentially being outpaced by climate change, and the ability of plant populations to naturally migrate or shift their distribution accordingly may be limited by habitat fragmentation. Restoration practitioners and natural area managers have a general understanding of the importance of matching the inherent adaptations of source populations with the current and/or future site conditions where those seeds or propagules are planted. However, for many species used in seed-based restoration, there is a lack of empirical evidence to guide seed sourcing decisions, which are critical for the longevity and ecological function of restored natural communities. With the goal of characterizing, synthesizing, and applying experimental research to guide restoration practice, we conducted a systematic review of the literature on provenance testing of taxa undertaken to inform seed sourcing strategies for climate resiliency. We found a strong bias in the choice of study organism: most studies have been conducted on tree species. We also found a strong bias regarding where this research has been conducted, with North America (52%) and Europe (31%) overrepresented. Experiments were designed to assess how propagule origin influences performance across both climatic (26%) and geographic (15%) distance, with some studies focused on determining how climate normal conditions (39%) impacted performance related to survivorship, growth and other parameters. We describe the patterns and gaps our review identified, highlight specific topics which require further research, and provide practical suggestions of immediate and longer-term tools that restoration practitioners can use to guide and build resilient natural communities under future climate scenarios.</p

Table_1_Seed sourcing strategies for ecological restoration under climate change: A review of the current literature.xlsx

Climate change continues to alter the seasonal timing and extremes of global temperature and precipitation patterns. These departures from historic conditions along with the predicted variability of future climates present a challenge to seed sourcing, or provenance strategy decisions, within the practice of ecological restoration. The “local is best” for seed sourcing paradigm is predicated upon the assumption that ecotypes are genetically adapted to their local environment. However, local adaptations are potentially being outpaced by climate change, and the ability of plant populations to naturally migrate or shift their distribution accordingly may be limited by habitat fragmentation. Restoration practitioners and natural area managers have a general understanding of the importance of matching the inherent adaptations of source populations with the current and/or future site conditions where those seeds or propagules are planted. However, for many species used in seed-based restoration, there is a lack of empirical evidence to guide seed sourcing decisions, which are critical for the longevity and ecological function of restored natural communities. With the goal of characterizing, synthesizing, and applying experimental research to guide restoration practice, we conducted a systematic review of the literature on provenance testing of taxa undertaken to inform seed sourcing strategies for climate resiliency. We found a strong bias in the choice of study organism: most studies have been conducted on tree species. We also found a strong bias regarding where this research has been conducted, with North America (52%) and Europe (31%) overrepresented. Experiments were designed to assess how propagule origin influences performance across both climatic (26%) and geographic (15%) distance, with some studies focused on determining how climate normal conditions (39%) impacted performance related to survivorship, growth and other parameters. We describe the patterns and gaps our review identified, highlight specific topics which require further research, and provide practical suggestions of immediate and longer-term tools that restoration practitioners can use to guide and build resilient natural communities under future climate scenarios.</p

STRUCTURAL VERSATILITY OF PEPTIDES FROM C-ALPHA-ALPHA-DIALKYLATED GLYCINES .2. AN IR ABSORPTION AND H-1-NMR STUDY OF HOMO-OLIGOPEPTIDES FROM C-ALPHA-ALPHA-DIETHYLGLYCINE

The conformational preferences of the N-trifluoroacetylated homo-peptides of Cα,α-diethylglycine from monomer to pentamer in chloroform solution were determined by using ir absorption and 1H-nmr. Intramolecular hydrogen bonding was found to be the dominant factor for all NH groups