Multiexcitons confined within a sub-excitonic volume: Spectroscopic and dynamical signatures of neutral and charged biexcitons in ultrasmall semiconductor nanocrystals

The use of ultrafast gating techniques allows us to resolve both spectrally and temporally the emission from short-lived neutral and negatively charged biexcitons in ultrasmall (sub-10 nm) CdSe nanocrystals (nanocrystal quantum dots). Because of forced overlap of electronic wave functions and reduced dielectric screening, these states are characterized by giant interaction energies of tens (neutral biexcitons) to hundreds (charged biexcitons) of meV. Both types of biexcitons show extremely short lifetimes (from sub-100 picoseconds to sub-picosecond time scales) that rapidly shorten with decreasing nanocrystal size. These ultrafast relaxation dynamics are explained in terms of highly efficient nonradiative Auger recombination.Comment: 5 pages, 4 figures, to be published in Phys. Rev.

Peptide exchange on MHC-I by TAPBPR is driven by a negative allostery release cycle.

Chaperones TAPBPR and tapasin associate with class I major histocompatibility complexes (MHC-I) to promote optimization (editing) of peptide cargo. Here, we use solution NMR to investigate the mechanism of peptide exchange. We identify TAPBPR-induced conformational changes on conserved MHC-I molecular surfaces, consistent with our independently determined X-ray structure of the complex. Dynamics present in the empty MHC-I are stabilized by TAPBPR and become progressively dampened with increasing peptide occupancy. Incoming peptides are recognized according to the global stability of the final pMHC-I product and anneal in a native-like conformation to be edited by TAPBPR. Our results demonstrate an inverse relationship between MHC-I peptide occupancy and TAPBPR binding affinity, wherein the lifetime and structural features of transiently bound peptides control the regulation of a conformational switch located near the TAPBPR binding site, which triggers TAPBPR release. These results suggest a similar mechanism for the function of tapasin in the peptide-loading complex

Ionoluminescent response of several phosphor screens to keV ions of different masses

We have characterized the ionoluminescent response of several phosphor powder materials when irradiated with ions of different masses H+ ,He+ ,Ar+ accelerated to keV energies. In particular, we have determined the absolute luminosity in terms of the number of photons per incident ion emitted by luminescent screens of Y2O2S:Tb P45, Y3Al5O12 :Ce P46, Y2SiO5 :Ce P47, Y2O3 :Eu P56, and SrGa2S4 :Eu TG-green. Their ionoluminescence has been studied as a function of ion beam energy and current and ion fluency. The energy trend and mass dependence of selected experimental results are compared relative to stopping and range of ions in matter SRIM code predictions.Ministerio de Educación y Ciencia FTN2003-090

Schumpeter: Theorist of the Avant-Garde

This paper argues that Schumpeter’s 1911 edition of ‘Theory of Economic Development’ can be fruitfully read as a theory of the avant-garde, in line with such theories developed by artistic avant-garde around the same time, in particular by the Italian Futurists. In particular it will show that both Schumpeter and other avant-garde theorists sought to break with past (1), identify an avant-garde who could force that break (2), find new ways to represent the dynamic world (3), embrace the new and dynamic (4) and promote a perpetual dynamic process, instead of a specific end-state or utopia (5). This new reading helps us to understand the cultural meaning of this seminal text in economics. Secondly it greatly facilitates our understanding of the differences with the later interwar German edition and English edition, which were more cautious in their embrace of the new, less focused on the individual qualities of the entrepreneur and placed more emphasis on historical continuity. Thirdly this reading suggests a different reason for the bifurcation between Schumpeter and the rest of the Austrian school of economics. Traditionally this split is explained by Schumpeter’s affinities with the Lausanne School, this paper instead suggests that the crucial break between Schumpeter on the one hand and Böhm-Bawerk, Wieser and later members of the Austrian School on the other hand is their theory of and attitude toward social change

Reprogramming the assembly of unmodified DNA with a small molecule

The ability of DNA to store and encode information arises from base pairing of the four-letter nucleobase code to form a double helix. Expanding this DNA ‘alphabet’ by synthetic incorporation of new bases can introduce new functionalities and enable the formation of novel nucleic acid structures. However, reprogramming the self-assembly of existing nucleobases presents an alternative route to expand the structural space and functionality of nucleic acids. Here we report the discovery that a small molecule, cyanuric acid, with three thymine-like faces reprogrammes the assembly of unmodified poly(adenine) (poly(A)) into stable, long and abundant fibres with a unique internal structure. Poly(A) DNA, RNA and peptide nucleic acid all form these assemblies. Our studies are consistent with the association of adenine and cyanuric acid units into a hexameric rosette, which brings together poly(A) triplexes with a subsequent cooperative polymerization. Fundamentally, this study shows that small hydrogen-bonding molecules can be used to induce the assembly of nucleic acids in water, which leads to new structures from inexpensive and readily available materials

Analysis of two methods of isometric muscle contractions during the anti-G straining maneuver

This study investigated the difference in Mean Arterial Pressure (MAP) and Cardiac Output (CO) between two methods of isometric muscle contractions during the Anti-G Straining Maneuver (AGSM). 12 subjects (ages 18 to 38 yrs, height 176.8 +/- 7.4 cm, body mass 78.8 +/- 15.6 kg, percent body fat 14.3 +/- 6.6%) participated in the study. The study was a one-way within-subject design with test conditions counterbalanced. Two methods of isometric muscle contractions lasting 30 seconds each were assessed; an isometric push contraction and an isometric muscle tensing contraction. The dependent parameters were MAP and CO. The average MAP during the push contraction was 123 mmHg, SD +/- 11 and for tense was 118 mmHg, SD +/- 8. CO was 7.6 L/min, SD +/- 1.6 for push and 7.9 L/min, SD +/- 2.0 for tense method. Dependent t-tests revealed t(11) = 1.517, p = 0.157 for MAP and t(11) = 0.875, p = 0.400 for CO. This study demonstrated that the two methods of isometric muscle contractions were not statistically different with regards to MAP and CO. Therefore, both forms of isometric contractions may be potentially useful when performing the muscle contraction portion of the AGSM

Schumpeter's Idea of a Universal Science

This paper deals with methodological principles of Schumpeter’s academic writings. Those principles led Schumpeter to create diverse works and were reflected systematically in some of his writings, where Schumpeter emerged as a theorist of science. Besides working on specific topics, Schumpeter dealt systematically with methodological issues in different works. Schumpeter’s History of Economic Analysis, in particular, must be regarded as the one study among his diverse works, which is considered not only his latest but also his most relevant analysis concerning social sciences and the role of economics in relation to sociology, history and other academic branches. The substantial preface of the History of Economic Analysis can be regarded as a manual on how to refer to different academic branches and integrate them into a coherent universal social science, which is far removed from being an autistic, narrow economic science of some modern representation. Although Schumpeter’s History of Economic Analysis has been extensively printed in several editions, the idea is that the preface especially reveals somewhat neglected thoughts in Schumpeterian discourse. While Schumpeter is mostly regarded as a pioneer of evolutionary economics, this paper argues that Schumpeter could also, perhaps primarily, be interpreted as a well-reasoning institutionalist aiming at a universal social science. From today’s point of view, Schumpeter is a truly interdisciplinary theorist