Mechanics of collective unfolding

Mechanically induced unfolding of passive crosslinkers is a fundamental biological phenomenon encountered across the scales from individual macro-molecules to cytoskeletal actin networks. In this paper we study a conceptual model of athermal load-induced unfolding and use a minimalistic setting allowing one to emphasize the role of long-range interactions while maintaining full analytical transparency. Our model can be viewed as a description of a parallel bundle of N bistable units confined between two shared rigid backbones that are loaded through a series spring. We show that the ground states in this model correspond to synchronized, single phase configurations where all individual units are either folded or unfolded. We then study the fine structure of the wiggly energy landscape along the reaction coordinate linking the two coherent states and describing the optimal mechanism of cooperative unfolding. Quite remarkably, our study shows the fundamental difference in the size and structure of the folding-unfolding energy barriers in the hard (fixed displacements) and soft (fixed forces) loading devices which persists in the continuum limit. We argue that both, the synchronization and the non-equivalence of the mechanical responses in hard and soft devices, have their origin in the dominance of long-range interactions. We then apply our minimal model to skeletal muscles where the power-stroke in acto-myosin crossbridges can be interpreted as passive folding. A quantitative analysis of the muscle model shows that the relative rigidity of myosin backbone provides the long-range interaction mechanism allowing the system to effectively synchronize the power-stroke in individual crossbridges even in the presence of thermal fluctuations. In view of the prototypical nature of the proposed model, our general conclusions pertain to a variety of other biological systems where elastic interactions are mediated by effective backbones

Directed forgetting of source memory in normal aging and Alzheimer's disease

BACKGROUND AND AIMS: Using the source directed forgetting method, the present paper investigated whether older adults and Alzheimer\u27s disease (AD) patients were able to inhibit source information. METHODS: Younger adults, older adults and AD participants were presented with two sets of six items each: Set1 and Set2. Each item was presented by one of two sources: an experimenter black- or white-gloved hand. After the presentation of the Set1 items, participants were instructed either to forget or to continue remembering the source of the items. Afterward, all participants were presented with the Set2 items, and were asked to remember their source. Finally, subjects were exposed to the Set1 and Set2 items, and were asked to recall, for each item, its original source presentation (i.e., the experimenter black- or white-gloved hand). RESULTS: In comparison with younger adults, older adults and AD participants showed no differences in remembering the source of the Set1 and Set2 items. In other words, they failed to inhibit the source information. DISCUSSION AND CONCLUSION: Our outcomes are discussed in terms of retrieval inhibition deficits and changes in adaptive nature of memory in normal aging and AD

Inactivation of Plasmodium falciparum in whole blood by riboflavin plus irradiation.

BACKGROUND: Malaria parasites are frequently transmitted by unscreened blood transfusions in Africa. Pathogen reduction methods in whole blood would thus greatly improve blood safety. We aimed to determine the efficacy of riboflavin plus irradiation for treatment of whole blood infected with Plasmodium falciparum. STUDY DESIGN AND METHODS: Blood was inoculated with 10(4) or 10(5) parasites/mL and riboflavin treated with or without ultraviolet (UV) irradiation (40-160 J/mL red blood cells [mL(RBCs)]). Parasite genome integrity was assessed by quantitative amplification inhibition assays, and P. falciparum viability was monitored in vitro. RESULTS: Riboflavin alone did not affect parasite genome integrity or parasite viability. Application of UV after riboflavin treatment disrupted parasite genome integrity, reducing polymerase-dependent amplification by up to 2 logs (99%). At 80 J/mL(RBCs), riboflavin plus irradiation prevented recovery of viable parasites in vitro for 2 weeks, whereas untreated controls typically recovered to approximately 2% parasitemia after 4 days of in vitro culture. Exposure of blood to 160 J/mL(RBCs) was not associated with significant hemolysis. CONCLUSIONS: Riboflavin plus irradiation treatment of whole blood damages parasite genomes and drastically reduces P. falciparum viability in vitro. In the absence of suitable malaria screening assays, parasite inactivation should be investigated for prevention of transfusion-transmitted malaria in highly endemic areas

Governance gaps in eradicating forced labor: from global to domestic supply chains

A growing body of scholarship analyzes the emergence and resilience of forced labor in developing countries within global value chains (GVCs). However, little is known about how forced labor arises within domestic supply chains concentrated within national borders, producing products for domestic consumption. We conduct one of the first studies of forced labor in domestic supply chains, through a cross-industry comparison of the regulatory gaps surrounding forced labor in the United Kingdom. We find that understanding the dynamics of forced labor in domestic supply chains requires us to conceptually modify the GVC framework to understand similarities and differences across these contexts. We conclude that addressing the governance gaps that surround forced labor will require scholars and policymakers to carefully refine their thinking about how we might design operative governance that effectively engages with local variation

Internal Dust Correction Factors for Star Formation Rates Derived for Dusty \HII Regions and Starburst Galaxies

Star formation rates in galaxies are frequently estimated using the Balmer line fluxes. However, these can be systematically underestimated because dust competes for the absorption of Lyman continuum photons in the ionized gas. Here we present theoretical correction factors in a simple analytic form. T These factors scale as the product of the ionization parameter, ${\cal U}$, and the nebular O/H abundance ratio, both of which can now be derived from the observation of bright nebular line ratios. The correction factors are only somewhat dependent upon the photoelectron production by grains, but are very sensitive to the presence of complex PAH-like carbonaceous molecules in the ionized gas, providing that these can survive in such an environment.Comment: 13 pages, 1 figures, Accepted for publication in ApJ. (Feb 1, 2003

Microscopic nanomechanical dissipation in gallium arsenide resonators

We report on a systematic study of nanomechanical dissipation in high-frequency (approximatively 300 MHz) gallium arsenide optomechanical disk resonators, in conditions where clamping and fluidic losses are negligible. Phonon-phonon interactions are shown to contribute with a loss background fading away at cryogenic temperatures (3 K). Atomic layer deposition of alumina at the surface modifies the quality factor of resonators, pointing towards the importance of surface dissipation. The temperature evolution is accurately fitted by two-level systems models, showing that nanomechanical dissipation in gallium arsenide resonators directly connects to their microscopic properties. Two-level systems, notably at surfaces, appear to rule the damping and fluctuations of such high-quality crystalline nanomechanical devices, at all temperatures from 3 to 300K

Management à distance et santé au travail : Quels sont les impacts de l’éloignement et de la méconnaissance du travail réel ?

Cette recherche explore deux cas d’entreprises développant un management à distance. On montrera que ce management focalisé essentiellement sur un contrôle formel de l’activité créé des distorsions entre les représentations du management et celles des salariés. Or, les salariés étant confrontés à une forte incertitude lors de périodes de mutations exigeantes en termes de management des ressources humaines, ces distorsions génèrent chez eux perte de confiance, désengagement, stress et désespoir, qui peuvent avoir un impact important sur leur santé

An Analytical Approach to Neuronal Connectivity

This paper describes how realistic neuromorphic networks can have their connectivity properties fully characterized in analytical fashion. By assuming that all neurons have the same shape and are regularly distributed along the two-dimensional orthogonal lattice with parameter $\Delta$, it is possible to obtain the accurate number of connections and cycles of any length from the autoconvolution function as well as from the respective spectral density derived from the adjacency matrix. It is shown that neuronal shape plays an important role in defining the spatial spread of network connections. In addition, most such networks are characterized by the interesting phenomenon where the connections are progressively shifted along the spatial domain where the network is embedded. It is also shown that the number of cycles follows a power law with their respective length. Morphological measurements for characterization of the spatial distribution of connections, including the adjacency matrix spectral density and the lacunarity of the connections, are suggested. The potential of the proposed approach is illustrated with respect to digital images of real neuronal cells.Comment: 4 pages, 6 figure

Destination memory for emotional information in older adults

Background/Study Context: Destination memory, remembering the destination of the information that one tells, shows significant age-related decline. In the present paper, the authors sought to determine whether destination memory can be improved in older adults using emotional stimuli. This aim was motivated by findings showing better context memory for emotional than for neutral information in older adults. Methods: Younger and older adults were asked to tell neutral facts to three types of faces: a neutral one, an emotionally positive one, and an emotionally negative one. On a later recognition test, participants were asked to associate each previously told fact with the face to whom it was told. Results: Destination memory performance was better for facts told to negative than to positive faces, and the latter memory was better than for neutral faces in older adults. Conclusion: Older adults seem to place higher emphasis on emotional material relative to neutral faces, showing better memory for the association between statements and emotional faces