295 research outputs found
Exploiting disorder for perfect focusing
We demonstrate experimentally that disordered scattering can be used to
improve, rather than deteriorate, the focusing resolution of a lens. By using
wavefront shaping to compensate for scattering, light was focused to a spot as
small as one tenth of the diffraction limit of the lens. We show both
experimentally and theoretically that it is the scattering medium, rather than
the lens, that determines the width of the focus. Despite the disordered
propagation of the light, the profile of the focus was always exactly equal to
the theoretical best focus that we derived.Comment: 4 pages, 4 figure
The strength of the corticospinal tract not the reticulospinal tract determines upper-limb impairment level and capacity for skill-acquisition in the sub-acute post-stroke period
Background. Upper-limb impairment in patients with chronic stroke appears to be partly attributable to an upregulated reticulospinal tract (RST). Here, we assessed whether the impact of corticospinal (CST) and RST connectivity on motor impairment and skill-acquisition differs in sub-acute stroke, using transcranial magnetic stimulation (TMS)–based proxy measures. Methods. Thirty-eight stroke survivors were randomized to either reach training 3-6 weeks post-stroke (plus usual care) or usual care only. At 3, 6 and 12 weeks post-stroke, we measured ipsilesional and contralesional cortical connectivity (surrogates for CST and RST connectivity, respectively) to weak pre-activated triceps and deltoid muscles with single pulse TMS, accuracy of planar reaching movements, muscle strength (Motricity Index) and synergies (Fugl-Meyer upper-limb score). Results. Strength and presence of synergies were associated with ipsilesional (CST) connectivity to the paretic upper-limb at 3 and 12 weeks. Training led to planar reaching skill beyond that expected from spontaneous recovery and occurred for both weak and strong ipsilesional tract integrity. Reaching ability, presence of synergies, skill-acquisition and strength were not affected by either the presence or absence of contralesional (RST) connectivity. Conclusion. The degree of ipsilesional CST connectivity is the main determinant of proximal dexterity, upper-limb strength and synergy expression in sub-acute stroke. In contrast, there is no evidence for enhanced contralesional RST connectivity contributing to any of these components of impairment. In the sub-acute post-stroke period, the balance of activity between CST and RST may matter more for the paretic phenotype than RST upregulation per se
Constructing Dirac linear fermions in terms of non-linear Heisenberg spinors
We show that the massive (or massless) neutrinos can be described as special
states of Heisenberg nonlinear spinors. As a by-product of this decomposition a
particularly attractive consequence appears: the possibility of relating the
existence of only three species of mass-less neutrinos to such internal
non-linear structure. At the same time it allows the possibility that neutrino
oscillation can occurs even for massless neutrinos
Colored Motifs Reveal Computational Building Blocks in the C. elegans Brain
Background: Complex networks can often be decomposed into less complex sub-networks whose structures can give hints about the functional
organization of the network as a whole. However, these structural
motifs can only tell one part of the functional story because in this
analysis each node and edge is treated on an equal footing. In real
networks, two motifs that are topologically identical but whose nodes
perform very different functions will play very different roles in the
network.
Methodology/Principal Findings: Here, we combine structural information
derived from the topology of the neuronal network of the nematode C.
elegans with information about the biological function of these nodes,
thus coloring nodes by function. We discover that particular
colorations of motifs are significantly more abundant in the worm brain
than expected by chance, and have particular computational functions
that emphasize the feed-forward structure of information processing in
the network, while evading feedback loops. Interneurons are strongly
over-represented among the common motifs, supporting the notion that
these motifs process and transduce the information from the sensor
neurons towards the muscles. Some of the most common motifs identified
in the search for significant colored motifs play a crucial role in the
system of neurons controlling the worm's locomotion.
Conclusions/Significance: The analysis of complex networks in terms of
colored motifs combines two independent data sets to generate insight
about these networks that cannot be obtained with either data set
alone. The method is general and should allow a decomposition of any
complex networks into its functional (rather than topological) motifs
as long as both wiring and functional information is available
Focusing and Compression of Ultrashort Pulses through Scattering Media
Light scattering in inhomogeneous media induces wavefront distortions which
pose an inherent limitation in many optical applications. Examples range from
microscopy and nanosurgery to astronomy. In recent years, ongoing efforts have
made the correction of spatial distortions possible by wavefront shaping
techniques. However, when ultrashort pulses are employed scattering induces
temporal distortions which hinder their use in nonlinear processes such as in
multiphoton microscopy and quantum control experiments. Here we show that
correction of both spatial and temporal distortions can be attained by
manipulating only the spatial degrees of freedom of the incident wavefront.
Moreover, by optimizing a nonlinear signal the refocused pulse can be shorter
than the input pulse. We demonstrate focusing of 100fs pulses through a 1mm
thick brain tissue, and 1000-fold enhancement of a localized two-photon
fluorescence signal. Our results open up new possibilities for optical
manipulation and nonlinear imaging in scattering media
Achievement motives and emotional processes in children during problem-solving: Two experimental studies of their relation to performance in different achievement goal conditions
In two studies, the influence of key emotional and motivational factors on performance in different achievement goal-type situations is examined. In study 1, based on 314 sixth-graders, two types of goal situations were induced; performance and mastery. The goals were examined with respect to important antecedents (e.g., motive dispositions) and several consequences (e.g., performance, satisfaction, pleasant affect, worry, and emotionality). The results showed that the motive to achieve success (Ms) produced positive affects, satisfaction, and increased performance, whereas the motive to avoid failure (Mf) produced worries and performance reduction. In study 2, based on 331 sixth-graders, three types of goal situations were induced; performance–approach, performance–avoidance, and mastery goals. The findings revealed that the most important single factors positively related to performance were Ms and mastery–goal situation. In addition, high Ms pupils performed better under mastery condition than under performance condition. Finally, avoidance-goal situation accentuate the negative effects of high Mf on performance
The Spectrin Cytoskeleton Is Crucial for Adherent and Invasive Bacterial Pathogenesis
Various enteric bacterial pathogens target the host cell cytoskeletal machinery as a crucial event in their pathogenesis. Despite thorough studies detailing strategies microbes use to exploit these components of the host cell, the role of the spectrin-based cytoskeleton has been largely overlooked. Here we show that the spectrin cytoskeleton is a host system that is hijacked by adherent (Entropathogenic Escherichia coli [EPEC]), invasive triggering (Salmonella enterica serovar Typhimurium [S. Typhimurium]) and invasive zippering (Listeria monocytogenes) bacteria. We demonstrate that spectrin cytoskeletal proteins are recruited to EPEC pedestals, S. Typhimurium membrane ruffles and Salmonella containing vacuoles (SCVs), as well as sites of invasion and comet tail initiation by L. monocytogenes. Spectrin was often seen co-localizing with actin filaments at the cell periphery, however a disconnect between the actin and spectrin cytoskeletons was also observed. During infections with S. Typhimurium ΔsipA, actin-rich membrane ruffles at characteristic sites of bacterial invasion often occurred in the absence of spectrin cytoskeletal proteins. Additionally, early in the formation of L. monocytogenes comet tails, spectrin cytoskeletal elements were recruited to the surface of the internalized bacteria independent of actin filaments. Further studies revealed the presence of the spectrin cytoskeleton during SCV and Listeria comet tail formation, highlighting novel cytoplasmic roles for the spectrin cytoskeleton. SiRNA targeted against spectrin and the spectrin-associated proteins severely diminished EPEC pedestal formation as well as S. Typhimurium and L. monocytogenes invasion. Ultimately, these findings identify the spectrin cytoskeleton as a ubiquitous target of enteric bacterial pathogens and indicate that this cytoskeletal system is critical for these infections to progress
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Differential epigenetic reprogramming in response to specific endocrine therapies promotes cholesterol biosynthesis and cellular invasion
Endocrine therapies target the activation of the oestrogen receptor alpha (ERα) via distinct mechanisms, but it is not clear whether breast cancer cells can adapt to treatment using drug-specific mechanisms. Here we demonstrate that resistance emerges via drug-specific epigenetic reprogramming. Resistant cells display a spectrum of phenotypical changes with invasive phenotypes evolving in lines resistant to the aromatase inhibitor (AI). Orthogonal genomics analysis of reprogrammed regulatory regions identifies individual drug-induced epigenetic states involving large topologically associating domains (TADs) and the activation of super-enhancers. AI-resistant cells activate endogenous cholesterol biosynthesis (CB) through stable epigenetic activation in vitro and in vivo. Mechanistically, CB sparks the constitutive activation of oestrogen receptors alpha (ERα) in AI-resistant cells, partly via the biosynthesis of 27-hydroxycholesterol. By targeting CB using statins, ERα binding is reduced and cell invasion is prevented. Epigenomic-led stratification can predict resistance to AI in a subset of ERα-positive patients
Identification and Characterization of Ixodes scapularis Antigens That Elicit Tick Immunity Using Yeast Surface Display
Repeated exposure of rabbits and other animals to ticks results in acquired resistance or immunity to subsequent tick bites and is partially elicited by antibodies directed against tick antigens. In this study we demonstrate the utility of a yeast surface display approach to identify tick salivary antigens that react with tick-immune serum. We constructed an Ixodes scapularis nymphal salivary gland yeast surface display library and screened the library with nymph-immune rabbit sera and identified five salivary antigens. Four of these proteins, designated P8, P19, P23 and P32, had a predicted signal sequence. We generated recombinant (r) P8, P19 and P23 in a Drosophila expression system for functional and immunization studies. rP8 showed anti-complement activity and rP23 demonstrated anti-coagulant activity. Ixodes scapularis feeding was significantly impaired when nymphs were fed on rabbits immunized with a cocktail of rP8, rP19 and rP23, a hall mark of tick-immunity. These studies also suggest that these antigens may serve as potential vaccine candidates to thwart tick feeding
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