690 research outputs found
Resonant helical deformations in nonhomogeneous Kirchhoff filaments
We study the three-dimensional static configurations of nonhomogeneous
Kirchhoff filaments with periodically varying Young's modulus. This type of
variation may occur in long tandemly repeated sequences of DNA. We analyse the
effects of the Young's modulus frequence and amplitude of oscillation in the
stroboscopic maps, and in the regular (non chaotic) spatial configurations of
the filaments. Our analysis shows that the tridimensional conformations of long
filaments may depend critically on the Young's modulus frequence in case of
resonance with other natural frequencies of the filament. As expected, far from
resonance the shape of the solutions remain very close to that of the
homogeneous case. In the case of biomolecules, it is well known that various
other elements, besides sequence-dependent effects, combine to determine their
conformation, like self-contact, salt concentration, thermal fluctuations,
anisotropy and interaction with proteins. Our results show that
sequence-dependent effects alone may have a significant influence on the shape
of these molecules, including DNA. This could, therefore, be a possible
mechanical function of the ``junk'' sequences.Comment: 18 pages (twocolumn), 5 figures Revised manuscrip
Study of Plastic Deformation in Binary Aluminum Alloys by Internal-Friction Methods
The damping capacity of several aluminum-copper alloys has been investigated during tensile elongation. This damping is shown to depend on strain rate, strain, temperature, alloy content, and heat treatment. A tentative hypothesis, based on the acceleration of solute atom diffusion by deformation-produced vacancies, is proposed to account for the observed behavior. Internal-friction maxima are observed in deformed aluminum and aluminum-copper alloys at -70 deg and -50 deg C. The peaks appear to be relatively insensitive to frequency and alloy content, but they disappear after annealing at temperatures nearing the recrystallization temperature
On the causes of the African slave trade
This paper offers an integrated analysis of the forces shaping the emergence of the African slave trade over the early modern period. We focus our attention on two questions. First, why most of the increase in the demand for slaves during this period came exclusively from western Europeans. Second, and of most relevance for present-day development outcomes, why was the overwhelming majority of slaves of African origin. Technological differences in manufacturing technology, the specificities of sugar (and other crops') production, and the cultural fragmentation of the African continent all play a role in the analysis. Supporting evidence for each of our claims is provided from a broad corpus of relevant literature
Mdj1p, a novel chaperone of the DnaJ family, is involved in mitochondrial biogenesis and protein folding
Mdj1p, a novel member of the DnaJ family, is a heat shock protein that is associated with the inner membrane of mitochondria of Saccharomyces cerevisiae. Disruption of the MDJ1 gene resulted in a petite phenotype, loss of mitochondrial DNA, and inviability at 37°C. Import of precursor proteins was not affected by a lack of Mdj1p, but folding of newly imported proteins was markedly impaired. The efficiency of refolding of a tester protein, dihydrofolate reductase, was significantly reduced in mitochondria lacking Mdj1p after incubation at elevated temperature. We conclude that Mdj1p is an important mitochondrial chaperone that participates in the folding of newly imported proteins and in the protection of proteins against heat denaturation and aggregation
2075 Papillary muscles and trabeculations significantly impact ventricular volume, ejection fraction, and regurgitation assessment by cardiovascular magnetic resonance in patients with hypertrophic cardiomyopathy
Nonapeptide influences on social behaviour: effects of vasotocin and isotocin on shoaling and interaction in zebrafish
Nonapeptides are important regulators of social behaviour across vertebrate taxa. While their role in simple grouping behaviour has been explored in estrildid finches, other taxa are understudied, prompting us to investigate nonapeptide influences on shoaling behaviour in zebrafish. Subjects received injections of isotocin, an isotocin antagonist, vasotocin, a vasotocin antagonist, or saline, followed by a test of grouping behaviour. Vasotocin decreased social interaction with the shoal. Unexpectedly, the vasotocin antagonist also reduced social interaction with the shoal, as well as general shoaling behaviour. Isotocin and its antagonist had minimal effects on grouping behaviours. These results suggest social interaction and shoaling are discrete aspects of sociality differentially influenced by vasotocin, although we cannot discount possible anxiogenic effects of vasotocin. Contrasting these results with studies in other systems demonstrates that each nonapeptide’s role in social behaviour varies across taxa, and cautions against a simplistic characterisation of nonapeptides as prosocial regulators of behaviour
Atom lasers: production, properties and prospects for precision inertial measurement
We review experimental progress on atom lasers out-coupled from Bose-Einstein
condensates, and consider the properties of such beams in the context of
precision inertial sensing. The atom laser is the matter-wave analog of the
optical laser. Both devices rely on Bose-enhanced scattering to produce a
macroscopically populated trapped mode that is output-coupled to produce an
intense beam. In both cases, the beams often display highly desirable
properties such as low divergence, high spectral flux and a simple spatial mode
that make them useful in practical applications, as well as the potential to
perform measurements at or below the quantum projection noise limit. Both
devices display similar second-order correlations that differ from thermal
sources. Because of these properties, atom lasers are a promising source for
application to precision inertial measurements.Comment: This is a review paper. It contains 40 pages, including references
and figure
Do New Drugs Increase Life Expectancy? A Critique of a Manhattan Institute Paper
A recent study published by the Manhattan Institute “Why Has Longevity Increased More in Some States than in Others? The Role of Medical Innovation and Other Factors,” purported to show that the more rapid adoption of new drugs has substantial benefits in the form of increased life expectancy, higher productivity and lower non-drug health care expenditures. This study has been cited as evidence supporting the more rapid acceptance of new drugs in Medicaid, Medicare, and other public programs and has helped to shape public debate on the value of new drugs. This analysis questions the key conclusions of the study. It points out that the key statistical regressions appear to be misspecified, since they show anomalies such as a negative correlation between income growth and life expectancy and find no relationship between education and productivity growth. Methodological flaws addressed include lack of adjustment for infant mortality rates; inadequate proxy measures of health status; lack of adjustment for ages of individuals and other sociodemographic factors; inherent problems with the definition of drug age, or ‘vintage;’ and the failure to consider reverse causation as an obvious explanation for several findings. The Manhattan Institute study does not provide reliable evidence for favoring adoption of newer drugs in either public or private health care programs
Age-related prefrontal cortex activation in associative memory: an fNIRS pilot study.
Older adults typically perform more poorly than younger adults in free recall memory tests. This age-related deficit has been linked to decline of brain activation and brain prefrontal lateralization, which may be the result of compensatory mechanisms. In the present pilot study, we investigated the effect of age on prefrontal cortex (PFC) activation during performance of a task that requires memory associations (temporal vs. spatial clustering), using functional Near-Infrared Spectroscopy (fNIRS). Ten younger adults, ten cognitively high-performing older individuals, and ten low-performing older individuals completed a free recall task, where either a temporal or spatial strategy (but not both simultaneously) could be employed to retrieve groups of same-category stimuli, whilst changes in PFC haemodynamics were recorded by means of a 12-channel fNIRS system. The results suggest PFC activation, and right lateralization specific to younger adults. Moreover, age did not affect use of memory organization, given that temporal clustering was preferred over spatial clustering in all groups. These findings are in line with previous literature on the aging brain and on temporal organization of memory. Our results also suggest that the PFC may be specifically involved in memory for temporal associations. Future research may consider whether age-related deficits in temporal organization may be an early sign of PFC pathology and possible neurodegeneration
Local and global effects of strong DNA bending induced during molecular dynamics simulations
DNA bending plays an important role in many biological processes, but its molecular and energetic details as a function of base sequence remain to be fully understood. Using a recently developed restraint, we have studied the controlled bending of four different B-DNA oligomers using molecular dynamics simulations. Umbrella sampling with the AMBER program and the recent parmbsc0 force field yield free energy curves for bending. Bending 15-base pair oligomers by 90° requires roughly 5 kcal mol−1, while reaching 150° requires of the order of 12 kcal mol−1. Moderate bending occurs mainly through coupled base pair step rolls. Strong bending generally leads to local kinks. The kinks we observe all involve two consecutive base pair steps, with disruption of the central base pair (termed Type II kinks in earlier work). A detailed analysis of each oligomer shows that the free energy of bending only varies quadratically with the bending angle for moderate bending. Beyond this point, in agreement with recent experiments, the variation becomes linear. An harmonic analysis of each base step yields force constants that not only vary with sequence, but also with the degree of bending. Both these observations suggest that DNA is mechanically more complex than simple elastic rod models would imply
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