921 research outputs found
DNA hybridization catalysts and catalyst circuits
Practically all of life's molecular processes, from chemical synthesis to replication, involve enzymes that carry out their functions through the catalysis of metastable fuels into waste products. Catalytic control of reaction rates will prove to be as useful and ubiquitous in
DNA nanotechnology as it is in biology. Here we present experimental results on the control of the decay rates of a metastable DNA "fuel". We show that the fuel complex can be induced to decay with a rate about 1600 times faster than it would decay spontaneously. The original DNA hybridization catalyst [15] achieved a maximal speed-up of roughly 30. The fuel complex discussed here can therefore serve as the basic ingredient for an improved DNA hybridization catalyst. As an example application for DNA hybridization catalysts, we propose a method for implementing arbitrary digital logic circuits
Use of prescription medications with cardiovascular adverse effects among older adults in the United States
Background: Many commonly used prescription medications have cardiovascular adverse effects, yet the cumulative risk of cardiovascular events associated with the concurrent use of these medications is unknown. We examined the association between the concurrent use of prescription medications with known risk of a major adverse cardiovascular event (MACE) (“MACE medications”) and the risk of such events among older adults. Methods: A multi-center, population-based study from the Atherosclerosis Risk in Communities (ARIC) study of a cohort of 3669 community-dwelling adults aged 61–86 years with no history of cardiovascular disease who reported the use of at least one medication between September 2006 and August 2013 were followed up until August 2015. Exposure defined as time-varying and time-fixed use of 1, 2 or ≥3 MACE medications with non-MACE medications serving as negative control. Primary outcome was incident MACE defined as coronary artery revascularization, myocardial infarction, fatal coronary heart disease, stroke, cardiac arrest, or death. Results: In fully adjusted models, there was an increased risk of MACE associated with use of 1, 2, or ≥3 MACE medications (1 MACE: hazards ratio [HR], 1.21; 95% confidence interval [CI], 0.94–1.57); 2 MACE: HR 1.89, CI 1.42–2.53; ≥3 MACE: HR 2.22, CI 1.61–3.07) compared to use of non-MACE medications. These associations persisted in propensity score-matched analyses and among new users of MACE medications, never users of cardiovascular medications and subgroups of participants with increased risk of MACE. There was no association between the number of non-MACE medications used and MACE. Conclusions and Relevance: In this community-based cohort of older adults with no prior cardiovascular disease, the use of MACE medications was independently and consistently associated with an increased risk of such events in a dose–response fashion
Two-Boson Exchange Physics: A Brief Review
Current status of the two-boson exchange contributions to elastic
electron-proton scattering, both for parity conserving and parity-violating, is
briefly reviewed. How the discrepancy in the extraction of elastic nucleon form
factors between unpolarized Rosenbluth and polarization transfer experiments
can be understood, in large part, by the two-photon exchange corrections is
discussed. We also illustrate how the measurement of the ratio between
positron-proton and electron-proton scattering can be used to differentiate
different models of two-photon exchange. For the parity-violating
electron-proton scattering, the interest is on how the two-boson exchange
(TBE), \gamma Z-exchange in particular, could affect the extraction of the
long-sought strangeness form factors. Various calculations all indicate that
the magnitudes of effect of TBE on the extraction of strangeness form factors
is small, though can be large percentage-wise in certain kinematics.Comment: 6 pages, 5 figures, prepared for Proceedings of the fifth
Asia-Pacific Conference on Few-Body Problems in Physics (APFB2011), Seoul,
Korea, August 22-26, 2011, to appear in Few-Body Systems, November 201
Finite temperature phase diagram of spin-1/2 bosons in two-dimensional optical lattice
We study a two-species bosonic Hubbard model on a two-dimensional square
lattice by means of quantum Monte Carlo simulations and focus on finite
temperature effects. We show in two different cases, ferro- and
antiferromagnetic spin-spin interactions, that the phase diagram is composed of
solid Mott phases, liquid phases and superfluid phases. In the
antiferromagnetic case, the superfluid (SF) is polarized while the Mott
insulator (MI) and normal Bose liquid (NBL) phases are not. On the other hand,
in the ferromagnetic case, none of the phases is polarized. The
superfluid-liquid transition is of the Berezinsky-Kosterlitz-Thouless type
whereas the solid-liquid passage is a crossover.Comment: 9 pages, 13 figure
A jump-growth model for predator-prey dynamics: derivation and application to marine ecosystems
This paper investigates the dynamics of biomass in a marine ecosystem. A
stochastic process is defined in which organisms undergo jumps in body size as
they catch and eat smaller organisms. Using a systematic expansion of the
master equation, we derive a deterministic equation for the macroscopic
dynamics, which we call the deterministic jump-growth equation, and a linear
Fokker-Planck equation for the stochastic fluctuations. The McKendrick--von
Foerster equation, used in previous studies, is shown to be a first-order
approximation, appropriate in equilibrium systems where predators are much
larger than their prey. The model has a power-law steady state consistent with
the approximate constancy of mass density in logarithmic intervals of body mass
often observed in marine ecosystems. The behaviours of the stochastic process,
the deterministic jump-growth equation and the McKendrick--von Foerster
equation are compared using numerical methods. The numerical analysis shows two
classes of attractors: steady states and travelling waves.Comment: 27 pages, 4 figures. Final version as published. Only minor change
Coherent matter wave inertial sensors for precision measurements in space
We analyze the advantages of using ultra-cold coherent sources of atoms for
matter-wave interferometry in space. We present a proof-of-principle experiment
that is based on an analysis of the results previously published in [Richard et
al., Phys. Rev. Lett., 91, 010405 (2003)] from which we extract the ratio h/m
for 87Rb. This measurement shows that a limitation in accuracy arises due to
atomic interactions within the Bose-Einstein condensate
Comunidades de insectos fitófagos en árboles y lianas en el dosel y sotobosque del Parque Natural Metropolitano
The food and nutrient intake of Paleolithic hunter-gatherers (Homo erectus) and of Western populations (Homo economicus) show marked variations. With increase in wealth and affluence there is a decrease in the intake of omega-3 fatty acids, vitamins, antioxidants and amino acids and a significant increase in the intake of refined carbohydrates, fats (saturated & trans fats, omega-6 fatty acids) and salt in comparison with those of the Paleolithic period. The protein or amino acid intake was 2.5 fold greater (33 vs. 13%) in the Paleolithic diet of Homo erectus compared to that of the modern Western diet. Prior to the Agricultural Revolution, man's diet was based on an enormous variety of wild plants, eggs, fish and seeds. In comparison, today about 17% of plant species provide 90% of the world's food supply which is mainly contributed by grains produced from fertilizer-based rapidly grown crops potentially lower in nutrient density and higher in energy. Grains are high in omega-6 fatty acids and carbohydrates and low in omega-3 fatty acids and antioxidants compared to leafy green vegetables. The appropriate diet for Homo sapiens is characterized by high levels of protective essential nutrients; amino acids, minerals, vitamins, flavonoids, omega-6/3 fatty acids. Whereas the average diet of Homo erectus did comply with this evolutionary pattern, the modern Western dietary pattern of Homo economicus has excess of energy-rich refined carbohydrates, omega-6, trans and saturated fats. The consumption of such foods in wealthy countries in conjunction with sedentary behavior are associated with increased risk of deaths due to cardiovascular (CVDs) and other non-communicable diseases (NCDs). © Nova Science Publishers, Inc
Determination of the Deep Inelastic Contribution to the Generalised Gerasimov-Drell-Hearn Integral for the Proton and Neutron
The virtual photon absorption cross section differences [sigma_1/2-sigma_3/2]
for the proton and neutron have been determined from measurements of polarised
cross section asymmetries in deep inelastic scattering of 27.5 GeV
longitudinally polarised positrons from polarised 1H and 3He internal gas
targets. The data were collected in the region above the nucleon resonances in
the kinematic range nu < 23.5 GeV and 0.8 GeV**2 < Q**2 < 12 GeV**2. For the
proton the contribution to the generalised Gerasimov-Drell-Hearn integral was
found to be substantial and must be included for an accurate determination of
the full integral. Furthermore the data are consistent with a QCD
next-to-leading order fit based on previous deep inelastic scattering data.
Therefore higher twist effects do not appear significant.Comment: 6 pages, 3 figures, 1 table, revte
Observation of a Coherence Length Effect in Exclusive Rho^0 Electroproduction
Exclusive incoherent electroproduction of the rho^0(770) meson from 1H, 2H,
3He, and 14N targets has been studied by the HERMES experiment at squared
four-momentum transfer Q**2>0.4 GeV**2 and positron energy loss nu from 9 to 20
GeV. The ratio of the 14N to 1H cross sections per nucleon, known as the
nuclear transparency, was found to decrease with increasing coherence length of
quark-antiquark fluctuations of the virtual photon. The data provide clear
evidence of the interaction of the quark- antiquark fluctuations with the
nuclear medium.Comment: RevTeX, 5 pages, 3 figure
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