916 research outputs found

    A direct path to dependable software

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    What would it take to make software more dependable? Until now, most approaches have been indirect: some practices – processes, tools or techniques – are used that are believed to yield dependable software, and the argument for dependability rests on the extent to which the developers have adhered to them. This article argues instead that developers should produce direct evidence that the software satisfies its dependability claims. The potential advantages of this approach are greater credibility (since the argument is not contingent on the effectiveness of the practices) and reduced cost (since development resources can be focused where they have the most impact)

    Spintronics: Fundamentals and applications

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    Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes from the published versio

    Cardiovascular Dysfunction and Frailty among Older Adults in the Community: The ARIC Study

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    Background: The contribution of cardiovascular dysfunction to frailty in older adults is uncertain. This study aimed to define the relationship between frailty and cardiovascular structure and function, and determine whether these associations are independent of coexisting abnormalities in other organ systems. Methods: We studied 3,991 older adults (mean age 75.6 - 5.0 years; 59% female) from the Atherosclerosis Risk in Communities (ARIC) Study in whom the following six organ systems were uniformly assessed: cardiac (by echocardiography), vascular (by ankle-brachial-index and pulse-wave-velocity), pulmonary (by spirometry), renal (by estimated glomerular filtration rate), hematologic (by hemoglobin), and adipose (by body mass index and bioimpedance). Frailty was defined by the presence of ?3 of the following: low strength, low energy, slowed motor performance, low physical activity, or unintentional weight loss. Results: Two hundred eleven (5.3%) participants were frail. In multivariable analyses adjusted for demographics, diabetes, hypertension, and measures of other organ system function, frailty was independently and additively associated with left ventricular hypertrophy (odds ratio [OR] = 1.72; 95% confidence interval [CI] = 1.30-2.40), reduced global longitudinal strain (reflecting systolic function; OR = 1.68; 95% CI = 1.16-2.44), and greater left atrial volume index (reflecting diastolic function; OR = 1.60; 95% CI = 1.13-2.27), which together demonstrated the greatest association with frailty (OR = 2.10; 95% CI = 1.57-2.82) of the systems studied. Lower magnitude associations were observed for vascular and pulmonary abnormalities, anemia, and impaired renal function. Cardiovascular abnormalities remained associated with frailty after excluding participants with prevalent cardiovascular disease. Conclusions: Abnormalities of cardiac structure and function are independently associated with frailty, and together show the greatest association with frailty among the organ systems studied

    Robust and Fast Whole Brain Mapping of the RF Transmit Field B1 at 7T

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    In-vivo whole brain mapping of the radio frequency transmit field B1+ is a key aspect of recent method developments in ultra high field MRI. We present an optimized method for fast and robust in-vivo whole-brain B1+ mapping at 7T. The method is based on the acquisition of stimulated and spin echo 3D EPI images and was originally developed at 3T. We further optimized the method for use at 7T. Our optimization significantly improved the robustness of the method against large B1+ deviations and off-resonance effects present at 7T. The mean accuracy and precision of the optimized method across the brain was high with a bias less than 2.6 percent unit (p.u.) and random error less than 0.7 p.u. respectively

    Reduced stability of mRNA secondary structure near the translation-initiation site in dsDNA viruses

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    <p>Abstract</p> <p>Background</p> <p>Recent studies have demonstrated a selection pressure for reduced mRNA secondary-structure stability near the start codon of coding sequences. This selection pressure can be observed in bacteria, archaea, and eukaryotes, and is likely caused by the requirement of efficient translation initiation in cellular organism.</p> <p>Results</p> <p>Here, we surveyed the complete genomes of 650 dsDNA virus strains for signals of reduced stability of mRNA secondary structure near the start codon. Our analysis included viruses infecting eukaryotic, prokaryotic, and archaeic hosts. We found that many viruses showed evidence for reduced mRNA secondary-structure stability near the start codon. The effect was most pronounced in viruses infecting prokaryotes, but was also observed in viruses infecting eukaryotes and archaea. The reduction in stability generally increased with increasing genomic GC content. For bacteriophage, the reduction was correlated with a corresponding reduction of stability in the phage hosts.</p> <p>Conclusions</p> <p>We conclude that reduced stability of the mRNA secondary structure near the start codon is a common feature for dsDNA viruses, likely driven by the same selective pressures that cause it in cellular organisms.</p
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