826 research outputs found
Algorithm Diversity for Resilient Systems
Diversity can significantly increase the resilience of systems, by reducing
the prevalence of shared vulnerabilities and making vulnerabilities harder to
exploit. Work on software diversity for security typically creates variants of
a program using low-level code transformations. This paper is the first to
study algorithm diversity for resilience. We first describe how a method based
on high-level invariants and systematic incrementalization can be used to
create algorithm variants. Executing multiple variants in parallel and
comparing their outputs provides greater resilience than executing one variant.
To prevent different parallel schedules from causing variants' behaviors to
diverge, we present a synchronized execution algorithm for DistAlgo, an
extension of Python for high-level, precise, executable specifications of
distributed algorithms. We propose static and dynamic metrics for measuring
diversity. An experimental evaluation of algorithm diversity combined with
implementation-level diversity for several sequential algorithms and
distributed algorithms shows the benefits of algorithm diversity
Increased mortality in patients with congenital adrenal hyperplasia due to 21-hydroxylase deficiency
Context: Reports on mortality in patients with congenital adrenal hyperplasia (CAH) are lacking.
Objective: To study mortality and causes of death in CAH.
Design, Setting and Participants: We studied patients with CAH (21-hydroxylase deficiency, n=588; CYP21A2 mutations known, >80%), and compared them with controls (n=58800). Data were derived through linkage of national population-based registers.
Main Outcome Measures: Mortality and causes of death.
Results: The mean age of death was 41.2±26.9 years in CAH patients and 47.7±27.7 years in controls (P<0.001). Among CAH patients 23 (3.9%) had deceased compared to 942 (1.6%) of controls. The hazard ratio (and 95% confidence interval) of death was 2.3(1.2-4.3) in CAH males and 3.5(2.0-6.0) in CAH females. Including only patients born 1952-2009, gave similar total results but only patients with salt-wasting or with unclear phenotype had an increased mortality. The causes of death in CAH patients were adrenal crisis (42%), cardiovascular (32%), cancer (16%), and suicide (10%). There were seven additional deaths in CAH individuals with incomplete or reused personal identification number that could not be analyzed using linkage of registers. Of the latter all except one were deceased before the introduction of neonatal screening in 1986 and most of them in the first weeks of life, probably in an adrenal crisis.
Conclusions: CAH is a potentially lethal condition and was associated with excess mortality due to adrenal crisis. The salt-wasting phenotype seemed to have worse outcome also in children and adults due to adrenal crisis and not only before the introduction of neonatal screening.NonePublishe
Vortex nozzle interaction in solid rocket motors: A scaling law for upstream acoustic response
In solid rocket motors, vortex nozzle interactions can be a source of large-amplitude pressure pulsations. Using a two-dimensional frictionless flow model, a scaling law is deduced, which describes the magnitude of a pressure pulsation as being proportional to the product of the dynamic pressure of the upstream main flow and of vortex circu- lation. The scaling law was found to be valid for both an integrated noz- zle with surrounding cavity and a nozzle geometry without surrounding cavity that forms a right angle with the combustion chamber side wall. Deviations from the scaling law only occur when unrealistically strong circulations are considered
Aeroacoustic response of an array of tubes with and without bias-flow
Heat exchangers, consisting of tube arrays in a cross-flow are a vital component of power generation systems. They are of interest from an acoustic point of view, because they can reflect, transmit and absorb an incident sound wave; in other words, they have the potential to act as a sound absorber and even as a passive control device to prevent a thermoacoustic instability in the power generation system. This paper presents a fundamental study of the aeroacoustic response of a tube array with and without bias-flow (also called cross-flow). The study has a theoretical and experimental side. On the theoretical side, a new model, based on the assumption of quasi-steady flow, was developed to predict the acoustic reflection and transmission coefficient of a tube array with bias-flow. Also, the model by Huang and Heckl (Huang and Heckl, 1993, Acustica 78, 191–200) for the case without bias-flow was evaluated. On the experimental side, flow-duct experiments using a multi-microphone technique were performed to validate the predictions from both models. The agreement was found to be very good for low frequencies. The measurements revealed the limit of validity of the quasi-steady model in terms of the Strouhal number. Although this limit is quite low, our quasi-steady model can serve as a valuable tool for designers of heat exchangers
Are carriers of CYP21A2 mutations less vulnerable to psychological stress? A population-based national cohort study
Background Congenital adrenal hyperplasia (CAH) is one of
the most common monogenic autosomal recessive disorders
with an incidence of one in 15 000. About one in 70 individuals
in the general population are carriers of a severe CYP21A2
mutation. It has been suggested that this confers a survival
advantage, perhaps as a result of increased activity in the
hypothalamic–pituitary–adrenal axis. We investigated vulnerability
to psychological stress in obligate carriers.
Method The Swedish CAH Registry encompasses more than 600
patients. Parents, that is obligate carriers of the CYP21A2 mutation,
were identified through the Multigeneration Register. The
diagnosis of the child was used as the psychological stressor. Psychiatric
diagnoses before and after the birth of a child with CAH
were compared to those of controls derived from (i) the general
population, (ii) parents of children with hypospadias and (iii) parents
of children with diabetes mellitus type 1 (T1DM).
Results Parents of children with CAH had less risk of being
diagnosed with any psychiatric disorder (OR, 0 6), an affective
disorder (OR, 0 5) or substance misuse (OR, 0 5) after the diagnosis
of the child, compared to the general population. Their
risk was also decreased compared to parents of a child with
hypospadias (OR, 0 6, 0 4 and 0 2, respectively) and parents of a
child with T1DM (OR 0 7, 0 6 and 0 2, respectively). The
CYP21A2 carriers had a lower risk of developing mood and
stress-related disorders after the diagnosis of the child.
Conclusion Obligate CYP21A2 carriers had a reduced risk of a
psychiatric diagnosis and were less vulnerable to a psychologically
stressful situation, at least with respect to receiving a
psychiatric diagnosis. This indicates a better ability to cope with
psychological stress among heterozygous carriers of severe
CYP21A2 mutations, which may contribute to the apparent survival
advantageNoneAccepte
The Physicist's Guide to the Orchestra
An experimental study of strings, woodwinds (organ pipe, flute, clarinet,
saxophone and recorder), and the voice was undertaken to illustrate the basic
principles of sound production in music instruments. The setup used is simple
and consists of common laboratory equipment. Although the canonical examples
(standing wave on a string, in an open and closed pipe) are easily reproduced,
they fail to explain the majority of the measurements. The reasons for these
deviations are outlined and discussed.Comment: 11 pages, 10 figures (jpg files). Submitted to European Journal of
Physic
Implementing EM and Viterbi algorithms for Hidden Markov Model in linear memory
<p>Abstract</p> <p>Background</p> <p>The Baum-Welch learning procedure for Hidden Markov Models (HMMs) provides a powerful tool for tailoring HMM topologies to data for use in knowledge discovery and clustering. A linear memory procedure recently proposed by <it>MiklĂłs, I. and Meyer, I.M. </it>describes a memory sparse version of the Baum-Welch algorithm with modifications to the original probabilistic table topologies to make memory use independent of sequence length (and linearly dependent on state number). The original description of the technique has some errors that we amend. We then compare the corrected implementation on a variety of data sets with conventional and checkpointing implementations.</p> <p>Results</p> <p>We provide a correct recurrence relation for the emission parameter estimate and extend it to parameter estimates of the Normal distribution. To accelerate estimation of the prior state probabilities, and decrease memory use, we reverse the originally proposed forward sweep. We describe different scaling strategies necessary in all real implementations of the algorithm to prevent underflow. In this paper we also describe our approach to a linear memory implementation of the Viterbi decoding algorithm (with linearity in the sequence length, while memory use is approximately independent of state number). We demonstrate the use of the linear memory implementation on an extended Duration Hidden Markov Model (DHMM) and on an HMM with a spike detection topology. Comparing the various implementations of the Baum-Welch procedure we find that the checkpointing algorithm produces the best overall tradeoff between memory use and speed. In cases where sequence length is very large (for Baum-Welch), or state number is very large (for Viterbi), the linear memory methods outlined may offer some utility.</p> <p>Conclusion</p> <p>Our performance-optimized Java implementations of Baum-Welch algorithm are available at <url>http://logos.cs.uno.edu/~achurban</url>. The described method and implementations will aid sequence alignment, gene structure prediction, HMM profile training, nanopore ionic flow blockades analysis and many other domains that require efficient HMM training with EM.</p
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Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62917/1/441025a.pd
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