8,645 research outputs found
Transcobalamin C776G genotype modifies the association between vitamin B12 and homocysteine in older Hispanics.
Background/objectivesA common polymorphism, C776G, in the plasma B12 transport protein transcobalamin (TC), encodes for either proline or arginine at codon 259. This polymorphism may affect the affinity of TC for B12 and subsequent delivery of B12 to tissues.Subjects/methodsTC genotype and its associations with indicators of B12 status, including total B12, holotranscobalamin (holoTC), methylmalonic acid and homocysteine, were evaluated in a cohort of elderly Latinos (N=554, age 60-93 years) from the Sacramento Area Latino Study on Aging (SALSA).ResultsThe distribution of TC genotypes was 41.3% homozygous reference (776CC) and 11.6% homozygous variant (776GG). No differences between the homozygous genotypes were observed in total B12, holoTC, methylmalonic acid or homocysteine. The holoTC/total B12 ratio was lower in the 776GG group compared with the 776CC group (P=0.04). Significant interactions of TC genotype with total B12 (P=0.04) and with holoTC (P< or =0.03) were observed such that mean homocysteine concentrations and the odds ratios for hyperhomocysteinemia (>13 micromol/l) were higher in the 776CC subjects compared with all carriers of the G allele (776CG and 776GG combined) when total B12 (<156 pmol/l) or holoTC (<35 pmol/l) were low.ConclusionsThis population of older Latinos has a lower prevalence of the TC 776GG variant than reported for Caucasian populations. The association between vitamin B12 and homocysteine concentrations is modified by TC 776 genotype. It remains to be determined whether the TC C776G polymorphism has a significant effect on the hematological and neurological manifestations of B12 deficiency or on vascular and other morbidities associated with hyperhomocysteinemia
Exact Markovian kinetic equation for a quantum Brownian oscillator
We derive an exact Markovian kinetic equation for an oscillator linearly
coupled to a heat bath, describing quantum Brownian motion. Our work is based
on the subdynamics formulation developed by Prigogine and collaborators. The
space of distribution functions is decomposed into independent subspaces that
remain invariant under Liouville dynamics. For integrable systems in
Poincar\'e's sense the invariant subspaces follow the dynamics of uncoupled,
renormalized particles. In contrast for non-integrable systems, the invariant
subspaces follow a dynamics with broken-time symmetry, involving generalized
functions. This result indicates that irreversibility and stochasticity are
exact properties of dynamics in generalized function spaces. We comment on the
relation between our Markovian kinetic equation and the Hu-Paz-Zhang equation.Comment: A few typos in the published version are correcte
In-plane Theory of Non-Sequential Triple Ionization
We describe first-principles in-plane calculations of non-sequential triple
ionization (NSTI) of atoms in a linearly polarized intense laser pulse. In a
fully classically correlated description, all three electrons respond
dynamically to the nuclear attraction, the pairwise e-e repulsions and the
laser force throughout the duration of a 780nm laser pulse. Nonsequential
ejection is shown to occur in a multi-electron, possibly multi-cycle and
multi-dimensional, rescattering sequence that is coordinated by a number of
sharp transverse recollimation impacts.Comment: 4 pages, 4 figure
Complexity Results for Manipulation, Bribery and Control of the Kemeny Judgment Aggregation Procedure
We study the computational complexity of several scenarios of strategic
behavior for the Kemeny procedure in the setting of judgment aggregation. In
particular, we investigate (1) manipulation, where an individual aims to
achieve a better group outcome by reporting an insincere individual opinion,
(2) bribery, where an external agent aims to achieve an outcome with certain
properties by bribing a number of individuals, and (3) control (by adding or
deleting issues), where an external agent aims to achieve an outcome with
certain properties by influencing the set of issues in the judgment aggregation
situation. We show that determining whether these types of strategic behavior
are possible (and if so, computing a policy for successful strategic behavior)
is complete for the second level of the Polynomial Hierarchy. That is, we show
that these problems are -complete
A Parameterized Complexity View on Description Logic Reasoning
Description logics are knowledge representation languages that have been
designed to strike a balance between expressivity and computational
tractability. Many different description logics have been developed, and
numerous computational problems for these logics have been studied for their
computational complexity. However, essentially all complexity analyses of
reasoning problems for description logics use the one-dimensional framework of
classical complexity theory. The multi-dimensional framework of parameterized
complexity theory is able to provide a much more detailed image of the
complexity of reasoning problems.
In this paper we argue that the framework of parameterized complexity has a
lot to offer for the complexity analysis of description logic reasoning
problems---when one takes a progressive and forward-looking view on
parameterized complexity tools. We substantiate our argument by means of three
case studies. The first case study is about the problem of concept
satisfiability for the logic ALC with respect to nearly acyclic TBoxes. The
second case study concerns concept satisfiability for ALC concepts
parameterized by the number of occurrences of union operators and the number of
occurrences of full existential quantification. The third case study offers a
critical look at data complexity results from a parameterized complexity point
of view. These three case studies are representative for the wide range of uses
for parameterized complexity methods for description logic problems.Comment: To appear in the Proceedings of the 16th International Conference on
Principles of Knowledge Representation and Reasoning (KR 2018
Domain wall theory and exchange stiffness in Co/Pd multilayers
The stripe model of domain structure in multilayers is studied by micromagnetic simulation. The results indicate a strong reduction of the effective domain wall energy (by dipolar effects). Domain width measurements on sputtered Co/Pd multilayers are compared with the theory. The estimated exchange stiffness is comparable with that of bulk Co. The effects of interface roughness and of interlayer exchange are discussed
Algebraic Techniques for Low Communication Secure Protocols
Internet communication is often encrypted with the aid of mathematical problems that are hard to solve. Another method to secure electronic communication is the use of a digital lock of which the digital key must be exchanged first. PhD student Robbert de Haan (CWI) researched models for a guaranteed safe communication between two people without the exchange of a digital key and without assumptions concerning the practical difficulty of solving certain mathematical problems.
In ancient times Julius Caesar used secret codes to make his messages illegible for spies. He upped every letter of the alphabet with three positions: A became D, Z became C, and so on. Usually, cryptographers research secure communication between two people through one channel that can be monitored by malevolent people. De Haan studied the use of multiple channels. A minority of these channels may be in the hands of adversaries that can intercept, replace or block the message. He proved the most efficient way to securely communicate along these channels and thus solved a fundamental cryptography problem that was introduced almost 20 years ago by Dole, Dwork, Naor and Yung
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