2,674 research outputs found
A thermodynamic basis for prebiotic amino acid synthesis and the nature of the first genetic code
Of the twenty amino acids used in proteins, ten were formed in Miller's
atmospheric discharge experiments. The two other major proposed sources of
prebiotic amino acid synthesis include formation in hydrothermal vents and
delivery to Earth via meteorites. We combine observational and experimental
data of amino acid frequencies formed by these diverse mechanisms and show
that, regardless of the source, these ten early amino acids can be ranked in
order of decreasing abundance in prebiotic contexts. This order can be
predicted by thermodynamics. The relative abundances of the early amino acids
were most likely reflected in the composition of the first proteins at the time
the genetic code originated. The remaining amino acids were incorporated into
proteins after pathways for their biochemical synthesis evolved. This is
consistent with theories of the evolution of the genetic code by stepwise
addition of new amino acids. These are hints that key aspects of early
biochemistry may be universal.Comment: 16 pages, 2 tables, 4 figures. Accepted for publication in
Astrobiolog
Superconductors with two critical temperatures
We propose a simple model for superconductors endowed with two critical
temperatures, corresponding to two second-order phase transitions, in the
framework of the Ginzburg-Landau mean-field theory. For very large Cooper pair
self-interaction, in addition to the standard condensation occurring in the
Ginzburg-Landau theory, we find another phase transition at a lower temperature
with a maximum difference of 15% between the two critical temperatures.Comment: revtex, 3 pages, one eps figur
Probing the Higgs mechanism via
We investigate the sensitivity of the reaction to
the Higgs sector based on the complete one-loop corrections in the minimal
Standard Model and the gauged non-linear -model. While this sensitivity
is very strong for the suppressed cross-section of equally polarized photons
and longitudinal W bosons, it is only marginal for the dominant mode of
transverse polarizations. The corrections within the -model turn out to
be UV-finite in accordance with the absence of \log\MH terms in the Standard
Model with a heavy Higgs boson.Comment: 12 pages uuencoded postscrip
Associations between inattention and impulsivity ADHD symptoms and disordered eating risk in a community sample of young adults
BACKGROUND: Symptoms of attention deficit hyperactivity disorder (ADHD) and trait impulsivity have been associated with disordered eating but are seldom assessed in community studies, or longitudinally and little is known about the mediating mechanisms. METHODS: We tested associations between ADHD symptoms and disordered eating cross-sectionally and between trait impulsivity and disordered eating longitudinally. We utilised data from a normative cohort of young adults (642 participants: 65% female, M(age) = 23 years). Participants were classified as high risk or low risk for disordered eating using the SCOFF instrument. In the first two steps of both cross-sectional and longitudinal hierarchical logistic regression models, demographics and covariates were entered. For the cross-sectional regression, Adult ADHD self-report scale (ASRS) scores, separated into inattentive and hyperactive/impulsive symptoms, were entered in the third step. In a separate longitudinal model, Barratt impulsivity scale subscales (attentional, motor and non-planning impulsivity) were entered in the third step. Depression, as assessed by the moods and feelings questionnaire (MFQ), was examined as a mediator. RESULTS: Cross-sectionally, sex, MFQ score and inattentive symptoms predicted disordered eating risk (model R(2) = 20%). Longitudinally, sex, MFQ score and attentional impulsivity predicted disordered eating risk (model R(2) = 16%). The relationship between inattentive symptoms and the disordered eating risk was partially mediated by MFQ score, whereas the relationship between attentional impulsivity and the disordered eating risk was fully mediated by MFQ scores. CONCLUSIONS: These data highlight (1) a specific role for inattentive symptoms of ADHD and (2) the importance of both depression and impulsivity in predicting eating disorder risk
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Associations between inattention and impulsivity ADHD symptoms and disordered eating risk in a community sample of young adults.
BACKGROUND: Symptoms of attention deficit hyperactivity disorder (ADHD) and trait impulsivity have been associated with disordered eating but are seldom assessed in community studies, or longitudinally and little is known about the mediating mechanisms. METHODS: We tested associations between ADHD symptoms and disordered eating cross-sectionally and between trait impulsivity and disordered eating longitudinally. We utilised data from a normative cohort of young adults (642 participants: 65% female, Mage = 23 years). Participants were classified as high risk or low risk for disordered eating using the SCOFF instrument. In the first two steps of both cross-sectional and longitudinal hierarchical logistic regression models, demographics and covariates were entered. For the cross-sectional regression, Adult ADHD self-report scale (ASRS) scores, separated into inattentive and hyperactive/impulsive symptoms, were entered in the third step. In a separate longitudinal model, Barratt impulsivity scale subscales (attentional, motor and non-planning impulsivity) were entered in the third step. Depression, as assessed by the moods and feelings questionnaire (MFQ), was examined as a mediator. RESULTS: Cross-sectionally, sex, MFQ score and inattentive symptoms predicted disordered eating risk (model R2 = 20%). Longitudinally, sex, MFQ score and attentional impulsivity predicted disordered eating risk (model R2 = 16%). The relationship between inattentive symptoms and the disordered eating risk was partially mediated by MFQ score, whereas the relationship between attentional impulsivity and the disordered eating risk was fully mediated by MFQ scores. CONCLUSIONS: These data highlight (1) a specific role for inattentive symptoms of ADHD and (2) the importance of both depression and impulsivity in predicting eating disorder risk
N=4 supersymmetric mechanics with nonlinear chiral supermultiplet
We construct N=4 supersymmetric mechanics using the N=4 nonlinear chiral
supermultiplet. The two bosonic degrees of freedom of this supermultiplet
parameterize the sphere S(2) and go into the bosonic components of the standard
chiral multiplet when the radius of the sphere goes to infinity. We construct
the most general action and demonstrate that the nonlinearity of the
supermultiplet results in the deformation of the connection, which couples the
fermionic degrees of freedom with the background, and of the bosonic potential.
Also a non-zero magnetic field could appear in the system.Comment: 5 page
The Minimal Phantom Sector of the Standard Model: Higgs Phenomenology and Dirac Leptogenesis
We propose the minimal, lepton-number conserving, SU(3)xSU(2)xU(1)
gauge-singlet, or phantom, extension of the Standard Model. The extension is
natural in the sense that all couplings are of O(1) or forbidden due to a
phantom sector global U(1)_D symmetry, and basically imitates the standard
Majorana see-saw mechanism. Spontaneous breaking of the U(1)_D symmetry
triggers consistent electroweak gauge symmetry breaking only if it occurs at a
scale compatible with small Dirac neutrino masses and baryogenesis through
Dirac leptogenesis. Dirac leptogenesis proceeds through the usual
out-of-equilibrium decay scenario, leading to left and right-handed neutrino
asymmetries that do not fully equilibrate after they are produced. The model
contains two physical Higgs bosons and a massless Goldstone boson. The
existence of the Goldstone boson suppresses the Higgs to bb branching ratio and
instead the Higgs bosons will mainly decay to invisible Goldstone and/or to
visible vector boson pairs. In a representative scenario, we estimate that with
30 fb^-1 integrated luminosity, the LHC could discover this invisibly decaying
Higgs, with mass ~120 GeV. At the same time a significantly heavier, partner
Higgs boson with mass ~210 GeV could be found through its vector boson decays.
Electroweak constraints as well as astrophysical and cosmological implications
are analysed and discussed.Comment: 21 pages, 4 figures. Corrected typos and added references. To appear
in JHE
RNA secondary structure formation: a solvable model of heteropolymer folding
The statistical mechanics of heteropolymer structure formation is studied in
the context of RNA secondary structures. A designed RNA sequence biased
energetically towards a particular native structure (a hairpin) is used to
study the transition between the native and molten phase of the RNA as a
function of temperature. The transition is driven by a competition between the
energy gained from the polymer's overlap with the native structure and the
entropic gain of forming random contacts. A simplified Go-like model is
proposed and solved exactly. The predicted critical behavior is verified via
exact numerical enumeration of a large ensemble of similarly designed
sequences.Comment: 4 pages including 2 figure
The Triple Higgs Boson Self-Coupling at Future Linear e+e- Colliders Energies: ILC and CLIC
We analyzed the triple Higgs boson self-coupling at future
colliders energies, with the reactions . We evaluate the total cross-sections for both and ,
and calculate the total number of events considering the complete set of
Feynman diagrams at tree-level. We vary the triple coupling
within the range and +2. The numerical
computation is done for the energies expected to be available at a possible
Future Linear Collider with a center-of-mass energy and a luminosity 1000 . Our analysis is also extended to a
center-of-mass energy 3 and luminosities of 1000 and 5000
. We found that for the process , the
complete calculation differs only by 3% from the approximate calculation
, while for the process , the expected number of events, considering the decay products of both
and , is not enough to obtain an accurate determination of the triple Higgs
boson self-coupling.Comment: 19 pages, 12 figure
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