822 research outputs found
A stochastic model for early placental development
In the human, placental structure is closely related to placental function and consequent pregnancy outcome. Studies have noted abnormal placental shape in small-for-gestational age infants which extends to increased lifetime risk of cardiovascular disease. The origins and determinants of placental shape are incompletely under-stood and are difficult to study in vivo. In this paper we model the early development of the placenta in the human, based on the hypothesis that this is driven by dynamics dominated by a chemo-attractant effect emanating from proximal spiral arteries in the decidua. We derive and explore a two-dimensional stochastic model for these events, and investigate the effects of loss of spiral arteries in regions near to the cord insertion on the shape of the placenta. This model demonstrates that placental shape is highly variable and disruption of spiral arteries can exert profound effects on placental shape, particularly if this disruption is close to the cord insertion. Thus, placental shape reflects the underlying maternal vascular bed. Abnormal placental shape may reflect an abnormal uterine environment, which predisposes to pregnancy complications
Quark Effects in the Gluon Condensate Contribution to the Scalar Glueball Correlation Function
One-loop quark contributions to the dimension-four gluon condensate term in
the operator product expansion (OPE) of the scalar glueball correlation
function are calculated in the MS-bar scheme in the chiral limit of quark
flavours. The presence of quark effects is shown not to alter the cancellation
of infrared (IR) singularities in the gluon condensate OPE coefficients. The
dimension-four gluonic condensate term represents the leading power corrections
to the scalar glueball correlator and, therein, the one-loop logarithmic
contributions provide the most important condensate contribution to those QCD
sum-rules independent of the low-energy theorem (the subtracted sum-rules).Comment: latex2e, 6 pages, 7 figures embedded in latex fil
A QCD Analysis of the Mass Structure of the Nucleon
{}From the deep-inelastic momentum sum rule and the trace anomaly of the
energy-momentum tensor, I derive a separation of the nucleon mass into the
contributions of the quark and gluon kinetic and potential energies, the quark
masses, and the trace anomaly.Comment: 9 pages, MIT-CTP #2368, revtex with 1 tabl
A purely algebraic construction of a gauge and renormalization group invariant scalar glueball operator
This paper presents a complete algebraic proof of the renormalizability of
the gauge invariant operator to all orders of
perturbation theory in pure Yang-Mills gauge theory, whereby working in the
Landau gauge. This renormalization is far from being trivial as mixing occurs
with other gauge variant operators, which we identify explicitly. We
determine the mixing matrix to all orders in perturbation theory by using
only algebraic arguments and consequently we can uncover a renormalization
group invariant by using the anomalous dimension matrix derived from
. We also present a future plan for calculating the mass of the lightest
scalar glueball with the help of the framework we have set up.Comment: 17 page
Controllability and universal three-qubit quantum computation with trapped electron states
We show how to control and perform universal three-qubit quantum computation
with trapped electron quantum states. The three qubits are the electron spin,
and the first two quantum states of the cyclotron and axial harmonic
oscillators. We explicitly show how the universal gates can be performed. As an
example of a non-trivial quantum algorithm, we outline the implementation of
the Deutsch-Jozsa algorithm in this system.Comment: 4 pages, 1 figure. Typos corrected. The original publication is
available at http://www.springerlink.co
A General Field-Covariant Formulation Of Quantum Field Theory
In all nontrivial cases renormalization, as it is usually formulated, is not
a change of integration variables in the functional integral, plus parameter
redefinitions, but a set of replacements, of actions and/or field variables and
parameters. Because of this, we cannot write simple identities relating bare
and renormalized generating functionals, or generating functionals before and
after nonlinear changes of field variables. In this paper we investigate this
issue and work out a general field-covariant approach to quantum field theory,
which allows us to treat all perturbative changes of field variables, including
the relation between bare and renormalized fields, as true changes of variables
in the functional integral, under which the functionals Z and W = ln Z behave
as scalars. We investigate the relation between composite fields and changes of
field variables, and show that, if J are the sources coupled to the elementary
fields, all changes of field variables can be expressed as J-dependent
redefinitions of the sources L coupled to the composite fields. We also work
out the relation between the renormalization of variable-changes and the
renormalization of composite fields. Using our transformation rules it is
possible to derive the renormalization of a theory in a new variable frame from
the renormalization in the old variable frame, without having to calculate it
anew. We define several approaches, useful for different purposes, in
particular a linear approach where all variable changes are described as linear
source redefinitions. We include a number of explicit examples.Comment: 36 pages, 2 figures; v2: minor changes and proof corrections, EPJ
Polarized nuclear target based on parahydrogen induced polarization
We discuss a novel concept of a polarized nuclear target for accelerator
fixed-target scattering experiments, which is based on parahydrogen induced
polarization (PHIP). One may be able to reach a 33% free-proton polarization in
the ethane molecule. The potential advantages of such a target include
operation at zero magnetic field, fast (100 Hz) polarization reversal,
and operation with large intensity of an electron beam.Comment: 16 pages, 2 figure
Renormalization Group and Decoupling in Curved Space: II. The Standard Model and Beyond
We continue the study of the renormalization group and decoupling of massive
fields in curved space, started in the previous article and analyse the higher
derivative sector of the vacuum metric-dependent action of the Standard Model.
The QCD sector at low-energies is described in terms of the composite effective
fields. For fermions and scalars the massless limit shows perfect
correspondence with the conformal anomaly, but similar limit in a massive
vector case requires an extra compensating scalar. In all three cases the
decoupling goes smoothly and monotonic. A particularly interesting case is the
renormalization group flow in the theory with broken supersymmetry, where the
sign of one of the beta-functions changes on the way from the UV to IR.Comment: 27 pages, 8 figure
Two-hadron semi-inclusive production including subleading twist
We extend the analysis of two-hadron fragmentation functions to the
subleading twist, discussing also the issue of color gauge invariance. Our
results can be used anywhere two unpolarized hadrons are semi-inclusively
produced in the same fragmentation region, also at moderate values of the hard
scale Q. Here, we consider the example of polarized deep-inelastic production
of two hadrons and we give a complete list of cross sections and spin
asymmetries up to subleading twist. Among the results, we highlight the
possibility of extracting the transversity distribution with longitudinally
polarized targets and also the twist-3 distribution e(x), which is related to
the pion-nucleon sigma term and to the strangeness content of the nucleon.Comment: 16 pages, RevTeX4, 5 figures, revised notation of several formulae,
added text in Secs. III-V, added reference
Variable preterm oral microbiome stabilizes and reflects a full-term infant profile within three months.
OnlinePublBACKGROUND: Preterm infants suffer higher morbidity and mortality rates compared to full-term infants, but little is known about how changes to oral and respiratory tract microbiota may impact disease development. METHODS: Here, very preterm neonates (n = 50) were selected to study oral and respiratory microbiota development during the first few months post-birth, where 26 individuals were diagnosed with BPD and/or sepsis. These infants were compared to 14 healthy full-term infants and 16 adults. Microbiota diversity, composition, and species abundances were calculated from 16S ribosomal RNA gene sequences in buccal swabs and tracheal aspirates at two time points (within a week and 1-3 months post-birth). RESULTS: Collection time point was the biggest factor to significantly influence the preterm oral microbial diversity and composition. In addition, BPD and sepsis were linked to distinct preterm oral microbiota diversity and composition, and opportunistic pathogens previously associated with these diseases were identified in the initial sample for both healthy preterm neonates and those with the disease. Compared to the full-term infant and adult dataset, preterm infant diversity and composition was initially significantly different, but resembled full-term infant diversity and composition over time. CONCLUSION: Overall, consequences of microbiota development need further examination in preterm infant infections and later development. IMPACT: Non-gut microbiota research on preterm infants is limited. At one week post-birth, preterm infants harbor distinct oral microbiota that are not shared with full-term children or adults, eventually becoming similar to full-term infants at 36 weeks postmenstrual age. DNA from potential opportunistic pathogens was observed in the mouth and lungs of preterm infants within a week of birth, and microbes associated with BPD were identified in the lungs. Oral microbiota in preterm infants over the first 2-3 months is unique and may be connected to short- and long-term health outcomes in these children.Caitlin A. Selway, Carmel T. Collins, Maria Makrides, Thomas R. Sullivan, N3RO Steering Committee, and Laura S. Weyric
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