2,227 research outputs found
WIDE-ANGLE LIQUID CRYSTAL POLARIZATION SWITCH
A polarization switch includes a pair of liquid crystal cells operating in counter-phase such that the thickness-direction retardation of the polarization switch is substantially independent on the switching state, and thus may be passively compensated by a fixed retarder. A passive compensation structure is provided to convert the input polarization state to the first polarization state together with the first LC cell in the undriven state, and to convert the input polarization state to the second polarization state together with the second LC cell in the undriven state
Evaluation of qPCR reference genes in two genotypes of Populus for use in photoperiod and low-temperature studies
Background: Quantitative PCR (qPCR) is a widely used technique for gene expression analysis. A common
normalization method for accurate qPCR data analysis involves stable reference genes to determine relative gene
expression. Despite extensive research in the forest tree species Populus, there is not a resource for reference genes
that meet the Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE) standards for
qPCR techniques and analysis. Since Populus is a woody perennial species, studies of seasonal changes in gene
expression are important towards advancing knowledge of this important developmental and physiological trait.
The objective of this study was to evaluate reference gene expression stability in various tissues and growth
conditions in two important Populus genotypes (P. trichocarpa âNisqually 1â and P. tremula x P. alba 717 1-B4)
following MIQE guidelines.
Results: We evaluated gene expression stability in shoot tips, young leaves, mature leaves and bark tissues from
P. trichocarpa and P. tremula. x P. alba grown under long-day (LD), short-day (SD) or SD plus low-temperatures
conditions. Gene expression data were analyzed for stable reference genes among 18S rRNA, ACT2, CDC2, CYC063,
TIP4-like, UBQ7, PT1 and ANT using two software packages, geNorm
PLUS
and BestKeeper. GeNorm
PLUS
ranked TIP4-like
and PT1 among the most stable genes in most genotype/tissue combinations while BestKeeper ranked CDC2 and
ACT2 among the most stable genes.
Conclusions: This is the first comprehensive evaluation of reference genes in two important Populus genotypes
and the only study in Populus that meets MIQE standards. Both analysis programs identified stable reference genes
in both genotypes and all tissues grown under different photoperiods. This set of reference genes was found to
be suitable for either genotype considered here and may potentially be suitable for other Populus species and
genotypes. These results provide a valuable resource for the Populus research community.https://doi.org/10.1186/1756-0500-5-36
Elucidating the evolutionary history and expression patterns of nucleoside phosphorylase paralogs (vegetative storage proteins) in Populusand the plant kingdom
Nucleoside phosphorylases (NPs) have been extensively investigated in human and bacterial systems for their role in metabolic nucleotide salvaging and links to oncogenesis. In plants, NP-like proteins have not been comprehensively studied, likely because there is no evidence of a metabolic function in nucleoside salvage. However, in the forest trees genus Populus a family of NP-like proteins function as an important ecophysiological adaptation for inter- and intra-seasonal nitrogen storage and cycling. We conducted phylogenetic analyses to determine the distribution and evolution of NP-like proteins in plants. These analyses revealed two major clusters of NP-like proteins in plants. Group I proteins were encoded by genes across a wide range of plant taxa while proteins encoded by Group II genes were dominated by species belonging to the order Malpighiales and included the Populus Bark Storage Protein (BSP) and WIN4-like proteins. Additionally, we evaluated the NP-like genes in Populus by examining the transcript abundance of the 13 NP-like genes found in the Populus genome in various tissues of plants exposed to long-day (LD) and short-day (SD) photoperiods. We found that all 13 of the Populus NP-like genes belonging to either Group I or II are expressed in various tissues in both LD and SD conditions. Tests of natural selection and expression evolution analysis of the Populus genes suggests that divergence in gene expression may have occurred recently during the evolution of Populus, which supports the adaptive maintenance models. Lastly, in silico analysis of cis-regulatory elements in the promoters of the 13 NP-like genes in Populus revealed common regulatory elements known to be involved in light regulation, stress/pathogenesis and phytohormone responses. In Populus, the evolution of the NP-like protein and gene family has been shaped by duplication events and natural selection. Expression data suggest that previously uncharacterized NP-like proteins may function in nutrient sensing and/or signaling. These proteins are members of Group I NP-like proteins, which are widely distributed in many plant taxa. We conclude that NP-like proteins may function in plants, although this function is undefined.https://doi.org/10.1186/1471-2229-13-11
Towards a Big Crunch Dual
We show there exist smooth asymptotically anti-de Sitter initial data which
evolve to a big crunch singularity in a low energy supergravity limit of string
theory. This opens up the possibility of using the dual conformal field theory
to obtain a fully quantum description of the cosmological singularity. A
preliminary study of this dual theory suggests that the big crunch is an
endpoint of evolution even in the full string theory. We also show that any
theory with scalar solitons must have negative energy solutions. The results
presented here clarify our earlier work on cosmic censorship violation in N=8
supergravity.Comment: 27 pages, 3 figures;v2:minor correction
Nucleation of -Branes and Fundamental Strings
We construct a solution to the low-energy string equations of motion in five
dimensions that describes a circular loop of fundamental string exponentially
expanding in a background electric -field. Euclideanising this gives an
instanton for the creation of a loop of fundamental string in a background
-field, and we calculate the rate of nucleation. Solutions describing
magnetically charged strings and -branes, where the gauge field comes from
Kaluza-Klein reduction on a circle, are also constructed. It is known that a
magnetic flux tube in four (reduced) spacetime dimensions is unstable to the
pair creation of Kaluza-Klein monopoles. We show that in dimensions,
magnetic ``fluxbranes" are unstable to the nucleation of a magnetically
charged spherical -brane. In ten dimensions the instanton describes the
nucleation of a Ramond-Ramond magnetically charged six-brane in type IIA string
theory. We also find static solutions describing spherical charged -branes
or fundamental strings held in unstable equilibrium in appropriate background
fields. Instabilities of intersecting magnetic fluxbranes are also discussed.Comment: 28 pages, harvmac (b), reference added, typos correcte
Measles mimicking HIV seroconversion syndrome: a case report
<p>Abstract</p> <p>Introduction</p> <p>Measles is on the rise in the United Kingdom and must be considered in the differential diagnosis of any patient presenting with fever and rash. As a highly infectious disease, identified patients must be isolated in the hospital setting.</p> <p>Case presentation</p> <p>A 28-year-old Polish woman presented ill to the accident and emergency department of a district general hospital. She had painful genital ulceration, oral soreness, fever, and a facial rash. She became hypoxic within 24 hours of presentation and began to tire, thus requiring noninvasive ventilation. Her respiratory symptoms were out of proportion to the findings of her chest radiograph, which remained virtually normal. Human immunodeficiency virus seroconversion syndrome complicated by <it>Pneumocystis carinii </it>pneumonia was high among the differential diagnoses. She was given cotrimoxazole, high-dose steroids, broad spectrum antibiotics, and anti fungal cover.</p> <p>Human immunodeficiency virus polymerase chain reaction came back as negative and her symptoms resolved within 10 days of presentation. She was taken off all treatment and discharged home feeling well. Serological measles was confirmed as part of a viral screen, but its clinical suspicion was low.</p> <p>Conclusion</p> <p>The presentation of measles in this patient was unique and atypical. With its incidence rising in the United Kingdom, measles must be increasingly considered as a differential diagnosis in patients presenting with fever and rash.</p
Holographic Description of AdS Cosmologies
To gain insight in the quantum nature of the big bang, we study the dual
field theory description of asymptotically anti-de Sitter solutions of
supergravity that have cosmological singularities. The dual theories do not
appear to have a stable ground state. One regularization of the theory causes
the cosmological singularities in the bulk to turn into giant black holes with
scalar hair. We interpret these hairy black holes in the dual field theory and
use them to compute a finite temperature effective potential. In our study of
the field theory evolution, we find no evidence for a "bounce" from a big
crunch to a big bang. Instead, it appears that the big bang is a rare
fluctuation from a generic equilibrium quantum gravity state.Comment: 34 pages, 8 figures, v2: minor changes, references adde
Negative Energy Density in Calabi-Yau Compactifications
We show that a large class of supersymmetric compactifications, including all
simply connected Calabi-Yau and G_2 manifolds, have classical configurations
with negative energy density as seen from four dimensions. In fact, the energy
density can be arbitrarily negative -- it is unbounded from below.
Nevertheless, positive energy theorems show that the total ADM energy remains
positive. Physical consequences of the negative energy density include new
thermal instabilities, and possible violations of cosmic censorship.Comment: 25 pages, v2: few clarifying comments and reference adde
Non-Equilibrium Large N Yukawa Dynamics: marching through the Landau pole
The non-equilibrium dynamics of a Yukawa theory with N fermions coupled to a
scalar field is studied in the large N limit with the goal of comparing the
dynamics predicted from the renormalization group improved effective potential
to that obtained including the fermionic backreaction. The effective potential
is of the Coleman-Weinberg type. Its renormalization group improvement is
unbounded from below and features a Landau pole. When viewed self-consistently,
the initial time singularity does not arise. The different regimes of the
dynamics of the fully renormalized theory are studied both analytically and
numerically. Despite the existence of a Landau pole in the model, the dynamics
of the mean field is smooth as it passes the location of the pole. This is a
consequence of a remarkable cancellation between the effective potential and
the dynamical chiral condensate. The asymptotic evolution is effectively
described by a quartic upright effective potential. In all regimes, profuse
particle production results in the formation of a dense fermionic plasma with
occupation numbers nearly saturated up to a scale of the order of the mean
field. This can be interpreted as a chemical potential. We discuss the
implications of these results for cosmological preheating.Comment: 36 pages, 14 figures, LaTeX, submitted to Physical Review
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