516 research outputs found
Quantified vegetation change over 42 years at Cape Hallett, East Antarctica
This paper reports on the remapping of a carefully documented vegetation plot at Cape Hallett (72°19′S 170°16′E) to provide an assessment of the rates of vegetation change over decadal time scales. E.D. Rudolph, in 1962, mapped in detail the vegetation of a site approximately 28 m by 120 m at Cape Hallett, Victoria Land, Antarctica. This site was relocated and remapped in January 2004 and changes were assessed using GIS techniques. This appears to be the longest available time period for assessing vegetation change in Antarctica. The analysis indicated that considerable change had occurred in moss and algae distribution patterns and this seems to have been caused by increased water supply, particularly in wetter areas. There was also evidence of some change in lichen distribution. The extent of the change indicates that vegetation cover can be used for monitoring change in areas as extreme as the Ross Sea region. For this analysis to be successful it was important that the mapping techniques used were totally explicit and could easily be replicated. Fortunately, Rudolph had defined his cover classes and the site was also clearly marked. The application of GIS mapping techniques allows the mapping to be more explicitly defined and easily replicated
A Symplectic Structure for String Theory on Integrable Backgrounds
We define regularised Poisson brackets for the monodromy matrix of classical
string theory on R x S^3. The ambiguities associated with Non-Ultra Locality
are resolved using the symmetrisation prescription of Maillet. The resulting
brackets lead to an infinite tower of Poisson-commuting conserved charges as
expected in an integrable system. The brackets are also used to obtain the
correct symplectic structure on the moduli space of finite-gap solutions and to
define the corresponding action-angle variables. The canonically-normalised
action variables are the filling fractions associated with each cut in the
finite-gap construction. Our results are relevant for the leading-order
semiclassical quantisation of string theory on AdS_5 x S^5 and lead to
integer-valued filling fractions in this context.Comment: 41 pages, 2 figures; added references, corrected typos, improved
discussion of Hamiltonian constraint
DDF and Pohlmeyer invariants of (super)string
We show how the Pohlmeyer invariants of the bosonic string are expressible in
terms of DDF invariants. Quantization of the DDF observables in the usual way
yields a consistent quantization of the algebra of Pohlmeyer invariants.
Furthermore it becomes straightforward to generalize the Pohlmeyer invariants
to the superstring as well as to all backgrounds which allow a free field
realization of the worldsheet theory.Comment: 17 pp, minor typos corrected, references to papers by Isaev and
Borodulin added, which contain essentially the same results as reported her
Axion and neutrino physics from anomaly cancellation
It has been recently shown that the requirement of anomaly cancellation in a
(non-supersymmetric) six-dimensional version of the standard model fixes the
field content to the known three generations. We discuss the phenomenological
consequences of the cancellation of the local anomalies: the strong CP problem
is solved and the fundamental scale of the theory is bounded by the physics of
the axion. Neutrinos acquire a mass in the range suggested by atmospheric
experiments.Comment: 9 pages, RevTeX
Hybridized Affleck-Dine baryogenesis
We propose a novel scenario for Affleck-Dine baryogenesis in the braneworld,
considering the hybrid potential for the Affleck-Dine field. Destabilization of
the flat direction is not due to the Hubble parameter, but is induced by a
trigger field. The moduli for the brane distance plays the role of the trigger
field. Q-balls are unstable in models with large extra dimensions.Comment: 10pages, plain latex2e, references added, to appear in PR
A multicenter, longitudinal, interventional, double blind randomized clinical trial in hematopoietic cell transplant recipients residing in remote areas: Lessons learned from the late cytomegalovirus prevention trial
AbstractPurposeThe logistics of conducting double-blinded phase III clinical trials with participants residing in remote locations are complex. Here we describe the implementation of an interventional trial for the prevention of late cytomegalovirus (CMV) disease in hematopoietic cell transplantation (HCT) subjects in a long-term follow-up environment.MethodsA total of 184 subjects at risk for late CMV disease surviving 80 days following allogeneic HCT were randomized to receive six months of valganciclovir or placebo. Subjects were followed through day 270 post-transplant at their local physician's office within the United States. Anti-viral treatment interventions were based on CMV DNAemia as measured by polymerase chain reaction (PCR) (>1000 copies/mL) and granulocyte colony stimulating factor (G-CSF) was prescribed for neutropenia (absolute neutrophil count (ANC < 1.0 × 109 cells/L). Blood samples for viral testing and safety monitoring were shipped to a central laboratory by overnight carrier. Real-time communication was established between the coordinating center and study sites, primary care physicians, and study participants to facilitate starting, stopping and dose adjustments of antiviral drugs and G-CSF. The time required to make these interventions was analyzed.ResultsOf the 4169 scheduled blood specimens, 3832 (92%) were received and analyzed; the majority (97%) arriving at the central site within 2 days. Among subjects with positive CMV DNAemia (N = 46), over 50% received open label antiviral medication within one day. The median time to start G-CSF for neutropenia was <1 day after posting of laboratory results (range 0–6; N = 38). Study drug dose adjustments for abnormal renal function were implemented 203 times; within one day for 48% of cases and within 2 days for 80% of cases.ConclusionComplex randomized, double-blind, multicenter interventional trials with treatment decisions made at a central coordinating site can be conducted safely and effectively according to Good Clinical Practice (GCP) guidelines over a large geographic area
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Research and theory for nursing and midwifery: Rethinking the nature of evidence
Background and Rationale: The rise in the principles of evidence-based medicine in the 1990s heralded a re-emerging orthodoxy in research methodologies. The view of the randomised controlled trial (RCT) as a “gold standard” for evaluation of medical interventions has extended recently to evaluation of organisational forms and reforms and of change in complex systems—within health care and in other human services. Relatively little attention has been given to the epistemological assumptions underlying such a hierarchy of research evidence.
Aims and Methods: Case studies from research in maternity care are used in this article to describe problems and limitations encountered in using RCTs to evaluate some recent policy-driven and consumer-oriented developments. These are discussed in relation to theory of knowledge and the epistemological assumptions, or paradigms, underpinning health services research. The aim in this discussion is not to advocate, or to reject, particular approaches to research but to advocate a more open and critical engagement with questions about the nature of evidence.
Findings and Discussion: Experimental approaches are of considerable value in investigating deterministic and probabilistic cause and effect relationships, and in testing often well-established but unevaluated technologies. However, little attention has been paid to contextual and cultural factors in the effects of interventions, in the culturally constructed nature of research questions themselves, or of the data on which much research is based. More complex, and less linear, approaches to methodology are needed to address these issues. A simple hierarchical approach does not represent the complexity of evidence well and should move toward a more cyclical view of knowledge development
D-terms and D-strings in open string models
We study the Fayet-Iliopoulos (FI) D-terms on D-branes in type II Calabi-Yau
backgrounds. We provide a simple worldsheet proof of the fact that, at tree
level, these terms only couple to scalars in closed string hypermultiplets. At
the one-loop level, the D-terms get corrections only if the gauge group has an
anomalous spectrum, with the anomaly cancelled by a Green-Schwarz mechanism. We
study the local type IIA model of D6-branes at SU(3) angles and show that, as
in field theory, the one-loop correction suffers from a quadratic divergence in
the open string channel. By studying the closed string channel, we show that
this divergence is related to a closed string tadpole, and is cancelled when
the tadpole is cancelled. Next, we study the cosmic strings that arise in the
supersymmetric phases of these systems in light of recent work of Dvali et. al.
In the type IIA intersecting D6-brane examples, we identify the D-term strings
as D4-branes ending on the D6-branes. Finally, we use N=1 dualities to relate
these results to previous work on the FI D-term of heterotic strings.Comment: 29 pages, 5 figures; v2: improved referencin
Genetic and phenotypic characterization of indolent T-cell lymphoproliferative disorders of the gastrointestinal tract.
Indolent T-cell lymphoproliferative disorders of the gastrointestinal tract are rare clonal T-cell diseases that more commonly occur in the intestines and have a protracted clinical course. Different immunophenotypic subsets have been described, but the molecular pathogenesis and cell of origin of these lymphocytic proliferations is poorly understood. Hence, we performed targeted next-generation sequencing and comprehensive immunophenotypic analysis of ten indolent T-cell lymphoproliferative disorders of the gastrointestinal tract, which comprised CD4 <sup>+</sup> (n=4), CD8 <sup>+</sup> (n=4), CD4 <sup>+</sup> /CD8 <sup>+</sup> (n=1) and CD4 <sup>-</sup> /CD8 <sup>-</sup> (n=1) cases. Genetic alterations, including recurrent mutations and novel rearrangements, were identified in 8/10 (80%) of these lymphoproliferative disorders. The CD4 <sup>+</sup> , CD4 <sup>+</sup> /CD8 <sup>+</sup> , and CD4 <sup>-</sup> /CD8 <sup>-</sup> cases harbored frequent alterations of JAK-STAT pathway genes (5/6, 82%); STAT3 mutations (n=3), SOCS1 deletion (n=1) and STAT3-JAK2 rearrangement (n=1), and 4/6 (67%) had concomitant mutations in epigenetic modifier genes (TET2, DNMT3A, KMT2D). Conversely, 2/4 (50%) of the CD8 <sup>+</sup> cases exhibited structural alterations involving the 3' untranslated region of the IL2 gene. Longitudinal genetic analysis revealed stable mutational profiles in 4/5 (80%) cases and acquisition of mutations in one case was a harbinger of disease transformation. The CD4 <sup>+</sup> and CD4 <sup>+</sup> /CD8 <sup>+</sup> lymphoproliferative disorders displayed heterogeneous Th1 (T-bet <sup>+</sup> ), Th2 (GATA3 <sup>+</sup> ) or hybrid Th1/Th2 (T-bet <sup>+</sup> /GATA3 <sup>+</sup> ) profiles, while the majority of CD8 <sup>+</sup> disorders and the CD4 <sup>-</sup> /CD8 <sup>-</sup> disease showed a type-2 polarized (GATA3 <sup>+</sup> ) effector T-cell (Tc2) phenotype. Additionally, CD103 expression was noted in 2/4 CD8 <sup>+</sup> cases. Our findings provide insights into the pathogenetic bases of indolent T-cell lymphoproliferative disorders of the gastrointestinal tract and confirm the heterogeneous nature of these diseases. Detection of shared and distinct genetic alterations of the JAK-STAT pathway in certain immunophenotypic subsets warrants further mechanistic studies to determine whether therapeutic targeting of this signaling cascade is efficacious for a proportion of patients with these recalcitrant diseases
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