338 research outputs found
Synchronicity of historical dry spells in the Southern Hemisphere
A shift in climate occurred during the mid-1970s that affected the
hydroclimate of the Southern Hemisphere resulting in drying trends across
continental regions including Australia, New Zealand and southern and western
Africa. There is also anecdotal evidence of other periods of climatic
synchronicity in the Southern Hemisphere (e.g., the 1920s and 1940s),
indicating that the mid-1970s event may not be anomalous. This paper
identifies periods within the last ~120 years using statistical
analysis where dry spells (in terms of annual to multi-decadal rainfall
deficiencies) have coincided across the continental Southern Hemisphere in
order to characterize temporal consistency. It is shown that synchronicity of
dry spells is (a) most likely common over the last 120 years and (b)
associated with changes in the large-scale climate modes of the Pacific,
Indian and Southern Oceans. Importantly, the findings presented in this paper
have marked implications for drought management and drought forecasting
studies in the Southern Hemisphere
U(N) Instantons on N=1/2 superspace -- exact solution & geometry of moduli space
We construct the exact solution of one (anti)instanton in N=1/2 super
Yang-Mills theory defined on non(anti)commutative superspace. We first identify
N = 1/2 superconformal invariance as maximal spacetime symmetry. For gauge
group U(2), SU(2) part of the solution is given by the standard
(anti)instanton, but U(1) field strength also turns out nonzero. The solution
is SO(4) rotationally symmetric. For gauge group U(N), in contrast to the U(2)
case, we show that the entire U(N) part of the solution is deformed by
non(anti)commutativity and fermion zero-modes. The solution is no longer
rotationally symmetric; it is polarized into an axially symmetric configuration
because of the underlying non(anti)commutativity. We compute the `information
metric' of one (anti) instanton. We find that moduli space geometry is deformed
from hyperbolic space (Euclidean anti-de Sitter space) in a way anticipated
from reduced spacetime symmetry. Remarkably, the volume measure of the moduli
space turns out to be independent of the non(anti)commutativity. Implications
to D-branes in Ramond- Ramond flux background and Maldacena's gauge-gravity
correspondence are discussed.Comment: 39 pages, 3 figures, JHEP style; v2. typos corrected + a paragraph
adde
Links between the Big Dry in Australia and hemispheric multi-decadal climate variability – implications for water resource management
Southeast Australia (SEA) experienced a protracted drought during the
mid-1990s until early 2010 (known as the Big Dry or Millennium Drought) that
resulted in serious environmental, social and economic effects. This paper
analyses a range of historical climate data sets to place the recent drought
into context in terms of Southern Hemisphere inter-annual to multi-decadal
hydroclimatic variability. The findings indicate that the recent Big Dry in
SEA is in fact linked to the widespread Southern Hemisphere climate shift
towards drier conditions that began in the mid-1970s. However, it is shown
that this link is masked because the large-scale climate drivers responsible
for drying in other regions of the mid-latitudes since the mid-1970s did not
have the same effect on SEA during the mid- to late 1980s and early 1990s.
More specifically, smaller-scale synoptic processes resulted in elevated
autumn and winter rainfall (a crucial period for SEA hydrology) during the
mid- to late 1980s and early 1990s, which punctuated the longer-term drying.
From the mid-1990s to 2010 the frequency of the synoptic processes associated
with elevated autumn/winter rainfall decreased, resulting in a return to
drier than average conditions and the onset of the Big Dry. The findings
presented in this paper have marked implications for water management and
climate attribution studies in SEA, in particular for understanding and
dealing with "baseline" (i.e. current) hydroclimatic risks
Interacting Dipoles from Matrix Formulation of Noncommutative Gauge Theories
We study the IR behavior of noncommutative gauge theory in the matrix
formulation. We find that in this approach, the nature of the UV/IR mixing is
easily understood, which allows us to perform a reliable calculation of the
quantum effective action for the long wavelength modes of the noncommutative
gauge field. At one loop, we find that our description is weakly coupled only
in the supersymmetric theory. At two loops, we find non-trivial interaction
terms suggestive of dipole degrees of freedom. These dipoles exhibit a channel
duality reminiscent of string theory.Comment: LaTeX 11 pages, 4 figures; v.2 minor changes and some references
added; v.3 many more technical details added and significantly different
presentation, use REVTeX 4, to appear in PR
Graviton-Scalar Interaction in the PP-Wave Background
We compute the graviton two scalar off-shell interaction vertex at tree level
in Type IIB superstring theory on the pp-wave background using the light-cone
string field theory formalism. We then show that the tree level vertex vanishes
when all particles are on-shell and conservation of p_{+} and p_{-} are
imposed. We reinforce our claim by calculating the same vertex starting from
the corresponding SUGRA action expanded around the pp-wave background in the
light-cone gauge.Comment: 26 pages, harvmac One reference added. A few comments changed in the
introduction. The "cyclic perms." term removed from some equations as
unnecessary and equations (2.38) and (3.19) are corrected accordingl
Preclinical correction of human Fanconi anemia complementation group A bone marrow cells using a safety-modified lentiviral vector.
One of the major hurdles for the development of gene therapy for Fanconi anemia (FA) is the increased sensitivity of FA stem cells to free radical-induced DNA damage during ex vivo culture and manipulation. To minimize this damage, we have developed a brief transduction procedure for lentivirus vector-mediated transduction of hematopoietic progenitor cells from patients with Fanconi anemia complementation group A (FANCA). The lentiviral vector FancA-sW contains the phosphoglycerate kinase promoter, the FANCA cDNA, and a synthetic, safety-modified woodchuck post transcriptional regulatory element (sW). Bone marrow mononuclear cells or purified CD34(+) cells from patients with FANCA were transduced in an overnight culture on recombinant fibronectin peptide CH-296, in low (5%) oxygen, with the reducing agent, N-acetyl-L-cysteine (NAC), and a combination of growth factors, granulocyte colony-stimulating factor (G-CSF), Flt3 ligand, stem cell factor, and thrombopoietin. Transduced cells plated in methylcellulose in hypoxia with NAC showed increased colony formation compared with 21% oxygen without NAC (P<0.03), showed increased resistance to mitomycin C compared with green fluorescent protein (GFP) vector-transduced controls (P<0.007), and increased survival. Thus, combining short transduction and reducing oxidative stress may enhance the viability and engraftment of gene-corrected cells in patients with FANCA
Tropical cyclone perceptions, impacts and adaptation in the Southwest Pacific: an urban perspective from Fiji, Vanuatu and Tonga
The destruction caused by tropical cyclone (TC) Pam in March 2015 is considered one of the worst natural disasters in the history of Vanuatu. It has highlighted the need for a better understanding of TC impacts and adaptation in the Southwest Pacific (SWP) region. Therefore, the key aims of this study are to (i) understand local perceptions of TC activity, (ii) investigate impacts of TC activity and (iii) uncover adaptation strategies used to offset the impacts of TCs. To address these aims, a survey (with 130 participants from urban areas) was conducted across three SWP small island states (SISs): Fiji, Vanuatu and Tonga (FVT). It was found that respondents generally had a high level of risk perception and awareness of TCs and the associated physical impacts, but lacked an understanding of the underlying weather conditions. Responses highlighted that current methods of adaptation generally occur at the local level, immediately prior to a TC event (preparation of property, gathering of food, finding a safe place to shelter). However higher level adaptation measures (such as the modification to building structures) may reduce vulnerability further. Finally, we discuss the potential of utilising weather-related traditional knowledge and non-traditional knowledge of empirical and climate-model-based weather forecasts to improve TC outlooks, which would ultimately reduce vulnerability and increase adaptive capacity. Importantly, lessons learned from this study may result in the modification and/or development of existing adaptation strategies
Thermodynamics of doubly charged CGHS model and D1-D5-KK black holes of IIB supergravity
We study the doubly charged Callan-Giddings-Harvey-Strominger (CGHS) model,
which has black hole solutions that were found to be U-dual to the D1-D5-KK
black holes of the IIB supergravity. We derive the action of the model via a
spontaneous compactification on S^3 of the IIB supergravity on S^1*T^4 and
obtain the general static solutions including black holes corresponding to
certain non-asymptotically flat black holes in the IIB supergravity.
Thermodynamics of them is established by computing the entropy, temperature,
chemical potentials, and mass in the two-dimensional setup, and the first law
of thermodynamics is explicitly verified. The entropy is in precise agreement
with that of the D1-D5-KK black holes, and the mass turns out to be consistent
with the infinite Lorentz boost along the M theory circle that is a part of the
aforementioned U-dual chain.Comment: 21 pages, Revte
Interacting Open Wilson Lines in Noncommutative Field Theories
In noncommutative field theories, it was known that one-loop effective action
describes propagation of non-interacting open Wilson lines, obeying the flying
dipole's relation. We show that two-loop effective action describes cubic
interaction among `closed string' states created by open Wilson lines. Taking
d-dimensional noncommutative [\Phi^3] theory as the simplest setup, we compute
nonplanar contribution at low-energy and large noncommutativity limit. We find
that the contribution is expressible in a remarkably simple cubic interaction
involving scalar open Wilson lines only and nothing else. We show that the
interaction is purely geometrical and noncommutative in nature, depending only
on sizes of each open Wilson line.Comment: v1: 27 pages, Latex, 7 .eps figures v2: minor wording change +
reference adde
Effective Action for Membrane Dynamics in DLCQ theory on a Two-torus
The effective action for the membrane dynamics on the background geometry of
the -sector DLCQ theory compactified on a two-torus is computed via
supergravity. We compare it to the effective action obtained from the matrix
theory, i.e., the (2+1)-dimensional supersymmetric Yang-Mills (SYM) theory,
including the one-loop perturbative and full non-perturbative instanton
effects. Consistent with the DLCQ prescription of theory {\em a la}
Susskind, we find the precise agreement for the finite -sector
(off-conformal regime), as well as for the large limit (conformal regime),
providing us with a concrete example of the correspondence between the matrix
theory and the DLCQ theory. Non-perturbative instanton effects in the SYM
theory conspire to yield the eleven-dimensionally covariant effective action.Comment: 11 pages, latex, no figure
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