4,959 research outputs found
The frequency response of temperature and precipitation in a climate model
Dynamic aspects of the climate's response to forcing are typically explored through transient simulations in the time domain. However, because of the large range of time-scales involved, some features are more easily observed in the frequency domain. We compute the frequency-response of the HadCM3L general circulation model (GCM) to sinusoidal perturbations in solar radiative forcing, with periods between 2^(â1/2) and 2^9 (512) years. The global mean temperature response decreases with increasing frequency, and the frequency scaling at time-scales longer than one year is consistent with the behavior of diffusion into a semi-infinite slab. The land-sea contrast and land-averaged precipitation, however, exhibit relatively little dependency on the frequency of the imposed perturbation, with significant response at both short and long periods. Understanding these relative characteristics of different climate variables in the frequency domain is important to understanding the transient response of the climate system to both anthropogenic and natural (e.g., volcanic) forcings; the frequency response is also relevant in understanding the spectrum of natural variability
Applications of Geographic Information Systems for the Analysis of Apartment Rents
This study is the first to incorporate comprehensive regional factors into the analysis of the variations of apartment rent in a particular metropolitan area. A Geographic Information Systems (GIS) procedure is developed to generate regional variables for the analysis. Results show that not only the individual apartment's characteristics, but also the regional factors are important in determining apartment rents.
Open String and Morita Equivalence of the Dirac-Born-Infeld Action with Modulus \Phi
Based on the canonical quantization of open strings ending on D-branes with a
background B field, we construct the open string propagator. We demonstrate the
relation between the T duality of the underlying string theory and the Morita
equivalence of the interpolating general Dirac-Born-Infeld theory on a
noncommutative torus in the nonzero modulus \Phi sector. The general
noncommutative Dirac-Born-Infeld action with the Wess-Zumino terms expressed by
the background R-R fields is shown to be Morita invariant.Comment: 10 pages, LaTex2e, no figure
An Associative and Noncommutative Product for the Low Energy Effective Theory of a D-Brane in Curved Backgrounds and Bi-Local Fields
We point out that when a D-brane is placed in an NS-NS B field background
with non-vanishing field strength (H=dB) along the D-brane worldvolume, the
coordinate of one end of the open string does not commute with that of the
other in the low energy limit. The degrees of the freedom associated with both
ends are not decoupled and accordingly, the effective action must be quite
different from that of the ordinary noncommutative gauge theory for a constant
B background. We construct an associative and noncommutative product which
operates on the coordinates of both ends of the string and propose a new type
of noncommutative gauge action for the low energy effective theory of a
Dp-brane. This effective theory is bi-local and lives in twice as large
dimensions (2D=2(p+1)) as in the H=0 case. When viewed as a theory in the
D-dimensional space, this theory is non-local and we must force the two ends of
the string to coincide. We will then propose a prescription for reducing this
bi-local effective action to that in D dimensions and obtaining a local
effective action.Comment: 23 pages, LaTeX2e, 1 figur
Gauge Bundles and Born-Infeld on the Noncommutative Torus
In this paper, we describe non-abelian gauge bundles with magnetic and
electric fluxes on higher dimensional noncommutative tori. We give an explicit
construction of a large class of bundles with nonzero magnetic 't Hooft fluxes.
We discuss Morita equivalence between these bundles. The action of the duality
is worked out in detail for the four-torus. As an application, we discuss
Born-Infeld on this torus, as a description of compactified string theory. We
show that the resulting theory, including the fluctuations, is manifestly
invariant under the T-duality group SO(4,4;Z). The U-duality invariant BPS
mass-formula is discussed shortly. We comment on a discrepancy of this result
with that of a recent calculation.Comment: 22 pages, LaTeX2e. Small errors correcte
Non-commutativity, Zero modes and D-brane Geometry
The non-commutative geometry is revisited from the perspective of a
generalized D p-brane. In particular, we analyze the open bosonic string
world-sheet description and show that an effective non-commutative description
on a D p-brane corresponds to a re-normalized world-volume. The world-volume
correlators are analyzed to make a note on the non-commutative geometry. It is
argued that the U(1) gauge symmetry can be viewed in a homomorphic image space
for the non-commutative space of coordinates with an SO(p) symmetry. In the
large B-field limit, the non-commutativity reduces to that among the zero modes
and the world-volume description is precisely in agreement with the holographic
principle.Comment: 15 pages, LaTex, v2: typos corrected, to appear in Nucl.Phys.
Dimensionally Reduced Yang-Mills Theories in Noncommutative Geometry
We study a class of noncommutative geometries that give rise to dimensionally
reduced Yang-Mills theories. The emerging geometries describe sets of copies of
an even dimensional manifold. Similarities to the D-branes in string theory are
discussed.Comment: 12 pages, Latex, minor correction
D0-branes in an H-field Background and Noncommutative Geometry
It is known that if we compactify D0-branes on a torus with constant B-field,
the resulting theory becomes SYM theory on a noncommutative dual torus. We
discuss the extension to the case of a H-field background. In the case of
constant H-field on a three-torus, we derive the constraints to realize this
compactification by considering the correspondence to string theory. We carry
out this work as a first step to examine the possibility to describe transverse
M5-branes in Matrix theory.Comment: 15 pages, LaTeX; some comments added, typos corrected, to appear in
Nucl. Phys.
Acoustic droplet vaporization, cavitation, and therapeutic properties of copolymer-stabilized perfluorocarbon nanoemulsions
Journal ArticleAcoustic and therapeutic properties of Doxorubicin (DOX) and paclitaxel (PTX)-loaded perfluorocarbon nanoemulsions have been investigated in a mouse model of ovarian cancer. The nanoemulsions were stabilized by two biodegradable amphiphilic block copolymers that differed in the structure of the hydrophobic block. Acoustic droplet vaporization (ADV) and cavitation parameters were measured as a function of ultrasound frequency, pressure, duty cycles, and temperature. The optimal parameters that induced ADV and inertial cavitation of the formed microbubbles were used in vivo in the experiments on the ultrasound-mediated chemotherapy of ovarian cancer. A combination tumor treatment by intravenous injections of drug-loaded perfluoropentane nanoemulsions and tumor-directed 1-MHz ultrasound resulted in a dramatic decrease of ovarian or breast carcinoma tumor volume and sometimes complete tumor resolution. However, tumors often recurred three to six weeks after the treatment indicating that some cancer cells survived the treatment. The recurrent tumors proved more aggressive and resistant to the repeated therapy than initial tumors suggesting selection for the resistant cells during the first treatment
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