3,832 research outputs found
Improving nitrogen use efficiency in irrigated cotton production
Irrigated cotton in Australia is mainly grown on heavy textured soils which are prone to waterlogging, resulting in significant losses of nitrogen (N) via denitrification and surface run-off. This study investigated fertiliser nitrogen use efficiency (fNUE) over three seasons on five commercial cotton farms using the N tracer technique. Fertiliser NUE was consistently low across all fertilised treatments, with on average 47% of the applied fertiliser lost and only 17% of the N taken up by the crop derived from fertiliser. There was no significant effect of different N fertiliser products and rates on cotton lint yield. High lint yields (0.9–3.6 Mg ha) could be achieved even without the application of N fertiliser, demonstrating mineralisation of soil organic N, residual fertiliser, or N returned with crop residues, as key source of N in these cropping systems. Using the nitrification inhibitor DMPP and overhead instead of furrow irrigation showed potential to reduce N fertiliser losses. The results demonstrate that under current on-farm management fNUE is low on irrigated cotton farms in Australia and highlight the need to account for soil N stocks and mineralisation rates when assessing optimized fertiliser rates. There is substantial scope to improve fNUE and reduce N losses without any impact on lint yield, by adjusting N fertiliser application rates, in particular in combination with the use of the nitrification inhibitor DMPP. Using overhead instead of furrow irrigation is a promising approach to improve not only water use efficiency, but also fNUE in irrigated cotton systems
A Neutron Star with a Massive Progenitor in Westerlund 1
We report the discovery of an X-ray pulsar in the young, massive Galactic
star cluster Westerlund 1. We detected a coherent signal from the brightest
X-ray source in the cluster, CXO J164710.2-455216, during two Chandra
observations on 2005 May 22 and June 18. The period of the pulsar is 10.6107(1)
s. We place an upper limit to the period derivative of Pdot<2e-10 s/s, which
implies that the spin-down luminosity is Edot<3e33 erg/s. The X-ray luminosity
of the pulsar is L_X = 3(+10,-2)e33 (D/5 kpc)^2 erg/s, and the spectrum can be
described by a kT = 0.61+/-0.02 keV blackbody with a radius of R_bb =
0.27+/-0.03 (D/5 kpc}) km. Deep infrared observations reveal no counterpart
with K1 Msun. Taken together,
the properties of the pulsar indicate that it is a magnetar. The rarity of slow
X-ray pulsars and the position of CXO J164710.2-455216 only 1.6' from the core
of Westerlund 1 indicates that it is a member of the cluster with >99.97%
confidence. Westerlund 1 contains 07V stars with initial masses M_i=35 Msun and
>50 post-main-sequence stars that indicate the cluster is 4+/-1 Myr old.
Therefore, the progenitor to this pulsar had an initial mass M_i>40 Msun. This
is the most secure result among a handful of observational limits to the masses
of the progenitors to neutron stars.Comment: 4 pages, 5 figures. Final version to match ApJL (added one figure
since v2
Magnetic levitation of metamaterial bodies enhanced with magnetostatic surface resonances
We propose that macroscopic objects built from negative-permeability
metamaterials may experience resonantly enhanced magnetic force in
low-frequency magnetic fields. Resonant enhancement of the time-averaged force
originates from magnetostatic surface resonances (MSR) which are analogous to
the electrostatic resonances of negative-permittivity particles, well known as
surface plasmon resonances in optics. We generalize the classical problem of
MSR of a homogeneous object to include anisotropic metamaterials, and consider
the most extreme case of anisotropy where the permeability is negative in one
direction but positive in the others. It is shown that deeply subwavelength
objects made of such indefinite (hyperbolic) media exhibit a pronounced
magnetic dipole resonance that couples strongly to uniform or weakly
inhomogeneous magnetic field and provides strong enhancement of the magnetic
force, enabling applications such as enhanced magnetic levitation.Comment: 19 pages, 5 figure
Refractive-index sensing with ultra-thin plasmonic nanotubes
We study the refractive-index sensing properties of plasmonic nanotubes with
a dielectric core and ultra-thin metal shell. The few-nm thin metal shell is
described by both the usual Drude model and the nonlocal hydrodynamic model to
investigate the effects of nonlocality. We derive an analytical expression for
the extinction cross section and show how sensing of the refractive index of
the surrounding medium and the figure-of-merit are affected by the shape and
size of the nanotubes. Comparison with other localized surface plasmon
resonance sensors reveals that the nanotube exhibits superior sensitivity and
comparable figure-of-merit
Minimal Model Holography for SO(2N)
A duality between the large N 't Hooft limit of the WD_N minimal model CFTs
and a higher spin gravity theory on AdS3 is proposed. The gravity theory has
massless spin fields of all even spins s=2,4,6,..., as well as two real scalar
fields whose mass is determined by the 't Hooft parameter of the CFT. We show
that, to leading order in the large N limit, the 1-loop partition function of
the higher spin theory matches precisely with the CFT partition function.Comment: 21 pages, LaTe
Theory of structural response to macroscopic electric fields in ferroelectric systems
We have developed and implemented a formalism for computing the structural
response of a periodic insulating system to a homogeneous static electric field
within density-functional perturbation theory (DFPT). We consider the
thermodynamic potentials E(R,eta,e) and F(R,eta,e) whose minimization with
respect to the internal structural parameters R and unit cell strain eta yields
the equilibrium structure at fixed electric field e and polarization P,
respectively. First-order expansion of E(R,eta,e) in e leads to a useful
approximation in which R(P) and eta(P) can be obtained by simply minimizing the
zero-field internal energy with respect to structural coordinates subject to
the constraint of a fixed spontaneous polarization P. To facilitate this
minimization, we formulate a modified DFPT scheme such that the computed
derivatives of the polarization are consistent with the discretized form of the
Berry-phase expression. We then describe the application of this approach to
several problems associated with bulk and short-period superlattice structures
of ferroelectric materials such as BaTiO3 and PbTiO3. These include the effects
of compositionally broken inversion symmetry, the equilibrium structure for
high values of polarization, field-induced structural phase transitions, and
the lattice contributions to the linear and the non-linear dielectric
constants.Comment: 19 pages, with 15 postscript figures embedded. Uses REVTEX4 and epsf
macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/sai_pol/index.htm
Quantum Nonlocality without Entanglement
We exhibit an orthogonal set of product states of two three-state particles
that nevertheless cannot be reliably distinguished by a pair of separated
observers ignorant of which of the states has been presented to them, even if
the observers are allowed any sequence of local operations and classical
communication between the separate observers. It is proved that there is a
finite gap between the mutual information obtainable by a joint measurement on
these states and a measurement in which only local actions are permitted. This
result implies the existence of separable superoperators that cannot be
implemented locally. A set of states are found involving three two-state
particles which also appear to be nonmeasurable locally. These and other
multipartite states are classified according to the entropy and entanglement
costs of preparing and measuring them by local operations.Comment: 27 pages, Latex, 6 ps figures. To be submitted to Phys. Rev. A.
Version 2: 30 pages, many small revisions and extensions, author added.
Version 3: Proof in Appendix D corrected, many small changes; final version
for Phys. Rev. A Version 4: Report of Popescu conjecture modifie
B(H) Constitutive Relations Near H_c1 in Disordered Superconductors
We provide a self-contained account of the B vs. H constitutive relation near
H_c1 in Type II superconductors with various types of quenched random disorder.
The traditional Abrikosov result B ~ [ln (H - H_c1)]^{-2}, valid in the absence
of disorder and thermal fluctuations, changes significantly in the presence of
disorder. Moreover, the constitutive relations will depend strongly on the type
of disorder. In the presence of point disorder, B ~ (H - H_c1)^{3/2} in
three-dimensional (thick) superconductors, as shown by Nattermann and Lipowsky.
In two-dimensional (thin film) superconductors with point disorder, B ~ (H -
H_c1). In the presence of parallel columnar disorder, we find that B ~ exp[-C /
(H - H_c1)] in three dimensions, while B ~ exp[-K / (H - H_c1)^{1/2}] in two
dimensions. In the presence of nearly isotropically splayed disorder, we find
that B ~ (H - H_c1)^{3/2} in both two and three dimensions.Comment: 37 pages, 12 figures included in text; submitted to Physica
A tunable delivery platform to provide local chemotherapy for pancreatic ductal adenocarcinoma
Pancreatic ductal adenocarcinoma (PDAC) is one of the most devastating and painful cancers. It is often highly resistant to therapy owing to inherent chemoresistance and the desmoplastic response that creates a barrier of fibrous tissue preventing transport of chemotherapeutics into the tumor. The growth of the tumor in pancreatic cancer often leads to invasion of other organs and partial or complete biliary obstruction, inducing intense pain for patients and necessitating tumor resection or repeated stenting. Here, we have developed a delivery device to provide enhanced palliative therapy for pancreatic cancer patients by providing high concentrations of chemotherapeutic compounds locally at the tumor site. This treatment could reduce the need for repeated procedures in advanced PDAC patients to debulk the tumor mass or stent the obstructed bile duct. To facilitate clinical translation, we created the device out of currently approved materials and drugs. We engineered an implantable poly(lactic-co-glycolic)-based biodegradable device that is able to linearly release high doses of chemotherapeutic drugs for up to 60 days. We created five patient-derived PDAC cell lines and tested their sensitivity to approved chemotherapeutic compounds. These in vitro experiments showed that paclitaxel was the most effective single agent across all cell lines. We compared the efficacy of systemic and local paclitaxel therapy on the patient-derived cell lines in an orthotopic xenograft model in mice (PDX). In this model, we found up to a 12-fold increase in suppression of tumor growth by local therapy in comparison to systemic administration and reduce retention into off-target organs. Herein, we highlight the efficacy of a local therapeutic approach to overcome PDAC chemoresistance and reduce the need for repeated interventions and biliary obstruction by preventing local tumor growth. Our results underscore the urgent need for an implantable drug-eluting platform to deliver cytotoxic agents directly within the tumor mass as a novel therapeutic strategy for patients with pancreatic cancer. Keywords: Pancreatic cancer; Chemoresistance; Local delivery; Patient-derived xenograft; Paclitaxel; Poly(lactic-co-glycolic acid)National Institutes of Health (U.S.) (Grant P30-CA14051
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