780 research outputs found
Residues and Topological Yang-Mills Theory in Two Dimensions
A residue formula which evaluates any correlation function of topological
Yang-Mills theory with arbitrary magnetic flux insertion in two
dimensions are obtained. Deformations of the system by two form operators are
investigated in some detail. The method of the diagonalization of a matrix
valued field turns out to be useful to compute various physical quantities. As
an application we find the operator that contracts a handle of a Riemann
surface and a genus recursion relation.Comment: 23 pages, some references added, to appear in Rev.Math.Phy
Learning with Biased Complementary Labels
In this paper, we study the classification problem in which we have access to
easily obtainable surrogate for true labels, namely complementary labels, which
specify classes that observations do \textbf{not} belong to. Let and
be the true and complementary labels, respectively. We first model
the annotation of complementary labels via transition probabilities
, where is the number of
classes. Previous methods implicitly assume that , are identical, which is not true in practice because humans are
biased toward their own experience. For example, as shown in Figure 1, if an
annotator is more familiar with monkeys than prairie dogs when providing
complementary labels for meerkats, she is more likely to employ "monkey" as a
complementary label. We therefore reason that the transition probabilities will
be different. In this paper, we propose a framework that contributes three main
innovations to learning with \textbf{biased} complementary labels: (1) It
estimates transition probabilities with no bias. (2) It provides a general
method to modify traditional loss functions and extends standard deep neural
network classifiers to learn with biased complementary labels. (3) It
theoretically ensures that the classifier learned with complementary labels
converges to the optimal one learned with true labels. Comprehensive
experiments on several benchmark datasets validate the superiority of our
method to current state-of-the-art methods.Comment: ECCV 2018 Ora
Influence of microwave annealing on GMI response and magnetization of an amorphous Fe73.5Nb3Cu1Si13.5B9 ribbon
The resistive and reactive components of magneto-impedance was studied for
the as-quenched and microwave annealed amorphous Fe73.5Nb3Cu1Si13.5B9 ribbon as
a function of biasing d.c magnetic fields (-60 to +60 Oe) and excitation
frequencies (0.1, 1, 10 and 20MHz). The magneto-impedance (both components)
response was much reduced for the microwave annealed ribbon and the changes
were more discernable at higher excitation frequencies. The imaginary component
of magneto-impedance showed maxima at finite (non-zero) d.c magnetic fields for
both the as-quenched and microwave annealed ribbons. Magnetization measurements
performed for both the as-quenched and microwave annealed ribbons revealed the
magnetic hardness of the latter. The initial susceptibility decreases by two
orders of magnitude for the microwave-annealed ribbon. XRD measurements
indicated the transformation of the surface of the ribbon from the amorphous
state to the crystalline one.Comment: 14 pages, 6 figure
Low-dose megavoltage cone-beam CT imaging using thick, segmented scintillators
Megavoltage, cone-beam computed tomography (MV CBCT) employing an electronic portal imaging device (EPID) is a highly promising technique for providing soft-tissue visualization in image-guided radiotherapy. However, current EPIDs based on active matrix flat-panel imagers (AMFPIs), which are regarded as the gold standard for portal imaging and referred to as conventional MV AMFPIs, require high radiation doses to achieve this goal due to poor x-ray detection efficiency (~2% at 6 MV). To overcome this limitation, the incorporation of thick, segmented, crystalline scintillators, as a replacement for the phosphor screens used in these AMFPIs, has been shown to significantly improve the detective quantum efficiency (DQE) performance, leading to improved image quality for projection imaging at low dose. Toward the realization of practical AMFPIs capable of low dose, soft-tissue visualization using MV CBCT imaging, two prototype AMFPIs incorporating segmented scintillators with ~11 mm thick CsI:Tl and Bi 4 Ge 3 O 12 (BGO) crystals were evaluated. Each scintillator consists of 120 _ 60 crystalline elements separated by reflective septal walls, with an element-to-element pitch of 1.016 mm. The prototypes were evaluated using a bench-top CBCT system, allowing the acquisition of 180 projection, 360° tomographic scans with a 6 MV radiotherapy photon beam. Reconstructed images of a spatial resolution phantom, as well as of a water-equivalent phantom, embedded with tissue equivalent objects having electron densities (relative to water) varying from ~0.28 to ~1.70, were obtained down to one beam pulse per projection image, corresponding to a scan dose of ~4 cGy–-a dose similar to that required for a single portal image obtained from a conventional MV AMFPI. By virtue of their significantly improved DQE, the prototypes provided low contrast visualization, allowing clear delineation of an object with an electron density difference of ~2.76%. Results of contrast, noise and contrast-to-noise ratio are presented as a function of dose and compared to those from a conventional MV AMFPI.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90773/1/0031-9155_56_6_001.pd
A new path to measure antimatter free fall
We propose an experiment to measure the free fall acceleration of neutral antihydrogen atoms. The originality of this path is to first produce the Hbar+ ion
Finite Automata for the Sub- and Superword Closure of CFLs: Descriptional and Computational Complexity
We answer two open questions by (Gruber, Holzer, Kutrib, 2009) on the
state-complexity of representing sub- or superword closures of context-free
grammars (CFGs): (1) We prove a (tight) upper bound of on
the size of nondeterministic finite automata (NFAs) representing the subword
closure of a CFG of size . (2) We present a family of CFGs for which the
minimal deterministic finite automata representing their subword closure
matches the upper-bound of following from (1).
Furthermore, we prove that the inequivalence problem for NFAs representing sub-
or superword-closed languages is only NP-complete as opposed to PSPACE-complete
for general NFAs. Finally, we extend our results into an approximation method
to attack inequivalence problems for CFGs
Very large Magneto-impedance and its scaling behavior in amorphous Fe73.5Nb3Cu1Si13.5B9 ribbon
Magneto-impedance (MI) effects have been observed for amorphous
Fe73.5Nb3Cu1Si13.5B9 ribbon which has been excited by an a.c. magnetic field
parallel to the length of the ribbon. Maximum relative change in MI as large as
-99% was observed which has never been reported before. The relative change in
MI, when plotted against scaled field was found to be nearly frequency
independent. A phenomenological formula for magneto-impedance, Z(H), in a
ferromagnetic material, is proposed based on Pade approximant to describe the
scaled behavior of MI.Comment: 20 pages, 7 figures, article in press, Physica B (2007
Quiver Theories from D6-branes via Mirror Symmetry
We study N=1 four dimensional quiver theories arising on the worldvolume of
D3-branes at del Pezzo singularities of Calabi-Yau threefolds. We argue that
under local mirror symmetry D3-branes become D6-branes wrapped on a three torus
in the mirror manifold. The type IIB (p,q) 5-brane web description of the local
del Pezzo, being closely related to the geometry of its mirror manifold,
encodes the geometry of 3-cycles and is used to obtain gauge groups, quiver
diagrams and the charges of the fractional branes.Comment: 30 pages, citations adde
Targeted Molecular Iron Oxide Contrast Agents for Imaging Atherosclerotic Plaque.
Overview: Cardiovascular disease remains a leading cause of death worldwide, with vulnerable plaque rupture the underlying cause of many heart attacks and strokes. Much research is focused on identifying an imaging biomarker to differentiate stable and vulnerable plaque. Magnetic Resonance Imaging (MRI) is a non-ionising and non-invasive imaging modality with excellent soft tissue contrast. However, MRI has relatively low sensitivity (micromolar) for contrast agent detection compared to nuclear imaging techniques. There is also an increasing emphasis on developing MRI probes that are not based on gadolinium chelates because of increasing concerns over associated systemic toxicity and deposits1. To address the sensitivity and safety concerns of gadolinium this project focused on the development of a high relaxivity probe based on superparamagnetic iron oxide nanoparticles for the imaging of atherosclerotic plaque with MRI. With development, this may facilitate differentiating stable and vulnerable plaque in vivo. Aim: To develop a range of MRI contrast agents based on superparamagnetic iron oxide nanoparticles (SPIONs), and test them in a murine model of advanced atherosclerosis. Methods: Nanoparticles of four core sizes were synthesised by thermal decomposition and coated with poly(maleicanhydride-alt-1-octadecene) (PMAO), poly(ethyleneimine) (PEI) or alendronate, then characterised for core size, hydrodynamic size, surface potential and relaxivity. On the basis of these results, one candidate was selected for further studies. In vivo studies using 10 nm PMAO-coated SPIONs were performed in ApoE -/- mice fed a western diet and instrumented with a perivascular cuff on the left carotid artery. Control ApoE -/- mice were fed a normal chow diet and were not instrumented. Mice were scanned on a 3T MR scanner (Philips Achieva) with the novel SPION contrast agent, and an elastin-targeted gadolinium agent that was shown previously to enable visualisation of plaque burden. Histological analysis was undertaken to confirm imaging findings through staining for macrophages, CX3CL1, elastin, tropoelastin, and iron. Results: The lead SPION agent consisted of a 10 nm iron oxide core with poly(maleicanhydride-alt-1-octadecene), (-36.21 mV, r2 18.806 mmol-1/s-1). The irregular faceting of the iron oxide core resulted in high relaxivity and the PMAO provided a foundation for further functionalisation on surface -COOH groups. The properties of the contrast agent, including the negative surface charge and hydrodynamic size, were designed to maximise circulation time and evade rapid clearance through the renal system or phagocytosis. In vitro testing showed that the SPION agent was non-toxic. In vivo results show that the novel contrast agent accumulates in similar vascular regions to a gadolinium-based contrast agent (Gd-ESMA) targeted to elastin, which accumulates in plaque. There was a significant difference in SPION signal between the instrumented and the contralateral non-instrumented vessels in diseased mice (p = 0.0411, student's t-test), and between the instrumented diseased vessel and control vessels (p = 0.0043, 0.0022, student's t-test). There was no significant difference between the uptake of either contrast agent between stable and vulnerable plaques (p = 0.3225, student's t-test). Histological verification was used to identify plaques, and Berlin Blue staining confirmed the presence of nanoparticle deposits within vulnerable plaques and co-localisation with macrophages. Conclusion: This work presents a new MRI contrast agent for atherosclerosis which uses an under-explored surface ligand, demonstrating promising properties for in vivo behaviour, is still in circulation 24 hours post-injection with limited liver uptake, and shows good accumulation in a murine plaque model
Evidence of a high incidence of subclinically affected calves in a herd of cattle with fatal cases of Bovine Neonatal Pancytopenia (BNP).
BACKGROUND: Bovine Neonatal Pancytopenia (BNP) is a disease of calves characterised by bone marrow trilineage hypoplasia, mediated by ingestion of alloantibodies in colostrum. Suspected subclinical forms of BNP have been reported, suggesting that observed clinical cases may not represent the full extent of the disease. However to date there are no objective data available on the incidence of subclinical disease or its temporal distribution. This study aimed to 1) ascertain whether subclinical BNP occurs and, if so, to determine the incidence on an affected farm and 2) determine whether there is evidence of temporal clustering of BNP cases on this farm. To achieve these aims, haematological screening of calves born on the farm during one calving season was carried out, utilising blood samples collected at defined ages. These data were then analysed in comparison to data from both known BNP-free control animals and histopathologically confirmed BNP cases. An ordinal logistic regression model was used to create a composite haematology score to predict the probabilities of calves being normal, based on their haematology measurements at 10–14 days old. RESULTS: This study revealed that 15% (21 of 139) of the clinically normal calves on this farm had profoundly abnormal haematology (<5% chance of being normal) and could be defined as affected by subclinical BNP. Together with clinical BNP cases, this gave the study farm a BNP incidence of 18%. Calves with BNP were found to be distributed throughout the calving period, with no clustering, and no significant differences in the date of birth of cases or subclinical cases were found compared to the rest of the calves. This study did not find any evidence of increased mortality or increased time from birth to sale in subclinical BNP calves but, as the study only involved a single farm and adverse effects may be determined by other inter-current diseases it remains possible that subclinical BNP has a detrimental impact on the health and productivity of calves under certain circumstances. CONCLUSIONS: Subclinical BNP was found to occur at a high incidence in a herd of cattle with fatal cases of BNP
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