201 research outputs found
Electroweak Strings: A Progress Report
I describe the string solutions in the standard electroweak model and argue
that they may be stabilized by quark, lepton or other bound states. I then
reinterpret the sphaleron in terms of electroweak strings and show that it can
be viewed as a loop of W-string or a segment of Z-string. (Talk presented at
Texas/Pascos 1992 at Berkeley.)Comment: 7 pages, TUTP-92-12. (One figure - available on request.
Answering some questions about structured illumination microscopy.
Structured illumination microscopy (SIM) provides images of fluorescent objects at an enhanced resolution greater than that of conventional epifluorescence wide-field microscopy. Initially demonstrated in 1999 to enhance the lateral resolution twofold, it has since been extended to enhance axial resolution twofold (2008), applied to live-cell imaging (2009) and combined with myriad other techniques, including interferometric detection (2008), confocal microscopy (2010) and light sheet illumination (2012). Despite these impressive developments, SIM remains, perhaps, the most poorly understood 'super-resolution' method. In this article, we provide answers to the 13 questions regarding SIM proposed by Prakash et al. along with answers to a further three questions. After providing a general overview of the technique and its developments, we explain why SIM as normally used is still diffraction-limited. We then highlight the necessity for a non-polynomial, and not just nonlinear, response to the illuminating light in order to make SIM a true, diffraction-unlimited, super-resolution technique. In addition, we present a derivation of a real-space SIM reconstruction approach that can be used to process conventional SIM and image scanning microscopy (ISM) data and extended to process data with quasi-arbitrary illumination patterns. Finally, we provide a simple bibliometric analysis of SIM development over the past two decades and provide a short outlook on potential future work. This article is part of the Theo Murphy meeting issue 'Super-resolution structured illumination microscopy (part 2)'
Zero Modes on Linked Strings
We study linked loops of string in the presence of bosonic condensates and
fermionic zero modes on the strings. We find that the strings necessarily carry
a current if the bosons have an Aharanov-Bohm interaction with the string. The
fermionic case is analyzed in the context of the standard model where there are
lepton and quark zero modes on strings. Here we find that the fermionic
ground state in the linked string background is lower than the ground state
when the loops are unlinked but otherwise identical. As in the bosonic case,
the strings carry a non-vanishing electric current in the ground state. The
baryon number of the linked configuration is found to agree with previous
indirect results. We also evaluate the angular momentum, electromagnetic charge
and baryonic three current on the linked string configuration. Finally we
point out a possible gravitational analogue of the linked string system.Comment: LaTeX, 27 text pages + 2 figures, Fig. 1 file fixe
Multisphalerons in the Weinberg-Salam Theory
We construct multisphaleron solutions in the Weinberg-Salam theory. The
multisphaleron solutions carry Chern-Simons charge , where is an
integer, counting the winding of the fields in the azimuthal angle. The
well-known sphaleron has . The multisphalerons possess axial symmetry and
parity reflection symmetry. We vary the Higgs mass and the mixing angle. For
small the energies of the multisphalerons are on the order of times the
energy of the sphaleron and their magnetic dipole moments are on the order of
times the magnetic dipole moment of the sphaleron.Comment: 18 pages, latex, 17 figures in uuencoded postscript files. THU-94/1
Vortex Solutions in Two-Higgs-Doublet Systems
We analyze the existence of string-like defects in a two-Higgs-doublet system
having as gauge group. We are
able to show that, when certain relations among the parameters hold, these
configurations satisfy a set of first order differential equations (Bogomol'nyi
equations) and their energy is proportional to their topological charge.}Comment: 9 page
NBLAST: Rapid, Sensitive Comparison of Neuronal Structure and Construction of Neuron Family Databases.
Neural circuit mapping is generating datasets of tens of thousands of labeled neurons. New computational tools are needed to search and organize these data. We present NBLAST, a sensitive and rapid algorithm, for measuring pairwise neuronal similarity. NBLAST considers both position and local geometry, decomposing neurons into short segments; matched segments are scored using a probabilistic scoring matrix defined by statistics of matches and non-matches. We validated NBLAST on a published dataset of 16,129 single Drosophila neurons. NBLAST can distinguish neuronal types down to the finest level (single identified neurons) without a priori information. Cluster analysis of extensively studied neuronal classes identified new types and unreported topographical features. Fully automated clustering organized the validation dataset into 1,052 clusters, many of which map onto previously described neuronal types. NBLAST supports additional query types, including searching neurons against transgene expression patterns. Finally, we show that NBLAST is effective with data from other invertebrates and zebrafish. VIDEO ABSTRACT.This work was supported by the Medical Research Council [MRC file reference U105188491] and European Research Council Starting and Consolidator Grants to G.S.X.E.J., who is an EMBO Young Investigator.This is the final version of the article. It first appeared from Cell Press via http://dx.doi.org/10.1016/j.neuron.2016.06.01
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ELM: super-resolution analysis of wide-field images of fluorescent shell structures.
It is often necessary to precisely quantify the size of specimens in biological studies. When measuring feature size in fluorescence microscopy, significant biases can arise due to blurring of its edges if the feature is smaller than the diffraction limit of resolution. This problem is avoided if an equation describing the feature's entire image is fitted to its image data. In this paper we present open-source software, ELM, which uses this approach to measure the size of spheroidal or cylindrical fluorescent shells with a precision of around 10 nm. This has been used to measure coat protein locations in bacterial spores and cell wall diameter in vegetative bacilli, and may also be valuable in microbiological studies of algae, fungi and viruses. ELM is available for download at https://github.com/quantitativeimaging/ELM
Bound States Can Stabilize Electroweak Strings
We show that the electroweak string can be stabilized by the presence of
bound states of a complex scalar field. We argue that fermions coupled to the
scalar field of the string can also make the string stable and discuss the
physical case where the string is coupled to quarks and leptons. This
stabilization mechanism is expected to work for other embedded defects and also
for unstable solutions such as the sphaleron.Comment: 11 pages (1 figure available on request), Tufts preprint# TU-92-1
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