13,762 research outputs found
Gun facilitates adhesive bonding of studs to surfaces
Gun facilitates adhesive bonding of thermoplastic-backed studs to smooth, hard surfaces. Such studs can be used for mounting loads where defacement with drilled holes cannot be tolerated. These studs can be easily removed by softening the plastic bonding with heat from the gun
Computer programs for shielding problems in manned space vehicles
Computer programs for shielding problems in manned space vehicles - proton penetration code
Vacuum-UV negative photoion spectroscopy of CF3Cl, CF3Br and CF3I
Using synchrotron radiation negative ions have been detected by mass spectrometry following vacuum-UV photoexcitation of trifluorochloromethane (CFCl), trifluorobromomethane (CFBr) and trifluoroiodomethane (CFI). The anions F, X, F, FX, CF, CF and CF were observed from all three molecules, where X = Cl, Br or I, and their ion yields recorded in the range 8-35 eV. With the exception of Br and I, the anions observed show a linear dependence of signal with pressure, showing that they arise from unimolecular ion-pair dissociation. Dissociative electron attachment, following photoionization of CFBr and CFI as the source of low-energy electrons, is shown to dominate the observed Br and I signals, respectively. Cross sections for ion-pair formation are put on to an absolute scale by calibrating the signal strengths with those of F from both SF and CF. These anion cross sections are normalized to vacuum-UV absorption cross sections, where available, and the resulting quantum yields are reported. Anion appearance energies are used to calculate upper limits to 298 K bond dissociation energies for (CF-X) which are consistent with literature values. We report new data for (CFI-F) ≤ 2.7 ± 0.2 eV and (CFI) ≤ (598 ± 22) kJ mol. No ion-pair formation is observed below the ionization energy of the parent molecule for CFCl and CFBr, and only weak signals (in both I and F) are detected for CFI. These observations suggest neutral photodissociation is the dominant exit channel to Rydberg state photoexcitation at these lower energies
Constraints on radiative decay of the 17-keV neutrino from COBE Measurements
It is shown that, for a nontrivial radiative decay channel of the 17-keV
neutrino, the photons would distort the microwave background radiation through
ionization of the universe. The constraint on the branching ratio of such
decays from COBE measurements is found to be more stringent than that from
other considerations. The limit on the branching ratio in terms of the Compton
parameter is for an
universe.Comment: 7 pages. (figures will be sent on request) (To appear in Phys. Rev.
D.
Spectral networks
We introduce new geometric objects called spectral networks. Spectral
networks are networks of trajectories on Riemann surfaces obeying certain local
rules. Spectral networks arise naturally in four-dimensional N=2 theories
coupled to surface defects, particularly the theories of class S. In these
theories spectral networks provide a useful tool for the computation of BPS
degeneracies: the network directly determines the degeneracies of solitons
living on the surface defect, which in turn determine the degeneracies for
particles living in the 4d bulk. Spectral networks also lead to a new map
between flat GL(K,C) connections on a two-dimensional surface C and flat
abelian connections on an appropriate branched cover Sigma of C. This
construction produces natural coordinate systems on moduli spaces of flat
GL(K,C) connections on C, which we conjecture are cluster coordinate systems.Comment: 87 pages, 48 figures; v2: typos, correction to general rule for signs
of BPS count
Simultaneous Border-Collision and Period-Doubling Bifurcations
We unfold the codimension-two simultaneous occurrence of a border-collision
bifurcation and a period-doubling bifurcation for a general piecewise-smooth,
continuous map. We find that, with sufficient non-degeneracy conditions, a
locus of period-doubling bifurcations emanates non-tangentially from a locus of
border-collision bifurcations. The corresponding period-doubled solution
undergoes a border-collision bifurcation along a curve emanating from the
codimension-two point and tangent to the period-doubling locus here. In the
case that the map is one-dimensional local dynamics are completely classified;
in particular, we give conditions that ensure chaos.Comment: 22 pages; 5 figure
Livestock Producers and Researchers - A Case Study of an Effective Partnership
The Sustainable Grazing Systems Programme (SGS) ran from 1996-2002 with 11 regional producer committees (Regional Producer Network - Simpson et al., 2003) and 6 research sites (National Experiment Andrew & Lodge, 2003) distributed throughout the high rainfall zone of temperate Australia. Each regional committee had a core of producers, with invited scientists and extension practitioners and a paid facilitator. The chair was always a producer and rotated annually. Each regional committee conducted a number of paddock-sized demonstrations of improved grazing management practices on a number of farms within the themes; grazing management and weeds, high input systems, innovative grazing methods for production and the SGS adoption process. Each demonstration was on a producer\u27s property assisted by a local management committee with objective data collected by the regional facilitator. The National research sites investigated the effects of grazing management on sustainable livestock production through five themes; water, nutrients, pastures, animals and biodiversity. Producers had a significant input into the design of the National Experiment and each site had a local advisory committee
Multi-level Optical Switching by Amorphization in Single- and Multi- Phase Change Material Structures
The optical properties of phase-change materials (PCM) can be tuned to
multiple levels by controlling the transition between their amorphous and
crystalline phases. In multi-material PCM structures, the number of discrete
reflectance levels can be increased according to the number of PCM layers.
However, the effect of increasing number of layers on quenching and
reversibility has not been thoroughly studied. In this work, the phase-change
physics and thermal conditions required for reversible switching of single and
multi-material PCM switches are discussed based on thermo-optical phase-change
models and laser switching experiments. By using nanosecond laser pulses, 16
different reflectance levels in Ge2Sb2Te5 are demonstrated via amorphization.
Furthermore, a multi-material switch based on Ge2Sb2Te5 and GeTe with four
discrete reflectance levels is experimentally proven with a reversible
multi-level response. The results and design principles presented herein will
impact active photonics applications that rely on dynamic multi-level
operation, such as optical computing, beam steering, and next-generation
display technologies.Comment: 25 pages, 8 figure
Multi-Level Optical Switching by Amorphization in Single- and Multi-Phase Change Material Structures
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