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Rapid Steel Tooling Via Solid Freeform Fabrication
With increasing part complexity and requirements for long production runs, tooling has
become an expensive process that requires long lead times to manufacture. This lengthens the
amount oftime from "art to part". Rapid tooling via stereolithography (SLA), filled epoxies, etc.
have been stopgap measures to produce limited prototyping runs from (10 to 500 parts). This
gives poor dimensional analysis and does not allow for limited production runs of 1000+ parts.
The method ofproducing prototype tooling with a powdered metal process has been developed
that produces tooling with a hardness greater than 35 HRC and total shrinkage less than 0.5%.
This tooling process manufactures production ready tooling that will perform extended cycle
runs (100,000+). Manufacturing ofthis tooling takes 1 to 2 weeks and will compare favorably
with production grade steel tooling. Originals drawn in 3D CAD can be used to prototype the
master that will allow for the production ofthe rapid metal tool set.
process starts with a rapid prototyped model made by whatever process is desired or
a machined master. For this paper a Sander's Model Maker II® rapid prototyping machine was
used to fabricate the model. After the model ofthe tool set is made, a silicone rubber negative is
cast around that model. After the silicone rubber model is made, a heated slurry ofmetal
powders and polymers is poured into the mold to create the green tool set. The tool set is left to
cool, and then removed from the silicone rubber mold. The tool set is then debound and sintered
to produce a final tool set with properties approaching hardened tool steel.Mechanical Engineerin
Deciphering the Seesaw Nature of Neutrino Mass from Unitarity Violation
If neutrino masses are obtained via the canonical seesaw mechanism, based on
an underlying 2X2 mass matrix, unitarity violation of the neutrino mixing
matrix is unavoidable, but its effect is extremely small. On the other hand, in
the inverse (and linear) seesaw mechanisms, based on an underlying 3X3 mass
matrix, it can be significant and possibly observable. This 3X3 matrix is
examined in more detail, and a NEW variation (the lopsided seesaw) is proposed
which has features of both mechanisms. A concrete example based on U(1)_N is
discussed.Comment: 7 pages, no figure, linear and lopsided seesaws discusse
Heavy Quarks Above the Top at the Tevatron
Recent developments in models with warped extra dimensions have opened new
possibilities for vector-like quark studies at hadron colliders. These new
vector-like quarks can mix sizably with light Standard Model quarks without
violating low energy constraints. We perform a model-independent analysis to
determine the Tevatron reach in the search for new quarks. We find that the
Tevatron has great potential to observe such quarks via their electroweak
single production due to their mixing with valence quarks. With 4 (8) fb-1
integrated luminosity, one may reach a 5\sigma statistical significance for a
heavy quark of mass 580 (630) GeV if the heavy quark-Standard Model quark
mixing parameter is order one.Comment: Version published in Phys. Rev. D; 19 pages, 4 figures; extended
version including model building example; added Table
Upper Bounds on Lepton-number Violating Processes
We consider four lepton-number violating (\lv) processes: (a) neutrinoless
double-beta decay (0\nu\beta\beta), (b) Delta L = 2 tau decays, (c) Delta L = 2
rare meson decays and (d) nuclear muon-positron conversion. In the absence of
exotic \lv interactions, the rates for these processes are determined by
effective neutrino masses _{\ell_1\ell_2}, which can be related to the sum
of light neutrino masses, the neutrino mass-squared differences, the neutrino
mixing angles, a Dirac phase and two Majorana phases. We sample the
experimentally allowed ranges of _{\ell_1\ell_2} based on neutrino
oscillation experiments as well as cosmological observations, and obtain a
stringent upper bound _{\ell_1\ell_2} \lsim 0.14 eV. We then calculate the
allowed ranges for _{\ell_1\ell_2} from the experimental rates of direct
searches for the above Delta L = 2 processes. Comparing our calculated rates
with the currently or soon available data, we find that only the
experiment may be able to probe _{ee} with a sensitivity
comparable to the current bound. Muon-positron conversion is next in
sensitivity, while the limits of direct searches for the other Delta L = 2
processes are several orders of magnitude weaker than the current bounds on
_{\ell_1\ell_2}. Any positive signal in those direct searches would indicate
new contributions to the \lv interactions beyond those from three light
Majorana neutrinos.Comment: 20 pages, revtex4, 2 figures (5 files), Version published in Physical
Review
Parametrically controlling solitary wave dynamics in modified Kortweg-de Vries equation
We demonstrate the control of solitary wave dynamics of modified Kortweg-de
Vries (MKdV) equation through the temporal variations of the distributed
coefficients. This is explicated through exact cnoidal wave and localized
soliton solutions of the MKdV equation with variable coefficients. The solitons
can be accelerated and their propagation can be manipulated by suitable
variations of the above parameters. In sharp contrast with nonlinear
Schr\"{o}dinger equation, the soliton amplitude and widths are time
independent.Comment: 4 pages, 5 eps figure
MeV sterile neutrinos in low reheating temperature cosmological scenarios
It is commonly assumed that the cosmological and astrophysical bounds on the
mixings of sterile with active neutrinos are much more stringent than those
obtained from laboratory measurements. We point out that in scenarios with a
very low reheating temperature T_RH << 100 MeV at the end of (the last episode
of) inflation or entropy creation, the abundance of sterile neutrinos becomes
largely suppressed with respect to that obtained within the standard framework.
Thus, in this case cosmological bounds become much less stringent than usually
assumed, allowing sterile neutrinos to be ``visible'' in future experiments.
Here, we concentrate on massive (mostly sterile) neutrinos heavier than 1 MeV.Comment: 14 pp, 7 fig
Controlling pulse propagation in optical fibers through nonlinearity and dispersion management
In case of the nonlinear Schr\"odinger equation with designed group velocity
dispersion, variable nonlinearity and gain/loss; we analytically demonstrate
the phenomenon of chirp reversal crucial for pulse reproduction. Two different
scenarios are exhibited, where the pulses experience identical dispersion
profiles, but show entirely different propagation behavior. Exact expressions
for dynamical quasi-solitons and soliton bound-states relevant for fiber
communication are also exhibited.Comment: 4 pages, 5 eps figure
A clean signal for a top-like isosinglet fermion at the Large Hadron Collider
We predict a clean signal at the Large Hadron Collider (=14 TeV for
a scenario where there is a top-like, charge +2/3 vectorlike isosinglet
fermion. Such a quark, via mixing with the standard model top, can undergo
decays via both flavour-changing Z-boson coupling and flavour-changing Yukawa
interactions. We concentrate on the latter channel, and study the situation
where, following its pair-production, the heavy quark pair gives rise to two
tops and two Higgs boson. We show that the case where each Higgs decays in the
channel, there can be a rather distinct and background-free signal
that can unveil the existence of the vectorlike isosinglet quark of this kind.Comment: 14 pages, 5 figures, 4 table
Prospects for top-prime quark discovery at the Tevatron
We show that a top-prime quark as heavy as 600 GeV can be discovered at the
Tevatron, provided it is resonantly pair-produced via a vector color octet. If
the top-prime originates from a vectorlike quark, then the production of a
single top-prime in association with a top may also be observable, even through
its decay into a Higgs boson and a top. A color octet with mass of about 1 TeV,
which decays into a top-prime pair, may account for the CDF excess of
semileptonic (Wj)(Wj) events.Comment: 22 pages, 6 ps figures. v2: Note added about the new D0 search for
(Wb)(Wb) resonances; section 4.1 expanded; single-top constraint updated in
section 2; references adde
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