1,115 research outputs found
Upstream Volatility in the Supply Chain: The Machine Tool Industry as a Case Study
Working Draft, May 1995Cyclicality is a well known and accepted fact of life in market-driven
economies. Less well known or understood, however, is the phenomenon of
amplification as one looks "upstream" in the industrial supply chain. This
paper discusses and explains the amplification phenomenon and its
implications through the lens of one "upstream" industry that is notorious
for the intensity of the business cycles it faces: the machine tool industry.
Using a sparse simulation model, we have replicated much of the behavior
seen in the industrial world in which machine tool companies operate. This
model has allowed us to test and confirm many of our hypotheses. Two
results stand out. Even though machine tool builders can do little to reduce
their production volatility through choice of forecast rule, a longer view of
the future leads companies to retain more of their skilled workforce. This is
often cited as one of the advantages that European and Japanese companies
have enjoyed: lower skilled employee turnover. The second, and most
important result is that machine tool customers can do a great deal to reduce
the volatility for machine tool builders through their choice of order forecast
rule. Companies which use a longer horizon over which to forecast orders
tend to impose less of their own volatility upon their supply base.MIT -- Leaders for Manufacturing, the
International Motor Vehicle Program, the Industrial Performance Center, the International
Center for Research on the Management of Technology, and the Japan Program; Chrysler, Intel, Sematech, and Texas Instruments
A Model for the Schottky Anomaly in Metallic
We present a simple model for the doped compound , in
order to explain some recent experimental results on the latter. Within a
Hartree-Fock context, we start from an impurity Anderson-like model and
consider the magnetic splitting of the - ground state Kramers doublet
due to exchange interactions with the ordered moments. Our results are in
very good agreement with the experimental data, yielding a Schottky anomaly
peak for the specific heat that reduces its amplitude, broadens and shifts to
lower temperatures, upon doping. For overdoped compounds at low
temperatures, the specific heat behaves linearly and the magnetic
susceptibility is constant. A smooth transition from this Fermi liquid like
behavior ocurrs as temperature is increased and at high temperatures the
susceptibility exhibits a Curie-like behavior. Finally, we discuss some
improvements our model is amenable to incorporate.Comment: 7 pages, 5 figures, and 13 reference
The fine-tuning cost of the likelihood in SUSY models
In SUSY models, the fine tuning of the electroweak (EW) scale with respect to
their parameters gamma_i={m_0, m_{1/2}, mu_0, A_0, B_0,...} and the maximal
likelihood L to fit the experimental data are usually regarded as two different
problems. We show that, if one regards the EW minimum conditions as constraints
that fix the EW scale, this commonly held view is not correct and that the
likelihood contains all the information about fine-tuning. In this case we show
that the corrected likelihood is equal to the ratio L/Delta of the usual
likelihood L and the traditional fine tuning measure Delta of the EW scale. A
similar result is obtained for the integrated likelihood over the set
{gamma_i}, that can be written as a surface integral of the ratio L/Delta, with
the surface in gamma_i space determined by the EW minimum constraints. As a
result, a large likelihood actually demands a large ratio L/Delta or
equivalently, a small chi^2_{new}=chi^2_{old}+2*ln(Delta). This shows the
fine-tuning cost to the likelihood (chi^2_{new}) of the EW scale stability
enforced by SUSY, that is ignored in data fits. A good
chi^2_{new}/d.o.f.\approx 1 thus demands SUSY models have a fine tuning amount
Delta<<exp(d.o.f./2), which provides a model-independent criterion for
acceptable fine-tuning. If this criterion is not met, one can thus rule out
SUSY models without a further chi^2/d.o.f. analysis. Numerical methods to fit
the data can easily be adapted to account for this effect.Comment: 10 pages (v3: small comment added
Ferromagnetic phase transition and Bose-Einstein condensation in spinor Bose gases
Phase transitions in spinor Bose gases with ferromagnetic (FM) couplings are
studied via mean-field theory. We show that an infinitesimal value of the
coupling can induce a FM phase transition at a finite temperature always above
the critical temperature of Bose-Einstein condensation. This contrasts sharply
with the case of Fermi gases, in which the Stoner coupling can not lead
to a FM phase transition unless it is larger than a threshold value . The
FM coupling also increases the critical temperatures of both the ferromagnetic
transition and the Bose-Einstein condensation.Comment: 4 pages, 4 figure
The Hubbard model with smooth boundary conditions
We apply recently developed smooth boundary conditions to the quantum Monte
Carlo simulation of the two-dimensional Hubbard model. At half-filling, where
there is no sign problem, we show that the thermodynamic limit is reached more
rapidly with smooth rather than with periodic or open boundary conditions. Away
from half-filling, where ordinarily the simulation cannot be carried out at low
temperatures due to the existence of the sign problem, we show that smooth
boundary conditions allow us to reach significantly lower temperatures. We
examine pairing correlation functions away from half-filling in order to
determine the possible existence of a superconducting state. On a
lattice for , at a filling of and an inverse
temperature of , we did find enhancement of the -wave correlations
with respect to the non-interacting case, a possible sign of -wave
superconductivity.Comment: 16 pages RevTeX, 9 postscript figures included (Figure 1 will be
faxed on request
Stakeholder narratives on trypanosomiasis, their effect on policy and the scope for One Health
Background
This paper explores the framings of trypanosomiasis, a widespread and potentially fatal zoonotic disease transmitted by tsetse flies (Glossina species) affecting both humans and livestock. This is a country case study focusing on the political economy of knowledge in Zambia. It is a pertinent time to examine this issue as human population growth and other factors have led to migration into tsetse-inhabited areas with little historical influence from livestock. Disease transmission in new human-wildlife interfaces such as these is a greater risk, and opinions on the best way to manage this are deeply divided.
Methods
A qualitative case study method was used to examine the narratives on trypanosomiasis in the Zambian policy context through a series of key informant interviews. Interviewees included key actors from international organisations, research organisations and local activists from a variety of perspectives acknowledging the need to explore the relationships between the human, animal and environmental sectors.
Principal Findings
Diverse framings are held by key actors looking from, variously, the perspectives of wildlife and environmental protection, agricultural development, poverty alleviation, and veterinary and public health. From these viewpoints, four narratives about trypanosomiasis policy were identified, focused around four different beliefs: that trypanosomiasis is protecting the environment, is causing poverty, is not a major problem, and finally, that it is a Zambian rather than international issue to contend with. Within these narratives there are also conflicting views on the best control methods to use and different reasoning behind the pathways of response. These are based on apparently incompatible priorities of people, land, animals, the economy and the environment. The extent to which a One Health approach has been embraced and the potential usefulness of this as a way of reconciling the aims of these framings and narratives is considered throughout the paper.
Conclusions/Significance
While there has historically been a lack of One Health working in this context, the complex, interacting factors that impact the disease show the need for cross-sector, interdisciplinary decision making to stop rival narratives leading to competing actions. Additional recommendations include implementing: surveillance to assess under-reporting of disease and consequential under-estimation of disease risk; evidence-based decision making; increased and structurally managed funding across countries; and focus on interactions between disease drivers, disease incidence at the community level, and poverty and equity impacts
Critical Behavior of the Supersolid transition in Bose-Hubbard Models
We study the phase transitions of interacting bosons at zero temperature
between superfluid (SF) and supersolid (SS) states. The latter are
characterized by simultaneous off-diagonal long-range order and broken
translational symmetry. The critical phenomena is described by a
long-wavelength effective action, derived on symmetry grounds and verified by
explicit calculation. We consider two types of supersolid ordering:
checkerboard (X) and collinear (C), which are the simplest cases arising in two
dimensions on a square lattice. We find that the SF--CSS transition is in the
three-dimensional XY universality class. The SF--XSS transition exhibits
non-trivial new critical behavior, and appears, within a
expansion to be driven generically first order by fluctuations. However, within
a one--loop calculation directly in a strong coupling fixed point with
striking ``non-Bose liquid'' behavior is found. At special isolated
multi-critical points of particle-hole symmetry, the system falls into the 3d
Ising universality class.Comment: RevTeX, 24 pages, 16 figures. Also available at
http://www.cip.physik.tu-muenchen.de/tumphy/d/T34/Mitarbeiter/frey.htm
(d,n) Reaction Studies at 80 MeV
This research was sponsored by the National Science Foundation Grant NSF PHy 87-1440
Classification of a supersolid: Trial wavefunctions, Symmetry breakings and Excitation spectra
A state of matter is characterized by its symmetry breaking and elementary
excitations.
A supersolid is a state which breaks both translational symmetry and internal
symmetry.
Here, we review some past and recent works in phenomenological
Ginsburg-Landau theories, ground state trial wavefunctions and microscopic
numerical calculations. We also write down a new effective supersolid
Hamiltonian on a lattice.
The eigenstates of the Hamiltonian contains both the ground state
wavefunction and all the excited states (supersolidon) wavefunctions. We
contrast various kinds of supersolids in both continuous systems and on
lattices, both condensed matter and cold atom systems. We provide additional
new insights in studying their order parameters, symmetry breaking patterns,
the excitation spectra and detection methods.Comment: REVTEX4, 19 pages, 3 figure
Application of Time Transfer Function to McVittie Spacetime: Gravitational Time Delay and Secular Increase in Astronomical Unit
We attempt to calculate the gravitational time delay in a time-dependent
gravitational field, especially in McVittie spacetime, which can be considered
as the spacetime around a gravitating body such as the Sun, embedded in the
FLRW (Friedmann-Lema\^itre-Robertson-Walker) cosmological background metric. To
this end, we adopt the time transfer function method proposed by Le
Poncin-Lafitte {\it et al.} (Class. Quant. Grav. 21:4463, 2004) and Teyssandier
and Le Poncin-Lafitte (Class. Quant. Grav. 25:145020, 2008), which is
originally related to Synge's world function and enables to
circumvent the integration of the null geodesic equation. We re-examine the
global cosmological effect on light propagation in the solar system. The
round-trip time of a light ray/signal is given by the functions of not only the
spacial coordinates but also the emission time or reception time of light
ray/signal, which characterize the time-dependency of solutions. We also apply
the obtained results to the secular increase in the astronomical unit, reported
by Krasinsky and Brumberg (Celest. Mech. Dyn. Astron. 90:267, 2004), and we
show that the leading order terms of the time-dependent component due to
cosmological expansion is 9 orders of magnitude smaller than the observed value
of , i.e., ~[m/century]. Therefore, it is not possible
to explain the secular increase in the astronomical unit in terms of
cosmological expansion.Comment: 13 pages, 2 figures, accepted for publication in General Relativity
and Gravitatio
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