1,441 research outputs found
Erosion and cultivation effects on the loss of organic matter from prairie soils
Non-Peer Reviewe
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
Emotional and non-emotional memories are suppressible under direct suppression instructions
Research on retrieval suppression has produced varying results concerning whether negatively valenced memories are more or less suppressible than neutral memories. This variability may arise if, across studies, participants adopt different approaches to memory control. Cognitive and neurobiological research points to two mechanisms that achieve retrieval suppression: thought-substitution and direct suppression (Benoit & Anderson, 2012; Bergström, de Fockert, & Richardson-Klavehn, 2009). Using the Think/No-think paradigm, this study examined whether participants can inhibit neutral and negatively valenced memories, using a uniform direct suppression strategy. Importantly, when strategy was controlled, negative and neutral items were comparably inhibited. Participants reported high compliance with direct suppression instructions, and success at controlling awareness predicted forgetting. These findings provide the first evidence that direct suppression can impair negatively valenced events, and suggest that variability in forgetting negative memories in prior studies is unlikely to arise from difficulty using direct suppression to control emotionally negative experiences
Energies and collapse times of symmetric and symmetry-breaking states of finite systems with a U(1) symmetry
We study quantum systems of volume V, which will exhibit the breaking of a
U(1) symmetry in the limit of V \to \infty, when V is large but finite. We
estimate the energy difference between the `symmetric ground state' (SGS),
which is the lowest-energy state that does not breaks the symmetry, and a `pure
phase vacuum' (PPV), which approaches a symmetry-breaking vacuum as V \to
\infty. Under some natural postulates on the energy of the SGS, it is shown
that PPVs always have a higher energy than the SGS, and we derive a lower bound
of the excess energy. We argue that the lower bound is O(V^0), which becomes
much larger than the excitation energies of low-lying excited states for a
large V. We also discuss the collapse time of PPVs for interacting many bosons.
It is shown that the wave function collapses in a microscopic time scale,
because PPVs are not energy eigenstates. We show, however, that for PPVs the
expectation value of any observable, which is a finite polynomial of boson
operators and their derivatives, does not collapse for a macroscopic time
scale. In this sense, the collapse time of PPVs is macroscopically long.Comment: In the revised manuscript, Eq. (22), Ref. [8], and Notes [13], [15]
and [17] have been adde
Noise Can Reduce Disorder in Chaotic Dynamics
We evoke the idea of representation of the chaotic attractor by the set of
unstable periodic orbits and disclose a novel noise-induced ordering
phenomenon. For long unstable periodic orbits forming the strange attractor the
weights (or natural measure) is generally highly inhomogeneous over the set,
either diminishing or enhancing the contribution of these orbits into system
dynamics. We show analytically and numerically a weak noise to reduce this
inhomogeneity and, additionally to obvious perturbing impact, make a
regularizing influence on the chaotic dynamics. This universal effect is rooted
into the nature of deterministic chaos.Comment: 11 pages, 5 figure
Dark Energy and Extending the Geodesic Equations of Motion: Its Construction and Experimental Constraints
With the discovery of Dark Energy, , there is now a universal
length scale, , associated with the
universe that allows for an extension of the geodesic equations of motion. In
this paper, we will study a specific class of such extensions, and show that
contrary to expectations, they are not automatically ruled out by either
theoretical considerations or experimental constraints. In particular, we show
that while these extensions affect the motion of massive particles, the motion
of massless particles are not changed; such phenomena as gravitational lensing
remain unchanged. We also show that these extensions do not violate the
equivalence principal, and that because Mpc, a
specific choice of this extension can be made so that effects of this extension
are not be measurable either from terrestrial experiments, or through
observations of the motion of solar system bodies. A lower bound for the only
parameter used in this extension is set.Comment: 19 pages. This is the published version of the first half of
arXiv:0711.3124v2 with corrections include
Anisotropic optical properties of single-crystal GdBa2Cu3O7-delta
The optical spectrum of reduced-T(c) GdBa2Cu3O7-delta has been measured for polarizations parallel and perpendicular to the ab plane. The sample was an oxygen-deficient single crystal with a large face containing the c axis. The polarized reflectance from this face was measured from 20-300 K in the spectral region from 30-3000 cm-1, with 300 K data to 30 000 cm-1. Kramers-Kronig analysis was used to determine the spectral dependence of the ab and the c components of the dielectric tensor. The optical properties are strongly anisotropic. The ab-plane response resembles that of other reduced-T(c) materials whereas the c axis, in contrast, shows only the presence of several phonons. There is a complete absence of charge carrier response along c above and below T(c). This observation allows us to set an upper limit to the free-carrier spectral weight for transport perpendicular to the CuO2 planes
Wear of human teeth: a tribological perspective
The four main types of wear in teeth are attrition (enamel-on-enamel contact), abrasion (wear due to abrasive particles in food or toothpaste), abfraction (cracking in enamel and subsequent material loss), and erosion (chemical decomposition of the tooth). They occur as a result of a number of mechanisms including thegosis (sliding of teeth into their lateral position), bruxism (tooth grinding), mastication (chewing), toothbrushing, tooth flexure, and chemical effects. In this paper the current understanding of wear of enamel and dentine in teeth is reviewed in terms of these mechanisms and the major influencing factors are examined. In vitro tooth wear simulation and in vivo wear measurement and ranking are also discussed
Lectures on Chiral Disorder in QCD
I explain the concept that light quarks diffuse in the QCD vacuum following
the spontaneous breakdown of chiral symmetry. I exploit the striking analogy to
disordered electrons in metals, identifying, among others, the universal regime
described by random matrix theory, diffusive regime described by chiral
perturbation theory and the crossover between these two domains.Comment: Lectures given at the Cargese Summer School, August 6-18, 200
Elasticity-driven interaction between vortices in type-II superconductors
The contribution to the vortex lattice energy which is due to the
vortex-induced strains is calculated covering all the magnetic field range
which defines the vortex state. This contribution is compared with previously
reported ones what shows that, in the most part of the vortex state, it has
been notably underestimated until now. The reason of such underestimation is
the assumption that only the vortex cores induce strains. In contrast to what
is generally assumed, both core and non-core regions are important sources of
strains in high- superconductors.Comment: 10 pages, 1 figure, revtex
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