79,980 research outputs found
Lubrication handbook
Information on lubricants from government reports, military specifications, qualified parts lists, and suppliers of commercial lubricants has been consolidated in one source. Handbook includes data on chemical and physical properties of solid, bonded solid, and liquid lubricants; dispersions and composites; and greases, oils, and hydraulic fluids
Nonlinear softening as a predictive precursor to climate tipping
Approaching a dangerous bifurcation, from which a dynamical system such as
the Earth's climate will jump (tip) to a different state, the current stable
state lies within a shrinking basin of attraction. Persistence of the state
becomes increasingly precarious in the presence of noisy disturbances. We
consider an underlying potential, as defined theoretically for a saddle-node
fold and (via averaging) for a Hopf bifurcation. Close to a stable state, this
potential has a parabolic form; but approaching a jump it becomes increasingly
dominated by softening nonlinearities. If we have already detected a decrease
in the linear decay rate, nonlinear information allows us to estimate the
propensity for early tipping due to noise. We argue that one needs to extract
information about the nonlinear features (a "softening") of the underlying
potential from the time series to judge the probability and timing of tipping.
This analysis is the logical next step if one has detected a decrease of the
linear decay rate. If there is no discernable trend in the linear analysis,
nonlinear softening is even more important in showing the proximity to tipping.
After extensive normal form calibration studies, we check two geological time
series from paleo-climate tipping events for softening of the underlying well.
For the ending of the last ice age, where we find no convincing linear
precursor, we identify a statistically significant nonlinear softening towards
increasing temperature. The analysis has thus successfully detected a warning
of the imminent tipping event.Comment: 22 pages, 11 figures, changed title back, corrected smaller mistakes,
updated reference
Cougar Dispersal and Natal Homing in a Desert Environment
We present a review of cougar dispersal literature and the first evidence of natural (i.e., unmanipulated) homing behavior by a dispersing male cougar (Puma concolor) that sustained severe injuries crossing the northern Mojave Desert. Based on Global Positioning System and ground tracking data, the male traveled a total distance of 981.1 km at 5.03 km/d, including 170.31 km from the Desert National Wildlife Refuge to the northwestern Grand Canyon, where he sustained severe injuries. The interkill interval increased from 7.1 ± 2.7 d while he was in his natal range to 17.5 ± 4.9 d during dispersal. While homing, the male appeared to consume only reptiles until he died, 33.7 km from his capture site. In desert environments where prey availability is low, homing behavior may be an important strategy for dispersing cougars, providing a mechanism for persistence when the best quality habitats they encounter are already occupied by adult residents. Therefore, managing for habitat connectivity can ensure successful homing as well as dispersal on a greater scale than has been previously suggested. Elucidating the mechanisms that trigger homing during dispersal may provide critical insight into animal movements often overlooked as mundane behavior
Double wells, scalar fields and quantum phase transitions in ions traps
Since Hund's work on the ammonia molecule, the double well potential has
formed a key paradigm in physics. Its importance is further underlined by the
central role it plays in the Landau theory of phase transitions. Recently, the
study of entanglement properties of many-body systems has added a new angle to
the study of quantum phase transitions of discrete and continuous degrees of
freedom, i.e., spin and harmonic chains. Here we show that control of the
radial degree of freedom of trapped ion chains allows for the simulation of
linear and non-linear Klein-Gordon fields on a lattice, in which the parameters
of the lattice, the non-linearity and mass can be controlled at will. The
system may be driven through a phase transition creating a double well
potential between different configurations of the ion crystal. The dynamics of
the system are controllable, local properties are measurable and tunnelling in
the double well potential would be observable.Comment: 6 pages, 5 figure
Amniotic-Fluid Ingestion Enhances the Central\ud Analgesic Effect of Morphine
Amniotic fluid and placenta contain a substance (POEF) that when ingested enhances opioid-mediated analgesia produced by several agents (morphine injection, vaginal/cervical stimulation, late pregnancy, footshock), but not that produced by aspirin injection. The present series of experiments employed quaternary naltrexone, an opioid antagonist that does not readily cross the blood-brain barrier, in conjunction with either peripheral or central administration of morphine, to determine whether amniotic-fluid ingestion (and therefore POEF ingestion) enhances opioid-mediated analgesia by affecting the central and/or peripheral actions of morphine. The results suggest that POEF affects only the central analgesic effects of morphine
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