640,934 research outputs found

### Pioneer Anomaly and the Helicity-Rotation Coupling

The modification of the Doppler effect due to the coupling of the helicity of
the radiation with the rotation of the source/receiver is considered in the
case of the Pioneer 10/11 spacecraft. We explain why the Pioneer anomaly is not
influenced by the helicity-rotation coupling.Comment: LaTeX file, 1 figure, 6 pages, v2: note and figure added at the end
of the paper, to be published in Phys. Lett.

### Experimental Investigation of the Recovery of Gas and Oil by Spontaneous Water Imbibition

Imperial Users onl

### Lessons Learned from the Pioneers 10/11 for a Mission to Test the Pioneer Anomaly

Analysis of the radio-metric tracking data from the Pioneer 10/11 spacecraft
at distances between 20--70 astronomical units (AU) from the Sun has
consistently indicated the presence of an anomalous, small, constant Doppler
frequency drift. The drift is a blue-shift, uniformly changing with rate a_t =
(2.92 +/- 0.44) x 10^(-18) s/s^2. It can also be interpreted as a constant
acceleration of a_P = (8.74 +/- 1.33) x 10^(-8) cm/s^2 directed towards the
Sun. Although it is suspected that there is a systematic origin to the effect,
none has been found. As a result, the nature of this anomaly has become of
growing interest. Here we discuss the details of our recent investigation
focusing on the effects both external to and internal to the spacecraft, as
well as those due to modeling and computational techniques. We review some of
the mechanisms proposed to explain the anomaly and show their inability to
account for the observed behavior of the anomaly. We also present lessons
learned from this investigation for a potential deep-space experiment that will
reveal the origin of the discovered anomaly and also will characterize its
properties with an accuracy of at least two orders of magnitude below the
anomaly's size. A number of critical requirements and design considerations for
such a mission are outlined and addressed.Comment: 11 pages, invited talk given at ``35th COSPAR Scientific Assebly,''
July 18-24, 2004, Paris, Franc

### Collapsing Sub-Critical Bubbles

In the standard scenario, the electroweak phase transition is a first order
phase transition which completes by the nucleation of critical bubbles.
Recently, there has been speculation that the standard picture of the
electroweak phase transition is incorrect. Instead, it has been proposed that
throughout the phase transition appreciable amounts of both broken and unbroken
phases of $SU(2)$ coexist in equilibrium. I argue that this can not be the
case. General principles insure that the universe will remain in a homogenous
state of unbroken $SU(2)$ until the onset of critical bubble production.Comment: 7 pages plus three figures. OHSTPY-HEP-T-92-016 A topdrawer file of
the figures is appended to the en

### On an SO(5) unification attempt for the cuprates

In this note we bring out several problems with the SO(5) unification attempt
of Zhang [cond-mat/9610140].Comment: 3 pages, latex (revtex

### Conventional Forces can Explain the Anomalous Acceleration of Pioneer 10

Anderson, et al. find the measured trajectories of Pioneer 10 and 11
spacecraft deviate from the trajectories computed from known forces acting on
them. This unmodelled acceleration (and the less well known, but similar,
unmodelled torque) can be accounted for by non-isotropic radiation of
spacecraft heat. Various forms of non-isotropic radiation were proposed by
Katz, Murphy, and Scheffer, but Anderson, et al. felt that none of these could
explain the observed effect. This paper calculates the known effects in more
detail and considers new sources of radiation, all based on spacecraft
construction. These effects are then modelled over the duration of the
experiment. The model reproduces the acceleration from its appearance at a
heliocentric distance of 5 AU to the last measurement at 71 AU to within 10
percent. However, it predicts a larger decrease in acceleration between
intervals I and III of the Pioneer 10 observations than is observed. This is a
2 sigma discrepancy from the average of the three analyses (SIGMA, CHASMP, and
Markwardt). A more complex (but more speculative) model provides a somewhat
better fit. Radiation forces can also plausibly explain the previously
unmodelled torques, including the spindown of Pioneer 10 that is directly
proportional to spacecraft bus heat, and the slow but constant spin-up of
Pioneer 11. In any case, by accounting for the bulk of the acceleration, the
proposed mechanism makes it much more likely that the entire effect can be
explained without the need for new physics.Comment: Final minor changes for publication - added explanation of acronyms,
added to RTG asymmetry argument.. Was: 12 pages, 9 figures, major revision.
Added discussion of gas leaks and spin history, a radiation based explanation
of spin changes, and references to re-analysis of Markwardt. Fixed radio
forces, tuned models. Was: 7 pages, 5 figures; added liklihood calculations
in body and abstract per suggestio

### Variational Principles for Natural Divergence-free Tensors in Metric Field Theories

Let $T^{ab}=T^{ba}=0$ be a system of differential equations for the
components of a metric tensor on $R^m$. Suppose that $T^{ab}$ transforms
tensorially under the action of the diffeomorphism group on metrics and that
the covariant divergence of $T^{ab}$ vanishes. We then prove that $T^{ab}$ is
the Euler-Lagrange expression some Lagrangian density provided that $T^{ab}$ is
of third order. Our result extends the classical works of Cartan, Weyl,
Vermeil, Lovelock, and Takens on identifying field equations for the metric
tensor with the symmetries and conservation laws of the Einstein equations

### The ground state and the long-time evolution in the CMC Einstein flow

Let (g,K)(k) be a CMC (vacuum) Einstein flow over a compact three-manifold M
with non-positive Yamabe invariant (Y(M)). As noted by Fischer and Moncrief,
the reduced volume V(k)=(-k/3)^{3}Vol_{g(k)}(M) is monotonically decreasing in
the expanding direction and bounded below by V_{\inf}=(-1/6)Y(M))^{3/2}.
Inspired by this fact we define the ground state of the manifold M as "the
limit" of any sequence of CMC states {(g_{i},K_{i})} satisfying: i. k_{i}=-3,
ii. V_{i} --> V_{inf}, iii. Q_{0}((g_{i},K_{i}))< L where Q_{0} is the
Bel-Robinson energy and L is any arbitrary positive constant. We prove that (as
a geometric state) the ground state is equivalent to the Thurston
geometrization of M. Ground states classify naturally into three types. We
provide examples for each class, including a new ground state (the Double Cusp)
that we analyze in detail. Finally consider a long time and cosmologically
normalized flow (\g,\K)(s)=((-k/3)^{2}g,(-k/3))K) where s=-ln(-k) is in
[a,\infty). We prove that if E_{1}=E_{1}((\g,\K))< L (where E_{1}=Q_{0}+Q_{1},
is the sum of the zero and first order Bel-Robinson energies) the flow
(\g,\K)(s) persistently geometrizes the three-manifold M and the geometrization
is the ground state if V --> V_{inf}.Comment: 40 pages. This article is an improved version of the second part of
the First Version of arXiv:0705.307

### The distribution of species range size: a stochastic process

The major role played by environmental factors in determining the geographical range sizes of species raises the possibility of describing their long-term dynamics in relatively simple terms, a goal which has hitherto proved elusive. Here we develop a stochastic differential equation to describe the dynamics of the range size of an individual species based on the relationship between abundance and range size, derive a limiting stationary probability model to quantify the stochastic nature of the range size for that species at steady state, and then generalize this model to the species-range size distribution for an assemblage. The model fits well to several empirical datasets of the geographical range sizes of species in taxonomic assemblages, and provides the simplest explanation of species-range size distributions to date

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