347 research outputs found
Contact-Induced Nonlinearity in Oscillating Belts and Webs
This study is motivated by issues in belt dynamics and paper forming where the oscillatory motion of the contact point between the belt and pulley or the web and roll is important. The objective is to evaluate the influence of the nonlinear contact boundary conditions on the dynamics of the belt or web. To accomplish this objective, two models are analyzed using perturbation methods. The first model represents a string on an elastic foundation (an approximation of the paper forming process) and the second model represents a tensioned beam (accessory drive belt). The first correction to the fundamental natural frequency and the dynamic belt/web length are determined as a function of the governing parameters. For both models, the change in belt length is found to be proportional to the radius of the pulley/roll and the initial belt/web energy.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69021/2/10.1177_107754639500100404.pd
Assessing the potential for crop albedo enhancement in reducing heatwave frequency, duration, and intensity under future climate change
Adapting to the impacts of future warming, and in particular the impacts of heatwaves, is an increasingly important challenge. One proposed strategy is land-surface radiation management via crop albedo enhancement. This has been argued to be an effective method of reducing daily hot temperature extremes regionally. However, the influence of crop albedo enhancement on heatwave events, which last three or more days, is yet to be explored and this remains an important knowledge gap. Using a fully coupled earth system model with 10 ensemble members, we show that crop albedo enhancement by up to +0.1 reduces the frequency of heatwave days over Europe and North America by 10 to 20 days; with a larger reduction over Europe under a future climate driven by SSP2-4.5. The average temperature anomaly during heatwaves (the magnitude of the event), is reduced by 0.8 °C to 1.2 °C where the albedo was enhanced, but reductions in mean heatwave duration are limited. There was a marked reduction in the mean annual cumulative heatwave intensity across most of Eurasia and North America, ranging from 32 °C to as high as 80 °C in parts of southern Europe. These changes were largely driven by a reduction in net radiation, decreasing the sensible heat flux, which reduces the maximum temperature, and therefore, heatwave frequency and intensity. These changes were largely localised to where the albedo enhancement was applied with no significant changes in atmospheric circulation or precipitation, which presents advantages for implementation. While our albedo perturbation of up to +0.1 is large and represents the likely upper limit of what is possible with more reflective crops, and we assume that more reflective crops are grown everywhere and instantly, these results provide useful guidance to policy makers and farmers on the maximum possible benefits of using more reflective crops in limiting the impacts of heatwaves under future climate
Microphysics of SO(10) Cosmic Strings
We uncover a rich microphysical structure for SO(10) cosmic strings. For the
abelian string the electroweak symmetry is restored around it in a region
depending on the electroweak scale. A rich structure of nonabelian strings is
found. Some of these also restore the electroweak symmetry. We investigate the
zero mode structure of our strings. Whilst there are right handed neutrino zero
modes for the abelian string, they do not survive the electroweak phase
transition. In general the nonabelian strings do not have fermion zero modes.
We consider the generalisation of our results to other theories and consider
cosmological consequences of them.Comment: 34 pages, LATEX. Replaced version is restructured, and has small
correction to fermion zero mode analysis. To be published in Physical Review
Baryon number violation, baryogenesis and defects with extra dimensions
In generic models for grand unified theories(GUT), various types of baryon
number violating processes are expected when quarks and leptons propagate in
the background of GUT strings. On the other hand, in models with large extra
dimensions, the baryon number violation in the background of a string is not
trivial because it must depend on the mechanism of the proton stabilization. In
this paper we argue that cosmic strings in models with extra dimensions can
enhance the baryon number violation to a phenomenologically interesting level,
if the proton decay is suppressed by the mechanism of localized wavefunctions.
We also make some comments on baryogenesis mediated by cosmological defects. We
show at least two scenarios will be successful in this direction. One is the
scenario of leptogenesis where the required lepton number conversion is
mediated by cosmic strings, and the other is the baryogenesis from the decaying
cosmological domain wall. Both scenarios are new and have not been discussed in
the past.Comment: 20pages, latex2e, comments and references added, to appear in PR
Scaling anomaly in cosmic string background
We show that the classical scale symmetry of a particle moving in cosmic
string background is broken upon inequivalent quantization of the classical
system, leading to anomaly. The consequence of this anomaly is the formation of
single bound state in the coupling interval \gamma\in(-1,1). The inequivalent
quantization is characterized by a 1-parameter family of self-adjoint extension
parameter \omega. It has been conjectured that the formation of loosely bound
state in cosmic string background may lead to the so called anomalous
scattering cross section for the particles, which is usually seen in molecular
physics.Comment: 4 pages,1 figur
New limits on nucleon decays into invisible channels with the BOREXINO Counting Test Facility
The results of background measurements with the second version of the
BOREXINO Counting Test Facility (CTF-II), installed in the Gran Sasso
Underground Laboratory, were used to obtain limits on the instability of
nucleons, bounded in nuclei, for decays into invisible channels ():
disappearance, decays to neutrinos, etc. The approach consisted of a search for
decays of unstable nuclides resulting from and decays of parents
C, C and O nuclei in the liquid scintillator and the water
shield of the CTF. Due to the extremely low background and the large mass (4.2
ton) of the CTF detector, the most stringent (or competitive) up-to-date
experimental bounds have been established: y, y, y and y, all at 90% C.L.Comment: 22 pages, 3 figures,submitted to Phys.Lett.
Phi meson production in Au+Au and p+p collisions at sqrt (s)=200 GeV
We report the STAR measurement of Phi meson production in Au+Au and p+p
collisions at sqrt (s)=200 GeV. Using the event mixing technique, the Phi
spectra and yields are obtained at mid-rapidity for five centrality bins in
Au+Au collisions and for non-singly-diffractive p+p collisions. It is found
that the Phi transverse momentum distributions from Au+Au collisions are better
fitted with a single-exponential while the p+p spectrum is better described by
a double-exponential distribution. The measured nuclear modification factors
indicate that Phi production in central Au+Au collisions is suppressed relative
to peripheral collisions when scaled by the number of binary collisions. The
systematics of versus centrality and the constant Phi/K- ratio versus beam
species, centrality, and collision energy rule out kaon coalescence as the
dominant mechanism for Phi production.Comment: 6 pages, 3 figures, submitted to Phys. Rev. Let
Single Spin Asymmetry in Polarized Proton-Proton Elastic Scattering at GeV
We report a high precision measurement of the transverse single spin
asymmetry at the center of mass energy GeV in elastic
proton-proton scattering by the STAR experiment at RHIC. The was measured
in the four-momentum transfer squared range \GeVcSq, the region of a significant interference between the
electromagnetic and hadronic scattering amplitudes. The measured values of
and its -dependence are consistent with a vanishing hadronic spin-flip
amplitude, thus providing strong constraints on the ratio of the single
spin-flip to the non-flip amplitudes. Since the hadronic amplitude is dominated
by the Pomeron amplitude at this , we conclude that this measurement
addresses the question about the presence of a hadronic spin flip due to the
Pomeron exchange in polarized proton-proton elastic scattering.Comment: 12 pages, 6 figure
Longitudinal double-spin asymmetry and cross section for inclusive neutral pion production at midrapidity in polarized proton collisions at sqrt(s) = 200 GeV
We report a measurement of the longitudinal double-spin asymmetry A_LL and
the differential cross section for inclusive Pi0 production at midrapidity in
polarized proton collisions at sqrt(s) = 200 GeV. The cross section was
measured over a transverse momentum range of 1 < p_T < 17 GeV/c and found to be
in good agreement with a next-to-leading order perturbative QCD calculation.
The longitudinal double-spin asymmetry was measured in the range of 3.7 < p_T <
11 GeV/c and excludes a maximal positive gluon polarization in the proton. The
mean transverse momentum fraction of Pi0's in their parent jets was found to be
around 0.7 for electromagnetically triggered events.Comment: 6 pages, 3 figures, submitted to Phys. Rev. D (RC
Azimuthal anisotropy and correlations in p+p, d+Au and Au+Au collisions at 200 GeV
We present the first measurement of directed flow () at RHIC. is
found to be consistent with zero at pseudorapidities from -1.2 to 1.2,
then rises to the level of a couple of percent over the range . The latter observation is similar to data from NA49 if the SPS rapidities
are shifted by the difference in beam rapidity between RHIC and SPS.
Back-to-back jets emitted out-of-plane are found to be suppressed more if
compared to those emitted in-plane, which is consistent with {\it jet
quenching}. Using the scalar product method, we systematically compared
azimuthal correlations from p+p, d+Au and Au+Au collisions. Flow and non-flow
from these three different collision systems are discussed.Comment: Quark Matter 2004 proceeding, 4 pages, 3 figure
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