5,920 research outputs found
The Effects of High Liquid Water Content on Thunderstorm Charging
Charge transfer to a riming graupel target during interactions with ice crystals has been investigated in the laboratory. When liquid water contents sufficiently high to cause wet growth are achieved, the charge transfer falls to values which are insignificant to thunderstorm electrification. The implications of this null result to a recent analysis of thunderstorm-charging processes by Wiliams et al. (1991) are discussed
Time-domain Brillouin Scattering as a Local Temperature Probe in Liquids
We present results of time-domain Brillouin scattering (TDBS) to determine
the local temperature of liquids in contact to an optical transducer. TDBS is
based on an ultrafast pump-probe technique to determine the light scattering
frequency shift caused by the propagation of coherent acoustic waves in a
sample. Since the temperature influences the Brillouin scattering frequency
shift, the TDBS signal probes the local temperature of the liquid. Results for
the extracted Brillouin scattering frequencies recorded at different liquid
temperatures and at different laser powers - i.e. different steady state
background temperatures- are shown to demonstrate the usefulness of TDBS as a
temperature probe. This TDBS experimental scheme is a first step towards the
investigation of ultrathin liquids measured by GHz ultrasonic probing.Comment: arXiv admin note: substantial text overlap with arXiv:1702.0107
Quintessence Models and the Cosmological Evolution of alpha
The cosmological evolution of a quintessence-like scalar field, phi, coupled
to matter and gauge fields leads to effective modifications of the coupling
constants and particle masses over time. We analyze a class of models where the
scalar field potential V(phi) and the couplings to matter B(phi) admit common
extremum in phi, as in the Damour-Polyakov ansatz. We find that even for the
simplest choices of potentials and B(phi), the observational constraints on
delta alpha/alpha coming from quasar absorption spectra, the Oklo phenomenon
and Big Bang nucleosynthesis provide complementary constraints on the
parameters of the model. We show the evolutionary history of these models in
some detail and describe the effects of a varying mass for dark matter.Comment: 26 pages, 20 eps figure
Update on the Direct Detection of Supersymmetric Dark Matter
We compare updated predictions for the elastic scattering of supersymmetric
neutralino dark matter with the improved experimental upper limit recently
published by CDMS II. We take into account the possibility that the \pi-nucleon
\Sigma term may be somewhat larger than was previously considered plausible, as
may be supported by the masses of exotic baryons reported recently. We also
incorporate the new central value of m_t, which affects indirectly constraints
on the supersymmetric parameter space, for example via calculations of the
relic density. Even if a large value of \Sigma is assumed, the CDMS II data
currently exclude only small parts of the parameter space in the constrained
MSSM (CMSSM) with universal soft supersymmetry-breaking Higgs, squark and
slepton masses. None of the previously-proposed CMSSM benchmark scenarios is
excluded for any value of \Sigma, and the CDMS II data do not impinge on the
domains of the CMSSM parameter space favoured at the 90 % confidence level in a
recent likelihood analysis. However, some models with non-universal Higgs,
squark and slepton masses and neutralino masses \lappeq 700 GeV are excluded by
the CDMS II data.Comment: 25 pages, 28 eps figure
Non-universal scalar-tensor theories and big bang nucleosynthesis
We investigate the constraints that can be set from big-bang nucleosynthesis
on two classes of models: extended quintessence and scalar-tensor theories of
gravity in which the equivalence principle between standard matter and dark
matter is violated. In the latter case, and for a massless dilaton with
quadratic couplings, the phase space of theories is investigated. We delineate
those theories where attraction toward general relativity occurs. It is shown
that big-bang nucleosynthesis sets more stringent constraints than those
obtained from Solar system tests.Comment: 28 pages, 20 figure
Evolving Marine Biosecurity in the Galapagos Islands
Some of my co-authors and I have just returned from one of the paradises on earth and a natural history mecca – The Galapagos Islands, Ecuador
Digital media inhibit self-regulatory private speech use in preschool children: The “digital bubble effect”
Preschoolers spend much time with digital media and some are concerned about impacts on language development. Private speech (PS) is self-talk children use during play, representing a necessary form of self-regulation. This study examined whether modality (material vs. digital) matters for children's PS. Twenty-nine White 5-yr-olds (52% female) completed the Tower of London task twice - once as a material version and once on a tablet. Children used more PS on the material than digital version of the task (d=0.46). During the material task, the typical pattern of increased PS as difficulty increased appeared. However, during the digital task, PS declined as difficulty increased. Digital games may inhibit children's use of PS for self-regulation, having implications for executive function development
Observations of Rapid Disk-Jet Interaction in the Microquasar GRS 1915+105
We present evidence that ~ 30 minute episodes of jet formation in the
Galactic microquasar GRS 1915+105 may sometimes entirely be a superposition of
smaller, faster phenomena. We base this conclusion on simultaneous X-ray and
infrared observations in July 2002, using the Rossi X-ray Timing Explorer and
the Palomar 5 meter telescope. On two nights, we observed quasi-periodic
infrared flares from GRS 1915+105, each accompanied by a set of fast
oscillations in the X-ray light curve (indicating an interaction between the
jet and accretion disk). In contrast to similar observations in 1997, we find
that the duration of each X-ray cycle matches the duration of its accompanying
infrared flare, and we observed one instance in which an isolated X-ray
oscillation occurred at the same time as a faint infrared "subflare" (of
duration ~ 150 seconds) superimposed on one of the main flares. From these
data, we are able to conclude that each X-ray oscillation had an associated
faint infrared flare and that these flares blend together to form, and entirely
comprise, the ~ 30 minute events we observed. Part of the infrared emission in
1997 also appears to be due to superimposed small flares, but it was
overshadowed by infrared-bright ejections associated with the appearance of a
sharp "trigger" spike in each X-ray cycle that were not present in 2002. We
also study the evolution of the X-ray spectrum and find significant differences
in the high energy power law component, which was strongly variable in 1997 but
not in 2002. Taken together, these observations reveal the diversity of ways in
which the accretion disk and jet in black hole systems are capable of
interacting and solidify the importance of the trigger spike for large
ejections to occur on ~ 30 minute timescales in GRS 1915+105.Comment: 17 pages, 9 figures; accepted for publication in The Astrophysical
Journa
Gravity Dual of Gauge Theory on S^2 x S^1 x R
We (numerically) construct new static, asymptotically AdS solutions where the
conformal infinity is the product of time and S^2 x S^1. There always exist a
family of solutions in which the S^1 is not contractible and, for small S^1,
there are two additional families of solutions in which the S^1 smoothly
pinches off. This shows that (when fermions are antiperiodic around the S^1)
there is a quantum phase transition in the gauge theory as one decreases the
radius of the S^1 relative to the S^2. We also compare the masses of our
solutions and argue that the one with lowest mass should minimize the energy
among all solutions with conformal boundary S^2 x S^1 x R. This provides a new
positive energy conjecture for asymptotically locally AdS metrics. A simple
analytic continuation produces AdS black holes with topology S^2 x S^1.Comment: 17 pages, 4 figures, v2: minor changes, added reference
- …