3,670 research outputs found
Dye staining and excavation of a lateral preferential flow network
International audiencePreferential flow features have been found to be important for runoff generation, solute transport, and slope stability in many areas around the world. Although many studies have identified the particular characteristics of individual features and measured the runoff generation and solute transport within hillslopes, no studies have determined how individual features are hydraulically connected at a hillslope scale. In this study, we used dye staining and excavation to determine the morphology and spatial pattern of a preferential flow network over a large scale (30 m). We explore the feasibility of extending small-scale dye staining techniques to the hillslope scale. We determine the lateral preferential flow features that are active during the steady state flow conditions and their interaction with the surrounding soil matrix. We also calculate the velocities of the flow through each cross-section of the hillslope and compare them to hillslope scale applied tracer measurements. Finally, we investigate the relationship between the contributing area and the characteristics of the preferential features. The experiment revealed that larger contributing areas coincided with highly developed and hydraulically connected preferential features that had flow with little interaction with the surrounding soil matrix. We found evidence of subsurface erosion and deposition of soil and organic material laterally and vertically within the soil. These results are important because they add to the understanding of the runoff generation, solute transport, and slope stability of these types of hillslopes
Physics with Cosmic Neutrinos, PeV to ZeV
We begin with a brief overview of highest-energy cosmic ray data, and the
experiments which will perform neutrino astronomy. We then discuss two particle
physics aspects of neutrinos. They are possible long-lifetime decay of the
neutrino, and a measurement of the neutrino-nucleon cross-section at a CMS
energy orders of magnitude beyond what can be achieved with terrestrial
accelerators. Measurement of an anomalously large neutrino cross-section would
indicate new physics (e.g. low string-scale, extra dimensions, precocious
unification), while a smaller than expected cross-section would reveal an
aspect of QCD evolution. We then discuss aspects of neutrino-primary models for
the extreme-energy (EE) cosmic ray data. Primary neutrinos in extant data are
motivated by the directional clustering at EE reported by the AGASA experiment.
We discuss the impact of the strongly-interacting neutrino hypothesis on
lower-energy physics via dispersion relations, the statistical significance of
AGASA directional clustering, and the possible relevance of the Z-burst
mechanism for existing EE cosmic ray data.Comment: 19 pages including 6 figures, Proc. YITP "Neutrinos" Oct. 200
Causality-Violating Higgs Singlets at the LHC
We construct a simple class of compactified five-dimensional metrics which
admits closed timelike curves (CTCs), and derive the resulting CTCs as analytic
solutions to the geodesic equations of motion. The associated Einstein tensor
satisfies all the null, weak, strong and dominant energy conditions. In
particular, no negative-energy "tachyonic" matter is required. In
extra-dimensional models where gauge charges are bound to our brane, it is the
Kaluza-Klein (KK) modes of gauge-singlets that may travel through the CTCs.
From our brane point of view, many of these KK modes would appear to travel
backward in time. We give a simple model in which time-traveling Higgs singlets
can be produced by the LHC, either from decay of the Standard Model (SM) Higgs
or through mixing with the SM Higgs. The signature of these time-traveling
singlets is a secondary decay vertex pre-appearing before the primary vertex
which produced them. The two vertices are correlated by momentum conservation.
We demonstrate that pre-appearing vertices in the Higgs singlet-doublet mixing
model may well be observable at the LHC.Comment: 55 pages, 5 figures, v4: Version updated to include in single
manuscript the contents of Erratum [Phys. Rev. D 88, 069901(E) (2013)], Reply
[Phys. Rev. D 88, 068702 (2013)], Comment [Phys. Rev. D 88, 068701 (2013),
arXiv:1302.1711], and original published article [Phys. Rev. D 87, 045004
(2013), arXiv:1103.1373]. Positive conclusions remain unchange
An Early & Comprehensive Millimeter and Centimeter Wave and X-ray Study of Supernova 2011dh: A Non-Equipartition Blastwave Expanding into A Massive Stellar Wind
Only a handful of supernovae (SNe) have been studied in multi-wavelength from
radio to X-rays, starting a few days after explosion. The early detection and
classification of the nearby type IIb SN2011dh/PTF11eon in M51 provides a
unique opportunity to conduct such observations. We present detailed data
obtained at the youngest phase ever of a core-collapse supernova (days 3 to 12
after explosion) in the radio, millimeter and X-rays; when combined with
optical data, this allows us to explore the early evolution of the SN blast
wave and its surroundings. Our analysis shows that the expanding supernova
shockwave does not exhibit equipartition (e_e/e_B ~ 1000), and is expanding
into circumstellar material that is consistent with a density profile falling
like R^-2. Within modeling uncertainties we find an average velocity of the
fast parts of the ejecta of 15,000 +/- 1800 km/s, contrary to previous
analysis. This velocity places SN 2011dh in an intermediate blast-wave regime
between the previously defined compact and extended SN IIb subtypes. Our
results highlight the importance of early (~ 1 day) high-frequency observations
of future events. Moreover, we show the importance of combined radio/X-ray
observations for determining the microphysics ratio e_e/e_B.Comment: 9 pages, 5 figures, submitted to Ap
Electric-field-induced transport of microspheres in the isotropic and chiral nematic phase of liquid crystals
The application of an electric field to microspheres suspended in a liquid crystal, causes particle translation in a plane perpendicular to the applied field direction. Depending on applied electric field amplitude and frequency, a wealth of different motion modes may be observed above a threshold, which can lead to linear, circular or random particle trajectories. We present the stability diagram for these different translational modes of particles suspended in the isotropic and the chiral nematic phase of a liquid crystal, and investigate the angular velocity, circular diameter, and linear velocity as a function of electric field amplitude and frequency. In the isotropic phase a narrow field amplitude-frequency regime is observed to exhibit circular particle motion whose angular velocity increases with applied electric field amplitude, but is independent of applied frequency. The diameter of the circular trajectory decreases with field amplitudes as well as frequency. In the cholesteric phase linear as well as circular particle motion is observed. The former exhibits an increasing velocity with field amplitude, while decreasing with frequency. For the latter, the angular velocity exhibits an increase with field amplitude and frequency. The rotational sense of the particles on a circular trajectory in the chiral nematic phase is independent of the helicity of the liquid crystalline structure, as is demonstrated by employing a cholesteric twist inversion compound
Discovery of Radio Outbursts in the Active Nucleus of M81
The low-luminosity active galactic nucleus of M81 has been monitored at
centimeter wavelengths since early 1993 as a by-product of radio programs to
study the radio emission from Supernova 1993J. The extensive data sets reveal
that the nucleus experienced several radio outbursts during the monitoring
period. At 2 and 3.6 cm, the main outburst occurred roughly in the beginning of
1993 September and lasted for approximately three months; at longer
wavelengths, the maximum flux density decreases, and the onset of the burst is
delayed. These characteristics qualitatively resemble the standard model for
adiabatically expanding radio sources, although certain discrepancies between
the observations and the theoretical predictions suggest that the model is too
simplistic. In addition to the large-amplitude, prolonged variations, we also
detected milder changes in the flux density at 3.6 cm and possibly at 6 cm on
short (less than 1 day) timescales. We discuss a possible association between
the radio activity and an optical flare observed during the period that the
nucleus was monitored at radio wavelengths.Comment: To appear in The Astronomical Journal. Latex, 18 pages including
embedded figures and table
Band structure of semimagnetic Hg1-yMnyTe quantum wells
The band structure of semimagnetic Hg_1-yMn_yTe/Hg_1-xCd_xTe type-III quantum
wells has been calculated using eight-band kp model in an envelope function
approach. Details of the band structure calculations are given for the Mn free
case (y=0). A mean field approach is used to take the influence of the sp-d
exchange interaction on the band structure of QW's with low Mn concentrations
into account. The calculated Landau level fan diagram and the density of states
of a Hg_0.98Mn_0.02Te/Hg_0.3Cd_0.7Te QW are in good agreement with recent
experimental transport observations. The model can be used to interpret the
mutual influence of the two-dimensional confinement and the sp-d exchange
interaction on the transport properties of Hg_1-yMn_yTe/Hg_1-xCd_xTe QW's.Comment: 12 pages, 4 figure
Linear-response theory of the longitudinal spin Seebeck effect
We theoretically investigate the longitudinal spin Seebeck effect, in which
the spin current is injected from a ferromagnet into an attached nonmagnetic
metal in a direction parallel to the temperature gradient. Using the fact that
the phonon heat current flows intensely into the attached nonmagnetic metal in
this particular configuration, we show that the sign of the spin injection
signal in the longitudinal spin Seebeck effect can be opposite to that in the
conventional transverse spin Seebeck effect when the electron-phonon
interaction in the nonmagnetic metal is sufficiently large. Our linear-response
approach can explain the sign reversal of the spin injection signal recently
observed in the longitudinal spin Seebeck effect.Comment: Proc. of ICM 2012 (Accepted for publication in J. Korean Phys. Soc.),
typos correcte
Dust observations of Comet 9P/Tempel 1 at the time of the Deep Impact
On 4 July 2005 at 05:52 UT, the impactor of NASA's Deep Impact (DI) mission
crashed into comet 9P/Tempel 1 with a velocity of about 10 km/s. The material
ejected by the impact expanded into the normal coma, produced by ordinary
cometary activity.
The characteristics of the non-impact coma and cloud produced by the impact
were studied by observations in the visible wavelengths and in the near-IR. The
scattering characteristics of the "normal" coma of solid particles were studied
by comparing images in various spectral regions, from the UV to the near-IR.
For the non-impact coma, a proxy of the dust production has been measured in
various spectral regions. The presence of sublimating grains has been detected.
Their lifetime was found to be about 11 hours. Regarding the cloud produced by
the impact, the total geometric cross section multiplied by the albedo was
measured as a function of the color and time. The projected velocity appeared
to obey a Gaussian distribution with the average velocity of the order of 115
m/s. By comparing the observations taken about 3 hours after the impact, we
have found a strong decrease in the cross section in J filter, while that in Ks
remained almost constant. This is interpreted as the result of sublimation of
grains dominated by particles of sizes of the order of some microns.Comment: Accepted by A&
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